USGS Professional Paper No. 987 _1976

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Physical, Chemical, and
Biological Aspects of
Subsurface Organic Waste Injection
near Wilmington, North Carolina
By J. A. LEENHEER, R. L. MALCOLM, and W. R. WHITE
GEOLOGICAL SURVEY PROFESSIONAL PAPER 987
UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1976

UNITED STATES DEPARTMENT OF THE INTERIOR
THOMAS S. KLEPPE, Secretary
GEOLOGICAL SURVEY
V. E. McKelvey, Director
Library of Congress Cataloging in Publication Data
Leenheer, J. A.
Physical, chemical, and biological aspects of subsurface organic waste injection near Wilmington, North Carolina.
(Geological Survey Professional Paper 987)
Supt. of Docs. no.: I 19.16:987
Bibliography: p.
1. Waste disposal in the ground —North Carolina —Wilmington region.
I. Malcolm, R. L., joint author. I1. White, W. R., joint author. III. Title: Physical, chemical, and biological aspects of
subsurface organic waste injection... IV. Series: United States Geological Survey Professional Paper 987.
TD761.1,43 628'.36 76-608225
For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, D.C. 20402
Stock Number 024-001-02915-4

CONTENTS
Page
English -metric equivalents--------------------------------------------------------------------
IV
Abstract-----------------•--------... --- ----------------------------------------------------------------
-- 1
Introduction ---------- ---------------------------
2
Acknowledgments. ------...........................-------.........------.............
4
Hydrogeology, By H. M. Peek and R. C. Heath ------_----..-_--_ ...............
5
Case history of waste injection------------------------------------------------------------
6
Installation and operation of initial well system
6
Construction and operation of expanded injection system --------
9
Field sampling methods ------.
11
Industrial waste analysis.. ----- ---------------
12
Organic analysis ---------------------------------- ------------
12
Inorganic analysis ---------------------------------- .............--
15
Physical properties ---------------------------------------------------------------------------
17
Hydrochemistry of native ground water ------------------- -----------------------------
17
Waste -aquifer interactions........................................................
18
Sitestudy --- _ --- --------------------------------------------------------------------------------
18
Initial conditions ..----- -------------------------
18
Initial conceptual model of injected -waste reactivity
andmovement--------------------------------------------------------------------.
19
Reactions observed at wells 1, 2, 3, 4, and 5--------------------------
19
Reactions observed at well 9-----------------------
20
Reactions observed at wells 11, 14, and 15
20
Page
Waste -aquifer interactions — Continued
Site study — Continued
Possible flow systems associated with injection
activities--------------------------
23
Microbiological study -- ...........................................................
26
Laboratory waste -aquifer reactivity studies ---------------------------------------
27
Introduction -_----..._-------------------- .__----
27
Methods and materials .. . .................................................... ..
. 27
Aquifer material ------------ ___ -----------------------------------------------------
27
Characterization of aquifer material ....................................
27
Waste constituent analyses --------------
27
Modified Hassler sleeve core holder ......................................
28
Pressurization core -testing apparatus -------------
28
Experimental design------------------
-- 28
Testing the pressurization core -testing apparatus ......................
29
Leaktesting--------------------------------------....------......------....--------------
29
Packing the Teflon sleeve with aquifer material ----------------
29
Experiment 1—kinetic study of waste ..........................................
30
Experiment 2—core solubilization study --------------------------------------
34
Experiment 3—waste saturation study ----------------------------------------
37
Final conceptual model of waste movement and reactivity --------------
39
Summary and conclusions. -- -. .................................................. ...
. 41
Selectedreferences ---------------------------- --------_.-._ ---------------- --_-----------------
42
ILLUSTRATIONS
Page
FIGURE 1.
Hercules Inc. DMT Plant, Wilmington, North Carolina ---------------------------------------------- ............................................................
3
2.
Location of Hercules Inc., plant site ------...... ----- --- ---- -- -- ---------------------------------- ----------------------..........................
4
3.
Diagram showing hydrogeologic conditions and injection -well construction for well I-7A------------------------.......................................
5
4.
Map of waste -injection and observation wells---------------------------------------------------------------------- ................................. I......
7
5.
Monthly average injection rate-----------------------------------------------------------------------------------------------
7
6.
Graph of highest wellhead injection pressures --------------------_---- -.-----------------------.----------------
8
7.
Location of wells in initial system and pressure surface, Junuary 1969....................................................................................
8
8.
Map of pressure surface, September 1970---------------------------------------------------------------------- --------------..-....--------------------------------------------
9
9.
Map of pressure surface and approximate limits of waste travel, October 1972........................................
10
10.
Map of pressure surface with no injection, April 1973 --------------------------------------------------------------------------------------------------------------------
10
11.
Construction features of observation well 14............................................................................................. .. ..............................
11
12.
Analytical scheme of organic waste analysis .......... --------------------------------------------------.. --------------------------------------------------------------------
-
13
13.
Gas chromatogram of acetic and formic acids-----------------------------.--.......................................----------------------------..------------
13
14.
Gas chromatogram and mass spectra of methylated -acid ether extract....................................................................................
14
15.
Gas chromatogram of alkaline ether extract-------------------------------..--------------------------------------
14
16.
Gas chromatogram of neutral, volatile, waste constituents---------------------------------------------------------------------------------------------------....
15
17.
Initial conceptual model of injected -waste reactivity and movement-----------------------.----------............----------------------------
19
18.
Variations in pH and residue on evaporation from samples taken during observation of waste front in wells 1 and 5....
20
19.
Variables observed during passage of waste front in well 14........... ..................................................................................... ........
21
20.
Constituents measured during passage of waste front in well 11..................---------------
23
21.
Hypothetical areal distribution of waste at the upper and lower boundaries of the injection zone
24
22.
Probable internal circulation of ground water within well 14......................................................................................................
25
23.
Comparison of number of bacteria per millilitre (as colony -forming units) in waste front (well 14) and in
uncontaminatedaquifer (well 11)---------------------------------------------------....... -.................................................. -----------
26
24.
Diagram of modified Hassler sleeve core holder .................................................................................... ... .. ... .. ... .. .........
28
III

IV
CONTENTS
FIGURE 25.
Schematic diagram of pressurization core -testing apparatus......................................................................................................
28
26.
Specific conductance breakthrough curve during leak -testing of Hassler sleeve core holder------------------------------------------------
29
27.
Sodium, chloride, and DOC breakthrough curves for experiment 1(flow rate=2 ml/hr)...................................................................
31
28.
Sodium, chloride, and DOC breakthrough curves for experiment 2 (flow rate=4 ml/hr)-------------------------------------------------------------------
31
29.
Iron and silica dissolution during experiment 2 ....................... ----
33
30.
Iron and silica dissolution during experiment 1 -------------------------------------------------------------------------------------------------------------------------------------
33
31.
Relative sorption of formaldehyde, acetic acid, and formic acid during experiment 2..............................................._.....................---
34
32.
Relative sorption of phthalic, terephthalic, and p-toluic acids during experiment I ---------------------------------------------------------------------------
35
33.
Hypothetical movement of injected waste within injection subzones..........................................................................................
39
34.
Final conceptual model of injected -waste reactivity and movement.........................................................................................
39
TABLES
Page
TABLE 1.
Chronology of significant events during injection -------------------
2.
Injection -system well data-------------------------------------••---------------------....---....----................----...............---..................------...........................
7
3.
Average organic analysis of waste ....................................... --------------------------------------------------------------------------------- .-----------------------------
16
4.
Inorganic waste analysis ----------------------------------------------------------------------------------------------------------•-----------......_...-•----------------------------------
16
5.
Inorganic analysis of native ground water found in aquifers at waste -injection site..............................................................
17
6.
Change in water composition with waste contamination..............................................................................................................
19
7.
Well 14 gas analyses...............................................................••---------------------------------.............---................---.....--...-•--....................-----
21
8.
Relative organic composition of injected waste found in wells 11,14, and 15............................................................................
22
9.
Observation well flow -test data-----------------------------------------••-----....................................-........---...............................---------------------------
24
10.
Identification of isolates from well 11-----------------••-----------------------..................---.......---...............-----....................-------------------------------
26
11.
Laboratory chemical data for waste -aquifer reactivity experiment 1(flow rate =2 ml/hr)----------------------------------------------------
31
12.
Laboratory chemical data for waste -aquifer reactivity experiment 2 (flow rate=4 ml/hr)----------------------------------------------------
32
13.
Organic chemical data during waste -effluent monitoring of experiment 2................................................................................
34
14.
Organic chemical data during waste -effluent monitoring of experiment 1................................................................................
35
15.
Sorptive capacities of aromatic organic acids on aquifer material during experiment 2--------------------------------------------------------
36
16.
Organic and inorganic carbon analyses of fractionated and unfractionated injection -zone aquifer material ....................
36
17.
Particle size analysis of injection -zone aquifer material................................................................................................................
37
18.
Fe, Al, and Mn analyses by graphite furnace technique of selected waste effluent fractions during experiment 2 ..........
37
19.
Chemical data during waste effluent monitoring of experiment 3..............................................................................................
38
20-36.
Basic -data tables
20. Organic waste analyses .........................................................................................................................................................
46
21. Waste inorganic analyses -sample collected 11-7-73......................................................................................................
46
22. Inorganic analyses of water from surficial sand aquifer..................................................................................................
46
23. Inorganic analyses of water from 300-ft zone....................................................................................................................
46
24. Inorganic analyses of water from 500-fi zone.........................................................................................•-•------------------------
46
25. Inorganic analyses of water from 700-fi zone....................................................................................................................
47
26. Inorganic analyses of water from well 7..............................................................................................................................
47
27. Inorganic analyses of water from well 11............................................................................................................................
48
28. Inorganic analyses of water from well 12----------------------------------------------------------------------------------------------------------------------------
49
29. Inorganic analyses of water from well 14............................................................................................................................
48
30. Inorganic analyses of water from well 15............................................................•----------..............----....•------------------••----------
50
31. Inorganic analyses of water from well 16............................................................................................................................
51
32. Inorganic analyses of water from wells 2, 3, 4, and 5........................................................................................................
51
33. Gas analyses.............................................................................................................................................................................
50
34. Organic analyses of water from well l l..............................................--------------------------------------------------------- ---------------------
51
35. Organic analyses of water from well 14..............................................•----.................-........---......---.....-------------------------------
51
36. Organic analysesof water from well 15.............................................•--.....,...........-.......-........-.............------------------------------
51
ENGLISH-METRIC EQUIVALENTS
foot (ft) = 0.3048 metre (m)
inch (in) = 25.4 millimetres (mm)
mile (mi) = 1.609 kilometres (km)
pound per square inch (psi) = .068947 bar
gallon (gal) = 3.785 litres (1)

PHYSICAL, CHEMICAL, AND BIOLOGICAL ASPECTS OF
SUBSURFACE ORGANIC WASTE INJECTION
NEAR WILMINGTON, NORTH CAROLINA
By J. A. LEENHEER, R. L. MALCOLM, and W. R. WHITE
ABSTRACT
From May 1968 to December 1972, an industrial organic waste
was injected at rates of 100 to 200 gallons per minute (6.3 to 12.6
litres per second) into a sand, gravel, and limestone aquifer of Late
Cretaceous age by Hercules Inc. located near Wilmington, North
Carolina. This report presents both field and laboratory data per-
taining to the physical, chemical, and biological effects of waste
injection into the subsurface at this particular site, a case history of
the operation, predictions of the reactions between certain organic
wastes and the aquifer components, and descriptions of the effects of
these reactions on the subsurface movement of the wastes.
The case history documents a situation in which subsurface waste
injection could not be considered a successful means of waste dis-
posal. The first injection well was used only for 1 year due to exces-
sive wellhead pressure build-up above the specified pressure limit of
150 pounds per square inch (10.3 bars). A second injection well
drilled as a replacement operated for only 5 months before it too
began to have problems with plugging. Upward leakage of waste into
shallower aquifers was also detected at several wells in the
injection -observation well system. The multiple problems of plug-
ging, high pressures, and waste leakage suggested that the reactive
nature of the waste with the aquifer into which it was injected was
the primary reason for the difficulties experienced with waste injec-
tion.
A site study was initiated in June 1971 to investigate waste -
aquifer interactions. The first stage of the study determined the hy-
drogeologic conditions at the site, and characterized the industrial
waste and the native ground water found in the injection zone and
other aquifers. The injection zone consisted of multiple permeable
zones ranging in depth from about 850 to 1,000 feet (259 to 305
metres) below land surface. In addition to the injection zone, aquifers
were found near depths of 60, 300, 500, and 700 feet (18, 91, 152, and
213 metres) below land surface. The aquifers from 300 feet (91
metres) down to the injection zone were flowing artesian with the
natural pressure of the injection zone being 65 feet (20 metres) above
land surface at the site.
The dissolved solids concentration in the native ground water
increased with depth to an average value of 20,800 mg/1 (milligram
per litre) (two-thirds that of seawater) in the water from the injection
zone. Sodium chloride was the major dissolved solid, and all of the
ground water below 300-feet (91-metres) depth was slightly alkaline.
Dissolved organic carbon of the industrial waste averaged 7,100
mg/1 and 95 percent of the organic carbon was identified and quan-
tified. The major organic waste constituents in order of decreasing
abundance were acetic acid, formic acid, p-toluic acid, formaldehyde,
methanol, terephthalic acid, phthalic acid, and benzoic acid. Prior to
injection, the waste was neutralized with lime to pH 4 so that the
major inorganic waste constituent was calcium at a concentration of
1,300 mg/1.
The second stage of the site study involved the observation of
waste -aquifer interactions at various wells as the waste arrived and
passed by the wells. Water samples obtained from three observation
wells located 1,500 to 2,000 feet (457 to 607 metres) from the original
injection well gave evidence for biochemical waste transformations
at low waste concentrations. Gas that effervesced from these water
samples contained up to 54 percent methane by volume. Ferrous iron
concentrations as high as 35 mg/1, hydrogen sulfide gas, and sulfide
precipitates were additional indicators of biochemical reductive pro-
cesses in the subsurface environment. Approximately 3,000 or-
ganisms per millilitre were found in uncontaminated ground water
from the injection zone whereas in waste -contaminated wells, the
number increased to levels as high as 1,000,000 organisms per mil-
lilitre. High concentrations of waste were found to be toxic to mi-
croorganisms. Most of the organisms isolated from uncontaminated
wells were facultative, aerobic genera whereas the population
changed to anaerobic strains in the contaminated wells.
Methanogenic bacteria of the genus Methanobacterium and genus
Methanococcus were isolated in pure culture from ground -water
samples in which methane was found.
The relative ratios of formic acid, p-toluic acid, and terephthalic
acid to acetic acid were lower in these ground -water samples than in
the injected waste indicating degradation or sorption of formic,
p-toluic, and terephthalic acids relative to acetic acid during the
period of waste travel to these observation wells. The construction of
the screened section of the observation wells allowed dilution of the
waste and internal circulation of ground water so that it was impos-
sible to determine quantitative waste concentrations in the various
waste -receiving zones within the injection zone.
Highly contaminated ground -water samples obtained from five
observation wells located near (50 to 150 feet) (15 to 46 metres) the
injection wells gave evidence for waste dissolution of aquifer carbon-
ates and iron oxides. These samples contained carbon dioxide gas,
calcium concentrations to 3,900 mg/1, and iron concentrations to 310
mg/1.Organic complexation as well as acid dissolution was suspected
to be the cause for the high iron concentrations. There was no
microbiological activity apparent in these wells and samples.
Concurrent with and after the site study, a laboratory study was
conducted in which waste was injected into cores of aquifer material
obtained from the injection lone. The laboratory injection pressure
was that of the hydrostatic pressure found in the injection zone.
When a known volume of waste was injected into a core, the acidic

SUBSURFACE ORGANIC WASTE INJECTION, NORTH CAROLINA
waste initially dissolved the carbonates, and sesquioxide coatings on
the primary minerals as evidenced by high concentrations of iron,
aluminum, silica, and manganese. Iron concentrations as high as
200 mg/l were obtained, but this dissolved iron was eventually repre-
cipitated further on in the core when the pH of the waste rose to 5.5
to 6.0 because of neutralization of the waste by aquifer carbonates
and oxides. Exhaustive leaching of a core by the acidic waste quan-
titatively dissolved the aquifer carbonates and removed approxi-
mately 12 percent of the extractable iron.
Sorption of the waste organic compounds upon the aquifer mineral
constituents was found for all the waste organic acids. Formaldehyde
was not sorbed. Sorption increased as the pH of the waste decreased
with the exception of phthalic acid. Phthalic acid was complexed
with dissolved iron, and its concentration decreased as the pH of the
waste increased because it coprecipitated with the iron hydroxide
precipitate. The waste solution was supersaturated with respect to
terephthalic acid, and this constituent was found to be both highly
adsorbed and precipitated in the core.
At the conclusion of this study, a conceptual model was con-
structed which by combining the results of the field and laboratory
studies, detailed the various stages of injected waste reactivity and
movement in the subsurface from the injection well to the edge of the
waste front. The excessive pressure build-up in the injection wells
was thought to be the result of a number of factors: reprecipitation of
aquifer constituents initially dissolved by the acidic waste, precipita-
tion of terephthalic acid, formation of carbon dioxide and methane
gases, and the relatively low permeability and porosity of the injec-
tion zone. The leak problems were thought to arise from the dissolu-
tion of the cement grout around the casing by the waste acids of the
injection wells and certain observation wells.
INTRODUCTION
Injection of liquid wastes into subsurface strata is a
concept in waste management which has found wide-
spread use in industry only since 1960. A recent survey
by Warner and Orcutt (1973) noted that only 22 waste
injection wells were constructed before 1960, and by
1964, the number of injection wells had doubled. In
spite of growing opposition to subsurface waste injec-
tion because of its largely unknown long-term en-
vironmental effects, the number of waste -injection
wells has continued to increase until there are pres-
ently (1973) about 278 industrial waste -injection wells
which have been constructed in 24 states. Wells used to
reinject brines brought to the surface during oil and
gas production were not included in this survey. In
1973, chemical, petrochemical, and pharmaceutical
companies accounted for 57 percent of the industrial
waste -injection wells.
This study is part of a nationwide effort by the U.S.
Geological Survey to evaluate the environmental ef-
fects of subsurface waste injection. The specific objec-
tives of this study were to: (1) Predict the reactions and
interactions between certain organic wastes and
aquifer components when organic wastes are placed in
the subsurface environment and (2) define the effects
that physical, chemical, and biological reactions have
upon the distribution and movement of organic wastes
in the subsurface.
In January 1971, the subsurface waste -injection sys-
tem operated by Hercules Inc. near Wilmington, N.C.,
was selected for study. The site had several distinct
advantages for this study: First, the industrial waste
being injected into the subsurface contained high con-
centrations of several water-soluble organic com-
pounds which were liable to react and be transformed
in the subsurface environment. Prior to this study,
problems with an injection well pressure build-up after
a period of waste injection indicated that the reactivity
of the injected waste with the injection zone was an
important aspect concerning the operation of this
waste -injection system. Secondly, a network of 14 ob-
servation wells located at various distances from the
injection wells, and drilled to different depths, enabled
the monitoring of waste movement and the collection
of waste samples in both horizontal and vertical direc-
tions from the points of waste injection. Third, the
relatively shallow depth to the waste -injection zone
(1,000 feet or 300 metres) facilitated chemical and mi-
crobiological experimentation under the simulated
pressures of the injection zone without the use of very
high pressure equipment. Last but not least, excellent
cooperation and support was provided by the Company
and various state and federal agencies.
Disadvantages of this site were that the two injec-
tion wells and complex hydrogeologic nature of the
injection zone made it very difficult to predict the rate
and direction of waste movement. Therefore, no at-
tempt was made to model the hydrological effects of
waste injection. Second, because this study was in-
itiated after the waste -injection system was planned,
constructed, and brought into operation, there was no
chance to influence the design, construction, place-
ment, coring, and logging of the injection and observa-
tion wells which might have increased their utility as a
research facility.
At the inception of this study, it was recognized that
an interdisciplinary approach, which included organic
chemistry, inorganic chemistry, microbiology, and
hydrogeology, was necessary to understand and de-
scribe the several aspects of subsurface organic waste
injection. Therefore, in this report, the organic and
inorganic chemistry is the work of the authors; the
microbiology and the hydrogeology are based on the
work of others. (See section, "Acknowledgments".)
The Hercules Inc. plant is located on the Atlantic
Coastal Plain approximately 4 miles northwest of
Wilmington, N.C. A photograph of the plant is shown
in figure 1, and its location is shown on the map of
figure 2. The product of the plant is dimethyl
terephthalate (DMT), which is used in the production
of synthetic polyester fibers. The organic byproducts of
DMT manufacture were injected into the subsurface
from May 1968 until December 1972.

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cond ct of thi: study, a nd provid ng histo rival and
back and ini ation. a drily E of oh4e
tion ells an 1 the hyd rogeologi -.al studi s at the
wastt -injection site resu Llted fro waste- nitoring
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HYDROGEOLOGY
metal analysis. Donald W. Fisher, U.S. Geological
Survey, Reston, Va., determined dissolved gases in the
water samples.
HYDROGEOLOGY
By H. M. PEEK and R. C. HEATH
The Wilmington Area is underlain by coastal -plain
sedimentary units more than 1,000 ft (305 m) thick.
The sediments are predominantly of Late Cretaceous
age and include ascending the Cape Fear, Middendorf,
Black Creek, and Peedee Formations. The Castle
Hayne Limestone of Eocene age overlies the Peedee in
much of the area, but does not extend as far west as the
Hercules site. Undifferentiated sands (probably of
Pleistocene age), about 75 to 100 ft (23 to 30 m) thick,
overlie the Cretaceous strata at the Hercules site. As
shown in figure 3, these units generally consist of in-
terbedded sand, silty sand, clay, and some thin beds of
limestone. The sediments are fine grained, with clay
the predominant lithic unit. The beds of sand are thin
and generally fine grained.
The surficial sand is the only freshwater aquifer
beneath the site. The sand is very permeable and is a
productive source of water. The rate of recharge is high
as most of the precipitation enters the sand. Individual
wells yield about 300 gal/min (1,136 1/min), and the
total withdrawal at the site is more than 6 million
gal/day (23 million 1/day).
There are several relatively permeable artesian
aquifers in the Cretaceous sediments, but none are
very productive and all of them contain brackish wa-
ter. The principal aquifers occur at depths of 300 to 350
ft (91 to 107 m), 475 to 500 ft (145 to 152 m), 660 to 700
ft (201 to 213 m), 850 to 1025 ft (259 to 312 m), as
indicated in figure 3.
The "300-ft" zone was sampled and the head was
measured at several well sites during construction.
Well 13 is the only well completed in this zone. The
water from this well had a chloride concentration of
2,600 mg/l. The head is about 29 ft (8.8 m) above sea
level.
No wells have been constructed in the "500-ft" zone;
however, samples for water analysis were collected
during construction of wells 14 and 15, and the
chloride concentration of water from this zone was
near 7,000 mg/l. The artesian head was not measured.
Three wells have been constructed in the "700-ft"
zone and, in addition, water -quality and water -level
data were obtained during the construction of deeper
wells. The chloride concentration of the water in this
zone is about 10,000 mg/1 and the natural head in this
zone was about 38 ft (12 m) above sea level.
The zone between depths of 850 and 1,025 ft (259 to
312 m) is the injection zone. The water from this zone
Geologic
Chloride
Water
Injection
well
log
(mg/1)
level
I-7A
(ref
LS)
0
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EXPLANATION
Sand Gravel
Clay �t� Shell
Rock
FIGURE 3.—Diagram showing hydrogeologic conditions and
injection -well construction for well I-7A.
has a chloride concentration of nearly 12,000 mg/l. The
artesian head in this zone is unusually high, about 65
ft (20 m) above land surface at the site, or about 90 ft
(27 m) above sea level. This zone was selected for waste
injection for reasons of its greatest depth below the
fresh ground -water zone, the high salinity of the
ground water in this zone, and permeability which
would permit waste injection at the rate of 200 gal/min
(7571/min).
The artesian conditions appear to be regional as in-
dicated by the presence of freshwater to only very shal-
low depths over a large area along the Cape Fear arch,
as first observed by LeGrand (1955), and more directly
by recent exploration. The injection zone and the thick
overlying confining bed are identifiable in a well near

6 SUBSURFACE ORGANIC WASTE INJECTION, NORTH CAROLINA
Calabash, about 45 mi (72 km) southwest of the Her-
cules site, which is approximately along the line of
strike. The elevation of the artesian head is about 100
ft (30 m) above sea level at Calabash. The water from
this well has a chloride concentration of about 4,000
mg/l. The artesian head of a well completed at a depth
of about 650 ft (198 m) at the Calabash site has an
elevation of about 35 ft (11 m) above sea level, and the
water has a chloride concentration of about 650 mg/1.
The aquifer serving as the injection zone at the Her-
cules site consists of multiple layers of sand, silty sand,
clay, and some thin beds of limestone. The overall
permeability of this section, which is about 150 to 175
ft (45 to 43 m) thick, is very low although the permea-
bility of the salty zones is relatively high. A tempera-
ture survey indicated that much of the waste entered a
thin subzone at a depth of about 1,000 ft (305 m) in the
initial injection well (I--6).
No long-term pumping test was made on the injec-
tion well prior to placing the system in operation. The
injection rates fluctuated so greatly during the initial
injection period that the data cannot be used to
evaluate the hydraulic characteristics of the sub -zones.
Tests on wells drilled later could not be made properly
as the system was in operation and injection rates were
not stable.
The high artesian pressure, particularly in the deep-
er aquifers, the generally low permeabilities of the
aquifers, the thick zones of clay and silty sands, and
the shallow depth to brackish water suggest slow
natural circulation of water in the Cretaceous beds.
CASE HISTORY OF WASTE INJECTION
A chronology of the significant events which oc-
curred during the four and one-half years of waste
injection is given in table 1. A map showing locations
of injection and observation wells is given in figure 4.
INSTALLATION AND OPERATION OF INITIAL
WELL SYSTEM
The initial well system consisted of one injection
well (I-6) and four observation wells (numbers 1, 2, 4,
and 5) completed at a depth of about 855-1025 ft
(260-312m). Well 3 was completed in the first aquifer
above the injection zone at about 660-690 ft (201-
213m) depth. The wells were cased with a special 10-in.
(250-mm) diameter fiberglass casing and equipped
with stainless steel screens of 6-in. (150-mm) diameter.
The screens were set at the depths shown in table 2.
The deep observation wells were equipped with plastic
sampling tubes extending from the wellhead to the
injection zone. Each well was equipped with a pressure
gage on the wellhead and a manometer located at a
central station. As shown in figure 4, the observation
wells were only located at a maximum distance of 150
ft (45 m) from the injection well, which was too close to
indicate the magnitude and pattern of pressure change
or to permit a reliable measurement of the travel time
of the waste.
The injection of waste into the system was begun in
TABLE i.Chronology of significant events during waste injection
Date
Event
May 1968
Injection well I-6, and observation wells 1, 2, 4,
and 5 completed to 1,025-ft depth. Observation
well 3 completed to 700-ft depth.
May 1968
Waste injection begun through injection well I-6.
September 1968
Waste was detected in wells 1, 2, 4, and 5.
June 1969
Waste injection shifted from well I-6 to wells 4 and
5 because of excessive injection pressures in well
I-6.
November 1969
Injection well I-6 damaged during an attempt to
reclaim the well. Waste injection continued
through well 5.
December 1970
Observation well 8 completed to 700-ft depth.
January 1971
Observation well 9 completed to 700-ft depth.
February 1971
Leakage of waste into the 700-ft zone was detected
at well 3.
April 1971
Injection well I-7A was completed to 1,050-ft
depth.
May 1971
Waste injection shifted from wells 4 and 5 to well
I-7A.
May 1971
Observation wells 7 and 11 completed to 1,050-ft
depth.
May 1971
Wells 1 and I-6 were cemented to stop waste -
leakage into the 700-ft zone.
June 1971
Observation well 12 completed to 1,050-ft depth.
October 1971
Waste injection renewed through well 4 because
well I-7A was not accepting all the waste at the
specified injection pressure limit.
November 1971
Observation well 13 completed to 300-ft depth.
December 1971
Waste detected in well 9 indicated waste leakage
into the 700-ft zone in that area.
December 1971
Pressure decrease in well 5 indicated possibility of
waste leakage into an aquifer above the injec-
tion zone.
March 1972
Pressure decrease in well 2 indicated possibility of
upward leakage of waste.
May 1972
Observation wells 14, 15, and 16 were completed to
1,050-ft depth.
June 1972
Waste was detected in well 14, and a weekly sam-
pling program was instituted to monitor the
passage of the waste front.
October 1972
Wells 2 and 5 were cemented to stop waste -leakage
into the 700-ft zone.
November 1972
Waste injection was gradually phased over to sur-
face treatment of the waste.
December 1972
Waste injection terminated.
January 1973
Waste disappeared from well 14 after injection
termination.

