ARCHIVED REPORTS_RPT OF WASTE DISCHARGE FOR WASTEWATER DISPERSAL 2011

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APPENDIX B Diamond Pet Food Processors of Ripon,LLC June 30,2011 Report of Waste Discharge—Groundwater Modeling Page 4 of 5 An evapotranspiration boundary was set for the uppermost layer of the model, again using values measured at Ripon (Figure B-2). Specified-head nodes were set for the downgradient (northern) edge of the model at elevations representative of the average water-table elevations in that area. A river boundary represented the Stanislaus River. In Modflow, a river boundary allows water to move into the model from, or out of the model to, the river, depending on the river stage. If the river stage is higher than groundwater elevations, water will move from the river to groundwater; if the river stage is lower, water will move from groundwater into the river. The river stage boundary was based on the stage measured at the gauging station near the southwest corner of the Diamond site. Figures B-3 and B-4 show the measured river stage, flow, and specific conductance of the Stanislaus River at the gauge near the site. Three pumping wells were placed in the model, to represent Diamond wells PW-6, PW-7, and PW-8, the currently active wells. Pumping rates were based on the proposed pumping rates per Diamond personnel. Diamond proposes using only PW-6,pumping at about 160 gpm. The model used this value for all modeling periods. For the transport modeling, concentration boundaries were established for the applied water and potential inflow from the river. Total dissolved solids content of the river was calculated from the specific conductance measurements at the Stanislaus River gauge (TDS = SC X 0.75; Figure B-4). Total dissolved solids content for applied water was based data from the cogen discharge and the anticipated TDS of the Diamond discharge (see Table 1, main text of the ROWD). The applied water TDS was set at the value calculated by mixing the various water streams. CALIBRATION The flow model previously was calibrated using groundwater levels. The calibration period was divided into calendar quarters. For input into the model, the various source/sink measurements were averaged over the stress periods; that is, the model runs in stress-period increments, not daily. Thus, the results reflect averages over each stress period. To assess the degree of calibration(how well the model replicates historical conditions), time-series data for the site's observation wells was entered into the model for comparison with modeled values. Because most of the modeling parameters (hydraulic conductivity,recharge, and evapotranspiration) are fairly well constrained through measurements, other parameters that have not been measured at the site, such as vertical anisotropy,were adjusted to reduce the error. 010107.00, Task I Lawrence&Associates w:Iclientsldiamondpetfoods1010107.00-riponrow&diamondpet rowd_june2011 draft.docx