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Extended Plume Defnitian.-7500 W 11th St., Tracy,CA. Page 9 4.0 ADDITIONAL MONITORING WELLS TO REFINE PLUME DEFINITION To expand definition of the plume of hydrocarbon-affected groundwater emanating from the 7500 West Eleventh Street property, in April 2004, seven additional groundwater-quality monitoring wells were installed at the site. Details of those wells are presented below. 4.1 Well Locations The seven new groundwater-quality monitoring wells, which are designated MW-13 through MW-19, were installed at the locations shown on Figure 2. Monitoring Well MW-15 and MW-17 were installed on the western side of the plume of affected groundwater to improve plume definition in that area and Monitoring Well MW-19, which was installed at the intersection of South Chrisman Road and Carmelo Avenue, is located in advance of the estimated down-gradient limit of the plume so that the northerly extent of the plume could be checked. It also can serve as a monitoring point in the event of further northern advance of the plume front. Monitoring Wells MW-13, MW-14, MW-16 and MW-18 were installed along the approximate axis of the plume of affected groundwater so that, together with existing Monitoring Wells MW-7 and MW-11, they can be used to sample groundwater along that axis and investigate the relationship between the concentrations of analytes of concern with distance down-gradient from the area on the 7500 West Eleventh Street property where the fuel hydrocarbons had been released. 4.2 Permitting Prior to the commencement of exploratory drilling and groundwater-quality monitoring well construction at the site, the necessary drilling permits were obtained from the SJCEHD. Encroachment permits for installation of groundwater-quality monitoring wells along both Chrisman Road and West Eleventh Street were obtained from the San Joaquin County Department of Public Works (SJCDPW). Bonds for the maintenance and eventual removal of those wells were also obtained to comply with the requirements of that agency. 4.3 Detection of Underground Utilities Prior to drilling for the new groundwater-quality monitoring wells, application was made to United Services Agency (USA) for records of underground utilities that might be affected by the drilling. Where such were present, that Agency marked the gas and water supply pipes, electric lines and other utility infrastructure present beneath the surface at, or near, the well locations. 4.4 Well Installation and Soil Sampling 1 During the period April 19-22, 2004, borings for five 2-in. diameter monitoring wells (MW- 15 through MW-19) were drilled using an 8-in., open-stem auger mounted on a drilling rig operated by Spectrum Exploration, Inc., a drilling contractor holding a C57 license issued by the California Contractors State License Board. In addition, borings for two 6 in. diameter .�� wells (MW-13 and MW-14) were drilled using a 12 in., open-stem auger. Each well boring SJC