by Thomas K. Pendergast
The City has begun testing its new system of blending groundwater
into west side water supplies in April but, as of presstime, it had not begun to start the
process on a full-time basis.
“Part of the testing involved some introduction of groundwater
into the system intermittently, which means we’re not running
the pumps all day, every day. The initial pump station to deliver
water is the Lake Merced pump station and it has been introducing
a small amount starting on the 18th of April,” said
Suzanne Gautier, manager of communications and public outreach
for the SF Public Utilities Commission (SFPUC), which controls the water system.
“So, we’ll see somewhere around 100,000 gallons perhaps,although I’m not
positive on the number. (This approach) allows us to test the system while the
water ’s being introduced smoothly,” Gautier said. “Over
the next four or so years, it would get up to a maximum of
15 percent (of the total). That will take several years.
Sometime within this year we will be up to the capacity of one
million gallons a day; that would be about three percent.”
She said this would start when all of the “initial” well stations
start up and will be at full capacity when the final wells in Golden Gate Park
are brought online. It is the distribution of the “blended” groundwater, however,
that has raised eyebrows from many in the Richmond and Sunset districts,
both of which will get the blended water. Only about 60 percent
of the geographical area of the City will be getting blended water, but not the east
side of town. It is unknown how many of the city’s water customers will get the
blended water since about two-thirds of the city’s population
lives on the east side.
“It really comes down to a matter of engineering,” said Jeff Gilman, a project
manager for the SF Groundwater Supply Project. “Part of good engineering is always
to do a cost-benefit analysis and that’s why we did not consider it feasible
to try to blend the San Francisco groundwater throughout 100 percent of the City.
“This really comes down to engineering, pipeline design, pumping,” Gilman
explained. “We looked at pumping groundwater from the wells right into our
distribution lines. In other words, taking a fairly large water main that’s located near
a well location and pumping directly in there. What we found is some people
would get a very high percentage of groundwater and other people would get
very little. We felt it’s best to mix it all up first and then distribute it.”
But then why not pump from wells on the east side of town?
Gilman said they looked at doing the same blending at the University Mound
Reservoir, which serves that area, but decided against it.
“We ruled out trying to put wells in the groundwater basins on the east side
because we don’t think the quality would be as good, because that area
has had industrial development and also that area has different geology
and would be more prone to land subsidence. So, there are
environmental considerations,” he said.
But Gilman also admitted that a formal cost-benefit analysis for building a
groundwater pipeline to a reservoir on the east side of town was not actually facilitated,
describing the PUC’s method a “judgment call.”
“It really comes down to gravity. We had two choices when we designed the
project,” Gilman explained. “The wells are all on the west side and, as is done in
many communities, they pump from the well directly into the distribution system.
“And we said, ‘OK, how else can we do that?’ We said, ‘Well, we can pump to
our largest reservoir in the City through a dedicated pipeline and blend the groundwater
and then gravity takes care of the rest.’ The distribution area reflects what
we call the ‘pressure zone’ from the Sunset Reservoir.”
“Some of the blend at the higher elevation is the Sutro pressure zone. So, in
order for us to serve (the east side of the city) area, we would have had to build a
pipeline clear across the City to the University Mound Reservoir, which is
our second-largest reservoir, and that would have been cost-prohibitive.” But, if there
was no cost-benefit analysis,then how did the SFPUC come to this conclusion?
“Back 30-something years ago … at one point they were considering this big
pipeline, a sewage pipeline clear across the City, and that was rejected at the time.
It would just be too impractical, too expensive and cause too much disruption.”
But, a part of the high cost for the sewer pipeline was because it was slated to go
through a tunnel that would have been bored through the hills that separate the
east and west sides of San Francisco. According to Gautier, when the SFPUC
completed the full cost estimate for constructing all of the pipelines in the
new system on the west side of town, they figured it would be about $10 million.
The plan is to pump the groundwater from six wells into, primarily, the Sunset
Reservoir as well as the Sutro Reservoir. In those reservoirs that groundwater will
be mixed or blended with water that now comes either from Hetch Hetchy or one of
the five reservoirs in the Bay Area that also contribute to the San Francisco water
supply. City officials say the usual overall average blend is about 85 percent from
Hetch Hetchy. The other 15 percent is from those reservoirs, which get their water
from rain runoff in watershed areas.
The ultimate goal is to blend 10 million gallons of ground-water per day into
the city’s water supply. Planning for the project started in 2004
and the SFPUC approved the plan in 2008.
City sells Hetch Hetchy water
“The Hetch Hetchy water system goes through 167 miles of pipeline before it
gets here. Part of the approval of that pipeline, the original approval of that
pipeline before it was built, was that San Francisco would commit to serving other
communities before it gets to San Francisco,” said Manisha Kothari, an SFPUC
water resources planner. “That was the way in which we got the
water secured to come to San Francisco – that we will commit to provide water to
other communities, that’s the other two-thirds wholesale customers – as an obligation,”
Kothari said. “That obligation has not changed.
“We needed to do upgrades on the system and that was a $4.6 billion program
that we did go to the voters for, that was bond-funded and we went to the voters to
do that project. That project, the environmental review that was associated with
that project required (that) we will commit to developing 10 million gallons a day
of local supply and start diversifying our supply and not relying entirely on Hetch
Hetchy. The other customers of that pipeline also committed to building at
least 10 million gallons a day of local resources.”