CASE HISTORY OF WASTE INJECTION
TABLE 2. Iniection-system well data
well
Date drilled
Total
Screened
No.
Purpose
(mo-day-yr)
depth (ft)
interval (A)
Water Level'
Remarks
1
Observation
6-1-67
1,025
855-1025
93
Abandoned 5/71
2
Observation
7-27-67
1,025
855-1025
93
Abandoned 10/72
3
Observation
8-8-67
690
660-690
40
4
Observation
3-13-68
1,025
854-1025
93
Also used as injection
well 6/68-8/68 and
10/71-12/72
Observation 1-27-68 1,025 854-1025 93 Also used as injection
well 6/68-5/71. Abandoned
10/72
6
Injection
2-3-68
1,025
855-1025
93 Abandoned 5171
7
Observation
5-7-71
1,040
805-1036
111
7A
Injection
4-29-71
1,110
830-1008
195
8
Observation
12-3-70
709
694-704
41
9
Observation
1-28-71
743
727-737
32
11
Observation
5-28-71
1,043
855-1035
127
12
Observation
6-23-71
1,015
838-974
150
13
Observation
11-16-71
300
283-293
29
14
Observation
5-23-72
1,010
843-972
—
15
Observation
5-23-72
1,030
843-977
—
16
Observation
5-23-72
1,010
843-983
—
'In feet above mean sea level on date drilled. Water levels need to be considered in light of injection history.
the latter part of May 1968 by intermittently inject-
ing batch quantities at a rate of about 200 gal/min
(7571/min). As the volume of waste increased and the
-14
-1 1
0
�15
Al rSP
Pf
01-7A
Plant
R
�g
P
P
A,
16
E
A2
Al
1-60
Al
®4
®5
0
c
E
0
75
J150 FEET
3
0
20
40 METRES
0 1000 2000 FEET
0 300 600 METRES
EXPLANATION
O Injection well
A Observation well
® Observation well used
as injection well
Plant location — Let 34' 19' N.;
Long 77 58' W.
FIGURE 4.—Map of waste -injection and observation wells.
periods of injection lengthened, the pressure rose
sharply in the injection well and in the aquifer. The
average monthly injection rate and the highest well-
head injection pressures, measured monthly or more
frequently, are plotted on the graphs in figures 5 and
6 and reflect the early history of the system.
By September 1968, the waste was detected in sam-
ples collected from all existing observation wells
(wells 1, 2, 4, and 5) in the injection zone. Only pH and
dissolved solids were determined on samples collected
during the passage of the waste front through the
observation wells. There were no determinations of
any gas constituents evolved from subsurface waste
reactions, and no measurement of organic waste con-
tent. By May 1969, pressure in the injection well had
reached the equivalent of 400 ft (91 m) above sea
level, and about 165 ft (50 m) in the observation wells.
240
220
200
w tso
Z
z
2 160
Q
.140
0
Q 120
100
WELLS USED FOR WASTE INJECTION
1-6 4& 5 5 1-7A 1-7A ♦4
u� OZ
Q�i�QwO2�LL-',-'.QNO�ii�Q�-',-�,Q
Q
2Q2 2O
O
in ZO
a -
Q
�u�QU/OZO
1969
1970
1971
1972
FIGURE 5.—Monthly average injection rate. Injection ceased December
1972.

8 SUBSURFACE ORGANIC WASTE INJECTION, NORTH CAROLINA
INJECTION PRESSURE IN FEET ABOVE LAND SURFACE
200 300 400 500
June
July
Aug
I
Sept
I
a
Oct
I
Nov
I
Deg
Jan
I
I
Feb
I
Mar
I
Apr
May
I
June
July
Aug
Sept
I Shifted Injection from well 4 to well 5
Oct
I Injection well (6) out of service
Nov
Dec
Jan
I
Feb
Recirculation during work on
Mar
Apr
Injection well No. 6
May
z
June
,I
.. 3
o
Juiy
oI
Aug
I3
Sept
`I O
Oct
Nov
6 m
Dec
Jan
m I a
`I
Feb
I m
Mar
Apr
May
Began injection through
June
well I-7A
July
Aug
Injection stopped In well 5
Sept
Began injection through well 4-
Oct
Nov
ec
Jan
Feb
Mar
Apr
May
p
June
J."
Aug
Sept
I
Oct
I
Nov
Dec
I njection ceased December 1972
FIGURE 6.—Graph of highest wellhead injection pressures.
Figure 7 shows the oval pattern of the pressure sur-
face in the injection zone in January 1969 which
suggested the greatest waste movement to the north-
west from well I-6. The injection pressure continued
to rise to a high of more than 450 ft (137 m) by June
1969.
Because of the pressure build-up in the injection
well, it was not possible to continue injection of waste
at the rate of 300,000 gal/day (1,136,000I/day), with-
out exceeding the allowable limits of 150 psi (10.3
bars) specified by the injection permit. As the obser-
vation wells were of limited benefit after the waste
had passed, the North Carolina Board of Water and
Air Resources granted permission to the company for
injection of the waste through wells 4 and 5 as an
emergency measure to allow the plant to continue
operating.
In November 1969, an attempt was made to reclaim
the injection well by replacing the screened section,
but this reclamation attempt was not successful and
apparently damaged the casing because of subsequent
A2
233 4I
At
245
06 A
260
r'S
O
?AO
??S
&4 ?�
170
�5
153
'ems
0 50 100 FEET
0 10 20 30 METRES
EXPLANATION
0 Injection well
o Observation well — injection zone
♦ Observation well — 700-foot zone
5 Upper number is well number
153 Lower number is altitude of the pres-
sure surface; in feet above mean
sea level. Contour interval variable
FIGURE 7—Location of wells in initial system and pressure surface,
January 1969.
waste leakage at this well. The pressure surface in
late September 1970, is shown in figure 8. Well 6, the
injection well, was out of service and well 5 was serv-
ing as the injection well. As may be noted, the low
pressure at well I-6 indicates leakage from the injec-
tion zone through this well. In February 1971, a sud-
den pressure increase was noted in well 3 which is
screened in the aquifer at a depth of 660-690 ft (201-
210 m) and one month later in March, waste was
detected in this well.
A caliper log taken in May 1971 just prior to the
cementing, the injection well 6 showed a break in the
casing of the well near 500 fit (152 m) depth. Appar-
ently leakage of the waste had occurred for a long
period of time into the aquifer at a depth of 500 ft
(152 m). This leakage had not been detected previously
because of the absence of wells in the zone. A sonic log
taken at this time indicated poor bonding between the

CASE HISTORY OF WASTE INJECTION
cement casing and the formation between the injection
zone and the 700-ft zone; therefore, the leak into the
700-ft zone most likely originated from the injection
zone with the waste rising into the 700-ft zone around
the outside of the well casing (C. Sever, oral commun.,
1973). Well 1 in addition to injection well 6 was sealed
with cement in May, 1971 because low pressure in well
1 indicated possible waste leakage also at this point.
After cementing, the leakage apparently stopped be-
cause the pressure in the 700-ft zone returned to nor-
mal within a few weeks, with most of the decline occur-
ring within hours.
A request by the company to double the waste injec-
tion rate from 300,000 gal/day to 600,000 gal/day was
denied by the North Carolina Office of Water and Air
Resources in March, 1970. After a review of the opera -
0 50 100 FEET
0 10 20 30 METRES
EXPLANATION
Injection well — out of service
Observation well — injection zone
• Observation well — 700-foot zone
5 Upper number is well number
153 Lower number is altitude of the
pressure surface; in feet above
mean sea level. Contour interval
10 feet
FiGuRE 8.—Map of pressure surface, September 1970.
tion of the system, in July 1970 the North Carolina
Office of Air and Water Resources concluded that the
operation of the system had not been successful, and
that continued waste injection would require the in-
stallation of at least one new injection well and a
larger network of observation wells.
CONSTRUCTION AND OPERATION OF
EXPANDED INJECTION SYSTEM
The second injection well, I-7A, was drilled approx-
imately 2,500 ft (762 m) northeast of injection well I-6
(fig. 9). The second injection well was to be located at
the present site of observation well 7; however, the
permeability was too low for injection at this site and
well 7 was completed as an observation well. During
the development of well I-7A, waste and gas were
pulled into the well. The gas was accidentally ignited
by welding equipment, and later analysis by Hercules
Inc. indicated the gas to be predominantly methane.
Identification of formic acid in water samples con-
firmed the presence of waste.
Waste injection through well I-7A began in May
1971 at an average rate of 120 gal/min (4541/min), and
injection of waste through well 5 ceased. By October
1971, this new well was not accepting all the waste
within the specified pressure limit, and waste injection
was resumed in well 4. Waste injection continued
through both well 4 and injection well I-7A until the
termination of injection in December, 1972.
The spacing of the second observation -well network
installed to monitor waste movement from both the old
and new injection wells was 10-15 times the distance
used in the original network. Observation wells 11,12,
14, 15, and 16 were installed during the period from
May 1971 to May 1972, to monitor pressure and waste
movement in the injection zone. Observation wells 8
and 9, which were completed into the 700-ft (213 m)
aquifer, were operational when the second injection
well was completed.
In December 1971, waste was detected in well 9
concurrent with an increase in pressure, indicating the
leakage of waste into the 700-ft aquifer at the new
injection site. This leak apparently was through the
annular space around the casing of well I-7A. Pressure
decreases in well 5 during December 1971, and in well
2 during March 1972, indicated that these wells also
had possibly become channels for leakage of the waste
into shallower zones. Wells 2 and 5 were later sealed
with cement to prevent leakage, but well I-7A has not
yet been sealed (April,1974).
Figure 9 shows the well system, the reduced pres-
sure surface of the injection aquifer, and the approxi-
mate limits of waste travel in October 1972. At this
time, the areal extent of the waste in the subsurface
does not coincide with the pressure surface because
although the major quantity of waste was injected

10 SUBSURFACE ORGANIC WASTE INJECTION, NORTH CAROLINA
through wells I-6, 4, and 5, the highest injection pres-
sure at this time was at well I-7A thus biasing the
pressure surface to the northeast of the waste -
contaminated area. The waste had apparently passed
well 14, about 1,500 ft (457 m) north of the initial
injection site, by the time it was completed, and also
had passed well 15, about 3,000 ft (914 m) west of the
initial injection site. During August 1972, the waste
was detected in Well 11 as indicated by the dissolved
organic carbon (DOC) content, which has proved to be
J14�124 11 \
\ 12 127
1
1
128�,013I 276
•
14® 6 05i 9 `
200� /168 / I
119 8 160 �i /
7 740�-��
\�?p
0 1000 2000 FEET
0 300 600 METRES
EXPLANATION
•
injection well
0
Observation well — injection zone
•
Observation well — 700-foot zone
O
Observation well — 300-foot zone
®
Observation well used as injection
well
----
Original system
-- —
Approximate limits of waste travel
—160—
Pressure -surface contour
--140 --
Estimated pressure -surface contour
124
Upper number is altitude of the pres-
sure surface, in feet above mean
sea level. Contour interval 20 or
40 feet
7 Lower number is well number
FIGURE 9.—Map of pressure surface and approximate limits of waste
travel, October 1972.
the best index for monitoring waste movement in the
subsurface at this site.
In July 1971 the North Carolina Office of Air and
Water Resources stipulated that the waste -injection
permit would not be extended beyond the July 1, 1973
deadline. Therefore, in November 1972, a conventional
surface waste -treatment facility was completed by the
company and the injection of the waste was gradually
reduced as the new facility was placed in operation.
During December 1972, injection of waste ceased, al-
though injection of freshwater continued at a rate of
about 15-20 gal/min (57-76 I/min) in both wells I-7A
- N
1100 \\
10 14p102 11 0
A J 02 r�'P
15 2p —1 12 c�
p1 I
1®6!®31 .17A
5 9
I
115 16 A
104� 110 /
7 8
Q
0
e a� QZ
of �P
0 1000 2000 FEET
0 300 600 METRES
EXPLANATION
• injection well
0 Observation well — Injection zone
A Observation well — 700-foot zone
0 Observation well — 300-foot zone
® Observation well used as injection
well
----- Original system
— 115— Pressure -surface contour
--100-- Estimated pressure -surface contour
5 Lower number is well number
116 Upper number is altitude of the
pressure surface, in feet above
mean sea level. Contour inter-
val 5 feet
FIGURE 10.—Map of pressure surface with no iWection, April 1973.

FIELD SAMPLING METHODS
and 4 to maintain both wells operable in case they
would be needed for waste injection before July 1973.
Injection of freshwater was stopped for a period of
about 9 days in March and April 1973, and figure 10
shows the pressure surface of the aquifer at the end of
the 9-day period. Freshwater injection ceased in May
1973. At present (April 1974), waste injection through
wells is prohibited by law in North Carolina.
FIELD SAMPLING METHODS
The collection of ground -water samples can best be
explained by first considering the construction of ob-
servation well 14 as shown in figure 11. The construc-
tion of this well is representative of most of the obser-
vation wells which are completed in the injection zone.
Because the natural artesian head of the water in the
injection zone is about 65 ft (20 m) above land surface,
water samples were collected by simply opening the
valve at the top of the plastic sampling tubing. The
small diameter (64 mm ID) sampling tubing enabled
collection of a representative water sample after only a
30-minute flush period with minimal wastage dis-
charge of ground water. Roughly three void volumes of
water pass through the plastic sampling tube at a flow
rate of 1,200 ml/min during the 30-minute flush peri-
od. The twin sampling tubes were placed for the pur-
pose of water collection from the well in the center of
the screened injection zone at 935 ft (285 m) depth and
from above the screened zone at 822 ft (251 m). Water
samples obtained from above the screened section of
the observation well were of little value as they did not
represent water present in the injection zone. A 3-foot
section of tygon tubing was connected to each outlet of
the two sampling valves to facilitate sample collection.
Sampling methods were designed to be applicable to
uncontaminated ground water as well as the concen-
trated waste for both organic and inorganic parame-
ters. Dissolved organic carbon (DOC) was used to esti-
mate the waste concentration because it is a quantita-
tive organic parameter, and most of the organic waste
constituents are water soluble. Water samples for DOC
were pressure filtered on site immediately after collec-
tion through a silver membrane filter with 0.45-µm
(-micrometre) porosity. The DOC sample was collected
in a 50 ml glass serum bottle sealed with an
aluminum -foil -covered rubber septum stopper. An ex-
tensive discussion of the merits of the DOC parameter
and the method of DOC sample collection is given in a
paper by Malcolm and Leenheer (1973).
Two samples were collected for standard inorganic
water analysis: one litre of filtered water acidified to
pH 2 with nitric acid for analysis of the cations, Al, Ca,
Fe, K, Na, Mg, and Zn; and one litre of filtered non -
acidified sample for analysis of the anions, Cl, F, SO4,
11
4" Gate valve
Valve for
lower sample
—Valve for
Sampling tube
upper sample
outlets
Valve for
Valve for
sampling casing
pressure /
water
gauge
Concrete pad
0'
Concrete
casings
V-15" hole
—j
725'
—10" ID -steel
pipe casing
822
852'
860,
870'
893'
908'
929'
944'
962'
972'
993'
1010'
4" ID steel
pipe casing
-%" OD X ''/a" ID
I mpolene tubing
10" hole
20' of V'stainless
steel pipe
2" PVC screen
2"PVC pipe
Silica sand
Guide plug, back
pressure valve and
wash plug assembly
3%a' hole
FiGuRE 11.—Construction features of observation well 14.
NO2-NO3, and SiO2. The water was pressure -filtered
on site through a vinyl metricell membrane filter of
0.45-µm porosity in a plexiglass filtration assembly
(Skougstad and Scarbro, 1968). Compressed carbon -
free nitrogen was used to pressurize the filter because
ferrous iron will oxidize and precipitate as ferric hy-
droxide during filtration if air is used to pressurize the
filter. Both the acidified and non -acidified samples
were collected in acid -washed, 1-litre polyethylene bot-
tles.
A filtered 1-gallon (3.8-1) sample for trace elements
was collected in an identical manner as the sample for
standard inorganic analysis. After collection in an
acid -washed, gallon plastic jug, high purity nitric acid

12 SUBSURFACE ORGANIC WASTE INJECTION, NORTH CAROLINA
was added to acidify the sample to pH 2. The amount of
nitric acid pipetted into the sample was recorded for
the purpose of acid blank analyses.
The last type of water sample collected was a litre of
unfiltered sample which was used to characterize the
organic compounds. This sample was not filtered be-
cause filtration may introduce low-level adsorption
and contamination problems, and filtration will also
remove organic compounds of low solubility which are
adsorbed and occluded on sediments. This sample was
collected in a litre glass bottle previously heated to
350°C (Celsius) to free it of organic contamination, and
was sealed with a metal screw cap with a teflon liner.
After collection, the glass bottle was placed in a molded
styrofoam packer for shipment, and was chilled in
crushed ice to minimize sample degradation. Blank
samples of uncontaminated ground water were col-
lected as well as waste -contaminated samples to test
for the presence of organic compounds such as phtha-
late esters originating from the plastic sampling tub-
ing. Organic contamination arising from the sampling
tubing did not prove to be a problem in comparison
with the high concentrations of organic waste con-
stituents in the contaminated ground water.
When gas was present in the observation wells, gas
which effervesced from the ground water because of
changes in pressure, temperature, and solubility, was
collected in the following manner. The outflow from
the tygon outlet tube was directed into an inverted
100-ml graduate cylinder filled with water, and the
rate of gas collection was determined over a timed
period at a measured flow rate. After measurement of
the rate of gas effervescence, the inlet of a 250-ml
cylindrical glass gas collector tube was attached to the
tygon outlet tube, and the well water was allowed to
flow through and displace the air in the collector tube
which was held in the vertical position with both the
inlet and outlet stopcocks open. After all the air was
displaced, the gas collector tube was placed in the hori-
zontal position, and well water was allowed to flow
through the tube until 5 to 10 ml of gas had been
collected in the upper portion of the tube. The gas and
water were sealed in the tube by simply closing the
inlet and outlet stopcocks.
After all the samples were collected, measurements
of pH, alkalinity, and specific conductance were per-
formed on site. Alkalinity was determined by titrating
the water sample with standard acid to pH 4.5.The
water samples were shipped air freight to Denver in a
large ice chest filled with crushed ice. Most of the
organic analyses were performed by the authors. The
gas samples were sent by parcel post to the U.S.
Geological Survey, Washington, D.C. where Donald W.
Fisher performed the gas analyses. The samples for
standard inorganic analysis and trace metal analysis
were shipped to the Geological Survey's Central Labo-
ratory, Salt Lake City, Utah. The samples were col-
lected on a periodic basis by trained observers at the
site.
INDUSTRIAL WASTE ANALYSIS
ORGANIC ANALYSIS
The major emphasis in the industrial waste analysis
was upon the organic analysis because the chemical
constituents of the waste were predominantly organic
in nature. An analysis of the organic waste and
methodology were used whereby one could test for the
presence or absence of these organic waste compounds
in waste -contaminated ground -water samples. Com-
parisons of the organic analyses of waste -contaminated
ground water sampled at various points in the subsur-
face with the organic waste analysis indicated what
reactions and transformatins were occurring between
the waste and the injection zone for different periods
after waste injection and for different distances of
waste migration in the subsurface. The organic waste
constituents are thought to be more reactive than the
inorganic waste constituents because of ease by which
they are transformed and broken down by microbiolog-
ical reactions. Certain organic waste acids are thought
to be active in the formation of organic -metal complex-
es, and thus injection of these organic complex -forming
compounds causes the translocation of inorganic
aquifer constituents.
The parameter used to quantify organic waste con-
centrations was DOC which is defined as that portion
of total organic carbon which passes through a silver
membrane filter of 0.45-µm porosity. DOC was deter-
mined on the total carbon channel of a Beckman 915
Carbon Analyzer' after inorganic carbon had been re-
moved from the sample by acidifying with phosphoric
acid followed by nitrogen gas purge. Losses of volatile
organic carbon during the nitrogen gas purge were
found to be minimal for the water-soluble organic
waste constituents.
A number of analytical methods were used to iden-
tify and quantify the organic waste constituents such
that nearly all of the organic carbon in the waste was
accounted for. The analytical scheme used to separate
and identify organic waste constituents is given in
figure 12. The recovery and efficiency of each step in
the analytical scheme was measured by determining
the DOC which was separated or remained in the
waste solution.
Steam distillation was used to separate acetic and
formic acids from other dissolved constituents. A
100-ml sample acidified to pH 1 with sulfuric acid was
steam distilled until 200 ml of condensate was col-
' The use of brand names in this report is for identification purposes only and does not
imply endorsement by the U.S. Geological Survey-

INDUSTRIAL WASTE ANALYSIS
13
lected. Recovery studies with acetic and formic acid
standards indicated that 55 percent of the acetic acid
and 45 percent of the formic acid was steam distilled.
The pH of the distillates was adjusted to pH 10 with
sodium hydroxide to render the acetic and formic acids
non-volatile, and the samples were concentrated by
evaporation on a hot plate.
The concentrates were acidified with concentrated
phosphoric acid and injected into a Varian Aerograph
2700 gas chromatograph equipped with a flame ioniza-
tion detector. The column was glass (4 ft x 2 mm I.D.)
and was packed with 100/120 mesh Porapak Q coated
with 3 percent phosphoric acid. The gas chromatogram
showing the separation of acetic and formic acids is
given in figure 13. Formaldehyde, methanol, and
p-toluic acid in the waste were also found to be steam
volatile, but these compounds did not interfere in the
quantification of acetic and formic acid by gas
chromatography. A more complete discussion of a new
method for the gas chromatographic analysis of acetic
and formic acid is given in a report by White and
Leenheer (1975).
The majority of the organic waste constituents were
identified and measured in ethyl ether extracts. A
100-ml sample was first adjusted to an alkaline pH by
adding 3-5g of sodium carbonate. Extractable bases
and neutral compounds were then extracted by two
successive 100-ml portions and followed by one 50-ml
portion of ether. All of the extractions were performed
in a 500 ml separatory funnel. The extracts were col-
lected in a 250-ml Erlenmeyer flask and dried with 40
g of anhydrous sodium sulfate for four hours. Organic
acids were extracted in an identical manner using the
same samples which were previously extracted for
neutral and basic compounds after acidification to pH 1
with concentrated sulfuric acid. Recovery studies using
Add Hz SO..
II
WASTE
Dgast wrtn Dlra<, GC
<nromotropic erm nanono
�ttnYlltprmeta,l
SOLUTION
ea N.,CO„ axtrect
wiM atpylaMx
I
a.emua ont Bete
acid
1 ao,an,
EMer wmnm
w.
.ver
onon-.olatde
manmpr
olw,. wltn
zoanic end
HzSO. � lunon
.j.
rpemc tom -Neutralize
I
Ory witn N.z50,
AGtl HsSO..
extract
ppunasl w�tn tvaOH
`IYa
�
n eM«
yl
Colorlm.t'c
Kuw.naoa`­n
ConcAantrata by
.ta 'o
ui,armlal—,de
nc
co a urn
Etnara lut�on
Waterlayer
t�
eve on
Y
�,r
I
Inon ........
and
v n
wlt
Dry wih Naz SO,
%
,It,O
OC tlexrminatlon of
co pounds)
m�metnYl aucclnats
Kcon rna Oa
GC nemrm,nauon
banzyl
�n
-entreto
.na
m rmYl
Y
MetnYlanon
static adds
nvl
t . p Malata
wren CH,N,
�
GC dedrmmanon
.Old sytc�mc aOld,o
tnepntbabc acid,
pn1-10 aed.
11
FIGURE 12. — Analytical scheme of organic waste analysis.
t
w
Z
0
N
w
¢
0
¢
0
0
M
I
A. Air
B. Formic acid 10.7 mg/ml)
C. Acetic acid (0.7 mg/ml)
(Attenuation-32X 1012 ampr/mv)
A A
C
0 1 2 3 4 5
II
A B C
16 X 10 12amps/mv 64 X 10 t'amps/mv A t n-
O 1 2 3 4 5
TIME, IN MINUTES
FIGURE 13. — Gas chromatogram of acetic and formic acids.
standards indicated that this ether extraction obtained
86 to 98 percent of the compounds of interest in the
gas -chromatographic analysis.
The ether extracts were concentrated by 250 ml
Kuderna-Danish evaporative concentrators equipped
with 3-ball Snyder columns. The concentrators were
placed in a fluidized -bed sand bath at 690C. A time
period of 30 minutes was required to concentrate 250
ml of ether to 5 ml. The ether concentrate containing
the neutral and basic compounds was directly injected
into the gas chromatograph for analysis. The concen-
trate containing the organic acids was esterified with
diazomethane to produce the methyl esters of the or-
ganic acids. The methyl esters of the waste organic
acids possessed sufficient volatility for gas -chromato-
graphic analysis whereas the free organic acids, with
the exceptions of acetic and formic acids, are non-
volatile. The methylation procedure using
diazomethane is given in the Methods Manual for
Analysis of Organic Substances in Water (Goerlitz and
Brown,1972, p. 37).
The majority of organic compounds extracted by

14 SUBSURFACE ORGANIC WASTE INJECTION, NORTH CAROLINA
ethyl ether were found in the acid extract. A 10 ft x
2mm I.D. glass column packed with 10 percent dieth-
yleneglycol succinate on Gas-Chrom Q was used to
separate the esterified acids in the methylated acid
extract. The gas chromatogram is shown in figure 14 of
the esterified acid extract. Mass spectra were obtained
on each peak of the gas chromatogram by using an
equivalent column in a Finnigan GC -MS Model 150
system. The mass spectra of methyl p-toluate and di -
methyl terephthalate shown in figure 14 is correlated
with the gas chromatogram by the spectrum numbers.
Spectrum numbers are points in the time of the analy-
sis where complete mass spectra can be obtained in the
GC -MS system. "Background spectra" were subtracted
100
80
60
40
20
0
100
a
1. Dimethyl methylsuccinate
2. Methyl benzoate
3. Dimethyl succinate
4. Methyl-p-toluate
5. Dimethyl terephthalate
6. Dimethyl phthalate
s
2
1
3
6
0 20 40 60 80 100 120 140 160 180
SPECTRUM NUMBER
2 4 6 8 10 12 14 16 18 20
MINUTES
Y
a
W 80
W
a
m 60
0
W
a 40
Z
W
W
1U 20
a
Spectrum Number 68-65
Meth y I-p-tol u ate
20 40 60 80 100 120 140 160 180 200
ATOMIC MASS/ELECTRONIC CHARGE
100
Y
a
W 80
W
a
m 60
LL
O
W
Q 40
F
Z
W
(U 20
W
a
Spectrum Number 154-151
Dimethyl terephthalate
0
20 40 60 80 100 120 140 160 180 200
ATOMIC MASS/ELECTRONIC CHARGE
FIGURE 14.—Gas chromatogram and mass spectra of methylated -acid
ether extract.
by the computer in the system to give the mass spectra
of the pure component. Characteristic mass spectra
fragmentation patterns were used along with appro-
priate standards to identify the organic compounds
separated in the gas chromatograph. An electronic dig-
ital integrator was used to determine the peak areas
of each organic component in the gas chromatogram.
Quantitative analysis was accomplished by compari-
son of peak areas with standard curves.
The ether extract for neutral and basic compounds
was injected on the same diethyleneglycol succinate
column as was used for the methylated acids, and the
gas chromatogram of this fraction is shown in figure
15. There were no basic organic compounds found in
the waste, and the neutral compounds identified in the
ether extract accounted for less than one percent of the
organic carbon in the waste.
After comparing the quantity of organic carbon iden-
tified in the steam distillate and ether extracts with
the total DOC found in the waste, only about 75 per-
cent of the organic carbon was identified. Identified
organic carbon was determined by summing the prod-
ucts of the concentration times the percentage carbon
of the determined organic constituents. Because cer-
tain volatile compounds were lost during extraction
and concentration, direct injection of the waste itself
into a column packed with 10 percent Ethofat on
Chromosorb W was used to identify and quantify
methyl formate, methyl acetate, and methanol. The
gas chromatogram of this separation is shown in figure
16.
A few organic compounds do not give a sufficient
response on the flame ionization detector to be mea-
sured; therefore another analytical method must be
employed. Formaldehyde is such a compound and its
presence was suspected by its characteristic odor in the
waste residue after the other organic components had
MINUTES
FIGURE 15. — Gas chromatogram of alkaline ether extract.

