Water levels decreased an average of 9.26 feet at CSSA between December 1999 and March 2000. The decrease can be attributed to very little precipitation since the summer of 1999 and it is also due in part to the increase in water demand by surrounding residential and commercial developments.

The potentiometric maps indicate that the groundwater flow direction varied from south to southeast during the March 2000 sampling event.� Recent pumping of groundwater appears to have influenced the water table at CSSA, though it is unknown if pumping significantly affects off-base groundwater flow.

TCE, cis-1,2-DCE, and PCE concentrations decreased in Well 16 between December 1999 and March 2000.� This was the second consecutive sampling event where a reduction in the concentration of these three compounds occurred.� Unusually high TCE, PCE and cis-1,2-DCE concentrations were recorded in Well 16 during a November 1998 sampling event and were associated with an extremely large amount of rainfall in October 1998.� The concentration of trans-1,2-DCE fell below detection limits for the first time since February 1996.� Before this sudden decrease however, trans-1-2-DCE had exhibited a concentration increase by a factor of about 1.6 from September 1999 to December 1999.� This increase in trans-1-2-DCE concentration may have been attributable to the process of reductive dechlorination whereby trans-1-2-DCE is produced as a daughter product during natural biodegredation of the more highly chlorinated solvents.� Reductive dechlorination occurs by sequential dechlorination from PCE to TCE to DCE to vinyl chloride to ethene (Wiedemeier, Swanson, Moutoux, Gordon, Hansen, Haas, Wilson, Kampbell, and Chapelle, 1994).� It was noted by Bouwer (1994) that intermediate compounds of DCE formed during sequential dechlorination are more commonly found as cis-1,2-DCE rather than trans-1,2-DCE with 1,1-DCE being the least likely daughter product.

PCE and TCE concentrations above MCLs were observed in MW2.� The MW1 well had concentrations of these two compounds that were below MCLs.� Concentrations of both these contaminants in Well MW1 have been decreasing since the November 1998 sampling event.� The concentrations of these contaminants were much higher in Well MW1 at that time, possibly due to the high October 1998 rainfall.� Conversely, concentrations of TCE and PCE in Well MW2 have been relatively stable since November 1998.� Wells MW1 and MW2 also had concentrations of cis-1,2-DCE that were below MCLs.

Lead was detected above its action level in only a single well, Well 1, at a concentration of 0.0172 mg/L.� Lead concentrations have exceeded the MCL in this well twice before, once in January 1997, and in December 1995.� Lead occurred in Well 11 at a concentration of 0.0108 mg/l.� Lead has previously exceeded its action level (0.015 mg/L) in Wells 1, 2, 3, D, G, H, and I.

Well 1, which is a potable water supply well for CSSA, had concentrations of PCE, TCE, and chloroform that were below the RL during this sampling event and also during the December 1999 sampling event.� The PCE level in this well rose above the MDL for the first time in December 1999.� The TCE level in Well 1 was first detected above the MDL in November 1998.� Chloroform concentrations in this well first exceeded both the MDL and RL in November 1992 and have sporadically exceeded both levels since that time.