RA-2352_15092_CA_CAP_19990127

CORRECTIVE ACTION PLAN
In Accordance with .0106 (c)

C.W. CHAMBERS, JR. STORE
7130 BURLINGTON RD. (NC HWY. 49)
HURDLE MILLS, NORTH CAROLINA

NCDWM - UST GROUNDWATER INCIDENT No.: 15092
Risk Classification: High
Reason for Risk Classification: One impacted potable well and
numerous additional potable wells within 1,000' of the release area
Land Use: Residential
Latitude: 36° 18' 4" N Longitude: 79° 4' 19" W

Release Information
Date Discovered: 9/13-14/94
Estimated Release Quantity: Unknown
Release Cause/Source: Underground Storage Tank System
UST Capacities: two 10,000; two 2,000 gallon gasoline

Responsible Party: Property Owner:

C.W. Chambers, Jr. C.W. Chambers, Sr.
7802 Burlington Rd. 7130 Burlington Road
Hurdle Mills, North Carolina 27541 Hurdle Mills, North Carolina
27541

January 1999
TEC Project No. 02794

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TABLE OF CONTENTS

1.0 INTRODUCTION ........................................................................................................ 1

2.0 SUMMARY OF SITE ASSESSMENT RESULTS ....................................................... 7
2.1 Geology and Aquifer Characteristics ..................................................................... 7
2.1.1 Topography and Stratigraphy .......................................................................... 7
2.1.2 Subsurface Hydrology ...................................................................................... 9
2.1.3 Aquifer Characteristics ................................................................................... 12
2.2 Assessment of LNAPL ........................................................................................ 13
2.3 Soil Analyses and Impacts .................................................................................. 13
2.4 Groundwater Analyses ........................................................................................ 14

3.0 INITIAL ABATEMENT MEASURES ......................................................................... 16
3.1 UST Closure ........................................................................................................ 16

4.0 EXPOSURE ASSESSMENT AND CAP OBJECTIVES ............................................ 17
4.1 Physical and Chemical Characteristics of Contaminants .................................... 17
4.2 Regional Land Use .............................................................................................. 17
4.3 Site and Regional Water Supply ......................................................................... 18
4.3.1 Private Water Wells ....................................................................................... 18
4.4 Potential Human Exposure Pathways ................................................................. 18
4.5 Potential Effects of Residual Contamination ....................................................... 19
4.6 Goals and Target Cleanup Concentrations ......................................................... 19

5.0 REMEDIATION ALTERNATIVES ............................................................................. 21
5.1 Available Remediation Options ........................................................................... 21
5.2 Evaluation of Remediation Alternatives ............................................................... 22
5.2.1 Groundwater .................................................................................................. 22
5.2.2 Contaminated Soil.......................................................................................... 23
5.2.3 Discharge of Treated Groundwater ................................................................ 24

6.0 PROPOSED CORRECTIVE ACTION ...................................................................... 27
6.1 Overview ............................................................................................................. 27
6.2 Checklist of Regulatory Requirements ................................................................ 29
6.3 Groundwater Recovery ....................................................................................... 29
6.4 Soil Excavation .................................................................................................... 33
6.5 Air Sparging System ........................................................................................... 34
6.6 Treatment System Appurtenances ...................................................................... 35
6.6.1 Concrete Pad ................................................................................................. 35
6.6.2 Equipment Compound ................................................................................... 35
6.6.3 Trenching and Conduits ................................................................................. 36
6.7 System Controls and Safety Functions ............................................................... 36
6.7.1 Groundwater Recovery System Functions ..................................................... 36
6.7.2 Main System Control Panel ........................................................................... 37

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6.8 Proposed Implementation Schedule ................................................................... 38
6.9 Proposed Maintenance Program ......................................................................... 39
6.9.1 System Inspections ........................................................................................ 39
6.9.2 Preventative Maintenance ............................................................................. 40
6.10 Proposed Monitoring Program ....................................................................... 40
6.10.1 Monitoring Well Network ............................................................................. 40
6.10.2 Monitoring Schedule and Parameters ......................................................... 41
6.10.2.1 Groundwater Monitoring ...................................................................... 41
6.10.2.2 Remediation System and Discharge Monitoring ................................. 42
6.11 Termination of Remedial Actions ................................................................... 42

7.0 PERMITS AND NOTIFICATIONS REQUIRED ......................................................... 43

8.0 LIMITATIONS ........................................................................................................... 44

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REFERENCES

FIGURES:

1: Site Location Map
2: Potable Well Location Map
3: Site Vicinity Map
4: Site Layout and Monitoring Well Network
5: Geologic Cross-Sections
6: Potentiometric Surface Map (8/5/98)
7: Extent of Soil Contamination
9: Remediation System Layout
10: Groundwater Remediation System Schematic
11: Recovery Well Detail
12: Typical Trench Cross-Section
13: Estimated Extent of Soil Excavation

TABLES:

1: Former UST Information
2: Groundwater Elevation Data (8/5/98)
3: Groundwater Analytical Summary (8/6/98)
4: Physical and Chemical Properties of Selected Compounds
5: Groundwater Parameter Data (8/6/98)
6: Property Owners within 1,000 Feet of the Release Area
7: Summary of Exposure Pathways
8: Remedial Alternatives for Groundwater
9: Remedial Alternatives for Soil
TABLE OF CONTENTS (Cont’d)

APPENDICES:

A: Downgradient Property Owner Letters
B: Boring Logs and Monitoring Well Installation Details and Construction Records
C: Complete Groundwater Elevation and Analytical History
D: Aquifer Pumping Test Results
E: SVE Pilot Test Report
F: Recovery Well Capture Zone Modeling
G: Notification Letters
H: Permits Required

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1.0 INTRODUCTION

This Corrective Action Plan (CAP) has been prepared by Turner Environmental
Consultants, P.C. (TEC), on behalf of the responsible party, Mr. C.W. Chambers, Jr.
(Chambers), in response to a non-permitted release of petroleum products into the soil
and groundwater from a former UST system located at the C.W. Chambers Jr. Store in
Hurdle Mills, NC (Figure 1). The source of the release is the former underground
storage tank (UST) system consisting of four excavated USTs, ranging in size from
2,000 to 10,000 gallons, and the associated product lines and dispensers. The UST
system was closed in October 1994. Currently, the site does not sell petroleum
products. On March 21, 1996, the North Carolina Division of Water Quality (NCDWQ)
issued a Notice of Regulatory Response (NORR) to Chambers instructing him to
conduct a complete assessment and submit a CAP.

In July 1998, the UST portion of the NCDWQ was reorganized under the authority of the
North Carolina Division of Waste Management - UST Section (NCDWM - UST).
NCDWM - UST is used to identify this group throughout the remainder of this report.

This CAP was prepared under Title 15A NCAC 2L .0106 (c) regulations. This law
requires soil and groundwater contamination be actively cleaned up to the standards set
by the NCDWM - UST and Title 15A NCAC 2L Standards .0202(g) Groundwater Quality
Standards (referred to as the “2L Standards” hereafter), respectively. During the
development of the CAP, all of the corrective action methods, (c), (k), and (l), were
considered. The (k) and (l) options were eliminated based upon stipulations in Title
15A NCAC 2L .0106 (k) and (l), which specifies that surrounding properties must have
an available water supply which is independent of the shallow groundwater and the
surrounding property owner’s consent to Chambers’ request for a cleanup under the (k)
and (l) regulations. Neither of these conditions exist. All of the surrounding
properties’ sole potable water source are water wells, and the downgradient property
owners have denied Chamber’s “k” and “l” CAP requests. Copies of those letters are

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included in Appendix A. Figure 2 and 3 depict potable well locations within the site
vicinity.

Since the facility was classified an “A/B” class site and the Comprehensive Site
Assessment (CSA) was submitted to the NCDWM - UST prior to January 2, 1998, the
soil contamination at the site will be remediated to action limits set forth in the March
1997 NCDWM - UST Groundwater Section Guidelines of 10 parts per million (ppm) or
milligrams per kilogram (mg/kg) for low boiling point petroleum products (e.g. gasoline).

Previous investigations have documented the presence of petroleum constituents in the
soil and groundwater at the C.W. Chamber Jr. Store. In October 1994, TEC completed
an Underground Storage Tank (UST) Closure and Site Check Report documenting the
closure by excavation of four USTs and the release of petroleum into the subsurface.
Five (5) USTs were formerly operated at the facility. On September 13 and 14, 1994,
T1 - T4 were removed by C.W. Chambers Jr. In the Fall of 1996, tank T5 was removed
by the tank owner Foust Oil Company. The gasoline UST basins were backfilled with
local fill material. Pertinent information regarding the USTs is given in Table 1. In
addition, an aboveground storage tank (AST) containing heating oil is located behind
the retail store. Figure 4 illustrates the locations of all known on-site petroleum
hydrocarbon sources. The UST Closure Report was submitted to the NCDWM - UST
in October 1994. An Initial Site Characterization Report was completed in July 1996
and submitted to the NCDWM - UST.

