Water Supply Infrastructure

In this submission we include water supply infrastructure strategies that could increase the City’s water supply, or the system safety and reliability, or both. (The City Council’s statement of purpose for the Water Supply Advisory Committee included analyzing “future threats” to the water supply and “potential solutions to deliver a safe, adequate, reliable and environmentally sustainable water supply”.)

Recommendation—that the City conduct an evaluation of the cost, benefit, feasibility and environmental impact of the following:

1.  Aquifer recharge with potable water. Fugro and Associates (1999)—included in Carollo Engineers, Alternative Water Supply Study, 2000) makes a brief mention of the possibility of injection wells to recharge the aquifer in the vicinity of the Beltz wells. Using potable water for recharge would require water rights revisions, to allow diversion of San Lorenzo River water to storage.

2. Aquifer recharge on North Coast.   Fugro also recommended exploring the potential of aquifer recharge using a quarry at Wilder Ranch for infiltration and wells in the vicinity to recover groundwater during the dry season.

3. Adding a new water treatment facility—possibly at Bay St. reservoir. 

In the WSAC August agenda packet is Document Q, a Vulnerability Report from City staff. The report concludes:

One area that continues to receive attention is treatment redundancy. The City operates 2 treatment plants with over 90% of its water being treated at the Graham Hill Treatment Plant…A redundant facility would improve reliability and redundancy and meet emergency flows, at a minimum, should the Graham Hill Plant be out of service for an extended period of time.

The CDM study of system reliability[1] concluded,

…Major damage to or catastrophic failure of the finished water tank, backwash tank, or reclaimed water tank could render the Graham Hill Plant inoperable for significantly longer than the 7 days and 30 days[2] specified in the proposed reliability goals for emergency outages.

CDM makes the recommendation to “Evaluate the benefits/cost of a second surface water plant to provide redundancy.”

Water from the North Coast streams arrives at Bay St. reservoir by gravity. Historically the Bay St. reservoir supplied the City via gravity. The advantage of a gravity-powered water supply will once again be appreciated in a future of high electricity prices and potential electricity brown-outs and black-outs. Adding an array of solar panels at the Bay St. reservoir, and DC-powered pumps, would add the ability to treat water and/or pump water to higher elevations in the system during extended electricity black-outs.

There is a potential need for additional water treatment capacity if the City and neighboring water agencies adopt a plan for water transfers. According to a report from County Water Resource Director, John Ricker[3], one option calls for the Graham Hill Plant capacity to be upgraded from 10mg/day to 16 mg/day capacity. If a redundant water treatment facility were built at the Bay St site, this would have the potential to free up sufficient capacity at Graham Hill Treatment Plant so that no expansion there would be necessary to maximize the yield from water transfers.

4. Wells to tap Santa Margarita Aquifer in Live Oak area

Carollo Engineers (2000) recommended this strategy and reported that there are no existing wells that are deep enough to tap this aquifer. The City built a test well to provide information about this option.

5. Relocate the main San Lorenzo River diversion upstream

The San Lorenzo River at the site of the Tait St. diversion used to have a higher velocity flow in the dry season of past years than it currently does. The diversion site is just about ten feet upstream from stagnant ponding. This will be exacerbated by sea level rise, with the lagoon at the river mouth extending farther upstream.

The CDM report on system reliability notes that the City’s principal diversion on the San Lorenzo River and adjacent pump station are vulnerable to floods. The 1982 flood nearly inundated the pump station. The California Climate Adaptation Strategy (2009) reports,  “With a sea level rise of approximately one foot, the anticipated 100‐year flood event in Santa Cruz is expected to occur every 10 years, increasing the likelihood of storm‐related inundation.”

Moving the City’s main diversion upstream of Paradise Park will also improve source water quality, as septic systems in Paradise Park have insufficient distance from the river.

6. Accelerate the replacement of old pipes in the distribution system

Bill Kocher once reported to the Water Commission that the City would have to invest eight times the amount of money it currently spends on replacing water mains in order to meet the standard recommended by the AWWA.

Investing in pipe replacement is a water conservation strategy, since old pipes leak. The Draft Master Conservation Plan calls for expanded main replacement and active leak detection.[4] The Draft lists the estimated cost per million gallons of water saved is $2,344, which ranks this measure in the top tier of potential conservation measures. The cost of main replacment should be understood in the context that the mains would need replacement at some point anyway. Hence the expenditure is not really discretionary. With that in mind, it makes good economic sense to expand the main replacement well beyond the amount envisioned by Maddaus in the Draft Conservation Plan.

Even more important than the conservation value of this measure is the benefit to system reliability. As CDM notes in their study, in the 1989 earthquake it took six weeks to restore the 82 breaks in distribution mains.  “Aging cast-iron, galvanized steel, and asbestos-cement distribution lines suffered approximately 75% of the failures.” The earthquake damage to distribution pipes meant that fire protection was compromised.

[1] CDM, “Technical Memo No. 2, System Service Reliability Goals”, (2002)

[2] 6 million gallons per day within 7 days;  12 million gallons per day within 30 days

[3] John Ricker, progress report to Soquel Creek Water District, Nov 5, 2013

[4] Maddaus, “Draft Master Conservation Plan”, Measure #1, Water Loss Control Program

Leave a Reply

Your email address will not be published. Required fields are marked *

 characters available

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>