SITE INFORMATION AND CORRESPONDENCE

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CALIFORNIA REGIO&WATER QUALITY CONTROL BOARD • Cal/EPA I CENTRAL VALLEY R6. ON 3443 Routier Road,Suite A vsq�� Sacramento.CA 95827-3098 Phone(916)255-3000 FAX(916)255-3015 _ Pete Wilson,Governor 21 August 1997 Mr. Rob Donovan Tesoro Refining, Marketing and Supply Company 320 S.W. Stark, Ste. 511 Portland, Or. 97204 WELLS PROPOSED FOR DECOMMISSIONING AT STOCKTON TERMINALS SITES(SAN JOAQUIN COUNTY, CALIFORNIA) Staff has reviewed the workplan dated 15 May 1997 submitted by EMCON on behalf of the Stockton Terminals Technical Committee (STTC) for decommissioning a number of monitoring wells and water supply wells at the Committee's facilities in Stockton. In reviewing the proposal and workplan, staff considered, and discussed with EMCON staff, several issues. The issues included questions about the rationale for the proposed decommissioning, potential usefulness of the wells in monitoring efforts, location, construction and condition of the wells, and potential for spreading contamination by serving as conduits to deeper water-bearing zones. Most of these issues were recognized in the workplan. Staff also discussed with management of POSDEF,the cogeneration plant on whose facility grounds some of the wells in question are located, whether they had any concerns. Both EMCON and San Joaquin County Environmental Health staff were consulted during the review process. This letter (1)summarizes staff's understanding of the results of the decommissioning efforts undertaken to date, (2) documents the requests for further efforts that have been made by Board staff and San Joaquin County Environmental Health staff, and(3) responds specifically to the proposed decommissioning of certain monitoring wells at the facilities. i. Resuits of work to date: As you know,we approved the decommissioning of the two water supply wells, 17A1 and 8R2,by letter dated 11 July 1997. Field work subsequently undertaken by EMCON has been discussed in several telephone conversations between Board staff and staff of EMCON and San Joaquin County Environmental Health. Based on these conversations, staff understands that well 8R2 was found already to have been decommissioned. Staff also understands that a water supply well that was found in the vicinity of well 17A1 could not be positively identified as 17AI. Neither the observed diameter nor the depth as sounded (90 feet rather than 200 feet) coincided with the description given on the driller's log obtained from the California Department of Water Resources (DWR). In addition, there was some question as to whether the location was the same as given on the DWR log. (All discussants agree that the notation of the DWR log regarding distance to the well from a known point is difficult to read clearly). Last and most important, four feet of floating product were found in the well.. 2 Staff requests for further efforts to identify the well and the product: Regulatory staff of both San Joaquin County and the Board concur in requesting further confirmation that this well is 17AI, and have asked for analysis of the product, videologging of the well, and, if further confirmation is needed, Reryded Paper Our mission is to preserve and enhance the quality of California's water resources.and ensure their proper allocation and efficient use for the benefit of present and future generanons.