Results from the closure and initial characterization activities indicated that a release of
petroleum products occurred from the former UST system. Confirmation soil samples
taken during the closure revealed total petroleum hydrocarbons (TPH) as gasoline at
concentrations up to 8,343 ppm. Analytical results from soil samples taken during the
construction of monitoring wells MW1 and MW2 were disregarded since they were
taken from below the water table. Analysis of groundwater samples collected from the
three monitoring wells installed during the initial site characterization revealed dissolved

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petroleum concentrations in two of the monitoring wells. In addition, four (4)
surrounding potable wells were sampled for dissolved hydrocarbons. Potable wells
PW-1 - PW-3 revealed no detectable petroleum concentrations. Potable well PW-4
contained a methyl tert butyl ether (MTBE) concentration of 5 parts per billion (ppb).

During the completion of the Comprehensive Site Assessment (CSA) Report, the extent
of soil and groundwater contamination at the facility as well as the hydrological
characteristics of the subsurface phreatic aquifer were delineated. The zone of soil
contamination was determined to be concentrated in the vicinity of the former UST
basins and pump island. The extent of groundwater contamination as well as the
direction of groundwater flow was determined from the monitoring well network installed
during this phase of assessment. In three of these monitoring wells, slug tests were
performed to determine hydraulic conductivity and groundwater velocity of the
subsurface phreatic aquifer. The UST Closure and Site Check, Initial Site
Characterization, and CSA reports are on file with the Raleigh Regional Office of the
NCDWM- UST.

Previous permits issued to Chambers for this facility consist of monitoring well
installation permits. Permit numbers are indicated on well construction records on file
with the NCDWM - UST. Boring logs and well construction records for wells installed
during the CAP are included in Appendix B.

Key assessment activities, corrective actions, correspondence, and report submittals to
date include the following items, which are listed in chronological order:

¾ August 22, 1994 - Chambers notifies the NCDWM - UST Section Raleigh
Regional Office (RRO) of his intent to close the UST system at the C.W.
Chambers, Jr. Store.

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¾ September 13 - 14, 1994 - Chambers closed the UST system at the site. The
UST system consisted of two 5,000 gallon and two 2,000 gallon gasoline USTs.
Approximately 80 - 100 yd3 of petroleum contaminated soil was excavated and
stockpile on an adjacent property owned by C.W. Chambers, Sr. On behalf of
Chambers, TEC reports the release to the NCDWM - UST RRO.

¾ October 1994 - TEC submitted the Underground Storage Tank Closure and Site
Check Report to the NCDWM - UST RRO.

¾ March 21, 1996 - The NCDWM - UST RRO issued a NORR to Chambers
directing them to comply with the release response and corrective action
requirements of Title 15A NCAC 2N and 2L.

¾ June 18, 1996 - TEC requests and receives a 90-day extension of the June
21,1996 CSA deadline on behalf of Chambers. The new CSA due date is
September 21, 1996.

¾ June 19, 1996 - TEC supervised the installation of three monitoring wells (MW1 -
MW3) within and upgradient of the former UST system to monitor groundwater
quality and determine groundwater flow direction.

¾ July 22, 1996 - TEC submitted the Initial Site Characterization Report. The
report summarized initial abatement measures and presented the results of the
site check in accordance with rules under Title 15A NCAC 2N .0702, .0703, and
.0705.

¾ September 20 ,1996 - TEC requests and receives a 120-day extension of the
September 21, 1996 CSA deadline on behalf of Chambers. The new CSA due
date is January 19, 1997.

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¾ Fall, 1996 - Foust Oil Company of Mebane, NC removes a 1,000-gallon kerosene
UST located on site. They are the registered owners of the UST according to
the North Carolina UST database. The date and results of the closure are
unknown. A UST Closure Report has not been located in the files of the
NCDWM - UST RRO.

¾ November 12, 1996 - TEC personnel installed four temporary groundwater
monitoring wells in the vicinity of monitoring well MW2 to test for the presence of
free product. Free product was suspected due to the high contaminant
concentrations revealed in the analytical results. No free product was detected.

¾ December 9, 1996 - TEC gains access to the James and Lynwood Chambers’
properties downgradient of the site where monitoring wells are needed to define
the extent of groundwater impact resulting from the release.

¾ December 31, 1996 - The NCDWM - UST RRO issues Chambers Well
Construction Permit No. WM0500349.

¾ January 28, 1997 - TEC requests and receives a 120-day extension of the
January 19, 1997 CSA deadline on behalf of Chambers. The new CSA due date
is April 10, 1997. The letter cited the holidays, driller scheduling, and
client/consultant contract difficulties as reasons for the delay.

¾ January 27 - 28, 1997 - TEC supervised the installation of six (6) Type II
groundwater monitoring wells (MW4 - MW9). These wells were installed to
delineate groundwater impact for the development of a CSA.

¾ February 3, 1997 - TEC collects twenty-eight (28) soil samples to delineate the
extent of vadose zone impact for the development of a CSA.

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¾ March 3 - 4, 1997 - TEC supervised the installation of one (1) Type II
groundwater monitoring well (MW11) and one Type III monitoring well (MW10).
These wells were installed to complete the delineation of the horizontal and
vertical extent of groundwater impact for the development of a CSA. TEC also
supervises the abandonment of three potable wells located across Highway 49
from the C.W. Chambers, Jr. store as per the request of the NCDWM - UST
RRO.

¾ April 1, 1997 - TEC requests and receives a 30-day extension of the April 10,
1997 CSA deadline on behalf of Chambers. The new CSA due date is May 10,
1997.

¾ May 9, 1997 - TEC submits the CSA to the NCDWM - UST RRO. The CSA
Report detailed the horizontal and vertical extent of petroleum impact in both the
vadose zone and shallow aquifer. The report discussed in detail the
hydrogeology of the site.

¾ June 16, 1997 - TEC personnel install several soil vapor extraction (SVE)
piezometers for the forthcoming SVE test.

¾ June 18, 1997 - TEC supervises the installation of two piezometers (RW-1 and
PZ-1) necessary for monitoring water levels during the forthcoming groundwater
pumping test.

¾ July 17, 1997 - TEC performs a SVE test to determine critical vadose zone
parameters necessary for the design of a SVE system.

¾ July 29 - 31, 1997 - TEC performs the step-drawdown and 24-hour groundwater
aquifer tests. The groundwater pumping test was necessary to determine

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critical aquifer parameters for the design of a groundwater pump and treat
system.

¾ August 28, 1997 - Chambers receives notice from property owners located
adjacent to the site denying Chambers’ request for corrective action of the
contaminated groundwater under Title 15A NCAC 2L .0106 (k) or (l). Chamber
must therefore perform corrective action under Title 15A NCAC 2L .0106 (c),
which specifies remediation of contaminated groundwaters to the Title 15A
NCAC 2L .0202 (g) Groundwater Quality Standards.

¾ December 9, 1997 - Chambers receives pre-approval for tasks associated with
the development of a CAP.

¾ April 22, 1998 and August 5, 1998 - Pre-CAP groundwater sampling events are
conducted to monitor the extents of the contaminant plume and to assist in CAP
development.

¾ October 29, 1998 - James Chambers denies access to his property, located in
the interpreted downgradient direction, to install a recovery well for the proposed
remediation system. TEC must redesign the recovery well layout and reevaluate
the treated water discharge options.

2.0 SUMMARY OF SITE ASSESSMENT RESULTS

This section summarizes the key elements of the site assessment. The reader is
referred to previous reports mentioned in Section 1.0 for additional assessment
information.

2.1 Geology and Aquifer Characteristics

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2.1.1 Topography and Stratigraphy

The site is located in the Piedmont Physiographic Province of North Carolina. The
Piedmont is characterized by a landscape of low to moderately high hills. The primary
topographic features in the site vicinity are gently sloping hills and numerous unnamed
ponds. Topographic elevations in the vicinity range from approximately 570 feet above
mean sea level (MSL) along a tributary of the South Flat River to 690 feet MSL at the
C.W. Chambers, Jr. facility. Regionally, drainages are primarily oriented to the
north/northwest and the southeast, since the site is located along a hydrologic divide.
North of site, surface water drains towards Hyco Lake. Surface water at the front
portion of the property, where the contaminant plume is located, flows to the south
towards the South Flat River. There are numerous ponds that lie within 1,500 feet of
the site. Hyco Lake is approximately 5 miles north of the site and, the South Flat River
is approximately 1.5 miles southeast of the site. Figure 1 illustrates topographic
features for the area.

The site location lies within the Carolina Slate Belt (CSB) geological province of
north-central North Carolina (Brown, et al, 1985). The CSB is usually described as a
sequence of volcanic and sedimentary rocks metamorphosed to lower greenschist
grade. Major rock units in the site vicinity given on the Geologic Map of North
Carolina are metamorphosed gabbro and diorite, metamorphosed granite, and
metamorphosed basaltic flows and tuffs. During the course of the assessment bedrock
was not encountered during the drilling nor were any outcrops of native rock observed
at the site or in the vicinity. However, the regolith or soil overlying the bedrock was
probed and analyzed by TEC field personnel. In order to characterize the
unconsolidated sediments better, a soil sample was collected for a grain-size analysis.
Results of this test indicate that the shallow aquifer materials in the vicinity of monitoring
well MW1 are characterized as a tan, fine sandy clayey silt. The remaining subsurface
geology of the site and immediate vicinity collected by split-spoon sampling and hand
auger soil borings essentially concurs with this classification. This lithology is thought

9
to extend from the surface to approximately 65 feet below ground level (BGL). With
increasing depth, the sand becomes medium to course grained. Vertical lithology is
discussed further in the next section.

