SITE INFORMATION AND CORRESPONDENCE_FILE 1

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PUBLIC HEALTH SERVICES SAN JOAQUIN COUNTY ENVIRONMENTAL HEALTH DMSION Karen Furst, M.D., M.P.H., Health Officer 40� / • `�iIFOR,~ 304 East Weber Avenue, Third Floor • Stockton, CA 209/468-3420 TILE ED RALSTON FR 04 1M9 TOSCO MARKETING COMPANY 1380 LEAD HILL ROAD,SUITE 120 ROSEVILLE, CA 95661 RE: UNOCAL STATION#5886 SITE CODE: 1176 2701 MARCH LANE STOCKTON CA As a result of reviewing the January 29, 1999 Quarterly Summary Report (QSR) submitted by Environmental Resolutions Incorporated (ERI) on behalf of Tosco Marketing Company (Tosco) for the above referenced site, San Joaquin County Public Health Services Environmental Health Division (PHS/EHD)provides the following comments and directives. The data in this report clearly shows the instability of this groundwater plume. All monitor wells, deep and shallow now show evidence of MtBE in groundwater with the exception of monitor well 7S (shallow). This evidence suggests that MtBE in groundwater is migrating uncontrolled off-site since most wells on- site are located nearest the parcel boundaries. This uncontrolled off-site migration is unacceptable and the responsible party must take action immediately to define and abate these conditions. Previous reports for this site document the presence of several drinking water supply wells in close proximity(1000 feet). The QSR submitted requires corrections as a result of inaccurate reporting. A statement presented on page three of this report is incorrect "To date, Tosco has not received a response and/or approval of the Workplan addendum from the County." On three separate dates PHS/EHD has provided written approval for the proposed Workplan addendum [August 11, 1997, November 11, 1998 and January 14, 1999 (all approvals attached)]. - In the QSR dated January 29, 1999 submitted on behalf of Unocal/Tosco, all analytical data pages are marked draft in red. On the plot map Figure 2, also marked draft in red, monitor well 7D (deep) is incorrectly labeled as ND (non-detect) for MtBE although analytical data submitted confirms the presence of MtBE in this well. Please correct all errors listed in this correspondence or known to you and resubmit a final report to PHS/EHD by March 2, 1999. On July 24, 1997 PHS/EHD issued a written directive in accordance with corrective action regulation ordering Unocal Corporation to fully characterize the extent of soil and groundwater impacted by petroleum (fuel) hydrocarbons at the above referenced site. This directive was issued after documenting the existence of methyl-tertiary butyl ether(MtBE) in groundwater at concentrations as high as 20,000 ug/l. In that correspondence PHS/EHD directed Unocal to complete the following tasks with the following compliance schedule: 1. Submit a workplan addendum to PHS/EHD within 15 days of July 24, 1997 2. Submit a soil and water investigation report within 45 days of July 24, 1997 3. Complete and submit a Corrective Action Plan within 210 days of July 24, 1997 A Division of San Joaquin County Health Cate Service