Overview of mine remediation in the Bay-Delta Ecosystem

New Idria by Tom Hilton
New Idria mine (photo by Tom Hilton)
California is making progress on remediating abandoned mine sites, says Carrie Austin, San Francisco Bay Regional Water Board

The California Gold Rush, begun in 1849, brought rapid population growth, new technology, and economic growth to the state, propelling it to a center of the global imagination and making it the destination of hundreds of thousands of people practically overnight. Many pieces of this history are still with us today in the form of historic mining communities; abandoned mine shafts, tunnels, and facilities; and open scars on the landscape.

Open hydraulic mining pit, 1890-1900
Open hydraulic mining pit, 1890-1900

However, there are other parts of this mining legacy that are harder to see, such as the toxic substances from tailing piles and other remnants of mining production left behind in abandoned mining operations that have far reaching impacts to water quality and water supply even today.

Mercury is a contaminant of particular concern.  Otherwise known as “quicksilver”, mercury was used during the mining process to extract the gold from the ore. Hydraulic mining processes in the mountains washed large amounts of mercury-laden sediment downstream where it settled into waterways of the Central Valley until the process was banned in 1884.  In addition, large amounts of mercury-laden tailings and debris piles remain at many abandoned gold mining sites and this mercury and other toxic substances continue to be make their way downstream through creeks and rivers to lakes, reservoirs, the Sacramento-San Joaquin Delta, and the San Francisco Bay.

New Idria polluted water by mhlradioMercury contamination is a public health concern; most humans are exposed to harmful amounts of mercury through eating contaminated fish and shellfish. Toxic levels of mercury have been found to be present in more than 180 reservoirs and rivers in the state, making some of the fish unsafe for human or wildlife consumption.

Earlier this year, the Delta Science Program hosted a workshop to discuss the efforts being made to address mercury impacts statewide since a comprehensive strategy to address the problem was formulated in 2003.  In this presentation, Carrie Austin, an Environmental Engineer at San Francisco Bay Regional Water Board, updated attendees on the progress being made in the Bay-Delta ecosystem.

I’m going to start out with a question for all of us in this room which is why do we want to clean up mines? And how do we measure success?,” began Carrie Austin.

Noting that she has worked with several others over the past few years, today she would be giving an overview of mine remediation.  “I think that the 2003 mercury strategy is pretty darn good for mine sites,” she said.  “We’ve also made some progress on inventorying mine sites and even remediating them.”

The core components of the 2003 mercury strategy were to identify the mine sites; prioritize them for cleanup or remediation; pilot test remedial technologies; implement or remediate; and then to measure performance.  “I like this question in my work, because I’m a remediation engineer who would like to leave a positive impact when I’m gone,” she said.  “So where might mine remediation enable measurable and timely fish methylmercury reductions is a key question for us.”

Ms. Austin said that in this presentation, the term ‘mines’ will refer to all mine-affected landscapes, the mine sites themselves, and mercury contamination in all its different forms, whether it’s a tunnel dripping elemental mercury, a gold mine site with elemental mercury that was used for amalgamation, a mercury mine site with piles of tailings, or huge volumes of mercury contaminated calcines that have moved downstream; this all falls under the general term “mining waste’ or ‘mines’.

What we do is we evaluate the susceptibility to mobilization by erosion because stormwater transport is the main issue that we’re talking about in getting this mercury downstream to the San Francisco Bay Delta,” she said.


She began with the core component of the strategy – to identify mine sites, noting that she refers to this as an inventory.  “It’s an inventory of mercury contaminated, typically sediments, so it’s mining wastes of various forms and mining affected landscapes.  I would really like to be able to present to you a statewide database that cuts across all agencies, pull out a bunch of maps and be able to show you the inventory and how we prioritize and what our current status is.  That’s ten or fifteen years ahead of us; we’re not there yet. I have information from my sister agencies and my own agency and I can give you a bit of a rundown, but it’s going to take us quite a bit more time to put more together.”

Austin Mine Remediation_Page_04In terms of the inventories, she said they would like to refine the map by removing the mercury mines which were non-productive prospects because there’s almost no mercury leaving those sites, as well as the gold mines where mercury was not used.