Generalized subsurface lithologies are shown in the geologic cross-sections (Figure 5).
The geologic cross-sections are based on soil boring logs constructed during monitoring
well installation. A majority of the soil boring logs completed for the site are contained
in the CSA Report on file with the NCDWM - UST RRO.

2.1.2 Subsurface Hydrology

The Piedmont Physiographic Province is comprised of a thick sequence of silts, sands,
and clays. These unconsolidated sediments separate the shallow surficial or
unconfined aquifer from a deeper confined or bedrock aquifer. Contained within the
unconsolidated sediments is the surficial aquifer. In areas of thick silt and sand
accumulations, the water table aquifer may be used for drinking water supplies;
however, water quality and well yields are usually lower than in deeper aquifers.

Potable wells in the area are drilled into the deeper portions of the unconsolidated
sediments or the bedrock aquifer because water quality and well yields are usually
much higher within these aquifers. As discussed in the previous section, bedrock
within the site vicinity is mapped as metamorphosed gabbro and diorite,
metamorphosed granite, and metamorphosed basaltic flows and tuffs. Although the
bedrock aquifer has a much lower storage coefficient than an unconfined aquifer, larger
volumes of water can often be derived from them due to the expansion of the water and
compression of the aquifer during groundwater withdrawals.

Lithologic information gathered during the monitoring well and soil boring assessment
was used to construct two geologic cross-sections (Figure 5). Due to the
heterogeneous nature of the subsurface, lithologic generalizations were made in the

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construction of the two geologic cross-sections. Several soil borings were also plotted
on the cross-section in order to illustrate soil sample locations and the location of
impacted soil in relation to the potentiometric surface.

Analysis of the historical groundwater elevations reveals a highly variable potentiometric
surface. On March 17, 1997 , the average depth to water was 4.16 feet.
Depth-to-water measurements collected on August 5, 1998 averaged 11.3 feet. These
measurements took into account the fact that two of the monitoring wells were void of
any measurable amount of water. In both instances, the depth of the monitoring well
was entered as the depth-to-water value. The change in water depths is probably due
to the time of year the measurements were collected, wet season versus dry. The
scale of this variance is depicted in Figure 5.

Local hydrogeology is characterized by two aquifers. The first is the unconfined or
water table aquifer which exists in the sandy-clayey silt. This upper aquifer is open to
the atmosphere and is thus affected by changes in precipitation. The water table
aquifer is predominantly composed of lean clays and silts with varying amounts of
sand. Though not encountered, bedrock underlies the water table aquifer at a greater
depth constituting the second aquifer. According to the Geologic map of North
Carolina, the lithology is comprised of metamorphosed gabbro and diorite,
metamorphosed granite, and metamorphosed basaltic flows and tuffs. According to
Mr. Chambers, Sr., the estimated depth to bedrock at potable well PW-2 is
approximately 120 feet. Downgradient of the site, TEC estimated that depth to be 80 -
90 feet.

Fluid flow is driven by gravity. As with all fluid substances, water tends to flow from
areas of greater potential to ones of less potential. The fluid flow in the different
aquifers varies. Near the surface, the flow is interstitial and will move in the direction of
the steepest gradient (perpendicular to equipotential lines). As noted from a
topographic map, the site is located along a topographic high or hydrologic divide which

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indicates that the gradients are sloping away from the site to the north/northwest and
southeast.

Within the bedrock aquifer and the transitional sediments immediately overlying it, water
flows both interstitially and along relict structures such as fractures, faults, bedding
planes, and lithologic contacts. At depth, the bedrock may be completely consolidated
thus terminating interstitial flow. Flow within weathered and competent bedrock does
not strictly conform to flowing perpendicular to equipotential lines. Flow within these
lithologies will be in the direction of lesser potential, namely along structures.

All groundwater in both aquifers will flow until it reaches a discharge point. There are
many potential discharge points in the vicinity of the site such as ponds and streams.
Potable wells could even be discharge points for groundwater in the site vicinity.

The depth to the water table has historically been in the range of 2 - 6.5 feet BGL.
Table 2 summarizes recent water level measurements for the site collected from the
monitoring well network installed at the site. The monitoring well network is depicted in
Figure 4. A potentiometric surface map depicting the water table elevations on August
5, 1998 is depicted in Figure 6. Historical potentiometric surface maps reveal that the
primary groundwater flow direction (as interpreted from potentiometric surface maps) is
toward the south - southeast. Average hydraulic gradients recorded during the
development of the CSA and Pre-CAP monitoring events ranged from approximately
0.001 to 0.022. This variability can be attributed to the fluctuating water level
elevations recorded over the course of the assessment. A groundwater elevation
history for the monitoring wells is included in Appendix C.

Water level data from the Type III monitoring well (MW10) and an interpolated water
level value for the shallow aquifer in the vicinity of monitoring well MW10 were used to
determine if a vertical head gradient exists in the water table aquifer. The calculation
used to determine the gradient is presented in the CSA.

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Measurements collected on August 5, 1998 reveal that a downward head gradient of
0.003 exists between monitoring well MW10 and the shallow aquifer in its vicinity.
Positive head gradients, are indicative of downward flow trends commonly found in
recharge settings. In typical aquifer settings in which the area of interest lies in close
proximity to points of groundwater recharge, such as a hydrologic divide, groundwater
normally follows a downward flow path. As one moves away from the recharge area,
groundwater flow lines become less steep and begin to flatten out. On the distant end
of the flow regime, groundwater flow paths would turn upward near groundwater
discharge areas. Given the very small vertical head gradient and the proximity to a
point of groundwater discharge, the site may lie in the central recharge portion of the
groundwater flow regime where groundwater flow lines flatten out. Further to the south
- southwest, the groundwater flow lines may turn upward and discharge into the South
Flat River. The charge in vertical gradients since the CSA (-0.0058 was determined
during the CSA) can be attributed to the variability of the depth-to-groundwater and the
fact that the depth at which monitoring well MW10 is set probably does not constitute a
different aquifer.

2.1.3 Aquifer Characteristics

In order to provide preliminary estimates for hydraulic conductivity (K) and groundwater
flow velocity (v) for the water table aquifer, slug tests were performed on monitoring
wells MW1, MW2, and MW8. The preliminary hydraulic conductivity estimates range
from 7.70 x 10-6 m/s in monitoring well MW2 to 1.77 x 10-6 m/s in monitoring well MW8.
These values for hydraulic conductivity fall within the range expected from a sandy
clayey silt. These results correspond with field observations made during the
installation of the monitoring wells and soil borings at the facility.

Using an average hydraulic conductivity value, an average groundwater flow velocity
value was determined to be 9.55x10-8 m/s. An effective porosity of 0.18 was used for

13
calculating the groundwater flow velocity (Heath, 1982). A complete explanation of the
slug test procedures, data obtained, and data reduction is included in the CSA Report.

TEC also performed a 24-hour aquifer pumping test in an aquifer test piezometer
(RW1). Test results were reduced using AQTESOLV aquifer test analysis software.
Appendix D contains the test results and software outputs. Based on the analysis, the
derived aquifer parameters are as follows:

Average Horizontal Conductivity: 1.29 x10-6 meters per second (m/s)
Average Vertical Conductivity: 1.13x10-6 m/s

These values are indicative of a silt and silty sand (Freeze and Cherry, 1979) and are
consistent with previous aquifer test data and lithologies observed during the installation
of monitoring wells and soil borings.

2.2 Assessment of LNAPL

No light-non-aqueous-phase liquid (LNAPL) in the form of gasoline or kerosene has
been detected in any of the monitoring wells or piezometers installed at the site.

2.3 Soil Analyses and Impacts

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Twenty-eight (28) soil borings B1 - B28 were advanced at the site to determine the
horizontal extent of vadose zone impact around the UST basins, product lines, and
pump island. All soil samples were collected using a stainless steel hand auger. The
soil samples were collected at varying depths and screened for petroleum organic
vapors. Soil samples exhibiting the highest volatile organic compound (VOC)
concentration were submitted to a North-Carolina certified laboratory for analysis.
These samples were used to define the total extent of soil impact at the site. Soil
borings B1(4') and B2(4') were analyzed for total petroleum hydrocarbons (TPH) by
EPA Method 5030 and 3550 which target low boiling point (gasoline) and high boiling
point (kerosene) fuels, respectively. These soil samples were analyzed for both
parameters due to their proximity to the former kerosene UST. The remaining soil
samples, B3 - B28 were analyzed per EPA Method 5030 only. Soil boring locations
and analytical data are depicted in Figure 7. A more complete discussion of the soil
survey is presented in the CSA Report. Contamination is defined by soils containing
greater than 10 ppm TPH (EPA Method 5030) and 40 ppm TPH (EPA Method 3550).

