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�a 28 February 2005 . AGE-NC Project No 99-0624 Page 3 of 12 6� 2 2 BATCH GROUND WATER REMOVAL Due to the amount of time required for state-required bench testing and pilot testing of the ozone sparging system prior to full utilization,AGE proposes to extract petroleum-impacted ground water from the most-impacted well, MW-.r2 The-ground water will be directly pumped into an on-site holding tank(batch removal) on a bi-monthly basis f r one quarter at which time the effectiveness of this method of remediation will be ve aluated,the holding tank will be trucked offsite for disposal , of the impacted ground water The objectives of batch removal of ground water are to reduce the concentration of MTBE in the area of well MW-2 and to exert hydraulic control to prevent additional offsite migration of impacted ground water This method cannot be utilized as a long-term remedial alternative because cost of tank rental,trucking,and offsite ground water disposal is high,especially if additional site investigation delineates a wider MTBE-impact zone than presently realized The cost of each batch removal is estimated at approximately $10,000 to $15,000 3.0. SITE CONCEPTUAL MODEL The site is located on essentially flat land that is developed into a car wash, convenience store and . fueling facility,the majority of the ground surface is covered by asphalt or concrete(Figure 2) Based on data collected to date from onsite and offsite soil borings and monitoring well installations,AGE has developed a site conceptual model for the release,migration and distribution of the contaminants in the subsurface Based on cone penetrometer test (CPT) logs and soil borings, the soil stratigraphy consists of an overall coarsening upwards sequence Below 85 feet below surface grade (bsg) to total depth (100 feet bsg), the sediments are dominantly stiff fine-grained sediments, with several thin, discontinuous clay and silt layers In the zone from 20 feet to approximately 85 feet bsg,the cross- sections generally depict thin,laterally continuous,mostly cemented sand layers,ranging in thickness from approximately 1 foot to approximately 5 feet, intercalated with fine-grained sediments, the frequency of occurrence of the sand layers appears to increase upwards as well as towards the south and east The upper 20 feet of soil generally consists of alternating silty to gravelly sand layers which fine upward to silts in the upper 7 feet Based on the soil stratigraphy, supplemented with pore-pressure data from the CPT logs, AGE developed a hydrogeologic model consisting of eight informal zones (Figure 3), a vadose (unsaturated)zone and seven hydrogeologic units(HUs), in general, low pore pressures associated with the sandy HUs would suggest more rapid pore-pressure dissipation (e g , higher hydraulic conductivities) Site assessment activities to date identified three areas where subsurface soil appears to be impacted Advanced GeoEnvironmentsl,Inc