Lower Pilarcitos Creek Groundwater Basin Study - Coastside ...

detailed in the section, Hydraulic Properties of the Marine Terrace Aquifer, this
groundwater outflow was estimated using Darcy’s Law. The amount of groundwater
outflow varies seasonally and is estimated at 1,175 AFY in summer and 2,334 AFY in
winter. For the overall water balance, an average value of 1,755 AFY is used.
Groundwater Pumping and Export. The only known groundwater pumping and
export from the basin is that of Ocean Colony Partners, operating four wells at the north
end of Balboa Boulevard near Kelly Avenue (Ocean Colony, August 27, 2002). The
water is pumped to irrigate 210 acres of the Half Moon Bay golf links, located south of
the groundwater basin. Annual water usage is 347 AFY; this represents an export from
the basin.
Groundwater Pumping and Consumption. Groundwater is pumped from the
groundwater basin and used for cropping, landscape irrigation, and domestic use.
Approximately 94 acres of cropland in the groundwater basin are irrigated
primarily with groundwater. Review of the soil moisture balance (Appendix 7) for
landscaping and cropland indicates that the irrigation water needed to supplement
rainfall and fulfill the full potential ET is 1.39 feet/year. It is assumed that all water
applied in excess of this amount percolates downward and returns to groundwater.
Accordingly, the amount of consumed water is the full potential ET, 1.39 feet/year.
Application of this rate to the 94 acres of irrigated cropland results in a groundwater
consumption of 131 AFY.
Most of the landscaping irrigation demand is supplied by the CCWD, which
serves local schools, parks, and multiple-unit housing developments with extensive
commons. Possible exceptions include wells operated by the Amesport Landing
Homeowners Association and Holiday Inn. This commercial groundwater pumping and
consumption for landscape irrigation is assumed insignificant.
Numerous domestic wells have been drilled in the groundwater basin. As
described in the previous section on Groundwater Development and Wells, 265 wells
were drilled during 1985 through 1991, most because CCWD connections were not
available. It is assumed that almost all of these were abandoned when CCWD
connections became available. As a result, it is estimated that 126 wells serve
households in the groundwater basin.
Assuming that these households use 0.273 AFY (the CCWD average water
usage for a single family home), then pumping from the 126 wells amounts to 34 AFY.
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