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December 1995 Quarterly Groundwater Monitoring Report
Quarterly groundwater monitoring was performed the week of December 11, 1995 at Camp Stanley Storage Activity (CSSA). This work was performed under contract F33615-89-D-4003, Order 67, Mod 2.
Groundwater elevations decreased between June 1995 and December 1995. Groundwater flow direction was to the southwest during this period. Historical groundwater elevations from October 1992 through December 1995 are shown in Table 1.
All wells were measured with an electric water level indicator (e-line) except wells 10 and 11 which were measured by the air-line method. The submersible pump and piping were removed from well 11 on December 14, 1995 by Venture II environmental drilling services to allow well 11 to serve as a monitoring well. Groundwater elevations for well 11 may now be taken by e-line.
Pumping recovery duration for wells 9 and 10 is unclear and the recovery time after pipe removal for well 11 was insufficient to permit an accurate water level reading. Pump and pipe removal also revealed that the pump depth of 483 feet below top of casing (BTOC) recorded for well 11 was incorrect. Actual pump depth was 507 feet BTOC.
Groundwater potentiometric elevations using e-line measurements from December 1995 are depicted on Figure 1. The potentiometric surface map indicates that the groundwater hydraulic gradient of 0.005 feet per foot is to the southwest. This flow direction is inconsistent with all previous monitoring results except for September 1994.
The average decrease in groundwater elevations from August to December 1995 was 6.59 feet. Groundwater monitoring results for September 1994 and December 1995 exhibit unique flow directions and similarly low groundwater elevations which may indicate a correlation.
The 1995 halogenated volatile organics (HVO) analytical results for groundwater samples collected in March, June, August, and December are shown in Table 2. Metals analyses were run on groundwater samples collected in December 1995 and re-tested on January 19, 1996. Analytical results for the metals are shown in Table 3. Groundwater samples at well 11 were taken by bailer as pump and piping were removed. December 1995 and January 1996 data has been validated by Parsons ES. Quality assurance summary reports are provided in Appendix A.
Volatile Organic Compound Analyses
Three compounds were dtected in wells 16 and D: trichloroethene (TCE), tetrachloroethene (PCE), and cis-1,2-dichloroethene (DCE). The concentrations of these compounds decreased from August to December 1995 in well 16 and increased in well D for the same period. Figure 2 and Figure 3 show the fluctuations in contaminant concentrations over time.
Metals Analyses
CSSA water wells were analyzed for arsenic (SW 7060), barium (SW 6010), cadmium (SW 6010), chromium (SW 6010), copper (SW 6010), lead (SW 7421), mercury (SW 7470), nickel (SW 6010), and zinc (SW 6010). Six CSSA wells exhibited values above maximum contaminant levels (MCLs) for lead. The wells above MCLs were re-tested January 19, 1996. Inchcape Testing Services was contracted to perform a lab audit on the re-test. Re-test analyses indicate agricultural wells G and I were above the MCL for lead, and well 1 was at the MCL. Well 2 was at the MCL for cadmium and zinc values were high in wells G and I.
Private Well Analyses
Four private off-site wells were sampled December 11 and 13, 1995 for the same VOC and metal analytes specified for CSSA wells. All VOC analyses were below MCLs with the exception of one well. Lead was present at 0.017 mg/L in OS-1. Results are listed in Table 4 and Table 5.
Water levels were an average of 6.59 feet lower in December 1995 than measured in August 1995.
The potentiometric map indicates a southwesterly groundwater flow direction.
PCE, TCE, and cis-1,2-DCE concentrations decreased in well 16 between August 1995 and December 1995.
PCE, TCE, and cis-1,2-DCE concentrations increased in well D between August 1995 and December 1995.
Lead was above the MCL in wells G and I, and at the MCL in well 1. Cadmium was at the MCL in well 2.