SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

batch number in either ascending or descending order, not both, with the appropriate supporting documentation (i.e. , chains-of-custody, and letters of verification from the laboratory) in front of each batch. Many of the laboratory sheets had no batch numbers, wells numbers or any identifying notations other than "See below" with many sheets identified this same way following or preceding, depending on which way the particular batch was organized (i.e. , ascending or descending) . GENERAL COMMENTS 16. Of some concern in the overall characterization of the groundwater contaminant plume, is the fact that only a very brief mention is made of the on-site water production wells. A work plan outlining abandonment of Water Well Nos. 1 and 2, and sampling of Well Nos. 4 , and 7 was presented in October 1991 by DDRW-Tracy. Based on our review of boring logs and well construction and history from that work plan, it seems evident that these wells may be much more important to the characterization of the possible downward migration of contaminants into the Lower Tulare than has been inferred by their brief mention in this report. According to that October 1991 work plan, analytical data from Well No. 7 could be very useful in a quarterly monitoring program in order to establish water quality data at the upgradient boundary of the DDRW-Tracy site. • Analytical data obtained from Well Nos. 1 and 2 should be incorporated into future RI/FS data analysis. 17 . Analytical results for well LM-88 , completed in the Lower Horizon, at the east-northeastern boundary of the site just east of Building 100 showed an increase in the detected concentration of tetracholoroethene (PCE) to 6. 18 µg/1. Prior to the August 1991 sampling round all three of the wells in this cluster (LM-75, LM-78 and LM-88) were below detectable limits for both TCE and PCE. 18. Well LM-24, completed in the Upper Horizon approximately 520 feet to the east (cross-gradient) from LM-88 has historically shown a high concentration of PCE. In the Radian, 1986 report, the results of laboratory analyses of a sampling round showed a concentration of PCE in LM-24 of 780 µg/1. This level decreased steadily to a level of 250 in 1987 , and to its level in the August 1991 sampling round of 11. 1 µg/1. Based on the historical analytical results and geologic cross-section presented in WCC Draft RI/FS (1991a; Figure 3 . 4-6) , it seems feasible that the source for the PCE in L24-88 may be in the area of LM-24 . PCE is heavier and 5 of 7