SITE INFORMATION AND CORRESPONDENCE_CASE 1

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substantiate that the contamination is migrating with the present data. The proposed remediation system should capture this contamination. If it does not it may become necessary to convert MW-1 to a pumping well and add an additional monitoring well to the west of MW-1. This will be determined during the system start-up and evaluation phase. 3. ) Question: The extent of soil contamination has not been defined at this site. Incorrect analytical methods were used on the soil samples- from the tank pits, the stockpiled soil, and the borings for MW-1 through MW-4. The "Headspace" analyses was used instead of the "purge and trap" method. In addition, soil samples from MW-5 and MW-6 were not analyzed. Propose a method to show the extent of soil contamination at this site and remediation plan for contaminated soil. Response: At the time samples from the tankpit, stockpiled soil, and borings MW-1 to MW-4 were analyzed, the "Headspace" method was an approved analytical method. In June 1988, SW846 was approved by the EPA and "purge and trap" became the approved method. The March 23, 1989 confirmation samples from the tank pit used the "purge and trap" method and did not report any BTEX or TPHG concentrations above method detection limits. The soil samples from MW-5 and MW-6 were not analyzed as the wells are nearly 100 feet upgradient from the tank pit and water samples would indicate any continuing source of contamination. At this time it is believed that soil contamination has been adequately delineated and any contamination above the historic high water table ( approximately 5 feet ) has been removed . Because of this no further action is warranted. Per our recent phone conversation, we will proceed with installing the remediation system and testing it . We will Pr a final remediation plan and receive approval from your office and the Regional Board prior to starting operation on a full--time basis.