Addressing mercury in the Delta: An update on the Delta Mercury Control Program

Bird in the brush at Three Mile Slough #1Presentation from the Central Valley Regional Water Board covers Phase 1 methylmercury control study progress reports and implementation of the Delta Mercury Exposure Control Program

Mercury contamination is a problem both in California and worldwide, present in the environment as a result of both natural processes and human activities. Mercury comes from many sources: it is transported by wind and rain from local and global emissions, it can be present in urban and industrial wastewater, and it can be naturally occurring in soils and springs, particularly in the Coast Range.

Pile of tailings left to erode at the abandoned New Idria mine
Pile of tailings left to erode at the abandoned New Idria mine (Photo by mhlradio)

Mercury contamination is especially acute in California, a legacy that remains from the Gold Rush era when miners used mercury to extract the gold ore. Estimates are that 26 million pounds of mercury was used for gold mining operations in Northern California, most of that in the Sierra Nevada and Klamath-Trinity mountain areas. Many abandoned gold and mercury mines have never been adequately cleaned up, and they continue to produce toxic runoff today.

The American, Bear, Feather and Yuba Rivers, which join the Sacramento River to flow into the San Francisco Bay, are the four most mercury-contaminated rivers in the state, and as a result, mercury is found throughout the San Francisco Bay-Delta estuary and its watershed at elevated concentrations in the sediments and biota.

Mercury is of most concern when it reaches a wetted environment, such as a wetland or a reservoir, where it settles to the bottom and the bacteria in the sediments convert it to the more toxic form called methylmercury.  The rate of methylmercury production varies mercuryupdate0423_Page_03by habitat and is affected by water chemistry factors, such as oxygenation and carbon availability.  Some of the methylmercury will be lost through degradation by sunlight or other bacteria, and some of it will move up the food chain.

People are exposed to methylmercury almost entirely by eating contaminated fish and wildlife that are at the top of aquatic foodchains.

In 2010, the Central Valley Regional Water Quality Control Board adopted the Delta Mercury Control Program as an amendment to the basin plan in 2010 to reduce levels of mercury in fish in the Delta. At the March meeting of the Central Valley Regional Water Quality Control Board, environmental scientist Janis Cooke updated the Board on the status of the Delta mercury control program.

The Delta Mercury Control Program was adopted as a total maximum daily load or TMDL program in 2010 to reduce levels of mercury in fish in the Delta. A TMDL is a regulatory term included in the Clean Water Act that is the maximum value of a pollutant that a body of water can receive and still meet water quality standard and designated beneficial uses.  The TMDL is a type of program needed when a water body does not meet standards and control of point sources alone is not going to correct the problem.

In 2010, the Board adopted water quality objectives for mercury in fish to protect both people and wildlife that eat Delta fish, and an implementation plan for meeting the objectives,” said Ms. Cooke. “The implementation plan has requirements to control both mercury and methylmercury; however, methylmercury is the form of mercury found in the environment that’s most toxic and that accumulates in fish tissue.”

2016 Feb Delta Mercury Update Item 7_Page_04The Delta Mercury Control Program was adopted with a phased approach. Phase 1 began in 2011 and will continue through 2018. In Phase 1, the focus is on methylmercury control studies to evaluate and test methylmercury management practices and evaluate their feasibility, as well as the exposure reduction program. If point sources had not already been required to implement pollution prevention programs, they did so at the beginning of phase 1.

At the end of the control study period, staff is going to review all the information and we will be bringing that information along with any proposed changes to the Delta Mercury Control Program back to you in about 2020,” said Ms. Cooke.  At the completion of phase 1, phase 2 will begin, which will include mercury and methylmuercury controls as well as wasteload and load allocations to address the problem.


The purpose of the methylmercury control studies was to evaluate the effectiveness and the feasibility of potential measures to control methylmercury from a wide variety of sources in the Delta. “The program started with requiring all entities that discharged methylmercury into the Delta or whose water management activities could affect methylmercury in the Delta to participate in the study program, and we encouraged collaborative studies,” she said.

The entities participating in the program submitted study work plans which were reviewed by a technical advisory committee and approved by the Executive Officer. “We’re at the point where we’ve just received progress reports and the main point of my report to you is what we found in those progress reports,” she said.

2016 Feb Delta Mercury Update Item 7_Page_05Within the control study program, we have methylmercury control studies for both nonpoint and point sources with nonpoint sources being managed wetlands, tidal wetlands, and irrigated agriculture. Methylmercury is produced in wetted sediment, so there is methylmercury being produced in the Delta channels and a study group working on that. We have study programs for urban runoff, municipal wastewater, dredging operations, and the Cache Creek settling basin.”