3
1 Standards
INDUSTRIAL WASTE ANALYSIS
Waste
sample
1. Methyl formate
2. Methyl acetate
3. Methanol
MINUTES MINUTES
nGURE 16.—Gas chromatogram of neutral, volatile, waste constit-
uents.
been removed by ether extraction and steam distilla-
tion. Formaldehyde was subsequently identified quan-
tified by its color reaction with chromotropic acid
(Bricker and Vail, 1950). None of the other organic
waste compounds interfere in the formaldehyde de-
termination. Formaldehyde was the last compound to
be identified in the waste, and its inclusion with the
other previously identified compounds accounted for 95
percent of the DOC in the waste.
This scheme of organic analysis which was applied to
the industrial waste prior to subsurface injection was
also applied to ground -water samples which were con-
taminated by the injected waste. The only changes in
the analytical scheme were that the initial sample size
was larger and the degree of concentration was greater.
Three waste samples were collected during 1972-73,
and the average analysis of these three samples is
given in table 3. The data of the individual analyses
are given in basic -data table 20. The DOC of these
waste samples ranged from 6300 to 7800 mg/l; how-
ever, there were only minor variations in the relative
concentrations of the various organic constituents.
All of the organic waste constituents can b& thought
of as reactants, impurities, byproducts, products, and
(or) catalysts directly related to the industrial prpcess-
es. The overall process at the Hercules plant is to
oxidize p-xylene to terephthalic acid in the presence of
methanol and acetic acid to give the primary product,
dimethyl terephthalate (DMT). There is also a small
formaldehyde plant which produces formaldehyde
15
from the oxidation of methanol. In the waste analysis,
methanol is a primary reactant; benzoic acid and
phthalic acid most likely result from the oxidation of
toluene and o-xylene impurities in the p-xylene
feedstock; p-toluic acid, p-methyl benzyl alcohol, and
methyl p-formylbenzoate are incomplete oxidation
products of p-xylene oxidation; succinic acid, methyl-
succinic acid, and propionic acid are probably the
fragments resulting from cleavage of the aromatic ring
duringp-xylene oxidation; formic acid is a byproduct of
methanol oxidation; formaldehyde, terephthalic acid,
and dimethyl terephthalate are products; and acetic
acid is a catalyst. The dimethyl terephthalate product
is purified after p-xylene oxidation and methylation by
distillation and recrystallization with the extraneous
organic constituents going to the waste.
Most of the organic acids found in the waste exist in
chemical equilibria with the methyl, monomethyl,
and dimethyl esters. These esters were generally found
only in trace quantities in the waste because the aque-
ous waste solution tends to favor hydrolysis of the
esters to the acids. No distinction was made between
the monomethyl esters and the free acids for the dicar-
boxylic acids in the waste because both types of com-
pounds were extracted in the acid fraction, and methy-
lation with diazomethane converted both the mono -
methyl ester and free acid to the same dimethyl ester.
For example, what is identified as terephthalic acid
may actually be monomethyl terephthalate in the
waste because methylation of both compounds will
produce dimethyl terephthalate. The fact that mono -
methyl terephthalate is much more water soluble than
terephthalic acid strongly suggests that the
monomethyl ester of terephthalic acid predominates in
the waste.
The organic waste analysis demonstrated that an
industrial organic waste can be characterized by using
a logical analytical scheme, by conducting a materials
balance with DOC, and screening for organic com-
pounds which are likely to be found in the waste as the
result of the industrial process.
INORGANIC ANALYSIS
Table 4 summarizes the inorganic constituents
found in the waste prior to injection. This table gives
averages of two inorganic waste analyses performed by
the WRD Central Laboratory, Salt Lake City, Utah,
with a few miscellaneous analyses performed
elsewhere. The data of the individual analyses are
given in Basic Data table 21. The elements determined
by atomic adsorption were Al, Mn, Ca, Mg, Na, K, Sr,
Mo, Ni, Cd, Cr, Co, Hg, Zn, and Cu. Automated co-
lorimetric methods were used to determine SiO2, Fe,
SO4, Cl, NO2-NO3, and PO4, and manual colorimetric
methods were used to determine As, Se, and F.

16
SUBSURFACE ORGANIC WASTE INJECTION, NORTH CAROLINA
TABLE 3. Average organic analysis of waste
Compound
Structural
formula
Concentration
(mg/l)
Concentration
as DOC (mg/0
Percentage
g
of DOC
Trace organic compounds (less than 0.5 mg/1 DOC)
Compound
Structural formula
Acetic acid
CH3-C'0-OH
9,350
3,740
52.6
01
C-OCH3
�
Dimethyl phthalate
1 i
0
0-4-0CH3
Formic acid
H-C, -OH
3,110
812
11.4
0
Dimethyl succinate
CH30- -CH2-02-C-003
-OH
0`L-OCH3
p-Toluic acid
1
CH3
1,140
805
11.3
Dimethyl terephthalate
1 0
�C-OCH3
0
Formaldehyde
H-C'0-H
1,800
720
10.1
Methyl acetate
CH3-C' _OCH3
H
p-Methylbenzyl alcohol
0
Methanol
CH30H
757
284
4.0
CH3
Methyl formate
H-C°0-OCH3
0,
L-OH '
Terephthalic acid
I
459
257
3.6
Methyl-p-formyl benzoate
0,
i \0CH3
C-OH
0'
H
0'
C'0-OH
CH3
Methylsuccinic
0
'c-CH2-CH-C`
Phthalic acid
I
76
43
.6
acid
NO- -OH
C; -OH
0
0'C-OCH3
0.
—OH
Methyl-p-toluate
I
Benzoic acid
I
54
37
.5
CH3
Propionic acid
CHTCH2-C110-OH
Waste DOC-7110 mg/1
Total
6,698
94.1
Succinic acid
NO-OC-CII2-%-e -OH
Of the inorganic parameters commonly found in mg/1
levels in ground water, only Ca, SiO2, and NO2-NO3
were significantly higher in the waste than in the
native ground water present in the injection zone.
TABLE 4.Inorganic waste analyses
Dissolved constituent Concentration Dissolved constituent Concentration
Milligrams per litre Micrograms per litre
Silica (SiO2) ...... _.. ................._....... __ 31 Calcium(Ca)........... 1300 Aluminum (Al), tot al...............----
6200
---._.- -
Magnesium (Mg) ......................- 31 Arsenic (As) ..........-------..........---.....------........- 3
Sodium (Na) --------------------- --- ------------------- 1.7 Cadmium (Cd) ---- ------------------ ---------___ 4
Potassium(K)........... .._.------------------------ 3.8 Chromium (Cr), total ................................ 260
Cobalt (Co)--.._ ---------------- ..................... . 1600
Sulfate (SO,) ...................... 25 Copper (Cu)--------------------------------------------- 100
Chloride (Cl) ------------ --- ----------------------- 5.4
Fluoride (F) 2.1 Iron (Fe), total....------------------------_----..._ 6600
........... ..- Lead(Pb)-_...--..........._.._......._........... ...... 7
Nitrite-nitrate-NOb)-..-----_.......----- 3.9
Orthophosphate (POd------------- ____ _.......28 Manganese(Mn)_..--------...------.......----._. 120
Hardness as CaCO2 (Ca, Mg).......... 3400 Mercury (Hg), total _--------------_...................... 1
Molybdenum(Mo)-------------------------------------- 2
Nickel (Ni) ........... ..... .-------------_------------------ 50
H---------------------- .................. 38 Selenium (Se) -------._......-------------------------- 24gpecifcmductn4660, Strontium (Sr) .......... ___ _------------------- 820
(monosa25eC
Zinc(Zn)----------------------------------------------------- 590
Prior to injection, the waste moved through a settling
basin, was passed through a filter to remove particles
over 20 µm in size, and was treated with lime to adjust
the pH to 4. The high levels of calcium and silica in the
waste undoubtedly come from the pre -injection lime
treatment in which the organic waste acids act to Sol-
ubilize calcium and silica. The levels of NO2-NO3 can
only be considered high in comparison to the native
ground water in which there is practically no nitrate or
nitrite. However, the presence of nitrate or nitrite in
the waste may be significant because it is an available
source of nitrogen for microorganisms that may be
degrading the waste in the subsurface environment.
Aluminum and cobalt were found in mg/1 concentra-
tions in the waste whereas they are usually found in
µg/1 concentrations in ground water. The source of
aluminum is probably from the pre -injection lime

HYDROCHEMISTRY OF NATIVE GROUND WATER
treatment, and its high concentration points out the
potential of the waste for dissolution of alumino-
silicate minerals. The high cobalt concentration is of
interest because cobalt salts are frequently used as
catalysts in the oxidation ofp-xylene.
None of the major inorganic waste solutes --calcium,
magnesium, silica, iron, aluminum, and sulfate -can
serve as satisfactory tracers of waste movement in the
subsurface. These solutes are common constituents of
the minerals in the injection zone, and their source
cannot be differentiated between the waste and the
injection zone. Nitrite -nitrate are assimilated by the
microorganisms in the injection zone because they are
essential nutrients in limited supply. Lastly, cobalt
might initially seem to be an ideal inorganic tracer for
waste movement because it is an element not com-
monly found in significant concentrations in ground
water or as a common constituent in aquifer minerals.
However, cobalt is a divalent cation which participates
in cation -exchange reactions with the minerals within
the injection zone, and is more strongly held and re-
tained by exchange complexes on the aquifer minerals
than is calcium or sodium which are the predominant
cations in the native ground water. The law of mass
action in ion -exchange reactions also indicates that
cobalt will be removed from the waste solution and
replaced by calcium and sodium from the exchange
complex because the ratio of calcium to cobalt is 100
times greater in the ground as compared to the waste,
and the ratio of sodium to cobalt is 10 million times
greater in the ground water than in the waste.
In summary, the dissolved ionic solutes of the indus-
trial waste solution consist primarily of calcium and
hydrogen as cations, and of acetate, formate, p-toluate,
and terephthalate as anions. All combinations of these
ionic species appear to be present in concentrations
below saturation solubilities except for calcium and
terephthalate which forms a precipitate when the
waste solution is cooled to 20°C.
PHYSICAL PROPERTIES
The waste prior to injection is a clear straw-colored
liquid with an acrid odor which is a combination of the
odors of acetic acid, formic acid, formaldehyde, and
p-toluic acid. The temperature at which the waste was
injected was about 45eC, and when the waste was
cooled to the temperature of the injection zone (22°C), a
white precipitate very slowly formed which was
primarily the calcium salt of terephthalic acid. This
precipitate may not appear until the waste is refriger-
ated or agitated because the waste is apparently easily
supersaturated with respect to terephthalic acid and
its inorganic salts.
The density of the waste at 20°C was determined to
be 1.006 g/ml, and the density of the ground water at
17
this temperature was 1.0142 g/ml. The injection tem-
perature was 45°C and the density of the waste at this
temperature is 0.9951. This density difference may
indicate that the lighter waste may tend to gravitate to
the upper part of the injection zone and move outward
from the injection well at a faster rate in the upper
portion of the injection zone if the injection zone has a
constant T (transmissivity) value throughout the 150-
foot injection interval. Most likely the T value varies
and the waste preferentially moves out into the zone
of the highest T value regardless of whether this zone
is at the top or bottom of the injection interval.
HYDROCHEMISTRY OF NATIVE
GROUND WATER
The mean chemical analyses of the native ground
water found in the five water -bearing zones at the
waste injection site are given in table 5. Most of the
inorganic water analyses were performed in the
Geological Survey's Water Resources Division
Laboratories in Raleigh, N.C., and Salt Lake City,
Utah. Each individual inorganic water analysis per-
formed on water samples obtained from observation
wells during the course of this study is found in basic -
data tables 22-32.
Water samples from the surficial sand aquifer were
collected from wells 14, 15, and 16 during well con -
TABLE 5. 4norganic analysis of native ground water found in
aquifers at waste -injection site
Dissolved constituent
Depth of aquiferbelow land surface
25-65 ft
275-330 ft
500-520 ft
664-740 R
800-1,025 ft
(7.6-20m)
(84-101m)
(152-158m)
(201-226m)
(244-312m)
62
82
7.8
7.7
7.4
rcoonductance
(micromhosat2VC)....-.._
48
8,890
19,800
27,200
31,800
T�perature(IC)..-.....__.....
18.5
20.1
20.0
20.9
22.7
Density(g/mlat20°C).__----
1.0000
1.0042
1.0042
1.0089
1.0142
_ Milligrams per litre
_
Silica (SiO2) ...........................
4.9
8.1
7.2
9.5
9.3
Calcium (Ca) .--__.-._.......
2.6
28
130
260
333
Mar um(Mp---------- ------
1.3
40
177
267
309
Sa$iun (Na) ........................
3.6
11900
4,620
6,000
6,750
Potassium(K)..............
.8
73
121
182
186
Bicarbonate (HOOs)_..........
. 6.5
578
354
303
230
Sulfate (SO4) .........................
2.9
214
763
595
273
Chloride (Cb .......................
6.0
2,610
6,970
91990
12,100
Fluoride (F)
.0
1.3
.8
.5
.5
Nitrite nitrate (NOs-NOa)
. 1.21
.22
.05
.30
.05
Orthophosphate(POO ..-----
Dissolved Organic carbon
.006
.005
.000
.047
.045
(DOC).
2
1
-
3
.5
Residue on evaporation
at 180°C.
35
319W
13,100
17,300
20,800
Hardness as CaCOs (Ca,Mg)
12
231
1,050
1,740
2,110
Micro rams per litre
Aluminum (Ab, total..........
109
280
613
343
242
Arsenic (As) .....
-
-
-
9
2
Barium (Ba) ....�..................
-
-
-
300
425
Cadmium(Cd) ...._...--........
-
-
-
60
69
Chromium(Cr),total._.-...._
-
-
-
10
18
Cobalt (Co) ............................ - - - 2 1
Copper(Cu)---------.---..-._...... 40 173 - 75 73
Irtgr, (Fe), total .._.._............. 76 1,450 - 2,640 2,260
Lead(Pb) ............................... - - - 3 2
Lithium (Li) ......................... - - - - 285
Manganese (Mn) 12 112
- 165
356
Me (Hg). total ............. - -
- 14
10
Mol nun (Mo) _...---..... - -
- 2
1
Nic el (Ni).... ..................... _. - -
- 3
2
Selenium (Se) ..................... - -
- 2
8
Strontiun (sr)---------------------- - 1,200
- 16,000
18,600

18 SUBSURFACE ORGANIC WASTE INJECTION, NORTH CAROLINA
struction, and from Company supply well C. Water was
obtained between depths of 25-65 ft (7.6-20 m) below
land surface, and data in table 4 for this aquifer were
averaged from the individual analyses. Data were also
averaged to characterize water found in the 300-ft,
500-ft, 700-ft, and injection zones. Water samples from
the 300-ft zone were obtained from wells 14, 15, and 16
during construction, and from well 13 which is
screened in the 300-ft zone. The only water samples
which were available to characterize water found in
the 500-ft zone were obtained from wells 14 and 15
during construction. For the 700-ft zone, uncontami-
nated water samples were obtained from well 8 and
from well 14 during construction. Well 3 which is com-
pleted in this zone was contaminated with waste before
samples were obtained. Well 9 in this zone produced
water with the same chemical composition as water
from the injection zone before it became contaminated
with waste. Uncontaminated ground water from the
injection zone was obtained from wells 7, 11, 12, and
16. Wells 2, 3, 4, and 5 were contaminated before sam-
ples could be obtained, and the injection zone was
found to be contaminated with waste when wells 14
and 15 were completed.
On the basis of dissolved solids content determined
by residue on evaporation at 180°C, water from the
surficial sand aquifer is classified as nonsaline, water
from the 300-ft zone is moderately saline, and water in
the 500-ft, 700-ft, and injection zones is very saline
(Swenson and Baldwin, 1965). Just as dissolved solids
increase with depth, so do calcium, magnesium,
sodium, potassium, strontium, manganese, chloride,
hardness, specific conductance, density, and tempera-
ture.
The parameters which do not increase with depth
are pH, bicarbonate, and sulfate. Bicarbonate and pH
attain their maximum values in ground water from the
300-ft zone, whereas sulfate content is the highest in
the 500-ft zone. Below the 300-ft zone, both bicarbon-
ate and pH decrease with depth, and sulfate content
decreases with depth below the 500-ft zone. This varia-
tion of sulfate content with depth may reflect varia-
tions in aquifer mineral constituents, bacterial reduc-
tion of sulfate in an anaerobic environment, or forma-
tion of barium and strontium sulfates. Water from the
700-ft zone and the injection zone contains a small
amount of hydrogen sulfide, as evidenced by its odor
and the formation of black sulfide precipitates; there-
fore, sulfate may be reduced in these zones by bacterial
reductive processes. Hem (1970, p. 168) states that
water containing 1 mg/1 of barium should contain no
more than a few milligrams per litre of sulfate, and
water containing 10 mg/l of strontium should contain
no more than a few hundred milligrams per litre of
sulfate. The water from the injection zone contains
about 10 mg/l of strontium and about 0.4 mg/1 of
barium; therefore, the concentrations of these two con-
stituents may well be the solubility controls on the
concentration of sulfate.
The change in bicarbonate and pH with depth may
also reflect variations in aquifer mineral constituents;
however, the decrease observed in the more highly
mineralized water may well be an artifact caused by
the precipitation of calcite during the sampling, stor-
age, and shipment of the samples before the analyses
were performed.
The only significant concentration of nitrite -nitrate
was found in the surficial sand aquifer where nitrite -
nitrate probably infiltrates from surface sources.
Phosphate concentrations were very low in all aqui-
fers. These low concentrations of essential nutrients
for microbial activity may be important in limiting the
amount of microbial waste degradation in the subsur-
face.
Lastly, the concentration of dissolved iron and dis-
solved organic carbon (DOC) is of interest because
these parameters are most affected by waste injection.
Above pH 4.8, the solubility of ferric iron is less than
10 µg/l unless there are significant concentrations of
organic substances capable of forming soluble com-
plexes (sequesterization) with ferric iron (Hem, 1970,
p. 116). Because the DOC concentrations are quite low
and the pH is slightly alkaline, it is probable that most
of the dissolved iron exists in solution in the more
soluble reduced form, ferrous iron.
WASTE -AQUIFER INTERACTIONS
After postulating a number of probable waste -
aquifer interactions at the inception of this study in
January, 1971, a two -fold study was undertaken to test
the predicted transformations of the waste after sub-
surface injection. A site study based on analysis of
water samples obtained from the observation well sys-
tem was initiated in June 1971 and terminated in
November 1973. A laboratory study which simulated
waste injection into cores of aquifer material was con-
ducted following the site study, and was terminated in
March 1974.
SITE STUDY
INITIAL CONDITIONS
The water -quality situation at the waste -injection
site at the beginning of this study in 1971 is shown in
table 6. Water samples from wells 2, 3, 4, and 5 had
analyses very similar to the inorganic analysis of the
waste given previously in table 2, and all of the ex-
pected reactions had apparently stopped or slowed to
rates where they were not observable. At this time,
native water samples from the injection zone could be
obtained from the recently constructed wells 7 and 11,

WASTE -AQUIFER INTERACTIONS
TABLE 6.-Change in water composition with waste contamination
19
Concentrations of dissolved constituents, in mg/1
Well
Specific conductance,
in µmhoalcm at 25°C
Date
pH
.SiO2
Al
Fe
Mn
Ca
Mg
Na
K
HCOs
SO&
Cl
F
P NOs
DOC
7
32,500
11/3/71
7.3
11
0.3
1.8
0.2
705
107
6800
330
230
280
12,000
0.9
0 0
1.2
11
32,000
11/3/71
7.2
8.6
.2
1.8
.3
537
195
6600
330
230
210
12,000
0.6
0 0
0.7
4
8,280
6/15/71
4.0
23
6.8
8.3
.3
2500
34
2.9
2.2
0
8.0
230
1.3
1.3 3.9
10,600
5
8,080
6/15/71
4.0
34
7.1
8.0
.3
2400
49
3.2
2.3
0
19
140
1.3
1.1 3.9
11,200
avg. concn wells 4 and 5
concn wells 7 and 11
2.9 28 5.1 1.0 3.9 0.27 .00046 .0068 0 0.055 0.02 1.7 - - 11,500
which were outside the area of waste contamination
and water obtained from these wells were complete-
ly free of waste. The data in table 6 represents the
two extremes between wastes and native ground wa-
ter. An objective of the site study was to observe the
organic and inorganic changes in the ground -water
analyses in going from an uncontaminated to a con-
taminated state and to relate these changes to the
initial hypothesized waste transformations (fig. 17) so
that the initial hypotheses could be confirmed or re-
jected, new hypothesis made and tested, and to formu-
late final conclusions concerning waste transforma-
tions as presented in this report.
INITIAL CONCEPTUAL MODEL OF INJECTED -WASTE
REACTIVITY AND MOVEMENT
The initial conceptual model of the various stages of
the waste in the subsurface environment is dia-
grammed in figure 17. This model is diagrammed for a
certain point in time after the beginning of waste injec-
tion when the various components of the model have
had a chance to form due to various waste -aquifer
interactions. With increasing time during waste injec-
tion, the dimensions of this model will expand and
move to the right. The leading volume of waste moving
outwards from the injection well is mixed and dis-
persed with the native aquifer fluids, and this area of
dispersion is called the waste front in this conceptual
model. The waste area which extends between the in-
jection well and the waste front is called the waste
INJECTION
WAS It INTtRIVR I WASTE FRVNI
WnCTFI CI nW-RFACTION
I
I 1I
I
jRelative percentage of waste to
percentage of ground water -
I I
I
I 1
I I
I I
I
FAST-
y tc
RIAI
POOL ZONE ZONE ZONE ACTIVITY
ZONE
WASTE MOVEMENT
FIGURE 17.-Initial conceptual model of injected -waste reactivity and
movement.
interior where the native ground water has largely
been replaced by the injected waste. The waste front
and waste interior are divided into five zones which are
labeled to describe the predominant types and
mechanisms of waste transformations within each
zone. Microbial waste degradation is thought to occur
only at the leading edge of the waste front, and this
zone is called the microbial activity zone.
The area behind the microbial activity zone is called
the transition zone because it is speculated to be a
region of transition between predominantly mi-
crobiological and chemical reactions which occur in the
injected waste. Few chemical reactions are thought to
occur in the transition zone because the reactions be-
tween the waste and the injection zone components are
essentially completed by the time the waste reaches
the transition zone. However, decreasing microbial ac-
tivity is expected throughout this zone because of in-
creasing concentrations of certain toxic organic com-
pounds such as formaldehyde, and because of the dis-
appearance of limiting nutrients such as nitrate and
phosphate.
The zone trailing behind the transition zone is called
the fast -reaction zone in which neutralization type
reactions occur between the waste acids and the
aquifer mineral constituents. Such reactions include
the acidic dissolution of aquifer carbonates and iron
oxide coatings. The pH of the waste solution changes
from four at the trailing edge of the zone to seven at the
boundary with the transition zone.
Reactions which occur in what is defined as the
slow -reaction zone are the slow solubilization of silica,
aluminum, and iron from the aluminosilicate minerals
in the injection zone. The last zone which is adjacent to
the injection well is called the waste pool because there
are no apparent reaction or changes with time going on
in the waste in this area.
REACTIONS OBSERVED AT WELLS 1, 2, 3, 4, AND 5
At the beginning of this study, limited data were
available from the Company concerning waste con-
tamination of wells 1, 2, 4, and 5 during the first few
months of waste injection. Residue on evaporation and
pH data for water samples obtained from wells 1 and 5
during waste contamination are shown in figure 18.
When the first samples were taken in July 1968, lower

