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Marin Water
Marin Water’s "Water Supply Roadmap"
According to the Marin Water’s (formerly known as the Marin Municipal Water District - MMWD) latest “Update on the Water Supply Roadmap, April 30, 2024, among the three proposals the agency will be evaluating to increase our water supply is the expansion of the capacity of the Soulajule Reservoir by raising the height of its earth-fill dam 39 feet. This would provide an additional storage of 20,000 acre-feet.
The Update notes,
“The volume of material needed to complete the raise of Soulajule is approximately 1.2 million cubic yards of fill. At a cost of $291M, this alternative appears economically and financially feasible.”
If this proposal is advanced to the MMWD Board later this year, it will be a major undertaking and represent a significant change in the source of Marin’s drinking water. However, few people know much about the Soulajule Reservoir or its history.
Located in northwestern Marin County, the Soulajule Reservoir (pronounced Soo-la-hoo-lee) was originally built in 1968 when the Arroyo Sausal tributary of Lagunitas Creek was dammed to provide water for a proposed housing development that never got built. It has never been permanently connected to the District’s distribution system or the power grid, so it has rarely been tapped except during severe drought periods. This may have been a good thing considering that environmental history includes the presence of abandoned mercury mines and mining tailings abutting it, in the uplands near it, and in the rock beneath it.
An Environmental Report published in the mid-1970s noted that there were geologic deposits of “mercury in underlying cinnabar rock” and that old mercury mine sites were submerged under the water and on some of the land adjacent to the water’s edge. The report noted that the old mines impacting the Soulajule included the Franciscan Mine, the Cycle Mine, and possibly other minor and unnamed mine sites that operated from 1955 to 1970.
Water from the Soulajule Reservoir
During a severe water shortage in 1976, MMWD proposed using the Soulajule Reservoir to supplement their other six district reservoirs. And though annual rainfall at Soulajule is typically only 24–32 inches, with little or no precipitation from May to October, the District believed that Soulajule would produce 5,000-acre-feet of water per year.
In 1979, the District built a new, larger earth-fill dam for the Soulajule Reservoir just downstream from the original dam. As it stands today, it is approximately 122 feet high and 700 feet long and its capacity is about 10,570-acre-feet.
Almost $15 million was spent for the land, damming, and water pipelines of that project, but a permanent connection to MMWD’s water network was never completed because the costs to go the last miles were deemed too high, since water from the Soulajule would be used so rarely.
In 1985, the “Soulajule Cooperative Report” by MMWD and the California Department of Fish & Wildlife (CDFW) mandated summer “water flow requirements [of untreated water from Soulajule Reservoir] to provide for the enhancement of salmon and steelhead fish populations in Walker Creek” and the watershed that empties into Tamales Bay.
And in the following year, a six-year drought began and MMWD brought in diesel generators to pump water from the Soulajule to the Nicasio Reservoir. And, in 1995, the State, again, ordered that a quarter of the untreated water in the Soulajule Reservoir had to be released annually into Lagunitas Creek, again, for the “benefit” of the fisheries downstream.
Mining and Mercury
Mining for valuable metals has been part of the history of California watersheds throughout the state, but Marin County has generally been spared the legacy of toxic pollution from the Gold Rush that has impacted many other areas. Mining in Marin has mostly been smaller scale and for specific metals such as mercury. However, in 1998, the “Study of Episodic Storms and Mercury“ by Whyte & Kirchner determined that there was a need to clarify reservoir baseline conditions and establish remedial actions to control soil erosion from old mining sites and sediments, particularly in periods of heavy rains and runoff.
In 1999, the San Francisco Bay Area Regional Water Board and the EPA undertook an emergency cleanup at the Gambonini Mine when, during heavy rains, a dam holding back toxic mine tailings from the mine’s processing plant failed, inundating the floodplain below it with mercury-laden mining waste and other toxic heavy metals. The cleanup involved the remediation of 200,000 cubic yards of mining waste containing 590,832 pounds of mercury.
The Gambonini Mine is downstream from the Soulajule Reservoir to it did not impact its water, but testing around that time indicated that mercury levels in wildlife and fish in the watershed had reached “alarmingly high levels.” As a result, the Water Board urged the District to oxygenate the Soulajule Reservoir’s water with onshore compression pumps to reduce methylmercury production in its waters.
