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�o 200003927 zgn-a4 79 Memorandum of Understanding Among Cornhusker Army Ammunition Plant, Environmental Protection Agency, Region VII, Nebraska Department of Environmental Quality and Central Platte NatTfa7 Resource District I. PURPOSE: This memorandum establishes procedures under which the Cornhusker Army Ammunition Plant ( CHAAP) will monitor and evaluate discharge from the Operable Unit 1 (OU1) treatment facility into the on -post drainage canals and Silver Creek. U. BACKGROUND: a. An interim Record of Decision (ROD) for OU 1 — Groundwater was signed and approved November 18, 1994, by the U.S. Environmental Protection Agency (EPA) Region VII, the U.S. Army Deputy Assistant Secretary (Environment, Safety, and Occupational Health) and the Nebraska Department of Environmental Quality (NDEQ). The decision document presented an interim remedial action for the groundwater in accordance with the Comprehensive Environmental Response, Compensation and Liability Act of 1980 (CERCLA), as amended by the Superfund Amendments and Reauthorization Act of 1986 (SARA), and, to the extent practicable, the National Oil and Hazardous Substances Pollution Contingency Plan (NCP). The objective of the interim action is to contain and prevent further migration of contaminants. The alternative provides an approach to containing and removing contaminant mass from the groundwater plume. The ROD outlined extraction and treatment of groundwater from both on and off -post with granular activated carbon and discharge to surface water. b. Due to chances in modeling, the total required extraction rate to capture the plume is significantly less than originally projected in the ROD for OU1. The flow rate has decreased by approximately 65% (5,000 gallons per minute (gpm) to 1750 gpm) and thus the discharge location was reevaluated. The original ROD outlined discharging to the Platte River (approximately 16 miles away); however, the decreased discharge rate allowed alternative surface water discharge locations to be evaluated. y After several modeling studies were conducted to understand the effect 1750 gpm discharge could have to Silver Creek, it was determined there would not be a significant impact to the surrounding area. At that point an Explanation of Significant Difference (ESD) was issued to the ROD. The ESD documents the change. The potential cost savings were determined to be $6 inillion and the need to gain real- estate access to 91 different property owners was eliminated. The cost savings, the reduced real - estate requirements, and the shortened time to operation were realized because the discharge would be on the CHAAP property. ZXHIBIT "B" ATTACRZD TO AND HADZ A PART or DACA45 -2 -00 -6022