20
U 2
SUBSURFACE ORGANIC WASTE INJECTION, NORTH CAROLINA
Well
• L Weld— Iw • .• ■
7-1 7-21 8-10 8-30 9-19 10-9 10-29
7_11 7-31 8-20 9-9 9-29 10-19 11-9
DATE (1968)
RGURE 18.—Variations in pH and residue on evaporation from sam-
ples taken during observation of waste front in wells 1 and 5.
residue on evaporation values indicated that waste
was already present in observation well 1, which was
only 50 ft (15 m) from injection well 1-6, whereas ob-
servation well 5, at a distance of 150 ft (46 m), was
waste -free.
Observation well 5 remained waste -free until the
beginning of October, when both the pH and residue on
evaporation started to decrease. The pH decreased be-
cause of the acidity in the waste and the residue on
evaporation decreased because the native ground
water was replaced by the waste which had a lower
dissolved solids content.
The fast -reaction zone in which the waste acids are
neutralized is shown by the data from observation well
1. From July 28 to October 15, 1968, the pH remained
between 5 and 6, during which time carbonates and
iron oxides within the injection zone were reacting
with the waste. The mixture of free organic acids and
organic -acid salts from the neutralization reaction re-
sulted in a pH between 5 and 6. When the fast waste -
neutralization reactions stopped, the pH abruptly de-
creased to the pH of the injected waste (pH 4) on Oc-
tober 18, and has remained near this level to the pres-
ent. Residue on evaporation in this well also decreased
at this time to levels found in the injected waste.
Water samples collected while the waste was react-
ing with carbonate minerals contained large amounts
of dissolved carbon dioxide, which is a product of the
acid -carbonate reaction. A sample of gas which effer-
vesced from a water sample collected from well 3 con-
tained 70 percent carbon dioxide by volume as shown
in basic -data table 33.
REACTIONS OBSERVED AT WELL 9
The first opportunity to observe an aquifer during
the process of waste contamination occurred at well 9
in which waste suddenly appeared in high concentra-
tions in December 1971. The first inorganic analysis
determined on a sample collected on June 15, 1971
(basic -data table 25), indicated that the composition of
samples obtained from this well (screened in the 700-ft
zone) was essentially the same as water obtained from
the injection zone. This was an indication that ground
water from the injection zone had somehow leaked into
the 700-ft zone before waste injection was begun in the
second injection well 1-7A; therefore, it was not very
surprising when waste appeared in this well after
waste injection had started in well I-7A.
By June 1972, a sample collected from well 9 con-
tained 5,800 mg/1 DOC, 78 mg/1 iron, 3,900 mg/1 cal-
cium, with a pH of 5.8. These high concentrations of
calcium and iron were indicators of waste dissolution
of aquifer carbonates and iron oxides. The analysis of a
sample collected almost a year later (basic -data table
25) showed that the DOC concentration had increased
only slightly to 6,300 mg/1, the pH was 4.5, the calcium
concentration had decreased to 3,100 mg/1, and the iron
concentration had increased to 310 mg/1, which is an
extremely high concentration of iron in natural water.
These changes observed in two samples collected a
year apart indicate that the reaction of the waste with
aquifer carbonates occurs previous to, and at a higher
pH than, dissolution of iron oxides. Carbon dioxide gas
was also present in the June 1972 water sample
(basic -data table 33), whereas no gas at all was present
in the June 1973 sample. The very high concentration
of iron in the June 1973 sample indicates that the
phthalic acids found in the waste were probably form-
ing water-soluble complexes with iron.
The indications of the carbonate and iron oxide dis-
solution reactions found in the 700-ft zone tend to con-
firm the hypothesized reactions found in the fast -
reaction zone; however, these reactions occurred in an
aquifer overlying the injection zone as the result of a
leak, and well 9 was not regarded as a completely
satisfactory sampling point to obtain information con-
cerning reactions in the waste -injection zone.
REACTIONS OBSERVED AT WELLS I I, 14, AND 15
The major share of information concerning waste -
aquifer interactions was derived from analysis of water
samples obtained from wells 11, 14 and 15 during the
time the waste front could be sampled in these wells.
Waste was found in wells 14 and 15 at the time (May
1972) they were completed in the injection zone as

WASTE -AQUIFER INTERACTIONS
21
shown by the high biological oxygen demand (BOD)
values determined by company analysis not given in
this report. Waste appeared in well 11 in December
1972, detected on the basis of DOC concentrations
being above background levels. Well 11, 14, and 15
were sampled on a periodic basis from June 1972 to
October 1973 by trained observers at the site. Data
obtained on water samples from wells 11, 14, and 15
during this period are found in basic -data tables 34, 35,
and 36, respectively.
Waste was present in well 15 for only a short time
after it was completed. The DOC data in basic -data
table 36 shows that all except a trace of the waste was
gone from this well by December 1972. The presence of
acetic acid, p-toluic acid, and terephthalic acid defi-
nitely confirmed the presence of waste in this well
during the period of elevated DOC levels.
Waste was present in well 14 in much higher con-
centrations than well 15, and it did not disappear until
January 1973. The significant variable parameters de-
termined during the period when waste was present in
this well are plotted in figure 19. The waste concentra-
tions never became sufficiently high to cause detecta-
ble effects on pH, alkalinity, specific conductance, and
the inorganic anions and cations with the exception of
iron. Pressure changes measured at wellhead were
plotted to establish a possible relation between (1) the
U 400
Z E
Q
ZO 300
0-
° 200
>Z
z
0. U 100
.Z
ao
- ao
Z E
2 30
_D
O F
20
0
w w
w U 10
OZ
O
V
800
E
O Z 600
�s
a�
u < aoo
WZ
wZ
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Z
a 16
D E
V
Q ZO 12
U —
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a 6
z
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O
Dissolved 019an1c
erbon
O Pressure difference
• Dissolved iron
O Gas effervescence
Acevc and
O Formic and
� p-Toluic acid
O Terephthahc acid
DATE (1972-1973)
020 u
z_
.015 w 3
E
010
.005 W E
Q
O
16 E
16 ° \
QE
Z
2 U O
FIGURE 19.—Variables observed during passage of waste front in
well 14.
decreases in wellhead pressure difference in the injec-
tion zone between the injection well I-7A and well 14
and (2) the decrease in DOC in well 14. Gas efferves-
cence was defined as the volume of gas which evolved
from an equivalent volume of water under atmospheric
pressure at the sampling site.
From June through October 1972, the waste content
(DOC) in well 14 appeared to be increasing (fig. 19);
however, the waste content abruptly decreased at the
beginning of November and there was no sign of waste
in the well by late January 1973. Although there were
large pressure variations caused by variations in the
injection rate during conversion to surface treatment,
the DOC tended to decrease as the pressure difference
decreased. This direct relationship between DOC and
pressure difference indicated some change in the
ground -water flow system with the cessation of waste
injection.
The first period (June 20 to August 1) of increasing
waste concentration showed only an increase in DOC
as evidence of waste in the well. No gas was found in a
sample collected on August 1, but gas appeared ab-
ruptly in a sample collected only 2 days later. For the
period August 3 to October 31, the amount of gas con-
tinued to increase as DOC increased, and throughout
November, the amount of gas decreased as DOC de-
creased until there was no gas present in the well early
in December. A summary of the gas analyses obtained
during this period is given in table 7.
TABLE 7. — well 14 gas analyses
INA ,not detected]
Percent of total gas volume
Date of
sampling
Hs
Nz
CH4 CO2
1128
8-1-72
N.d.
25
50 11
NA
8-7-72
N.d.
21
54 11
NA
8-14-72
0.2
36
40 11
0.8
10-11-72 N.d. 68 6.0 4.8 N.d.
11-2-72 N.d. 64 33 3.8 N.d.
11-22-72 N.d. 68 12 1.5 N.d.
The appearance of gas, which contained methane
concentrations up to 54 percent of the total gas vol-
ume, was the first indication of anaerobic microbial
decomposition of the organic waste. The following
reactions show how acetic and formic acid are con-
verted to methane by the microorganisms:
a. CH3COOH +H2O —3 CHa +H2CO3
(Lawrence and McCarty,1969)
b. 4HCOOH+1120 —3CH4+3H2CO3
(Siebert and Hattingh,1967)
The most probable reason why microbial degrada-
tion of the waste did not begin immediately with the
appearance of the waste is because there is a time lag
during which the microbes are building up numbers
large enough to significantly degrade the waste.

22 SUBSURFACE ORGANIC WASTE INJECTION, NORTH CAROLINA
The total iron concentration plotted in figure 19 is
very closely related to the waste concentration. Oborn
and Hem (1961) suggest that microbial activity re-
sulting from organic substrates can indirectly in-
crease the iron concentration by a two -stage process:
(1) Microbial oxidation of waste to carbon dioxide and
water lowers Eh by oxygen depletion and lowers pH
by solution of carbon dioxide; (2) lowering of Eh and
pH converts insoluble ferric iron to more soluble fer-
rous iron. Iron may also be brought into solution by
complexation with the aromatic dicarboxylic acids
found in the waste (Ringbom, 1963). A likely com-
plexation reaction is shown below:
-2 -2
0 0 0
c-o c-o o-c''
X I X Fe /
c-o c-o' �\0-c �
0
o° o° o
phthalic acid phthalic acid -ferrous iron
anion complex anion
In samples collected up to September 4, 1972, there
was considerable evidence of microbial sulfate reduc-
tion to sulfide in the form of black sulfide precipitates
and the hydrogen sulfide gas found during the gas
analysis. In later samples, sulfide precipitates and
hydrogen sulfide gas were absent, and the level of
dissolved iron increased, possibly because insoluble
ferrous sulfide precipitates were no longer forming.
Waksman (1952) showed how sulfate can be reduced
with the microorganisms using acetic acid as a source
of energy:
CaSO4 +CH3COOH —0 112S +CaCO3 +CO2 +H2O.
Methane production, iron reduction, and sulfur re-
duction are believed to be indicators of anaerobic mi-
crobial activity induced by waste concentrations in
the ground water. These waste degradation reactions
are a strong confirmation of the microbial activity
zone in the waste front which was postulated in the
initial conceptual model.
One of the most important aspects of this study was
to define changes in the organic composition of the
waste as it traveled from the injection well to an
observation well. Acetic acid, formic acid, p-toluic
acid, and terephthalic acid were determined on water
samples collected from wells 11, 14, and 15 during
waste contamination. Formaldehyde and phthalic
acid were not found in samples obtained from these
wells, and methanol was not determined because
there was no way to quantitatively concentrate or
extract methanol from the ground -water samples for
its determination. Benzoic acid, succinic acid, and
methylsuccinic acid were found in trace amounts in
several samples, but were not quantitatively deter-
mined.
The concentration curves for acetic acid, p-toluic
acid, and terephthalic acid closely follow the DOC
concentration curve in figure 19 for well 14. However,
the formic acid concentration curve did not peak at
the October 31 sample as did the other parameters.
To determine the changes in the relative composi-
tion of the organic waste constituents, the percentage
of DOC was computed for acetic acid, formic acid,
p-toluic acid, and terephthalic acid for each individual
analysis in wells 11, 14, and 15; then the percentages
were averaged for each well and compared with the
averaged waste percentage DOC composition for
these constituents. The results are shown in table 8.
TABLE 8. Relative organic composition of injected waste found in
wells 11, 14, and 15
INA., not detected]
Percentage of DOC
Constituent Waste Before
Well 11 Well 14 Well 15
Acetic Acid ....................
52.6
73.5
78.7
72.5
Formic Acid ....
11.4
N.d.
.4
N.d.
p-Toluic Acid ................
11.3
N.d.
2.7
5.9
Terephthalic Acid --------
3.6
1.9
.9
1.5
Of the four organic compounds determined in well
14, the inorganic salts of acetic and formic acids are
the most soluble in the ground water, and they should
not be significantly adsorbed by aquifer constituents
after waste injection. Acetic acid (sodium acetate)
comprises the majority of the DOC found in well 14,
but formic acid (sodium formate) only constitutes 0.4
percent whereas it constitutes 11.4 percent of the
DOC in the injected waste. Assuming that the rela-
tive composition of the injected waste was fairly con-
stant during the 41/2 years of waste injection, formic
acid must have decomposed during the time it
traveled from the injection well to well 14. The non -
characteristic formic acid concentration curve in fig-
ure 19 also indicates formic acid degradation within
well 14. Siebert and Hattingh (1967) stated that for-
mic acid appears to play a central part in the forma-
tion of methane, and is the organic compound most
readily converted to methane by anaerobic bacteria.
The percentage composition for p-toluic acid and
terephthalic acid also decreases in samples obtained
in well 14 as compared to the injected waste (table 8).
Because aromatic acids are much less biodegradable
than aliphatic acids, it is likely thatp-toluic acid and
terephthalic acid are depleted during waste move-
ment in the subsurface by adsorption on the aquifer
sediments rather than being depleted by microbiolog-
ical degradation. Terephthalic acid and p-toluic acid
are much less water soluble than acetic and formic
acid and therefore are more easily adsorbed.
Indications of waste in well 11 appeared in De-
cember 1972 and samples were collected for analysis

WASTE -AQUIFER INTERACTIONS
23
from January through July 1973. The waste concen-
tration as represented by the DOC curve increased
very slowly in almost a linear manner during this
period as shown in figure 20. Plots of concentration
versus time are also given for acetic acid, terephthalic
acid, and dissolved iron in figure 20. Formic acid,
formaldehyde, and p-toluic acid were not detected in
water samples from this well. There was no gas pro-
duced or evidence of sulfate reduction. The dissolved
iron concentration curve does not show any discerna-
ble correlation with the waste concentration. Dis-
solved iron was essentially constant while the waste
concentration was increasing.
Apparently the waste concentration did not become
sufficiently high to induce microbial waste degrada-
tion as was found in well 14. In well 14, the first
evidence of microbial waste degradation, methane
gas, occurred when the DOC concentration was at
about 25 mg/l. The highest DOC concentration in well
11 was only 18 mg/1. Therefore, as in well 14, mi-
crobiological waste degradation does not seem to
occur below a threshold level of waste concentration.
Both the acetic acid and terephthalic acid concen-
tration curves increase in the same manner as the
DOC curve in figure 20. Acetic acid constitutes about
the same percentage of the DOC in well 11 as in well
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1-1 2-9 3-21 4-30 6-9 7-19 8-28
1-20 3-1 4-10 5-20 ,6-29 8-8
DATE (1973)
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FiGuRE 20.—Constituents measured during passage of waste front
in well 11.
14; however, terephthalic acid was present in greater
relative amounts, whereas p-toluic acid was not even
detected (table 8). The relative abundance of
terephthalic acid to p-toluic acid was reversed for the
few samples collected from well 15 although the per-
centage of DOC due to acetic acid was about the same
as for wells 11 and 14.
The different ratios of terephthalic acid to p-toluic
acid in each of these three wells leads one to question
the assumption that the waste composition was essen-
tially constant during the 4Y2 years of waste injection.
It is most probable that the organic waste collected
from wells 11, 14, and 15 was injected at three differ-
ent points in time and contained different ratios of
terephthalic top -toluic acid. It is remarkable that the
acetic acid contribution to DOC is about the same in
these three wells as is shown in table 8. Regardless of
the wide variations of the ratio of terephthalic acid to
p-toluic acid in samples obtained from these three
wells, both terephthalic and p-toluic acids were below
concentrations at which they were found in the in-
jected waste. It is likely that these compounds were
adsorbed by aquifer sediments during their travel
from the injection well to the observation well.
POSSIBLE FLOW SYSTEMS ASSOCIATED
WITH INJECTION ACTIVITIES
The history of waste concentrations in wells 11, 14,
and 15 suggests that the ground -water flow system
associated with injection activities is very complex
both vertically and areally in the injection zone. In
addition, a true measure of waste concentrations
could not be obtained because the 150-ft (45-m)
screened section of the observation wells permitted
cross -circulation and dilution of waste -contaminated
ground water with uncontaminated ground water,
and it is very unlikely that the injected waste moved
in uniform directions and rates in all permeable zones
within the injection interval.
Examination of the driller's logs (Black, Crow, and
Eidsness, Inc., 1971) of wells 7, I-7A, 11, and 12 show
that from two to four permeable zones may exist at
different points within the injection interval. Insuffi-
cient hydraulic data exist at this site to define the
natural, preinjection flow system, and it is unknown
whether the multiple permeable zones within the in-
jection interval are interconnected and have the same
artesian head, or whether they are independent and
there is a differential, vertical distribution of head
through the injection interval. The complex hy-
drogeology, the lack of hydraulic data, sampling lim-
itations imposed by observation well construction,
and the complexity introduced by waste injection at
various rates and pressures at multiple sites all pro-
hibit the modeling of injected -waste movement, and

24 SUBSURFACE ORGANIC WASTE INJECTION, NORTH CAROLINA
only various possibilities can be presented in this re-
port.
A realistic hypothetical portrayal of the limits of
waste movement at the upper and lower boundaries of
the injection zone is represented in figure 21. The
amoebic shapes of the areal waste distributions is
intended to represent waste movement in directions
of highest permeability. Non -coincidence of the lower
boundary with the upper boundary shows that waste
at the bottom of the injection zone may be moving in a
different lithologic unit in directions independent of
the waste in the upper part of the injection zone. The
areal extent of the waste is represented to be much
greater at the upper boundary of the injection zone
because the specific gravity of the waste is less than
the native ground water. However, if the permeabil-
ity of the injection zone is greater near the lower
N
L14 �11
15 //\� O /"\ �12 �ffi
\ 14 30
®6- � I l/ 7A•� �r
i t ®51 t o \ 9�� P
&16 W
�J E
76 AS
0 1000 2000 FEET
0 300 600 METRES
EXPLANATION
• Injection well
Observation well - Injection zone
Observation well - 700-foot zone
O Observation well - 300-foot zone
a Observation well used as injection well
- - - - - Original system
Limit of waste travel (upper boundary)
--- Limit of waste travel (lower boundary)
FIGURE 21.-Hypothetical areal distribution of waste at the upper
and lower boundaries of the injection zone.
boundary, the relative sizes of the areas invaded by
the waste may be opposite from that shown in figure
21. Because the major quantity of waste was injected
through wells I-6, 4, and 5, the areal waste distribu-
tion is biased around this cluster of injection wells
rather than around injection well I-7A, where a lesser
quantity of waste was injected. Lastly, because waste
injection occurred at multiple sites, the formation of
"pools" of uncontaminated ground water surrounded
by waste is also shown in figure 21.
Changes which occurred in the waste content in
samples obtained from wells 11,14, and 15 during the
2 months after the cessation of waste injection indi-
cated either a major change in waste distribution, or a
change in water being sampled by these wells.
Therefore, the last experiment performed for the
site study was to allow wells 11, 14, and 15 to flow on
November 1-2, 1973, to determine if waste could be
drawn into these wells. It was hypothesized that if
waste did not reappear after withdrawing a limited
quantity of ground water, the waste distribution had
likely changed. However, if waste appeared after a
short period of well flow, it is likely that the disap-
pearance of waste with termination of injection re-
sulted from changes in internal circulation of ground
water within and adjacent to the observation well.
This internal circulation is diagrammed in figure 22.
Allowing the well to flow should withdraw water from
all the permeable zones within the injection zone,
which is screened from 850 to 1,000 f1 (259-305 m) in
the observation wells.
The wells were allowed to flow by disconnecting the
pressure gages and opening the 1-inch ball valve on
the wellhead assemblies. The results of this flow test
are summarized in table 9.
TABLE 9. -Observation well flow -test data
[Nd., not detected]
Flow
Total Acetic Formic
p-Toluic
Terephthalic
Sample
period
flow DOC acid acid
acid
acid
No.
(min)
(gal) (mg/1) (mg/1) (m9/1)
(m9/1)
(M911)
Well-11(flow rate = 25 galtmin)
1
0
0 18 38 NA
NA
0.58
2
235
5,875 75 107.4 2.16
2.71
2.75
3
400
10,000 90 160.1 2.76
2.16
2.61
4
1,050
26,250 170 201.3 3.61
4.43
3.44
5
1,190
29,750 185 348.0 6.63
5.07
3.74
Well-14 (flow rate = 10 gal/min)
1
0
0 1.0 - -
-
-
2
270
2,700 1.0 - -
-
-
3
435
4,350 1.0 - -
-
-
4
1,075
10,750 1.0 - -
-
-
5
1,255
12,550 2.0
-
-
Well-15 (flow rate = 60 gal/min
1
0
0 1.0 - -
-
-
2
160
9,600 5.0
3
375
22,500 47.0 73.45 1.54
1.24
1.06
The flow from well 15 was stopped after 375 minutes
because of concern about the withdrawn saltwater in-
filtrating to the supply wells. Because this well had the
highest flow rate of about 60 gal/min (227 1/min),
enough water was withdrawn from this well in this
period of time to pull the waste into the well. The last

WASTE -AQUIFER INTERACTIONS
sample taken had a DOC of 47 mg/1 and contained
acetic acid, formic acid, terephthalic acid, andp-toluic
acid in the amounts shown in table 7.
Well 11 initially contained a small amount of waste
at the beginning of the flow period, and the amount of
During waste injection
---------------------------
w ; ,W° ° W w° .'w °w —. w °..—W. Wo---� e
w° W W oOW opy°
° w°
W______ __ _____
w.
w —__--______________-
w° — —2 --- ----- -----------------------------
After waste injection
--------------------------
85o'— -------------------------
2"PVC ,�, ---- e-_----a -- --- _ -_
screens
2 0
---- ---3—_----------- --o -
---------------------
---------------------------
-------------------
--------------------------
Silica sand --------------------- — — — —
Bedroc
EXPLANATION
Sand and gravel
Clay
iD, -,@ Pressure gradient
------- Direction of ground
water flow
W Injected waste
FIGURE 22.—Probable internal circulation of ground water within well
14.
25
waste increased steadily during the flow period to the
last sample, which had a DOC of 185 mg/l. The relative
composition of the organic constituents changed in
each successive sample. Formic acid and p-toluic acid
appeared in sample two, whereas they were not de-
tected at the beginning of flow. By the end of the flow
period, the ratio of terephthalic acid to p-toluic acid
had reversed with p-toluic acid being present in the
greater concentration. A gas sample obtained during
the period the well was flowing contained methane at a
concentration of 18 percent of the gas volume (basic -
data table 33). The presence of methane indicated that
microbiological waste degradation was occurring in
the injection zone near well 11, although the waste
concentrations were not high enough in well 11 to
induce methane formation before flow was started.
Waste was not drawn into well 14 during the period
of flow. The flow rate of well 14 was only 10 gal/min (38
1/m) and table 7 shows that only about half as much
water was withdrawn from well 14 as was withdrawn
from wells 11 and 15. A gas sample was obtained which
contained methane at 30 percent by volume (basic -data
table 33), but this methane only indicated that waste
had been present at a previous period in the injection
zone. Methane apparently exists as a gas at the pres-
sure found in the injection zone, and this gas was
entrapped by the aquifer sediments and did not move
away from the well with the waste when internal cir-
culation displaced waste from the well. It is quite
likely that waste would have been drawn into well 14 if
it had been allowed to flow for another day and a
volume of ground water equivalent to wells 11 and 15
had been withdrawn.
The results of the observation well flow experiment
tended to confirm the hypothesis that waste was in the
immediate vicinity of wells 11, 15, and most likely well
14. It is still possible that after injection stopped, the
areal distribution of waste as shown in figure 21
changed because of the influence of the natural, re-
gional flow system in moving the waste away from the
observation wells. However, it would be unlikely that
the waste would move in such a manner that it would
quickly reappear when the wells were allowed to flow.
In the opinion of the authors, the disappearance of
waste was a result of internal circulation changes
within the screened section of the observation wells,
thus preventing waste from being drawn into the sam-
pling tube. This experiment shows that in a study of
this type an observation well which has its screened
section opened to several water -bearing zones may not
serve its purpose as an observation well because it may
not yield injected waste at low -flow rates of the sam-
pling tubes; thus when the dominant proportion of the
waste is present in one of the zones, the samples ob-
tained may not be representative.

26 SUBSURFACE ORGANIC WASTE INJECTION, NORTH CAROLINA
MICROBIOLOGICAL STUDY
The results of the microbiological study are in a
report by DiTommaso and Elkan (1973), and only the
significant findings will be discussed in this report.
The waste, prior to injection, was found to be void of
any bacterial contamination. Likewise, samples ob-
tained from observation wells containing high levels of
waste did not support microbial flora. Approximately
3,000 organisms per millilitre were present in water
samples obtained from the uncontaminated injection
zone, and this count remained constant for the dura-
tion of the study. This count was somewhat high ac-
cording to G. G. Ehrlich (oral commun., 1973), who
cited a range of 10-1,000 microorganisms per millilitre
as representative for uncontaminated ground waters.
These native organisms were isolated and identified as
shown in table 10. Although anaerobic, methanogenic
bacteria were found in certain waste -contaminated
wells, most of the organisms isolated from the uncon-
taminated wells were facultative or aerobic genera
rather representative of the normal microflora of
aquatic environments.
The most common genera found included Agrobac-
terium, Pseudomonas, Proteus, Bacillus, Aerobacter,
Corynebacter, Arthrobacter, and Micrococcus. In labo-
ratory studies, isolates of these genera, either singly or
in combination, were inoculated into a medium in
which various dilutions of the waste served as the sole
carbon and energy source. None of these well isolates
were able to grow and decompose waste under these
conditions. In addition to these microorganisms, a very
low number of obligate anaerobes were detected. Be-
cause there is little or no organic -energy substrate in
the uncontaminated injection zone, these obligate
anaerobes can be present only in limited number.
When a readily available carbon and energy source
was added in the form of the injected waste, these
anaerobes increased in number and constituted the
waste -decomposing microflora.
On July 7, 1972, a 20-week study was initiated to
study bacterial decomposition of waste which was oc-
curring at that time in well 14 as was evidenced by
methane gas formation. A rapid increase in the micro-
bial population resulting from the presence of dilute
concentrations of waste in well 14 occurred during the
20-week period, and this increase is shown graphically
in figure 23. The colony -forming units per millilitre in
the control well (well 11) remained approximately con-
stant at 3,000 organisms per millilitre, whereas in well
14, the population increased to approximately
1,000,000 organisms per millilitre.
E
Z
Z
2
cc
0
LL
Z
0
J
O
O
106
Well 14
(in waste front)
105
10°
Well 11
(uncontaminated)
103 n 4 & 12 16 20 24
TIME, IN WEEKS
nGuRE 23.—Comparison of number of bacteria per millilitre (as
colony -forming units) in waste front (well 14) and in uncontami-
nated aquifer (well 11).
Methanogenic bacteria were isolated in pure culture
from water samples obtained from well 14 during the
20-week study. Gram stains were performed in an at-
tempt to classify these bacteria according to genus.
Two different morphologic types were observed. The
first was a gram -negative, slightly -curved rod, which
was tentatively placed in the genus Methanobacte-
TABLE 10. Identiftcation of isolates from uncontaminated deep well 11
[—, negative reaction; +, positive reaction; A, acid produced; A*, weak positive reaction; AG, acid and gas produced]
Carbohydrate utilization
Organism
Sulfide Reduction Catalase Starch Indole
Identified
Gram stain Morphology Motility
production of nitrate production hydrolysis production
Sucrose
MannitoI
Lactose
Glucose
Maltose
Agrobacterium
— Rod +
— — + — —
—
—
—
A
A*
Pseudomonas
— Rod +
— + + — —
A
AG
AG
AG
AG
Proteus
— Rod +
— + + — —
A
AG
AG
A
AG
Bacillus
+ Rod —
— + + + —
—
A*
A*
A
A
Aerobacter
— Rod —
— + + — —
A
AG
AG
AG
AG
Corynebacter + Rod — — + + — — A A A —
Arthrobacter — Rod — — + + + — A A A A A
Micrococcus + Cocci — — + + — — — — A A A
Pseudomonas
fluorescens — Rod + — + + + — — — — — A*

