Page 26 - Beaumont Basin Watermaster

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

classification of 50/50, half of the length of the interval was used to calculate the thickness of
coarse-grained sediment.

The textural analysis resulted in contour maps of percent coarse-grained values at each borehole
location for each aquifer (see Figures 20 and 21). Contours were generated by Spatial Analyst
(ESRI, 2009) through inverse distance weighting interpolation between control points. The
textural analysis was used as a guide for assigning initial hydraulic conductivity values to areas
of the groundwater flow model where pumping test data was not available.

3.3.2.2 Transmissivity

Transmissivity is a measure of the ability of groundwater to flow within an aquifer and is defined
as the rate of groundwater flow through a unit width of aquifer under a unit hydraulic gradient
(Fetter, 1994). Multiple sources of data for estimating transmissivity were obtained, reviewed,
and analyzed, including published reports (Rewis et al., 2006), studies (SGPWA, 1991), and well
completion reports (Geoscience, 2002; Geoscience, 2005; Geoscience, 2006a; Geoscience,
2006b).

The most reliable transmissivity estimates were obtained from controlled, long-term (i.e. 24 hrs
or more) constant-rate pumping tests in wells within the Study Area. Transmissivity estimates
from constant rate pumping test data were available for 11 wells (see Figure 22; Appendix C).
Four of these tests were conducted after the previous USGS model (BCVWD Wells 24, 25, 26
and 29). Analysis of constant-rate pumping tests show aquifer transmissivity ranging from
2
2
approximately 3,700 ft /day to 27,800 ft /day in the Study Area.
In the absence of controlled pumping tests, additional transmissivity estimates were developed
from short-term specific capacity pumping tests. Although transmissivity estimates from
specific capacity data are not as representative as estimates from long-term pumping tests,
specific capacity data was available from more wells across a larger portion of the Study Area
and allowed for a more spatially distributed assessment (see Figure 22). Specific capacity data
was obtained from Rewis et al. (2006), SGPWA (1991), and well efficiency tests (i.e. Edison
Tests). Specific capacity was used to estimate transmissivity based on Theis et al. (1963) and the
following relationship:

Where:

2
T = Transmissivity (gpd/ft; later converted into ft /day)

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