Desal Alternatives Endorses Water Supply Advisory Committee Recommendations

Santa Cruz Desal Alternatives Statement on Water Supply Advisory Committee Recommendations

Santa Cruz Desal Alternatives applauds the work of the City’s Water Supply Advisory Committee, and we support the Committee’s final recommendations to the City Council.

The Water Supply Advisory Committee (WSAC) recommendations include strengthened conservation practices, expanded supply capacity through regional cooperation to share and store river water underground, a backup concept to address concerns about risks in an uncertain future, and clear guidelines for assessing our progress toward long-term water security.

We are especially pleased that the WSAC recommends expansion of the 2014 Water Conservation Master Plan to more fully enable our homes, schools, and businesses to incorporate deep conservation as common sense, not sacrifice.

We strongly support the Committee’s central recommendation to increase available supply by using excess winter flows from the San Lorenzo river and replenishing our over-tapped local aquifers with water to be available during drought periods.

River-water aquifer recharge can begin this winter and build up over the next several years, allowing Santa Cruz to store more than three times the water needed for the worst-case climate-change scenario of an eight-year drought. Together with the commitment to increased conservation, this strategy can securely meet our water supply needs for the foreseeable future.

Recent scientific studies have shown the potential for this surface-water aquifer recharge strategy. For supply, there is a huge volume of winter water available that the City may capture from the river. Gary Fiske, the City’s primary water consultant, formally concluded in his report to the City’s Water Supply Advisory Committee that ”The harvesting and storage of winter flows has the potential to completely address the City’s water supply challenges and enable the City to meet projected future demands. This is the case even with current water rights, the DFG-5 instream flows [required for fish], and climate change.”

To hold that water for drought periods, the new hydro-geological measurements indicate an immense amount of underground storage capacity – “a total of over 12 billion gallons of potential storage” – available in Scotts Valley and mid-County aquifers that have been pumped down over past decades. This is four times the 3 billion gallons of added storage needed to protect against the City’s worst-case shortfall.

The aquifers can be recharged in two ways using treated winter flows. The water can be transferred to neighboring water districts for use in lieu of pumping their wells, allowing the aquifers time to recharge naturally. In addition, the water can be pumped into reverse wells for direct injection into the aquifers.

Recharging the aquifers will provide substantial benefits for natural habitat. As they refill, the aquifers will feed the regular flow levels in local streams, steadily improving conditions for fish, birds, and streamside plants. Recharging the aquifer near the coast will reverse seawater intrusion threatening to taint wells and soils. This water supply strategy will also allow the City to finally resolve longstanding negotiations with the Department of Fish and Wildlife over reserving year-round flows expressly for fish habitat in the river.

A river-water aquifer recharge system provides flexibility and water security because it can be developed in separate investment stages that cumulatively increase our water reserves. Implementation can be scaled up to expand both the amount of winter water captured and the available storage capacity utilized. The City’s goals for sufficient stored water could be achieved long before the system reaches full scale. Recharging aquifers uses low-impact technologies in common use throughout the country and adaptable to our local geology.

Even with the confidence that the river-water aquifer recharge system can provide, it is appropriate to include a backup supply plan in case unforeseen circumstances prevent the system from meeting the supply-demand gap.

The WSAC recommends investigating a backup supply from advanced treatment of wastewater, or desalination if treated wastewater doesn’t pan out. We are concerned about the public health, environmental, and energy impacts of these systems, and we would oppose any premature pursuit of either that reduces the City’s commitment to the primary river-water aquifer recharge strategy.

Any discussion of switching to a backup supply must be held in an open public process that investigates both the remaining supply-demand gap and the available options. We believe that the assessment guidelines recommended by the WSAC, combined with an involved and informed public, can provide a sensible and accountable framework for these deliberations.

Taken together, the WSAC recommendations provide an approach to water supply security that uses adaptable technologies, requires the least added infrastructure investment, uses less energy than other approaches, and provides an important added benefit of cumulative habitat enhancement. It is an environmentally sensitive approach ideally suited to the natural resources of our setting and consistent with Santa Cruz values. This is a water-supply strategy that everyone in the community can support.

