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0 <br />ROUND ZERO <br />ANALYSIS, INC. <br />March 31, 2014 <br />Mr. Marty Thorpe <br />Jim Thorpe Oil, Inc. <br />357 North Beckman Road <br />Lodi, CA 95240 <br />Subject: Chromium Leaching Potential <br />Former Stockton Rapid Transit District Site, <br />1533 East Lindsay Street, Stockton, California <br />Dear Mr. Thorpe: <br />0 <br />1172 Kansas Avenue, Suite A <br />Modesto, CA 95351 <br />209.522.4119 — PH <br />209.5224227 - FAX <br />groundzeroanalysis.com <br />RECEIVED <br />APR 0 2 2014 <br />ENVIRONMENTAL <br />HEALTH DEPARTMENT <br />Since three of the composite soil samples collected during the recent underground storage tank <br />removal contained concentrations of total chromium which appear to exceed naturally - <br />occurring background levels, a leaching evaluation was conducted. A "Designated Level" for <br />soluble chromium was computed using the method prescribed in the publication Designated <br />Level Methodology for Waste Classification and Cleanup Level Determination (RWQCB June <br />1989). Where: <br />Soluble Designated Level = (Water Quality Goal) x (Environmental Attenuation Factor) /10 <br />= (0.05 mg/1) (100)/10 <br />= 0.5 mg/l <br />A "generic" Environmental Attenuation Factor of 100 was used as per the guidance document. <br />The Water Quality Goal is the Primary Maximum Contaminant Level (MCL) for total <br />chromium in drinking water of 0.05 milligrams per liter (mg/1). A soluble concentration of <br />total chromium of less than 0.5 mg/l would pose no threat to groundwater quality. Using the <br />proposed MCL for hexavalent chromium of 0.01 mg/l, the designated level would be 0.1 mg/1. <br />Sample SP (1,2,3,4) which contained the highest concentration of total chromium (210 mg/kg) <br />was analyzed by Argon Laboratories for soluble chromium by the CA Title 22 Waste <br />Extraction Test (WET) using both the standard citric acid solvent (WET) and by using <br />deionized water as the solvent (DI -WET). The DI -WET would be expected to better replicate <br />actual field conditions as opposed to the WET which is intended to replicate acidic landfill <br />