SITE INFORMATION AND CORRESPONDENCE

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Flag City Chevron • - 8 - • 20 March 2012 6421 Capitol Ave., Lodi, San Joaquin County four extraction wells (EW-5 through EW-9) upgradient from CSA 31-2.) Note that through June 2011, CSA 31-2 was not impacted and is not threatened by either New West or Flag City Chevron releases. In letters dated 15 June 2006, 26 June 2006, and 13 July 2006, the Site consultant responded to the comments. Regional Board staff reviewed the responses, and concurred that they adequately addressed the New West Petroleum and SJCEHD comments. After responding to the comments, the Site continued to monitor groundwater quarterly and submit quarterly monitoring reports through 2006 per the CAO. In December 2006, the Site counsel requested a status update on the possible closure; and met with Regional Board staff and counsel on 24 January 2007. In that meeting, Regional Board staff, with counsel's concurrence, agreed to proceed with the closure pending submittal of additional information depicting the groundwater gradients, plume dimensions, and concentrations over time. The Site counsel and consultant also requested a cessation of quarterly monitoring, pending the outcome of the closure request. On 28 February 2007, Regional Board staff issued a letter suspending quarterly monitoring until further notice. With approval by Regional Board staff, several monitoring wells were destroyed in 2007 until funding ran out and all work stopped at the Site. On 16 February 2012, the remaining monitoring wells were destroyed under the supervision of the State contractor and Regional Board staff through the State Water Resources Control Board Emergency, Abandoned, and Recalcitrant (EAR) Account of the UST Cleanup Fund, with grout inspection conducted by the SJCEHD. Discussion: MTBE is the primary constituent of concern at the Site. During the investigation, impacts to soil were adequately characterized and delineated. Soil over-excavation and groundwater pump and treatment were effective in removing the majority of the Chevron MtBE mass from soil and groundwater. The RDW-1 well was replaced by public water, eliminating a preferential pathway to the deeper drinking water aquifer. Analytical results of soil gas samples showed concentrations of CDCs to be below the current Region 2 ESLs. In late 2001, the Site groundwater plume was defined by the existing monitoring well network. However, in early 2002 the groundwater pump and treat system pulled the New West Petroleum MTBE plume on-site, as indicated by the analytical data from on-site monitoring well MW-8A, which is located up gradient from the Site UST complex and downgradient from the New West Petroleum site. Monitoring well MW-8A showed no impacts to groundwater from MTBE from the initial sampling in May 2000 through December 2001. In March 2002 MW-8A was impacted with MTBE at a concentration of 700 ug/L. Similarly, grab groundwater samples obtained in soil borings P36 through P38 in October 2002 did not contain MTBE, but grab samples from borings P39 through P43, located in the same general area, in January 2004 contained MTBE at concentrations as high as 570 ug/l. Impacts to MW-8A were identified during each sampling event from March 2002 to December 2006, when sampling ceased at the Site.