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UIRS 0 Mr. Ross Atkinson Regional Water Quality Control Board–Central Valley Region May 20, 2011 Page 6 of 10 Enterprises site,the most conservative approach would be to designate its use as municipal or domestic water supply. Based on this designation,the federal and state maximum contaminant level(MCL)and secondary MCLS (SMCLs)would apply. The Water Quality Control Pian(Basin Plan)for the California Regional Water Quality Control Board– Central Valley Region(2009) specifies that: "At a minimum, ground water designated for use as domestic or municipal supply shall not contain concentration of chemical constituents in excess of the maximum contaminant level specified in the following provisions of Title 22 of the California Code of Regulations,which are incorporated into this plan: Table 64431-A (Inorganic Chemicals) of Section 64431, and Tables 64449-A(Secondary Maximum Contaminant Levels-Consumer Acceptance Levels)and 64449-B (Secondary Maximum Contaminant Level-Ranges)of Section 64449." In its letter dated February 20, 2007, RWQCB specified water quality goals of the following eight constituents: TDS at 450 mg/L; aluminum at 0.050 mg/L; arsenic at 0.0021 mg/L; barium at 0.49 mg/L; iron at 0.3 mg/L; lead at 0.002 mg/L; manganese at 0.050 mg/L; and nickel at 0.012 mg/L. EPA and California Department of Health Services EPA has established National Primary Drinking Water Regulations that set mandatory water quality standards for drinking water contaminants. These enforceable standards—MCLs—are established to protect the public against consumption of drinking water contaminants that present a risk to human health. An MCL is the maximum allowable amount of a contaminant in drinking water which is delivered to the consumer. In addition, EPA has established National Secondary Drinking Water Regulations that set non- mandatory water quality standards for 15 contaminants. EPA does not enforce these SMCLs, which act only as guidelines to assist public water systems in managing their drinking water for aesthetic considerations,such as taste, color and odor. These contaminants are not considered to present a risk to human health at the SMCL. Of the eight inorganic constituents identified by RWQCB as being above their respective water quality goals, MCLs are established for five constituents (aluminum at 1 mg/L by California Department of Health Services [DHS]; arsenic at 0.01 mg/L by EPA and DHS; barium at 2 mg/L by EPA and 1 mg/L by DHS; lead at 0.015 mg/L by EPA and DHS; and nickel at 0.1 mg/L by DHS)and SMCLs are established for four constituents (aluminum [color] at 0.05 to 0.200 mg/L and 0.2 mg/L by DHS; iron [color and taste] at 0.3 mg/L by EPA and DHS; manganese [color and taste] at 0.05 mg/L by EPA and DHS; and TDS [color and taste] at 500 mg/L by EPA and DHS). CONCLUSIONS AND RECOMMENDATIONS MW-2 is located within the landfill and if the source of a potential constituent is located within the landfill, the highest concentration of the potential constituent is expected from this well. The groundwater flow direction is typically to the east-northeast or to the northeast based on the data H:AWprocess\25532\WoridEnteipriseAClosureA05201 l.doc