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Revised Site Characterization Work Plan SMH Mountain House,LLC Page 4 by EPA Method 120AM, total nitrogen by EPA Methods 351.3/300.0, and 10 metals by EPA Methods 6010B, 7471A, and 7740 (metals to include arsenic, cadmium, chromium, copper, lead, mercury, molybdenum, nickel, selenium, and zinc). The laboratory will retain the unused portions of the discrete samples in a freezer until the project is completed in case additional sampling will be desirable. The laboratory will provide certificates of analysis. 4.2.2 Risk Evaluation Upon receipt of the laboratory results, Condor will compare the results of liner subsoil testing to background data.The accumulated soil data from Reclamation Areas 2 and 3 (Attachment 2)will be used as the background data set. The evaluation of potential risks of groundwater degradation will be conducted by applying the following four criteria for determining whether a parameter is a constituent of potential concern(COPC): 1) Compare the highest liner subsoil concentration with the highest background concentration. If the highest liner subsoil concentration is equal to or less than the highest background concentration then the constituent will be eliminated as a COPC. 2) Compare the liner subsoil and background arithmetic mean concentrations. If the means are comparable, the constituent may be eliminated as a COPC. Means will be considered comparable if the percent difference is 10 percent or less. The percent difference will be calculated according to the following formula: Percent Difference= 100 x I (Ml-MZ)I/(Mt+MZ) where: Mt=mean of sample MZ=mean of background 3) Statistically evaluate the overlap of the background and liner subsoil distributions using a Wilcoxon Rank-Sum Test or similar valid statistical procedure to determine if they come from the same population. If they do the constituent may be eliminated as a COPC. 4) Additional information on eliminating constituents as COPCs can be found in the February 1997 publication, Selecting Inorganic Constituents as Chemicals of Potential Concern at Risk Assessments at Hazardous Waste Sites and Permitted Facilities — Final Policy, prepared by the Human and Ecological Risk Division(HERD), Department of Toxic Substances Control(DTSC). If any COPC are identified that are above background levels, an analysis of their potential to degrade groundwater will be performed and a supplemental Work Plan will be filed with the Regional Water Board staff identifying the methods that will be used to define the extent of pollution and methods for soil remediation, prior to decommissioning the ponds. If no COPC are identified, decommissioning will proceed as described below. 4.23 Residual Solids Removal Solids remaining on top of the liner in Reservoir 1B consist of formerly-sandbagged ballast materials used to weigh down the liners, sacking material, windblown sand and tumbleweed. Because wastewater was historically discharged to Reservoir 1 B, solids from that reservoir shall be handled and disposed of as waste, due to potential for pathogens to be present in the material. Solids will be collected and placed in containers for shipment to a sanitary landfill. These materials will be manifested and recorded in the final closure report described in Section 5. 0.41 CONDOR