LABORATORY WASTE -AQUIFER REACTIVITY STUDIES
27
rium. The other was a coccus which was gram positive
and occurred in masses; it was tentatively placed in the
genus Methanococc us.
Although the waste was found to be decomposable by
microorganisms, the system appeared to have low effi-
ciency. Laboratory studies showed the waste to be toxic
even in moderate concentrations. The major localization
of waste decomposition was found in wells located at the
periphery of the waste front where the waste is highly
dilute.
The site study of waste -aquifer interactions provided
qualitative evidence for a number of reactions and
waste -decomposition processes which have occurred in
the subsurface as the result of waste injection. A labora-
tory study was conducted which simulated waste injec-
tion into cores of aquifer material obtained from the
injection zone. The objectives of this study were: (1) To
better define the waste -aquifer interactions in a quan-
titative manner, (2) to substantiate in the laboratory
waste -aquifer interactions which were observed on -site,
and (3) to test for waste -aquifer interactions which could
not be observed on -site because of the construction and
placement of the observation wells.
LABORATORY WASTE -AQUIFER
REACTIVITY STUDIES
INTRODUCTION
The disposal site at Wilmington, N.C., offered a de-
sirable and somewhat unique situation to study the
chemical and microbial aspects of subsurface waste
injection because of the large number of observation
wells. The movement and the reactions occurring be-
tween the waste and the disposal aquifer could be
studied at various stages of the passage of the waste
through or past observation wells. Most injection -well
systems do not have observation wells which can be
used for waste monitoring; therefore other means must
be employed to gain an insight on waste movement and
reactivity.
A possible means of evaluating waste reactivity is to
conduct waste -aquifer reactivity studies in the labora-
tory. Such studies are usually conducted during the
initial stages of injection -well construction to evaluate
the "compatibililty" of the waste with the receiving
zone. These tests are essentially engineering oriented,
are usually simplistic in nature, and are somewhat
analogous to comparative permeability testing with
the native ground water and the waste. A positive
compatibility is achieved if the permeability of the
waste saturated core is the same as or greater than
that of the native ground water. A negative compati-
bility, or a decrease in permeability of the waste -
saturated core could result from precipitation or coagu-
lation of the waste, a reduction in porosity due to dis-
persion and plugging with aquifer or waste solids, the
swelling of aquifer solids, or other reactions which
decrease the porosity of the core matrix.
The laboratory waste -aquifer reactivity tests in this
study were designed to evaluate organic and geochem-
ical reactions instead of the ordinary compatability
testing such as changes in permeability and hydraulic
conductivity. The general objectives of the laboratory
tests were to determine (1) if the passage of the waste
front through the injection zone could be simulated in
the laboratory; (2) if the chemical and physical reac-
tions which were predicted to occur between the waste
and the aquifer materials in the receiving zone at the
injection site would occur under laboratory conditions;
and (3) to determine how well laboratory findings cor-
related with field data and observations.
METHODS AND MATERIALS
AQUIFER MATERIAL
During the drilling of observation well 12, cores
were taken from various depths. Coring of the poorly
consolidated, sandy receiving zone at 960 ft (293 m)
was difficult, but several kilograms of aquifer material
was obtained by screening. This material was sealed in
a plastic container and remained moist until labora-
tory studies were conducted.
CHARACTERIZATION OF AQUIFER MATERIAL
The chemical and physical properties of the aquifer
material from the receiving zone were characterized by
several methods. Particle size analysis was ac-
complished by wet -sieving and sedimentation after
mechanical dispersion at pH 9.5 with NaOH. Aquifer
pH was determined on duplicate 10-gram samples in
deionized water with a solid:liquid ratio of 1:1. The
suspensions were allowed to stand for 1 hour and
stirred during reading of pH. Free iron was determined
by the citratedithionite method of Mehra and Jackson
(1960), total Kjeldahl nitrogen by the method of
McKenzie and Wallace (1954), and organic and inor-
ganic carbon by the method of Malcolm and others
(1973).
Mineralogical analyses were accomplished by X-ray
diffraction and thin -section techniques. X-ray diffrac-
tion analyses were conducted by the authors on size -
fractionated, K-saturated and Mg -saturated samples
placed on ceramic mounts by the method of Kunzie and
Rich (1959). Thin -section analyses and porosity and
specific gravity determinations were performed by the
U.S. Geological Survey Hydrologic Laboratory in Den-
ver, Colo.
WASTE CONSTITUENT ANALYSES
A bulk sample of the industrial organic waste was
obtained from Wilmington, N.C., on November 7,1973.
The organic and inorganic analyses of this sample as

28 SUBSURFACE ORGANIC WASTE INJECTION, NORTH CAROLINA
presented in tables 3 and 4 show that the sample is
representative of the injected waste. All the methods
for specific organic component identification and DOC
in the original waste and the reacted effluent waste
from the laboratory aquifer -waste reactivity tests were
performed as described in the previous method section.
The identification of organic components sorbed on the
aquifer material during testing was accomplished by
placing 10 grams of aquifer -core material into a 250-ml
glass Erlenmeyer flask, acidification to pH 1 with
H2SO4, and triple extraction with 100-ml portions of
ether after 24-hour equilibration at room temperature.
Specific conductance and pH were determined on
standardized laboratory equipment. Total iron, silica,
and sulphate were determined by the authors by stan-
dardized Technicon Autoanalyzer procedures. Sodium,
calcium, magnesium, and chloride were determined on
the reacted waste effluent by the U.S. Geological Sur-
vey Central Laboratory in Salt Lake City, Utah.
MODIFIED HASSLER SLEEVE CORE HOLDER
The laboratory waste -aquifer reactivity studies were
conducted in a modified Hassler sleeve core holder as
shown in figure 24. The core tester was designed ac-
cording to the general specifications as supplied by
Charles D. Haynes of Austin, Texas. The advantages of
this design include the testing of large amounts of core
material of various sizes and lengths, the use of rubber,
plastic, or Teflon sleeves, and the implementation of
confining pressure, which is analogous to overburden
pressure and (or) hydrostatic pressure, if Teflon sleeves
are used. This design also enables the maintenance of a
pressure differential between the confining pressure
and the internal core pressure.
PRESSURIZATION CORE -TESTING APPARATUS
The schematic of the pressurization core -testing ap-
paratus is shown in figure 25. The apparatus is pres-
surized with nitrogen gas from a large reservoir tank.
The conversion of gas pressure to hydrostatic pressure
in the hydraulic separator and the liquid accumulator
End cap
... `.'.`:'':`:'::::::`•:::':`•`::':::':•'::'
Steels
Pins
:::0- ring Confining
Pressure
FIGURE 24.—Diagram of modified Hassler sleeve core holder.
® Liquid
Gas
Collection
FIGURE 25.—Schematic diagram of pressurization core -testing appa-
ratus.
tank prevents possible problems with entrained gases
within the core or possible air leaks from the confining
pressure reservoir into the sleeve core holder. The driv-
ing force for the movement of liquid through the
aquifer material is hydraulic pressure from the hy-
draulic separator. The maintenance of a constant and
accurate gas pressure to within 2 psi at 500 psi was
accomplished by a Grove pressure regulator and a
United States mirrored scaled gage.
Adequate valving arrangements enabled the refill-
ing of the hydraulic separator from a plastic liquid
refilling reservoir while maintaining a constant high
pressure within the core holder. The conductivity and
temperature of the core effluent were monitored with
inline sensors at the outlet of the core holder. All com-
ponents were connected with 0.125 inch (3.17 mm)
stainless steel tubing except the tygon tubing for col-
lection and monitoring of the reacted waste effluent
from the core holder.
EXPERIMENTAL DESIGN
In order to accomplish the laboratory waste -aquifer
reactivity experimental objectives, three experiments
were conducted. Experiments 1 and 3 emphasized
chemical changes which were manifested by changes
in the liquid waste, whereas experiment 2 emphasized
chemical reactivity which could be manifested by
chemical and physical changes within the aquifer core
material.
Experiment 1 was designed to simulate the passage
of the waste front through an observation well or a
given static point within a waste -receiving zone. The
Teflon sleeve of the core holder was packed with
aquifer material and the waste injected into the pres-
surized core at a rate of 2 ml/hr which approximated a
waste movement under field conditions of 0.6 ft/day
(0.2 m/day).
Experiment 2 was designed to simulate changes
which would be manifested within the aquifer core

LABORATORY WASTE -AQUIFER REACTIVITY STUDIES
material with passage of the waste front extending
into the slow -reactivity zone. To accomplish this, waste
was injected into a pressurized aquifer core at a flow
rate of 4 ml/hr, which approximated a waste movement
under field conditions of 1.25 ft/day (0.38 m/day). The
organic and inorganic composition of the reacted waste
effluent was monitored as in experiment 1. At the end
of experiment 2, the reacted core was fractionated into
eight equal sections and analyzed for physical and
chemical changes.
Experiment 3 was designed to simulate changes
which a unit of the very front edge of the injected waste
would undergo as it moved outward through the injec-
tion zone from the injection well. To accomplish this
objective, a given amount of waste was passed or
injected through successive fresh cores of aquifer
material.
TESTING THE PRESSURIZATION
CORE -TESTING APPARATUS
LEAK TESTING
The Hassler sleeve core holder was designed to ac-
cept Teflon sleeves. It was assumed that a confining
pressure, simulating overburden pressure, greater by
150 to 200 psi (pounds per square inch) than the inter-
nal ' core pressure, simulating bottom hole injection
pressure, would facilitate the seal between the end of
the Teflon sleeve and the core -holder plug. The appli-
cation of appropriate confining pressure greater than
internal core pressure may also prevent channeling at
the interface between the core material and the Teflon
sleeve.
The core -testing apparatus was first tested with
sand in the core holder. Internal core pressure and
confining pressure were adjusted to 450 and 600 psi,
respectively. Chloride breakthrough curves, conductiv-
ity breakthrough curves, and the drop in water level
within the accumulator tank indicated leakage. With
confining pressure exceeding the internal core pres-
sure by 150 psi, the 1.5-inch (38.1-iiim) Teflon sleeve
with 0.094-inch (0.38-mm) wall thickness was slightly
deformed, which probably added to the leakage at the
plug seal. An increase in the milled thickness of the
Teflon sleeve, variation in packing and tightening of
the core holder, and the reduction of confining pressure
to that of internal core pressure at 450 psi failed to
solve the initial leakage problem.
The leakage problem was resolved by milling a 2
degree undersize taper on both ends of a thicker walled
(0.187 inch or 4.75 mm), more rigid Teflon sleeve with
confining and internal pressures both at 500 psi. A
sodium chloride solution conductivity breakthrough
curve for medium sand in this sleeve at a flow rate of
100 ml/hr is shown in figure 26.
Rej
After the specific conductance of the effluent salt
solution was essentially the same as the input solution,
the flow was stopped, and the core allowed to stand
under pressure for a 15-hour period. After standing,
the specific conductance of the effluent remained con-
stant at the value of the specific conductance of the
input salt solution. This test insured a leakproof sys-
tem for the waste -aquifer core reactivity experiments.
During the initial pressurization of the core holder
with confining and internal pressure, it is essential to
increase both pressures at the same rate or possible
leakage will occur at the junction of the end plug and
the Teflon sleeve. It is also essential that during the
refilling of the hydraulic separator with fresh waste
during experiments 1 and 2 that the confining pressure
and internal core pressure remain constant at 500 psi.
Adequate valving isolates the core holder from the
hydraulic separator. After filling the hydraulic
separator, that portion of the system is first returned to
500 psi before simultaneously returning the confining
and internal core pressure to the entire system.
PACKING THE TEFLON SLEEVE WITH AQUIFER MATERIAL
The aquifer material used in the laboratory studies
was maintained in a moist condition (approximately 11
percent moisture by weight) in a sealed plastic con-
tainer until used for experimentation. The moisture in
the aquifer sample was diluted native ground water.
In preparation for sleeve packing, the top tightening
ring was placed on the top end plug. The Teflon sleeve
was fitted snugly to the end plug and held in place by a
ring stand clamp. Small portions of representative
aquifer material were packed into the Teflon sleeve
with a glass rod until the sleeve was approximately
fN
0
x
0
cc
U_
U
Z
—a
W W
U
cr
Z cr
aW
U
U �
D�
oZ
Z W
0 U
U 2
U as
LL
U
lb
EFFLUENT VOLUME, IN MILLILITRES
FIGURE 26.—Specific conductance breakthrough curve during leak -
testing of Hassler sleeve core holder.

30 SUBSURFACE ORGANIC WASTE INJECTION, NORTH CAROLINA
one-fourth filled. In experiments 1 and 2, native
ground water was slowly introduced into the sleeve
from the bottom through the end plug displacing most
of the air within the column. Ground water addition
was stopped when the water level reached the upper-
most surface of the aquifer material. This process was
repeated several times until the Teflon sleeve was
filled with aquifer material. A stainless steel screen
was then placed on top of the aquifer material. The
packed sleeve was inserted into the body of the core
holder and both ends screwed tight. The core holder
with packed sleeve in place was inverted and secured
into place such that the screen was then at the bottom
of the column.
In experiments 1 and 2, the packed core was equili-
brated with over 500 ml of native ground water before
introduction of the industrial waste.
A minimum dilution of the injected waste by native
ground water was desired in experiment 3. The four
cores in this experiment were packed only with firm
tapping with a glass rod. The reacted waste from each
successive pass through previous cores was slowly in-
troduced into the bottom of the new core at low pres-
sure. The waste slowly filled the packed core displacing
the entrained air. After the column was filled, the
stainless steel screen centered into place, the end plug
inserted and tightened, the core holder was inverted
and then pressurized.
All experiments were conducted with confining pres-
sure and internal core pressure remaining constant at
500 psi. The same Teflon sleeve, which was 13 inches
(330 mm) in length, 1.25 inches (3.17 mm) inside
diameter, and 0.187 inches (4.75 mm) in thickness, was
used in all experiments. The packed core of aquifer
material in each experiment was approximately 11.75
inches (295 mm) in length, 410 grams in weight on an
oven dry basis having a specific gravity of 2.68 g/cm3,
and a pore space of 33 percent, which resulted in a
calculated pore volume of 76 ml. The compressibility at
500 psi was approximately 2 percent. The dead volume
in the effluent end of the column was approximately 5
MI.
All laboratory experiments were conducted at room
temperature, which fluctuated within ±3°C of 25°C.
This temperature approximated the temperature
within the receiving zone at the injection site.
EXPERIMENT 1-KINETIC STUDY OF WASTE
This experiment was designed to simulate the pas-
sage of a waste front through an observation well or a
static point within a waste -receiving zone. Sampling
during experiment 1 as shown in table 11 was con-
ducted by collecting increment samples at 5-hour
intervals over a 6-day period at an average flow rate of
2 ml/hr. The actual flow rate during the 10-ml sample
collection was approximately 15-20 ml/hr. Analyses
were performed on the waste effluent, but no analyses
were performed on the core material at the end of the
experiment.
The inorganic aspects of experiment 1 were essen-
tially duplicated in the waste effluent monitoring por-
tion of experiment 2 with the exception that the flow
rate was 4 ml/hr with the collection of a 20-ml sample
every 5 hours. The inorganic waste effluent composi-
tion of experiment 2 will be discussed along with ex-
periment 1.
The breakthrough data and breakthrough curves for
DOC, chloride, and sodium as shown in tables 11 and
12 and figures 27 and 28, respectively, indicate that
the pore volume of each experiment is between 70 and
80 ml, which verifies the calculated value of 76 ml. The
experimental pore volume is substantiated by the coin-
cidence of the inflection point of the breakthrough
curves and the 50 percent concentration factor, both of
which are suggestions of pore volume. The break-
through curve for chloride should be the same or pre-
cede the DOC breakthrough, because some organic
material is sorbed, whereas chloride is not. This ap-
pears to be the case in experiment 2, but both chloride
and sodium lag DOC in experiment 1. The apparent
discrepancy may be due to the fact that most parame-
ters such as DOC, chloride, and sodium can be more
accurately determined at low to moderate concentra-
tions than at high concentrations. DOC concentrations
are low and chloride concentrations are high at the
initial portion of the breakthrough curve. The insen-
sitivity of the chloride data is also suggested by large
changes in pH and DOC while the chloride concentra-
tion remains constant.
The DOC breakthrough lags the chloride and sodium
breakthrough throughout experiment 2 and for the
greater portion of experiment 1. The lag of the DOC is
much more pronounced with decreasing pH of the
effluent waste. Increased sorption of organics on the
core with decreasing pH is expected as physical sorp-
tion and anion exchange is facilitated at lower pH's.
The marked solubilization of Fe and Si02 is shown in
tables 11 and 12 and figures 29 and 30. Silica dissolu-
tion precedes Fe dissolution and then reaches a steady
state concentration of near 70 mg/1. Silica solubiliza-
tion appears to be somewhat independent of Fe sol-
ubilization, is independent of pH effects in the pH
range of 5-7 in the experiments, and appears to be
initially dependent only on the concentration of the
waste. Fe dissolution on the other hand appears to be
more dependent on pH than DOC concentration be-
cause no solubilization occurs until the pH of the
aquifer core material is reduced to approximately pH
6. Below pH 6, Fe solubilization appears to be pH
independent, but is dependent upon the kinetics of

LABORATORY WASTE -AQUIFER REACTIVITY STUDIES 31
TABLE 11.-Laboratory chemical data for waste -aquifer reactivity experiment 1 (flow rate=2 ml/hr).
Specific
Concentration in mg/l
Cumulative
Conductance
Time
Fraction
volume
(µmhoslcm
(hr)
number
(ml)
at25°C)
pH
DOC
Fe
si
Na
Ca
Mg
Cl
0
1
10
31,100
6.70
190
0.3
12
7000
490
290
12,000
5
2
20
32,000
7.60
76
0.3
13
7100
430
300
12,000
10
3
30
31,200
7.65
170
0.5
14
7000
450
310
12,000
15
4
40
30,500
7.30
590
1.1
16
7200
580
310
12,000
20
5
50
30,000
7.20
1100
0.6
22
6700
730
330
12,000
25
6
60
28,100
7.15
1900
0.3
27
6300
920
340
11,000
30
7
70
26,900
7.00
2500
1.6
34
-
-
-
-
35
8
80
25,000
6.85
3200
0.4
39
5200
1500
330
7,600
40
9
90
22,500
6.80
4100
1.4
43
-
-
-
-
45
10
100
21,100
6.80
4400
0.8
47
3900
2200
310
5,400
50
11
110
19,200
6.20
5000
29
51
3090
2300
278
4,200
55
12
120
18,000
6.10
5600
-
54
-
-
-
-
60
13
130
16,900
6.10
5800
48
57
2190
-
238
2,900
65
14
140
15,600
6.10
6100
-
60
-
-
-
-
70
15
150
14,600
5.90
6500
73
63
-
-
-
-
75
16
160
14,200
5.85
6800
-
63
1290
3200
188
1,600
80
17
170
13,700
5.80
6800
90
61
-
-
-
-
85
18
180
13,600
5.75
6900
94
64
-
-
-
-
90
19
190
13,200
5.70
7100
112
66
-
-
-
-
95
20
200
12,800
5.60
7200
121
68
720
3900
158
753
100
21
210
12,600
5.55
7200
129
69
-
-
-
-
105
22
220
12,700
5.50
7100
139
70
-
-
-
-
110
23
230
12,600
5.45
7400
142
70
-
-
-
-
115
24
240
12,400
5.40
7500
151
71
310
4200
128
353
120
25
250
12,000
5.35
7500
161
72
-
-
-
-
125
26
260
12,500
5.30
7600
167
71
-
-
-
-
130
27
270
11,900
5.30
7600
167
72
-
-
-
-
135
28
280
12,000
5.28
7600
180
72
110
4200
108
133
140
29
290
11,750
5.28
7700
183
73
-
-
-
-
145
30
300
11.600
5.25
7700
202
73
40
4300
100
83
dissolution as shown by flow rate relationships. At the
high flow rate during experiment 2, the Fe concentra-
tion reached a steady state of approximately 115 mg/l.
During experiment 1 at low flow rate, the Fe concent-
ration kept increasing in a curvilinear fashion to above
200 mg/l.
Total and corrected values for Fe and Si concentra-
8000
6000
4000
2000
0 Q 0
W
Q
3000 tr
2000
J
J
f
Z_
6000
Z
2 4000
F
a
IL
9000 W
U
Z O 6000
U
12,000
0 100 200 300 r
EFFLUENT VOLUME, IN MILLILITRES
x
/Xi 00 pp0 O O
X x 00 O 00
0
X/ 00
0
O O
X
O Doc
■ Chloride
y X Sodium
IX PORE VOLUMES
1 2 3
FIGURE 27.-Sodium, chloride, and DOC breakthrough curves for
experiment 1(flow rate=2 ml/hr).
tions in the reacted waste during Experiments 1 and 2
are shown in tables 11 and 12. The background con-
centration of Fe within the unreacted waste was 6
mg/l. While standing in the stainless steel lines and
hydraulic separator, the waste very slowly solubilized
Fe from these components of the pressurization core -
testing apparatus. This rate was determined to be 0.02
W
Ir W
W
¢ 800
F
J
T
c.
LU
Q 600
Q
J
i
Z 400
Z
0
a
Z 200
III
Z
O
U
U
O
O
0 J O
2 J
W 0C
a W
a
� N
Q �
3000 1750 ¢
J �
J J
� J
Z
Z
6000 Z 3500 -
O Z
O
a
(r a
I- ¢
Z I-
9000 U 5250 W
Z U
O OZ
W U
a 2
12,000p 7000 0
J 0 400 800 1200 1600 I Oy
U
EFFLUENT VOLUME, IN MILLILITRES
FIGURE 28.-Sodium, chloride, and DOC breakthrough curves for
experiment 2 (flow rate=4 ml/hr).

32
SUBSURFACE ORGANIC WASTE INJECTION, NORTH CAROLINA
TABLE 12. -Laboratory chemical data for waste -aquifer reactivity, experiment2 (flow rate=4 mllhr)
Time
(hr)
Fraction
number
Cumulative
volume
(MI)
Specific
conductance
(µmhos/cm
at25°C)
pH
DOC
Fe
Si
Concentration in mg/1
Na Ca
Mg
SO,
Cl
0
1
20
27,800
7.50
1.5
0.3
11
6100
490
250
420
10,200
5
2
40
26,900
6.30
1270
0.3
20
5000
1100
240
400
8,200
10
3
60
22,500
5.90
2820
2.0
32
3900
1800
210
350
6,600
15
4
80
17,500
5.60
3510
9.5
53
3000
2100
180
330
-
20
5
100
16,100
5.30
4320
12
56
2500
2500
170
300
3,800
25
6
120
15,300
5.10
4700
16
59
-
-
-
290
-
30
7
140
14,900
5.00
5050
24
63
1600
2800
140
280
2,200
35
8
160
13,730
4.90
5050
-
64
-
-
-
-
-
40
9
180
12,380
4.85
5750
37
-
1100
2800
120
220
1,460
45
10
200
11,000
4.75
5850
-
64
-
-
-
-
-
50
11
220
10,750
4.70
5800
41
-
780
2800
110
160
-
55
12
240
10,500
4.65
5800
-
65
-
-
-
-
880
60
13
260
10,150
4.60
6000
48
,
-
670
2800
110
90
-
65
14
280
10,250
4.55
6200
-
68
-
-
-
-
-
70
15
300
9,940
4.50
6300
49
-
-
-
-
20
600
75
16
320
9,850
4.48
7000
-
68
400
2600
95
-
-
80
17
340
9,690
4.45
7000
58
-
-
-
-
-
-
85
18
360
9,560
4.40
6600
-
70
-
-
-
-
-
90
19
380
9,170
4.35
7150
67
-
340
2600
92
-
-
95
20
400
9,170
4.35
7100
-
68
-
-
-
-
360
100
21
420
9,050
4.35
7050
70
-
-
-
-
-
-
105
22
440
9,050
4.35
6950
66
230
2400
80
<1
-
110
23
460
8,290
4.30
7150
79
-
-
-
-
-
-
115
24
480
7,900
4.30
7250
-
65
-
-
-
-
-
120
25
500
8,040
4.30
6900
80
-
170
2400
78
-
180
125
26
520
8,160
4.25
6900
-
67
-
-
-
-
-
130
27
540
7,000
4.20
7450
-
-
-
-
-
-
-
135
28
560
8,160
4.15
7200
-
72
-
-
-
-
-
140
29
580
7,720
4.15
7200
-
-
140
2400
74
<1
-
145
30
600
7,460
4.15
7300
-
69
-
-
-
-
160
150
31
620
7,720
4.20
7400
90
-
-
-
-
-
-
155
32
640
7,720
4.15
7400
-
72
-
-
-
-
-
160
33
660
7,650
4.15
7200
95
-
120
2300
70
-
-
165
34
680
7,710
4.10
7550
-
72
-
-
-
-
-
170
35
700
7,800
4.10
7200
93
-
-
-
-
-
-
175
36
720
8,040
4.10
7500
-
69
-
-
-
-
-
180
37
740
7,780
4.10
7600
96
-
100
2300
66
-
-
185
38
760
7,630
4.10
7600
-
71
-
-
-
-
-
190
39
780
7,360
4.10
7500
97
-
-
-
-
-
-
195
40
800
7,600
4.08
7550
-
60
-
-
-
-
120
200
41
820
7,580
4.05
7350
102
-
88
2200
66
-
-
205
42
840
7,400
4.05
7400
-
69
-
-
-
-
-
210
43
860
7,420
4.00
7400
96
-
-
-
-
-
-
215
44
880
7,160
4.00
-
-
56
-
-
-
-
-
220
45
900
7,150
4.00
7600
99
-
78
2100
62
-
-
225
46
920
7,120
4.00
-
-
56
-
-
-
-
-
230
47
940
7,080
4.00
-
99
-
-
-
-
-
-
235
48
960
6,810
4.00
-
-
54
-
-
-
-
-
240
49
980
6,840
4.00
-
112
-
-
-
-
-
-
245
50
1000
6,910
4.00
-
-
56
75
2000
59
<1
100
250
51
1020
6,920
4.00
7700
113
-
-
-
-
-
-
255
52
1040
7,000
4.00
-
-
57
-
-
-
-
-
260
53
1060
6,740
4.00
-
108
-
-
-
-
-
-
265
54
1080
5,150
3.95
Sample sacrificed for gas analysis
270
55
1100
6,740
3.95
7800
-
56
-
-
-
-
-
275
56
1120
6,760
3.95
-
109
-
-
-
-
-
-
280
57
1140
6,630
3.95
-
-
58
-
-
-
-
-
285
58
1160
6,370
3.90
-
108
-
-
-
-
-
-
290
59
1180
6,440
3.90
-
-
54
38
1900
56
<1
-
295
60
1200
6,310
3.90
7850
110
-
-
-
-
-
-
300
61
1220
6,120
3.90
-
-
56
-
-
-
-
-
305
62
1240
5,990
3.90
-
114
-
-
-
-
-
-
310
63
1260
5,940
3.90
-
-
54
-
-
-
-
-
315
64
1280
6,190
3.90
7850
115
-
-
-
-
-
-
320
65
1300
5,990
3.90
-
-
55
-
-
-
-
-

LABORATORY WASTE -AQUIFER REACTIVITY STUDIES 33
TABLE 12. —Laboratory chemical data for waste -aquifer reactivity, experiment 2 (flow rate=4 ml/hr)—Continued
Spec'fic
Cumulative conductance
Concentration in mg/1
Time Fraction volume (µmhos cm
(hr) number (m1) at 25°C) pH DOC Fe
Si Na Ca Mg SOa Cl
325 66 1320 5,990 3.85 — 108
— — — — — —
330 67 1340 5,940 3.85 — —
54 — — — — —
335 68 1360 5,940 3.85 7850 110
— — — — — —
340 69 1380 5,810 — — —
-- — — — —
345 70 1400 5,680 3.80 — 108
— 23 1700 49 <1 —
350 71 1420 5,860 3.80 — —
52 — — — — —
355 72 1440 5,860 3.80 — 112
— — — — — —
360 73 1460 5,630 3.80 — —
54 — — — — —
365 74 1480 5,660 3.80 7900 110
— — — — — —
370 75 1500 5,800 3.80 — —
58 — — — — —
375 76 1520 5,800 3.80 — 109
— — — — — —
380 77 1540 5,740 3.80 — —
53 — — — — —
385 78 1560 5,660 3.80 — 109
— — — — — —
390 79 1580 5,660 3.80 — —
56 20 1700 50 <1 —
395 80 1600 5,610 3.80 — 112
— — — — —
400 81 1620 5,550 3.75 — —
56 — — — — —
405 82 1640 5,590 3.75 — —
— — — — — —
410 83 1660 5,525 3.75 — —
57 — — — — —
415 84 1680 5,525 3.75 7900 110
— — —
mg/l/day in three independent measurements during
dent chemical parameters. Therefore, pH and specific
experiments 1 and 2. The reported values of Fe are
conductance are of limited usefulness except as general
corrected for background and solubilization within the
continuous monitoring indicators.
apparatus. This small concentration of background Fe
The initial appearance of gas at the outlet of the core
concentration should have no effect upon the rate of Fe
holder at fraction 11 during experiment 1 was accom-
solubilization from aquifer material. The high
panied with a large drop in pH from 6.80 to 6.20 and an
background concentration of Si in the injected waste
abrupt appearance of dissolved Fe. The initial appear -
probably had an effect upon Si dissolution of aquifer
ance of gas during experiment 2 occurred in fraction 3
material. The high initial Si concentration probably
accompanied by incipient Fe dissolution. The pH was
decreased the rate of Si dissolution and probably de-
lower at pH 5.9 due to the rapid flush of unreacted
creased the total amount of Si dissolution because the
waste acids. Although all the CO2 gas produced during
high background enabled pseudo -equilibrium concen-
carbonate dissolution within the core was believed to
trations of Si to be attained more quickly than if no Si
have remained in solution while within the core, out -
were present in the initial waste.
gassing of CO2 during sampling was an immediate
Specific conductance and pH are gross chemical indi-
cators which are affected by a number of interdenen-
W
I—
Ir
W
(n
cc
_O
J
J
2
0
O
f-
Cc
Q
F
W
is
O
2
O
U
Q
_U
J
y
80
• • • ••• ••i ••• • ••
• •• &A • •• •
60 • • • •
• • • • •
•
• • • • •• •• • • • •
•
•
40 •
• ••
•
•
20 • Iron
•
• Silica
•• PORE VOLUMES
5 10 15 20
0 •
120
90
60
30
0
0 300 600 900 1200 1500 1800
EFFLUENT VOLUMES, IN MILLILITRES
FIGURE 29.—Iron and silica dissolution during experiment 2.
so
•
60 • • •
♦ • •
♦ •
•
•
•
40 • •
•
•
•
• • Iron
•
20 • • Silica
•
•••
•
PORE VOLUMES
1 2 3 4
200 Ir
150
100
50
0 100 200 300
EFFLUENT VOLUME, IN MILLILITRES
FIGURE 30.—Iron and silica dissolution during experiment 1.