Ms. Austin noted that there are several other agencies doing inventory work, such as the U.S. Bureau of Land Management, the California Department of Conservation, the Department of Toxic Substances Control, as well as the Central Valley and the San Francisco Bay water boards which have mine inventory efforts underway.  “In California, it’s captured under an agency workgroup, the California Abandoned Mine Lands Agency workgroup, so we’re trying to work together on this inventory effort and remediating mines.”

Austin Mine Remediation_Page_05She presented a map of the mines in the San Francisco Bay Regional Water Board’s watershed, noting that it is a much smaller watershed compared to what the Central Valley Regional Water Board oversees, and so she was able to go out and personally inventory every mercury mine in their region, a task not possible for the Central Valley water board.

Ms. Austin noted that in the San Francisco Bay region, they are evaluating the construction sites applying for stormwater permits that might be located on or near or in the drainages from these mercury mine sites, and they are setting up an automated system that will notify them of additional erosion control measures that are needed to ensure they are not discharging mercury downstream.  “When we got this really up and rolling in the San Francisco Bay region, we’ll introduce it to our sister water board agencies and see if it works for their regions as well.”


There were three concepts they used for prioritization:  transport, fate, and feasibility.  The staff hypothesis they wanted to test as they went through the prioritization was to ask where mine remediation might enable measurable 20% reduction and achieve timely fish methylmercury reductions – about 10 years.

The reason we chose 20% is that we think it’s the smallest amount that is measurable; it’s not that we only we want 20%, we are very hopeful for more, but we think that 20% is a measurable amount,” Ms. Austin said.  “In terms of timeliness, we are thinking from the time to remediate the mine site to have the benefits and the fates downstream, and then the fish to grow, we think the shortest time frame there is about ten years, so that’s how we have come up with this.

Ms. Austin then said she’d be presenting photographs from some of the mine sites in the San Francisco Bay region; they are some of the smaller mines in the state, but the concepts she would be presenting about transport potential and mercury amassed can apply to any type of mining waste, whether it’s on the landscape or already in the stream.

Transport potential

Austin Mine Remediation_Page_07She presented a slide of two different mine sites, noting that she would prioritize the mine on the left as a higher priority on the right.  “On the left, this is how we typically disposed of the mining waste; we dumped them into the nearby creek; there is a creek on the other side of this mine tailings pile, and it is coming through and especially eroding it at the bottom, so we have this huge mass wasting process,” she said.  “It’s a completely unvegetated pile and it remains on site with 6,000 cubic yards; it’s very, very big.  This has mass wasting and very high transport potential – it’s roasted mercury ores, it’s calcines, it’s high mercury concentrations with high transport potential, and high mercury mass so that’s a high priority.”

On the right side, what we have is a very small pile of calcines left that do not evidence of mass wasting processes, which is not to say that we don’t have any concerns here, we just have lower concerns,” she said.  “This is an extremely steep hillside.  It’s a horse ranch and the horses actively graze through here; hence there are no larger bushes, which are known to be much better erosion control than just the grasses here.”

Fate of the mercury

The second question to ask is what is the fate of the mercury when it goes downstream.

Austin Mine Remediation_Page_08She presented a graph, noting that on the horizontal access is total mercury concentration in reservoir sediment, and the vertical axis are fish methylmercury concentrations, and the horizontal red dotted line is the fish target of .2 milligram per kilogram.  She noted that she is using a reservoir as a proxy for the Bay-Delta because the transport process is the same, and methylation and bioaccumulation have similar mercury cycles in reservoirs and the Bay Delta, so the reservoir data is a proxy for the process in the Delta.

What you see with the dots that are plotted is that black squares are the fish in reservoirs that have background sediment total mercury and the red circles are the reservoirs where the bottom sediment is elevated compared to natural background in their region,” she said.  “We have this gray linear regression line, so we have this trend line on this log-log plot of increases of fish methylmercury levels with increases in sediment total mercury when it’s brought in from the mines is what we’re thinking about, so the fate here is the measurement.  Does the reservoir have elevated mercury from the mines? That’s the fate question.”


