|
Getting your Trinity Audio player ready...
|
Palo Alto recently wrapped up a multi-year “One Water Plan” effort to determine our best option for water in dry years. This became a priority when our current water supplier SFPUC warned of possible shortages. (1) So Palo Alto Utilities staff worked with consultant Carollo Engineers to evaluate and rank a wide variety of proposals for augmenting our water supply during periods of severe drought. They concluded that our best option is to conserve more water and then to treat and consume our wastewater. This conclusion holds pretty much regardless of how different aspects of the various solutions (e.g., cost and reliability) are weighed.
If you, like me, are not excited about drinking or showering in treated wastewater, then we have two hopes. One is that SFPUC finds a way to maintain adequate supply during upcoming droughts. And the other is that this study is wrong. I’m going to walk you through some parts of the study and tell you what I’ve concluded.
Palo Alto did a thorough job, looking at 27 (!) different options for additional water supply. In general, the One Water team was looking for solutions that were either high volume in dry years or inexpensive or both. They also considered how ecologically friendly they were and how simple to accomplish.
More than half of the options were ruled out early on. In dry years, we aren’t likely to be able to buy much water from another agency, extract large amounts from the atmosphere, or get much from rainwater capture. (2) Custom solutions for irrigating city parks (special wells or storage tanks) don’t end up saving much water. Collecting water from construction sites that are “dewatering” for a few weeks or months (e.g., for basements) ends up being expensive due to the need to truck the water. And the idea of using Lake Lagunita as a recharge basin to capture water to augment groundwater reservoirs runs into environmental and legal concerns. (The temporary wetlands that are there now are home to the protected California tiger salamander and many other species.)
So that leaves us with a handful of options. All of these can provide a decent amount of water in dry years, but costs vary.
- Conserving more water
- Using groundwater (via wells)
- Using more (non-potable) recycled water
- Building a desalination plant
- Building a treatment plant for wastewater
Conserving more water
Palo Altans have been terrific at conserving water. Whenever asked, we have met or exceeded the guidelines. For example, when the state mandated a 24% reduction in 2015, we reduced usage by 31% (by restricting landscape irrigation to twice a week, among other things).
When we conserve during droughts, some of that savings becomes permanent, which means over time we have used less water per capita and in fact less water overall, even as our population has grown.
Somewhat ironically, this strong record of conservation makes it harder for us to conserve in the future — our demand has “hardened”. Nevertheless the One Water team still sees some opportunity for us to conserve, particularly by focusing on irrigation and grass turf. They estimate we could reduce our water use by about 10%. The city also proposes to replace old and inefficient toilets in low-income households and high-use commercial properties.
Some of these programs cost more than others. Enforcing a 3-day watering week, for example, at $159 per acre-foot (AF), is a small fraction of what we pay for water today ($2210/AF). In contrast, improving our program to help residents replace turf works out at $4133 per acre-foot (AF). Is that worth it, even with the environmental/biodiversity benefit? Toilet replacement is not only pricey at $2300-$3300/AF, but it yields very little in savings. Perhaps the city is considering these more expensive options so the program is more appealing for residents and businesses.
The full suite of conservation programs that staff put together nets out to an estimated $888/AF, less than half of what we pay for water today. The Utilities Advisory Commission expressed interest in getting started with them. But once we’ve done what we can on the demand side, we have to look at supply. Where can we get more water in dry years?
Extracting groundwater
One idea is to “punch water wells”, as a commenter put it last week, to tap our groundwater. In fact, Palo Alto already has eight wells with plenty of capacity, more than we normally buy from SFPUC. But there are restrictions on how we can use the wells.
Groundwater modeling done in 2018 estimated that we can sustainably take out about 3000 acre-feet (AF) per year. With filtering, that would net about 2250 AF, which is 20% of the approximately 11,000 AF we buy today.
We would need to use two different wells to access that amount of water, which means building two separate treatment plants. (3) That raises the cost. In addition, Valley Water assesses a fee for groundwater extraction. The price right now is similar to what SFPUC charges, but the fee is growing at about 9.5% per year, at least through 2032. That makes groundwater 50% more expensive than Hetch Hetchy in eight years, even with no treatment. If you add in about $50 million in capital costs for the two treatment plants and a few miles of pipeline, this becomes a pretty expensive proposition at $4663/AF, about twice what we pay SFPUC today.
The final caveat with relying on groundwater during dry years is that it is not clear whether, during a severe drought, we would be allowed to use all 3000 acre-feet. In the past Valley Water has requested reductions in groundwater pumping during droughts. If they did so, it would limit the scale and increase the cost of this option. (4)
Using more (non-potable) recycled water for irrigation
Another idea for creating more water during dry years is to expand our (non-potable) recycled water system. Today “purple pipe” is available only near the Bay, but the city examined extending it up through Page Mill Road’s commercial properties to Foothills Park and nearby areas.