34 SUBSURFACE ORGANIC WASTE INJECTION, NORTH CAROLINA
manifestation of carbonate dissolution. The marked
increase in Ca content of the waste effluent as high as
4,300 mg/l during experiment 1 was an accurate indi-
cator of carbonate dissolution. Gas effervescence dur-
ing sample collection at the end of experiment 1 and at
fraction 20 of experiment 2, occupied over 50 percent
by volume of the collection tube.
During experiment 2, gas effervescence declined
with Ca concentration. Only small amounts of gas re-
mained at fraction 50, and gas was essentially absent
after fraction 75. Ca concentrations did not approach
zero during experiment 2 becaue the concentration of
the injected waste was 1,400 mg/1.
The carbonate in the injection zone was probably low
in dolomite because the Mg concentration constantly
decreased at the expense of Ca. Magnesium and
sodium, which were competitive with Ca for the ex-
change sites on the native aquifer material, were
gradually leached from the core with Ca and hydrogen
becoming the dominant exchange ions.
EXPERIMENT 2 - CORE SOLUBILIZATION STUDY
Experiment 2 was designed to simulate changes
which would be manifested within the aquifer material
with the passage of the waste front extending into the
slow -reaction zone. Sampling of the waste effluent dur-
ing this experiment as shown in tables 13 and 14 was
conducted at 5-hour intervals over an 18-day period at
an average flow rate of 4 ml/hr. At the termination of
experiment 2, the waste in the pore space within the
core was displaced by passing 180 ml of native ground
water through the core. At this volume, the specific
conductance of the effluent was constant at the specific
conductance of the native ground water. The core hold-
er was then disassembled, the aquifer core material
extruded from the Teflon sleeve, and the core fraction-
ated into eight equal sections of 1.5 inches (38 mm).
Sections 1 through 8 were numbered from the top
(waste entry end) of the column.
The lag in the DOC breakthrough curve behind
chloride during experiments 1 and 2 as shown in fig-
ures 26 and 27 indicates that organic components are
being sorbed onto the aquifer material throughout the
entire duration of both experiments. In addition to
DOC, six specific organic compounds (formaldehyde,
acetic acid, formic acid, phthalic acid, terephthalic
acid, and p-toluic acid) were monitored. These com-
pounds collectively comprised over 80 percent of the
DOC in the waste. All of these compounds except for-
maldehyde were sorbed onto the aquifer core material.
The breakthrough curve and breakthrough data for
formaldehyde during experiment 2 as shown in figure
. o
6000 J X Formamanvtla
A-- acid
• Formic ec�tl
2000 PORE VOLUMES
5 10 5
300 600 900 1200 1500
EFFLUENT VOLUME, IN MILLILITRES
FIGURE 31.-Relative sorption of formaldehyde, acetic acid, and for-
mic acid during experiment 2.
TABLE 13-Organic chemical data during waste effluent monitoring of laboratory experiment2
Concentration (mg/1)
Concentration (mg/1)Acetic/formic
Phthalic:
Time
Fraction
Cumulative
Formic
Acetic
acid
Phthalic
Terephthalic
p-Toluic
terephthalic:
(hr)
number
volume
DOC
Formaldehyde
acid
acid
ratio
acid
acid
acid
p-toluic ratio
0
1
20
1.5
0
-
-
-
-
-
-
5
2
40
1270
370
340
1980
5.8
36
56
58
1:1.5:1.6
10
3
60
2820
745
780
3620
4.6
45
75
103
1:1.6:2.3
15
4
80
3510
925
735
4410
5.9
95
145
188
1:1.5:1.8
20
5
100
4320
1200
863
5840
6.7
119
162
204
1:1.4:1.7
30
7
140
5050
1520
1050
6510
6.2
179
209
226
1:12:1.3
40
9
180
5750
1840
1210
6870
5.6
191
295
399
1:1.5:2.1
50
11
220
5800
1840
1710
7620
4.4
160
280
407
1:1.8:2.6
60
13
260
6000
2080
1660
8140
4.9
180
302
435
1:1.7:2.4
75
16
320
7000
2120
1700
8610
5.1
177
364
606
1:2.0:3.4
90
19
380
7150
2100
1890
8440
4.8
152
357
563
1:2.3:3.7
105
22
440
6950
2150
2170
8290
3.8
153
343
571
1:22:3.7
120
25
500
6900
2100
2030
8660
4.2
157
348
557
1:22:3.5
140
29
580
7200
2050
2110
8190
3.9
184
303
524
1:1.6:2.8
160
33
660
7200
2120
2410
8890
3.7
190
453
803
12.4:42
180
37
740
7600
2100
2110
9480
4.5
157
334
551
1:22:3.5
200
41
820
7350
2020
2470
10,500
4.2
171
315
539
1:1.9:3.1
220
45
900
7600
2080
2280
9130
4.0
140
356
639
1:2.5:4.5
245
50
1000
7675
-
2320
10,700
4.6
134
355
618
1:2.7:4.6
270
55
1100
7750
-
2280
9690
4.2
225
289
392
1:1.3:1.8
295 60 1200 7850 - 2800 9160 3.2 226 352 512 1:1.5:2.3
320 65 1300 7850 - 2640 10,200 3.8 168 330 517 1:1.9:3.1
Waste
analysis 7900 2100 2780 10,200 3.6 169 358 596 1:2.1:3.5

LABORATORY WASTE -AQUIFER REACTIVITY STUDIES
35
31 and table 13, respectively, indicate that formal-
dehyde is not sorbed because its breakthrough curve is
essentially the same as for chloride. After fraction 16,
the formaldehyde concentration is constant at 2,100
mg/l, which is the formaldehyde concentration of the
injected waste. This finding suggests that formal-
dehyde may be used as an organic tracer under similar
chemical conditions as existed in this experiment and
that the degree of sorption of all other organic con-
stituents can be measured as a difference between
their concentration in the reacted effluent waste and
that of the original injected waste.
Formic acid was the most strongly sorbed organic
compound on a percent by weight basis as shown in
figure 31 and table 13. Formic acid was sorbed during
most of the experiment with the exception of the very
latter stages. At fraction 16, the formic acid concentra-
tion was only 60 percent of its concentration in the
injected waste. Formic acid sorption was marked not
only at the initial portion of the experiment, but was
also considerable during the middle to latter portion of
the experiment after considerable Fe and SiO2 dissolu-
tion when the pH was between 4.10 and 4.00.
The formic acid molecule is quite liable or subject to
chemical and (or) catalytic decomposition. It is possi-
ble that the apparent sorption of formic acid was not
sorption, but decomposition of a portion of the formic
acid. This possible chemical or catalytic decomposition
could have occurred with the diverse components of the
core material until the incompatible chemical core
constituents were consumed or possible catalytic sites
were exhausted or hindered by sorption of other or-
ganic constituents. A possible data interpretation is
that formic acid concentration in the waste effluent
gradually approached its concentration within the ini-
tial waste only after the possible chemical or catalytic
activity ceased within the core.
Acetic acid was the second most strongly sorbed or-
ganic compound on a percent by weight basis. At frac-
tion 16, the acetic acid concentration was 84 percent of
its concentration in the injected waste. Acetic acid is
not initially strongly sorbed as its breakthrough curve
parallels the non-sorbed formaldehyde component.
From fraction 8 through fraction 30, acetic acid is
strongly sorbed coincident with marked Fe and SiO2
solubilization. After fraction 30, acetic acid is less
strongly sorbed and gradually attains the same con-
centration as in the injected waste.
The sorption of phthalic and terephthalic acids are
only vaguely suggested during the initial waste
monitoring portion of experiment 2 as shown in table
13. The sorption of p-toluic acid is indicated by the
phthalic:terephthalic-p-toluic acid ratio inclusive of
fraction 16. The relative sorption of these three aromat-
ic acids by waste effluent monitoring is dramatically
manifested during the slow flow rate of experiment 1.
As shown in figure 32 and table 14, there is initial
sorption of all three aromatic acids. The flow rate of
experiment 2 was too rapid to obtain the necessary
detail for aromatic acid sorption.
Phthalic acid is strongly sorbed only during the first
150-ml of waste input. This sorption is suggested by
PH
25.L b.25 b.b
ioo
loo
Phthalic
i
00 �
--"PORE VOLUMES
i� 2 3
0
n inn 9nn
EFFLUENT VOLUME. IN MILLILITRES
30C
FIGURE 32.—Relative sorption of phthalic, terephthalic, andp-toluic
acids during experiment 1.
TABLE 14. —Organic chemical data during waste effluent monitoring of laboratory experiment 1
Percent of fraction DOC accounted
Concentration in mg/1
for by compound
Phthalic:
Time
Fraction
Cumulative
Phthalic
Terephthalic
p-Toluic
terephthalic:
Phthalic
Terephthalic
p-Toluic
(hr)
number
volume
DOC
acid
acid
acid
p-toluic ratio
acid
acid
acid
30
7
70
2500
24
81
124
1:3.2:5.0
0.010
0.032
0.050
40
9
90
4100
42
113
193
1:2.7:4.6
.010
.028
.047
55
12
120
5600
65
186
304
1:2.8:4.6
.012
.033
.054
70
15
150
6500
150
273
428
1:1.8:2.9
.023
.042
.065
90
19
190
7100
160
390
450
1:1.8:2.8
.021
.030
.048
105
22
220
7100
217
324
481
1:1.5:2.2
.030
.045
.068
125
26
260
7600
142
350
600
1:2.4:4.2
.018
.046
.078
140
29
290
7700
164
338
591
1:2.1:3.6
.021
.044
.076
Waste
7900
169
358
596
1:2.1:3.5
.021
.045
.075

36 SUBSURFACE ORGANIC WASTE INJECTION, NORTH CAROLINA
the aromatic acid ratio in table 14 and confirmed by
the percentage of fraction DOC accounted by phthalic
acid. Aproximately 50 percent of the phthalic acid in
the waste effluent had been sorbed.
Terephthalic acid is sorbed during the first 220-ml of
waste input. The most marked sorption occurs after
phthalic acid sorption as indicated by the plateau in
the breakthrough curve between 150 and 250 ml in
figure 31, by the low aromatic acid ratio in this region
of the breakthrough curve, and by the percentage of
fraction DOC accounted by terephthalic acid in table 4.
Approximately 30 percent of the terephthalic acid in
the effluent waste through fraction 22 was sorbed onto
the aquifer material.
The sorption of p-toluic acid during the initial por-
tion of experiment 2 is strongly supported by the
p-toluic acid breakthrough curve during experiment 1
as shown in figure 32 and table 14. p-Toluic acid is
sorbed in the same region of the breakthrough curve as
terephthalic acid with continued sorption in the 220- to
260-ml region. Strong sorption of p-toluic acid is indi-
cated by the plateau in the 150- to 250-ml region of the
breakthrough curve, by the low aromatic acid ratios in
this region, and by the percentage of fraction DOC
accounted by p-toluic acid. Approximately 30 percent
of the p-toluic acid in the effluent waste was sorbed
onto the aquifer material up through fraction 26.
The sorption of phthalic, terephthalic, and p-toluic
acids were also confirmed by sediment extraction at
the termination of experiment 2. The sorptive
capacities as determined on four sections of the reacted
core are listed in table 15. Exclusive of section 1, the
sorptive capacities are in a ratio of 1.0:5.5:4.7. This
ratio as compared to the ratio of these compounds in
the injected waste (1.0:2.1:3.5), indicate a sorptive pref-
erence for terephthalic and phthalic acids with the
greatest preference for terephthalic acid.
TABLE 15.-'orptiue capacities of aromatic organic acids on aquifer
material during experiment
Milligrams of acid sorbed per gram of sediment
Phthalic:
Core section
terephthalic:
number
Phthalic
Terephthalic
p-Toluic
p-toluic ratio
1
0.011
0.090
0.0059
1:9:0.6
3
.025
.117
.116
1:4.7:4.6
6
.020
.106
.106
1:5.3:5.3
8
.019
.127
.081
1:6.6:4.3
The sorptive capacities as shown in table 15 should
be considered as minimal sorptive capacities because
some portion of the organic acids were desorbed during
the saturation of the aquifer core material with native
saline water at the end of the experiment. This ex-
change or desorption of organic compounds is assured
by mass action theory and supported by the extremely
low sorptive capacities in section 1 at the input end of
the column which was in contact with the saline water
for the longest time period. The conclusion is limited
by the fact that the clay fraction which would be ex-
pected to sorb most of the organic substances was
somewhat depleted from section 1.
The overwhelming concentration of these com-
pounds in the waste saturating the interstitial pore
liquid would have precluded the analysis of sorbed
material without flushing with native ground water.
The ratio of the sorptive capacities suggests some lim-
ited validity of the sorptive capacities as determined
because the ratio of the sorbed acids is markedly dif-
ferent from that of the injected waste. The relative
meaning of the sorptive capacities will be discussed in
detail after the presentation of supporting data ob-
tained during experiment 3.
Carbonate dissolution was evident during experi-
ment 2 by the high levels of Ca in the waste effluent
(table 12) and by CO2 gas effervescence during waste
effluent collection. Gas first appeared at fraction 3 and
was present until fraction 75. Carbon dioxide gas per-
sisted in the waste effluent much longer than expected
for the low carbonate percentage of the aquifer mate-
rial (table 16, 0.98 percent CaCO3=0.12 percent inor-
ganic carbon) and the high organic acid concentration
of the injected waste.
TABLE 16.Organic and inorganic carbon analyses of fractionated
and unfractionated injection -zone aquifer material
oC lc� Cacosl
(percent) (percent) (percent)
Whole aquifer material, ground .................... 0.15 0.12 0.98
Clay fraction (<2microns)._. 1.40 .14 1.18
Silt fraction (2-64 microns) ............................ .52 .22 1.82
Fine sand (0.064-0.4 mm), unground ---------- .10 .84
Medium sand (0.4-1.0 mm), unground._._._.. .05 .40
Combined sand (0.064-2 mm), unground.... .08 .65
Combined sand (0.064-2 mm), ground -------- .03 .09 .71
Analysis by modified Van Slyke method.
Temperature, pressure, the concentration of weak
acid solutions, and the distribution of carbonate within
the aquifer material are obviously important consid-
erations for carbonate dissolution. The addition of the
injected waste solution, acid concentration of approxi-
mately 2 percent by weight, to a sample of finely
ground (less than 60 mesh) aquifer material at room
temperature produced no observable gas effervescence.
Upon standing at room temperature for 24 hours, only
Y3 of the carbonate was dissolved from the sample. The
remainder of the carbonate in the sample was con-
verted to CO2 gas upon boiling for a period of 10 min-
utes. On the other hand, addition of 3 percent HCl, a
strong acid, at room temperature produced strong gas
effervescence. Upon standing for 3 hours over 90 per-
cent of the carbonate was converted to CO2 gas.
A large portion of the carbonate in the aquifer mate-
rial is secondary cementation carbonate because no
detrital carbonates and few carbonaceous shells are

LABORATORY WASTE -AQUIFER REACTIVITY STUDIES
observed with either the binocular microscope or thin -
section analysis. Approximately 15-20 percent of the
carbonate in the aquifer material is contained within
the primary mineral sand grains which comprise over
75 percent of the aquifer material (table 17). As shown
in table 16, the carbonate percentage for the unground
combined sand fraction is approximately 10 percent
less than the ground combined sand fraction. This car-
bonate would only be available to react with the acid
waste by slow diffusion processes and with breakdown
of the mineral grains.
TABLE 17.—Particle size analysis of injection -zone
aquifer material
Percentage by weight
Gravel (> 2 mm)........................................ 1
Coarse Sand (1-2 mm)------------------------------ 4
Medium Sand (0.4-1.0 mm)-------------------- 28
Fine Sand (0.064-0.4 mm) 43
Silt (2-64 microns) ................................... 20
Clay (< 2 microns) --------------_-_---............ 4
With the previously discussed supporting experi-
mental evidence, it is readily understood why carbon-
ate dissolution was slow during experiment 2. The
experiment was conducted at room temperature, not
elevated temperatures, carbonate dissolution was slow
in the presence of the weak acid composition of the
waste, and a portion of the carbonates were contained
as primary mineral grains within sand grains. The 500
psi experimental pressure may have a positive effect
upon carbonate dissolution because the CO2 gas pro-
duced would remain in solution at that pressure which
would increase the carbonic acid or hydrogen ion con-
centration of aquifer fluids.
Carbonate analyses of the core sections at the termi-
nation of experiment 2 indicated that only a trace
amount of carbonate was present in the aquifer core
material. This trace carbonate level (less than 2 per-
cent of the total carbonate percentage) represented the
carbonate within the center portion of undecomposed
sand grains.
With passage of the waste through the aquifer mate-
rial, the pH of the core decreased from 8.2 to 3.73, the
pH of the injected waste. The cation exchange complex
was changed from a mixed population of Ca, Mg, and
Na to a predominantly Ca-H system at the end of the
experiment.
It was hoped that the marked dissolution of Si02 and
Fe during experiment 2 would be manifested in the
analyses of the core material at the end of the experi-
ment. The core material was the same reddish -brown
color both at the beginning and the end of the experi-
ment. Waste effluent analysis indicated that only 12
percent of the total extractable iron (0.4 percent of the
sample weight) was removed during the experiment.
The redistribution of the clay fraction within the core
and the low amount of Fe solubilized during the exper-
37
invent precluded Fe analyses of the core material. The
iron which was dissolved from the core material was
believed to have been amorphous sesquioxide coatings.
This conclusion is supported by the associated Mn
analyses in table 18, because Mn, Fe, and Al ses-
quioxides are common coatings of aquifer grains.
TABLE 18.-'e, Al, and Mn analyses by graphite furnace technique of
selected waste effluent fractions during experiment 2
Sample
Designation
Concentration in mg/1
Fe Al Mn
Native ground water ................................
<.2
<.7
0.17
Injected waste --------------------------------------------
6.3
6.2
.5
Fraction 40----------------------------------------------
116
8.7
6.7
50 ..............................................
77
5.0
3.6
60-------------------
116
8.7
4.7
90----------
... 182
9.7
4.5
The small amount of SiO2 dissolved during the ex-
periment as compared to the overwhelming amount
comprising primary and secondary minerals certainly
precluded computation of SiO2 losses by core analysis.
The high values for dissolved silica could result from
dissolution of amorphous and crystalline clay miner-
als. The solubilization of Al -containing clay minerals
is supported by the high Al values for fractions 40, 50,
60, and 90 as shown in table 18.
The clay mineralogy of the original aquifer sample
was approximately 25-40 percent 2:1-2:2 intergrade
and mixed layered montmorillonite-intergrade, 25-35
percent montmorillonite, 5-10 percent illite, 5-10 per-
cent amorphous clay minerals, and 2-4 percent quartz.
X-ray diffraction data at the termination of experi-
ment 2 showed only a slight change in the stability of
the 2:1-2:2 intergrade clay mineral. This suggested
some removal of hydroxy Al and Fe polymers from
interlayer space. A detailed discussion of the mineral-
ogy of the waste -injection zone and mineralogical
changes associated with waste injection is given by
Malcolm, Leenheer, and Weed (1976).
EXPERIMENT 3 — WASTE -SATURATION STUDY
Experiment 3 was designed to simulate a unit of
injected waste at the very edge of the waste front as it
moved outward from the injection well. A 300-ml sam-
ple of waste was repeatedly reacted with fresh aquifer
material until the waste was neutralized and "satu-
rated' with dissolved aquifer constituents. The flow
rate for the entire experiment was approximately 20
ml/hr. The waste was passed twice through each of the
four consecutive cores. A 2-ml sample of the waste
effluent was taken for specific conductance, pH, DOC,
SiO2, and Fe analyses after each pass through the
aquifer material. At the end of the experiment the
waste effluent was analyzed for phthalic, terephthalic,
andp-toluic acids.
The moisture content of the aquifer material was 11
percent by weight. This resulted in a 15 percent dilu-

38 SUBSURFACE ORGANIC WASTE INJECTION, NORTH CAROLINA
tion of the waste when introduced into each fresh core,
and a total dilution of 60 percent for the entire experi-
ment. This calculated dilution factor agrees well with
the DOC experimental data (table 19), which indicates
an actual dilution factor of 57 percent. Specific conduc-
tance cannot be used to calculate the dilution factor
because conductance is increased with carbonate dis-
solution.
TABLE 19.-Chemical data during waste effluent monitoring of Lab-
oratory experiment3
Contact time
Specific
Concentration(mg/1)
Sample
Laboratory
perpore
conductance
number
identification
volume (hr)
(µmho)
pH
DOC
Fe
Si
1
Core 1-Run 1
4
6600
4.30
6400
9.3
49
2
Core 1-Run 2
4
8400
4.65
6400
18.6
55
3
Core 2-Run 1
4
9000
5.10
5600
7.0
49
4
Core 2-Run 2
4
9200
5.30
5600
6.7
51
5
Core 3-Run 1
4
9600
5.95
4400
.5
44
6
Core 3-Run 2
4
9700
6.30
4350
.4
42
7
Core 4-Run 1
4
10,000
7.15
3500
.2
28
8
Core 4-Run 2
8
9900
7.20
3400
.2
30
The monitoring data for experiment 3 is shown in
table 19. The pH data suggested that carbonate disso-
lution was initially rapid during the first pass of the
waste through the core. Only small incremental
changes in waste pH were observed with the second
pass through the same core. The Fe data again showed
the dramatic effect of pH on Fe solubilization. At pH
values below 5, Fe dissolution was rapid, was moderate
between pH 5 and 6, and was essentially zero above pH
6. Silica solubilization by the waste showed the typical
U-shaped curve for silica solubility (Jones and Hand-
reck, 1967). Silica solubility was high at low pH and
decreased gradually with increasing pH. Silica solubil-
ity would be expected to again increase with pH above
PH 10.
The concentration of phthalic, terephthalic, and
p-toluic acids at the end of the experiments were 27,
87, and 151 mg/1, respectively. The resultant ratio of
these three compounds were 1.0:3.2:5.6, which is very
different from the 1.0:2.1:3.1 ratio that they appear in
the injected waste. The low concentrations of all acids
indicate sorption on the aquifer material and the ratio
indicated preferential sorption of phthalic acid.
An additional experiment was designed to test the
hypothesis that Fe complexed with phthalic acid pre-
cipitated above pH 6.5. Solutions of phthalic acid
(0.001 M (molar)=164 mg/1) and FeCl3 (0.01 M=590
mg/1) were mixed at pH 2.8. These concentrations are
similar to phthalic acid concentrations in the waste
and the experimental concentration range of Fe with
waste passage within the aquifer as determined in the
previously discussed laboratory experiments. The pH
was increased to 6.5 by small additions of dilute
NaOH. Iron and Fe-phthalic acid complex precipitated
from solution. Gas chromatographic analysis on the
supernatant solution indicated that over 50 percent of
the phthalic acid was removed from solution into the
precipitated phase.
The sorptive capacities for phthalic, terephthalic,
and p-toluic acids during experiment 3 are 0.01, 0.02,
and 0.03 mg/g of aquifer material. These sorptive
capacities are relative and not absolute sorptive
capacities because they were computed on the basis of
1,600 g of aquifer core material (four cores) used dur-
ing the experiment. A more correct sorptive capacity is
believed to be 0.02, 0.02, and 0.03 because phthalic
acid was only sorbed on the last two cores of the exper-
iment (800 g of sediment) when the pH was above pH
6; whereas terephthalic and p-toluic acids were sorbed
by all the cores. This conclusion is also supported by
the sorptive data and curves as shown in table 12 and
Figure 32, respectively, where phthalic acid is only
sorbed between pH 6-7, but terephthalic and p-toluic
acids are sorbed over the entire pH range of experi-
ment 1.
The sorptive capacities of phthalic, terephthalic, and
p-toluic acids as determined during experiment 3 (0.02,
0.02, and 0.03 mg/g) by waste monitoring, during ex-
periment 2 (0.02, 0.10, and 0.10) by sediment extrac-
tion, and the sorptive curves in figure 31 during exper-
iment 1 may mistakenly be interpreted to be in con-
flict. The differences really reflect the dependence of
sorptive capacity on pH, the nature of the sorptive site,
and the charge on the organic molecule. The composi-
tion of the reactive surface, its charge, and charge
density, change with dissolution of Fe, SiO2, and Al.
The reactive surfaces are primarily amorphous coat-
ings of Fe, Al, Mn, and Si02 at the beginning of the
experiments when pH is high. With dissolution of
these coatings and carbonates, the reactive surface
gradually becomes a more crystalline alumino-silicate
clay mineral and crystalline sesquioxide surface. The
PH within the core also gradually becomes more acidic.
The solubility of the aromatic acids, their hy-
drophilic character, and negative charge (acid dissocia-
tion) decreases with decreasing pH. The relative rate of
magnitude of these changes are dependent on the con-
figuration of the molecule and the relative changes in
the reactive surface. All data indicate that phthalic
acid is preferably sorbed at high pH whereas p-toluic
and terephthalic acids are preferably sorbed at lower
PH with less Fe on the reactive surfaces.
The 0.15 percent organic carbon component of the
native aquifer material is also an important factor in
organic waste acid sorption by the core. Many organic
compounds have a profound affinity or attraction for
like or similar compounds. The amphoteric nature of
natural organic substances would facilitate organic
acid sorption through the entire pH range of the exper-
iments _(pH 3.7-8.2) by hydrogen bonding, Van der
Waals forces, or direct exchange processes.
The bridge bonding of Fe, Al, and Mn on the core
colloids to organic acids in the interstitial waste liquid

