Lower Pilarcitos Creek Groundwater Basin Study - Coastside ...

Conclusions
This study indicates that a Lower Pilarcitos Creek groundwater project is
technically and economically feasible. The following key conclusions have been
developed:
• The perennial or safe yield is 1,300 AFY and is defined here by the amount of
groundwater that can be pumped without inducing significant adverse
impacts, primarily saltwater intrusion from the ocean. This perennial yield
value amounts to 60 percent of the estimated 2,200 AFY of total inflow to the
groundwater basin, reflecting the unlikelihood that all of the basin inflow can
be safely captured without incurring adverse impacts.
• The estimated total annual perennial yield of 1,300 AFY takes into account
long-term pumping. Relatively recent increases in pumping from the Balboa
wellfield (140 AFY) should be included in the 1,300 AFY. The remainder
(1,160 AFY) is sufficient for the potential Lower Pilarcitos wellfield and
additional development by CCWD.
• The estimated total yield of the five wells of the proposed Lower Pilarcitos
wellfield ranges between 129 and 259 MGY for drought and normal years.
For costing purposes, an average value of 194 MGY (595 AFY) is assumed.
Pumping rates are limited by groundwater level changes, particularly in the
dry season.
• Estimated construction, operations and maintenance cost for the proposed
Lower Pilarcitos Creek groundwater project are comparable to the current
costs of surface water purchase and treatment.
• Groundwater in the marine terrace aquifer is confined and not in direct
hydraulic connection with Pilarcitos Creek; accordingly, pumping of the
proposed wells would not deplete creek flows.
• Should CCWD decide to proceed with evaluation of the proposed Lower
Pilarcitos Creek wellfield, the recommended next step is installation and
testing of a pilot production well. In addition, stream flow monitoring is
recommended.
62