In 2006, following new test findings, the Regional Water Quality Control regulators informed MMWD that elevated mercury levels were found in largemouth bass, channel catfish, black crappie, and other fish in the Soulajule Reservoir, and directed MMWD to find ways to lower the toxic mercury readings in the waters. The regulators also raised concerns about whether the fish were safe for human consumption.
A 2006 article in the Marin IJ noted,
“When mercury is taken in by invertebrates that live in sediment in the bottom of a body of water, such as clams or worms, bacteria in those organisms transform the mercury into a more toxic form called methylmercury. Small fish eat the invertebrates and those fish are eaten in greater numbers by predatory fish, increasing the load of methylmercury.
“As a result, methylmercury accumulates in fish at levels many times greater than in the surrounding water. Methylmercury can have subtle but damaging effects on the nervous system, particularly for a fetus and young children who still are developing. It can be passed from a mother to child through breast milk. Visual memory, fine motor skills, language and attention span can be affected.”
Testing by MMWD at this time indicated that none of this posed a threat to Marin County drinking water. Water Board Member, Jared Huffman, noted that Soulajule water had only been used twice since the reservoir was built.
“Water from the Soulajule is too expensive to use because of pumping cost and quality. The water is turbid and hard to treat; so we use it only in critical dry years.”
Still, critical data on the extent of the reservoir’s water toxicity remained scant. It was not until the issuance of State Water Resources Control Board Resolution No. 2009-0082, in October of 2008 (an order issued to force water districts to conform to federal clean water standards) that toxic limits were set for the Soulajule Reservoir, Walker Creek, and “their tributaries and to waters of the Guadalupe River watershed.”
That report candidly admitted that for the Soulajule Reservoir,
“We have no reservoir aqueous methylmercury data (SFBRWQCB 2007)”
Among other things, the Resolution noted,
“Mercury poses potential hazards to birds, mammals, and other wildlife. Birds and mammals that consume fish and other aquatic organisms can be exposed to significant quantities of mercury. In birds, mercury can adversely affect survival. It can affect cell development and reproductive success, and cause developmental problems in the young. It can cause reduced feeding, weight loss, lack of coordination, hyperactivity and hypoactivity, and liver and kidney damage. In mammals, mercury can reduce speed and agility, making it more difficult to obtain food and avoid predation (USEPA 1997d). The embryos of birds and other vertebrates are more sensitive to mercury exposure than adults (Wiener et al. 2003)” As in humans, the principal route for mercury exposure in wildlife is through the consumption of mercury-containing fish (USFWS 2005).”
Technical reports by Brown & Caldwell and Stillwater Sciences done in 2012, 2013, and 2018 found disturbed road cut materials, mine waste, and abandoned mining equipment at several abandoned mine sites around the Soulajule Reservoir and very high mercury levels in Soulajule waters in proximity to those mines and tailings’ waste. They recommended immediate actions to reduce methylmercury levels and bioaccumulation of harmful substances. And by 2017, MMWD was moving forward with a water resources management plan, mandated by state agencies, to control toxins and reduce bioaccumulation in animals and fish in the Marin County watershed reservoirs, streams, and creeks.
It should be noted that during this time, periodic testing did not show levels of mercury or other heavy metals in the Marin County public water supply that exceeded federally mandated limits. However, the consumption of locally caught fish and wildlife in the watershed remained and still remains a concern and warning signs are posted at the Soulajule.
The MMWD Water Resources Plan 2040
One of the stated goals of the MMWD Water Resources Plan 2040 are,
“…to improve water supply resiliency under shortage conditions noting the greatest source of uncertainty in future projections is wide variation in model rainfall projections.”
However, the Plan makes no mention of toxic mercury contamination in the Soulajule Reservoir and the downstream watershed even though various reports in the past 15 years have noted that discharge from the Soulajule Reservoir contained dissolved hydrogen sulfide and low dissolved oxygen during late summer and fall. And, reports by Stillwater Sciences noted that much of Soulajule Reservoir was shallow and “eutrophic”[1] so in the summer, water temperatures, abundant phosphorus, and bioavailable nitrogen creates conditions where blue-green algae (cyanobacteria) thrive.
This relationship between temperatures, chemicals, nutrients, and algae is important because, as noted in the Stillwater Sciences’ studies, algae blooms are caused by low-dissolved-oxygen environments, which increase toxic mercury methylation in the water.
Raising the Soulajule Dam
If the dam is raised and water from the Soulajule Reservoir is to be permanently connected to the MMWD water supply, it will require the construction of permanent piping to the Nicasio Reservoir and the installation of electrical power lines to power pumping equipment.