Ms. Cooke noted that there is a lot of work going on outside the study process that staff will draw on for the revisions to the program, but for the purposes of this presentation, she will focus on the 14 progress reports received from the phase 1 process. Most of these studies are ongoing.

One of the sources of mercury is urban and industrial runoff. “We had four studies participating in this part of the program, and they were all evaluating the performance of currently used management practice measures for stormwater treatment and evaluating their effect on controlling methylmercury, and specifically these were low impact development and retention basins,” she said. “We also had Army Corps examining the effect of dredging operations on methylmercury, both in the dredging operation itself and in methylmercury that returns in the return flow at the disposal sites. This is not a concern with our annual maintenance dredging operations but were there to be a large ship channel dredging process, we needed some information.”  (See progress report here: MeHg Sampling Report for Maintenance Dredging, Sacramento & Stockton Deep Water Ship Channels)

Groups were encouraged to work collaboratively; one of the groups formed was the Delta Methylmercury Nonpoint Source Workgroup. “They obtained 319H federal grant funding to put together a report that identified and ranked different management options that could be used in wetlands and in agriculture, and it also looked at possible implementation sites,” said Ms. Cooke. “That report was completed in 2013 and it’s very valuable.” (See progress report here:  Identification and Prioritization of Management Practices to Reduce Methylmercury Exports from Wetlands and Irrigated Agricultural Lands, Environmental Management)

One of the big questions is the amount of methylmercury that is produced in tidal wetlands, which is important to know because of the habitat restorations that are being proposed. “The Department of Water Resources is working on an extensive study that is monitoring methylmercury concentrations and loads in existing tidal wetlands,” she said. “The goal of this study is to be able to monitor enough tidal wetlands over time so that we can look at the effects of methylmercury concentrations and match them with the different characteristics of the wetlands: such as hydrology, vegetation type, and inundation regime. It’s a challenging process to do this. I’ve been out in the field with them and I must say the biggest issue is measuring the flow because you’re in a tidal situation.” (See progress report here:  Methylmercury import and export studies in tidal wetlands)

There was some data available going into the program on methylmercury from rice agriculture but not other types of crops, so EPA worked with water board staff to complete a project of monitoring methylmercury concentrations in flood and flow irrigated crops in the Delta, she said.

CVCWA Municipal Wastewater Study

Another source for methylmercury is municipal wastewater. “The Central Valley Clean Water Association organized a large study that involved 18 different facilities; we also had two individual studies for this source type,” she said. “All were evaluating and comparing performance of different treatment systems at controlling methylmercury.

2016 Feb Delta Mercury Update Item 7_Page_09The Central Valley Clean Water Association’s study involved monitoring methylmercury in both influent and effluent and in some cases in the middle of the treatment process at facilities in and outside the Delta,” she said, presenting a graph from the study of the concentrations of methylmercury in effluent. “The CVCWA study really proved the hypothesis which was that treatment systems that involve nitrification and denitrification provide excellent methylmercury control. The ovals here show the treatment systems that use nitrification-denitrification both with the tertiary and the secondary systems and they have almost non-detectable levels of methylmercury in the effluent.

The study looked at data but also did predictions looking at the levels of treatment that are currently required in the Delta and the ones that are anticipated in permits. “We expect that all the wastewater treatment facilities in the Delta will be meeting their wasteload allocations for methylmercury, no questions there. Additional controls are probably going to see a negligible benefit to methylmercury in the Delta.”(See progress report here:

Mathematical models for the Delta and Yolo Bypass

The Open Water Study Group is conducting a study for the Delta channels that looks how changing the water management by the state and federal agencies can affect methylmercury in the Delta. Since it isn’t possible to do a pilot test, the study plan involves developing mathematical models for the Delta and the Yolo Bypass. Ms. Cooke explained why this is valuable.

2016 Feb Delta Mercury Update Item 7_Page_10The figure on the left is the mercury mass balance from the Delta mercury TMDL, it’s a box model showing that the level of information that we had for the TMDL at the time was that we could calculate this mass balance showing average methylmercury inflow and outflow within the Delta and the Yolo Bypass – the sources and the sinks, but only an annual average basis.”

