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I INFORMATION SHEET 2 J. R. SIMPLOT COMPANY SURFACE IMPOUNDMENTS SAN JOAQUIN COUNTY 2. Class II surface impoundments: Simplot is proposing to retrofit the asphalt- lined pond with a double synthetic liner consisting of a 40 mil PVC liner overlain by a 45 - mil Hypalon liner with a leachate collection and removal system (LCRS) between the two liners. Simplot is also proposing to retrofit the Hypalon - lined ponds with a new 45 - mil Hypalon primary liner underlain by an LCRS. These liner systems are proposed as an engineered alternative to the composite liner as required by Chapter 15. 3. Site description: Simplot's site is underlain by a complex sequence of interbedded sand, silt, and clay and ground water is approximately ten feet below the waste management units. Shallow ground water contains concentrations of TDS between 800 and 1000 mg/l. Mean annual rainfall is approximately 14 inches and net evaporation is 42 inches per year. The 100 - year, 24- hour precipitation event is estimated to be 3. 25 inches and the 100- year wet season is estimated to be approximately 25 inches of rain. The site is not in a 100- year flood plain and there are no known active faults in the area. 4. Other findings: The newly lined ponds will be certified to meet the requirements of Chapter 15 as described in Finding No. 32. Revision of these WDRs is exempt from CEQA in accordance with Title 14 of the California Code of Regulations (see Finding No. 33). 5. Basis for draft permit conditions: The conditions or requirements in these WDRs are authorized pursuant to Sections 13260 through 13273 (Chapter 4, Article 4, Waste Discharge Requirements) of the California Water Code. Applicable regulations,prescriptive standards and performance goals of Chapter 15 of Division 3 of Title 23 of the California Code of Regulations are implemented by these requirements. These requirements also implement the water quality objectives of the Water Quality Control Plan for the San Joaquin Basin (5C) (Basin Plan) adopted by the Regional Board on 31 March 1989. 6. Derivation and explanation of discharge requirements and special conditions: Simplot has proposed an engineered alternative to the composite liner described in the construction standard of Chapter 15 (i.e., a synthetic liner underlain by a compacted clay liner.) Simplot has demonstrated that the clay liners used in a composite liner system are incompatible with the high TDS wastes (primarily calcium sulfate). Simplot has shown that compacted clay liners are primarily sodium montmorillonite clays composed of aluminum and magnesium silicates. The high concentrations of calcium in Simplot's discharge will replace the sodium thereby making the clay liner more pervious. Simplot also pointed out that calcium sulfate in its Gypsum form is sold as a commercial product to improve water penetration in soils with high clay content. Therefore, Simplot has proposed a