The initial phases of the work have already begun. In 2023, MMWD published a Request for Proposals (RFP) for,
“Professional engineering services for this project shall include areas of Civil, Geotechnical, Land Survey, Environmental and Real Property and other disciplines necessary to fully design and construct the Project. The District will be requiring professional engineering services for the design of new pipeline from the point of termination of our Soulajule pipeline. The Project would tie into the existing pipeline discharge point and convey the water into the main body of the Nicasio Reservoir with a discharge structure.”
Later that year, the District proposed a $7.2 million project to connect Soulajule Reservoir to the electrical grid by 2025. Then in April of 2024, MMWD published its Update on the Water Supply Roadmap, which references the Recreation Management Planning Feasibility Study. That study lists the expansion of the Soulajule reservoir as “the best prospect” for adding more water capacity to the MMWD water supply. However, there is no mention of mercury contamination or the potential costs of toxic remediation that may be required.
The question is simple: If the dam is raised by 39 feet, as MMWD is proposing, to what extent will the uplands soils and the toxic mining tailings that have already been identified (from remnants of the old Franciscan and Cycle mercury mines), which will be inundated by the rise in the water level, potentially increase the levels of toxic metals contamination in the reservoir’s water?
One hopes that MMWD will consider this carefully.
Is MMWD water safe?
There is nothing in the record at this time to suggest that MMWD’s water supply is unsafe to drink. But common sense dictates that if the fish in the Soulajule are unsafe to eat because the reservoir’s contaminated water has caused toxins to bio-accumulate in their bodies, what will that water do to human beings that drink it over decades? Initial queries to the District about water safety testing requirements solicited this response from their communications representative Adriane Mertens.
“The District does test its water for heavy metals, including lead, mercury, cadmium, as well as many other contaminants. Approximately 115,000 water quality and process control tests are performed annually, from watershed to faucet, to ensure the water delivered to customers is safe to drink. This includes ongoing process control testing at Marin Water treatment plants as well as laboratory testing. Many of these samples undergo chemical, bacteriological and physical analyses in the District’s water quality laboratory, which is certified by the California State Water Resources Control Board’s Environmental Laboratory Accreditation Program. In addition, the District sends other samples to specialty labs. We just published our latest Annual Water Quality Report this past week and you can review it here: marinwater.org/sites/default/files/2024-05/AWQR_English_2023.pdf.
“The tables in this report show the average level and range of each contaminant detected in the water supply from January through December of 2023. All water supplied to customers during 2023 met or exceeded all state and federal regulatory standards.”
Ms. Mertens added,
“Metals are tested for annually. When the District examines the water in Soulajule for mercury at levels that are called for in drinking water regulations, 2 parts per billion (0.002 mg/L), [the maximum allowed] we don’t find it. The EPA has determined that at this level (2ppb) is the highest level of protection based on the best available data in order to prevent potential health issues. At this time the District does not foresee water quality as a critical component of evaluating a raise of Soulajule dam.” [Emphasis added.]
In response to more detailed questions about water quality, treatment technology, and contaminants removal, she connected me with Paul Sellier, the Water Resources Director at MMWD.
I found Mr. Sellier to be thoughtful and concerned with water safety. And I appreciate the unique financial challenges faced by small water districts like the Marin Municipal Water District, which, ironically, is the oldest municipal water district in the state.
All in all, I seemed like the “science guys” at MMWD are doing the best they can with what they have to work with. But, I can’t say that I have the same confidence that the MMWD Board of Directors will make the best decisions or have their spending priorities in order. As the District goes through the process of evaluating how to best supplement and expand the District’s water supply, one hopes they will give ample attention to some of the following issues.
Water Treatment, Filtration, and Real-Time Monitoring
Reverse osmosis, distillation, Granular Activated Carbon filters, lime softening, specialized adsorbent filters, and chemical precipitation are among the most common and effective methods to remove mercury contamination from water. That said, MMWD currently employs “conventional” water treatment methods.
The Safe Drinking Water Foundation describes this process as follows:
“Many water treatment plants use a combination of coagulation, sedimentation, filtration and disinfection [chlorine] to provide clean, safe drinking water to the public. Worldwide, a combination of coagulation, sedimentation and filtration is the most widely applied water treatment technology, and has been used since the early 20th century.”
