WORK PLANS - Laserfiche WebLink

Home Browse Search

y I..r MIGRATION POTENTIAL MODELING REPORT AND MONITOR WELL CLOSURE WORK PLAN +-� JULY 22, 1999 ,r 1. INTRODUCTION This Report includes conceptual modeling of contaminant migration potential and a work plan for monitor well closure for the New Jerusalem School located at 31400 Koster Road in Tracy, California (Figure 1, Appendix A). This Work Plan was prepared by Condor Earth Technologies, Inc. (Condor) on behalf of Mr. Dennis Boyer, Superintendent of the New Jerusalem School District. The work described in this report was requested by Ms. Carol Oz of the San Joaquin County Public Health Services Environmental Health Division (PHS/EHD) in a Memo dated May 7, 1999. This report includes a site background, a description of the groundwater characteristics, contaminant mass estimates, �.. a discussion of contaminant migration potential, and a monitor well closure work plan. 2. SITE BACKGROUND " A 1,000-gallon UST and a 350-gallon UST were removed from the site in July, 1989. See Figure 2, Appendix A for a site map. Analyses of a soil sample collected from beneath the 350-gallon UST indicated the presence of gasoline contamination. Analyses of a soil sample collected from seven feet below the ground surface (bgs) indicated that concentrations of benzene, toluene, ethyl benzene, and xylene (BTEX) ranged from 130 to 680 pg/kg and the concentration of total petroleum hydrocarbons quantified as gasoline (TPHG) was 37 mg/kg. A Preliminary Investigation and Evaluation Report (PIER) dated February 27, 1997 was prepared by Advanced GeoEnvironmental, Inc (AGE). The fieldwork was conducted by AGE on November 18, 1996. According to the PIER, the field investigation included the installation and sampling of three soil borings(P1, P2,and P3) and the results indicated that �.. gasoline and gasoline constituents were present in the soil and groundwater at the site. Analyses of one soil sample collected at 10 feet bgs beneath the former 350 gallon UST location indicated BTEX concentrations ranging from 0.21 to 62 mg/kg and TPH-G at 930 mg/kg. Laboratory analysis of the remaining five soil samples reported non-detect for fuel constituents (Table 1). The PIER also reported that groundwater was encountered at approximately 12 feet bgs and that the regional groundwater flow was toward the northeast. Analyses of the groundwater sample (P-2) collected from the former 350 gallon UST location indicated that BTEX compounds were detected at concentrations ranging from 140 to 4,700 µg/l and TPHG at 28 mg/I. Also,trace levels of gasoline and gasoline constituents were detected in the sample(P-3) located south of the former 350-gallon UST location(Table 3). Ms. Oz of the PHS/EHD subsequently directed the New Jerusalem School to submit a work plan to conduct additional investigative activities at the site. The investigation included the installation and s� sampling of three monitor wells, sampling and laboratory analyses of the on-site domestic well water and irrigation well water, and conducting a groundwater receptor survey within a 2,000-foot radius of the site. Three monitor wells (MW-1, MW-2, and MW-3) were installed at the site on December 21, 1998, using hollow-stem-auger drilling techniques. See Figure 2, Appendix A for a site map. The boreholes for monitor wells MW-1, MW-2, and MW-3 were drilled to depths of approximately 23,25, and 25 feet bgs, respectively. Groundwater was encountered at approximately ten feet bgs in each boring. Soil saA&S 6.e t� CONDOR