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 I of S INTRODUCTION The model used to evaluate potential groundwater impacts from wastewater dispersal at the Diamond Pet Foods plant(Diamond)previously was developed to evaluate the various alternatives for improving groundwater quality beneath the site (previously owned by Fox River Paper Company). Lawrence &Associates (L&A) developed a three-dimensional, numerical groundwater model for the site that allowed assessment of the relative water-quality changes that would come from changes in various operating or engineering improvements. Groundwater flow and transport of total dissolved solids (TDS) were modeled; other parameters were not modeled, as it was assumed that TDS would represent transport of the other salts in the effluent. Modeling results are relative to existing conditions at the facility. The model does not account for other dischargers in the area that may be contributing to degraded groundwater quality, such as the neighboring City of Ripon wastewater treatment plant. That is, the model results are intended to be used solely to compare the relative changes in TDS attributable to actions at the Diamond facility. The commercial groundwater modeling software Visual Modflow Pro ver. 2009.1 was used for the thre-dimensional modeling of groundwater flow and transport. Visual Modflow is an add-on"shell" to the U.S. Geological Survey's Modflow groundwater model developed for the public domain, one of the most widely used and accepted groundwater modeling programs. MODEL DEVELOPMENT AND CALIBRATION MODEL AREA Groundwater models in Modflow are three dimensional. That is, the model can have multiple layers in which the program will compute groundwater flow in both horizontal (x and y) and vertical (z) directions. A model is set up with a grid coordinate system defining rows and columns that can be moved or resized to enhance the accuracy of the model at a given location(e.g.,when adding a pumping well). The intersection of the rows, columns, and layers defines nodes which are the basic units used by the model; Modflow mathematically calculates groundwater flow into and out of each node, from all directions. The total number of nodes in a model is defined as (# of columns, x direction) x (#of rows, y direction)x (# of layers, z direction). The model used for the current study has 5 layers, 50 rows, and 60 columns. The model area covers an area of about 6,830 feet in an east-west direction by 5,360 feet in a north- south direction, with the Project site located in the central part of the model domain. The Stanislaus River, the southern boundary of the site, cuts across the model domain; cells to the south of the river 010107.00, Task I Lawrence&Associates w:Iclientsldiamondpetfoods1010107.00-riponrow&diamondpet rowd_june2011 draft.docx