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Hydrogeologic Report for Evaluation of Groundwater Contamination
Section 5 - Preliminary Assessment
A preliminary assessment was performed to evaluate the current status of all water wells and determine the hydrogeologic conditions of the site without using invasive techniques such as drilling. This information was necessary to prepare a work plan for an SI of groundwater contmination. The assessment involved a well inventory, a well survey, well sampling, a downhole video camera survey, aerial photo research, and a site geologic survey. In addition, records of waste management were reviewed with respect to seven previously identified solid waste management units (SWMUs) near well 16, the inactive drinking water supply well known to contain halogenated volatile organics above the federal maximum contaminant limits (MCLs).
Well records were researched and a site visit was conducted by ES to verify the well location and condition. Water level measurements, well depths, and other pertinent information were obtained. Table 5.1 is a compilation of these well data. Figure 2.2 and Figure 4.1 show the locations of the wells. Photographs of each well head are shown in Appendix B, and well schedules and well logs are in Appendix C.
Well 1 (identified in CSSA records as "Schasse well") is located southeast of the CSSA on Camp Bullis property. This well was initially drilled in 1918 to a depth of 1,022 feet below ground level (BGL), although one report from CSSA indicates the well to have been drilled to 2,500 feet BGL. This was reportedly an exploratory well to see if water could be obtained from the deeper Paleozoic metamorphic rocks. No appreciable amount of good-quality water was obtained from the deeper rocks; therefore, the well was plugged back to a depth of 451 feet BGL, and the casing was perforated in the lower Glen Rose Formation (middle Trinity aquifer). The static water level was measured at 105.3 feet below top of casing in October 1992. The well is housed with a locked protective shelter. It is equipped with an electric submersible pump, is currently active, and is capable of producing up to 150 gallons per minute. The well is a drinking water source for CSSA.
Wells 2, 3, and 4 are located in the northern portion of the inner cantonment area. The well depths and water levels are listed in Table 5.1. The wells were historically used a s a source for livestock water and were equipped with windmill pumps. The source of water is the middle Trinity aquifer. Currently the wells are inactive and have no lift equipment. A removable concrete plug was inserted into the well casings in wells 2 and 3, but only a board covered well 4 at the time of the well inventory. No other protective structures exist. The wells are located in a potentially flood-prone area, and there is no protection from surface runoff.
Well 5 is located west of building 103, with a total depth measured at 157.9 feet BGL. The well appears to have debris or blockage in it because no water was detected in the wellbore. The historical use is unknown; currently the well is inactive. The water source is unknown but is most likely the middle Trinity aquifer. Over the well is welded a steel plate with a hole cut in it. The well is not in a flood-prone area, bit is susceptible to surface runoff.
Well 6 is located at the southwest corner of the installation. The well was measured at 120 feet and had a static water level of 117 feet BGL in October 1992. The well appears to be clocked by debris at 120 feet BGL and is covered at the surface by a metal lid. The well was historically used as a water supply well and is currently inactive. It is unknown what the original water-bearing unit is because the wellbore is blocked and there are no drilling records. The well is not in a flood-prone area, but is susceptible to receive surface runoff.
Wells 9, 10, and 11 are located near the western boundary in the central portion of CSSA. These wells are currently active and are used as a drinking water source from the middle Trinity aquifer. Wells 9 and 10 are equipped with electric submersibel pumps and operate automatically by pressure sensors in the water tank. Well 11 is not used because of its reported low yield. The wells are housed in locked protective structures and are maintained by CSSA personnel.
Well 16 is located near the north fenceline of the inner cantonment boundary. The well depth is reported to be 442 feet BGL, although one report indicates the well was drilled to 500 feet BGL and plugged back to 425 feet BGL. A static water level of 152.35 feet below top of casing was measured in October 1992. The well was taken out of service in August 1991 because it exhibited halogenated volatile organic contamination above the federal MCLs, but it was part of the public water supply system for CSSA. The well is housed in a locked protective structure. Currently the well is under investigation and is the focus of the preliminary assessment.
