Water Quality The growth of Los Angeles had always forced the City to be
concerned with the adequacy of its supply, and consequently its
attention had always been directed outward in its search.
The new emphasis on managing the water resource brought
protection of water quality to the forefront as the primary goal of good
management. Today, Los Angeles is the second largest city in the
nation.
In December 1995, Los Angeles joined the "Partnership For
Safe Water Program" in an agreement with the U.S. Environmental
Protection Agency to self-assess and potentially implement additional
drinking water safeguards and treatments. Los Angeles met Partnership
eligibility requirements because of its good standing under current
regulations and a commitment to undertake various phases of the program. There are three sources for Los Angeles’ water:
approximately 60% comes
from the Eastern Sierra via the Los Angeles Aqueduct system, 15% from the San Fernando groundwater basin, and
25% from the
Metropolitan Water District’s Colorado and Feather River supplies. Water from the Owens River watershed is
protected from industrial and agricultural contamination by DWP land
management practices. However,
some turbidity arises as water from the watersheds travels through
unlined channels in a natural rural setting before being diverted into
the two aqueducts for its journey to the City. The DWP determined that a filtration plant would be
necessary to reduce this turbidity and in 1986 Los Angeles completed its
first filtration plant. Using
ozone and rapid rate deep bed filters, the $146 million Los Angeles
Filtration Plant treats up to 600 million gallons of water each day.
It is the largest direct filtration plant in the U.S. and the
second largest ozone plant in the world. One benefit resulting from the use of ozonation as a
disinfectant process is the reduction in formation of trihalomethanes
(THMs). These chemical
compounds are formed when chlorine combines with naturally occurring
organic material in the water. By
using ozone as a disinfectant in the initial treatment process instead
of chlorine, the City is able to reduce THMs by as much as 50%. In August of 1999, Los Angeles began to fluoridate its water at the Los Angeles Aqueduct Filtration Plant. Natural background levels of fluoride are boosted to optimal levels that help prevent tooth decay. Additional fluoridation facilities have already, or will soon, come on line at groundwater treatment sites and at MWD service connections. The next 25% of the City’s water comes from MWD.
As Arizona begins to exercise its increased rights on the
Colorado River, the MWD will need to rely more on northern California
water supplied through the State Water Project.
When water from the State Water Project flows through the
Sacramento-San Joaquin Delta it picks up organic material from the
riverbeds. With increased use of water containing a greater amount of
organic material, higher levels of THMs in the MWD supply would have
been likely. However, by
using chloramines, a combination of chlorine and ammonia, as a primary
disinfectant, the MWD has taken steps to reduce this problem. The San Fernando groundwater basin not only supplies 15% of
Los Angeles’ domestic needs, but it also acts as a vast underground
reservoir where water accumulates during years of abundant rainfall and
is stored for use in the future. In 1980, newly available sensitive monitoring equipment
detected trace amounts of trichloroethylene (TCE) and perchloroethylene
(PCE), as well as smaller amounts of other industrial chemicals in the
San Fernando groundwater supply.
Some of the contaminated wells have been abandoned. The loss of production from the abandoned wells, has been made up by developing new well field such as Tujunga Well Field (12 new wells) which is located up gradient of the significant contaminant plumes. The San Fernando Groundwater Quality Management Plan was issued in July 1983. The objective of this effort is to protect and upgrade the quality of the stored water in the Basin. Special emphasis is placed on monitoring and removing the organic contaminants TCE and PCE found in the groundwater. The Plan recommends systematic installation of sanitary sewers in designated areas through the San Fernando Valley in order to eliminate existing commercial and industrial Private Sewage Disposal Systems and their discharge of wastewater to the groundwater basin. The State-mandated Underground Storage Tank Program headed by the City of Los Angeles Fire Department focuses on the monitoring and removal of gasoline, and their related constituents from the soils, in order to prevent contamination of the underlying groundwater. The
North Hollywood Aeration Facility removes and treats the contaminated
groundwater in the upper zone of the aquifer and prevents the migration
of the contaminants downward into the San Fernando groundwater basin.
The water from seven contaminated shallow wells is pumped to the top of
the aeration tower. As the water flows downward an upward air blower,
flows counter-current through the water. Volatile gases trapped in the
water then vaporize and join the air stream. This air stream is filtered through
activated carbon to be sure
none of the contaminants are released to the atmosphere. The Pollock Wells Treatment Plant was dedicated on March 17th 1999. The PWTP restores the contaminated Pollock production wells back to operation. The Plant uses four granular activated carbon pressurized vessels to remove dissolved organic chemicals down to non detect levels in the groundwater. The operation of Pollock wells also limits excessive rising groundwater discharges from the San Fernando Basin to the Los Angeles River. The
DWP is participating in several research projects aimed at developing
new technologies that will assist in the removal and destruction of
source water contaminants. One
such technology, known as advanced oxidation, uses ozone and hydrogen
peroxide to oxidize groundwater contaminants into harmless by-products
such as chloride and carbon dioxide.
The Department of Water and Power continually monitors the purity
and quality of its water supply. More
than 60,000 laboratory and field analyses are made yearly, 15,000 for
bacteriological control and the balance for chemical, physical, and
radiological inspections. Sampling occurs at all sources; watershed, reservoirs,
distribution mains, and consumer taps.
Water carrying and storage facilities are also checked. DWP is required by State and Federal law to regularly test City water. Monitoring of over 90 regulated chemicals and bacteriological contaminants is required at varying frequencies based on the type of constituent and the type of source water. There are constituents found in drinking water that are not yet regulated. Some of these “unregulated constituents” are monitored because they could be candidates for future regulations or are of interest to our customers. The DWP has a crew of field and laboratory personnel who sample and test City water every day of the year, including weekends and holidays. The distribution system water samples are collected from secured water sampling taps installed throughout the city. Regular water samples are also collected from watersheds, reservoirs, groundwater supply wells, storage facilities and other locations. There are over 170 different constituents which DWP tests for in the water. The people of Los Angeles today enjoy safe drinking water
from high quality sources that meets or exceeds all standards set by
state and federal agencies. The
Los Angeles Department of Water and Power is constantly working to
assure that this continues into the future. |
The
concentration of these contaminants is very small, measured in parts per
billion (a part per billion is equivalent to a few drops in a swimming
pool).