The city of San Diego could save hundreds of millions of dollars in upgrade and expansion costs for its Point Loma sewage treatment plant, and get more drinking water in the bargain, according to a final draft study given to the city in late May.
With
the savings, recycling sewage to drinking water standards costs roughly
the same as importing more water, according to the final draft of the
San Diego Recycled Water Study. The precise numbers depend on what
assumptions are made about which costs can be avoided.
If the
study's recommendations are followed, new sewage treatment plants would
be built in Point Loma, University City and the South Bay. The cost of
upgrading the existing Point Loma sewage plant would drop from an
estimated $1.2 billion to $710 million.
Release of the final draft study comes as the county's main water supplier is in the late stages of negotiating for another new water supply, desalinated sea water from a plant to be built off the coast of Carlsbad.
Poseidon Resources
Corp. is negotiating a water purchase agreement with the San Diego
County Water Authority, which supplies most of the water used in the
county. The authority says it expects to get a completed contract ready
this summer for a 60-day public review before a final vote is held.
Under
the draft study, sewage treated to drinking water standards would yield
100 million gallons a day, about 20 percent of the region's water use.
Assuming the study's numbers are accurate, the net cost to the city per
unit of water amounts to about half that estimated for water from the
proposed desalination plant.
The study presented three scenarios
for the cost of repurified sewage in dollars per acre foot. One
acre-foot is about 326,000 gallons:
- $1,200, counting avoided costs from reduced usage of the Point Loma sewage treatment plant,
- $1,100, including a "salt credit" for removing salt from the treated sewage
- $700, including those savings along with avoided costs of upgrading of the Point Loma plant, which discharges treated sewage into the ocean.
"These costs compare well to the existing untreated water cost
of $904 per acre foot, and are more economical than most other new water
supply concepts being proposed," the report stated.
Peace with
local environmentalists would be another potential benefit.
Environmentalists have long complained that the treated sewage, expelled into the ocean 4.4 miles off the coast at a depth of 320 feet, harms marine life. The city disputes the claim.
Livia Borak,
an attorney from Coast Law Group, urged the city to forgo the Poseidon
desalination proposal and choose sewage recycling instead. Borak spoke
at a May meeting of the Water Authority, She pointed out that the city
has great leverage with the agency because of its weighted vote.
City clout
The
city of San Diego contains a little more than half the 3.1 million
population of San Diego County, with proportionate clout on regional
agencies such as the Water Authority. So what San Diego decides to do
will greatly influence the water supply picture for the whole region.
Moreover, the city faces water- and sewage-related financial considerations that don't apply to North County.
San Diego's potential costs for upgrading the Point Loma plant exceed $1 billion.
So far, the city has obtained waivers, the latest of which expires in
2015. There is no guarantee the city, already reeling from high water
bills, will receive another waiver.
Counting those avoided costs,
the net cost to the city of San Diego for recycled sewage amounts to
about half that of buying water from the proposed desalination plant.
In water industry jargon, recycling sewage to drinking water standards is called indirect potable reuse,
or IPR. The purified sewage is sent to reservoirs or underground
storage, then drawn off with new supplies for treatment and
distribution. This contrasts with direct potable reuse, in which
reclaimed water is directly put back into treated drinking water
pipelines.
The study's numbers for IPR seem reasonable, said water policy expert David Zetland,
who has long researched Southern California's water infrastructure.
Zetland said he did not review the study, but was making a general
observation about the cost of indirect potable reuse compared to
seawater desalination.
"IPR can easily be cheaper than
desalination, as it takes partially-treated wastewater and further
cleans it for consumption," said Zetland, a senior water economist
at Wageningen University in the Netherlands. "That's why the "marginal"
cost will be quite low. A new IPR plant can also be cheaper than desal,
since there are fewer salts to remove."
The desalinated ocean water from the Carlsbad plant would cost about $1,865 per acre-foot, according to an estimate made last year by Poseidon Resources, based in Stamford, Conn.
While
the city of San Diego would not directly buy the desalinated water, the
plant's 50 million gallons a day capacity would increase the region's
total supply by about 10 percent. Desalinated water from Carlsbad would
also bring a new source of local water to the arid county, which has
seen its traditional sources of imported water threatened by drought,
environmental restrictions, over-optimistic assumptions, and legal
challenges.
Recycling sewage to drinking water would also provide a reliable local supply to the county. But the city's leaders and the San Diego Union-Tribune, now U-T San Diego, have rejected it because of discomfort of what's been dubbed "toilet to tap."
Regardless,
the approach is being used in Orange County, and scientists have said
evidence indicates indirect potable reuse can provide water as safe as
that from untreated imported water. A new report from the respected
National Research Council encouraged exploration of its use.
"The
report presents a brief summary of the nation’s recent history in water
use and shows that, although reuse is not a panacea, the amount of
wastewater discharged to the environment is of such quantity that it
could play a significant role in the overall water resource picture and
complement other strategies, such as water conservation," the NRC study
stated.
With water costs skyrocketing and imported supplies
increasingly more difficult to come by, the city of San Diego
commissioned the study to get a fresh look at the pros and cons of
repurified sewage.
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