This is surprisingly expensive. In 2019 the project was priced at about $63 million total, but after adjusting to today’s costs the estimate is a whopping $148 million. The 15 miles of pipeline on its own comes in at $60 million (see “Conveyance” entry below). Somewhat unexpectedly, expanding our use of recycled water for irrigation ends up being one of the most expensive options at $9685/AF.
Desalinating water from the Bay
Desalination plants are also not cheap, coming in at $6768/AF to build and operate a plant sized appropriately for our city. That cost does not include any treatment of the waste brine beyond dumping it in the Bay, something that might be necessary in the future. (5) On the plus side, this option generates plenty of water, almost half of our normal use, and it is unlikely to be rationed even during drought. The report mentions that desalination technology has improved since this estimate was done in 2015, so a revised estimate could be somewhat cheaper. (The One Water team adjusted the estimate to today’s costs, but did not update the technical specs.)
Using treated wastewater
The final option is using our treated wastewater. “Wastewater” refers to a blend of black water (sewage), gray water (laundry, irrigation), and other sources of runoff. There are three main options for treating our wastewater. One is for Palo Alto to build its own facility and blend the treated output directly with the Hetch Hetchy water. This is estimated to cost about $3594/AF and provide plenty of water, similar in yield to the desalination plant.
A second option is to inject the treated water into our groundwater and then pump an equivalent amount up. This “indirect” reuse is more appealing to many people but it is somewhat more expensive since water has to be piped to injection sites and then treated again once it is extracted. The estimated cost is $3881/AF without groundwater pumping fees, and a much higher $4992/AF if Valley Water charges us even though we are injecting an equivalent amount. (6)
Finally, a third option is for Valley Water to build a facility, treat our wastewater for us, and charge us a processing fee. They have expressed interest in doing this, but they are also considering a site in San Jose, which in some ways is a better location for them. With this third option, we would get only about one-third of the water we would get if we built our own facility, and the report estimates it would be more expensive than building our own, at $4024/AF.
Of these options we might prefer the first two. However, in 2019 we signed a contract giving Valley Water an option to half of our wastewater. If they take us up on that, it would make those first two options infeasible. So there are some balls in the air here, depending on where Valley Water chooses to build a plant and whether it opts to take our wastewater. Those questions may not be resolved until 2032.
Conclusion
It is kind of frustrating that our city’s multi-year effort with considerable public outreach concluded with “We need to save more water and drink our pee”. The Utilities Advisory Commission (UAC) was quite reluctant to approve this report. But Karla Dailey, Assistant Director of Utilities who led this effort, stands by the work and wants to be very clear that “The City is not proposing anything right now. We may not need alternative water supplies, and, if we do, other opportunities or regional partnerships may arise. This study did eliminate some infeasible options, but nothing is proposed.” It is certainly very helpful to see all of this analysis summarized in one place.
My sense is that we need to be more careful with our assumptions, more generous with our solution space, more thoughtful about sequencing, and then take a scalpel to costs for the projects we prefer. This effort began in part because of SFPUC’s warning that 50% rationing might be needed in future dry years. Commissioner Greg Scharff commented in a June 2024 UAC meeting that 50% rationing is politically impossible. “Half the Bay Area relies on SFPUC …. Think about the political mayhem that would cause.”
Indeed, SFPUC is very interested in drought-proofing its supply. (7, 8) While the One Water Team also modeled 30% rationing (and came up with similar proposals), SFPUC Assistant General Manager Steven Ritchie mentioned in a November 2024 meeting with the UAC that he doesn’t even think 20% rationing is achievable given how much people have already saved. So in my opinion the assumptions behind this study are questionable.
It is also the case that this study didn’t look at combinations of solutions beyond conservation, and didn’t prioritize solutions that could be intermittent. Solutions with very high capital costs make most sense if used all the time, drought or no drought. Building those would have us permanently walk away from the Hetch Hetchy supply, even during normal and wet years when there is plenty of water to go around. We might want to look harder at using our own wells, where capital costs are less and the supply could perhaps more easily be intermittent.
Finally, I’m not sure that the difficulties of public acceptance are given enough weight in evaluating these options. I remember attending a One Water meeting designed to get public input about priorities a few years ago. Public acceptance was lumped under the category of “How easy is it to do this solution”. I didn’t rate that as high as Cost or Reliability. But it could well be that if people are given a choice between “Replace your lawn” or “Drink your pee”, they are more likely to conserve.
Dailey is very interested in hearing from residents about which features we consider to be most important in our water supply, and how we would evaluate different options. Are we interested in using less water from the Tuolumne? How do we feel about cost vs reliability? Do we want to dump the filtered waste from treatment plants directly into the Bay? Please share your thoughts or questions in the comments.
