Laserfiche WebLink
L <br /> Risk-Based Corrective Action Assessment& Over-Excavation Request <br /> ./ Moore Petroleum,Inc.,5491 ­F"Street,Banta,CA <br /> Page 3 <br /> map of the site on January 16, 1998. The groundwater analytical results indicated 810 parts-per- <br /> billion (ppb) of total petroleum hydrocarbons, as diesel (TPHd) in monitoring well MW-1. The <br /> groundwater elevation data and the groundwater analytical results are summarized in Tables 1 and <br /> 2. <br /> SOIL SAMPLING RESULTS <br /> On April 28, 1989, Delta collected soil samples during the drilling and installation of monitoring <br /> wells MW-1 and MW-2. The soil analytical results indicated the soil sample collected from soil <br /> boring MW-1 at 10 feet below ground surface (bgs) had TPHd, benzene, ethylbenzene and <br /> xylenes at 450, 0.3, 4.8 and 8.5 parts-per-million (ppm), respectively. The results of the <br /> investigation were documented by Delta in"Preliminary Hydrogeologic Assessment Report," <br /> dated September 8, 1989 (PHAR). <br /> DOMESTIC WELL AND SITE HYDROGEOLOGIC SURVEY <br /> In 1989, Delta conducted a survey of the domestic wells located within one-half miles of the site. <br /> A total of 20 water wells were located. The summary of the well survey and a well location map <br /> are included in Appendix A. <br /> Delta also conducted slug tests on wells MW-1 through MW-3 to determine the hydraulic <br /> conductivity values at the site. The average hydraulic conductivity at the site was determined to <br /> be 5.18 feet/day, and the average groundwater velocity at the site was 0.068 feet/day. The results <br /> of the well survey and site hydrogeologic tests were also documented by Delta in the PHAR. <br /> RISK-BASED CORRECTIVE ACTION ASSESSMENT <br /> This RBCA assessment was performed to determine the site-specific subsurface cleanup goals for <br /> the subject site. The assessment indicates that due to the close proximity of the off-site domestic <br /> wells, Apex proposal for soil over-excavation and de-watering in the area around MWA are <br /> warranted in order to prevent the soil and groundwater impact from migrating off site. <br /> Background Information <br /> The computer model used in this RBCA assessment is RBCA Spreadsheet System (Version 1.0,1) <br /> developed by Groundwater Services, Inc. of Houston, Texas (GSI System). The GSI System is <br /> designed to complete all calculations required for Tier 1 and Tier 2 of the RBCA planning <br /> processes, as defined in the American Society for Testing Materials' E-1739 Standard for Risk- <br /> Based Corrective Action at Petroleum Release Sites. The GSI System calculates Risk-Based <br /> Screening Levels (RBSLs) in Tier 1 modeling and/or Site-Specific Target Levels (SSTLs) in Tier <br /> 2 modeling, for maximum acceptable soil and groundwater concentrations based on information <br /> ' provided by the user. Risk assessment procedures employed in the GSI System are consistent <br /> JY:D:1_PROJECTIE'S1ERA02.004-Moore Petroleum,Banta\Qmrfl 19$_CRIRBCAAssessment.doc <br />