Page 25 - Beaumont Basin Watermaster

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

approximately 1,100 ft is more consolidated and less permeable. In addition, groundwater below
approximately 1,100 ft is more enriched in sodium and potassium relative to calcium as opposed
to groundwater above 1,100 ft which is more enriched in calcium relative to sodium and
potassium. Based on these data, the boundary between the Upper Aquifer and Lower Aquifer at
BCVWD Well 24 was set at 1,100 ft bgs.

Contours of the contact between the Upper Aquifer and the Lower Aquifer are shown on
Figure 19. The five deep wells with data used for differentiating between the aquifers are shown
on the map and include BCVWD Wells 23, 24, 25, 26, and 29. The contours for the remaining
Study Area were inferred based on information provided in Rewis et al. (2006) and a review of
driller’s logs for the area.

Although the upper portion of the Upper Aquifer is likely unconfined, pumping test data from
the deeper portion of the Upper Aquifer indicate that the deeper portion is semi-confined. Given
the highly stratified nature of the sediments in the subsurface and the pumping test data from the
deeper portion, the Upper Aquifer is assumed to become more confined with depth. The Lower
Aquifer is assumed to be confined.

3.3.2.1 Textural Analysis
General characteristics of the aquifer system in the Study Area were initially determined based
on a textural analysis of Upper and Lower Aquifers following the methodology of Faunt (2009).
Textural descriptions were inferred from driller’s logs and detailed lithologic logs from
boreholes or wells drilled within the Study Area. Detailed lithologic logs compiled by a
geologist were given preference over driller’s logs. When a detailed lithologic log was not
available, driller’s logs were selected for the analysis according to location and degree of detail
of geologic description. The target density of logs was one for every quarter section (one-quarter
mile by one-quarter mile). Based on these criteria, 41 borehole logs were selected from the 204
available within the Study Area.

The textural analysis resulted in a percentage of coarse grained sediment at each borehole
location. Depth-specific log entries were categorized as fine-grained (predominantly silt and/or
clay), coarse-grained (predominantly sand and/or gravel), or 50 percent coarse-grained/50
percent fine-grained (50/50). Entries were assigned 50/50 if they included both fine- and coarse-
grained sediment with no qualifier to indicate predominance of one over the other. The
percentage of coarse-grained sediment for each aquifer was estimated by dividing the combined
thickness of coarse-grained sediment by the total thickness of the aquifer, as defined by the
contour map shown on Figure 19. For the Lower Aquifer, only boreholes that penetrated greater
than 50 percent of the aquifer were used in the analysis. If a lithological entry was assigned a

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