Wells A, B, C, and D are located along the north fenceline of the inner cantonment boundary. These wells are inactive, and only well D is open below the table. Wells A and C are plugged at the surface with concrete; no information on plugging or total depth is available. No information is available on the historical use of these wells.
Wells E and F are located in the north pasture area. These wells are inactive and filled or plugged with debris; therefore, no total depth or water level measurements were made. Well F was measured at 20 feet BGL. The three wells are reported as old windmill wells that were used for livestock. There is no information on which formation yields water to the wells.
Wells G, H, and I are also located in the north pasture area. These wells are currently active and are leased by CSSA to the Texas Department of Agriculture for livestock use. Well I is currently not in use because the well is not equipped with a motor. Table 5.1 lists depth and water level information for well I only. Wells G and H were in service, and their pump equipment made water level measurement impossible.
A well survey was performed to located each well with respect to state plane coordinates and determine the elevation of top of casing with respect to mean sea level. The survey was performed by Northstar Land Surveying on November 17 through 20, 1992. This information was used to determine the groundwater potentiometric surface elevations and probable groundwater flow direction. The survey data are presented in appendix D.
Previous well sampling and analysis by the TDH and the TWC in August and December 1991 indicated the presence of dissolved halogenated volatile organics in the groundwater from well 16. The results of the TWC analyses were provided to CSSA over the phone in January 1992, and the TDH results are in Appendix E.
ES performed well sampling in November 1992 on wells 2, 3, 4, 10, 16, D, G, H, and I to determine the current concentrations of halogenated volatile organics in the groundwater. Sampling was performed similarly to the TWC sampling so that the data would be comparable. Wells that contained pumps (wells G, H, I, 1, 10, and 16) were sampled from the sample ports, while wells which did not contain pumps (2, 3, 4, and D) were sampled with a downhole bailer. All samples were preserved on ice and shipped to the ES Atlanta analytical laboratory using established chain-of-custody procedures.
The water samples were analyzed for halogenated volatile organics using EPA method SW8010. The results of the November 1992 analysis confirmed the 1991 TDH and TWC findings and indicated the presence of tetrachloroethylene and trichloroethylene below the federal MCLs in wells 2, 3, and 4 and above the MCLs in wells D and 16. Well 16 contained the highest levels of halogenated compounds, while well 2 contained the lowest levels. The November 1992 analytical results were slightly lower than the TWC analytical results of December 1991 and at least 4 times lower than the August 1991 analytical results. In addition, cis- and trans-1,2-dichloroethylene were not detected in the November 1992 sampling. Well D was sampled near the top of the water column and near the bottom of the well to estimate if any differences occurred in the water column. The results were essentially the same (about 8 ug/L PCE). Water samples from wells numbered 1, 10, G, H, and I did not contain halogenated volatile organics. The trip blank did not indicate cross-contamination of samples.
Dichloromethance was detected at low levels just above the compound's detection limit in a number of wells, but is suspected to be a laboratory contaminant as it is commonly used for extractions. This compound was also detected at low levels in the instrument blank sample. Bromodichloromethane, chloroform, and dibromochloromethane were also detected in well 1, but these constituents are suspected products of chlorination, which is required for drinking water by CSSA. The results of the analyses are listed in Table 5.2, and Figure 2.2 shows the locations of the wells. The laboratory reports and chain-of-custody records from the ES Atlanta laboratory and the TDH are in Appendix E.
A downhole video camera survey was performed on wells D, 2, 3, 4, 6, and 16. The objectives of the survey were (1) to visually inspect the well casings for leakage and depth of casing, (2) to determine the potential for shallow water infiltration into the well, (3) to define the stratigraphic intervals, if possible, and (4) to determine obstructions and conditions for potential well abandonment. The survey was performed by Specialty Maintenance, Inc., during the week of December 8, 1992.
