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On May 5, 1999 an Administrative Consent Order was issued to CSSA pursuant to �3008(h) of the SWDA, as amended by the RCRA, and further amended by the HSWA of 1984. In accordance with the RFI requirements of the Consent Order concerning groundwater characterization, this report has been prepared to document installation of three groundwater monitoring wells. Parsons performed this effort under the U.S. Air Force AFCEE Contract F41624-94-D-8136, Delivery Order DO23. AFCEE provided technical oversight for the delivery order.
Based upon the project SOW, a set of work plans to govern the fieldwork was established. These include:
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| Work Plan Addendum (Volume 1-1, DO23 Work Plan Addendum); |
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| Related Work Plan Addendum (Volume 1-2, RL83 Work Plan); |
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| Field Sampling Plan (Volume 1-4, DO23 Addendum); and |
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| Health and Safety Plan (Volume 1-5, DO23 Addendum). |
For this report, Section 1 provides the report purpose and regulatory basis. Section 2 describes well installation methodology. Section 3 summarizes the conclusions and provides recommendations. References cited in this report can be found in the Bibliography (Volume 1-1 of the Environmental Encyclopedia).
This project was conducted to monitor groundwater downgradient of SWMU B-3 and SWMU O-1 located at CSSA. SWMU B-3 and SWMU O-1 are believed to be sources of tetrachloroethene (PCE) and other chlorinated solvents found in groundwater samples from Well CS-16. See Figure 1, Well Location Map. The scope of work included installation of three new monitoring wells in the vicinity of these two SWMUs. Data from the monitoring wells are expected to aid in determining groundwater contamination sources and further define the local hydrogeology. The new wells are designated CS-MW3-LGR, CS-MW4-LGR, and CS-MW5-LGR, the �LGR� referring to installation of the wells in the Lower Glen Rose Formation. Evaluation of data from these new wells, in conjunction with 12 wells installed under a separate delivery order (AMC RL83), will be used to help determine attitudes and extent of faulting around Well CS-16, whether faults act as barriers or conduits for groundwater flow, whether fault zones affect groundwater gradient and flow direction, and the direction and rate of contaminant migration. The overall hydrogeologic evaluation will be reported under RL83. This report is intended to summarize only the work associated with wells CS-MW3-LGR, CS-MW4-LGR, and CS-MW5-LGR.
As a branch of the Department of Defense, CSSA is subject to federal and state environmental laws. Specifically, the Safe Drinking Water Act (SDWA) applies to wells that serve at least 25 people. When in active use, Well CS-16 was subject to SDWA rules. The EPA Administrative Consent Order issued to CSSA pursuant to �3008(h) of the SWDA, as amended by the RCRA, and further amended by the HSWA of 1984, requires the characterization of groundwater. Furthermore, 40 Code of Federal Regulations (CFR) Part 260, promulgated under RCRA, establishes requirements and standards for groundwater protection. Upon verification of solvent contamination in Well CS-16 (August 23, 1991) CSSA inactivated Well CS-16 and notified water users as required by state and federal regulations. CSSA then voluntarily initiated a groundwater investigation. Additional information concerning groundwater investigation activities completed to date at CSSA can be found in the Groundwater (Volume 5 of the Environmental Encyclopedia).
This project is authorized under AL/OEB Contract F41624-94-D-8136/DO23, data item No. A001a. AFCEE provided technical oversight for this delivery order. The SOW defined preliminary evaluation actions such as record reviews, groundwater sampling, and preparation of project plans. The SOW was modified to include investigation actions to define possible contaminant source areas and the installation of monitoring wells. Based on the applicable SOW, a work plan under the DO23 Work Plan Addendum was established (Volume 1-1, Section 8, D023 Work Plan Addendum). To streamline work efforts, the drilling program included wells under orders DO23 and RL83, accomplished under the same technical specifications and quality control as appropriate.
