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GEOMATRIX ' Groundwater samples from MW-15 previously contained detectable concentrations of chloroform, 1,2- DCP DBCP and the organochlorine pesticide dieldrin. However, the concentrations of these constituents in groundwater have been decreasing at an exponential rate. For example, the concen- tration of 1,2-DCP decreased from 55 to 0.6 ug/C between the first sample in April 1996 and March ' 1997. There have been no concentrations of any organic constituent above the method detection limit in MW-15 since July 1997. DBCP concentrations in samples collected from MW-15 have similarly ' decreased to less than the analytical detection limit. This suggests that the elevated concentrations of 1,2-DCP and DBCP detected in groundwater samples from this well may be an artifact of well construction and may not be representative of groundwater quality in the intermediate zone. Similarly, ' the single detections of chloroform and dieldrin at concentrations slightly higher the detection limits in the first sample collected from MW-15 may also be artifacts of well construction. ' Groundwater samples collected from the four intermediate zone monitoring wells at the Facility also ' contain the inorganic constituents chloride, nitrate, and TDS at concentrations comparable to those detected in upgradient intermediate zone well MW-17. Historically, chloride concentrations range between 270 and 660 mg/C, nitrate concentration range between non-detected (less than 0.5 mg/C) and 0.42 mg/C, and total dissolved solids(TDS)concentrations range between 940 and 2,200 mg/f. Downgradient Area Analysis of groundwater samples collected from three shallow-zone monitoring wells located down- gradient of the Facility indicate that shallow groundwater has been impacted by Facility operations. ' Shallow groundwater samples collected from two of these shallow zone monitoring wells contain detectable concentrations of several organic constituents, including: • the VOCs chlorobenzene, chloroform, and 1,2-DCP; ' . the triazine pesticide atrazine; • the chlorinated herbicide dinoseb; and ' . the fumigant DBCP. In addition, groundwater samples collected from several shallow zone monitoring wells contained the t inorganic constituents ammonia, chloride, nitrate, and TDS at elevated concentrations compared to the upgradient shallow zone well (MW-16). Historically, concentrations of ammonia range from non- detected (ND) to 17 mg/f, concentrations of chloride range from 180 to 890 mg/t, concentrations of nitrate range from 34 to 400 mg/C, and concentrations of TDS range from 1,900 to 3,700 mg/C. There are no intermediate zone monitoring wells located downgradient of the Facility. However, discrete-depth groundwater samples have been collected from the intermediate zone and deeper zone at ' three locations downgradient of the Facility. These intermediate and deeper zone groundwater samples BPROMMC383%1 U8 383 37. 8