We can split this up by season, but it still doesn’t give us as much information as if we could couple this with what the water flows are actually doing in the Delta and that’s exactly what DWR’s doing with their model,” she said. “In the graphic on the right, all the orange dots are nodes in the hydrodynamic model where information about water flow direction, residence time, tides, etc. will be then coupled with rate and methylmercury production and loss information to give us a much better picture of what’s going on with methylmercury within the Delta.”

The model is a first generation model. “We’re going to be able to get at least semi-quantitative information from it,’ she said. “What the model will enable us to do then is ask questions like what if we do change water management in the Delta, such as residence time is significantly increased in the Central Delta, what would that do to our methylmercury concentrations in the water and fish.

The modeling effort will not only be able to test scenarios, but there’s a lot of interest in this model because it would let us integrate information being produced by the different studies that would be collected through the Delta Regional Monitoring Program, she said. “It’s a difficult effort, and for some parts of this they have to create the code for connecting the mercury pieces to the sediment and water flow components of the model. Our target date for completion of the methylmercury control study period was October of 2018; we don’t expect to have the model results until the end of 2019.”  (See progress report here:  Open Water Workgroup Progress Report (Model Development))

Cosumnes River Preserve Study

Ms.Cooke noted there’s been a significant amount of effort put into evaluating management practices in wetlands and learning more about the processes for control methylmercury in wetlands. One of those efforts is at the Cosumnes River Preserve where the USGS and BLM are testing the effect of polishing ponds at reducing the concentrations of mercury coming from a seasonal wetland. The seasonally flooded wetlands tend to have high rates of producing methylmercury because of a wetting and drying cycle; there’s also food for the bacteria to grow, yet they are highly favored for habitat, such as for migratory birds.

2016 Feb Delta Mercury Update Item 7_Page_11This project is testing what happens when you take the flow from the seasonal wetland shown in the blue outline and put it through a deeper pond before it enters the drainage channel,” she said. “The polishing pond would be kept as a permanent pond and the seasonal pond is going to be dry and growing seed crops for birds in the summertime. Even though we’re only in year 1 of a 2-year study and not all the data have yet been analyzed, the polishing pond was effective of reducing the methylmercury exports from the seasonal wetland in a flow-through condition by 30 to 50%. In that aspect, it looks like a really promising management practice. We’re going to have to be working with land managers to find out the next step would be evaluating feasibility. I don’t expect this is going to work everywhere simply because of elevation and we won’t have the water in every place to put these in, but it does seem to be effective.”

This wetland study is an example of the issues that we’re going to need to examine as we think about the methylmercury controls for the level of reduction expected from our wetlands because we do need to balance the habitat and ecosystem needs for the wetlands,” she said. “For example, the seasonal wetlands over at Cosumnes River Preserve are there to provide particular habitat needs, so when we change from a seasonal wetland to a polishing pond, that changes what the ecosystem benefits that that wetland is providing. It’s a balancing, but it is encouraging.”  (See progress report here:

Other wetland projects that are ongoing are looking at different methods of vegetation management, or different hydrology changes for managing the seasonal wetlands, she said.

Cache Creek Settling Basin Improvement Feasibility Study

DWR is conducting a study at the Cache Creek Settling Basin, a sediment retention basin that is located at the base of Cache Creek where it enters the Yolo Bypass near the city of Woodland.

2016 Feb Delta Mercury Update Item 7_Page_12The Cache Creek watershed is highly erosive; it’s also enriched in mercury so the concentrations of mercury in sediment that leave the Cache Creek watershed and enter the Yolo Bypass are four to five times higher than the concentrations of mercury in sediment that comes over the Fremont Weir, so we think it’s a very important place to focus some effort,” Ms. Cooke said. “It wouldn’t have the immediate benefits that you would get from reducing the actual methylmercury production, but reducing the concentration of methylmercury in sediment throughout the Yolo Bypass will eventually contribute to reducing the methylmercury that’s formed there.”

The outline of the settling basin is shown in red. A lot of the land in the settling basin is farmed in the summertime, but in a high flow event, the settling basin would be full of water; the basin slows down the flow for the particles to settle out.

DWR has put in extensive amount of work looking at a wide variety of things, from methylmercury concentrations in songbirds in the basin to mercury in cores to looking at the hydrology of the watershed upstream,” she said. “Our next steps are to work with DWR and to talk with them about the potential feasibility options for improving the settling basin. We also need to make sure that the operation is maintained because it is filling with sediment and there are flood control issues that need to be addressed when selecting a preferred option, so we need to work with our agency partners in deciding the next steps.