The survey technique was to send a downhole video camera equipped with a fisheye lens and underwater capability to the total depth of the well. The camera was lowered on a cable while a VHS videotape was recorded. Technicians played back the tape and looked for signs of groundwater movement above the water table. The camera was also lowered into the water to examine the wellbore and to detect the total depth of the well.
The borehole videos displayed series of smooth concentric walls with varying size and frequency of solution cavities and conduits, high-angle to vertical fractures, solution along bedding planes, and honeycombed walls. All wells have at least 21 feet of casing except well 4, which has 2 to 4 feet of casing or hardened cement, and well 6, which has 7 feet of casing. Casing was often moist, algae covered, and rusty in areas. Well 4 had thick roots at 10 feet BGL, and a spider with cobweb was seen in well 6. Leaves and twigs were common debris at the water surfaces. Frogs were observed at the water surface in wells 4 and 2 and small insects in well 6. Wells 2 and 6 contained small albino invertebrates below water surface. Well 2 also had an albino salamander at the bottom. Twigs were lodged below water level in the wall of wells 2, 3, and 16. Metal banks were also found in well 16 lodged in the borehole wall and near the bottom. Rocks were seen in the bottoms of wells 2 and 4. In well 6, a rock was lodged in the sidewall and prevented access to the rest of the well. Approximately one foot of wood with two nails embedded in it was at the bottom of well 3. Water clarity varied with the amount of suspended silt. At about 230 feet BGL in well 2, the ES geologist noted an increased amount of suspended silt. It is unknown whether sediment was knocked off the borehole wall or was associated with moving the camera up and down the water column.
The survey results showed the depths of casing and the extent of subsurface fracturing and solution cavities in each of the surveyed wells. The cased intervals were underlain by moist to wet zones. Shallow water was seen entering the borehole in the six wells at elevations beginning from 1,150 to 1,170 feet above mean sea level (approximately 50 to 85 feet BGL). The shallow water was observed moving along bedding planes, fractures, and solution cavities and entering the uncased section of the boreholes. These observations manifest horizontal and vertical pathways for transmission of water. Additional zones of fractures and solution cavities were seen almost the entire length of each borehole's unsaturated zone. Stratigraphic intervals such as the Bexar Shale were not observed in any of the videos. A log of each well and a schematic cross-section of the observed water zones are presented in appendix F.
ES performed a surface geologic survey of the CSSA site and surrounding area on November 16 and 17, 1992. The purpose was to confirm regional and local geologic features described on the Geologic Atlas of Texas San Antonio sheet and other publications and literature. The survey was also intended to identify local features such as sinkholes, springs, and faults that might affect the migration of contaminants and the characteristics of these features, including strike and dip of fault planes and the pH, conductivity, and flow rate of water discharged from any springs identified.
The survey focused primarily on the area near well 16, along the various creek beds, and on areas where the underlying rock was exposed at the surface. Figure 4.1 shows the various structures or features that were found.
Two small caves were observed on the northwest corner of the inner cantonment area. Both caves were found approximately 50 feet apart just east of an abandoned gravel pit. The smaller cave is 18 to 24 inches long, 3 to 4 inches wide, and though it extended laterally, it did not appear to be very deep. The larger cave has a round opening about 24 to 30 inches wide. The cave appeared to be large enough for entry but was not entered for safety reasons. Inspection of the cave was made through the opening with a flashlight. The bottom and lateral extent of the cave could not be determined.
While inspecting a small pond located in the east pasture due east of well 16, ES observed a small fracture opening (see Figure 4.1). The pond was dry, and part of the sediment in the bottom had pushed aside by a bulldozer, exposing the fracture. The fracture opening was approximately 12 to 18 inches long and 2 to 3 inches wide. The fracture was aligned northwest to southeast.
