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EXECUTIVE SUMMARY

Valley Water Report 2003 [Luhdorff & Scalmanini Consulting Engineers, 2004]). These reports
provide ranges of values for groundwater extractions from the Alluvial Aquifer and the
Saugus Formation during average/normal years and dry years. For the modeling analysis,
the locations and temporal variation in pumping from the Alluvial Aquifer were defined
from the operational plan and from historical records of the year-to-year variability in local
hydrology. Simulated pumping from the Saugus Formation was defined from the
operational plan, historical pumping records, and operational constraints and historical
patterns of water supply availability for water supplies that are imported from the State
Water Project (SWP). Pumping rates at individual wells were assigned using the recent and
planned production schedules for each well and by evaluating the type of pumping plan
that will meet the perchlorate containment objectives for the impacted wells.

The Regional Model was run using a synthetic 78-year period that was derived from
historical records of year-to-year variations in both the local hydrology and the hydrology of
the SWP system. The 78-year period simulates the following conditions:
1. Average rainfall during this period is similar to the long-term mean of approximately
18 inches per year, as measured at the Newhall-Soledad rain gage. The period includes
long periods (i.e., on the order of decades) of relatively dry conditions and relatively wet
conditions.
2. For the Saugus Formation, the simulation period includes 18 years of SWP drought and
corresponding dry-year pumping during the 78-year period, including two droughts
that last for 3 years and two droughts that last for 2 years. Dry-year pumping from the
Saugus Formation ranges between 15,000 and 35,000 AF/yr, compared with
15,000 AF/yr or less in nondrought years (see Table ES-2).
3. For the Alluvial Aquifer, the 78-year period includes 24 years of dry-year pumping,
which is approximately 5,000 AF/yr lower than the pumping that occurs during years of
normal or above-normal rainfall and streamflows. This period includes one drought
lasting for 4 years and two droughts that last 3 years.

Model results were evaluated as follows:
1. Time-series plots (hydrographs) of water budget terms and groundwater elevations
were used to forecast the effects of the pumping plan at the impacted wells and across
the basin.
2. Groundwater flowpaths were forecast using three-dimensional particle-tracking
techniques to identify the degree to which pumping from the impacted Saugus
Formation production wells contains perchlorate migrating westward toward these
wells from the Whittaker-Bermite property.

ES.5 Conclusions from the Modeling Analysis

The major conclusions from the modeling analysis are as follows:
1. Operating production wells SCWC-Saugus1 and SCWC-Saugus2 at rates of 1,200 gpm
each on a nearly continual basis will effectively contain perchlorate migrating westward
in the Saugus Formation from the Whittaker-Bermite property, and will also contain
perchlorate that is present at Saugus wells MP-5 and VWC-157. This is shown by Figure

RDD/041840005 (CLR2612.DOC) ES-5