(Mercury Control Study of the Cache Creek Settling Basin)

Costs of the control studies

2016 Feb Delta Mercury Update Item 7_Page_13Lastly, she presented a slide showing the costs for the studies to date, noting that it’s definitely in the millions of dollars. “We do have a serious problem that we want to correct but finding the right answer isn’t easy or cheap,” she noted.

For more information …




Ms. Cooke then turned to the other significant part of the methylmercury control program in phase 1, the Mercury Exposure Reduction Program. The program’s administrative partners in this effort are the Delta Conservancy and the California Department of Public Health, as well as other agencies.

The program recognizes that it’s going to take decades or more to reduce mercury levels in fish, and so the TMDL addressed the public health impacts by conducting public outreach or (“exposure reduction activities”) to protect people who eat locally caught fish.  The objective of this effort to protect people who consume Delta fish while the studies and the mercury reductions are occurring, she said.

2016 Feb Delta Mercury Update Item 7_Page_16There are four main types of activities: New educational materials have been developed and translated; small grants have funded local community groups to help deliver the message; pier warning signs are being developed and produced; and the Department of Public Health staff is developing training modules that then could be used for trainer events.

We’re hoping that by putting in place pieces of the education and outreach program like this, these can be used when we no longer have staff funded for the program,” she said.

She noted that the educational materials are available in eight non-English language translations, and they are based on the fish consumption advisories that the Office of Environmental Health hazard assessment issues for the Delta and to make it complicated, there are three different advisories for the Delta.

Effectiveness of the program

The mercury exposure reduction program is relatively small and there isn’t a lot of funding, so the focus is on doing the outreach and education, but there are ways to track performance incorporated into the program, particularly looking at quantifying the numbers of people that are reached and using pre and post activity questionnaires, Ms.Cooke said.

For the number of people reached, we’ve asked that the small grantees track the people they are reaching through a variety of measures,” she said. “They get out the message through meetings, community events, health fairs – they are actually trying to do one on one talking with people; our small staff can’t get to everyone, so it’s a tremendous benefit.”

As for other types of outreach, the health program staff are trying to coordinate with ongoing programs in the Delta; they’ll be tracking the number of signs posted at fishing locations as well as checking out the media interest in the program, she said.

The Department of Public Health estimates that the program has reached somewhere between 8500 and 12,000 individuals through the materials, the grantee activities, and the outreach outside of the grants. She noted there aren’t any numbers for our signs yet. “I recall that the consumption survey that Frasier Schilling did for the Delta looking at people who might have high rates of consumption and their families, it was estimated at 40,000 people, so we still have some work to do,” she said.

2016 Feb Delta Mercury Update Item 7_Page_20The second metric for testing the effectiveness of the program is using questionnaires. “We’re looking to see if people are likely to change their behavior or if their education level has been increased, so we give them the questionnaire both before and after the activity, and that lets us test our level of increase in the knowledge,” she said. “These questionnaires also had to our information about characterizing fish consumption in the Delta, and that helps us target our information delivery.

Funding for the program

2016 Feb Delta Mercury Update Item 7_Page_21The mercury exposure reduction program has funding from several different sources. “We received an award from the clean up and abatement account of $370,000; that is largely being used to fund the health program specialist working with DPH to carry out the activities,” Ms. Cooke said. “The dischargers in the Delta are required to participate in the exposure reduction program; they’ve made contributions in proportion to methylmercury discharged to the Delta. That was a 6-year program, so we do have a small amount of funding expected to still be coming in. We front loaded the payments from the dischargers when we knew we had the cleanup and abatement account funding, and we also have a lot of significant in-kind support, staff here, and at the DPH. DWR is supporting the program with graphics assistance, and we’re also trying to coordinate with ongoing Delta programs, so we’re relying on their staff as well.


We received these progress reports for the methylmercury control studies in Fall of 2015, so the next step with those is to work with the technical advisory committee on review of those progress reports,” she said. “I anticipate working with the technical advisory committee chair on some particular questions pertinent to each study. We don’t want to interrupt studies that are ongoing; we did just get progress reports. The due date according to the basin plan for the control studies is October 2018. There’s an option for executive officer to extend that if significant progress is being made; we have a due date for the modeling study to be done in 2019.”

The exposure reduction program is continuing; the cleanup and abatement account money will be spent probably in fall of 2017, but we do have funds to continue on a maintenance level at least replacing signs and materials, and we’ll bring this whole program back to you somewhere about 2020,” Ms. Cooke concluded.


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