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Groundwater Investigation and Associated Source Characterization
Section 4 - Preliminary Assessment
The groundwater evaluation at CSSA began in October 1992 with actions intended to provide sufficient data to prepare plans of work. Therefore, the preliminary evaluation included a review of available records, an inventory and survey of existing water wells at CSSA, groundwater sampling and analysis, a geologic field survey, and a downhole camera survey. Four deliverables were submitted in 1993 to CSSA, EPA, and TNRCC.
Publications regarding the geology and hydrogeology of the area were reviewed for pertinent information about the CSSA area. Records on file with CSSA were also reviewed to gather information about potential source areas of groundwater contamination. The results of the geologic and hydrogeologic records review were discussed in the hydrogeologic report (ES,1993a). Information indicative of source areas was incorporated in the work plan (ES,1993c).
Parsons ES identified at least six potential source areas regarding halogenated volatile organic contamination of groundwater (ES, 1993c). Each site was located by researching historical aerial photos for indications of graded areas, trenches, and distressed vegetation and was field-verified. More than thirty solid waste management units at CSSA are identified (ES,1993d). Table 4.1-1 summarizes the results of the records review for the seven SWMUs that were identified for the well 16 source characterization.
4.2 - Water Well Inventory and Surveying
A preliminary assessment was performed to evaluate the current status of all CSSA water wells and determine the hydrogeologic conditions of the site without using invasive techniques, such as drilling. Well records were researched and a site visit was conducted by Parsons ES to verify the well location and condition. Water level measurements, well depths, and other pertinent information were obtained during the visit. Figure 2.4-5 shows the locations of the wells.
Information obtained from the record search included date drilled, total depth, casing depth, historical use of the well, location, and lithologic logs when available. Geophysical logs of wells 9, 10, and 11 from1958 TWDB records were also located. An in-depth discussion of the well locations and conditions are discussed in the hydrogeologic report(ES,1993a).
After locating the wells, Northstar Land Surveying performed a survey to locate each well with respect to state plane coordinates and determine the elevation of top-of-casing (TOC) with respect to mean sea level (MSL). This information was used to determine the groundwater potentiometric surface elevations and probable groundwater flow direction. The survey data is in Appendix E.
4.3 - Groundwater Sampling and Analysis
Previous well sampling and analysis by the TDH and the TWC (now TNRCC) in August and December 1991 indicated the presence of dissolved halogenated volatile organics in the groundwater from well 16, then an active water supply well. The results of the TWC analysis were provided to CSSA over the phone in January 1992.
In November 1992, Parsons ES performed water level measurements and groundwater sampling in wells 1, 2, 3, 4, 6, 10, 16, D, G, H, and I to determine the current concentrations of halogenated volatile organics in the groundwater. 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 PCE and TCE below MCLs in wells 2, 3, and 4 and above MCLs in 16 and D. The results of the groundwater sampling event are further discussed in the hydrogeologic report (ES,1993a) and in Section 8.2. Historical groundwater data is located in Appendix G.
Downhole video camera surveys were conducted in wells D, 2, 3, 4, 6, and 16. The objectives of the survey were (1) to inspect the well casings for leakage and the depth of casing, (2) to determine the potential for shallow water infiltration into the well, (3) to define stratigraphic intervals, if possible, and (4) to determine obstructions and conditions for potential well abandonment. The survey was performed by Specialty Maintenance, Inc., of Houston, Texas, during the week of December 8, 1992.
A downhole video camera equipped with a fisheye lens and underwater capability was lowered 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 the supervising geologist looked for signs of groundwater movement above the water table while making observations about the condition and depth of casing, any features noted in the open borehole, and the total depth of each 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 had at least 21 feet of casing except well 4, which had 2 to 4 feet of casing or hardened cement, and well 6, which had 7 feet of casing. Casing was often moist, algae covered, and rusty in areas. Other observations included roots, spiders, leaves, twigs, frogs, insects, albino invertebrates, an albino salamander, metal banding, wood, and rocks in various wells. Water clarity varied with the 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 video survey also showed 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 MSL (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 more in-depth discussion of the downhole video survey is discussed in the hydrogeologic report and a log of each well and a schematic cross-section of the observed water zones are presented in an appendix of the report (ES, 1993a).
A field survey was conducted at CSSA over several days to verify locations of the upper and lower members of the Glen Rose Formation, to search for type localities of the contact between the two, and to attempt identification of structural features such as faults, sinkholes, and springs. As time was limited, the survey concentrated on published locations of outcrops for verification, creek beds, and quarries. The results primarily indicated that the predominant stratigraphic unit at CSSA is the upper Glen Rose, and that features such as small caves, an occasional sinkhole, and several seeps exist. The locations of these features were placed on a topographic map that included locations of the upper and lower Glen Rose members and a known fault located along the southern areas of the post published in the Geologic Atlas of Texas San Antonio sheet (1983), and an inferred fault trending northeast-southwest through the central portion of CSSA taken from an unplublished master's thesis (Watterus, 1992). Results and the map are discussed in the hydrogeologic report (ES, 1993a).
Four documents were prepared following the preliminary assessment to further define the next phase of the investigation. These deliverables were:
| A hydrogeologic report, | |
| A workplan, | |
| A sampling and analysis plan, and | |
| A health and safety plan. |
Objectives were to determine the source(s) for the contamination in well16and to evaluate the hydrogeologic systems beneath CSSA. The hydrogeologic report described the regional and site hydrogeology and stratigraphy, as well as the results of the preliminary assessment. The work plan set forth a plan of action to determine the extent and magnitude of the groundwater contamination and to assess potential sources of contamination in preparation for remedial action. The sampling and analysis plan defined the responsibilities and procedures of field actions, technical evaluations, analytical tests, and QA/QC procedures. The purpose of the health and safety plan was to establish personnel protection standards and mandatory safety procedures for all work conducted in association with the source characterization and hydrogeologic evaluation.