No sinkholes were observed during the survey. One sinkhole, however, was reported buried in the gravel pit at the southern end of the site. Differential erosion had occurred in several washout areas along the creek beds. Washouts result from exposure in the creek of a resistant limestone layer underlain by less resistant layers. During periods of high flow in the creek, the less resistant layers are eroded, causing holes to be formed in the creek bottom. A washout area was observed in the creek northeast of well D. Differential erosion was also observed along the road cuts on the east side of the inner cantonment area (see Figure 4.1). The erosion produced a "stair-stepped" appearance in the outcrop, which is characteristic of the Upper Glen Rose Formation.
Because vegetation and soil cover most of the site, no indications of faults were observed. The fault traversing the southern end of the site (according to the geologic atlas sheet) could not be found. However, another small fracture opening similar to the one in the east pasture was observed in the gravel pit at the southern end of the site (see Figure 4.1). The fracture hole was about 24 to 30 inches long and 2 inches wide. The sides of the fracture hole were slickensided, indicating that there might have been some movement vertically along the fracture. This fracture may be a result of the fault indicated in the atlas.
Located about 75 feet north of the fracture opening was a bed of Carycorbula harveyi fossils exposed at the surface. This layer of fossils, known as the Corbula bed, is the marker bed which indicates the contact between the Upper Glen Rose and the Lower Glen Rose Formations. Below the Corbula bed is the top of the Lower Glen Rose.
No springs were observed. The creeks were dry with the exception of some water in low areas along the Salado Creek bed. All of the ponds observed during the survey were manmade and recharged by surface runoff. The water levels in most of the ponds were low, and a few were dry. There was evidence of seeps along the sides of some hills. The soil in these areas was generally damp with some moss growth. As these seeps were on hillsides and flow is intermittent in these areas, the seeps are probably the result of rainfall infiltration moving laterally along horizontal fractures or bedding planes. Some of the seeps were observed along the creek bed upstream of the pond near well I (see Figure 4.1).
Given the stair-stepped structures and the location of the Corbula bed observed during the survey, the CSSA facility appears to be entirely on Upper Glen Rose limestone. The depth of the Upper Glen Rose appears to thin to the south across the site. The numerous caves and fracture openings indicate that there are probably several caves, solution cavities, and fractures in the Upper Glen Rose beneath CSSA.
Research of Potential Source Areas
ES initiated review of CSSA waste management records under this project and identified at least seven potential source areas regarding halogenated volatile organic contamination of groundwater. There are more than twenty waste management areas at CSSA which ES is currently evaluating in a separate project of environmental assessment. This report is due to CSSA in spring 1993. Should the Environmental Assessment identify additional areas of concern to the groundwater contamination, those areas will be addressed in the future SI.
The seven potential source areas that may be related to groundwater contamination in wells 16, 2, 3, 4, and D are shown in Figure 2.2. These areas are listed by CSSA as burn areas 1 through 4, burn areas 10 and 11, and an oxidation pond (O-1). Burn areas 1 and 2 are located north of well 16 in the north pasture areas while burn areas 3, 4, 10, and 11 are located just downgradient (southeast) of well 16. The oxidation pond (O-1) was located adjacent to burn area 4.
Burn areas 1 and 2 are reported to have been used in 1954 for incineration of small arms ammunition, powder, and incendiary materials. No liquid wastes are reported to have been disposed of at this location.
CSSA records indicate that burn area 3 was used for general refuse disposal. No dates of service were reported, but the area was filled in during 1990 and 1991.
Burn area 4 was apparently used as a "classified" burn pit. The materials burned were reportedly classified papers.
CSSA used burn area 10 as an ammunition burn area. No information on dates of service is reported. This area, which is identified by a filled-in trench, is topographically lower than the oxidation pond location. A shallow excavation is in the same area as B-10 and shows signs of holding water periodically, judging from the black lichens observed on limestone outcrops in the excavation. This excavation is identified as B-11.