Lastly, there are feasibility questions for prioritizing the mines for remediation.

Ms. Austin said there were two aspects to feasibility:  whether the mine site is localized to a relatively small area of the watershed as it is feasible to clean up a small proportion of a watershed and not the entire watershed, and if the mines located near the reservoirs – within about 10 kilometer length.

The thinking here is that it’s feasible to clean up the mine site and some stretch of the creek, but not the full length of the creek.  We’re going to rely on the natural processes such as big storms coming through to wash out the accumulated mercury laden sediments in the creek and then bring in the clean sediments from the watershed for a burial process in the reservoirs to reduce the reservoir bottom sediment mercury.  It would then be a few more years for the fish population to change over and have lower bioaccumulation.”


After prioritization, the 2003 mercury strategy advocates pilot testing of remediation, but Ms. Austin said that pilot testing isn’t really needed.  “I think we’re pretty much ready to go full scale to remediation,” she said.  “There are not many places that we need pilot tests.  Pilot tests to me as an engineer imply innovation, and we know how to remediate mine sites.”

There is plenty of guidance available on mine remediation, Ms. Austin pointed out.  “Even before the 2003 mercury strategy was released, in August of 2000, US EPA had their guidance on how to characterize and remediate mine sites,” she said.  “Our sister agency the Department of Conservation has a terrific manual for California mines for rehabilitation of disturbed lands in California.  Additionally, the water boards operate under California Code of Regulations Title 27 for mining waste cleanup’; I like how this code is organized because it classifies mining waste into four different categories with respect to the threat to water quality, so when there’s a lower threat to water quality, we can use lower cost remedial technologies to address a mine site problem.”

There may be pilot testing needed to do sizing of treatments, but in general, this isn’t rocket science,” Ms. Austin said.  “This is well-founded engineering, geotechnical engineering, botany, etc., and we’ve done it for decades.”


After remediation, it’s important to be able to measure the effectiveness of the remediation, Ms. Austin said.

Austin Mine Remediation_Page_13She presented a slide of two pictures of the Gambonini Mercury Mine located in Marin County within the San Francisco Bay region.  “In the left ‘before’ photo, there was a mass-wasting process,” she said.  “I know this looks like a small site from this photo but those gullies are impressive; there were cars dumped in the bottom of those gullies.  It wasn’t really vegetated, so it was a huge mass wasting problem that was coming downstream.”

The San Francisco Bay Water Board staff went out and did extensive water quality measurements as well as collecting grab samples beforehand.  “My predecessors did a mass loading calculation that showed that over 80 kilograms of mercury were released from this site in a two month period in a wet El Nino winter in January-February 1998,” she said.

There was a wonderful response to this quantified problem,” Ms. Austin said. “US EPA Superfund emergency response came out and they remediated the site.  They treated like a typical land slide situation and a landslide repair, so what you can see on the right are the engineering results.  They brought out the heavy equipment and moved a lot of the mining waste into the pit; they filled a dynamited hill at the top of the hill, and then benched and properly sloped the front face of that mining waste pile.  They put in storm drainage controls so the runon is directed away from the front face, and each of those benches has a V ditch that connects either to pipes or to creeks, so that you don’t have the water running down the front face, you have it running across the side and not causing erosion.

Austin Mine Remediation_Page_14Ms. Austin emphasized that this was treated as an erosion control site, not a landfill with a liner and a cover.  “The mining waste was simply moved around, compost was added, and a big native seed gathering and plants were germinated; lots of seeds were broadcast over it and the effectiveness if really terrific,” she said.  “There’s greater than 90% load reduction in mercury leaving this site and greater than 55-60% sediment load reduction.  I think that this is very translatable to other sites and I don’t think we need very many (if any) more of these kinds of detailed load studies of the effectiveness of remediation of this type.  And furthermore, I would argue that where a landfill is built with a liner and a cap, we’re going to get even greater than 90% mercury load reduction.”

