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2.2 Site Geology and Hydrogeology Soils underlying the Site consist of three laterally extensive fine-grained sand layers: Sand A, Sand B, and Sand C (Secor, 2006). Sand A is located 5 to 8 feet below ground surface (bgs) and is 3-to 10-thick. A clay layer has been encountered at approximately 10 to 15 feet bgs and is approximately two feet in thickness. Sand B is located between 25 to 35 feet bgs and is between 7-to 18-feet thick. Sand C is located between 50 and 65 feet bgs and is between 15-to 25-feet thick. Groundwater was observed in each of the three sand layers. The existing monitoring wells are screened across Sand A, except for monitoring wells MWO-1X and MW-8, which are screened across Sand B. Based on last quarter's groundwater sampling event, depth to groundwater is approximately eight feet bgs. Groundwater flow is reported to be to the northeast with a gradient of 0.00075 feet per foot(ft/ft). The results of the Fourth Quarter 2006 groundwater gauging event indicate that groundwater flow has shifted to the west at a gradient of 0.0017 foot/foot. A pump test conducted by Secor(June, 2006) used groundwater monitoring wells MW-2 and MWO-1X,which are screened across Sand A and Sand B, respectively. Similar amounts of measured drawdown were observed in both wells while pumping Y; ✓ on the well in the other sand strata, suggesting hydraulic connectivity between Sand trt` � A and Sand B. In addition, groundwater analytical results from samples collected from Sand B indicate concentrations of MTBE also suggesting that Sand zones A and B are connected hydraulically in the source area. 2.3 Contaminant Distribution The contaminant of concern for this Site appears to be MTBE. MTBE has been detected in the subsurface groundwater on and off the site since February of 2000. MTBE has been detected in the Sand A Zone since 2000. The lateral extent of the Sand A groundwater impact has not been defined. The lateral extent of MTBE migration extends beyond well MWO-3 (475 feet north of the former UST location) and beyond well MW-11 (600 feet Northeast of the source area). The lateral extent of MTBE impact in groundwater is defined to the west of the former UST location by well MW-6 and to the south by well MW-5. MTBE has been detected at high concentrations (>750 ug/1) in Sand Zone B (MWO- IX) since early 2002. Further evidence of B Zone groundwater MTBE impact is M W 1P \ detections in well IyyIW-8. MTBE has already migrated in the Bzone_NortWnDxthwest. of the-forrner_UST,.location beyond 225 feet and north/northeast beyond 260 feet. The MTBE concentrations have seen significant reduction in Zone B Sands (MWO- 1 X) over the past four years. Since no groundwater remediation has taken place at this Site and there is evidence of MTBE migration in Sand A,the reduction in MTBE concentrations in well MWO-1X is likely due to migration in Zone B sand. The site data suggests that groundwater in Sand B is likely impacted off site to the north and northeast of the former UST location. This is due to the historically highest detected concentration N T M in the `B Zone"to the.north/northwest of the source area. ( ormer UST location).No additional off site assessment has been completed in the Environmental Remediation Group Page 2 Site Assessment Work Plan Project No.0406 Joe's Travel Plaza