The oxidation pond was constructed in 1975 for the disposal of waste liquids from bluing operations, a process in which arms are treated for rust prevention. These liquids were reported to have contained metals in a water base, but also may have contained metals in a water base, but also may have contained some halogenated compounds. The recorded pond dimensions were 42 feet by 60 feet by 2.5 feet, and the pond was lined with a 10-year life-expectancy vinyl plastic. No liquids or sludges were reported as removed prior to closure. The pond was filled in 1985 by bulldozing. The vinyl liner was left in place although rendered useless. The area is currently flat with no vegetation.
ES obtained aerial photos from 1986 of the CSSA area from the Texas Natural Resources Information Service (TNRIS). Additional photos were purchased from United Aerial mapping for the years 1966, 1973, and 1991. These photos were reviewed and compared for historical locations of potential source areas of groundwater contamination.
Burn area 1 appeared to have more vegetation in the 1966 photo than in subsequent years. Burn area 2 shows minor zones of disturbed vegetation in the 1966 photo. In the 1973 photo, there are two distinct graded areas in the center of that burn area. In the 1986 and 1991 photos, the graded areas appear to have some regrowth of vegetation and are not distinct.
In the 1966 photo, burn area 3 appears to cover a larger extent than in the later photos. Burn area 4 does not show up in the 1966 photo. In the 1973 photo, a small square is cleared in that vicinity. The 1986 and 1991 photos show an enlarged zone cleared of vegetation. The oxidation-evaporation pond is clearly observed in the 1989 and 1991 photos. According to the records, the pond was constructed in 1975; a relatively small cleared area, however, can be seen in the 1973 photo.
Summary of Hydrogeologic Conditions
The Trinity group aquifer is the only source of drinking water in northern Bexar County. This aquifer is divided into three hydrologic units consisting of the lower, middle, and upper Trinity aquifers. The lower Trinity aquifer is composed of the Hosston Sand and the Sligo Limestone, the middle Trinity aquifer is composed of the Cow Creek Limestone and the lower Glen Rose Limestone, and the upper Trinity aquifer is composed of the upper Glen Rose Limestone.
The lower Trinity aquifer is not widely used in the Bexar County because of its great depth to water and poor water quality. The upper Trinity aquifer is also not used widely because of its poor water quality and low yield. The middle Trinity aquifer is the most widely utilized of the three hydrologic units.
Middle Trinity water is recharged by surface infiltration and stream flow losses across exposed rock units. Solution-enlarged fractures and solution cavities are the primary routes of groundwater recharge. In areas where the upper Trinity (upper Glen Rose) is appreciably thick, vertical migration of water is inhibited by marl and clay layers in the upper unit. This water is usually discharged by natural rejection in the form of springs.
Groundwater flow in the middle Trinity is to the south and southeast. In areas of heavy pumpage, the flow gradients are influenced by pumping wells. Water levels in the middle Trinity are related to rainfall amounts and amount of water pumped. During times of drought, recharge is limited and water levels decline. In areas of heavy pumpage, water levels have declined and have remained low because of the aquifers' low capability to transmit water.
All wells at CSSA are completed in the middle Trinity aquifer. The aquifer appears to be under unconfined (water table) conditions, and the estimated flow gradient is to the south-southeast at a rate of 0.003 foot per foot. The upper Trinity aquifer exists only as isolated perched zones which transmit water horizontally. The relatively thin upper Glen Rose does not contain any sitewide confining layer to which restricts vertical migration. Therefore, most water that infiltrates the CSSA surface soils may have vertical pathways to the middle Trinity aquifer through solution cavities and fractures.
Most water wells at CSSA are open-hole completion type wells. Only well 1 is cased the entire depth of the hole, with an unknown interval perforated for water entry. Well 10 has 390 feet of surface casing while wells 2, 3, 4, 6, 9, 16, and D have up to 60 feet of casing. The wells without deep casing are susceptible to water infiltration through permeable layers in the shallow subsurface.