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John and Margaret Marci January 11, 2011 2969 E. Loomis Road Page 2 of 3 the 5YRU and pursue developing the technical argument to justify closing your site as a low-risk site. The EHD has determined that your site can currently be characterized as follows: O The primary contaminant of concern is TPHd, a class of hydrocarbons considerably less soluble, volatile and toxic compared to total petroleum hydrocarbons quantified as gasoline(TPHg)or chlorinated hydrocarbons. C The plume of TPHd-impacted soil is adequately delineated laterally by data derived from borings MW-6 and CPT-5 toward the south, CPT-4 toward the west, MW-8 and CPT-9 ., toward the west-northwest, CPT2 and CPT-10 toward the north, MW-104 and CPT-7 toward the east and CPT-6 toward the southeast. The plume of TPHd-impacted soil appears to be adequately defined vertically by soil analytical data from boring MW-4—in the former tank pit area at approximately 75 feet below surface grade (bsg), where TPHd concentrations drop to less than 5 milligrams per kilogram (mg/Kg), but was in the thousands of mg/kg in 12 soil samples collected between 15 feet and 65 feet bsg. Boring LB-1, location uncertain, shows the same general trend,although TPHd was detected at 26.5mg/kg at 76 feet bsg in that boring. • The plume of impacted -groundwater is adequately delineated vertically by sample analytical data from monitoring wells MW-104, MW-105 and MW-106, all screened approximately 90 to 95 feet bsg; MW-104 also providing a down-gradient extent in the 90-to 95-foot depth interval based on the predominant groundwater flow direction at that depth interval. • The lateral extent of impacted groundwater is defined in several directions, but less well so toward the south or east, the directions in which several water supply wells are located. Lateral delineation is established toward the east by the deep zone MW-2 which is down-gradient; toward the northeast by deep zone MW-3; toward the west-northwest by MW-8; and toward the south by MW-6,which is moderately impacted by TPHd. • The available monitoring data is not inconsistent with a stable plume of impacted groundwater, although the TPHd concentration range fluctuates from less-than- detectable concentrations (ND) to a few thousand micrograms per liter (pg/L); the concentrations have not exceeded 10,000 pg/L since February 2008 when rising groundwater elevation went over screen in MW-5. GTI has noted an inverse relationship between groundwater elevation and contaminant concentrations in MW-4 and possibly in MW-7 and MW-5. The EHD suspects that decline to have been caused by rising groundwater elevation going over the screen intervals of these wells. To assist the EHD to more fully consider your site for closure as a low-risk site, you are directed to conduct conformational sampling to demonstrate a low-risk status for the site; the target for conformational sampling should be groundwater between the source area on your site and the water supply wells in the down-gradient and obliquely down-gradient directions in the unmonitored depth intervals where impacted groundwater commonly occurs on site. Also sample the water supply wells within 600 feet of the site and monitoring wells MW-1, MW-4, MW-5, MW-6, and MW-7. Analyze all samples for TPHd, benzene, toluene, ethylbenzene, total xylenes (BTEX) and naphthalene. Submit a work plan to obtain the confirmation grab groundwater samples to the EHD by February 28, 2011. Anticipating favorable analytical results, the report of findings may be reported in a no further action request(NFAR) as part of a Confirmation Sampling Directive Letter and Request for No Further Action Request Report 0111