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March 2003 On-Post Quarterly Groundwater Monitoring Report
Section 5 - Summary
An average decrease in water levels of 8.47 feet occurred between December 2002 and April 2003. CSSA had 5.49 inches of rainfall between December 16, 2002 and March 15, 2003. Rainfall events during the 3-month period show the majority of rainfall occurred in mid February 2003. One rainfall event exceeded 1 inch during a 24-hour period.
The groundwater potentiometric surface map (Figure 2-1) for April 2003 shows groundwater flow to be variable throughout the facility; in the southwest corner of the facility, groundwater flow is to the southwest and south. Flow in other areas of CSSA is generally to the south and southeast, with exceptions to the northwest at the central portion of CSSA. Groundwater extraction from both on- and off-post drinking water supply wells, varying rates of recharge from rain events, and differences in well completions all contribute to the complexity of the potentiometric surface at CSSA.
The LGR potentiometric surface map near Building 90 indicates a groundwater flow to the south in April 2003, consistent with the flow direction in December 2002 (south). The flow direction in the CC formation is to the south in April 2003.
Two newly-installed wells were sampled during this event (CS-MW1-BS and CS-MW1-CC). All detections in these wells were below the applicable MCLs.
Three wells (CS-MW16-LGR, CS-D, CS-MW1-LGR) had detections above the applicable MCL for some or all of PCE, TCE, and cis-1,2-DCE. Wells CS-MW16-LGR, CS-D, CS-MW1-LGR.
Eliminating toluene results due to sampling methodology, 10 other wells had detections of VOCs above the RL for one or more of the following analytes: bromoform, bromodichloromethane, chloroform, cis-1,2-DCE, 1,1-DCE, trans-1,2-DCE, dibromochloromethane, methylene chloride, naphthalene, PCE, TCE, and vinyl chloride. These wells consisted of monitoring and livestock wells CS-MW1-BS, CS-MW2-LGR, CS-MW4-LGR, CS-MW5-LGR, CS-MW9-LGR, CS-MW10-LGR, CS-MW19-LGR, and current and former drinking water wells CS-1-NP, CS-10 and CS-11.
Eliminating toluene results due to sampling methodology, 21 other wells had VOC concentrations detected above the MDL, but below the RL (F flagged results) for one or more of the following analytes: chloroform, chloromethane, cis-1,2-DCE, methylene chloride, naphthalene, PCE, TCE, 1,2,4-trimethylbenzene, and styrene. These wells consisted of monitoring and livestock wells CS-2, CS-MW1-CC, CS-MW6-LGR, CS-MW6-BS, CS-MW6-CC, CS-MW7-LGR, CS-MW7-CC, CS-MW8-LGR, CS-MW8-CC, CS-MW9-BS, CS-MW9-CC, CS-MW10-CC, CS-MW12-CC, CS-MW12-BS, CS-MW17-LGR, CS-MW18-LGR, CS-MWH-LGR and drinking water wells CS-1, CS-10-NP, CS-9-NP, and CS-9.
Eliminating toluene results due to sampling methodology, four other wells had no VOC detections above the MDL for any analyte (CS-11, CS-MW3-LGR, CS-MW12-LGR, and CS-MWG-LGR).
On-post drinking water wells CS-1, CS-9, and CS-10 each had a detection of PCE above the MDL at concentrations of 0.08 mg/L, 0.055 �g/L, and 0.09 �g/L, respectively. TCE exceeded the MDL in CS-1 at a concentration of 0.15 �g/L. Samples collected prior to purging (CS-1-NP, CS-9-NP, and CS-10-NP) reported no PCE and/or TCE detections. Results from non-purged samples were inconclusive on the affect of purging on concentrations. Additional non-purged samples should be collected at the next groundwater monitoring event.
Of the wells sampled for metals in March 2003, no concentrations were above the appropriate MCL, AL, or secondary standard.
PCE concentrations increased this quarter in monitoring wells CS-MW2-LGR, CS-MW4-LGR, CS-MW5-LGR, CS-MW8-LGR, CS-MW17-LGR and CS-MW19-LGR as well as in drinking water well CS-9.
TCE concentrations increased this quarter in monitoring wells CS-D, CS-MW2-LGR, CS-MW4-LGR, CS-MW5-LGR, CS-MW6-BS, and CS-MW8-LGR.
Cis-1,2-DCE concentrations increased this quarter in monitoring wells CS-D, CS-MW2-LGR, CS-MW4-LGR, CS-MW5-LGR, CS-MW6-CC, CS-MW8-LGR, CS-MW9-LGR, CS-MW9-CC, and CS-MW18-LGR.
PCE concentrations decreased this quarter in monitoring wells CS-MW16-LGR, CS-MW1-LGR, and CS-MW10-LGR, as well as in drinking water well CS-1 and CS-10.
TCE concentrations decreased this quarter in monitoring wells CS-D, CS-MW16-LGR, and CS-MW1-LGR, as well as in drinking water well CS-1.
Cis-1,2-DCE concentrations decreased this quarter in monitoring well CS-MW1-LGR.
Figure 5-1, Figure 5-2, and Figure 5-3 are included for evaluation of the concentrations of PCE, TCE, and cis-1,2-DCE over time in wells where these compounds have exceeded the MCL (CS-D, CS-MW16-LGR, CS-MW1-LGR, and CS-MW2-LGR). Concentrations have varied greatly over time with generally increasing trends over the last three months of groundwater monitoring in well CS-D. PCE and TCE concentrations in well CS-MW16-LGR decreased slightly over the last three months. Concentrations of PCE and TCE in well CS‑D were the highest since the well was first sampled in December 1991. Wells CS-MW1-LGR and CS-MW2-LGR concentrations have remained relatively constant.