Overview of control studies for the Delta methylmercury TMDL

Yolo Bypass flooded field by Chris AustinDr. Stephen McCord discusses the progress made so far on the phase one control studies; final reports are due October, 2018

Mercury comes from many sources, both natural and human.  A byproduct of coal combustion and volcanic eruptions, it can be transported by wind and rain; it can also be naturally occurring in soils and springs, particularly in California’s Coast Range. And in many areas of California, it is a legacy contaminant from gold rush mining, nestled into the sediments that line the rivers, streams, and floodplains of the Central Valley.  Even today, there are some abandoned mines from the Gold Rush era that are still leaching mercury into the environment.

The source of most of the mercury in California’s environment is from gold and mercury mines and atmospheric deposition; there are minor contributions from industrial and municipal wastewater discharges and urban stormwater run-off.  Most of these sources provide mercury in a non-toxic inorganic form, but when the mercury reaches a wetted environment, such as a wetland, it settles to the bottom where bacteria in the sediments convert it to the more toxic, organic form called methylmercury.  The rate of methylmercury production varies by habitat and is affected by water chemistry factors, such as oxygenation and carbon availability.

The methylation of mercury is a key step in the entrance of mercury into the food web, as methylmercury is a bioaccumulative pollutant which concentrates as it moves up the food chain, from algae to zooplankton to prey fish and the predators that eat them, such as trout and bass.

To address mercury contamination in the environment, the State Water Board has been developing a statewide water quality control program for mercury to protect humans and wildlife that will include a mercury control program for reservoirs and mercury water quality objectives.  The objectives will likely be expressed as a methylmercury concentration in fish tissue that will apply to California’s inland surface waters, enclosed bays, and estuaries.

As part of the development of the Delta Mercury Control Program, the first phase requires entities responsible for reducing methylmercury in the Delta to participate in studies to develop and evaluate ways to manage methylmercury.   The studies underway focus on different methylmercury source types by means of monitoring, pilot testing, or modeling.  Study work plans were approved in October 2013, progress reports were due in October 2015, and final study reports are due in October of 2018.

McCord Overview Control Studies Delta TMDL_Page_03At the mercury workshop held earlier this year, Dr. Stephen McCord, a consultant who has worked for several years with the Delta Tributaries Mercury Council, discussed the progress of the phase one studies.  He began by pointing out that the water quality regulations present a conundrum that is much like a rock and a hard place: how to reduce methylmercury discharges without worsening conditions on site.

In this case, it’s where are you concerned about,” he said.  “A regulatory situation is concerned about water leaving some site, a point source or a wetland, it’s going into somewhere and now it’s bad.  But there’s also things happening on the site.  You have to recognize you change the land use or what you do on the land, that might make it better offsite, but it may make it worse onsite, or it’s going to cost at any rate, so just recognize those two pieces of the puzzle.”

McCord Overview Control Studies Delta TMDL_Page_04He presented a map showing mercury concentrations in the Delta’s open waters, noting that the Eco Restore program is looking at restoring 30,000 acres of wetlands, mostly in the Yolo Bypass.  “It would be great to restore wetlands, but look,” he said.  “The Yolo Bypass has among the highest mercury concentrations; the Central Delta has the lowest, which is good.”

McCord Overview Control Studies Delta TMDL_Page_05Dr. McCord then presented a pie chart from the TMDL program showing the various sources of mercury to the Delta.  He noted that there’s a non-point sources workgroup for agriculture and wetlands, and there’s also what he calls the ‘1%’ club, which is wastewater and stormwater.  “The wastewater on the chart here shows it is 4%, but more recent data shows that wastewater treatment plants are less than that, more like 1%, and then stormwater is even less,” he said.

He noted that he put a question mark next to open water.  “The pie chart format doesn’t recognize where you have with open water, there are arrows going in both directions,” he said.  “There is settling and demethylation, and then there is production from the sediment, so the percentage here is just the number in, not accounting for the numbers out.”

He noted that the tributaries are not currently being addressed in the regulatory program; the program is just looking at the Delta right now.

