Page 24 - Beaumont Basin Watermaster

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

3.3.1.3 Southwestern Area

The southwestern boundary of the Beaumont Basin was originally postulated by Bloyd (1971) to
be an unnamed fault, based on groundwater level differences observed between wells in the
southern Beaumont area with wells in the northern Beaumont area (see Figure 17). The fault
was extended by Bloyd (1971) to the northwest to intersect the postulated extension of the
Banning Fault (see Figure 11), although no supporting data was provided as a basis for its
location. Although significant groundwater level differences have been observed on either side
of the Bloyd (1971) boundary in the downtown Beaumont area, no significant groundwater level
changes have been observed across the boundary in the area where Noble Creek merges with San
Timoteo Creek and the fault previously shown in this area by Bloyd (1971) does not appear in
Rewis et al., 2006). As such, no groundwater flow barriers were simulated in this area of the
model used to estimate the Safe Yield of the Beaumont Basin.

3.3.2 Aquifer Characteristics
The aquifer system in the Study Area is characterized by lenticular sand and gravel deposits of
varying thickness and lateral extent that are separated by less permeable deposits of silt and clay.
The upper portions of these deposits are approximately correlated with the unconsolidated
quaternary surficial deposits of Rewis et al. (2006) and, where saturated, represent the Upper
Aquifer of the Beaumont Basin. At depth, the quaternary surficial deposits overlie younger
sedimentary deposits correlated with the Upper San Timoteo beds as described in Rewis et al.
(2006). Although these deeper deposits have been shown to contribute water to wells, they are
more consolidated and less permeable than overlying younger deposits. The deeper, less
permeable aquifer sediments are referred to herein as the Lower Aquifer.

The boundary between the Upper Aquifer and Lower Aquifer was estimated based on analysis of
data from deep boreholes and wells. In the central part of the Beaumont Basin, five wells have
been drilled and constructed to depths between approximately 1,000 and 1,550 ft below ground
surface (bgs). Crystalline basement complex was not encountered during the drilling of any of
the deep wells (Geoscience, 2006). The types of data collected from these wells and analyzed to
differentiate between the aquifers included geophysical logs, downhole flow meter tests in the
completed wells, isolated aquifer zone testing, and depth-specific groundwater quality data.

An example of the aquifer layer analysis is shown for BCVWD Well 24 on Figure 18. In
general, the majority of flow contribution to this well is above a depth of approximately 1,130 ft.
Isolated aquifer zone testing results show that individual 20-ft zones typically produce greater
than approximately 100 gpm above 1,100 ft and approximately 50 to 60 gpm below 1,100 ft.
The flow meter and isolated aquifer zone test data suggest that the aquifer system below

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