SITE INFORMATION AND CORRESPONDENCE FILE 1

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Soil samples collected outside the immediate tank pit vicinity of the former tank location show that contaminants ` were not detected in the vadose zone soil or near the capillary fringe (at about 8-feet). Previous excavation in the tank area apparently remo ev d vadose zone contaminated soil. Wright interprets this data to indicate that the leakage under the tanks probably arrived very near the capillary fringe and then moved away as dissolved components. This agrees with the Remediation Risk Management (1993) data and observations of the excavation adjacent to the I building during tank removal. Remediation Risk Management borings SB-1 and SB-2 revealed that contaminants were not detected in groundwater upgradient of the former tank pit area. Response to Soil Sample Data The available soil data are compiled on the Tables attached to this response. These data is also included in the individual reports previously submittedto PHS EHD. Response to the Irrigation Pipeline Wright had never deemed excavation near the pipelines infeasible, but that the PHS-EHD representative did not believe excavation would be beneficial considering low concentrations of petroleum hydrocarbons, and concern for damage to other sections at the line once sections were removed during excavation process. The only way the West Side Irrigation District (WSI) would approve is if assurance was provided that any damaged line, leaking line was replace at others expense and testing was done to verify repair and condition before and after. According to the WSI, the pipeline is buried about 4 feet below grade and is 4' in diameter constructed of bell and socket concrete pipe in about 10 feet sections. This was installed in 1944 and is suspected to be in brittle shape and not able to V withstand huge earth moving equipment working on or around. Should one section be removed it maybe impossible to patch new section in, without continually damaging subsequent sections and therefore.replacing several hundred feet of pipe, resulting in very substantial costs, (see attached letter request and response to West Side Irrigation District Board of Directors(WSI)Board). Response to Potential Excavation Near or at the Irrigation Pipeline West Side Irrigation District Board of Directors considered request to excavate soil surrounding and below their I pipeline at a meeting which a Wright representative attended. After some discussion;WSI voted to deny. encroachment Rational for denial was due to aged condition of 4' diameter concrete line. Rationale for Not Conducting A Remediation Feasibility Study Cleanup and potential feasibility rationale for monitoring and limited cleanup and were previously submitted to the PHS-EHD at their request, in.reports dated July 29, 1996. and February 24, 1999, a summary of which follows. These were also discussed with the assigned PHS EHD representative during this work,and steps taken by WRIGHT were in response to those discussions. Assessment and Monitorine Summary Soil exploratory borings and monitoring wells were used to further define the extent of petroleum contaminants in 4" the vicinity of a former underground storage tank location and for additional well installation. Exploratory soil borings and reconnaissance groundwater sampling show that highly degraded TPHG and BTEX occurs downgradient of the former tank area, with the highest concentrations at PB-4, PB-7 and PB-8. Contaminant distribution is indicative of a slowly moving plume to the north in groundwater with some minor north-northeasterly movement near PB-7. The anomalous occurrence of contaminants is not typical of gasoline ranges according to the analytical laboratory, and is therefore interpreted to have arisen from another source other than this site. The existing groundwater monitoring well array was installed based upon this information, with the review and approval of PHS-EHD. Summary of Cleanup Approach Options Summary Cleanup actions of further soil excavation do not appear to be warranted given the data presented herein. Soil and groundwater extraction and treatment do not appear to be cost effective for the degraded contaminant composition and distribution and pending changes in State guidance. The vadose soil is not affected and the yield of this shallow aquifer is limited on the basis of preliminary field observations (logging and well sampling). Vapor extraction from a very thin capillary fringe zone depleted in volatiles was noteffective in Wright's opinion. Excavation was not Mr. Ed's Muffler Project No. 4090-P Page 2