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One aspect of plume interception is engineering design that must be conducted, which includes the following: 1. Developing a Scoping Document that complies with the National Contingency Plan (NCP) and Comprehensive Environmental Response, Compensation and Liability Act (CERCLA). 2. Establishing a conceptual model that can serve as a basis for remedial design; and, 3. Designing a preliminary five-year remedy and characterization effort that promotes a quick response to existing and potential future groundwater contamination and provides data for successive remedies. 4 PROJECT WORK TASKS The following sections provide a description of project tasks, sub -tasks and an estimate of the resources that are anticipated to be required to complete this work. It is intended that all aspects of this work will be performed in compliance with NCP and CERCLA guidelines. The cost estimate for this work, which totals $106,150,000, is shown in Table 1 and is based on past investigation and remediation efforts in the RCB. 4.1 TASK 1 - WATER SUPPLY RESTORATION Perchlorate removal by wellhead treatment systems is currently being performed on some wells to meet the immediate water supply needs of the community served by the four purveyors. While groundwater extraction at these wells is necessary to meet immediate water supply needs, there are other water supply wells in the region that are impacted by perchlorate whose reactivation (with water treatment) is critical. The goal of the wellhead treatment program is to stabilize the water purveyor operations, decrease the mass of contaminants in groundwater, reduce the time and resources required for aquifer restoration, and assure the continued ability of purveyors to meet the water supply needs of the community. Although the focus of cleanup is the RCB, wellhead treatment includes purveyor wells outside of the RCB within the purveyors' service areas. This is necessary to provide operational flexibility and to mitigate perchlorate contamination throughout the basins. This White Paper includes: 1) an estimate to install 10 new systems to treat 12 currently impacted wells, or where possible, groups of wells ; and, 2) eight existing treatment systems for 10 wells. This will restore water supplies for 22 wells, representing a combined capacity of more than 35,000 gallons per minute (gpm), of which 12 wells and 21,800 gpm are currently idle. Costs summarized herein represent known costs where possible, and estimated costs scaled for the required flow rates in gpm based on costs for existing systems. Rialto -Colton Basin Technical Committee— White Paper Revised 2/22/2006 3