General information and figures regarding the history and environmental setting of CSSA are provided in the Background Information Report (Volume 1-1 of the Environmental Encyclopedia). In that report, data regarding geology, hydrology, and physiography are also available for reference. Additional information regarding the environmental setting can be located in the Groundwater Investigation and Associated Source Characterization, June 1996 (Volume 5 of the Environmental Encyclopedia).
The Upper Glen Rose Formation is the uppermost geologic stratum in the area of drilling. The Upper Glen Rose consists of beds of blue shale, limestone, and marly limestone, with occasional gypsum beds. Generally, it outcrops in stream valleys and at the ground surface where soils are poorly developed or eroded. Where present at CSSA, the Upper Glen Rose may be up to 150 feet thick. It is underlain by the Lower Glen Rose, which is estimated to be 300 feet thick beneath CSSA. The Lower Glen Rose is a massive, fossiliferous, vuggy limestone that grades upward into thin beds of limestone, marl, and shale. The Lower Glen Rose is underlain by the Bexar Shale facies of the Hensell Sand, which is estimated to be from 60 to 150 feet thick under the CSSA area. The Bexar Shale consists of silty dolomite, marl, calcareous shale, and shaley limestone. The geologic strata dip approximately 10 to 12˚ to the south-southeast at CSSA.
Based on current published information, there are two known major fault (shatter) zones at CSSA: the North Fault Zone and the South Fault Zone. Additional information on structural geology at CSSA can be found in the Background Information Report, Soils and Geology (Volume 1-1 of the Environmental Encyclopedia). Drilling logs indicate that limestone was encountered at depths ranging from 4 to 11 feet below ground surface (bgs). (Appendix A).
In general, the uppermost hydrogeologic layer at CSSA is the unconfined Upper Trinity aquifer, which consists of the Upper Glen Rose Limestone. Locally at CSSA, low-yielding perched zones of groundwater can exist in the Upper Glen Rose. Transmissivity values are not available for the Upper Glen Rose. Regionally, groundwater flow is thought to be enhanced along the bedding contacts between marl and limestone; however, the hydraulic conductivity between beds is thought to be poor. This interpretation is based on the observation of different static water levels in adjacent wells completed in different beds. Principle development of solution channels is limited to evaporite layers in the Upper Glen Rose Limestone. Groundwater discharge occurs predominantly via natural springs, seeps, and pumping.
The Middle Trinity aquifer is unconfined and functions as the primary source of groundwater at CSSA. It consists of the Lower Glen Rose Limestone, the Bexar Shale, and the Cow Creek Limestone. The Lower Glen Rose Limestone outcrops north of CSSA along Cibolo Creek and within the central and southwest portions of CSSA. As such, principal recharge into the Middle Trinity aquifer is via precipitation infiltration at outcrops. At CSSA, the Bexar Shale is interpreted as a confining layer, except where it is fractured and faulted, therefore allowing vertical flow from the up-dip Cow Creek Limestone into the overlying, but down-dip Lower Glen Rose. Fractures and faults within the Bexar Shale may allow hydraulic communication between the Lower Glen Rose and Cow Creek Limestones. Regional groundwater flow within the Middle Trinity aquifer is toward the south and southeast and the average transmissivity coefficient is 1,700 gpd/ft (Ashworth 1983). Based on historical water level data from on-post wells, groundwater at CSSA generally flows in a north to south direction. However, local flow gradient may vary depending on rainfall, recharge, and possible well pumping.
Background information regarding groundwater investigations conducted to date can be found in the Environmental Encyclopedia (Volume 5-2, Groundwater List of Previous Investigation Reports). Since 1992 continued groundwater investigation incorporating existing and newly-installed wells has been performed under the following Work Plan Addendums: Order 67, DO23, RL74, DO5084 and RL83. Additional information concerning these Work Plans is available in the Environmental Encyclopedia (Volume 5-1, Groundwater, Previous Monitoring Reports).