SITE INFORMATION AND CORRESPONDENCE

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S� • • 26 November 2014 Mr. Paul Lambert - 2 - concentrations beneath the center of the shallow groundwater pollution range from 40 to 400 mg/L, and are about 100 mg/L southwest of the center. Extraction Work Plan The Extraction Work Plan proposes to withdraw groundwater primarily from extraction well AT-1 S near the center of the shallow groundwater pollution plume, and install 3 additional shallow groundwater extraction wells to the west of AT-1 S, where nitrate concentrations are lower. Extracted groundwater will be blended in an on-site mixing tank before being piped to the non-potable water supply pipeline. The City of Ripon operates the non-potable water supply pipe that provides water for landscape irrigation and cooling water for a biomass energy plant. In order to protect users of the non-potable water from elevated salts, the City of Ripon has imposed a limit of 1 ,000 mg/L nitrate (as nitrate) and 2,500 mg/L total dissolved solids with a flow rate limitation of 100 gallons per minute. Ripon Farm Service proposes to meet these limitations by extracting groundwater primarily from AT-1 S, and supplementing with the additional extraction wells to dilute AT-1 S as needed to meet the discharge limits. It is anticipated that each extraction well will be able to produce about 20 gallons per minute. Ripon Farm Service proposes to monitor water quality and flow rates at the extraction wells, in the mixing tank, and at the non-potable water supply input point two to four times a day until the system is at an operating equilibrium. Nitrate measurements will be made in the field with an ion-selective probe, complemented with weekly laboratory analyses. Groundwater surface elevations will be obtained from nearby monitoring wells about once a day during the startup phase. Following equilibrium, water quality monitoring will be reduced to once weekly with field equipment supplemented with monthly laboratory analyses. Ripon Farm Service proposes reporting semi-annually, corresponding with the groundwater monitoring reporting schedule. Central Valley Water Board staff additionally request monthly data submittals through the equilibrium period. These submittals may be in a spreadsheet format and may be transmitted electronically. Disagreement with Remediation Endpoint The Extraction Work Pian states that the remediation will be considered complete when groundwater from the extraction wells meet a background concentration of 200 mg/L nitrate as nitrate, or reach asymptotic conditions for nitrate. Central Valley Water Board staff recognize that there is an underlying condition of elevated nitrate in shallow groundwater at the facility, but it has not been demonstrated that a specific value of 200 mg/L nitrate as nitrate is appropriate. Additionally, the groundwater data also suggests that historical operations have contributed nitrogen into the second water- bearing zone. Central Valley Water Board staff request that if Ripon Farm Service wishes to define an ambient background concentration of nitrogen in groundwater, it needs to prepare a proposal to establish a background concentration. In the absence of an agreed-upon