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Information Sheet IS-17 Reissued Waste Discharge Requirements General Order R5-2013-0122 Existing Milk Cow Dairies Kings County and Merced County require pond liners to have a maximum seepage rate of 1 x 10-6 centimeters per second (cm/sec). Four of the top ten milk producing states (Wisconsin, Pennsylvania, Michigan, and Washington) require ponds to be designed to comply with the state's Natural Resources Conservation Service Practice Standard 313 (CPS 313). These states' CPS 313s have pond liner requirements that range from in-place soils (two to three feet thick with more than 50 percent fines or maximum permeability of 1 x 10-6 cm/sec), or a liner of one foot thick compacted clay with maximum permeability of 1 x 10-7 or maximum seepage rate of 1 x 10-6 if manure sealing cannot be credited or 1 x 10-5 cm/sec if manure sealing can be credited, minimum thickness of one foot) concrete, geomembranes, or geosynthetic clay liners3. One state (Idaho) requires pond liners to comply with NRCS Agricultural Waste Management Field Handbook Appendix 1 OD, which recommends either: two feet of in-place soils with maximum permeability of 1 x 10-6 cm/sec or a liner of compacted clay (minimum one foot thick with allowable seepage rate of 1 x 10-5 cm/sec if manure sealing credit allowed or 1 x 10-6 cm/sec if manure sealing credit not allowed), concrete, geomembrane, or geosynthetic clay. New Mexico and Texas require pond liners have a maximum permeability of 1 x 10-7 cm/sec and Minnesota requires pond liners with a maximum seepage rate of 5 x 10-7 cm/sec. California CPS 313 requires pond liners have a maximum target seepage rate of 1 x 10-6 cm/sec, except where aquifer vulnerability or risk is high in which case a synthetic liner or other alternative liner is required (see Table 1 of this Information Sheet). While these pond design requirements provide more groundwater protection than the Title 27 requirements, there are no known studies that fully evaluate the ability of any of these county, state, or NRCS pond liner requirements to protect groundwater quality. It would be difficult to determine if any proposed pond design would be protective of groundwater quality without an evaluation of information on depth to groundwater, existing groundwater quality beneath the facility, nature of the geologic material between the bottom of the retention pond and the first encountered groundwater, nature of the leachate from the retention pond, and proximity to existing supply wells. Proposed pond designs that do not include such an evaluation should be very conservative to assure protection of groundwater under any likely conditions. The most conservative pond design would include a double lined pond with a leachate collection and removal system between two geosynthetic liners. Such pond designs are currently being approved by the Central Valley Water Board at classified waste management units regulated under Title 27 of the California Code of Regulations (i.e., landfills and Class II surface impoundments) and a limited number of wastewater retention ponds at dairies. The Dairy General Order provides a two-tiered approach that will allow the Discharger two options for retention pond design. Tier 1 includes a retention pond designed to consist of a double liner constructed with 60-mil high density polyethylene or material of equivalent durability with a leachate collection and removal system (constructed in accordance with Cal. Code 3 National Resources Conservation Service,Agricultural Waste Management Field Handbook,Appendix 1 OD— Geotechnical, Design, and Construction Guidelines.