![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
So what are you doing in Leadville?
Oct. 22nd, 2016 02:20 pmI've now been in Leadville for just over a month, working on this project. So... what is it that we're doing here?
In short, we are working to prevent the formation of acid rock drainage (ARD) on one portion of the California Gulch Superfund Site. There are four parts to this project - three little ones & one big one. First, the little parts:
Then there's the big part of the project - the clean water diversion channel. Background: the area around Leadville was intensively mined for over 100 years, producing gold, silver, lead, & variety of other metals. Part of the legacy of this activity are large piles of mine tailings. This is rock that was removed while accessing the veins of metal ore. It contains a lot of pyritic minerals, which contain sulfur, which can create sulfuric acid when in contact with water. Once the water becomes acidified, it starts leaching heavy metals from the mine tailings - arsenic, zinc, manganese, cadmium, lead, chromium, etc. The resulting effluent is ARD. Treating ARD is expensive, so our approach right now is to reduce the amount of water that comes into contact with the mine tailings so less ARD has to be treated.
To this end, we are digging a channel that will intercept all the surface runoff & snowmelt from the mountainside above one particular set of mine tailings piles located in Stray Horse Gulch. The channel is lined with a plastic membrane to prevent any water from seeping through it. On top of the plastic membrane is a honeycombed web of plastic, which is filled with gravel.
This channel will divert the water around the piles & down another watershed (No-Name Gulch). The channel is about 2,400 feet long & ten feet wide. In order to give it enough slope to make sure the water flows across the hillside, we had to dig it pretty deep in some places - as much as 10 feet below the existing grade. The design requires us to make the side slopes no steeper than 3:1, so in places, the channel is 70 feet wide (30 feet on one side slope, 10-foot wide channel, 30 feet on the other side slope). We are moving about 8,000 cubic yards of soil, all told. It will look pretty nice once we get the side slopes revegetated.
One of the trickier parts of this project is that this channel runs smack dab through the middle of an eligible historic site, the Pyrenees headframe. It is a towering timber structure built over a mine shaft that extended 1,257 feet underground. Our channel runs right past its foundations, in part following the grade from a rail spur that used to haul off the bonanza of ore coming up from the Pyrenees mine. While excavating this section of the channel, we had an archaeologist on site to document anything we found. We have also had to excavate around some large concrete foundations, which probably used to house the giant hoist wheels that lifted men & materials out of the heart of the mountain. My nightmare is that one of the 50,000-lb. pieces of equipment I've got operating on this site will find a near-surface lateral by caving it in.
I think the project is going pretty well. We've been incredibly lucky with weather & I hope our luck last for just a couple more weeks. We've got to finish putting the layers in the channel, the gravel in the layers, then finish re-grading all the side slopes, covering all the slopes with erosion control blankets & seeding them with a blend of native grasses. We have one more culvert to install (in a berm at the outlet of the channel, which will control any floods that come down the channel, releasing them slowly through the culvert). We're building a small pond in an area where we dug out some topsoil. Then we will remove all of our construction roads, demobilize the office trailer, get all the equipment sent off, & go HOME.
In short, we are working to prevent the formation of acid rock drainage (ARD) on one portion of the California Gulch Superfund Site. There are four parts to this project - three little ones & one big one. First, the little parts:
- We are running a generator-powered pump in a groundwater well containing uncontaminated water (the GAW well) 24 hours a day, pumping approximately one million gallons per day into California Gulch (a small creek). We are doing this to keep the clean water from mixing with a plume of contaminated water, which would force a water treatment plant owned by the US Bureau of Reclamation (USBOR) to treat an increased volume of water.
- We were trying to rehabilitate an injection well (the Marian well) that pours ARD about 200 feet down a 14-inch-diameter PVC pipe into an old mine lateral, where it flowed into the Leadville Deep Mine Tunnel (LDMT), & then to the USBOR water treatment plant. This well, unfortunately, has completely collapsed at about 135 feet below ground surface (bgs) & probably can't be repaired. There is some evidence that the lateral has also collapsed. Next year, we may attempt to replace this well with a directionally-drilled well going straight to the LDMT. This will be a tricky bit of drilling, as the LDMT is about 500 feet away, about 200 feet bgs, & only about five feet wide. Also, we don't have any maps or other information about its specific location (it was built in the 1940s). Hitting it with a directional drill rig will be like shooting a bullseye on a buried target while wearing a blindfold.
- We are placing limestone gravel into several ARD ponds to see if the limestone can neutralize the ARD & the pond sediments. The ARD at the California Gulch site is intensely acidic, with a pH that is usually less than 2 & often less than 1 (for comparison, stomach acid is usually between pH 1.5 to 3.5). It is our hope that if we can raise the pH, the ARD will pick up fewer heavy metals & therefore will be easier to treat when it reaches the USBOR plant.
Then there's the big part of the project - the clean water diversion channel. Background: the area around Leadville was intensively mined for over 100 years, producing gold, silver, lead, & variety of other metals. Part of the legacy of this activity are large piles of mine tailings. This is rock that was removed while accessing the veins of metal ore. It contains a lot of pyritic minerals, which contain sulfur, which can create sulfuric acid when in contact with water. Once the water becomes acidified, it starts leaching heavy metals from the mine tailings - arsenic, zinc, manganese, cadmium, lead, chromium, etc. The resulting effluent is ARD. Treating ARD is expensive, so our approach right now is to reduce the amount of water that comes into contact with the mine tailings so less ARD has to be treated.
To this end, we are digging a channel that will intercept all the surface runoff & snowmelt from the mountainside above one particular set of mine tailings piles located in Stray Horse Gulch. The channel is lined with a plastic membrane to prevent any water from seeping through it. On top of the plastic membrane is a honeycombed web of plastic, which is filled with gravel.
This channel will divert the water around the piles & down another watershed (No-Name Gulch). The channel is about 2,400 feet long & ten feet wide. In order to give it enough slope to make sure the water flows across the hillside, we had to dig it pretty deep in some places - as much as 10 feet below the existing grade. The design requires us to make the side slopes no steeper than 3:1, so in places, the channel is 70 feet wide (30 feet on one side slope, 10-foot wide channel, 30 feet on the other side slope). We are moving about 8,000 cubic yards of soil, all told. It will look pretty nice once we get the side slopes revegetated.
One of the trickier parts of this project is that this channel runs smack dab through the middle of an eligible historic site, the Pyrenees headframe. It is a towering timber structure built over a mine shaft that extended 1,257 feet underground. Our channel runs right past its foundations, in part following the grade from a rail spur that used to haul off the bonanza of ore coming up from the Pyrenees mine. While excavating this section of the channel, we had an archaeologist on site to document anything we found. We have also had to excavate around some large concrete foundations, which probably used to house the giant hoist wheels that lifted men & materials out of the heart of the mountain. My nightmare is that one of the 50,000-lb. pieces of equipment I've got operating on this site will find a near-surface lateral by caving it in.
I think the project is going pretty well. We've been incredibly lucky with weather & I hope our luck last for just a couple more weeks. We've got to finish putting the layers in the channel, the gravel in the layers, then finish re-grading all the side slopes, covering all the slopes with erosion control blankets & seeding them with a blend of native grasses. We have one more culvert to install (in a berm at the outlet of the channel, which will control any floods that come down the channel, releasing them slowly through the culvert). We're building a small pond in an area where we dug out some topsoil. Then we will remove all of our construction roads, demobilize the office trailer, get all the equipment sent off, & go HOME.
