NCD991278953_20020703_National Starch & Chemical Corp._FRBCERCLA RA_Fracture Trace Analysis-OCR

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-. ·-· --
REPORT
Fracture Trace Analysis
National Starch & Chemical
Company
Cedar Springs Plant Site
Salisbury, North Carolina
July 2002
BBL
BlASlAND, BOUCK & LEE, INC.
engineers & scientists
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Fracture Trace Analysis
National Starch & Chemical Company
Cedar Springs Plant
Salisbury, North Carolina
July 2002
BLASLAND, BOUCK & LEE, INC.
engineers & sclen-TiSTs
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Table of Contents
Section 1. lntroduction .............................................................................................................. 1-1
1. 1 Geology ............................................................................................................................ 1-1
1.2 Hydrogeology ................................................................................................................... 1-1
Section 2. Fracture Trace Analysis .......................................................................................... 2-1
·Section 3. Summary and Recommendations .......................................................................... 3-1
Figures
1 Site Location Map
2 1980 Aerial Photo Analysis
3 Proposed Trench Locations
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BLASLAND. BOUCK & LEE. INC.
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1. Introduction
Blasland, Bouck & Lee, Inc. (BBL) has conducted a fracture trace analysis for National Starch & Chemical
Company's (NSCC's) Cedar Springs Plant located in Salisbury, North Carolina. Figure I presents a Site
Location Map. The purpose of this analysis is to identify bedrock fractures at the Site. The objectives of the
fracture trace analysis are to:
• identify potential fractures that serve as groundwater conduits from the Trench Arca to the area of the
Unnamed :ributary;
• provide information to direct overburden trenching efforts to locate the fracture(s) in the field; and-·
• aid in the siting of additional monitoring wells to be installed between the Trench Area and the area of
the Unnamed Tributary.
1.1 Geology
The site lies within the Charlotte belt of the central Piedmont physiographic province which is generally
characterized by relatively thick regolith over fractured igneous and metamorphosed igneous and sedimentary
bedrock. The land surface in the Piedmont is underlain by clay-rich, unconsolidated material derived from in-
situ weathering of the underlying bedrock. The unconsolidated material, which averages between about 30 and
60 feet thick and may be as much as 300 feet thick in some areas, is referred to as saprolite, which retains the
relic texture and structure of the parent bedrock. In the valleys of many larger streams, the flood plains are
underlain by relatively thin, moderately well sorted alluvium deposited by the streams. A transition zone
between saprolite and competent bedrock comprised of saprolite (thoroughly weathered rock), partially
weathered rock and competent rock fragments to boulders is typical in the Piedmont.
The topography of the Piedmont consists of low, rounded hills and long, rolling, generally northeast-southwest
trending ridges whose summits ranges from about 300 feet above mean sea level (msl) along its eastern
boundary with the Costa! Plain province to about 1,600 feet msl along its boundary with the Blue Ridge
province to the west. In general, the top of competent bedrock in this terrain is a subdued reflection of the land
surface topography.
The United States Geologic Survey Rowan Mills 7.5 minute·quadrangle map (shown on Figure 1) indicates the
topography in the vicinity of the site to be gently sloping uplands, cut by several small tributaries of Grants
Creek. Three such tributaries exist on the site and are internally referred to as the Northeast Tributary located
north and east of the production area, the Unnamed Tributary located southwest of the production area, and a
small tributary located northwest of the production area.
Based on literature reports and observation of rock core by RMT, Inc., primary rock type beneath the site is
either metamorphosed intrusive mafic rock (metagabbro) or mafic lava flows. The mafic rocks logged by RMT
contain a faint to well developed, steeply dipping foliation that could reflect a regional structural fabric imposed
during large scale folding and metamorphism, or is the result of local shearing. '
1.2 Hydrogeology
The site is located in the Piedmont Province of North Carolina. The conceptual model of groundwater flow in
the Piedmont includes groundwater compartments centered on streams with boundaries at, or near, the
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topographic highs which define the boundaries of the watershed. Two slope-aquifer systems comprise each
groundwater compartment. The entirety of the Piedmont hydrogeologic system is a collection of numerous
groundwater compartments of varying size.
The groundwater within these compartments enters the system as recharge from prec1p1tation and exits as
surface water flow from the stream. Within the groundwater system, the groundwater percolates through the
thin topsoil into the underlying saprolite, where it may flow horizontally and discharge to the stream or flow
vertically into the underlying transition zone. In the transition zone, groundwater may flow horizontally and
discharge to a stream or flow vertically into the underlying fractured bedrock or up into the saprolite, depending
on vertical hydraulic gradients. Groundwater which flows vertically into the bedrock will eventually flow
upwards into a stream. It is very rare, under non-pumping conditions, for groundwater to underflow perennial
streams or drainage divides and flow into other slope-aquifer systems.
