SITE INFORMATION AND CORRESPONDENCE

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California&gional Water Quality Con&l Board Central Valley Region Robert Schneider,Chair ` Linda S.Adams Arnold Secretaryjor Sacramento Main Office Schwarzenegger Environmental 11020 Sun Center Drive 9200,Rancho Cordova,California 95670-6114 Governor Protection Phone( . aterbo 1 •FAX(v/ce 4644645 RECE p ED http://www.waterboards.ca.gov/cen[ralvalley IfV_ \lV// SEP 2 9 2006 26 September 2006 ENVIRONMENT HEALTH Ms. Margaret Lagorio PERMIPSERVICES Supervising Registered Environmental Health Specialist San Joaquin County Environmental Health Department 304 East Weber Avenue, Third Floor Stockton, CA 95202 NON-CONCURRENCE TO SAN JOAQUIN COUNTY CASE CLOSURE REQUEST, ARCO SERVICE STATION NO. 760, 225 S. CHEROKEE LANE, LODI, CALIFORNIA, SAN JOAQUIN COUNTY On 5 June 2006, Regional Board staff received the San Joaquin County Environmental Health Department's (SJCEHD) Case Closure Summary (attached) for the ARCO Service Station No. 760 (Site) requesting that I concur with the proposed closure. Regional Board staff reviewed the Case Closure summary and the Site file, and do not recommend concurrence with the closure request (see attached checklist, memo and map) due to the following: • The fuel additive 1, 2-Dichoroethane (1,2-DCA) has been detected in three of the five monitoring wells (MW-1 through MW-3) across the Site (See Figure 2) most recently at 11 micrograms per liter (Ng/L), over an order of magnitude greater than the Water Quality Objective of 0.4 Ng/L. The source and extent of the 1,2-DCA has not been identified. • Quarterly groundwater monitoring data collected through the first quarter of 2006 at the Site do not support the conclusion that the plume has declining concentrations for all constituents. The 1,2-DCA concentrations in MW-2 showed a decreasing trend from October 2002 until January 2004, but have shown an increasing trend since January 2004 (See Graphs in Memo). While the overall trend from 2002 to 2006 is decreasing, there are insufficient data to show that the latest increasing trend will reverse itself or to estimate when Water Quality Objectives will be met. Additional data are needed to evaluate whether the Site is a source of the 1,2-DCA, which has impacted water quality. • Total Petroleum Hydrocarbons as gasoline (TPHg) groundwater analytical results for Monitoring Wells MW-2 and MW-3 also show increasing, not decreasing, trends in TPI-Ig concentrations (See Graphs in Memo). • The lateral extent of the petroleum hydrocarbon plume in groundwater is not defined in the downgradient direction to the south and southwest of the Site (See Figure 2). • Considerable gasoline (1,730 gallons) and diesel (1,390 gallons) were estimated as remaining in soil in 1997. Most of the mass was reportedly located less than 30 feet below ground surface. A Human Health Risk Assessment for potential soil vapor intrusion has not been conducted. California Environmental Protection Agency (5 Recycled Paper