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ADDITIONAL ASSESSMENT WORKPLAN JAMAR SERVICE, STOCKTON DECEMBER 2001 I • In December 1998 two 6,000 gallon and one 10,000 gallon gasoline USTs were excavated and removed from the site and replaced with a two compartment 20,000 gallon UST meeting EPA and State of California upgrade requirements Soil samples taken in conjunction with the tank removal contained detectable concentrations of petroleum hydrocarbons and on January 27, 1999, an Unauthorized Release form was filed with the County An additional Unauthorized Release was filed with the Country on June 11, 1999 In response to a directive from the County, John P Cummings & Associates (JPCA) conducted a subsurface investigation on September 8-9, 1999,by installing and sampling three monitoring wells (MW-1,MW-2, and MW-3) MW-1,MW-2,and MW-3 were drilled to approximately 78 feet bgs, 74 feet bgs, and 74 feet bgs, respectively and sampled every 5 feet Groundwater samples were collected from the three wells on September 23, 1999 On August 21,2000,JPCA did a further subsurface investigation by drilling and sampling one soil boring(B 1)and installing and sampling two additional monitoring wells(MW-4 and MW-5) The soil boring was drilled to approximately 115 feet bgs and sampled every 5 feet MW-4 and MW-5 were drilled to approximately 75 feet bgs with soil samples collected every 5 feet Groundwater samples were collected from MW-1,MW-2,MW-3, MW-4 and NIW-5 on August 30,2000 The results of this investigation are documented in JPCA's 2' Phase 11 Environmental Assessment Report dated October 25, 2000 GHH assumed responsibility of the site in July 2001,and has submitted Second and Third Quarter, 2001, Groundwater Monitoring Reports The County has directed further investigation at the site to define the extent of impacts to groundwater downgradient(southeast) of the site Objective The objective of flus workplan is to present a scope of work that will evaluate the extent of impacted groundwater where it is currently undefined to the southeast of the site This workplan proposes the installation of three groundwater monitoring wells to 75-feet bgs In addition, a sensitive receptor survey will be conducted to identify any water supply wells,surface water sources or other sensitive receptors within 2,000-feet of the site, which could be impacted by the petroleum hydrocarbon and fuel oxygenate levels in the groundwater A water sample will be taken of the closest domestic well identified during the sensitive receptor survey After monitoring well installation, the well elevations will be surveyed and the groundwater data from these wells will be used to evaluate the direction of groundwater flow and gradient The new wells will then be sampled and analyzed for TPH G, TPH D, BTEX, 1,2-DCA, EDB, and fuel oxygenates • 2 I