During phase one of the TMDL program, the entities responsible for reducing methylmercury in the Delta are participating in studies to develop and evaluate ways to manage methylmercury.  The progress reports were due in 2015, and the final reports are due in October of 2018.  The final reports need to show the effectiveness of the control method for reducing methylmercury at discharge, what the costs are of implementation, the potential and redirected impacts of the control method, and the feasibility or scalability of implementing the control methods.

This gets at that rock and a hard place,” Dr. McCord said.  “The effectiveness – can you meet the TMDLs goals of reducing loads off of site, but then the other one is costs.  Right now somebody is managing their water and they are optimizing it to the conditions that they have.  If you add another objective to their function of what they have to do, it’s going to cost more, because they are optimizing now, if they have to do anything different, it’s probably going to cost them more, or else they would have done less anyway. … There’s a cost associated with doing things.  Then there are also potential impacts; maybe by doing something that reduces it off site, it’s not always going to cost them more, but you could have unintended consequences on the site.”

McCord Overview Control Studies Delta TMDL_Page_07The TMDL regulatory program is currently in phase one.  Dr. McCord noted that there are some things that are required, and others listed at the bottom that don’t have to be done yet, but are good things to do if possible.  There is not a statewide objective or TMDL yet, but people are working on that.  Phase one is a gathering information and learning phase, he said.

In a few more years, by 2020, there will be a time when good information will be needed in order to control things under the TMDL, and there will be the need for more monitoring.  “The regulatory program talks about monitoring fish in 2025,” he said.  “We haven’t been monitoring currently so there’s not data right now; there are regional monitoring programs and funding being proposed for that.


McCord Overview Control Studies Delta TMDL_Page_08 Dr. McCord began by presenting a picture showing a water way covered in plants with a crocodile lurking beneath.  “The point is that you look at the Delta, and it’s all beautiful, but you have to recognize there’s crocodiles lurking out there, so you have to do the best thing you can and understand that, and be careful about it when you’re doing your studies.”

McCord Overview Control Studies Delta TMDL_Page_09He presented a slide showing the various entities involved in developing the TMDL and are now implicated in implementing it and doing these studies.  He would be focusing on wetlands and ag, municipal and industrial wastewater, and urban runoff. He noted that there’s not an entity per se that’s a stakeholder group right now.

Agricultural and wetlands workgroup

The control study workplan developed for the workgroup a few years ago had three pieces to it:  what do we know, so a synthesis of key findings and knowledge gaps; what do we do or the management practices described and scored; and then where to do it, or land uses by subarea.

McCord Overview Control Studies Delta TMDL_Page_11Dr. McCord then highlighted some of the recent findings.  He presented a graph showing mercury in the San Joaquin River at Vernalis and in silverside fish from August 2005 to November 2006.

What they found in this one year was that there were some water concentrations that weren’t a big deal, and then there’s a spring flood, and sure enough, you saw the spike in the fish as well.  That’s an indication that the methylmercury in the fish respond to what’s happening in the water, but there’s also a pulse effect, and it’s a rapid effect from the flooding cycle in the lower part of the valley.  So as a non-point source, that’s an interesting sort of thing to look at.”

McCord Overview Control Studies Delta TMDL_Page_12He then presented a slide from the Nigiri project in the upper Yolo Bypass where they are using flooded rice fields as rearing habitat for juvenile salmon.  “They call them floodplain fatties.  They put the juvenile salmon in there, and then they eat the bugs and everything and they grow like crazy and they migrate out and they are in better health because of it,” he said, noting that the two graphs show the difference between fish that were in the Sacramento River and those that were grown on the floodplain.  “It’s a good thing to do for migrating salmon.  They grow better and they are in better shape to go off to the ocean and do their thing for a few years before they come back.

