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ADDITIONAL ASSESSMENT WORKPLAN JAMAR SERVICE,STOCKTON APRIL 2002 Summary of Previous Investigations In 1995, a 300 gallon waste oil UST and a 500 gallon kerosene UST were excavated and removed from the site No environmental issues were documented with the removal of these tanks. In December 1998,two 6,000 gallon and one 10,000 gallon gasoline UST's 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),which 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(B1) 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 dniled to approximately 75 feet bgs with soil samples collected every 5 feet Groundwater samples were collected from all five monitoring wells on August 30, 2000 The results of this investigation are documented in JPCA's 2' Phase HEnvironmental 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 i The County has directed further investigation at the site to define the extent of impacts to groundwater downgradient(southeast) of the site using cone penetrometer techniques (CPT) to locate additional monitoring well locations, and also to install an extraction well immediately south of monitoring well MW-1 Objective The objective of this 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 ' i 2