Lower Pilarcitos Creek Groundwater Basin Study - Coastside ...

during droughts and 799 AFY (495 gpm; 0.71 MGD; 259 MGY) during an average water
year. For an average precipitation year, wet-season yields occurring from November
through March (5 months) are about 351 AF (527 gpm; 0.76 MGD); while dry-season
yields occur during the balance of the year (7 months) are 448 AF (476 gpm, 0.69
MGD). The wet- and dry-seasons are based on the precipitation patterns shown on
Figure 3. For drought years, wet-season yields are about 175 AF (261 gpm; 0.38 MGD);
while dry-season yields are 221 AFY (235 gpm; 0.34 MGD). However, the lowest
monthly yields may range between 4 and 53 AF (3 gpm to 33 gpm; 0.004 to 0.048
MGD).
In summary, well yields could vary between 129 and 259 MGY. Additional wells
could be installed to increase the capacity of the wellfield during the dry-season.
However, to provide a conservative estimate of water costs, an annual yield of 194 MGY
(average of 129 and 259 MGY) is used in this economic analysis in order to reduce the
water produced during this period at the Nunes WTP to meet water quality goals for
floriculture irrigation in the Coastside area.
The locations of these wells, together with that of the proposed pipelines
connecting to the Nunes WTP, are shown in Figure 22. Photographs of the well sites
and of the pipeline route are shown in Appendix 9. These photographs were obtained at
the time of the site visit to observe field conditions related to access and location in order
to estimate the construction cost of the facility including pipelines, electrical service, and
related features.
Water Quality and Treatment
The water quality obtained in January 1998 (Nelson, 1998) during the pumping
tests are summarized in Table 16 for the five wells. Also shown in Table 16 are (1) the
average of the groundwater quality for the wells, (2) the average for the current Nunes
WTP, (3) a blend of the Lower Pilarcitos Creek groundwater and surface water in
December through February with increasing amounts of Crystal Springs Reservoir water
in other months of the year, (4) comparison to CCWD’s other source of supply at the
Denniston Creek WTP, and (5) agricultural water quality objectives. Water quality of
individual “raw” water sources (i.e., Crystal Springs Reservoir, Pilarcitos Lake, and upper
Pilarcitos water wells) were not provided by CCWD. In addition, seasonal variations of
the water quality may occur for these raw water sources.
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