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* AM B R I A Ms Vicki McCartney April 6, 2006 CONCLUSIONS AND RECOMMENDATIONS Shell advanced six CPT borings (CPT-12 through CPT-17) on site, on the Best Western property east of the site, in West Charter Way, and to the sidewalk north of the site The purpose of the borings was to further assess the lateral and vertical extent of petroleum constituents in groundwater and the lateral extent of petroleum hydrocarbons to soil beneath and in the vicinity of the subject site Much of the soil data for this site was collected before SVE was conducted from 1992 to 1996 GWe-ZU 6� This historical soil data indicates that the areas near the former USTs and near well MW-9 were r impacted by elevated concentrations of petroleum hydrocarbons at depths ranging from 15 to 1O' l 30 fbg Following the conclusion of SVE, CPT-1 was advanced 1n the former UST excavation,- 5� and soil samples collected at 20 5 and 30 5 fbg did not contain detectable TPHg or BTEX IV 5 concentraty�CPT-4, CPT-14, and CPT-15 were advanced in the vicinity of the current USTs p J and-MW-9 Soil from these borings also did not contain TPHg or BTEX at 20, 30, and 40 fbg q Soil samples collected at depths of 20, 30, 41, and 50 fbg from CPT-17, located approximately %Pj6 115 feet downgradient of the site, also did not contain TPHg or BTEX Based on these data, b� iq, v� Shell does not recommend additional soil sampling at this time ail, �Str3z Shallow groundwater samples were collected from CPT-14 and CPT-16 to assess the lateral i� extent of MTBE and TBA detected in wells MW-8 and MW-9 The sample from CPT-14 - contained 12 ppb MTBE, and the samples from CPT-16 contained up to 65 ppb MTBE'Shell recommends installing a shallow groundwater monitoring well on the McDonald's property across West Charter Way to further assess the lateral extent of MTBE and TBA downgradient of MW-9 Data from boring CPT-14 and wells MW-2-through MW-7 adequately define the lateral exte t of fuel oxygenates detected in wells MW- and MW=9 in/all other directions / 0 Elevated TPHg and BTEX concentrations were detected to groundwater samples from borings CPT through CU-4 and CPT-10 at approximate depths of 45 to 50 fbg Groundwater samples from borings CPT-12, CPT-13, and CPT-17 at comparable soli types and depths did not contain detectable TPHg or BTEX concentrations To monitor this zone, S4ell recommends installing groundwater monitoring wells screened at this approximate depth near the current USTs, in the former UST excavation, near the subject property's northeast corner, on the Best Western property east of the site, and on the Delta Market property across West Charter Way Elevated TPHg and BTEX concentrations were also detected in groundwater samples from borings CPT 3, CPT-4, CPT-9, CPT-10, CPT-11, and CPT-13 at approximate depths ranging from 65 to 77 fbg Groundwater samples from borings CPT-12 and CPT-17 at comparable soil `0 types and depths did not contain elevated TPHg or BTEX concentrations (61 ppb TPHg in CPT-12 at 74 fbg) Shell recommends installing groundwater monitoring wells screened at this 7