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EXECUTIVE SUMMARY

ES-3, which displays groundwater flowpaths from MP-5, VWC-157, and the Whittaker-
Bermite property; and by Figure ES-4, which displays the areas within the Saugus
Formation where water is obtained by each of the impacted production wells and each
of the nonimpacted production wells that are located downgradient of SCWC-Saugus1
and SCWC-Saugus2.

2. Operating production wells SCWC-Saugus1 and SCWC-Saugus2 at rates as low as 700
to 800 gpm each will not fully contain groundwater that is migrating westward from the
Whittaker-Bermite property. Additionally, if these wells are operated at 1,000 gpm each,
perchlorate that is present in the Saugus Formation at wells MP-5 and VWC-157 will not
be captured, and will instead migrate to existing nonimpacted wells VWC-160 and
VWC-205.

3. No new production wells are needed in the Saugus Formation to meet the perchlorate
containment objectives.
4. Impacted well NCWD-11 is not a required component of the containment program.

5. Use of other water supplies in lieu of pumping at SCWC-Saugus1 and SCWC-Saugus2
will likely be detrimental to the long-term quality of groundwater in the Saugus
Formation. Pumping at these two wells is necessary to prevent migration of perchlorate
to other portions of the Saugus Formation.

6. The pumping plan for SCWC-Saugus1 and SCWC-Saugus2 may contain perchlorate that
is migrating in the Alluvial Aquifer from the northern portion of the Whittaker-Bermite
property, including perchlorate that has been detected in the Alluvial Aquifer at and
south of Bouquet Junction.

7. The operational plan for the impacted production wells will not cause detrimental short-
term or long-term effects to the groundwater and surface water resources of the Santa
Clarita Valley. In particular, the modeling analysis indicates that short- and long-term
variability in local rainfall and streamflows is the predominant cause of fluctuating
groundwater elevations, river flows, and groundwater storage volumes. This is
indicated by Figures ES-5 through ES-7, which together show that year-to-year changes
in groundwater recharge volumes and groundwater storage volumes are much greater
than year-to-year fluctuations in pumping. Compared to local hydrology, implemen-
tation of the operational pumping plan for the valley, including the planned use of wells
SCWC-Saugus1 and SCWC-Saugus2, has much less influence on the water resources of
the valley.
It is important to note that the model simulations described in this report distribute
pumping in a manner that is based on current and projected uses of both the Alluvial
Aquifer and the Saugus Formation. The conclusions presented in this report regarding
containment of perchlorate-containing groundwater will potentially be different if the
pumping plan for other Saugus Formation wells is significantly different than what was
simulated. In particular, a significant change in the Saugus Formation pumping regime in
the South Fork Santa Clara River area or near its mouth could potentially cause ground-
water flow patterns and capture zones to be notably different from those described in this
report. Changes that could appreciably alter groundwater flow patterns and capture zones
could include the operation of new wells in that area, or notably greater instantaneous

ES-6 RDD/041840005 (CLR2612.DOC)