This report presents an analysis of a plan to contain perchlorate that is present in the Saugus Formation aquifer, which lies beneath a portion of the Santa Clarita Valley (located in northwestern Los Angeles County, California). The containment plan consists of pumping from two deep production wells (SCWC-Saugus1 and SCWC-Saugus2) that have not operated in several years because of elevated concentrations of perchlorate in groundwater. The SCWC-Saugus1 and SCWC-Saugus2 wells will be pumped on a nearly continual basis at a rate of 1,200 gallons per minute (gpm) at each well. A third impacted well, NCWD-11, might be pumped seasonally (during the summer) at 1,200 gpm if it is put back into service. However, this well is not needed to meet the containment objectives and might be destroyed. The groundwater that is pumped from these wells will then be treated at a central location to remove perchlorate prior to entering the potable water conveyance system. The treated water will be pumped to the Rio Vista Intake Pump Station (owned and operated by the Castaic Lake Water Agency [CLWA]) for subsequent distribution, to help meet water demands. In addition to these containment operations, one perchlorateimpacted production well (VWC-157) that lies downgradient of SCWC-Saugus1 and SCWC-Saugus2 will be destroyed, rather than being used for containment. Also, a network of sentinel monitoring wells will be used for performance monitoring of the containment plan and for providing early warning of any changes that might occur in groundwater quality upgradient of the containment wells.

The selected pumping plan has been designed to cause perchlorate, which is migrating in groundwater from the nearby Whittaker-Bermite property, to be captured by these wells, thereby controlling its movement toward other portions of the aquifer, where additional water supplies could otherwise be impacted. The operation of these wells is also designed to capture perchlorate-containing groundwater that is present just downgradient of these two wells. The pumping rates have been selected by considering the water supply needs of the valley and analyses of groundwater flow patterns that are expected under the pumping plan for these wells. The analyses of groundwater flow patterns have been performed using a numerical regional-scale groundwater flow model of the valley, which was developed by the local water purveyors (herein referred to as the Purveyors) for use in managing the local groundwater resource. Figure ES-1 shows the study area, including the model boundaries (tables and figures are located at the end of this summary).

Returning perchlorate-impacted production wells to service with treatment requires the issuance of a permit by the California Department of Health Services (DHS) before the water can serve as a potable water supply. Before issuing a permit, DHS requires that formal studies and engineering work be performed to demonstrate that pumping these wells and treating the water will be protective of human health for the users of the water. To obtain a permit, the owner of the well must perform a detailed evaluation of the effects of returning the well to service. The process for conducting the evaluation is called the 97-005 process, named after the policy memo that describes the process (DHS, 1997). The policy memo also discusses the basic tenets under which the DHS Drinking Water Program evaluates proposals, establishes appropriate permit conditions, and approves returning an impacted well to service for direct potable use.

This report presents the modeling analysis of the Purveyors' preferred pumping plan for the Saugus Formation in the vicinity of the impacted Saugus production wells. This report also presents the objectives and general design of a groundwater quality monitoring program that will be implemented conjunctively with the pumping and treatment program, to identify any changes in groundwater quality that might adversely affect the treatment process. This monitoring program will include water level monitoring and groundwater modeling activities during startup of the long-term containment system, to verify that containment is being achieved and evaluate whether adjustments to the pumping program are warranted. This report has been prepared to support the source assessment and permitting process that the Purveyors are performing under the 97-005 Policy.