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Additional excavation or remediation solely targeted toward <br /> soils is not recommended at this site for the following <br /> reasons: <br /> I. Soil boring sample analysis has shown hydrocarbon levels <br /> to be below typical designated levels for the <br /> constituents HTEX. The levels that were detected during <br /> excavation bottom sampling were within the capillary <br /> fringe which is a saturated zone in continuity with the <br /> unconfined groundwater. <br /> 2. All contaminated soils above the historical high <br /> groundwater level in the tank area have been removed. If <br /> additional excavation of soil were undertaken the clean <br /> backfilled material would become recontaminated once <br /> water levels return to normal (less than 10 feet below <br /> grade based on County records, SJCF'CWCD, 1975, 1980, <br /> 1984, 1987). <br /> 3. In situ soil treatment methods such as vapor extraction <br /> are not effective in low permeability soils such as <br /> those documented for this site. <br /> 4. There is evidence of natural biodegradation/hydrocarbon <br /> attenuation within the shallow water zone. This is <br /> indicated by the strong discrepancy between calculated <br /> groundwater velocity and the distance contamination has <br /> moved in the downgradient direction.. <br /> 5. The groundwater remediation program will include <br /> hydraulic control and recovery of contaminated water. <br /> As water levels rise to normal levels any remaining <br /> hydrocarbons on soils which desorb and dissolve in <br /> groundwater will be recovered and treated. <br /> 5.0 GROUNDWATER REMEDIATION <br /> 5.1 Recovery of .Dissolved Hydrocarbon Constituents <br /> The work by McClaren and 2 subsequent quarterly sampling <br /> rounds performed by Watertlork Corp, show an area of <br /> dissolved hydrocarbons in groundwater. No free product is <br /> present in any of the monitoring wells. The dissolved <br /> hydrocarbon impacted area includes the former tank pit and <br /> extends downgradient approximately 70-100 feet. All water <br /> sample analysis performed to date is summarized on Table 2. <br /> The primary element of the groundwater remediation program <br /> at the site is the hydraulic control scheme. The proposed <br /> recovery well operation is based on the data developed from <br /> the short term pumping test. However, as pointed out in -.. <br /> Appendix-.4.,....-.short -term-data are_inhe=ently -suspect and the <br /> recovery rate must be aaiustable to .reflect long term <br /> aquifer response. <br /> 4 <br />