An average increase in water levels of 11.77 feet occurred at CSSA between March 2000 and June 2000. This average increase in water level during 2000 occurred after a continuous decrease between September 1999 and March 2000. The decrease in water levels is due to the inferred increase in water demand by surrounding residential and commercial developments and due to drought conditions that occurred throughout 1999 and have persisted into 2000.

The potentiometric maps indicate that the groundwater flow direction was generally to the southeast during the June 2000 sampling event. The potentiometric maps were developed on the assumption of the Middle Trinity Aquifer being one uniform formation and this has yet to be determined. �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.

A PCE concentration of 2.2 mg/L was detected in Well LS-7 during this monitoring event. TCE and chloroform were also detected at concentrations below the RL in this well.

TCE, cis-1,2-DCE, and PCE concentrations in Well 16 remained at levels similar to those found during the March 2000 sampling event. 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 concentrations of all three compounds have generally been decreasing since that time and there have been only two precipitation events of two inches or more since October 1998. The concentration of trans-1,2-DCE rose above the detection limit again after not being detected during the last sampling event which was the first non-detect of this compound in Well 16 since February 1996. The concentration of trans-1,2-DCE during the June 2000 sampling event was, however, below the RL. 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 biodegradation 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 was detected in Well 11 for this first time at a concentration of 0.41 mg/L during this monitoring event. This is a significant finding because Well 11 is located near the potable water supply Wells 9 and 10 and the western boundary of CSSA.

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 far below MCLs.

Lead concentration fell below its action level in Well 1 with a concentration of 0.0043 mg/l after rising above the MCL during the March 2000 sampling event. Lead concentrations have exceeded the MCL in this well three times before; December 1995, January 1997, and in March 2000. Lead has previously exceeded its action level (0.015 mg/L) in Wells 1, 2, 3, D, G, H, and I.�

Well 1 had concentrations of TCE and chloroform that were below the RL during this sampling event. PCE was not detected in Well 1 after two consecutive sampling events where it was detected although the levels were far below the MCL. 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.