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Sand B groundwater zone. It is not known if Sand C is connected hydraulically to Sand A and B. Sand zone C } r 1 has not been investigated therefore the vertical extent of MTBE distribution is not known. However, due to the historically high concentrations of MTBE(2002) in MWO-1X and the strong evidence of migration in the B Zone, it is likely that if MTBE has reached the C Zone that off site migration is also likely. It is also likely that migration in the C Zone would follow the observed patterns.in the B Zone and be to the north/nortl west.o the former i7ST location. P,(++e-,r r. t,o + 3.0 SCOPE OF WORK The scope of work and objective for this proposed site assessment includes the installation of four groundwater monitoring well clusters (MW-12 through MW-15) and the possible installation of two additional groundwater monitoring well clusters if laboratory results indicate that the extent of the plume is not identified. The location and justification for these monitoring wells is outlined below and shown on Figure 3: o One groundwater monitoring well (MW-12) will be located adjacent to well MW-8 and MW-9 to the northeast of the USTs. The purpose of this well is to collect a sample from Sand C and to determine if this zone is impacted by MTBE. This well will be screened in Sand C only since the adjacent wells are screened in Sand A (MW-9) and Sand B (MW-8). Both Sand A and Sand B have been impacted by MTBE in this area. MW-12 i will indicate if there is any vertical migration of the contaminants in this high concentration and downgradient area. o One groundwater monitoring well cluster(MW-13)will be located northwest of MWO-IX and MW-2 in the planter alongside the eastern edge of South Harlan Road. This well cluster will be used to define the -7 _ l western edge of the groundwater plume in the vicinitysf a hi concentr- ion,area. Due to MTBE concentrations detected in nearby well MWO-1X, which is screened in Sand B, this well will be screened with dK one screen for Sands A and B (MW-13A/B) and a separate well construction to intercept Sand C (MW-13C). The results of the recent pump test conducted by SECOR indicate that Sand A and Sand B are interconnected in this area. The similar concentrations in the two sand zones confirms this assessment. For this reason, one well screen will be constructed to intercept both Sand A and Sand B. MW-13C will be installed as a separate well adjacent to MW-13A/B to prevent any potential cross contamination between the upper and lower sand zones. MW-13C will be installed to collect a sample from Sand C to determine if there is any vertical migration of contaminants below Sand B in this area. o One groundwater monitoring well (MW-14) will be located in Chandra F'T Way and approximately 150 feet northeast of existing groundwater j monitoring well MW-11. MTBE concentrations in MWO-2 and MW-11 _ s indicate that groundwater impacts have moved towards the east in Sand A. Well MW-14 will be installed as a well cluster with separate constructions Environmental Remediation Group Page 3 Site Assessment Work Plan Project No.0406 Joe's Travel Plaza