We urge the City Council to adopt the WSAC recommendations, and we are committed to doing our part to see that the full potential for conservation and river-water aquifer recharge is realized.

— Santa Cruz Desal Alternatives, November 1, 2015


Understanding the Recommendations


Q. What are the basics of the plan?

There are three major components of the Portfolio that the WSAC is recommending: conservation; aquifer recharge and storage; and a backup strategy of either recycled wastewater or desalination. In addition, the WSAC has created a decision roadmap for the next 10-15 years that will guide the City’s implementation of these components.

1. Conservation: Increased investment in conservation will save between 200 and 250 million gallons of water a year by 2035. Conservation in normal years results in storing water that can be used in drought years. It is by far the least expensive source of water compared to other water supply options.

2. Aquifer Recharge and Storage: Captures water from the San Lorenzo River when the river is flowing high. Stores that water in the aquifers by way of two strategies:

* “In Lieu” Recharge, (Water Transfers Between Districts): Sends surface water (from river & streams) from the Santa Cruz treatment plant to Scotts Valley and Soquel Creek Water District. Those districts will use surface water in lieu of pumping their wells, allowing the aquifers to recharge naturally through rainwater infiltration. A portion of that water transferred to neighboring districts would be considered “banked” in the aquifer for use by Santa Cruz in drought years. The specific terms of the exchanges will be spelled out in negotiations between the City and districts following adoption of these recommendations.

* Injection Wells (Aquifer Storage & Recovery): Putting treated surface water into one or more regional aquifers using wells designed for injection.

The technical team advising the WSAC estimated that either in lieu recharge or recharge through injection wells could individually meet the goal of storing the necessary amount of water for drought years. The WSAC included a combination of both strategies in order to provide the City with flexibility in achieving the goal. The Water Department will design the specifics of the plan.

3. Back-up Strategy: The WSAC recommends treated wastewater in case the aquifer recharge strategy fails to meet objectives for providing adequate supply during droughts that are more severe than those in the historical record. Desalination would be a back-up to the back-up. Study of recycled water options would begin concurrently with implementation of the Aquifer Recharge and Storage strategies.

Decision Roadmap: The WSAC has developed guidelines for evaluating the progress of the Aquifer Recharge and Storage strategy and modifying that strategy as needed to achieve yield, timeliness, and cost goals. If it appears that those goals cannot be met within the cost metric, a thorough assessment process will be conducted to update supply and demand projections, and analyze the cost-effectiveness of implementing backup strategies.


Q: Why did the Committee choose Aquifer Recharge and Storage?

A: Santa Cruz gets 95% of its water from surface water sources and 5% from groundwater. This dependency on surface water exposes the City to shortfalls during drought years. Adding groundwater sources provides the City more reliability during droughts. There are a number of additional benefits of this strategy described below.


Q: Is there enough water in the river to recharge the aquifers?

Yes. In winter the City diverts a small portion of the water flowing down the San Lorenzo River. Over the last 80 years, from mid-January to mid-April, the median flow in the San Lorenzo River is above 100 cubic feet per second (cfs). The City diverts an average of 5 cfs to satisfy its needs. Even in dry winters such as 2014-15, there are days when the City can divert additional water from the river without negatively impacting fish reproduction. State and federal fisheries agencies have indicated their support of this plan.


Q: Is there enough storage space in the aquifers?

Yes. The technical team estimates that the City would need to have on hand 2.4 billion gallons of storage, the equivalent of another Loch Lomond Reservoir. Decades of over-pumping and paving over recharge zones have caused a depletion of the aquifers in the Scotts Valley area is estimated to be over 9 billion gallons and depletion of the Purisima Aquifer over 3 billion gallons. Thanks to local geology, the ground has not subsided and much of this vacated space can store water again.


Q: What are the additional benefits of Aquifer Recharge and Storage?

If the City chooses, it can continue the Aquifer Recharge and Storage operation beyond the 2.4 billion storage level, thus preparing the City for even worse climate change impacts than the one modeled by the WSAC.

1. Recharging the Purisima Aquifer will reverse salt water intrusion that threatens City and Soquel Creek production wells.

