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June 2000 On-Post Quarterly Groundwater Monitoring Report
Section 4 - June 2000 Analytical Results
Groundwater sampling was performed June 12 through 14, 2000 at CSSA. Nine onsite wells were sampled in June 2000: 1, 2, 9, 10, 11, 16, I, MW1, and MW2. In addition, one of the offsite wells, Well LS-7, was sampled during this monitoring event. As noted earlier, Well D was not sampled during this event because the water level was below the pump depth and Wells G and H were not sampled due to inoperable sucker rods in these wells. The data package RL74-08 contains the VOC and metal analytical results for this monitoring event. This data package was received by Parsons ES on July 11, 2000; validated and submitted to AFCEE by July 27, 2000; approved by AFCEE on August 14, 2000; and, resubmitted to AFCEE on January 12, 2001. Analytical results for June 2000 are presented in Table 2. VOC trends over time for Well 16 are depicted graphically in Figure 3.
4.1 - Volatile Organic Compound Analyses
Concentrations of TCE, PCE, and cis-1,2-DCE that exceeded maximum contaminant levels (MCLs) were detected in Well 16. The results for Well 16 showed that cis-1,2-DCE and TCE concentrations increased somewhat as compared to the March 2000 sampling event and that the concentration of PCE decreased slightly (as shown in Figure 3). Well MW2 was found to have PCE and TCE concentrations that exceeded MCLs and a cis-1,2-DCE concentration that was below the MCL. MW1 had concentrations of all three of the compounds that were below MCLs. The latest data support the assumption that it is possible that MW1 and MW2 are located on the outskirts of the same plume encompassing Well 16. In addition, levels of trans-1,2-DCE that were below the reporting limit (RL) but above the method detection limit (MDL) exist in Wells MW1 and MW2.
Concentrations of chloroform and TCE that were below the RL were found in Well 1. Well 10 had a chloroform concentration that was above the MDL. Chloroform was not detected in Well 11 after three consecutive sampling events where it was detected. A PCE concentration of 0.41 mg/L was detected for the first time in Well 11 during this monitoring event. Although Well 11 is out of service, the PCE detection is a significant finding because Well 11 is located near Wells 9 and 10, which are used for potable water at CSSA. In addition, Well 11 is located near the western boundary of CSSA.
The data package RL74-08 contains the metals analytical results for this monitoring event. No metal concentrations exceeded the MCLs during this sampling event.
4.3 - Offsite Groundwater Monitoring
A sample was collected from private Well LS-7 during this sampling event. No contaminant levels above MCLs were found, but a PCE concentration of 2.2 mg/L was detected. In addition, TCE and chloroform were detected at concentrations above the MDL but below the RL.