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EXECUTIVE SUMMARY

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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.

ES.2 Background

In 1997, two Saugus Formation production wells owned by the Santa Clarita Water
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Company (SCWC) (wells SCWC-Saugus1 and SCWC-Saugus2), one Saugus Formation
production well owned by the Newhall County Water District (NCWD) (well NCWD-11),
and one Saugus Formation production well owned by Valencia Water Company (VWC)
(well VWC-157) were shut down because perchlorate was detected in groundwater at these
wells. In 2002, an Alluvial Aquifer production well owned by SCWC (well SCWC-Stadium)
was shut down because of a perchlorate detection. The locations of the five impacted
production wells and nearby nonimpacted production wells are shown on Figure ES-2,
along with the locations of monitoring wells and exploratory borings that have been
installed to investigate the extent of perchlorate contamination. Figure ES-2 also shows
perchlorate concentrations at locations where perchlorate has been detected in groundwater.
At each of the five production wells, the detected perchlorate concentrations exceeded the
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State of California’s Action Level (AL) for perchlorate at the time of the detection .
Together, the four impacted production wells in the Saugus Formation pumped between
1,900 and 6,800 acre-feet per year (AF/yr) during the early and mid-1990s, prior to being
shut down. The average pumping from these four wells was 4,186 AF/yr from 1991 through
1996, the 6 years preceding the perchlorate detections (see Table ES-1). The four wells have a
combined instantaneous pumping capacity of 7,900 gpm. The Purveyors plan to return three
of the four impacted Saugus Formation production wells to service (SCWC-Saugus1,

2 The Purveyors and DHS require that water provided to customers contain no detectable perchlorate.
3 The SCWC was acquired by CLWA in 1999. It was formerly called the Santa Clarita Water Company and is now called the
Santa Clarita Water Division of CLWA.
4 The AL has varied over time. DHS initially established an AL of 18 micrograms per liter (µg/L) in 1997, at the same time the
four impacted Saugus Formation production wells were taken offline. In 2002, DHS revised the AL to 4 µg/L based on studies
by the U.S. Environmental Protection Agency (EPA). In March 2004, the AL was revised to 6 µg/L based on a public health
goal published by the Office of Environmental Health Hazard Assessment. See the internet site
http://www.dhs.ca.gov/ps/ddwem/chemicals/perchl/actionlevel.htm for further details.

ES-2 RDD/041840005 (CLR2612.DOC)