2. Recharging aquifers results in increased summer flow in area streams, enhancing habitat for native fish and wildlife.

3. The cost of the plan is likely to be lower than a plant for recycling or desalination.


Q: Will the Aquifer Recharge and Storage Plan Work?

Using surface water to recharge aquifers is a common practice throughout the country. In the 1930’s, Santa Clara County began recharging depleted groundwater with surface water impounded in the nearby hills. San Francisco has embarked on an in lieu program very similar to the one proposed for Santa Cruz. In normal rainfall years, San Francisco will provide Daly City, South San Francisco, and San Bruno with a higher-than-usual allotment of surface water. Those communities will use SF water in lieu of pumping from their own wells.

The in lieu strategy is how our community would use its water resources if Santa Cruz, Scotts Valley and Soquel Creek were all one district. It makes sense to stop pumping groundwater at times when billions of gallons of river water flow out to sea.

The injection well strategy also is a common practice. There are more unknowns about injection than there are about in lieu recharge. The chemistry of adding surface water to groundwater needs to be compatible. The geology of the aquifer needs to be suitable for receiving injected water. For these reasons it will take up to five years to better determine the productivity of the injection strategy.


Q: What are the timing advantages of the Aquifer Recharge and Storage strategy?

The City could receive groundwater from neighboring districts in less than five years. The backup strategy of direct potable recycled wastewater would take longer, in part because it is not yet legal in California.

Because of existing pipelines connecting Santa Cruz and Soquel Creek District, the in lieu exchange program can begin immediately. The timing of return transfers to Santa Cruz is a subject of negotiation. As the aquifer levels rise in response to the resting of District wells, the City will be able to receive larger quantities of water during droughts.

In the exchange with Scotts Valley, once the interconnecting pipeline and wells are built (less than 5 years), the City could draw from the aquifer in a drought, even if the water had not been fully “banked”, according to Scotts Valley Water Director, Piret Harmon.


Q: What are the cost advantages of the Aquifer Recharge and Storage strategy?

1. Neighboring districts will share costs. Revenues to the City from water transfers will be negotiated.

2. Much of the infrastructure of in lieu recharge has a long life. Pipelines, for example, last 70 years or more before needing replacement, whereas the life span of recycled water plant components is significantly shorter.

3. Investment in the strategy will be expended in stages. This advantage is not available with the choice of a recycled wastewater plant. Depending on the rate that groundwater levels rise, the City may be able to achieve its groundwater storage goal after the early stages of investment. The system has not yet been designed, but the following items are likely to comprise an initial stage:

* In lieu recharge using the existing interconnecting pipeline to Soquel Creek District (A pilot program is about to be implemented).

* Pipeline interconnect with Scotts Valley, pump station and six new groundwater wells to return water back to Santa Cruz. The WSAC tech team estimates the cost at $14 million.

* Retrofitting existing City production wells in order to be able to inject water. Cost = less than $1 million.

Other possible investments include expanding the capacity of pipelines to carry water to Soquel Creek District and constructing injection wells at suitable locations.

At some undetermined level of increased winter production, there may arise a constraint on the City’s capacity to treat water at its Graham Hill Treatment Plant. Costs for upgrading the plant have been estimated at $62 million. In the event that new treatment capacity is needed, an analysis of less expensive alternatives such as Ranney Collectors and satellite treatment facilities will be conducted.


Q: What are the energy use advantages of the Aquifer Recharge and Storage strategy?

The tech team estimates that the energy intensity (energy per gallon) of in lieu recharge is 70% of that of a wastewater recycling plant. However, the team did not include in this estimate the energy savings from resting wells in neighboring districts.

Moreover, a recycled water plant would need to operate 365 days a year every year. The in lieu recharge is seasonal, with water coming back to Santa Cruz only in dry years. The tech team’s preliminary estimate for production from a recycled water facility is 1.1 billion gallons per year, compared to an average of only 90 million gallons per year from in lieu. Thus the annual energy use of recycled water would be 17 times that of in lieu. (When accounting for energy saved from resting wells, this disparity is significantly greater.)


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Santa Cruz Desal Alternatives
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