FINAL CONCEPTUAL MODEL OF WASTE MOVEMENT AND REACTIVITY
was also an important possibility of organic acid sorp-
tion. The acidic functional group on the organic acid
could actively participate in initial Fe solubilization by
surface complexation with Fe. With time, decreasing
pH (increased protonation potential), and increasing
organic acid concentration, the Fe would leave the
surface of the colloid and become sequestered by the
organic acid. The active solubilization period or time
which the organic acid was in contact with the Fe on
the surface site would be manifested as organic acid
sorption.
FINAL CONCEPTUAL MODEL OF WASTE
MOVEMENT AND REACTIVITY
The final conceptual model of waste movement and
reactivity was more complex and detailed than the
initial hypothetical model. The initial model assumed
waste movement within a single permeable injection
zone; however, the logs and the observation well flow -
test indicated that the injection zone consists of multi-
ple subzones. Assuming independent subzones within
the injection zone as shown in figure 33, the waste
possibly moved preferentially into the upper subzones
because of favorable permeability and because the den-
sity of the waste is less than that of the ground water.
This density effect is shown in figure 33 by having the
lighter waste solution overriding the heavier ground
water in the lower two receiving subzones within the
injection zone. The flow system diagrammed in figure
33 is but one of many possibilities discussed in connec-
tion with figure 21. Therefore, waste obtained from
observation wells may be diluted by the ground water
within the waste -contaminated subzone because of the
density separation. Most of the variance in the waste
concentrations in samples obtained from wells 11, 14,
and 15 is believed to have been due to changing dilu-
tion factors caused by changing circulation patterns
between the waste -receiving subzones within the ob-
servation wells.
Injection well Observation
well
Sand
Gravel
800 Clay
® Waste
I-
w _
--- --- --- __
w --------------------
Z— — — — — — — — —— —— — — — — —
= goo
F-----------------------
a------------------------
plul
— — _ — _ — _ _ — — — — — —_
1000 =-- -----_--- — ----- —
39
Evidence that all the receiving subzones within the
injection zone were accepting waste was obtained from
wells 1, 2, 4, and 5. Samples obtained from these wells
which were located only 150 ft (46m) from injection
well I-6 were essentially free of ground water. The
large distance gap between the observation wells of the
initial injection network and the observation wells of
the expanded system did not allow observation of the
injection zone in regions where the injected.waste in-
terfaced with the native ground water in the lower
receiving subzones. Therefore, the distance of
injected -waste travel in these lower subzones is purely
speculative in figure 33.
Many of the postulations in the initial conceptual
model (fig. 17) are valid for the final conceptual model
shown in figure 34. This model, based on the findings
of this study, shows features of waste movement and
reactivity within an individual waste -receiving sub -
zone in the injection zone. Figure 34 does not show
vertical distribution of waste in an aquifer, but the
percentage of waste at a particular distance from the
injected well. Therefore, this model probably has dif-
ferent quantitative dimensions for each receiving sub -
zone depending on the distance and rate of waste travel
within each subzone. However, the relative dimensions
and order of reactivity should have validity for each
subzone. As with the initial model, the dimensions of
this model expand to the right with increasing time
during waste injection.
This final model is divided into a "waste front" and
"waste interior" at the point where the pH of the in-
jected waste begins to rise through neutralization reac-
tions. Most, but not all of the ground water has been
displaced from the receiving subzone at this point. The
curve, relative percentage of waste to percentage of
groundwater, was drawn with the ground water ex-
tending the waste -contaminated region because the
density difference between the injected waste and the
INJECTION pH PH pH pH
WELL WASTE INTERIOR 4 55 6 ] WASTE FRONT
Relative pe.cen[a9e pf waste [o
percentage of grpuntl water
O
VASTE SLOW REACTION FAST DIL TRANSITION MICRO UTIONN
POOL ZONE REACTION ZONE BIAL ZONE
ZONE ZONE
WASTE MOVEMENT
nGuR.E 33.—Hypothetical movement of injected waste within I FIGURE 34.—Final conceptual model of injected -waste reactivity and
injection subzones. movement.

40 SUBSURFACE ORGANIC WASTE INJECTION, NORTH CAROLINA
native ground water would cause stratification and
prevent rapid mixing.
The leading zone of the waste front prior to the
appearance of methane gas indicative of microbial ac-
tivity is called the "dilution zone" because the neu-
tralized (pH 7) waste appears as a very dilute solution
in ground water. Data from samples obtained from
wells 11 and 14 indicated that waste concentrations
had to attain a certain threshold value before there
was microbial waste decomposition. This zone may also
represent a lag time during which the microorganisms
are multiplying to numbers where they become sig-
nificant in waste decomposition. The waste showed no
detectable reactions within this zone, and had little
effect on the chemical quality of the ground water.
The zone which follows the dilution zone is called the
"microbial activity zone" because of indications of
anaerobic waste transformations within this zone.
Methane gas, sulfur reduction, and iron reduction were
observed either singly or in combination at various
periods in wells 11, 14, and 15. Two strains of
methane -producing organisms were isolated in sam-
ples obtained from well 14 during methane production.
However, the microbiological study revealed that the
waste was toxic to microorganisms in moderate con-
centrations, and waste decomposition occurred only at
the periphery of the waste front where waste concen-
trations were low.
The zone called the "transition zone" follows the
microbial activity zone. When the waste attains toxic
concentrations and when limiting nutrients such as
nitrogen are gone, there will be a die -off of microor-
ganisms in the injection zone and microbial activity
will cease. This zone is transitional between the zone of
microbial waste transformations and the zone in which
chemical reactions predominate.
Most of the chemical waste -aquifer interactions were
found to occur within the zone defined as the "fast -
reaction zone". The boundaries of this zone are defined
by pH. The pH changes from pH 4 at the trailing
boundary to pH 7 at the leading boundary. One of the
main features of this zone is the neturalization of the
acidic, injected waste at pH 4 by the aquifer carbonates
and sesquioxide minerals. Observations on site at well
9 and in experiments 1 and 2 of the laboratory waste -
aquifer reactivity studies indicate that at a given point
in receiving zone, the maximum rate of dissolution of
carbonate coatings occurs first followed by dissolution
of sesquioxide coatings of which the iron oxides pre-
dominate. Dissolution of both carbonates and Al, SiO2,
Fe, and Mn contained within the grains of primary
minerals occurs at a much slower rate than the disso-
lution of the coatings. High concentrations of dissolved
calcium and carbon dioxide are features of carbonate
dissolution, and sesquioxide dissolution is indicated by
elevated concentrations of aluminum, iron, and man-
ganese.
Iron solubilization data from experiments 1 and 2,
and iron precipitation data from experiment 3, suggest
a region of iron hydroxide precipitation within the
fast -reaction zone. As the pH of a unit of waste moving
outwards from the injection well changes from pH 5.5
to 6.0, hydroxide concentration increases to the point
where precipitation of iron hydroxide occurs. This re-
gion of iron hydroxide precipitation may be a signific-
ant factor in the chemical plugging of the waste -
receiving subzones because very high concentrations of
organically complexed iron were observed in the fast -
reaction zone below pH 5.5, and this dissolved iron was
essentially quantitatively reprecipitated as the pH of
the injected waste rose during its outward movement
and neutralization. Phthalic acid complexed with the
dissolved iron was found to be coprecipitated with the
iron hydroxide, and this is most likely the reason why
phthalic acid was not found in the neutralized waste
samples obtained from wells 11, 14, and 15. The corre-
lation of iron concentration with waste concentration
in well 14 most likely resulted from bacterial waste
decomposition processes; not from organic acid dissolu-
tion of iron oxide coatings because acid-solubilized iron
should have reprecipitated before the waste reached
well 14.
The laboratory waste -aquifer study substantiated
the "slow -reaction zone" of the initial conceptual model
which follows the fast -reaction zone. Reactions which
occur in this zone are the slow solubilization of silica,
aluminum, and iron from the crystalline primary min-
erals found in the waste -receiving subzones. Prior pas-
sage of acidic waste has dissolved most of the secon-
dary coatings found on the aquifer minerals, and the
only significant reactions which remain are the slow -
dissolution reactions of the primary minerals them-
selves. The pH in this zone is essentially the same as
the pH of the injected waste, pH 4, because the flow
rates and types of reactions do not significantly neu-
tralize the waste and affect the pH.
The reaction rates in the slow -reaction zone were
found to decrease as the quantity of injected waste
increased until no further reactions could be observed
between the waste and the aquifer constituents. The
area in the subsurface in the immediate environs of the
waste -injection well where there were no observable
reactions was called the "waste pool." Samples ob-
tained from wells 1, 2, 4, and 5 at the beginning of this
study were taken from the waste pool because their
elemental composition was essentially the same as the
injected waste. Only after the cessation of all observa-
ble reactions can the subsurface environment be re-
garded as a waste storage area because it is only in this
waste pool that the waste could be reclaimed in unal-

SUMMARY AND CONCLUSIONS
tered form after subsurface injection.
The various zones and interactions presented in this
final conceptual model of waste movement and reactiv-
ity cannot be considered to be well defined at all times
during waste injection. At the beginning of injection of
waste similar to that from the Hercules plant, it is not
likely that there is a microbial activity zone because
conditions change too suddenly within the waste front
for an establishment of a viable waste -degrading mi-
crobial population. It is only after the waste front has
moved a significant distance from the injection well
that its rate of movement will decrease to the point
which allows the formation of a microbial activity
zone. At the opposite extreme of the model, a waste
pool cannot form until a sufficient volume of waste has
been injected and enough time has passed so that all
the reactive aquifer constituents have been dissolved
and removed from the vicinity of the injection well. In
summary, this model is a static representation of a
dynamic situation. Specifically, this model was drawn
to represent the various stages of reaction of the in-
jected waste thought to exist in the subsurface after 4
years of waste injection at which time most of the
findings of this study were obtained.
SUMMARY AND CONCLUSIONS
The Hercules waste injection site near Wilmington,
N.C., has provided an opportunity for studying the
physical, chemical, and biological aspects of subsurface
organic waste injection. Most of the waste -aquifer in-
teractions which were predicted to occur at the incep-
tion of this study were verified by the site and labora-
tory studies. Differences between the initial and final
conceptual models of waste movement and reactivity
show however that the initial predictive model had to
be tested with data and modified to fit the findings of
this study.
Evidence was obtained at the site and in laboratory
studies to substantiate the following waste -aquifer in-
teractions:
1. Dissolution of the carbonate minerals in the injec-
tion zone by the waste organic acids.
2. Dissolution of the sesquioxide coatings on the pri-
mary minerals in the injection zone by waste organic
acids.
3. Dissolution of the primary aluminosilicate minerals
in the injection zone by the waste organic acids.
4. Dissolution and complexation of iron and man-
ganese oxides by the waste organic acids.
5. Reprecipitation of complexed dissolved iron during
waste neutralization.
6. Coprecipitation of phthalic acid complexed with
iron during iron hydroxide precipitation.
7. Methane gas production resulting from anaerobic
microbial waste degradation.
41
8. Microbial reduction of sulfates to sulfides.
9. Reduction of ferric to ferrous iron resulting from
decreases in Eh and pH due to microbial waste deg-
radation.
10. Retention of organic waste acids by adsorption and
anion exchange on the mineral constituents in the
injection zone at low pH values.
These waste -aquifer interactions prove that this in-
dustrial organic waste cannot be regarded as an inert
fluid which does not react after injection into the sub-
surface environment. The history of the plugging of
both injection wells after a period of waste injection
strongly indicates that serious consideration should be
given to the chemical compatibility of the waste with
the fluid and minerals of the zone into which injection
is planned. Problems of injection zone plugging may be
due in part to the reprecipitation of aquifer con-
stituents initially dissolved by the waste acids, and due
to the formation of gaseous reaction products such as
carbon dioxide and methane. Dissolution of aquifer
solids by the complexing organic acids in the waste
may be significant in the leakage problems at the in-
jection and observation wells. These organic acids may
dissolve the bond between the cement grout surround-
ing the well casing and the aquiclude confining beds to
allow upward leakage of waste into shallower zones. If
the waste leakage was due to dissolution reactions,
this problem would be accentuated at the injection
wells where the waste is the most acid (pH 4), the
warmest (45°C), the density difference with the native
ground water the greatest, and where the highest
pressure head occurs in the injection zone.
This study has shown the importance of conducting
compatibility tests of the injected waste with the
aquifer material before the initiation of waste injec-
tion. The data obtained by conducting three experi-
ments with the pressurization core -testing apparatus
demonstrated that field hydraulic conditions of waste
injection can be simulated within the laboratory. Most
of the chemical interactions which occurred on -site
were observed in the laboratory simulation of waste
injection into cores of material from the injection zone.
The laboratory study demonstrated precipitation and
dissolution reactions which pointed to problems of
aquifer plugging and leakage at the waste -injection
site. It also better defined waste -aquifer interaction in
a quantitative manner than did the site study. Such
laboratory tests should also be of considerable in-
terpretive value in waste -injection systems where
monitor wells are absent or are determined to be a
financially impractical part of the total injection sys-
tem.
A major limitation of the site study was imposed by
the construction features of the observation wells be-
cause they were open to various subzones within the

42 SUBSURFACE ORGANIC WASTE INJECTION, NORTH CAROLINA
injection zone. In any future study it would be desira-
ble to install packers in the observation wells to isolate
each subzone, so that undiluted samples could be ob-
tained from each.
The case history of the Hercules waste -injection sys-
tem is a documentation of a system which is no longer
used for several reasons. The major problem with the
waste appears to be its reactivity. Because the overall
permeability of the waste -injection zone was low, the
formation of coatings, precipitates, and (or) gases, even
in small quantities, decreased the permeability of the
injection zone to the point where plugging of the in41ec-
tion well occurred. If wastes of this type were neu-
tralized prior to injection, the injected neutralized
waste would not dissolve aquifer constituents such as
iron which is later reprecipitated. Carbon dioxide gas
would, therefore, not be formed which may constitute
part of the plugging problem other than the small
quantity produced by microbioal waste degradation.
The neutralized salts of organic acids are not nearly
adsorbed on aquifer sediments to the extent of free
acids which may form coatings and precipitates on
aquifer sediments. Cooling the neturalized waste prior
to its filtration and injection would allow precipitate
formation of any insoluble waste constitutents which
could be filtered from the waste before injection. These
actions would have made the waste more inert in the
subsurface environment, thus minimizing problems
with aquifer plugging and well leakage.
The microbiological study has shown that this in-
jected waste is very slowly biodegradable in the sub-
surface environment. Although the addition of nitro-
gen to the injected waste may greatly increase the
amount of microbial waste degradation and sub-
sequent methane formation, a large amount of
methane gas would undoubtedly be formed and would
plug the injection zone under site conditions similar to
that studied.
SELECTED REFERENCES
Black, Crow, and Eidsness, Inc., 1971, Engineering report on drilling
and testing of additions to the disposal well system for Hercules
Incorporated, Hanover Plant, Wilmington, N.C.: 103 p.
Bricker, C. E., and Vail, W. A., 1950, Microdetermination of formal-
dehyde with chromotropic acid: Anal. Chemistry, v. 22, no. 5, p.
720-722.
DiTommaso, Anthony, and Elkan, G. H., 1973, Role of bacteria in
decomposition of injected liquid waste at Wilmington, North
Carolina, in J. Braunstein, ed., Sept. 1973, Underground Waste
Management and Artificial Recharge: New Orelans, v. 1, p.
585-599.
Goerlitz, D. F., and Brown, Eugene, 1972, Methods for analysis of
organic substances in water: U.S. Geol. Survey Techniques
Water -Resources Inv., book 5, chap. A3, 40 p.
Hall, C. W., and Ballentine, R. K., 1973, U.S. Environmental Protec-
tion Agency policy on subsurface emplacement of fluids by well
injection, in J. Braunstein, ed., Sept. 1973, Underground Waste
Management and Artificial Recharge: New Orleans, v. 2, p.
783-789.
Hem, J. D., 1970, Study and interpretation of the chemical charac-
teristics of natural water [2d ed.]: U.S. Geol. Survey Water -
Supply Paper 1473, 363 p.
Jones, L. H. P., and Handreck, K. A., 1967, Silica in soils, plants and
animals: Advances in Agronomy, v. 19, p. 107-147.
Kunzie, G. W., and Rich, C. I., 1959, Certain properties of some
Southeastern United States soils and mineralogical procedures
for their study: Blackburg, Va., Virginia Agr. Exp. Sta., South-
ern Cooperative Series Bull. 61.
Lawrence, A. W., and McCarthy, P. L., 1969, Kinetics of methane
fermentation in anaerobic treatment: Water Pollution Control
Federation Jour., v. 1, part 2, p. 1-17.
Leenheer, J. A., and Malcolm, R. L., 1973a, Chemical and microbial
transformations of an industrial organic waste during subsur-
face injection: Anaheim, Calif., Inst. Environmental Sci. Proc.,
April 1973, p. 351-360.
1973b, Case history of subsurface waste injection of an indus-
trial organic waste, in J. Braunstein, ed., Sept. 1973, Under-
ground Waste Management and Artificial Recharge: New Or-
leans, v. 1, p. 565-584.
Le Grand, H. E ., 1955, Brackish water and its structural implica-
tions in Great Carolina Ridge, North Carolina: Am. Assoc. Pe-
troleum Geologists Bull., v. 39, no. 10, p. 2020-2037.
1960, Geology and ground -water resources of Wilmington -
New Bern area: North Carolina Dept. Water Resources
Ground -Water Bull. 1, 80 p.
Malcolm, R. L., Leenheer, J. A., 1973, The usefulness of organic
carbon parameters in water quality investigations: Anaheim,
Calif., Inst. Environmental Sci. Proc., April 1973, p. 336-340.
Malcolm, R. L., Leenheer, J. A., McKinley, P. W., and Eccles, L. A.,
1973, Supplement II -Dissolved organic carbon, in D. F. Goer-
litz and Eugene Brown, eds., Methods for analysis of organic
substances in water: U.S. Geol. Survey Techniques Water -
Resources Inv., book 5, chap. A3, 34 p.
Malcolm, R. L., Leenheer, J. A., and Weed, S. B., 1976, Dissolution of
aquifer clay minerals during deep -waste disposal of industrial
organic wastes: Mexico City, Internat. Clay Conf. Proc., 1975, p.
477-493.
McKeague, J. A., and Cline, M. G., 1963, Silica in soil solutions,
Parts I and II: Canadian Jour. Soil Sci., v. 43, p. 70-96.
McKenzie, H. A., and Wallace, H., 1954, The Kjeldahl of nitrogen: A
critical study of digestion conditions: Australian Jour. Chem., v.
7, p. 55-60.
Mehra, O. P., and Jackson, M. L., 1960, Iron -oxide removal from soils
and clays by a dithionite-citrate system buffered with sodium
bicarbonate: Clays and Clay Minerals, 7th Natl. Conf. on Clays
and Clay Min. Proc., 1960, p. 317-327.
North Carolina Department of Water and Air Resources, 1971, Satus
report on the feasibility of the injection of liquid waste into
saline ground water at Wilmington, North Carolina: Raleigh,
North Carolina, 26 p.
Oborn, E. T., and Hem, J. D., 1961, Microbiologic factors in the
solution and transport of iron: U.S. Geol. Survey Water -Supply
Paper 1459-H, p. 213-235.
Peek, H. M., and Heath, R. C., 1973, Feasibility study of liquid -waste
injection into aquifers containing salt water, Wilmington, North
Carolina, in J. Braunstein, ed., Sept. 1973, Underground Waste
Management and Artificial Recharge: New Orleans, v. 2, p.
851-875.
Ringbom, A., 1963, Complexation in analytical chemistry: New
York, Interscience Publishers, 395 p.
Siebert, M. L., and Hattingh, W. H. J., 1967, Estimation of
methane -producing bacterial numbers by the most probable
number (MPN) technique: Pergammon Press, Water Research,
v. 1, p. 13-19.

SELECTED REFERENCES
Skougstad, M. W., and Scarbro, G. F., Jr., 1968, Water sample filtra-
tion unit: Environmental Sci. and Technology, v. 2, p. 298-301.
Swenson, H. A., and Baldwin, A. L., 1965, A primer on water quality:
Washington, U.S. Govt. Printing Office, 27 p.
Waksman, S. A., 1952, Soil microbiology: New York, John Wiley &
Sons, 356 p.
43
Warner, D. L., and Orcutt, D. H., 1973, Industrial waste -water wells
in United States —Status of use and regulation, 1973, in J.
Braunstein, ed., Sept. 1973, Underground Waste Management
and Artificial Recharge: New Orleans, v. 2, p. 687-697.
White, W. R., and Leenheer, J. A., 1975, Determination of free formic
and acetic acids by gas chromatography using the flame ioniza-
tion detector: Jour. Chromatographic Sci., v. 13, p. 386-389.

BASIC -DATA TABLES 20-36

46 SUBSURFACE ORGANIC WASTE INJECTION, NORTH CAROLINA
TABLE 20. -Organic waste analyses TABLE 23.-Inorganic analyses ofground water from 300-fizone
Collection date (mo-day-yr)
9-14-72
7-6-73
11-7-73
Milligrams per litre
DOC.
6,700
6,400
7,900
Acetic acid -------------- .....___._-----------------
-- 9,500
8,500
10,000
Formic acid ..................
............ 3,100
3,300
2,900
Formaldehyde ............................................
1,600
1,700
2,100
Methanol...------_--_-- ..................-------_-----
260
0
2,000
p-Toluic acid ................................................ 1,200 1,100 1,000
Terephthalic acid ............. _._.__........... . 430 400 360
Phthalic acid .................. _-.___._-------------- 36 22 170
Benzoic acid ................................................ 35 32 95
Well No.
13
14 15
16
Zone (feet below
283-293
320-330 279-299
305-325
land surface).
Collection date---------------- --------_
----- 11-3-71
2-25-72 2-26-72
4-15-72
pH- ---- - ....
8.3
8.1 8.2
8.2
Specific conductance
9550
9000 7500
9500
("mhos at 25'C).
Milligrams per litre
Silica (SiO2) .... __...................................
2.3
9.7 9.5
11
Calcium (Ca) ._........___.. ---------
_--------- 32
19 13
47
Magnesium (Mg) .................................
34
46 32
45
Sodium (Na)...........................................
1850
2000 1650
2100
Potassium (K)--------- ..-----------------------
120
58 50
63
TABLE 21. -Waste inorganic analyses -sample collected 11-7-73 Sulfate (SO4nate (HCOs) 645 350 130 330
gSulfate(SO4)...._................._---................ 4b 350 130 330
[Analyzed by WRD Central Laboratory Salt Lake City Utah, except where noted by (a), Chloride (CD-------- --------- _---------- ... 2820 2780 2350 2480
Huffman laboratory, Wheatridge, Co{o., or by (b), V. b. Kennedy, U.S.G.S., Menlo Park, Fluoride (F) ................... ------- ..._ ......... 1.3 1.3 1.4 1.3
Calif.l Nitrite -nitrate (NO2-NOs) .2 .02 .6 .05
Analysis date
12-18-73
3-27-74
pH.................... -- - - -
- - 3.8
3.8
p; c conductance
4,560
4,530
(µmhos at 25'C).
Milligrams per litre
Silica (SiO2) -------------------------------------------
31
31
Calcium(Ca)_._._....................._.....................
1,300
1,300
Magnesium (Mg) ------------------------------------------------
30
32
Sodium (Na)---------------------------------
1.8
1.5
Potassium (K) ...... -_.....-_... ...----------
-- -
3.8
Sulfate(SO4).... ................................................
11
41
Chloride (Cl)
5.2
5.5
Fluoride(F)..........................................................
1.4
2.8
Nitrite-nitrate(NO2-NO:)....... .......... ___---.--
-
- 3.9(a)
Orthophospate (PO4)------------------------------------
0.28
-
Hardness as CaCOa (Ca, Mg) ----- ....................
3,400
3,400
Micrograms per litre
Aluminum (Al), total
- - -
_
Arsenic(As) -------- .............................................
3
-
Barium(Ba) ........... ............ .......-----
-- 0
-
Cadmium (Cd) - -- - - -- - -------------------
5
2
Chromium (Cr), total ........................................
260
-
Cobalt(Co) ---------------------- ------ --------------------
1,600
-
Copper(Cu) ........................ ........................
-
100
Iron (Fe), total ----------------------- ...........................
20
80 5,500(b)
Lead(Pb)...... - . -_ --------------------------------------
-
7
Manganese (Mn)------------- -----------------------------
160
80
Mercury (Hg), total - -- -------------------------
----- - 1.0
Molybdenum(Mo)..............................................
2
Nickel(Ni) ...................----------------------------------
100
Selenium (Se)...------ -- _ - - - --- -------------------
24
Strontium (Sr) - ...........................................
820
Zinc(Zn)
Orthophosphate (PO4) ---- _- --------- _-----
.02
.000 .000 .000
Residue on evaporation
5220
5560 4560 5970
at 180'C.
Hardness as CaCO2 (Ca, Mg)
200
236 164 303
Micrograms per litre
Aluminum (Al) ......................................
81
269 225 543
Copper (Cu)------- - -------
173
Iron (Fe)....................................................
5253
15 0 522
Lithium (Li) .........................................
77
- - -
Manganese(Mn) _....._.-__-....._-- ---.....
112
- - -
Strontium (Sr) .............. ___......... -_-------
1200
- - -
Zinc(Zn)---------- ---------------------------------------
10
- - -
TABLE 24.Inorganic analyses ofground water from 500-f$zone
Well No.
14
15
Zone (feet below land surface)
500-520
500-520
Collection date._ .................. ........................ --- ----------
3-4-72
3.5-72
pH....---- -..-----......_..__ ..... ...... -------------..
Specific conductance
.... 7.9
20,000
7.6
19,500
(µmhos at 25°C).
Milligrams per
litre
Silica (SiO2)-------- --------------- ............. . ..............
6.2
8.1
Calcium (Ca) ... ------------- .__........... _........... _--........
148
111
Magnesium (Mg) .................... ............................
169
185
Sodium (Na) ............-............- .............................
4,600
4,430
Potassium (K) .......... ........ ........... ............
123
118
Bicarbonate (HCO3).................................................. 337 371
- Sulfate (SO4).._.... ---------- - --------- - ----------- -...------- 765 760
2 Chloride(CI)................ ---__-..._.---- --_----_-- -----------_ - 6,990 6,950
- Fluoride (F) .......---_.............................................. .8 .7
- Nitrite-nitrate(NO2-NO2)------------------- ---------------- --_. .00 .09
590
TABLE 22. -Inorganic analyses ofground water from surf-icial sand
aquifer
Well
Hercules
Supply well
C 14
15
16
Zone (feet below
30-60
28-48
33-53
33-53
land surface).
Collection date ---- __--- _....................
6-15-71
2-25-72
2-26-72
5-19-72
pH ..................................
6.0
6.6
6.1
6.0
Specific conductance
29
46
85
31
(µmhos at 25-C).
Milligrams per litre
Silica (SiO2) ---------- ----------------------
5.0
4.8
5.7
4.1
Calcium (Ca) ------------ ---- ---------------------
1.8
2.0
5.0
1.5
Magnesium (Mg) ............ ............. _.........
.4
1.0
3.0
.9
Sodium (Na)----------------------------------------
3.0
4.9
4.5
2.1
Potassium (K) ----------------------
.5
.6
1.4
.5
Bicarbonate (HCO3)
4
10
5
7
Sulfate(SOO............................................
4.0
2.4
2.6
4.4
Chloride (Cl)------------------------- _--...... -......
5.2
6.4
9.0
3.4
Fluoride (F) ----------------- ---------------
0
.0
.0
.0
Nitrite -nitrate (NO2-NOs)
.2
.3
4.3
.02
Orthophosphate(PO4)
.00
.000
.013
.010
Residue on evaporation
22
33
56
29
at 1WC.
Hardness as CaCO3 (Ca, Mg)
6
9
25
7
Micrograms per litre
Aluminum (Ab, total ............................
53
107
37
239
Iron (Fe), total ------ ___----------------- __......
57
115
0
131
Manganese (Mn) -------------------- -------------
12
-
-
-
Copper (Cu) ..............-- - ............
40
-
-
-
Zinc (Zn) _----------------- -----------------
10
-
-
-
Orthophosphate(PO4)..__........ ._-- ----------- ___-------
.000
.000
Residue on evaporation at .......................................
13,300
12,800
180'C.
Hardness as CaCOs (Ca, Mg) -.- _--------------------------
1,060
1,040
Micrograms
per litre
Aluminum (Al), total -_ ...... ...-_-_.............................
613
613
Iron (Fe), total ........... -- .... - -- - ......
0
0