The saprolite and transition zone (which together comprise the regolith) collectively act as the storage zone for
groundwater. The bedrock generally has very low primary porosity and therefore does not act as an important
storage zone. More groundwater flow occurs in the transition zone than in the saprolite. This is due to
differences in conductivity and effective porosity. The saprolite is more fully weathered to fine materials than
the transition zone. Groundwater flow in the fractured bedrock is through secondary porosity, which is
primarily in the form of vertical or high angle fractures.
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2. Fracture Trace Analysis
The fracture trace analysis is completed using historical aerial photographs of the area including the site. Linear
features can often be seen on the photographs that reflect the presence of bedrock fractures. For example,
stream development often occurs along fractures; linear tonal contrasts are often visible in the soil of farm fields,
reflecting deeper and wetter soil overlying a fracture; topographic swales and depressions often develop along
fractures, due to greater erosion along a zone of broken up rock; and in wooded areas, trees are sometimes taller
along fractures, where soil moisture is higher.
Limited aerial photo coverage was available for the site. Photograph stereo pairs were obtained for the years
J 960 and 1980. The 1980 photograph was taken from high altitude and was of limited use during the analysis.
It is possible that other minor fracture traces are present at the site but were not able to be identified with the
limited resources available. The fracture traces identified are shown on Figure 2.
The fractures identified and depicted on Figure 2 are grouped into five sets:
• Fracture Set No. I - A major fracture trace set which trends northeast/southwest through the property.
Based on the photographs analyzed, the fractures appear to be spaced about 200 to 3 00 feet apart;
however, there are some indications of parallel lineations between those that are most visible. These
may be more apparent fractures that would be more visible if additional stereo pair photographs were
available.
• Fracture Set No. 2 -Orthogonal to Fracture Set No. 1 are three north-northwest trending fracture
traces, representing a second widely-spaced major fracture set. One of these sets is along the path of the
Unnamed Tributary.
• Fracture Set No. 3 -Another widely-spaced fracture trace set trending west-northw~st.
• Fracture Set No. 4 - A set of smaller, more closely spaced fractures in the western portion of the site in
the vicinity of the Unnamed Tributary trending east-northeast.
• Fracture Set No. 5 -A set of smaller fractures in the area between the trench area and the Unnamed
Tributary trending north-northeast.
Fracture Set No. 1 should have a strong influence on groundwater flow since this fracture set is almost parallel
to the slope of the land surface. The remaining fracture sets observed at the site are less likely to influence
groundwater flow, unless there is pumping or enhanced recharge along one of the fracture sets.
Results of the Hydrogeologic Evaluation performed during the Remedy Evaluation for Operable Unit One,
monitoring wells NS-29, NS-31 and NS-30 experienced significant recovery during shutdown of the Plume
Periphery Extraction System wells. The water level in NS-29 recovered rapidly following the shutdown of EX-
01. A connection between NS-29 and EX-01 is not readily apparent from the fractures identified on Figure 2.
However, the fractures identified on Figure 2 indicate surface expression of the fractures. Depending on the
dips of these apparent fractures, the fracture sets may be connected in the subsurface. The water level in
monitoring well NS-31 recovered rapidly following the shutdown of EX-01. NS-31 is located approximately
700 feet from EX-01, much further than EX-02 and EX-03. Based on the apparent fractures shown on Figure 2,
it is possible that fractures from Fracture Trace Set No. 2 and No. 3 intersect and provide a flowpath from EX-
01 to NS-31. The water level in NS-30 recovered rapidly following shutdown of EX-03. Based on the apparent
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fractures, it is possible that fractures from Fracture Trace Set No. 4 and No. 5 intersect and provide a flowpath
from EX-03 to NS-30. Other fractures may be interconnected to a greater extent than is shown on Figure 2
depending on the dips of the fracture trace sets identified.
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3. Summary and Recommendations
In summary, fracture trace analysis conducted for the Site indicates the following:
• a major fracture trace set is present trending northeast/southwest. This fracture set should have a strong
influence on groundwater flow since it is almost parallel to the slope of the land surface;
• other, minor fracture trace sets are present at the site, three sets in the area between the trench area and
the Unnamed Tributary. These sets are less likely than the major set to affect groundwater flow, but
may have a significant influence on groundwater flow if pumping occurs along the fractures; and
• field verification is necessary to confirm the presence and location of the apparent fractures.
Overburden trenching will be performed to locate the relic structure of the major bedrock fracture set identified
in the fracture trace analysis. It is possible that these fractures provide the conduit for groundwater flow from
the trench area to the area of the Unnamed Tributary, and specifically the area surrounding monitoring well NS-
29.