Laboratory results from soil samples collected at the site revealed the presence of
petroleum hydrocarbons. Since the CSA was submitted prior to January 2, 1998, the
March 1997 NCDWQ guidelines are applicable. Soil samples analyzed for 5030
revealed TPH concentrations in the soil ranging from 6.60 ppm in B10 (3') to 1,010 ppm
in B18 (3'). Soil samples collected for 3550 did not reveal any detectable
concentrations.

2.4 Groundwater Analyses

Table 3 summarizes the most recent groundwater analytical results from a pre-CAP
monitoring event conducted on August 6, 1998. The contaminant concentrations for
certain compounds above the 2L Standards and the approximate extent of the plume
are depicted in Figure 8. Physical and chemical properties of selected compounds are

15
listed in Table 4. A complete analytical history for each monitoring well at the site is
included in Appendix C.

During the completion of the CAP, groundwater monitoring events were conducted to
establish a contaminant concentration baseline and to monitor plume movement.
These pre-CAP groundwater monitoring events were conducted on April 22, 1998 and
August 6, 1998. Groundwater samples collected during the April 22, 1998 and August
6, 1998 events were analyzed for petroleum constituents by EPA Methods 6230D +
MTBE + IPE and EPA Methods 6210D + MTBE + IPE, 504.1 EDB (initial sampling only)
and for lead with a Method 3030c digestion, respectively. The analytical reports for
the above referenced sampling events are included in the first and second Pre-CAP
Monitoring Reports on file with the NCDWM - UST RRO. Analytical reports for all of
the groundwater monitoring events prior to April 22, 1998 are included in the CSA.

Analytical results from both sampling events revealed dissolved petroleum constituent
concentrations above groundwater quality standards in three monitoring wells - MW1,
MW2, and MW4. The primary contaminants detected were benzene, toluene,
ethylbenzene, and xylenes (BTEX), methyl tert butyl ether (MTBE), isopropyl ether
(IPE), 1,2-dibromomethane (EDB), 1,2-dichloroethane, naphthalene, n-propylbenzene,
1,2,4-trimethylbenzene, and 1,3,5-trimethylbenzene. The most recent sampling event
also revealed 2L Standard violations in monitoring wells MW6 - MW9. These violations
may indicate a plume movement or a seasonal groundwater quality fluctuation. Table 3
lists the analytical results from the August 6, 1998 sampling event. Groundwater
parameter data (dissolved oxygen, pH, conductivity, and temperature) were also
collected as part of the routine monitoring effort. The groundwater parameter results
are summarized in Table 5.
The current monitoring well network has defined the horizontal extent and geometry of
the contaminant plume. The detected concentrations of the BTEX constituents confirm
that the core of the contaminant plume remains centered at the release area. The
recent presence of contaminants in monitoring wells located lateral and downgradient of

16
the core of the plume may suggest contaminant migration. These results may also
indicate a seasonal variation in the plume geometry due in part to the fluctuating water
table elevations. The reason for the contaminants presence is unknown, and additional
data is required in order to provide a more definitive answer.

The continued presence of contaminants in the Type III monitoring well MW10 confirms
that the plume has a vertical extent of approximately 60' below ground level. The
vertical extent of 2L Standard violations is located between the depth of monitoring well
MW1 (27 feet) and the top of the screened interval of monitoring well MW10 (60 feet).
The estimated vertical extent of the 2L violations is estimated to be 40' BGL.
Lead concentrations exceeding the 2L Standards were detected in several monitoring
wells during the assessment phase. Lead concentrations ranged from 16 ppb in
monitoring well MW2 to 510 ppb in monitoring well MW4. Analytical results from the
most recent sampling event (August 1998) revealed that two samples, MW4 and MW8
(70 ppb and 290 ppb, respectively), contained a dissolved lead concentration in excess
of the 2L Standards. Lead concentrations are not considered valid at this site due to
the inherent problems with the sampling methodology. Specifically, acidification of
unfiltered samples in the field often leads to anomalous results which are due to the
digestion of metals contained on colloidal particles suspended in the water column.
Several observations also support the invalidity of the lead concentration data: 1)
Since metals are relatively immobile in groundwater, higher concentrations should be
detected at the source. Monitoring wells MW1and MW2 are located at the source,
while monitoring well MW4 is lateral to the source area and MW8 is located
downgradient; 2) Lead violations have been detected in monitoring wells that did not
contain any petroleum constituents and not detected in monitoring well within the
contaminant plume. Thus, the detection of lead does not directly correlate with the
plume geometry; 3) Lead can result from naturally occurring minerals which are
sometimes concentrated in Piedmont sediments. Based upon this information, the lead
results are not considered indicative of groundwater contamination.

17
3.0 INITIAL ABATEMENT MEASURES

3.1 UST Closure

The former UST system (primary source) was permanently closed by removal on
September 13 and 14, 1994. During the closure, approximately 80 - 100 yd3 of
petroleum contaminated soil (secondary source) was excavated and stockpiled on an
adjacent property. On June 16, 1996, TEC personnel collected a composite soil
sample from the stockpile following NCDWM - UST stockpiling sampling protocol. The
sample was analyzed for gasoline-type constituents by EPA Method TPH 5030.
Analytical results did not reveal any contaminant concentrations above the sample
detection limit of 2 ppm. Groundwater was not encountered during the tank closure.

TEC submitted an Underground Storage Tank Closure Report in October 1994. An
Initial Site Characterization Report was also submitted in July 1996. The reader is
referred to these documents for further information on the UST closure.

In addition, Foust Oil Company (Foust) of Mebane, NC removed a 1,000-gallon
kerosene UST in the fall of 1996. According to the North Carolina UST database,
Foust is the registered owner of the UST. The date of closure is unknown. The
location of the kerosene UST is depicted in Figure 4. It is unknown if any soil was
excavated by Foust during the closure.

4.0 EXPOSURE ASSESSMENT AND CAP OBJECTIVES

4.1 Physical and Chemical Characteristics of Contaminants

Physical and chemical properties of selected compounds are summarized in Table 4.

4.2 Regional Land Use

18

The site has one primary structure which provided retail space for the former gas
station. Land usage surrounding the site is agricultural and rural residential. The
nearest residences lie about 150 feet on either side of the site and across NC Hwy 49.
The nearest surface water body is a pond approximately 720 feet from the core of the
plume. Additional low lying areas and ponds are also located to the south of the site.
Figures 2 and 3 depicts land usage for the vicinity, names of surrounding property
owners, and their adjacent property locations. Table 6 lists the names and addresses
of owners of surrounding properties.
4.3 Site and Regional Water Supply

4.3.1 Private Water Wells

Water is currently supplied to the site from potable well (PW-2) located on the C.W.
Chambers Sr. property (Figure 3). Additional potable wells in the surrounding vicinity
include potable wells PW-1, PW-3, and PW-4. Potable well PW-1 at one time serviced
the site, but testing by the county health department revealed amounts of coliform
bacteria and service from the well was discontinued. Potable well PW-3 services the
Sharlow residence and the mobile home located behind the residence. The residences
across NC Hwy. 49 from the site were formerly serviced by potable well PW-4 prior to
the discovery of MTBE in that well. Currently, those residences are supplied water by
potable well PW-2. Potable well PW-5 is a backup for the C.W. Chambers, Sr.
residence. Potable wells PW-6 and PW-7 service an additional residence on the C.W.
Chambers, Sr. property and the Rogers residence respectively.

Three out-of-use potable wells, APW-1 - APW-3, were abandoned in compliance with
the NCDWM - UST RRO’s request. Each well was tremmied with grout from the
bottom to the surface. Figure 3 depicts the location of potable wells in the site vicinity.

4.4 Potential Human Exposure Pathways

19

Table 7 summarizes potential exposure pathways and the possibility of occurrence
associated with each pathway. The ratings are specific to the site and are assigned on
a subjective basis with consideration to site conditions.

4.5 Potential Effects of Residual Contamination

Residual soil contamination will continue to contribute to groundwater impact.
Petroleum hydrocarbons dissolved in groundwater will migrate by advective transport
and dispersion. These processes will extend the plume primarily in the downgradient
direction until the processes of retardation and biodegradation exceed advective and
dispersive forces. The most notable result of residual contamination would be the
impact to potable well PW-4, downgradient of the release source, or groundwater to be
used as a future potable water source.

4.6 Goals and Target Cleanup Concentrations

The goal of the corrective action is to alleviate potential threats to human health and
environmental quality which could arise from contamination at the site. To accomplish
this goal, the corrective action must meet the 15A NCAC 2L .0202 (g) Groundwater
Quality Standards. The 2L Standards are compulsory standards established by the
NCDWM - UST RRO.

As previously mentioned, prior to implementation of the corrective action, responsible
parties must evaluate the applicability of remediation under rules (k) and (l) prior to
proceeding with a cleanup. In order to proceed with a CAP under (k) or (l), parties
responsible for the cleanup must have the written consent of property owners of

20
adjacent properties on which the plume has migrated or is predicted to migrate, if those
properties are not served by a public water supply.

The downgradient property owners have denied Chambers’ request for clean up under
Rules (k) and (l) since they lack an onsite water supply which is independent of the
shallow groundwater. Therefore, corrective action will be performed under .0106 (c).