This method is generally adequate under normal conditions, however, the Foundation also comments that
“Safe drinking water requires a holistic approach that considers the source of water, treatment processes, and the distribution system. The water distribution systems may suffer from problems such as taste and odors, enhanced chlorine demand, and bacterial colonization or development of biofilms of microorganisms in water distribution systems.”[2]
So, is there anything else MMWD could be doing to protect the purity of the water coming from the Soulajule?
Ms. Mertens noted that “annual testing” of the water in the Soulajule was typically performed in “May to June.” However, the Stillwell Sciences’ studies show that the summer to early fall period (late July to early October) is when there is the highest instance of algae bloom and low-oxygen levels in the Soulajule water, which equates to the higher levels of toxic mercury methylation. So, is the May-June testing in May-June adequate?
When I asked about filtering and real-time monitoring toxins in the agency’s reservoirs and water distribution system, Ms. Mertens said,
“The District does not have equipment at its reservoirs to filter for heavy metals in real-time.”
I interpreted that to mean that filtration will happen at the water treatment plant. But considering how infrequently MMWD tests the Soulajule and its history of toxin accumulation in the animals and organisms in its water, this raises questions about the need to ensure adequate filtration and potentially real-time monitoring of contaminants, to ensure water safety.
I asked Mr. Sellier if MMWD’s filtration equipment automatically filters out all heavy metals, such as mercury, and whether the District had any equipment in place to alert the District about unforeseeable heavy metals contamination events.
He didn't respond to my question, directly, but said,
“We know from our drinking water testing that these compounds are not a concern and our level of water treatment is more than appropriate. Our water continues to meet or exceed all Federal and State standards.”
I take that to mean that based on the testing of the water they are delivering to the public (after treatment), unsafe levels of heavy metals are being removed from our water supply.
Still, when spending almost $300 million in situations where there are known contaminants in unknown amounts that may impact water quality, upstream, as is the case with mercury contamination in and around the Soulajule Reservoir, and where there is the possibility of a sudden change in levels of contamination due to erosion, weather-related runoff, or other geologically related events (as was the case with the collapse of containment of toxic mercury tailings at the Gambonini mine), I think it might make sense to be extra careful.
Admittedly, the probability of such a contamination event is low and the contaminant load would have to be particularly large to impact water safety in the District, but in the face of the increasing intensity and frequency of weather-related events due to climate change, going forward, it would make sense to consider instituting real-time monitoring or more frequent testing of the Soulajule’s water.
At the least, as an integral part of District’s water supply sustainability planning, budgeting should include a thorough, updated geological study of upland mercury contamination sites adjacent to the Soulajule Reservoir that will be inundated by the rising waters. This is important because if soils mitigation is determined to be required, the added costs could be significant.
Water Storage
Water storage goes hand in hand with water quality and may be an even bigger challenge in the years, ahead. After surviving an historic drought in the past decade, the effects of climate change are forcing water districts in California to rethink how they store water, and traditional open-air reservoirs may not be the best approach to ensure a sustainable future. Evaporation is acknowledged to be a significant source of water storage loss in our drought-prone state and the constant introduction of airborne and groundwater pollutants increase water qualify maintenance and treatment costs.
The City of Los Angeles and other districts have decided to find new methods.
The Los Angeles Department of Water and Power is currently constructing the Headworks Project, to replace two of their open-air reservoirs with underground storage tank reservoirs with a combined storage capacity of 110 million gallons. The Metropolitan Water District of Southern California is building the High Desert Water Bank near Lancaster, which will have the capacity to store up to 280,000 acre-feet (around 91 billion gallons) of groundwater.
Of course, Marin County doesn’t have anywhere near the magnitude of the challenges faced by Southern California. We are very lucky to have a combination of geography, climate, and a hydrological cycle that normally provides us with an adequate water supply. But the future is likely to be anything but “normal” and water supply management may not be able to depend on tradition water capture and storage methods, and the amounts these two Southern California agencies are spending is testament to this.
With all this in mind, one hopes MMWD is looking for solutions that are sustainable in the long run and not just charging forward with piecemeal solutions in reaction to the latest crisis.
[1] Rich in nutrients and so supporting a dense plant population [algae], the decomposition of which kills animal life by depriving it of oxygen.
[2] “Comprehensive Water Qualify and Purification,” 2014.
Bob Silvestri is a long-time Mill Valley resident, the Editor of the Marin Post, and the founder and president of Community Venture Partners, a 501(c)(3) nonprofit community organization dedicated to bringing the community's voice to government decision-making and funded exclusively by individuals and nonprofit donors. Please consider donating now to support our work.