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PROPOSED INITIAL 5 -YEAR GROUNDWATER CLEANUP APPROACH RIALTO-COLTON AND NEIGHBORING BASINS SAN BERNARDINO COUNTY, CALIFORNIA 1 INTRODUCTION Groundwater is the principal source of water for residents of southwestern San Bernardino County, California. Together, the Cities of Rialto and Colton, Fontana Water Company (PWC), and West Valley Water District (WVWD) (the purveyors) provide water to more than 235,000 consumers. Much of the water that is served by these purveyors comes from the Rialto -Colton groundwater basin (RCB) and adjoining portions of the neighboring basins (collectively referred to herein as "the basins") (Figure 1). Since 1997 when water purveyors in the region first began testing municipal production wells for perchlorate, the anion has been detected in numerous wells at concentrations that exceed the state notification level for drinking water. In response to detections of perchlorate, water purveyors were compelled to shut down more than 20 production wells in the region and/or put treatment on wells, thus significantly impacting the ability of purveyors to provide a stable and reliable source of water to the community. Recognizing these conditions, the City of Colton, City of Rialto, County of San Bernardino (the County), FWC and the WVWD formed the RCB Technical Committee (RCBTC) to collect the data needed to develop and initiate an appropriate strategy to cleanup groundwater. The goals of this strategy are to restore groundwater supplies to the four water purveyors and to accelerate groundwater cleanup. Working with the County of San Bernardino, the purveyors have agreed on a proactive approach that protects and begins to restore the public water supply, implements interception and treatment of groundwater contaminants, optimizes limited resources, and decreases the timeframe and overall costs required for cleanup of groundwater. This document identifies the groundwater cleanup approach that the RCBTC has developed to address perchlorate contamination. 2 PERCHLORATE IMPACTS/SOURCES Figure 2 depicts the distribution of perchlorate -impacted water production wells within the service areas of the purveyors. Groundwater investigations indicate that there are likely numerous sources of contamination in the area, with two generalized geographic sources of contamination within the former Rialto Ammunition Backup Storage Point (RABSP) in north Rialto being identified as the major currently known source of perchlorate contamination in the Rialto Colton Basin (Figure 2). The RABSP operated during World War II as a storage and loading complex where a large portion of the munitions used in the Pacific theater of war were temporarily stored. After the war, the RABSP property was sold, resold, sub -divided and used, leased, or rented to numerous Rialto -Colton Basin Technical Committee— White Paper Revised 2/22/2006 1