TEC did not conduct an evaluation of risk to the downgradient well or groundwater with
the aid of software, since the corrective action must be continued until the 2L Standards
are met and every attempt must be made for the plume not to migrate any further
offsite.

Site closure will occur once the 2LStandards are met or a petition for closure under
NCAC 2L .0106 (m) is submitted and approved once the asymptotic slope of the
decontamination of the contaminants has occurred. The following table is a list of the
2L Standards for certain targeted contaminants identified in monitoring wells within the
source area.

Target Cleanup Concentrations (TCCs)
C.W. Chambers, Jr. Store
Hurdle Mills, NC

ANALYTE
Maximum
Concentration Detected

TCCs
Benzene 53,600 1
Toluene 96,660 1,000
Ethylbenzene 4,630 29
Xylenes 24,400 580

MTBE 1,960 200
IPE 3,450 70
Styrene 220 100
1,2-Dibromoethane (EDB) 360 0.0004

21

1,2-Dichloroethane 474 0.38
Isopropylbezene 140 70
Naphthalene 1,760 21
n-Propylbenzene 443 70
1,2,4-Trimethylbenzene 2,100 350
1,3,5-Trimethylbenzene 480 350

p-Isopropyltoluene 76 SDL
Notes: 1. All results in parts per billion - ppb
2. SDL - Sample detection Limit
3. Analytical results are the highest concentrations
detected from the monitoring well MW1 and MW2
analytical results on various dates.

Using the analytical data to date, all of the above listed compounds have been detected
at concentrations which exceed the 2L Standards or Target Cleanup Concentrations
(TCCs). These compounds will be considered the indicator contaminants for the site.

The first criterion for determining site closure will be the reduction of concentrations in
the most contaminated groundwater to levels below the 2L Standards. The second
criterion will include the remediation of secondary sources of contamination such as
soil. A period of post-remediation monitoring will follow the groundwater cleanup
ensure that the established TCCs are met. Section 6.10 details the termination of
remedial actions.

5.0 REMEDIATION ALTERNATIVES

5.1 Available Remediation Options

Remediation activities address two primary objectives for petroleum contaminated sites:
groundwater remediation and soil remediation. Although the release source, the
leaking UST system, has been removed, vadose zone residuals and dissolved phase
compounds are present at levels which exceed allowable standards. This section will
evaluate potential methods for site remediation.

22

Options which have been considered for remediation of dissolved compounds in
groundwater include:

• Liquid phase recovery (Pump and treat);
• Enhanced in situ bioremediation (biosparging);
• Passive biodegradation (natural attenuation);
• Air sparging.

Options which have been considered for remediation of secondary sources in soil
include:

• In situ soil vapor extraction (SVE);
• In situ passive biodegradation (natural attenuation);
• In situ bioremediation (bioventing);
• Excavation and offsite treatment.

Tables 8 and 9 summarize the relative advantages, disadvantages, and costs of these
remediation options for groundwater and soil, respectively.

5.2 Evaluation of Remediation Alternatives

As of January 2, 1996, the NCDWM - UST RRO requires responsible parties seeking
reimbursement from the State Leaking Petroleum UST Trust Fund to evaluate the
applicability of Title 15A NCAC 2L .0106(k) and (l) for corrective action. As previously
detailed in this report, (k) and (l) are not applicable.

In July 1996, the State passed Senate Bill 1317 requiring the NCDWM - UST RRO to
rank all sites in accordance with a site priority ranking system. The site priority ranking
was brought about to address the continued solvency of the Leaking Petroleum
Underground Storage Tank Cleanup Funds. The site was ranked “A” indicating high

23
priority status. With an “A” ranking, cleanup to the 2L Standards is applicable. The
site is currently ranked a High Risk.

5.2.1 Groundwater

Even if (k) and (l) were applicable, C.W. Chamber Store is not suitable for alternative
cleanup levels or natural attenuation at this time. The dissolved concentrations in
groundwater would likely affect a downgradient potable well and unimpacted
groundwaters before they would become attenuated. Therefore, a more active and
aggressive remedial plan is needed. Alternatively, the use of enhanced in situ
bioremediation requires that sufficient nutrients, microbial populations, and other factors
are present to biodegrade contaminants. Although this method can reduce petroleum
concentrations more than pump and treat, its limitations are : 1) higher costs, 2) the
possible requirement of injection wells and trenches, 3) buffer zone constraints, and 4)
its inability to provide hydrodynamic control over the plume. Air sparging could
possibility be added to the treatment system once a majority of the groundwater
contaminant concentrations have been reduced. It is not applicable during the initial
remedial stage since the sparging process could assist in plume migration instead of
containment. (U.S. EPA, 1995 and Nyer et al, 1996).

Therefore, recovery of the groundwater through pump and treat is proposed.
Groundwater pumping will provide hydrodynamic control of the plume, and a treatment
system will remove dissolved petroleum concentrations.

5.2.2 Contaminated Soil

Gasoline contaminated soil has been located around the former UST basins, product
lines, and dispenser island. Natural attenuation of petroleum contaminated soil is not
permitted by the NCDWM - UST at this facility. In situ bioventing is not an ideal
remedial option because bioventing is generally reserved for remediation of high boiling
point fuels such as kerosene. While bioventing would work, the costs associated with

24
operating the system versus an soil vapor extraction (SVE) system would be cost
prohibitive. In addition, bioventing generally takes longer than soil vapor extraction to
remediate soils, because the remediation is primarily controlled by the process of
diffusion and the effects of bioremediation by indigenous microorganisms.

TEC performed a SVE pilot test on July 17,1997. Using HYPERVENTILATE, the SVE
data was reduced and favorable results were obtained (Appendix E). Used
aggressively, SVE would be effective for vadose zone remediation. A coincidental
benefit is the circulation of oxygenated air which facilitates aerobic degradation by
native microorganisms. However, due to the fluctuating potentiometric surface, which
at times limits the vadose zone to almost 3 feet below ground level, SVE would be
difficult to implement, thus minimizing its effectiveness.

A final and more viable option is excavation. This method is the most expeditious
method for soil remediation and based upon the estimated tonnage of soil and shallow
depth of contamination, the costs are comparable to the design, installation, and
operation of a SVE system for several years.

Residualized contamination within the capillary fringe or smear zone may be remediated
by several methods. These include cycling the pump and treat system to cause
groundwater level fluctuations and air sparging to increase oxygen levels within the
capillary fringe. After the pump and treat system has operated for some time, the
effectiveness of the system will be evaluated to determine if cycling and /or air sparging
needs to be added to increase the effectiveness of the remediation effort.

5.2.3 Discharge of Treated Groundwater

Groundwater recovery and treatment necessitates a discharge point for the treated
water be established. Options investigated for this site include the following:

25
· Discharge to a sanitary sewer (POTW permit)
• Spray irrigation, infiltration galleries, or injection wells (non-discharge permit);
· Water evaporator;
• Discharge to a surface water feature (NPDES permit).

Discharge to a municipal sanitary sewer system is not possible due to the rural nature of
the site’s surroundings. The only sewage disposal method for the site and adjacent
properties is leach-field septic systems.

Non-discharge either by spray irrigation, infiltration galleries, or injection wells are not
favored. While feasible due to the site’s rural surroundings, spray irrigation is not
applicable because the land located between the treatment system and spray irrigation
area is not owned by the site’s property owner or responsible party, thus mandating an
easement across the property. Due to the complex nature of these proceedings and
the reluctance of the responsible party to enter into an agreement with the adjacent
property owner, spray irrigation is not feasible. In addition, the field in question is
actively farmed and the owner has concerns regarding the effects of additional water
will have upon growing livestock feed crops and who will be responsible for moving the
irrigation system.

Infiltration galleries or injection wells cannot be utilized as a discharge option because of
the poor draining shallow soil, the need for hydrodynamic control over the plume, the
presence of nearby active, potable wells, and buffer requirements. Typically, low to
medium permeable soils are not suitable for treated water injection. According to the
Soil Survey of Person County, North Carolina, the site is located in Vance sandy loam
type lithology (VaB) (USDA, 1995). The permeability of the VaB lithology is considered
to be slow. In addition, hydraulic influence is more difficult with a closed-loop
remediation system, since injected water must be recaptured by the recovery well
system. Since the injected water typically increases the size of the capture zone,

26
additional recovery wells are needed, thus increasing the cost of the system.
Therefore, these methods are excluded.

An onsite water evaporator is another option, however, the equipment and operational
costs are very high and make this option a last resort. Equipment costs for a
moderately sized evaporator are greater than $ 30,000. In addition, the evaporator
uses propane gas to heat the water and based upon the amount of water to be treated
by the system (approximately 3,600 gallons/day), monthly fuel costs would be
substantially high as well.