A backhoe will be used to excavate trenches in the saprolite overburden parallel to the Unnamed Tributary. One
trench will run in a line to the northeast of monitoring wells NS-22, NS-29 and NS-30. Another trench will be
installed parallel to the first trench between extraction wells EX-2 and EX-3. The approximate locations of
these trenches are shown on Figure 3; however the actual locations of the trenches may differ based on field
conditions. A BBL geologist will be in the field directing and supervising the trenching activities. Additional
length of trenches and additional trenching locations may be excavated according to the field geologist,
depending on the results of the initial trenching.
A schedule for the trenching activities is currently being developed. At the conclusion of the trenching activities
a Technical Memorandum will be prepared describing the results of the trenching and proposed locations for
additional monitoring wells in the area between the Trench Area and the Unnamed Tributary.
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BLASLAND. BOUCK & LEE. INC.
engineers & scientists 3-1
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SOURCES:
ROWAN MILLS, CHINA GROVE,
NORTH CAROLINA
7.5 MINUTE QUADRANGLE
CONTOURINTERVAL=10FEET
~
QUADRANGLE LOCATION
7/03/02 CRA-TLF
05008002/05008802. CDR
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98 MILS O' IS'
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UTM GRID ANO 1987 MAGNETIC NORTH
DECLINATION AT CENTER OF SHEET
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2000' 0
Approximate Scale: 1" = 2000'
2000'
NATIONAL STARCH AND CHEMICAL COMPANY
CEDAR SPRINGS ROAD PLANT
SALISBURY, NORTH CAROLINA
FRACTURE TRACE ANALYSIS
SITE LOCATION MAP
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LEGEND
• MONITORING WELL LOCATION
♦ EXTRACTION WELL LOCATION
$ STREAM GAUGE LOCATION
--FRACTURE TRACE SET No. 1
FRACTURE TRACE SET No. 2
--FRACTURE TRACE SET No. 3
--FRACTURE TRACE SET No. 4
--FRACTURE TRACE SET No. 5
SOURCES:
-MAP ENTilliD "SITIE "'4AP' PREPARED FOR NATIONAL STARCH AND CHE"'4ICAL CO"'4PANY BY INTIERNATIONAL TIECHNOLOGY
CORPORATION, KNOXVILLE, TIENN., DA TIED 5/18/93.
-"'4ONITORING WELL SURVEY BY SCHULENBE,RGER SURVEYING COMPANY, SALISBURY, N.C., DATIED 1/21/97
-"'40NITORING WELL SURVf;Y BY TAYLOR WEISMAN & TAYLOR,
RALEIGH N.C., DA TIED 3/98
0 200'
;;;;;I
SCALE IN FEET
400'
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NATIONAL STARCH AND CHEMICAL COMPANY
CEDAR SPRINGS ROAD PLANT, SALISBURY, NORTH CAROLINA
FRACTURE TRACE ANALYSIS
1980 AERIAL PHOTO ANALYSIS
BIASIAND. l!OUCK & UE, INC.
engln••" I 1cl•n rJ1t1
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/ 5 I~-........:::. . , "\ °" \ "" , _ _ Y> <:::::, \ __ _ I,,,✓ :. ::..__ -"" \ \ r-..... ------..___..._ ~"" > " \. '\ . '\. '-....___ -'-.......___ ----------.. \ I \_ I/ _( { <;:> ) LEGEND • MONITORING WEU LOCATION ♦ EXTRACTION WEU LOCATION fl> STREAM GAUGE LOCATION --FRACTURE TRACE SET No. 1 FRACTURE TRACE SET No. 2 --FRACTURE TRACE SET No. 3 --FRACTURE TRACE SET No. 4 --FRACTURE TRACE SET No. 5 - -PROPOSED TRENCH LOCATION SOURCES: -MAP ENTITLED "SITE MAP' PREPARED FOR NATIONAL STARCH AND CHEMICAL COMPANY BY INTERNATIONAL TECHNOLOGY CORPORATION, KNOX\IILLE, TENN., DATED 5/18/93. -MONITORING WEU SUR'v1:Y BY SCHULE~BE}lGER SUR'v1:YING COMPANY, SALISBURY, N.C., DATED 1/21/97 -MONITORING WEU SURVE;Y BY TAYLOR WEISMAN & TAYLOR, RALEIGH N.C., DA TED 3/98 ~ 20tr .,,,, SCALE IN F'EET NATIONAL STARCH AND CHEMICAL COMPANY CEDAR SPRINGS ROAD PLANT, SALISBURY, NORTH CAROLINA FRACTURE TRACE ANALYSIS PROPOSED TRENCH LOCATIONS BBL 81,\SLAND. 80UC1C a. LEE. INC. englneert • 1clent1,,, FlGURE 3