Austin Mine Remediation_Page_15One of the challenges in terms of measuring performance is having a really robust data set of before and after, so there is a terrific tool for where you don’t have the instrumentation in but you have grab samples and both discharge,” she said, presenting a diagram.  “The x axis is the flow rate of the creek and the vertical axis is the total mercury concentration; the lines represent the suspended mercury load leaving the site.  The before curve is the top and the effectiveness of remediation is this change to the black curve below showing that for any given discharge of the creek, you have a lower concentration of mercury leaving the site, and that’s evidence of a mass load reduction.  So this is a tool that you can use for grab samples.”

Austin Mine Remediation_Page_16One of the great challenges in measuring effectiveness is having robust data sets for before and after, Ms. Austin said.  “On the left, the photo shows huge calcine piles which is just graveling and uncontrolled; it’s also an acid mine drainage problem.  On the right, you can see what it looks like after remediation where the slopes have been laid back and benched properly and the stormwater controls put in; this site does have a liner and two feet of clean cover.   We do have a performance measure, and we can do this broadly at many remediation sites, and that is how much mercury was contained onsite.  In this case, 13,000 kilograms of mercury will never go downstream.”

Austin Mine Remediation_Page_17I think we have fallen down completely in a very important performance measure for mine cleanup, and that’s the question of whether or not we are getting reductions in bioaccumulation and especially in fish methylmercury as a result of the mine cleanup,” she said.


Ms. Austin said that they have made progress.  “I think the 2003 mercury management strategy is pretty good, I question the pilot tests, and I talked about the challenges,” she said.  “The challenges aren’t truly daunting.  I think it just takes money.”

Doing an inventory isn’t rocket science, we just need high speed internet, decent computer software, and decent computers,” she said.  “There’s a lot of desktop analysis that can be done to inventory and then it’s really basic field skills to go out and do the analysis and some funding for laboratory analysis to confirm the mercury concentrations.”

That’s why I think that part’s just money and I think the remediation part is just money, and I think we know how to do it,” she said.  “I don’t think it’s rocket science holding us back, I think it’s willingness.  I am not optimistic that mine remediation will soon have a benefit on the San Francisco Bay Delta system, that it won’t have a measurable benefit, because mercury contamination is huge in the creeks downstream of the mines and that’s going to be really hard to clean up.  But I think we owe it to future generations to start or to continue what we’re doing it and ramp it up because it will make a difference eventually when we get most of it done.”


Austin Mine Remediation_Page_18Ms. Austin then said there is good news to share.  “We have made progress in this and so the green dots on this map show mine sites where we have made substantial remedial efforts.  We might not manage to clean them up completely, but we can make it a whole lot better, and we’ve done that at all of these green dots; the blue dots are where we already have plans underway.”

She then compared and contrasted New Idria and New Almaden.  “New Idria is located really far away from urban areas so they could not make a good use of those calcines whereas at New Almaden, they found they were really great for road bed material, so some of the mine calcines from New Almaden were used in the mining districts for the roadbed, but also we think throughout Santa Clara County,” she said.  “In New Almaden, we have really large rainstorms that have washed a lot of the calcines downstream, and we can measure that with cores in SF Bay.  At New Idria, I’m guessing that maybe they haven’t had the same kind of rainfall so they haven’t had the same kind of force to move the tailings downstream.  The New Idria calcine tailings are mine boggling – huge, huge mountains of calcines.”

At New Almaden, I have really good news to report to you,” she continued.  “I estimate that within about 5 years, we will have probably landfilled all the remaining calcines at New Almaden, so we started about 2000, and it’s almost done.  We have grant funds to wrap up the last bits of it.  But at New Almaden we have this huge challenge of contaminated creeks downstreams, they are well studied, we know that the creek beds are hugely contaminated with the mine tailings.”

ClearLakeCAIn the Oakland area, Ms. Austin said that a colleague oversaw enforcement at a sulphur mine as it was cleaned up, so that creek that drained to Mills College and through a residential district is no longer leaching the acids and the metals.

At Clear Lake, we have made a lot of improvement.  Nobody would say that we’re done at Clear Lake, but we’ve made a lot of improvements,” she said.  “My closing statement is that I’m so thrilled with what we’ve done at Iron Mountain.  Nobody would say that we’re done, but we no longer have 15 river miles of fish kills, so we are making progress in remediating the mine problem in California.”

Thank you.


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