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ADDITIONAL GROUNDWATER INVESTIGATION WORK PLAN BOYETT PETROLEUM 419 S. MAIN STREET MANTECA, CALIFORNIA 6w June 25, 2003 r 1.0 INTRODUCTION This work plan was prepared by Condor Earth Technologies, Inc. (Condor) to describe proposed groundwater investigation activities at the Boyett Petroleum(Boyett) facility located at 419 S. Main Street (site) in Manteca, California (Figures 1 and 2, Appendix A). On May 15, 2003, a Condor representative met with Mr. Nuel C. Henderson, Jr. and Mr. Jeffrey Wong of the San Joaquin County Environmental Health Department (SJCEHD) to review recommendations proposed in the First Quarter Groundwater Monitoring Report March 2003, dated April 3, 2003, and SJCEHD concerns regarding the site. In a letter dated May 29, 2003, Mr. Nuel C. Henderson, Jr. and Mr. Jeffrey Wong requested the submittal of a work plan to further investigate the lateral and vertical extent of groundwater contamination at the site. The purpose of the work is to evaluate the lateral and vertical extent of petroleum hydrocarbon contamination in groundwater up-gradient and down-gradient of the gasoline underground storage tanks (USTs) using direct push boring methods [cone penetrometer testing (CPT) and hydropunch]. This work plan includes project background information; a description of the field, laboratory, and reporting procedures proposed to conduct the work; and a project schedule. All work conducted by Condor will be under the supervision of a California Registered Geologist. r 2.0 SITE BACKGROUND On November 20 and 21, 1996, soil sampling was conducted at the site by WHF, Inc., (WHF) under the direction of Mr. Robert McClellon of the SJCEHD. One soil sample was collected from beneath each of the site's three existing fuel dispensers at a depth of approximately two feet below the dispenser piping and four discrete soil samples were collected to characterize approximately 44 cubic yards of material stockpiled at the site. The soil samples were analyzed for total petroleum hydrocarbons quantified as gasoline (TPH-G), for benzene, ethyl benzene, toluene, total xylenes (BTEX), and for methyl tert-butyl ether(MTBE). ` On October 5, 1998, WHF completed two soil borings to a maximum depth of 18 feet below ground surface (bgs) proximal to the fuel dispenser island. Three soil samples were collected from each boring at depth intervals of 4-6 feet, 9-11 feet, and 16 feet. One groundwater sample was collected from each boring from a depth of 18 feet for laboratory analyses. On August 27 and 30, 1999, WHF completed four soil borings. The borings, which varied in total depth ' from 26.5 to 36.5 feet bgs, were subsequently converted into monitor wells MW-1 through MW-4. Laboratory analytical results of eleven soil samples collected from the borings indicated no detectable concentrations of petroleum hydrocarbons with the exception of MTBE, which was detected in MW-1, V i Lei CONDOR �r