ARCHIVED REPORTS_DRYWELL CLOSURE AND INVESTIGATION

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' NOA Drywell Closure and Investigation Page 22 of 26 ' May 30, 2014 Section 2.6.2, the difference in groundwater levels is possibly due to measuring and sampling of ' the regional aquifer in DW-1, and a perched lens of groundwater in DW-2. The difference in the concentrations of TPH as Diesel and TRPH is therefore likely due to differences in concentrations of groundwater separated by an impermeable aquitard. The anticipated regional aquifer at 75 feet bgs has a higher concentration of COPCs than the perched lens at 58.5 feet i bgs. This indicates that the deeper, regional aquifer is impacted and that the perched lens may have been slightly impacted through capillary suctio f ' acted groundwater through the Ir aquitard, or contaminants were brought to t e upper perched zone uring n In activities. The field parameters collected for groundwater, including pH, temperature, EC, DO, and TDS, are within the recommended numerical limits for water quality objectives and averages for the area. 5.4.3 Ouality Control/Ouality Assurance Quality Control Equipment Blanks are used to assess the quality of field decontamination procedures. The sample collected for soil Equipment Blank Quality Control/Quality Assurance purposes contains levels of analytes well below ESLs. The sample collected for groundwater Equipment Blank Quality Control/Quality Assurance purposes contains analytes below the ESLs, except for Mercury. However, the Mercury concentration is below the EPA health-based MCL, ' which is applicable to the Site. Therefore, field decontamination procedures are adequate. Replicate Samples for Quality Control/Quality Assurance purposes are used to assess consistency in sampling procedures and analytical methods. A replicate sample was collected during soil sampling and split between two (2) containers labeled B1@60'-II-A and BI@60'-II-B, and a replicate sample was collected groundwater sampling and split between two (2) containers labeled W2-VII-A and W2-VII-B. For samples BI@60'-II-A and Bi@60'-II-B, the ' percent differences for individual chemical concentrations include the following: 0%, 1.6%, 4.1%, and 30.8%. For samples W2-VII-A and W2-VII-B, the percent differences for individual chemical concentrations include the following: 0%, 1.7%, 3.7%, 11.4% and 22.2%. Overall, ' most of the percent differences are small; the consistency of sampling procedures and analytical methods are acceptable. Field sampling methods and laboratory procedures meet Quality Control/Quality Assurance goals and standards. 5.4.4 Waste Characterization The Toxic Characteristic Leaching Procedure (TCLP) is a federal guideline used to simulate conditions in a landfill where COPCs can leach out of the solid waste and into groundwater. Two samples were analyzed using the TCLP extraction: Bi@51'-II (DW-1) and B2@51'4I (DW-2). The following analytes were detected in B1@51'-II: Barium at 1.1 mg/L and TPH-Gas at 0.18 mg/L. The detected concentrations of Barium and TPH-Gas are below the applicable Hazardous Waste TCLP limits and threshold for disposal at a standard MSW Type I Landfill, respectively. The following analytes were detected in B2@51'-II: Ethylbenzene at 0.0054 mg/L, Toluene at 0.021 mg/L, Trichloroethene at 0.0064 mg/L, 1,2,4-Trimethyl benzene at 0.012 mg/L, Xylenes at ' 0.032 mg/L and TPH-Gas at 0.13 mg/L. Only Trichloroethene has a regulated Hazardous Waste 902 Industrial Way• Lodi, CA 95240•209.367.3701 • Fax 209.333.8303 02014 Neil 0.Anderson It Associates, Inc.