Discharge to an onsite, manmade, groundwater-fed pond under NPDES General Permit
NCG510000 is possible and the most viable option for treated water discharge. Two
additional discharge options were initially considered; discharge into the North Carolina
Department of Transportation (NCDOT) roadside ditch and the low lying area adjacent
to the James Chamber’s residence across Highway 49. According to Frank Bowen of
the NCDOT Encroachment Office, surface discharge into a NCDOT culvert is forbidden.
In addition, TEC personnel determined that the low lying area adjacent to James
Chambers’ residence did not have a sufficient grade to allow for the runoff of discharged
water, and Mr. Chambers would not allow the water to be discharged onto his property
unless he was compensated. Since neither of these options are viable, the onsite pond
is the only area available for discharge. According to Jeff Myhra of the North Carolina
Division of Water Quality - NPDES Section this discharge method is allowed under the
NPDES regulations. The pond is approximately 600 feet from the proposed location of
the treatment system and is approximately 1.2 acres in size. With an average water
depth of 5 feet, the pond currently contains approximately 1.8 million gallons of water.
Conservatively, the pond has approximately four feet of freeboard and an overflow drain
that drains to an uninhabited low-lying area. Any overfill will flow into tributaries of
Hyco Lake, located approximately 5 miles from the site. Estimated capacity of the
pond is over 3.5 million gallons. With an average filled capacity of half the total
amount, the likelihood of the treatment system having an overwhelming effect on the

27
ponds maximum capacity is unlikely. Based upon an average flow of 2.5 gal/min, the
amount of water treated and discharged in a year’s time is approximately 1.3 million
gallons. Though the contribution of groundwater infiltration and rainfall must be
accounted for in determining the average volume of the pond, their total effect (volume)
does not likely increase the possibility of overfilling the pond and is counterbalanced by
the effects of soil absorbtion and evaporation. However the volume of water in the
pond will be monitored to allow for significant rain events, thus minimizing the chances
of overflow.

Figure 9 depicts the location of the pond in relation to the treatment system and the
plume area. Permitting requirements will be discussed further in Section 7.0.

6.0 PROPOSED CORRECTIVE ACTION

6.1 Overview

The proposed corrective action consists of a two - phase strategy for groundwater
treatment. The first phase focuses on removal of residual contaminant mass via active
remedial methods consisting of groundwater pumping. This active remediation will
continue until the 2L Standards have been achieved or a petition for closure under
NCAC 2L .0106 (m) is submitted and approved once the asymptotic slope of the
decontamination of the contaminants has occurred. The second consists of
post-remediation monitoring of the natural attenuation effects. This monitoring will
continue until the 2L Standards have been met or no violations are detected for a period
of one year.

Three recovery wells are proposed for liquid recovery. Recovered liquids will be
pumped to a shed containing treatment equipment.

Treatment begins with separation of aqueous and nonaqueous phases in an oil/water
separator, if free product is discovered. Raw water is routed through a pair of bag

28
filters that will assist in reducing the amount of sediment in the water and help prevent
iron fouling of subsequent treatment components. Following filtration, groundwater will
be treated in an aeration unit to strip volatile organics. Aerated water will then flow
through an additional bag filter to further remove suspended solids, followed by at least
two banks of activated carbon. Treated water will pass through a 50 mesh strainer
before being discharged through PVC piping to the point of discharge.

Contaminated soil will be excavated to a depth approximately 5 feet below ground level.
The overlying foot to a foot and a half of soil and gravel which make up the parking lot
subbase will be presumed to be clean unless determined to be otherwise during the
excavation effort. Based upon the zone of contaminated soil defined during the CSA,
approximately 894 tons of soil will be excavated and disposed of at a North
Carolina-permitted soil treatment facility.

After the system has been operated for some period of time and its effectiveness
evaluated, air sparging may be added to accelerate residualized groundwater
contamination. Sparging will possibly commence when the contaminant concentrations
are reduced and hydrodynamic control has been achieved.

Sections 6.3 through 6.10 detail the proposed remediation plan. Specific data including
design, installation, and operation will be prepared during the bid specification process.
Figure 9 depicts the remediation system layout. Figure 10 depicts the groundwater
remediation system schematic. Figures 11 and 12 provide details of various
components of the system.

Appendix F contains notes and results for modeling groundwater flow with Geraghty &
Miller, Inc.’s Quickflow Version 1.0. The model is used to help assess water table
depression and contaminant capture during pumping.

29
Figure 13 depicts the estimated extent of soil excavation based upon soil boring
analytical results. Volume calculations are also presented on the figure.

The schedule of implementation will depend on the NCDWM - UST review of the CAP
and pre-approval requests, equipment delivery, contractor availability, NPDES
permitting, property access, and the availability of funds to pay for environmental
services. Property access is required to install the remediation equipment, because
the responsible party does not own the property. Equipment specification and bidding
will take 8 to 10 weeks. Equipment delivery typically takes 8 to 10 weeks after the
order is placed. Installation and startup should take 3 to 4 weeks. Excavation and
backfill will take approximately one week. A proposed implementation schedule is
detailed in Section 6.8.

6.2 Checklist of Regulatory Requirements

Paragraph (c) of 15A NCAC 2L .0106 lists the necessary requirements for a site where
groundwater quality has been degraded by a nonpermitted release and must be
remediated to the 2L .0202 Standards. These conditions are summarized in the
following list.

1) Notify the NCDWM - UST of the release.

· All sources of contamination must be removed or abated.

2) Provide a comprehensive report assessing the cause, significance, and
extent of the violation.

3) Implement an approved corrective action plan for the restoration of
groundwater quality under an established schedule.

4) Public notice of the proposal must be provided in accordance with 15A
NCAC 2L .0114(b).

30
The above conditions have been met, are met within this CAP document, or will be met
with the execution of this CAP.

6.3 Groundwater Recovery

Any equipment specification herein was chosen on a conceptual basis. The exact
equipment to be used will be determined during the bid/specification process.

Recovery Wells

A total of 3 wells will be used for groundwater recovery. Figure 9 depicts the well
locations. Piezometer RW1, used as the pumping well during the aquifer pilot test, will
become recovery well RW1. Recovery well RW1 is located in the vicinity of the former
UST basin near the dispenser island. Recovery well RW2 is proposed to be located
downgradient of the dispenser island. Recovery well RW3 is proposed to be located
adjacent to monitoring well MW2 due to the high, dissolved concentrations of petroleum
compounds in MW2. The well locations were chosen to provide hydrodynamic control
over the plume and to prevent further offsite migration.

TEC used Quickflow Version 1.0 by Geraghty & Miller, Inc. to simulate recovery well
capture zones. Model outputs are included in Appendix F. Quickflow is a simple two
dimensional groundwater flow model which has particle tracking functions with variable
retardation. The particle tracking is used to observe capture zones under various
pumping and flow scenarios. The results of pumping from the proposed well network
at a total rate of 2.5 gal/min (gpm) indicates a capture zone which encompasses the
source area and most of the groundwater plume in the downgradient direction. As
previously noted, offsite access for the installation of a recovery well was denied;
therefore, recovery of that portion of the plume located across NC Hwy. 49 is not
possible according to the computer model.

31
A North Carolina licensed driller will install the new wells during the construction phase.
The wells will be installed to a depth of at least 32' BGL. A typical well detail is shown
in Figure 11. Each well will be constructed of 4-inch diameter PVC and 0.010 - inch
screen slot.

Groundwater Pumps

Recovery wells shall be equipped with submersible pneumatic pumps. The pumps
shall be top loading for total fluids recovery. They will cycle automatically by an
“on-board” controller, operating on demand at whatever flow rate is yielded by the well
(up to the pump’s capacity). Flow rate through the treatment system may be controlled
at the well head or at the oil/water separator of the treatment system.

Air Compressor

Compressed air shall be supplied for pump operation by an electric single-phase 5 hp
(nominal) air compressor. The compressor shall be reciprocating with two-stage
compression and an 80-gallon receiving tank. The tank shall be equipped with an
automatic drain valve. Filters for particulate and oil will be installed in the main air
supply line.

Pump Placement

The typical depth to groundwater at the site is 3.5' - 6' BGL. The recovery pumps will
be set in the central portion of the water column or at a depth of approximately 13' - 16'
BGL. During periods when groundwater levels drop below 10' BGL, the pumps will be
lowered. If free product is encountered after treatment has commenced then the
pumps will be moved to just below the product/water interface.

Primary Treatment - Oil/Water Separator

32

From the recovery pumps, liquids shall first flow through an oil/water separator. Free
product, if any, will be segregated from water. Product will accumulate in a holding
tank for disposal off site, and water will continue through the treatment system.
The unit shall include a coalescing medium to enhance droplet formation. The shell of
the unit shall be of fiberglass construction with a detachable, rainproof cover. It will be
elevated on a steel stand so that effluent from the separator will flow by gravity into the
influent water sump.

Transfer System - Influent Sump

Raw groundwater from the oil/water separator will flow by gravity into the influent sump.
From here water will be fed in batches to the bag filters and aeration unit. The tank
shall be of polyethylene construction and have a nominal volume of 70 - 100 gallons.
High and low water level switches in the tank will operate a centrifugal pump which will
draw from the tank and discharge to the bag filters and then the aeration unit. The
transfer tank shall also have a high-override water level switch, which when activated
will close the main air supply to the groundwater pumps. The pump discharge line shall
have a flow valve and visual flow meter for adjusting the feed rate into the aeration unit.

