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November 1998 Quarterly Groundwater Monitoring Report
Section 4 - Analytical Results
The 1995-98 volatile organic compounds (VOCs) analytical results for groundwater samples are shown in Table 2. Analytical results for metals are shown in Table 3. VOC trends over time for wells D and 16 are depicted graphically in Figures 5 and 6. Samples for alkalinity, total dissolved solids (TDS) and specific conductance were only analyzed in January 1997.
Laboratory analytical data collected in January 1997, October 1997 and November 1998 are used as screening data only, due to conflicts with laboratory procedures and AFCEE QAPP requirements. These conflicts are currently under resolution. However, the next quarterly groundwater monitoring event data will be analyzed by an AFCEE approved laboratory and the data is anticipated to be viable for environmental regulatory submittal and review. Pre-1997 data and 1997-1998 data may be compared for screening purposes. Data validation findings for the November 1998 event are provided in the ITIR (Appendix A).
4.1 - Volatile Organic Compound Analyses
October 1997: These data are used for screening purposes only, as it was analyzed by ITS. VOCs were analyzed by the EPA method SW8260A. Trichloroethene (TCE), tetrachloroethene (PCE), and cis-1,2-dichloroethene (cis-1,2-DCE) were detected in Wells 16 and D at concentrations above the maximum contamination levels (MCLs). TCE and PCE were detected in Wells MW1 and MW2 above the MCLs. These data support past analytical trends associated with these wells.
Concentration levels of TCE, PCE and cis-1,2-DCE in Wells 16 and D are very similar (see Table 2). These wells are in close proximity to each other and these results likely represent the same plume of contamination. Also, concentration levels of TCE and PCE in Wells MW1 and MW2 are similar. It is possible that MW1 and MW2 are located on the outskirts of the same plume encompassing Wells 16 and D. The absence of contamination in Wells 2, 3, and 4 indicate that the extent of the plume is limited and defined to the west of Wells 16, D, MW1 and MW2.
November 1998: These data are used for screening purposes only. VOCs were analyzed by the EPA method SW8260B. This sampling round only included Wells 1, 2, 3, 10, 16, MW1 and MW2. The results for Wells 16, MW1, and MW2 were similar to the October 1997 sampling event. Overall concentrations increased slightly in Wells 16 and MW2, and remained fairly constant in MW1. The increases in the concentration levels of TCE, PCE, and cis-1,2-DCE detected in the November 1998 samples may be due to the increased rainfall in October 1998. The October 1998 rainfall led to the highest recorded water table level at CSSA since 1991. Contamination that is trapped in fractures in the limestone or in karst topography features may be flushed out into the groundwater during elevated groundwater table periods. Continued sampling and more analytical data is needed to determine if the concentrations of the observed analytes is increasing, or if the elevated concentrations observed in the November 1998 sampling event were due to the elevated groundwater table.
4.2 - Metals Analyses
October 1997: These data are used for screening purposes only. CSSA water wells were analyzed for arsenic, barium, cadmium, chromium, copper, lead, mercury, nickel, and zinc. Only Well G exhibited a value of 0.020 mg/L for lead, which is above the EPA action level of 0.015 mg/L and consistent with past trends. All other wells were below maximum contaminant levels (MCLs) for the metals listed above.
November 1998: Groundwater samples were not analyzed for metals during this groundwater sampling event.