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25 March 2009 AGE-NC Project No. 95-0121 Page 4 of 9 Hydrocarbon impacted groundwaterwill be treated byprocessing through a tower-profile air stripper with a minimum of six to seven trays and subsequently through liquid-phase activated carbon. Treated ground water will be discharged under permit via on-site sanitary sewer conveyance system to the City of Stockton sanitary sewage conveyance system located on Navy Drive. A flow chart of the DPE system is depicted in Figure 6. Dii.1N 1V 3 .5 JUSTIFICATION FOR EXTRACTION WELL SELECTION Based on an evaluation of the on-site network of monitoring and remediation wells AGE recommends the use of wells EW- 1 , VW- and AW- 1 . The following is a brief justification for the use and selection of each well: • Extraction well EW- 1 , screened from 20 to 40 feet bsg, was selected based on findings during the Dual Phase Extraction Pilot Test performed during December 2007 and because of its location, which is centered in the "core" area of both the soil and ground water contaminant plumes (HU2/110). A two year evaluation of the analytical data collected from 13 September 2006 to 23 December 2008 indicates that EW4 is consistently one the most impacted wells onsite, with average concentrations of 185,000 micrograms per liter (µg/1) total petroleum hydrocarbons quantified as gasoline (TPH-g), 28,850 pg/I benzene, and 151 µg/I 1 ,2-Dichloroethane ( 152-DCA). • Vapor extraction well VW4 was selected on the basis the following characteristics: screening interval (screened 10 to 30 feet bsg), drawn-down capability, location relative to source/core area of the contaminant plumes, contaminant concentration, and ability to provide hydraulic control (HUI /HU2/HU3). In general, VW- is within the core area ofboth the soil and ground water plumes, and contains elevated levels of TPH-g (> I 00,000 µg/1 ), benzene (>10,000 µg/1), and 1 ,2-DCA (> 100 µg/1. During routine monitoring events VW- I consistently draws down to around 22 feet bsg after bailer purging of only 7.5 gallons (an average removal rate of 1 to 2 gallons per minute). • Air sparging well AW- 1 was selected based on its location to the "core" area of the soil and 25 . ground water plumes (HU2/HU3), the elevated concentrations of TPH-g (> 100,000 µg/1), Lyre nN r j r benzene (> I 0,000 µg/1), and 1 ,2-DCA (>50 µg/1), and the amount of drawdown noted during Z , . quarterly ground water monitoring events. Drawn down has been noted on a relatively consistent basis, likely an indication that the well will be able to depress the water table, while enhancing vapor phase hydrocarbon removal. Advanced GeoEnvironmental, Inc.