A summary of March 2004 detections above the MCL, below the MCL, below the RL, and increases and decreases for various VOCs since the December 2003 event is included in Table 6-1.

An average increase in water levels of 27.73 feet occurred between December 2003 and March 2004. CSSA had 6.35 inches of rainfall between December 8, 2003 and March 5, 2004.

The LGR groundwater potentiometric surface map (Figure 2-1) for March 2004 shows groundwater flow to be variable throughout the facility. Groundwater flow was to the east in the southwest corner of the facility. Flow in other areas of CSSA is generally to the south and southeast, with exceptions 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 the inherent complexity of groundwater flow in a fractured limestone aquifer, all contribute to difficulties in interpreting the potentiometric surface at CSSA.

The LGR potentiometric surface map near Building 90 indicated a groundwater flow to the east and the CC potentiometric surface map near Building 90 indicated a groundwater flow to the northeast in March 2004.

Figure 6-1 through Figure 6-3 are included for evaluation of the concentrations of PCE, TCE, and cis-1,2-DCE over time in wells where those compounds exceeded the MCLs (CS‑D, CS‑MW16‑LGR, CS‑MW1‑LGR, and CS‑MW2‑LGR).

Metals were sampled in March 2004 in drinking water wells, and no concentrations were above the appropriate MCL, AL, or secondary standard.

Low levels of vinyl chloride have been detected sporadically in CSSA monitoring wells. During the March 2004 sampling event, vinyl chloride was detected in two wells: CS‑MW12-BS and CS-MW16-CC. These detections, 0.099 and 0.29 mg/L, respectively, are below the MCL.

March 2004 laboratory results indicated methylene chloride in all samples. Historical data review indicates methylene chloride was introduced as a laboratory contaminant and was not present in the groundwater. Methylene chloride is a common laboratory contaminant and there are no known historical uses of methylene chloride on-post.