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June 2001 On-Post Quarterly Groundwater Monitoring Report
Section 1 - Water Level Measurements
Groundwater monitoring scoped under the AETC Contract F41689-96-D-0710, Delivery Order 5084, was performed the week of June 11, 2001 at CSSA. Groundwater monitoring conducted under this order was initiated with the June 2001 sampling event and will continue through the December 2001 sampling event. AFCEE/ERD and AFCEE/ERC provide technical oversight of the monitoring program.
The current objectives of the groundwater-monitoring program are to determine groundwater flow direction and water levels, determine groundwater contaminant concentrations for characterization purposes, and identify seasonal variations in physical and chemical properties. Appendix A identifies the DQOs for CSSA�s groundwater monitoring program, along with an evaluation of whether each DQO has been attained. The objectives listed in the table also reference appropriate sections of the Order. Overall DQOs for the investigations at CSSA are provided in Volume 1-1 behind the RFI Addendum tab (Section 11).
1.0 - Water Level Measurements
Twenty-five water level measurements were recorded during the June 2001 monitoring event. Water level measurements were taken in CSSA Wells 1, 2, 3, 4, 9, 10, 11, 16, D, G, H, I, MW1-LGR, MW2-LGR, MW3-LGR, MW4-LGR, MW5-LGR, MW6-LGR, MW6-CC, MW6-BS, MW8-LGR, MW8-CC, MW9-LGR, MW9-CC, and MW9-BS. All of the water levels were measured with an e-line except for Well 10, which was measured with an air-line apparatus. An average groundwater elevation for well FO-20 from the week of June 15 was obtained from Fair Oaks Ranch Utilities.
Groundwater levels declined 47.5 feet on average between March 19, 2001 and June 11, 2001. This average increase was calculated by averaging together the groundwater elevation changes for each well. The groundwater elevations derived from water level measurements are measured against mean sea level and are summarized in Table 1. The elevations of the new monitoring wells were estimated from topographic maps and their groundwater elevations are therefore approximate. The current groundwater elevations may be compared to the historical groundwater elevations from October 1992 through March 2001 that are shown in Table 3 of the Introduction to the Groundwater Monitoring Program at Camp Stanley (Parsons ES 2001).
An average groundwater elevation for each formation in the Middle Trinity aquifer is provided in Table 1 and was calculated by using the groundwater elevations from wells screened only in that formation. The average groundwater elevations in the Lower Glen Rose, Bexar Shale, and Cow Creek formations were 1104.0 feet, 1106.9 feet, and 1093.9, respectively. Although the Lower Glen Rose and Bexar Shale formations have similar average groundwater elevations, significant differences in groundwater elevations were observed in Lower Glen Rose and Bexar Shale wells that are in the same cluster of wells.
Well MW6-LGR had a groundwater elevation of 1084.3 feet and Well MW6-BS was found to have a groundwater elevation of 1097.2 feet. The groundwater elevation difference between these two wells is 12.9 feet. The groundwater elevations in Wells MW9-LGR and MW9-BS were 1096.6 and 1116.5, respectively, which created an elevation difference of 19.9 feet between these wells.
The groundwater elevation variations between Glen Rose and Cow Creek wells in the same cluster were not as large as those observed in Glen Rose and Bexar Shale cluster wells during the June 2001 sampling event. The groundwater elevation in MW6-CC was just 1.5 feet higher than that in MW6-LGR. Likewise, Well MW8-CC had a groundwater elevation that was 3.9 feet higher than MW8-LGR. The groundwater elevation in Well MW9-CC was 1.9 feet lower than that in MW9-LGR.