However, bioaccumulation of mercury is an issue.  “Over time, the Sacramento River fish accumulated a little bit of mercury as they growing, but these in the bypass were a lot higher, so that’s an onsite problem,” he said.  “With the understanding that with these salmon, they are only there as little juveniles and then they are gone to the ocean, and they are eating and living in the ocean, so it’s not a concern for them.  There doesn’t appear to be any impact on the fish, and it’s better for the fish to do this, but nonetheless, that is a concern that was identified in this study.  Nonetheless, they are generally below the TMDL threshold of concern there.

McCord Overview Control Studies Delta TMDL_Page_13He then presented a figure from a study showing mercury concentrations in rice fields and wetlands.  “Wild rice was highest at harvest, so there are certain times in the farming cycle when it was higher in these types of rice fields.  White rice was generally higher at flood up and in the winter, … and the permanent wetlands were lowest,” he said.

He pointed out that the dashed line indicates the water quality goal of .06 nanograms per liter in water.  “That’s sort of a level that sure would be nice if we had that so that the fish would be in attainment, but every single sample, water in and water out, hundreds of them, was way above that,” he said.  “Even in the permanent wetlands, it was still above … the average was about .3ish, so that’s about as good as you can get with these permanent wetlands.”

McCord Overview Control Studies Delta TMDL_Page_14For the second part of the workplan, Dr. McCord said they next published a paper that looked at all of the different management practices, putting them into different categories:  biogeochemistry type controls, such as applying coagulant; soil and vegetation practices, and hydrology.  “The problem is that we needed more data and they are working on that.  It’s tough to manage the soil and vegetation.  We ask the farmers to do things, they did, but there’s still a lot of residue there and residue is not a bad thing, necessarily.  There is particularly this rock and hard place thing.  The potential onsite impacts.  If you leave the water on longer, you can increase the salinity, you’re not optimizing for growing rice or whatever on land anymore, so there are effects.  So there’s concern for all of those.”

McCord Overview Control Studies Delta TMDL_Page_15The third part of the control studies for nonpoint sources was looking at where we could do things.  “So we divvied up the pie in terms of land use, and the key thing here is that most of the land in the Delta is agricultural in nature, but is only contributing 2% of the methylmercury load,” he said.  “In terms of the other land, some of them you can’t do much about.  These natural systems, we can add them or take them away, but we can’t effectively manage those because they are natural.  Then there is the flooded ag, the managed wetlands, and the permanent wetlands which are probably sinks anyway, so there’s not more you can do for that other than do some more of them.  So there are very few places that work can be done, and that just affects a small percentage piece of the pie.”

McCord Overview Control Studies Delta TMDL_Page_16Wastewater community

There are about 14 or 15 POTWs, or publicly owned treatment works in the Delta. “So 96% of the flow volume is represented by facilities that have been doing upgrades or will be doing upgrades to the treatment plants, so they are controlling mercury more currently and in the future than was considered in the TMDL,” he said.  “They are spending $3 billion on that; they do it for other reasons, but it’s affecting the 1%.   The focus of the control study that the group is doing is the effectiveness of pollution prevention, they are looking at sources in the service area, and the second part is about treatment improvements, so looking at that $3 billion and what investment and what benefit are we getting for that cost towards mercury.”

McCord Overview Control Studies Delta TMDL_Page_18He then presented a graph showing study results, noting that the treatment plants are broken down by the different types: Secondary is primarily settling stuff out, then there’s secondary and some biological treatment, then secondary plus various nitrogen removal techniques, and lastly tertiary treatment.  He noted again the dashed line indicating the 0.06 nanograms per liter goal.  “The inflows ought to be about the same, because the treatment plant didn’t affect anything upstream, but coming out of the treatment plants, you can see secondary didn’t quite make it, but the others do – they are all below the 0.06 …  So you can see they are getting a lot of benefits from that.”

The other part of this study was source control or pollution prevention.  “You’re not going to see much more, regardless of what you do as you’re way down there anyway, so there’s not much of an added benefit of doing source control,” Dr. McCord said.

