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' TASK 3 - FEASIBILITY STUDY AND CLOSURE OF HIGH EXPLOSIVES LAGOONS Purpose and Rationale ' The purpose of this task is to complete the feasibility study and closure of nine decommissioned, high explosives rinse-water lagoons in the High Explosives Process ' Area. Since 1985, LLNL has conducted investigations and testing of material in the lagoons. In April 1987, we submitted to the CRWQCB a conceptual closure plan for closure of the lagoons. A feasibility report for closure will be submitted by February 1988, and the lagoons will be closed by November 1988. ' Procedure ' The lagoons will be filled and capped with a minimum of two feet of compacted clay soil. The soil will meet CRWQCB compaction standards and will be free of HE compounds. A minimum of 18 inches of uncompacted topsoil will be placed over the clay caps to reduce the chance of bioturbidation of the caps. Final grading will be designed to provide positive drainage away from the lagoon sites. Interceptor trenches will be excavated upslope of the lagoons to divert surface runoff away from them. TASK 4 - REMEDIAL INVESTIGATION/FEASIBILITY STUDY AT B815 AND GSA Purpose and Scope ' The purpose of this task is to complete the remedial investigation of VOCs in soil, rocks, and ground water at Building 815 and the GSA by July 1988. The remedial investi- gation will be followed by a feasibility study, to be completed by March 1989. LLNL has discovered TCE in soil, rocks, and two water-bearing zones extending south from Building 815. In addition, VOCs have been detected in Site 300 standby water supply wells in the GSA, and in soils and shallow ground water near these wells. The water-bearing zones at ' B815 may be in hydraulic continuity with aquifers tapped by standby water supply wells in the GSA. Building 815 is thought to be the source of TCE in the B815 area and possibly in the GSA. By July 1988, LLNL plans to: 1. Complete the installation of a ground water monitoring system at Building 815 and the GSA. ' 2. Determine the vertical and horizontal extent of the TCE plumes in the area. 3. Determine the aquifer characteristics of the water-bearing zones through ' which the plumes move. 4. Confirm the B815 area as the source of TCE. ' Procedure To complete the remedial investigation, LLNL intends to install at least seven ' additional monitoring wells to define the limits of the TCE plumes south of B815. Each well will be completed in one water-bearing zone only, and will be constructed of 4.5 inch I.D. Schedule 40 PVC well casing and screen. The wells will be developed and ' -6-