Lower Pilarcitos Creek Groundwater Basin Study - Coastside ...

for recent years and for prior years What are the reasons for the difference, if
any, in the estimates What changes in total annual withdrawals have occurred
in the last ten years What changes in total annual withdrawals by current well
owners (other than the District) are anticipated in the next 10 years
The most important groundwater pumping in the basin is the Ocean Colony Partners
Balboa wellfield, which provides irrigation water for two golf courses south of the basin.
This groundwater pumping and export is 347 AFY. Groundwater pumping and
consumption within the basin is estimated at 163 AFY. The latter value accounts for
return flows to the basin. No previous estimates of total pumping are known.
Groundwater pumping amounts have changed little over the past years. While pumping
for landscaping has increased since the mid-1980s, pumping for crops in the
groundwater basin has declined. There are no known plans to increase golf course
pumping. For more information, see Hydrogeologic Setting, Groundwater Development
and Wells, and Groundwater Basin Water Balance.
4. What is the estimated total annual amount of groundwater currently potentially
available from the entire groundwater basin on a safe yield basis to the District
during normal precipitation periods and during drought periods Can these same
total amounts of groundwater be safely withdrawn during a portion of the year,
rather than evenly throughout a 12-month period Can the average annual rate
of withdrawal be safely increased by a factor of 50% or 100% for a short period
of time
The estimated total annual perennial yield (safe yield) of the Lower Pilarcitos
Groundwater Basin of 1,300 AFY takes into account long-term existing pumping
including agriculture and pumping from the Balboa wellfield for one golf course.
Relatively recent increases in pumping from the Balboa wellfield for a second golf course
(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.
Maximization of overall yield from the wellfield would involve seasonal operation with
greatest withdrawal during the winter and spring. Summer and autumn pumping will be
limited by lower groundwater levels and recommended operating criteria that avoid
dewatering of the aquifer and exposure of well screens. For more information, see
Groundwater Basin Water Balance, Perennial Yield, and Lower Pilarcitos Creek Test
Well Analysis, Wellfield Operation and Life Expectancy.
5. What is the total estimated annual amount of groundwater currently potentially
available on a safe yield basis from the District’s five existing test on a safe yield
basis during both normal precipitation periods and drought periods Can these
same annual total amounts be safely withdrawn during a portion of the year Can
the average annual rate of withdrawal be safely increased by a factor of 50% or
100% for a short period of time such as five days to meet customer demands
during a hot weather period
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. This total yield assumes seasonal
variation in pumping, with greater pumping during the winter and spring. Pumping rates
are limited by groundwater levels relative to the elevations of the top of the aquifer and
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