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r OIR " 12 190 14 : 26 FRO UNTER-ESE G-UILLEAtte-I-L PRGE . 002 C ��C.c�1zP i l�2s iM N°v uS/a�k . 4 CA srz} cam` R CiS �r -TE C-SHADRI , /SP-3.59 11/28/89 lies just above the shallowest true aqu fer unit. Wells 402A and 418A are older wells installed during the initial assessment effort at SHAD. Figs, 3.6-6 and 3.6-7 are cross sectioni perpendicular to the downgradient end of Plume 1. These fig res show that the B and C aquifer zones are apparently well inter onnected in this area. Differences in aquifer zone labeling ar4 not significant in Plume 1 because the lateral extent of the pl,=e is approximately equal in all three aquifer zones. Contaminant concentrations in almost all wells in this plume are generally trending lower due to the ope ation of the South Balloon Area groundwater treatment system. Concentr tions measured in well 418C had increased for a time (in late 1988) but now appear to be declining again. The extreme downgradient edge of Plume 1 is defined by well 445, where concentrations are always between the detection limit and the California State Action Level (CSAL) . Additional definition of the S- and C-zones on the downgradient edge of the plume is required to better monitor the performance of the treatment system and to select the location for an additional extraction well- The 11.The following additional wells are proposed for the Plume 1 area: PW1B--To monitor the western edge cf the B-zone aquifer plume for possible contaminant migration, i.e . , for lateral definition. PW2C--Definition of C-zone plume a tent to the northwest. PW3C and D--Definition of C-zone contamination in the plume to the southwest and possible D-zone contamination to the west-southwest. These wells are located between the plume and AGW-l. G-3--This is an additional extraction well designed to capture the downgradient end of the C-zone pluze. The location of this well will be selected after further assessment of the South Balloon C-zone aquifer capture zone is con cted, following the installation of the two additional -zone wells on the downgradient end of this plume. 3-89