SITE INFORMATION AND CORRESPONDENCE

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Mr Kirk Moon -2- July 16, 1990 USC, Stockton characterization and field investigation is scheduled to be completed in December 1990. The TPCA requires that a complete hydrogeological Assessment Report be submitted which addresses the information listed in Section 25208.8, H&SC. Under Section 25208.7, H&SC and Section 13267 of the Water Code, Board staff hereby requests that a complete Hydrogeological Assessment Report for the surface impoundment at your Stockton facility be submitted to this office by 31 January 1991. Hydrogeological Assessment Report The purpose of a Hydrogeological Assessment Report (HAR) is to provide a detailed, site specific characterization of the existing impoundment and wastes, the subsurface geology beneath the surface impoundment, and the local and regional hydrogeology. Most important, the HAR will define the areal extent of any hazardous constituents or leachate from the surface impoundment that have migrated into the vadose zone, surface water bodies, perched water, seasonal ground water, or other water-bearing strata. Enclosed is an outline of the HAR as developed by the Regional Board staff to assist owner/operators in preparing the HAR. The HAR must be prepared and certified by a qualified professional in accordance with Section 25208.2, H&SC. Cease Discharge and Closure of Impoundment The purpose of this requirement is to ensure that all material in the surface impoundment at or above hazardous concentrations is removed or otherwise prevented form contacting free liquids. The term "discharge" is defined by the TPCA to include placement, disposal , or storage of hazardous wastes. "Cease discharge" means removal of all liquid hazardous wastes, hazardous sludges, and hazardous portions of the subsoils. "Closure" includes any operations necessary to prepare the surface impoundment for postclosure maintenance. Specific closure activities will be dependent on the findings of the HAR. Closure of surface impoundments is regulated by California Code of Regulations(CCR) , Title 22, Section 67210, and Title 23 Section 2580. Regulations permit two types of final closure: clean closure and closure where waste remains in the subsoil . Before beginning closure, the Regional Board requires that USC submit a closure plan for review and approval . The plan must indicate how compliance with these regulations will be accomplished, and must include a time schedule to complete closure activities. If the surface impoundment is to continue to be used for containment of managed process wastewater and storm water runoff from the facility, it needs to be upgraded to meet Class II requirements, pursuant to Section 2532, 23 CCR. You are hereby requested to submit a plan and time schedule on methods you will use to cease discharge of hazardous wastes within your surface impoundment. This technical report must be submitted by 31 January 1991 and is requested pursuant to Section 13267 of the Water Code.