Secondary Treatment - Aeration Unit

Prior to entry into the aeration unit, water-to-be-treated will be sent through a pair of bag
filters to assist in particulate filtration and have a disposal filter media that will be
changed during monthly system maintenance.. The aeration unit shall be a low-profile
cascading multi-tray air stripper. Many suitable makes and models are available. TEC
will specify the performance requirements at the time of bidding. Concentrations will be
further reduced in tertiary treatment by activated carbon. A sensor measuring dynamic
air pressure shall monitor for low blower output which could indicate a blower problem.

33

Transfer System - Effluent Sump

Outflow from the aeration unit will collect in an effluent sump. The sump may be a
separate vessel or integral to the aeration unit. Figure 10 depicts the sump as a
separate vessel. This tank will operate identically to the influent sump, with water level
switches and pump. The pump shall discharge to tertiary treatment.

Tertiary Treatment - Filtration and Activated Carbon

The final stage of treatment will consist of particulate filtration through another bag filter
and removal of organic residuals by activated carbon (Figure 10). Vessels shall be
constructed for high-pressure operation (50 to 75 psi) and fitted with cam - lock
connectors. The quantity of carbon will be specified at bidding. During each system
maintenance visit, the bag filter will be replaced to prevent clogging.

Discharge of Treated Groundwater

After tertiary treatment, the groundwater passes through a 50 mesh strainer and is
discharged to an onsite farm pond under NPDES General permit NCG510000 (Figure
9). The discharge will require a NPDES permit from the NCDWQ. The discharge line
will be 2-inch I.D. Schedule 40 PVC pipe and buried in a trench below the freeze line.
Riprap will be placed at the drainage point to prevent soil erosion.

6.4 Soil Excavation

Soil excavation was chosen over SVE, based upon the comparable costs and the quick
remedial time compared to several years of operation of a SVE system. Other reasons
for selecting excavation over SVE include the shallow depth to water and rapid source
removal. Soil vapor recovery is difficult when the groundwater table is less than five

34
feet below ground level. The rapid removal of secondary sources of contamination
may significantly reduce the cleanup times for the pump and treat system by eliminating
the continuing source of petroleum compounds leaching into the groundwater. Soil is
proposed to be excavated to a depth approximately 5 feet below ground level. The
overlying foot to a foot and a half of soil will be presumed to be clean unless determined
to be otherwise during the excavation. Based upon the zone of contaminated soil
defined during the CSA, approximately 894 tons of soil will be excavated (see Figure
13). Soil in the former UST basins will not be reexcavated. Samples will be collected
at the limits of excavation to document the remaining soil quality. Analytical
requirements will be determined during the development of the Soil Excavation Work
Plan and pre-approval process. Contaminated soil will be disposed of at a North
Carolina-permitted treatment facility by a competitive bid process. The excavation will
extend vertically to the water table, so no soil samples will be collected from the base of
the excavation. Clean backfill will be replaced in the basin and compacted. Upon
completion of the backfill, the area will be paved to minimize the infiltration of rainwater
into the central portion of the plume. Once the excavation effort has been completed, a
report detailing the excavation procedures and results will be submitted to the NCDWM
- UST.

6.5 Air Sparging System

The intent of air sparging is to improve aquifer cleanup through volatilization and
enhanced biodegradation. Air sparging will increase the amount of oxygen (O2) in the
dewatered zone and expedite biodegradation of the residualized contaminants
(contaminants trapped below the water table). This treatment method is tentatively
proposed for the latter stages of remedial activities once hydrodynamic control of the
contaminant plume has been achieved and contaminant levels have been reduced.

The sparging system is presented here on a conceptual basis. The final proposal and
design will be presented in a system enhancement plan. This plan will be prepared

35
after the second phase of operation has begun. The current omission of a detailed
design allows for the possibility that air sparging may not be appropriate or necessary.
If air sparging is deemed to be a viable addition to the treatment system, a system
enhancement plan and subsequent pilot testing will be completed to size equipment.

6.6 Treatment System Appurtenances

6.6.1 Concrete Pad

A 4-inch thick (minimum) concrete pad will be poured for mounting treatment
equipment. Nominal slab dimensions are 12 x 25 feet and may vary depending on the
footprint of the chosen equipment shed. A minimum of 4 inches of compacted ABC
stone (or other suitable stone) will be provided as a base. Galvanized wire mesh 4" x
4" shall be placed at mid depth for reinforcement. The slab will be formed with wood.

6.6.2 Equipment Compound

The equipment compound will consist of the equipment shed, components mounted
outside on the concrete pad, and a wooden privacy fence. The oil/water separator will
be mounted outside. The remainder of the system shall be installed in the shed.

A dedicated power service pole and meter will be installed for the compound.
Single-phase 120/240 VAC (nominal) power is required. The system control panel will
be mounted inside the shed. A 100-amp breaker box will be included.

The shed shall be a prefabricated wood frame structure with aluminum or vinyl siding.
It shall be approximately 10 x 12 feet. The actual dimensions and construction shall be
specified by the equipment contractor to provide adequate space for equipment,
storage, and work space. The shed shall meet all state and local building and/or
zoning codes. Fluorescent lights, a heater, and a vent fan will be included.

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The shed will be oriented with the entrance at the edge of the slab. Outdoor equipment
will be placed on the slab at the rear of the shed. The privacy fence will be constructed
around the rear portion of the slab. The fence will be at least 7 feet high. A locking
gate will be provided, and the edges of the fence shall abut the shed.

6.6.3 Trenching and Conduits

Pipes and hoses to and from the equipment compound and wells will be installed
underground via shallow trenches. Hose and conduit schedules will be included in the
bid specification plans. The proposed layout is contingent upon the results of utility
locating and may change. Hoses carrying water will be buried at a depth of
approximately 2 feet below grade. A typical trench detail is shown in Figure 12.

Junction boxes will be spaced at key intersections, bends, and well heads to facilitate
pulling hoses through conduits. Boxes in traffic areas must be rated for H20 truck
loads and installed with stone fill and concrete collar as shown in Figure 11 (recovery
well detail). Boxes in grass do not require H20 load rating. They should be 2 x 2 feet
and 18 - 24 inches deep and installed with an 8 - inch wide concrete collar at least 6
inches deep.

6.7 System Controls and Safety Functions

6.7.1 Groundwater Recovery System Functions

The influent transfer pump will operate from high and low water level sensors in the
sump. The high switch will activate the pump, and the low switch will deactivate it. As
long as sufficient compressed air is supplied to the groundwater pumps, they will
operate at the well yield rate. Well yield is controlled by aquifer characteristics and the
pump depths. The pressure of the compressed air supply will be adjusted by

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regulators in the air supply. Total pumping rates will be controlled at the well head or at
the oil/water separator of the treatment system to minimize over pumping.

A solenoid-controlled air valve will be installed on the main air supply. The valve shall
be two-way normally-closed. The valve will close and the influent transfer pump will
disengage under the following conditions:

• A high level of product is detected in the product storage tank connected to the
oil/water separator.

• An unusually high water level is detected in the influent sump.

• A low air flow (measured as low dynamic air pressure) is detected in the blower
of the aeration unit. The electronic control shall be calibrated to the sensor for
activation at an air flow corresponding to the recommended minimum
air-to-water ratio for the design conditions.

• An unusually high water level is detected in the effluent sump.

After an alarm/shutdown is triggered, the system shall require a manual reset to
continue operation. The solenoid air valve will close in the event of power loss, halting
groundwater recovery.

6.7.2 Main System Control Panel

Control of the remediation system functions will be accomplished with an
electro-mechanical or programmable logic controller which will integrate monitoring
sensors to the operation of the various motors and control valves. The panel shall
have HOA switches for the aeration system blower, the influent transfer pump, the
effluent transfer pumps, the compressed air cutoff valve, the air stripper pressure
sensor, and the backwash valves. A master on-off switch will also be included. The
main disconnect and fuse box will be located adjacent to the control panel.

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The controller will perform the safety functions discussed above. They are summarized
as follows:

MAIN CONTROLLER SAFETY FUNCTIONS

CAUSE EFFECT
High Product Level Air Valve Closes, Infl. Pump Stops
High Influent Sump Level Air Valve Closes, Infl. Pump Stops
Low Stripper Air-Flow Air Valve Closes, Infl. Pump Stops
High Effluent Sump Level Air Valve Closes, Infl. Pump Stops

A monitoring and remote notification system (e.g. remote telemetry) will be integrated to
the control panel to alert the appropriate party of any alarm/shutdown mode initiated by
the controller. The system will provide notification by telephone message to a
preprogrammed phone number.

6.8 Proposed Implementation Schedule

The target startup and completion dates are summarized as follows:

ITEM COMPLETION DATE
Submittal of Permit Applications
1) NPDES Permit 45 days after CAP approval
2) Recovery Well Permit 45 days after CAP approval

Access Agreements 45 days after CAP approval
Equipment Bidding 90 days after CAP approval
System Purchase and Delivery 60 days after bid awarded
Recovery Well Installation 45 days after permit issued
System Construction/Installation 15 days after system delivery

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System Startup 30 days after installation
complete
System Shutdown unknown

The proposed startup dates are achievable assuming the following: 1) the timely
approval of permits required by the NCDWM - UST, local ordinances, other agencies,
etc., and 2) there are no problems associated with gaining site access. The proposed
completion dates do not take into account time required to gain pre-approval for
implementing various tasks associated with CAP implementation. The estimated time
from CAP approval to system startup is 195 days (approximately 6 months).

