SITE INFORMATION AND CORRESPONDENCE

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Mr. Alan Fetters and Mr. Buo uanOuden -2- 17 February 2010 /aquifer Test The deep well at the former location of the supply well shall also be used to develop an estimate of horizontal and vertical hydraulic conductivity. The scope of the pump test needs to be expanded to include an extraction test from this deeper well. The location of this deep well also provides an opportunity to pilot test the extraction of polluted groundwater from the deeper groundwater zone. Therefore, in order to maximize the information obtained from this deep well, and to minimize future investigative capital expenses, this well shall be designed and installed as an extraction well and shall be included in the aquifer pump test. Shallow Soil Cleanup Objectives The cleanup objective for nitrogen in shallow soil needs to be protective of groundwater through the leaching mechanism. The objective therefore depends primariy on the depth to groundwater, the intervening soil type, and the mobility of nitrogen. Site soils are predominately silts and sands, nitrogen is expected to be distributed in the soil column from the surface to first groundwater (about 20 feet bgs) at the bulk liquid storage locations and sumps, and nitrate is miscible in water. Therefore, a cleanup goal of 100 mg/kg for nitrate (as nitrogen) in soil would be protective of groundwater quality. More site specific information regarding the vertical distribution of nitrogen and its mobility in these soils at this site could result in a less conservative soil cleanup goal for these specific areas. For example, if the vertical profile shows that nitrogen in the soil matrix is not contributing to shallow groundwater pollution, or if it is shown through leachability tests (the Waste Extraction Test using de-ionized water as the extractant) that nitrate bound on soil surfaces is not expected to completely partition to the aqueous phase, then a higher cleanup goal for nitrogen could be considered. The leachability test is described in the Central Valley Water Board Staff Report, The Designated Level Methodology for Waste Classification and Cleanup Level Determination published in October 1986, updated in June 1989. This is available on the Water Board website at http://www.waterboards.ca.gov/centralvalley/plans_policies/guidance/dlm.pdf. If the responsible parties choose to follow the Designated Level Methodology to refine the soil cleanup goal, they should propose to collect a sufficient number of soil samples to include a range of nitrogen concentrations in soil and each sample should be analyzed for both total nitrogen and for the leachable nitrogen concentrations. Summary Central Valley Water Board staff are hereby directing the responsible parties to complete the assessment, close the data gaps, and prepare for remedial design. RF Land, Inc. and Ripon Farm Service, LLC need to install an extraction well near the old supply well, expand the scope of the aquifer test to include evaluation of the horizontal and vertical hydraulic conductivity, and obtain a vertical nitrogen profile near the concrete-lined ponds. Central Valley Water Board staff conditionally concur with the revisions displayed in the 1 February 2010 Revised Addendum (attached) provided the following additions are included in the work plan: The deep monitoring well proposed at the location of the former supply well shall be designed and installed as an extraction well.