BASIC -DATA TABLES
TABLE 25 -Inorganic analyses ofground water from 700-ftzone
[Values in parentheses are from analysis by E. A. Jenne, U.S.G.S., Menlo Park, Calif.]
47
Well No.
8
8
8
9
9
9
14
Zone (feet below
694-704
694-704
694-704
727-737
727-737
727-737
637-693
land surface).
Collection date......
..... 6-15-71
6-13-73
10-31-73
6-15-71
6-20.72
6-14-73
3-8-72
PH.................. ............... ..------------------- -------------
_ 7.5
-
-
7.4
5.8
4.5
7.8
Specific conductance
27,100
28,300
28,241
31,100
17,900
17,900
25,000
(µmhos at 25'C).
Minigrams per litre
Silica (SiO2) ...........-...........................................
8.8
12
11
8.0
60
27
6.2
Calcium (Ca) .......... ----- --------- -
265
270
280
321
3,870
3,100
223
Magnesium (Mg) ... .................
321
280
280
438
219
190
186
Sodium (Na) .................... ............... ____.-----------
5,900
5,900
6,300
6,750
1,700
-
5,900
Potassium(K)................................ __------ _....__
212
170
200
230
120
140
145
Bicarbonate (HCO3)..........................................
358
-
-
244
6,910
-
247
Sulfate(SOO...._...__................. ____-------------
__ 610
540
550
740
145
150
680
Chloride (Cl)--- ___----------- ........... _.......
9,650
10,000
11,000
11,400
2,550
3,000
9,300
Fluoride (F).......... _........................ ..................5
.4
.4
.4
3.6
3.2
.6
Nitrite-nitrate(NOs-NOa)................... -...-_-....
.8
-
.08
.6
1.8
-
.3
Orthophosphate W04)..._.................................
.02
-
.12
.02
.12
-
.000
Residue on evaporation
17,800
-
-
21,000
22,100
-
16,700
at 180'C.
Hardness as CaCOs (Ca, Mg)
1,980
1,800
1,900
2,600
10,600
8,500
1,270
Micrograms per litre
Aluminum (Al), total ............ __............
__.. 495
20
0
305
1,260
0
(<1)
858
Arsenic (As) - -------- ----------------- ------------
-------- -
9
-
-
-
0
-
Barium (Ba) .................................. .....................
-
300
-
-
-
2,300
-
Csdmium (Cd) ............. ---- ------------------........
-
60
-
-
-
170
(<.2)
-
Chromium (CO, total ---------------------
-
10
-
-
-
150
-
Cobalt (Co) --...- ........- ............
---- -
200
-
-
-
930
(20)
-
Copper(Cu)_............. .. .....-_... .._.....
120
30
-
269
-
90
(1.0)
-
Iron (Fe), total ................................ -------------
- 2,150
3,400
5,000
12,000
77,800
310,000
(205,000)
0
Lead (Pb) ------- ----- -............ --_........
--... -
4
1
-
-
15
(<3.5)
-
Manganese (Mn)
...... 180
150
-
179
-
5,200
(3300)
-
Mercury (Hg), total _.----------- --..........
-- -
14
-
-
-
.1
-
Molybdenum (Mo)---........ ---------------
-
2
-
-
-
2
(<1.2)
Nickel (Ni) .......... ................... ....... ....-
.. -
230
-
-
-
880
(67)
-
Selenium (Se) .................... ........ -- ------
- -
2
-
-
-
250
-
Strontium (Sr) ....
---- -
16,000
-
-
-
19,000
Zinc (Zn)............ ..........................................
....... 35
130
110
40
-
200
(160)
-
TABLE 26. Inorganic analyses of ground water from well 7,
805-I036 feet below land surface
Collection date
6-15-71
11-3-71
6.13-73
10.31-73
PH .. --- ----------------- --------
- 7.5
7.3
-
-
Specific conductance
31,800
32,500
31,500
32,635
(µmhos at 25'C).
Milligrams per litre
Silica (SiO2) __..... ..... _......... -.........
9.4
11
11
11
Calcium (Ca)
353
346
330
340
Maaggnnesium (Mg) ----------- -------............
370
315
300
300
Sad�um (Na)-------- ----------------
6,900
6,750
6,700
7,000
Potassium (K)
224
155
190
210
Bicarbonate WOO
233
231
Sulfate (SO4) ...................... ............. _...
385
280
270
270
Chloride(Cl)........................................
12,000
12,000
12,000
12,000
Fluoride (F)----------------------- -------
.5
.09
.5
.3
Nitrite -nitrate (NO2-NO2)
.3
0
-
.11
Orthophosphate (PO4)
.02
.03
-
.08
Residue on evaporation. ........... _---
21,100
20,700
-
-
Hardness as CaCOs (Ca, Mg) ...._ ...
2,400
2,200
2,100
2,100
Micrograms
per litre
Aluminum (Al), total
502
335
0
10
Arsenic (As)
-
-
6
-
Barium (Ba) ----------------------------------
-
-
400
-
Cadmium (Cd) ...... .......... ...........
-
-
80
-
Chromium (Cr), total
-
-
20
-
Cobalt(Co)..........................................
-
-
250
-
Copper (Cu)------ - ----- --------- -
-
211
40
-
Iron (Fe), total ......._......... - _------- .__
314
1,792
1,400
1,300
Lead(Pb)..............................................
-
-
3
0
Lithium (Li)
292
-
Manganese(Mn) ................................
222
190
250
-
Mercury (Hg), total ............................
-
-
8.2
-
Molybdenum (Mo)..............--........
-- -
-
3
-
Nickel (Ni)
-
-
250
-
Selenium(Se)....... _............................
-
-
10
-
Strontium (Sr)
-
17,300
2,500
Zinc (Zn) --------------- ------------------------------
-
20
60
100

48 SUBSURFACE ORGANIC WASTE INJECTION, NORTH CAROLINA
TABLE 27. -Inorganic analyses ofground water from well 11, 855-1035 feet below
[Values in parentheses are from analysis by E. A. Jenne)
11-3-71
1-15-73
1-26-73
2-9-73 2.23-73
3-16-73
3-30.73
4.13-73
5-10-73
6-16-73
pH .......... ........
7.2
-
7.7
- 7.3
7.4
7.6
-
-
-
Specific conductance
32,000
31,800
32,100
32,200 32,100
32,100
31,200
20,600
31,100
30,100
(µmhos at 25°C).
Milligrams per litre
silica (Sioz)...........
8.6
10
11
10 14
10
10
10
11
11
Calcium (Ca) ------------------- ----------
345
330
320
330 320
330
320
340
330
330
Magnesium(Mg)--.-------------_._
- ---_- _- -
308
290
290
290 290
300
280
290
290
300
S-
Sodium (Na)....................................._..._........
6,600
6,600
6,700
7,400 6,600
6,600
6,800
6,900
6,700
6,600
Potassium(K) ..._----- --- _--- _-------------
__.... 155
200
170
170 180
200
160
180
190
180
Bicarbonate (HCO3) ...... --------
- ---- 232
-
-
- -
-
-
-
-
-
Sulfate (SO4)................... ____._______..._...
210
210
220
220 200
180
230
210
210
190
Chloride(Cl)------------ --- .....___.........._.,__..
12,000
12,000
12,000
12,000 12,000
12,000
12,000
11,000
12,000
12,000
Fluoride (F)...._..._..................................
... .. .6
.7
.5
.8 .6
.5
.4
.3
.5
.5
Nitrite -nitrate (NO2-NO3)
.0
0
.01
.03 -
.10
-
-
-
-
Orthophosphate (PO4) ........._.._..............._..
.00
.06
.03
- -
.04
-
-
-
-
Residue onevaporation
20,400
-
-
- -
-
-
-
-
-
at180TC.
Hardness as CaCOa (Ca, Mg)
2140
2,016
2,000
2,000 920
2,100
2,000
2,000
2,000
2,100
Micrograms per litre
Aluminum (Al), total ........................
_.......... 186
30
10
20
10
0
lu
0
0
v
la.o)
Arsenic (As) . ----- ....-------....... -------------
--- -
-
-
-
-
-
-
-
-
0
Barium (Ba) --..---------------------------
-
-
-
-
-
-
-
-
-
500
Cadmium (Cd) ._...._......- .......... .....................
-
-
-
-
-
-
-
-
-
80
(<.2)
Chromium (Cr), total ---------- -------------------
-
-
-
-
-
-
-
-
-
20
Cobalt (Co) . -- ------ - ---
-
-
-
-
-
-
-
-
-
280
(A)
Copper(Cu)..................................
......... ..... 251
-
-
-
-
-
-
-
-
40
(1.2)
Iron (Fe), total _....... _...... ---- ---------------
_---- 1,730
1,700
1,300
1,400
1,200
1,100
1,200
1,300
1,100
590
(1900)
Lead(Pb)---------- ......................................
-
1
2.0
1
0
1
0
2
1.0
4
(<3.5)
Lithium (Li) _ ... ...
............. 284
-
-
-
-
-
-
-
-
-
Manganese (Mn)-------------- __.....................
325
-
-
-
-
-
-
-
-
420
(350)
Mercury (11g), total .......... ........
............. -
-
-
-
-
-
-
-
-
7.4
Molybdenum (Mo).----- .---- -------------
---------- -
-
-
-
-
-
-
-
-
0
(1.4)
Nickel (Ni) ....... .................................
-
-
-
-
-
-
-
-
-
330
(<.5)
Selenium (Se) _- _------------------
------- -
-
-
-
-
-
-
-
-
9
Strontium (Sr) ....- --- --- ------ ---------------------
16,600
-
-
-
-
-
-
-
-
25,000
Zinc(Zn)------------- ._.._-..........._-.......................
110
270
30
30
30
20
30
150
20
40
(4.2)
TABLE 29. -Inorganic analyses ofground water
Collection date
5-8-72
6.20-72
8-1-72
8-3-72
8-7-72
8-14-72
8.28.72
9.4.72 9-11-72
9-19.72
10-11-72
10-31-72
pp11 - - - _.---------- --
. 7.2
7.0
-
-
-
-
-
-
-
-
-
-
Speccconductance
25,300
30,500
31,600
31,900
32,000
31,600
32,100
31,900
32,100
32,000
31,400
32,600
(µmhos at 25').
Milligrams per
litre
silica(Si02)
6.9
11
10
10
10
10
10
10
10
10
9.5
9.5
Calcium (Ca) ...-................. ...._
663
465
330
330
330
340
320
330
330
330
340
380
Magnesium (Mg) ........................
252
209
270
280
280
270
280
270
270
280
280
280
Sodium (Na)----- _............ ------------
5,550
6,800
6,600
6,400
6,500
6,600
6,700
6,600
6,600
6,400
6,500
6,200
Potassium (K) ._.___............ _..
170
160
150
180
170
180
170
180
160
160
170
200
Bicarbonate (HCO3) ..................
2,120
307
-
-
-
-
-
-
-
-
-
-
Sulfate (SO4)- _........... __....... ..
980
215
180
190
180
170
180
190
190
170
170
140
Chloride(CI) --------------------------------
8,720
11,500
12,000
11,000
11,000
12,000
12,000
12,000
12,000
12,000
11,000
11,000
Fluoride(F).................................
.8
.8
.6
.6
.6 .5
.6
.6
.6
.6
.6
1.5
Nitrite -nitrate (NO2-NO3)
.2
-
.01
0
0
0
.02
0
.01
0
0
0
Orthophosphate(PO4).._.....__.
.047
.000
-
-
-
-
.05
-
-
-
-
-
Residue on evaporation
19,400
20,800
-
-
-
-
-
-
-
-
-
-
at 180°C.
Hardness at CaCOa
2,690
2,020
1,900
1,975
1,975
1,959
2,000
1,934
1,900
1,975
2,000
2,100
(Ca Mgt
Micrograms per litre
Aluminum (Al), total .------ -----
- 2,200
631
10
20 (3.4)1
0
10
10
0
0
0
0
0
Arsenic (As) ................................
-
-
0
-
0
1
1
0
1
0
0
0
Barium (Ba) ..--...--- - ------
-
-
1,200
-
500
500
0
1,200
500
700
0
0
Chromium (Cr), total ----------
-
-
10
-
20
10
10
10
10
20
20
20
Cobalt (Co) --------------------------------
-
-
1
-
0
2
1
1
2
1
1
0
Copper(Cu).._.__......_............_-.
-
-
20
- (15),
20
20
20
20
20 (30)1
30
40
30
Iron Te), total ...........................
327
2,090
5,100
3,600
4,200
5,300
5,400
8,100
13,000
7,500
35,000
34,000
Lead (Pb)..- ........ _------------------- ...._
-
-
1
2
1
1
4
2
2
2
2
0
Manganese (Mn) __..___.._..._..
-
-
610
- (8.9),
660
(1.7)1 950
2,300
610
950
860
2,300
2,500
Mercury (Hg), total
-
-
0
-
0
0
0
0
0
0
0
0
Molybdenum (Mo)_.__._......._._
-
-
1
-
0
1
0
1
-
2
0
0
Nickel (Ni) ........... .....................
-
-
2
-
4
2
2
2
2
12
15
0
Selenium (Se).._._ ........ .......... ..._
-
-
0
-
3
0
0
0
0
0
0
3
Strontium (Sr)
-
-
18,000
-
18,000
18,000
18,000
18,000
18,000
8,000
18,000
17,000
Zinc(Zn)................__..._............
-
-
40
10
20
50
40
30
10
90
30
70
Bromine (Br) .............._......._..-
-
-
-
- (96)1
-
(83)` -
-
-
- (95),
-
-
-
Vanadium(V) ------- -------- .----
-
-
-
-
-
(.4)1 -
-
-
-
-
-
-
'Analyst: L. Thatcher, U.S.G.S., Denver Colo.
2Analyst: E. A. Jenne, U.S.G.S., Menlo Bark, Calif

49
BASIC -DATA TABLES
land surface
TABLE 28. - Inorganic analyses of ground water from well 12, 838-
974
feet below land surface
[Values in parentheses are from analysis by E. A. Jenne]
7-3.73
7-20-73
9-14-73
10-31-73
Collection date
11-3-71
6-16-73
10-31-73
31,600
31,300
30,500
33,300
pH._-.___
_.........
7.2
peeificconductance
32,000
31,400
32,100
(µmhos at 25°C).
11
11
11
11
Milligrams per litre
320
330
320
330
Silica (SiO2)
9.0
7.7
3.6
200
6,900
290
6,800
290
7,000
300
6,800
........
Calcium (Ca) -------------------.
Magnesium (Mg) -------------------------------
338
310
310
300
180
300
170
170
190
210
Sodium (Na)-------- -- - - ------------------
6,650
6,600
7,000
Potassium (K)
150
190
210
200
12,000
210
12,000
160
12,000
170
14,000
Bicarbonate (HCO3)
Sulfate (SO4)........................................
233
250
240
220
.7
-
.7
.4
.3
Chloride(Cl)-__-- ---------- .----- -------------
11,900
12,000
12,000
-
.04
.10
Fluoride (F) _-
-------
.6
0.4
.2
90
Nitrite -nitrate (NOs-NOs).------------
.0
-
.03
-
-
-
-
Orthophosphate(PO4)--------------
.03
-
.13
2,000
2,000
2,000
2100
Residue on evaporation at
180°C.
20,600
-
-
_
Hardness as CaCO3 (Ca, Mg)
_._.....
2,150
2,000
1,900
0
20
10
10
Micrograms per litre
-
-
-
-
Aluminum (Al), total
445
0
(<1.0)
0
-
-
-
-
Arsenic (As) ...---- ..............................
-
0
-
-
-
-
-
Barium (Ba)
-
500
-
-
-
-
-
Cadmium (Ca) - - - - -------------------
- -
-
80
(.2)
-
Chromium (Cr), total .......................
-
20
-
480
510
350
290
Cobalt (Co) --- _----------------.-- --_-------
Copper(Cu)..............._._......................
-
256
250
50
(<.2)
(.9)
-
-
1
2
3
2
Iron (Fe), total -._ - -------------------------
5,253
31,100
(31,000)
37,000
Lead (Ph)
-
5
(<3.5)
0
-
-
-
-
Lithium (Li) ........................................
278
-
-
-
-
-
-
Manganese (Mn) .-
265
610
(320)
-
-
-
-
-
Mercury (Hg), total
-
10
-
Molybdenum (Mo)------------------------------
-
0
(<1.2)
-
-
Nickel (Ni) ------------------------------------
-
0
-
20
90
60
40
Selenium (Se)
Strontium (SO --- _-_--_----------------
---------
---- ----
-
16,600
0
23,000
-
-
Zinc (Zn)-----------------------------
. .
49
30
(2.8)
40
from well
14, 843-972 feet below land surface.
Collection date
11-7-72
11-13-72
11-22-72
11-30-72
12-5-72
12-13-72
12-19-72
12-29-72 1-15-73 1-26-73
2-9-73
2-23.73
6-16-73
10.31-73
7.5
7.3
32,700
32,000
31,900
31,700
32,300
30,700
31,968
31,458 20,300 21,500
31,000
31,400
29,400
31,395
Milligrams per litre
10
10
10
10
10
10
9.7
9.0 11 11
11
12
11
9.9
330
330
330
330
310
330
330
330 3 0 330
320
320
320
320
280
280
280
280
280
270
280
280 2P 290
270
280
280
280
6,400
6,400
6,900
6,000
6,800
6,100
6,900
6,900 6,800 6,200
6,500
6,500
6,500
6,600
170
170
190
170
200
180
170
170 180 160
170
180
180
200
170
170
240
240
220
230
210
250 190 180
210
210
190
230
12,000
11,000
12,000
11,000
12,000
12,000
12,000
12,000 11,000 12,000
12,000
11,000
11,000
12,000
.6
.02
0
.01
.03
.03
0
.02
.01 .02 .04
.11
-
-
.03
-
-
-
-
-
0
-
- .08 -
-
-
-
.07
42,000
1,975
2,000
2,000
119W
1,934
2,000
2,000 1,900 2,000
1,900
910
2,000
2,000
Micrograms per litre
10
0
10
20
0
0
0
0 10 10
0
0
10
(2.5)2
10
0
-
-
-
0
-
0
0 10 1
0
0
-
-
1,0
-
-
-
700
-
-
- - 300
-
400
-
-
20
-
-
-
10
-
-
- - 10
-
10
-
(<.2)2
-
1
-
-
-
0
-
-
- - 0
-
0
-
-
30
-
30
30
30
-
(.6)2
-
18,000
11,000
8,300
3,900
3,400
4,200
1,400
3,600 1,300 880
910
1,200
-
(.2)2
-
1
0
0
0
0
0
2
2 1 0
3
0
2,800
(6,500)2
5,400
650
-
-
-
280
-
-
- - 300
-
250
3
(1.0)2
0
0
-
-
-
0
-
-
- - 0
-
0
-
(620)2
-
1
-
-
-
1
-
-
- - 1
-
1
-
-
5
-
-
-
0
-
-
- - 0
-
1
-
(<1.2)2
-
0
-
-
-
4
-
-
- - 0
-
4
-
(<.5)2
-
18,000
119W
18,600
19,000
-
-
60
30
40
100
90
20
70
20 30 20
30
40
-
-
-
-
-
-
-
- - -
-
-
60
(5.7)2
80

50
SUBSURFACE ORGANIC WASTE INJECTION, NORTH CAROLINA
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xx

BASIC -DATA TABLES
51
TABLE 31. Inorganic analyses ofground water from well 16, 843-983
feet below land surface
[Values in parentheses are from analysis by E. A. Jenne]
Collection date
5-18-72
6-20-72
6-14-73
10-31-73
ppH
7.7
7.2
-
-
Specific conductance
31,000
31,800
31,600
32,118
(µmhos at 25°C)
Milligrams per litre
Silica (SiO2) _-__--_ _--_..--__----..--
9.8
10
9.7
9.8
Calcium (Ca) ------ ------
330
369
340
350
Magnesium (Mg) ............................
323
311
300
310
Sodium (Na)------------------------------------
7,350
6,750
6,600
7,000
Potassium (K)................................
175
175
190
220
Bicarbonate WOO ----------------------
228
220
Sulfate(SO4)....................................
615
255
240
280
Chloride(Cl) ------------------------------------
12,200
12,200
12,000
13,000
Fluoride (F)-- -- - ------ - - ---- -
----- .6
.6
.6
.3
Nitrite -nitrate (NO2-NO3)------------
.07
.00
-
.01
Orthophosphate(PO4)
.000
.000
-
.11
Residue on evaporation
21,300
21,000
-
-
at 180°C.
Hardness as CaCO3
2,150
2,200
2,100
2,200
(Ca, Mg)
Micrograms per litre
Aluminum (Al)
1,000
1,120
10
0
Arsenic (As) - ---------. -- ....... --
--- -
-
3
-
Barium (Be)
-
-
300
-
Cadmium (Cd)
-
-
70
(<.1)
-
Chromium (Cr), total ..-----------....
-
-
10
-
Cobalt (Co)
-
-
280
(.6)
-
Copper(Cu)......................................
-
-
30
(14)
-
Iron (Fe), total ---------
0
0
2,400
(5800)
2,600
Lead (Pb)
-
-
2
(<3.5)
0
Manganese (Mn) - ----------------.---
-
-
480
(390)
-
Memury (Hg), total --- ------- - ---------
-
-
13
-
Molyybdenum (Mo)
-
-
4
(<1.2)
-
Nicltel (Ni)-..................................
-
-
300
(<.5)
-
Selenium (Se) - ------
-
-
11
-
Strontium (Sr)
-
-
24,000
Zinc (Zn)-----------------------------------
-
-
0
(80)
40
TABLE 32. Inorganic analyses ofground water from wells 2, 3, 4,
Well No.
2
3
4
5
Zone (feet below land surface) ........
855-1025
660-690
854-1025
854-1025
Collection date ------------ __-__-------_--_-
6-15-71
6-15-71
6-16-71
6-15-71
pH............................................ -----------
3.9
4.3
4.0
4.0
Specific conductance
6,560
11,000
8,280
8,080
(µmhos at 25°C).
Milligrams per litre
Silica (SiO2) .._ ---- -_-- ------------- ---------
41
34
23
34
Calcium (Ca) .
1,760
3,186
2,525
2,364
Maaggnnesium(Mg)................................
24
85
34
49
Sodium (Na) ....----- ----- ------ ----- ----- - ----
12
198
2.9
3.2
Potassium(K)-----------------------------
4.1
56
2.2
2.3
Bicarbonate (HCO3) .-- -------------
0
0
-
-
Sulfate(SO4)........................................
9.6
35
8.0
19
Chloride(CI)----------------------------------------
64
-
230
144
Fluoride (F)--------_----- --_- -------------- ------
3.2
1.1
1.3
1.3
Nitrite -nitrate (NO2-NO2)----------- --
- 3.9
5.6
3.9
3.9
Orthophosphate (PO4) .
1.5
4.2
1.3
1.1
Residue on evaporation at
6,800
1,330
9,590
9,160
180°C.
Hardness as CaCO3 (Co. Mg) ._-------
4,500
8,300
6,440
6,100
Micrograms per litre
Aluminum (Al),total _--------------- --_-
6,900
3,250
6,800
7,100
Copper (Cu)-------- ---------------------- _..-------
50
900
167
110
Iron (Fe), total _----------------------------
8,780
31,000
8,280
8,000
Manganese (Mn) -----------_----------------
450
3,600
280
285
Zinc(Zn).........................._..._.........._.
167
5,900
136
125
TABLE 34. -Organic analyses ofground water from well 11
[ND, not detectedl
Date
1-15-73
1-26.73
2-9-73
2-23-73 3-16-73 3-30-73 4-13-73
5-10-73
6-16-73
7-3-73
7-20-73
Milligrams per litre
Acetic acid ..
13.85
4.37
9.65
18.52 20.97 22.45 24.07
26.32
29.42
41.52
24.24
Formic acid ------------ -------_------------------
ND
ND
ND
ND ND ND ND
ND
ND
ND
ND
p Toluic acid .......................................
......................................
ND
ND
ND
ND ND ND ND
ND
ND
ND
ND
Terephthalic acid
.301
.306
.19 .269 .49 .422
.538
.578
.488
.573
TABLE 35.-Organic
analyses ofground water from well 14
[ND, not detected]
Date
8-1-72
8.7-72
8-14-72
8-28-72 9-4-72 9-11-72
9-19-72
10-11-72
10-31-72
11-2-72
Milligrams per litre
Acetic acid.....- -
19.67
55.38
71.98
101.35 85.94 138.6
59.61
474.70
758.85
60.23
Formic acid ..........................................
ND
ND
ND
.16 .60 1.42
1.38
1.10
1.27
ND
peoluicacid.......--.____._-_.._._------
.462
1.78
1.528
1.688 1,508 1.449
.949
6.648
16.69
.856
Terephthalic acid ..............................
.227
.856
.754
.930 .790 .332
.182
3.327
7.45
.398
Date
11-7-72
11-13-72
11-22-72
11-30-72 12-5-72 12-13.72
12-19-72
12-29-72
1-15-73
2-9-73
Milligrams per litre
Acetic acid ...........................................
63.81
84.07
20.00
4.90 11.66 21.07
-
5.71
-
ND
Formic acid ------------------------------------------
3.08
.657
ND
ND .95 ND
-
ND
-
ND
j�eToluic acid.
1.258
1.386
.468
.131 .301 .493
.161
.151
.1
-
rephthalic acid ------------------------------
.617
.723
.200
.062 .187 .157
.051
.042
.044
TABLE 36. Organic analyses ofground water from well 15
[ND, not detectedl
Date
8-3-72 8-7-72 8-14-72 10-31-72 12-5-72
Milligrams per litre
Acetic acid ......................................
9.20 4.13 5.09 ND
ND
Formic
acid.
ND ND ND ND
ND
qToluacid
icerephthalic
.25 .242 .245 ND
ND
DO C ................................................
acid
.15 .064 .059 ND
5.5 5.0 5.5 3.0
ND
1.5
* U.S. GOVERNMENT PRINTING OFFICE 1976-777-034/20