Lower Pilarcitos Creek Groundwater Basin Study - Coastside ...

In addition, 128 wells have been drilled in the Half Moon Bay area for crop and
landscape irrigation. Within the groundwater basin, the cropland relying on wells for
irrigation supply is clustered along lower Pilarcitos Creek and near the confluence of
Arroyo Leon and Pilarcitos Creek. About 10 agricultural irrigation wells are still active in
the groundwater basin. Wells for landscaping irrigation include Ocean Colony Partners’
wells located along Balboa Boulevard near Pilarcitos Creek.
The Ocean Colony Partners Balboa wellfield is the most important groundwater
user in the basin. The wellfield consists of four, relatively low-capacity wells that are
pumped to provide water supply for two golf courses, the Half Moon Bay Golf Links
located south of the groundwater basin. The wellfield initially was developed in the early
1980s as the supply for one golf course, pumping an average of 207 acre-feet per year
(AFY), while current pumping for the two golf courses averages 347 AFY (Luhdorff &
Scalmanini, 2000). This pumping represents an export of water from the groundwater
basin.
Since the mid-1980’s the total amount of groundwater pumping has changed
little. Although numerous wells were drilled in the 1980s for domestic use, most of these
were subsequently abandoned. While the pumping for the Balboa wellfield has
increased since the mid-1980s, the cropland irrigated with local groundwater has
declined since 1987.
Figure 8 shows the areal distribution according to township/range section of the
614 wells listed in Appendix 2. Note that 432 or about 70 percent of the wells have been
drilled in the southwest quadrant of township 5W/5S, or in other words, in the Lower
Pilarcitos Creek groundwater basin. However, as noted above, many of these wells are
not currently in use.
Soils
Soils in the Pilarcitos Creek watershed and groundwater basin are generally
divided into upland soils and soils of the marine terraces, alluvial fans, and floodplains
(USDA SCS, 1961).
The Pilarcitos Creek watershed is marked by two major upland soil associations.
The Miramar-Sheridan soil association occurs generally north of Pilarcitos Creek and
includes soils developed on granitic rocks with shrub- or forest-covered steep slopes.
The Lobitos-Santa Lucia-Gazos soil association occurs generally south of the creek.
These soils are developed on sedimentary rocks with grass- or shrub-covered steep
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