Page 22 - Beaumont Basin Watermaster

Beaumont Basin Watermaster
2013 Reevaluation of the Beaumont Basin Safe Yield 3-Apr-15

Creek and groundwater from area wells reported lowered concentrations of pharmaceuticals and
personal care products (PPCPs) in downstream portions of the creek compared to discharges
from the City of Beaumont WWTP (University of California Riverside, 2012). The lower
concentrations downstream are likely a result of dilution from groundwater discharging to the
stream from the upgradient Beaumont Basin area.

3.3 Hydrogeology

3.3.1 Beaumont Basin Boundaries
The Beaumont Basin adjudication boundary is based on the Beaumont Storage Unit boundary as
defined by Bloyd (1971) (see Figure 2). This boundary was based on the location of faults as
they were mapped or inferred at the time. As originally depicted, the faults were inferred based
on groundwater level differences observed in wells on either side of the faults. The faults defined
the boundaries based on the premise that fault movement results in a low permeability zone that
inhibits groundwater flow, forming a hydrological boundary.

Geological mapping and hydrogeological analysis conducted since Bloyd (1971) have changed
our understanding of the location and characteristics of the faults that form the hydrogeological
boundary of the Beaumont Basin (Rewis et al., 2006). Many of the faults have been remapped
based on recent data such that they are no longer in the same location as mapped by Bloyd
(1971). These revisions have resulted in differences between the Beaumont Basin adjudication
boundary (as defined in the Judgment) and the physical hydrogeological boundaries of the basin
(see Figure 11).

In order to develop a representative Safe Yield estimate for the Beaumont Basin adjudicated
area, a larger Study Area was identified that included the entire Beaumont hydrogeological basin
(see Figure 11). The larger Study Area, which also became the domain for the groundwater flow
model, provided hydrological and hydrogeological context for the water budget of the Beaumont
Basin adjudicated area. It is emphasized that the Safe Yield estimate reported herein is specific
to the Beaumont Basin adjudicated area, as defined in the Judgment.

A more detailed analysis of hydrogeologic basin boundaries follows.

3.3.1.1 Northern Area
The northern Beaumont Basin adjudication boundary, which extends through the Cherry Valley
area, is not the hydrogeologic boundary of the basin. During a pumping test conducted in 1991
on BCVWD Well 16, which is located immediately south of the Beaumont Basin adjudication

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