In the meantime, maybe I am overstating the concern about “Direct Potable Reuse”. My daughter was home from college recently, and as I was researching this blog post I suggested she think twice about living here after graduating because we’d all be drinking our pee. She looked at me, totally unimpressed, and said “Well, it would be filtered, right?” I looked at her like she was from outer space, and then she reminded me that she’s been studying this at school — she had a whole class on water and sanitation. It appears she is thoroughly confident in the technology for treating wastewater and much more worried about, say, arsenic in groundwater. So maybe it’s like flying in airplanes, we’ll all just get used to it even though it seems like a horrific proposition.
I look forward to your comments and questions!
Notes and References
00. Thank you to Assistant Director of Utilities Karla Dailey for answering my questions and reviewing this blog post.
0. For more information about this topic: The One Water Plan final report published in October of 2024 cites numerous lengthy reports from recent years, including the Urban Water Management Plan and Water Shortage Contingency Plan published in June 2021 and various reports on recycled water, wastewater, stormwater, and more. The City’s One Water Plan site has a useful enumeration of resources.
1. SFPUC, the San Francisco Public Utilities District, is concerned about the effect of regulatory changes and climate change on the Hetch Hetchy system as discussed in my previous blog post.
2. The Los Angeles area makes great use of stormwater, capturing an impressive 108,000 acre-feet in 2023 according to CalMatters. (That is about ten times what Palo Alto uses in one year.) So it was something of a surprise to Assistant Director of Utilities Karla Dailey that this didn’t pan out better for Palo Alto. “Stormwater capture was a resource that had not been evaluated as a water supply option in previous planning efforts. We were surprised that this water supply alternative did not score higher.” Part of the problem is that we do not have a space for centralized stormwater capture, like LA does. So the city estimated the yield from the most promising capture areas including large parks, parking lots, and streets, but the yield was tiny (around 100 acre-feet).
3. The wells we would use to access groundwater are relatively new and access water that is testing as safe to drink. So we could forego treatment and mix this directly into the SFPUC water. That would be much cheaper, even less than the price we pay for water from SFPUC today. However, the One Water Plan report notes that “the higher mineral concentration in groundwater will result in a poorer taste of the blended water and will likely be less palatable to the public than the existing [Hetch Hetchy] supply. Additionally, the poorer-tasting blended water will disproportionately affect customers located near the wells.” Because of that, the report recommends treating the well water despite the considerable increase in cost.
4. We might be able to mitigate some of these limits by injecting some of our own water into the groundwater basin. The One Water Plan explores the possibility, for example, of taking water from our two permanent dewatering sites — one at the Oregon Expressway underpass and the other at City Hall — and piping them to a nearby well for injection. It would make sense to nail all of this down with Valley Water if we are interested in going this route.
5. The brine that remains after reverse osmosis in desalination plants can be ecologically harmful. The One Water Plan report says “The City’s recent discussions with the RWQCB (Regional Water Quality Control Board) indicate that RO (reverse osmosis) concentrate may be directly discharged through the existing RWCQP outfall without additional treatment. This may change in the future for numerous reasons and should be verified during preliminary design or other early evaluations if this project moves forward…. Brine disposal will be a key issue for Palo Alto staff to address including considering public input and environmental considerations.”
6. I asked Assistant Director of Utilities Karla Dailey why Valley Water would charge us given that we are putting water into the aquifer before extracting it. She replied: “We consulted Valley Water and made some assumptions about what percentage of the pumped water would be subject to Valley Water’s groundwater production charge. There are losses in the injection and recovery process. This is something Valley Water has not dealt with before (another agency injecting into the basin), so we would need to work with Valley Water through a public process to establish a policy.” Since it sounds to me like this could be negotiated, I have quoted water prices both with and without this fee.
7. When I asked Dailey why we feel the need to augment the SFPUC supply, when they have every motivation to make their supply ultra-reliable, she replied: “From a water supply planning perspective, it is good business practice to consider undesirable conditions and think through possible response strategies. Palo Alto does not operate the Regional Water System. Using SFPUC projections as one possible future scenario is prudent.”
8. It is not unlikely that SFPUC will bring treated wastewater into its supply to mitigate against drought risk. So we may well be drinking our own pee, or someone else’s pee, in the not-to-distant future. One question is whether SFPUC has access to enough wastewater for a regional supply. Wastewater-based solutions may be inherently local, since it is expensive to ship. BTW, one of the strangest things about researching this blog post is the way that wastewater is treated as a valuable commodity that is bought and sold and worried about when levels are low. Izh.
Current Climate Data
Global impacts (Year End 2024), US impacts (Year End 2024), CO2 metric, NOAA climate dashboard
Want to be Notified of New “A New Shade of Green” Blog Posts?
If you would like to be notified of new blog posts, please send an email to notify@newshadeofgreen.com with “Subscribe” in the subject.
Comment Guidelines
I hope that your contributions will be an important part of this blog. To keep the discussion productive, please adhere to these guidelines or your comment may be edited or removed.
- Avoid disrespectful, disparaging, snide, angry, or ad hominem comments.
- Stay fact-based and refer to reputable sources.
- Stay on topic.
- In general, maintain this as a welcoming space for all readers.