McCord Overview Control Studies Delta TMDL_Page_19He then presented a bar graph showing putting the mercury loads from wastewater treatment in context with other sources.  “This is the pie chart shown in a different way,” he said.  “The tributary inputs are the biggest one here but wastewater is just the little sliver on the top, so what they were looking at was if they do everything they are planning to do (the $3 billion investment), what benefit is that going to have overall? Then what if we do even more, what effect is it going to have?  There’s not a lot of additional benefit in doing that – that was the message.

The wastewater community and other members of the regulated community are doing other activities, such as participating in a mercury exposure reduction program, implementing the pollution prevention plans, looking further at nutrient removal, and then monitoring in non-drought conditions because a lot of their data is from the recent years when the state has experienced this extreme drought, he said.


With respect to stormwater, there are phase one communities participating:  Sacramento, Stockton, and Contra Costa;  they have their own individual permits and are doing their own individual studies, he said.

McCord Overview Control Studies Delta TMDL_Page_21Sacramento is looking into Low Impact Development or LID.  “They are looking at infiltration and the effect that would have on mercury leaving the site, and if it works, they can do more of that in any new development project, or even a retrofit type project,” he said.  “What they found was sure enough, it reduced the total mercury and methylmercury and the reactive mercury loads. It reduced concentrations a little bit also, but the main thing was the loads were decreased because the flows were decreased.”

In Stockton, they are studying retention basins.  “Basically whatever comes off of some area of that community goes into a big sort of pond and then it slowly drains out, so you shave off the peaks of the hydrograph,” he said.  “They found the total mercury was reduced, which makes sense, because these basins tend to accumulate sediment, so total mercury drops out and it goes.  Methylmercury really didn’t change, there wasn’t a statistical difference in concentration of methylmercury in flow versus outflow, and for a retention basin, you don’t lose water, it doesn’t infiltrate so much into the ground, it just slows it down, so the same volume of water coming as going out, and so it’s only the concentration that would do something.”

Contra Costa is also doing infiltration studies.  “They found that with some of those, they didn’t get any runoff; it would rain, it would infiltrate, and it was gone, so there zero load.  But where they did have any kind of runoff, they found that the methylmercury varied, sometimes it was actually increased, other times decreased, but the key point was that they found was the methylmercury is associated enough with the particulate material that there’s no way they are going to get to .06.  With stormwater programs, rain falls, and bad things happen.  You have to control for floods, you got to get rid of the water, and in the current best management practices in stormwater, they can only reduce the suspended material so much, and they got down to those pretty low levels for stormwater, just the sediment is going to exceed .06 numbers.  So they can’t get there from here, that’s the message.”

These are still all preliminary studies; they are still working on it,” he added.

Phase 2 are the smaller communities, and they are not doing any studies per se, but they are implementing sediment or erosion control, so the stuff that the phase 1 communities have found is most effective, dealing with all the sediment, they are doing that,” he said.

In terms of future focus for their studies, where they are right now in terms of progress is understanding the design factors of the various management practices, and how can they optimize this systems; doing a service-area wide assessment which gets into the scale up factor, and then long-term compliance.  Given that Contra Costa is saying they can’t get to that, what can they do, how good can they do it, and just regulate to that as best available technology and best management practices.


I’m an engineer and also a consultant, so I am trying to think long-term, what effect does this have and where are things going,” said Dr. McCord.  “So the long-term approach is that we need to go from conceptual to mechanistic to scale, so what can we do at the bigger scale and what is the ultimate effect of this.  Taking the science, going into the management practices, and then the land use analysis, and where are we going from here – that’s what I want to see so I can tell people this is what you can do and these are the benefits.

The long-term interests are getting at the cost-benefit, as society cares about that – you all care because you pay a sewer bill or a stormwater bill or you pay taxes that go to grants that add wetlands or whatever, so we all pay one way or another,” he said.  “There’s the attainability and trading – if there’s some kind of program where everybody puts some money into the right bin so we can do the best thing possible, modeling, recognizing climate change, and then reconciliation.  We can’t just look at a mercury box and say this is what we’re going to do, we have to say this is the best thing holistically for the Delta, for the environment, and for the people of California.”


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