(courtesy of the supply page of the LADWP website).
Based on my reivew of the LADWP reports during the 1980s,
the City obtained an average of 103 KAF/yr from wells
constructed in several basins of the Los Angeles River Basin. The largest
basin is the San Fernando Basin which accounted for around 85% of local
supply.
The local wells were operated under a "safe yield" concept. That
is, the long term extraction was set to approximate the average amount of
water that enters the basin. The inflow incudes natural percolation of precipitation
and runoff and the percolation of imported waters. The recharge of the ground
water supplies is enhanced by spreading grounds operated by the LADWP and
by the Los Angles County Flood Control District.
The ground water supply may be viewed as a large storage reservoir. It is
operated to help water utilities deal with variabilities in water supply
and demand. Under the "Watermaster's" rules for managing the Upper
Los Angeleds River Area, the City of Los Angeles could count on a dry year
yield of around 160 KAF/yr -- over 50% higher than the supply in an average
year. In a wet year, the City's may have pumped less than 50 KAF/yr from
local wells.
In 1980, trace levels of the industrial solvents TCE and PCE were found
in some of the wells in the San Fernando Basin. This discovery led to initial
concerns that well yields might eventually have to be reduced due to poor
water qualtiy. The LADWP completed a Groundwater Quality Management Plan
in July of 1983 which recommended a variety of measures to protect the quality
of this ground water resource.
Current Assessment
Current information on local wells may be found at the
water supply page of
the City's website. The City reports that groundwater extraction has accounted
for around 95 KAF/yr over the time interval from 1970 to 1995. The bar chart
below shows that the production from local wells has varied from a low of
around 30 KAF/yr to a high of around 130 KAF/yr. The chart also reveals
that pumping from the San Fernando Basin accounts for the vast majority
of the production.
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(courtesy of the supply page of the LADWP website). |