6.9 Proposed Maintenance Program

6.9.1 System Inspections

Inspection of the following items are suggested. Observations will be made by a
qualified inspector. The frequencies are nominal and may be varied as warranted by
experience with the system.

• Oil/water separator fouling or accumulations ........................................... Monthly
• Flow through the system ....................................................... Biweekly to Monthly
• Aeration blower operation ..................................................... Biweekly to Monthly
• SVE blower operation ........................................................... Biweekly to Monthly
• Pressure drop across air filters ................................................................ Monthly
• Air compressor oil level ............................................................................ Monthly
• Compressor tank automatic drain valve ................................ Biweekly to Monthly
• System controls and fail safe functions ...................... Quarterly to Semi-annually

6.9.2 Preventative Maintenance

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The following tasks and frequencies are suggested as preventative maintenance to
prolong equipment life and prevent accumulation of materials which could potentially
cause fouling. The tasks will be conducted by a qualified inspector or technician.

• Clean sediment and biological growth from O/W separator ..................... Monthly
• Remove sediment from sumps .............................................................. Quarterly
· Replace bag filters ................................................................................... Monthly
· Clean 50 mesh strainer ............................................................................ Monthly
• Change oil in air compressor ................................ Per Manufacturer’s Directions
• Descale air stripper and system piping ............................................... As Needed
• Service groundwater pumps ............................................................... As Needed

The listed frequencies are provided as a rough guide and may prove with experience to
be too long or short. They will be adjusted as warranted.

Oxidation and scaling of dissolved iron is almost certain to occur in the treatment
system, particularly in the air stripper. Flushing with a diluted hydrochloric acid solution
will remove iron scaling and maintain system performance. The required frequency will
depend on the severity of scaling.

6.10 Proposed Monitoring Program

6.10.1 Monitoring Well Network

Monitoring is conducted to assess the effectiveness of the remediation program, assess
the migration of contaminants, and ensure that discharge requirements are being met.

The network of existing wells will be used to monitor groundwater remediation. No
additional wells are proposed.

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6.10.2 Monitoring Schedule and Parameters

6.10.2.1 Groundwater Monitoring

First Year of Operation

During the first year of operation, each monitoring well (MW1 - MW11) will be sampled
on a quarterly basis. Potable wells PW1, PW-2 and PW-3 will be sampled quarterly
also. Potable wells PW-4 and PW-5 are not in service. If potable well PW-5 is
activated, it will be sampled also. Potable wells PW6 and PW7 will be sampled if the
extents of the plume change or if one of the sampled potable wells become impacted.
Refer to Figures 3 and 4 for potable well and monitoring well locations, respectively.
Results will be used to evaluate overall system performance and summarized in
quarterly reports.

Second and Subsequent Years

Beginning with the second year of operation, groundwater monitoring will be conducted
semi-annually. Groundwater samples will be collected from monitoring wells MW1,
MW2, MW4, MW8, and MW9. All other monitoring wells will be sampled annually
beginning at the end of the second year of operation. Potable wells PW1, PW-2 and
PW-3 will be sampled a semi-annually.

Monitoring Parameters

Each groundwater monitoring event will consist of the following measurements and
analyses:

• water level measurements;

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• lab analysis by EPA Method 6210D + IPE + MTBE;
• at closure, samples will be analyzed by EPA Method 504.1 (EDB).

Reporting frequency will correspond to the sampling frequency (e.g. quarterly for first
year and semi-annually thereafter). The reports will follow the general format, where
applicable, for groundwater monitoring reports as detailed in the Groundwater Section
Guidelines for the Investigation and Remediation of Soil and Groundwater, January 2,
1998 and will be submitted to the RRO of the NCDWM-UST.

6.10.2.2 Remediation System and Discharge Monitoring

Effluent from the groundwater remediation system will be sampled and analyzed to
meet requirements of the NPDES permit. Currently, this requirement is for monthly
sampling. Samples will be analyzed by EPA Method 6210D + MTBE + IPE or other
analytical method(s) as specified by the permit. Analytical results from the monthly
sampling will be summarized in an annual NPDES monitoring report.

Samples of water at various stages of treatment will be collected during the monthly
effluent sampling event to determine the effectiveness of the remediation system and
monitor possible contaminant break-through.

6.11 Termination of Remedial Actions

Remediation activities will proceed until the groundwater concentrations meet the Title
15A NCAC 2L .0202(g) Groundwater Quality Standards. If the groundwater
concentrations meet the 2L Standards, the system will be shut down and the site
monitored for one year. The monitoring well network will be sampled on a quarterly
schedule. If after a year the groundwater exceedences have not been detected, a
petition will be made for system removal. If 2L Standards exceedences occur during
that year, treatment will resume. Once the 2L standards have been achieved or when

43
monitoring reveals that additional corrective action will not result in a significant
reduction in the concentration of contaminants (e.g. asymptotic limit), a petition will be
made for site closure in accordance with Rules under 15A NCAC 2L .0106 (m).

7.0 PERMITS AND NOTIFICATIONS REQUIRED

In accordance with 15A NCAC 2L .0114 (b) Notification Requirements, parties that
submit a request under Rule .0106 (c) are required to notify the local Health Director
and the chief administrative officer of the political jurisdiction in which the contaminant
plume occurs. Notification consists of a description of the corrective action and the
reasons supporting it. Notification of the parties was made concurrently with the
submittal of this report. Notification letters and copies of the certified mail tickets are
included in Appendix G. Copies of certified mail return receipts will be forwarded to the
RRO of the NCDWM - UST upon receipt. Those parties being notified are as follows:

INDIVIDUALS REQUIRING NOTIFICATION

NOTIFIED PARTIES NAME AND ADDRESS OF PARTY

COUNTY HEALTH DIRECTOR

Person County
Mark Coleman
325 South Morgan Street
Roxboro, NC 27573
COUNTY MANAGER Person County Manager
William Hurdle, Interim Manager
304 South Morgan Street, Room 212
Roxboro, NC 27573

A permit from the NCDWM - UST is required to install the recovery wells. The permit
will be obtained prior to installation. A copy of the permit is included in Appendix H.
The proposed method of discharge will require coverage under a NPDES permit issued
by the NCDWQ. A copy of the permit and general policy is included in Appendix H.

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Currently, an air discharge permit for the air stripper is not required under NCAC 2Q
.0102B 1(k) 11 or unless the long-term average emission exceeds 5 tons of VOCs per
year. This cutoff roughly corresponds to 1,500 gallons of gasoline. Based on past
experience, it is unlikely that VOC emissions will exceed this value. It is possible that
at startup, the short-term average VOC emissions will exceed the 5 ton/yr average, but
the emissions should decline substantially after the initial startup phase.

An engineer’s certification will be obtained after construction to verify that the CAP has
been implemented according the intent of the plans and specifications. A licensed
North Carolina engineer will provide the certification.

8.0 LIMITATIONS

TEC has presented a thorough effort to develop a corrective action strategy which will
alleviate possible threats to human health and the environment. The chosen strategy
is based on the available data. The opinions and conclusions stated in this report are
in accordance with North Carolina Department of Environment and Natural Resources
regulations and guidelines and accepted engineering and hydrogeologic practices of the
field at this time and location. No warranty is implied or intended.

The focus of work at this site is limited to the investigation of petroleum hydrocarbons as
gasoline and kerosene. The results do not imply that other unforeseen adverse
impacts to the environment are not present at the facility, although none have been
detected. In addition, subsurface heterogeneities not identified during the current study
may influence the migration of groundwater or contaminants in unpredicted ways. The
limited amount of sampling and testing conducted during the assessment can not
practically reveal all subsurface heterogeneities. Furthermore, the subsurface
conditions, particularly groundwater flow, elevations, and water quality may vary through
time.

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The modeling efforts were conducted using mathematical techniques which simplify the
complexity of the subsurface environment. These simplifications are typical of
modeling applications and are necessary to solve complex mathematical formulations
using limited data. Consequently, model predictions are based on these
simplifications. Error can be introduced into model predictions when actual conditions
depart from the simplified representations used in the model.

REFERENCES

REFERENCES

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Fetter, C.W., 1988. Applied Hydrogeology, second edition. Merrill Publishing
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Freeze, R.A. and J.A. Cherry. 1979. Groundwater. Prentice-Hall, Inc., Englewood
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Heath, 1982, Basic Groundwater Hydrology, U.S. Geological Survey Water-Supply
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Lewis, R.J., Sr., 1993. Hawley's Condensed Chemical Dictionary, twelfth edition. Van
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Nyer, E.K., 1992. Groundwater Treatment Technology, second edition. Van Nostrand
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Nyer, E.K., 1993. Practical Techniques for Groundwater and Soil Remediation.
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Nyer, Evan K., D.F. Kidd, P.L. Palmer, et al. 1996. In Situ Treatment Technology.
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Soller, David R. and Mills, Hugh H., 1991, Surficial Geology and Geomorphology in The
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U.S. Department of Agriculture. June 1995. Soil Survey of Person County, North
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Walton, W.C., 1988. Practical Aspects of Groundwater Modeling - Third Edition.
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