How does mine waste affect water sources in Boulder County? A look at reclamation efforts in the Fourmile watershed offers a glimpse.

Maya MacHamer picked me up in a rattling 2011 Subaru Outback on a late July morning. The sun overhead already promised brutality. Co-founder and director of the Boulder Watershed Collective, MacHamer drove her car, with me in it, down roads that explained its rattle, and made the fact that it still ran remarkable.

MacHamer began working in Fourmile Canyon in 2015 to aid in the recovery of a watershed that had a wildfire in 2010 followed by a flood in 2013. Upon assessing the landscape, mines revealed themselves as the most pressing problem to downstream water sources.

“We never meant to do anything with mines,” she said. “We fell into it because we had to.”

So a big focus for the Boulder Watershed Collective is mine reclamation: undoing the negative effects of mining on the surrounding landscape. Heavy metals abound in the many piles of mine waste (rock pulled from the mine to get to valuables further down) and mine tailings (leftovers of rock processed to extract valuable metals from ore), and those heavy metals assimilate into water sources unless otherwise addressed. 

MacHamer agreed to take me on a tour of a mine reclamation her team had completed, and one yet to be done, in the Fourmile watershed. Accessed from Sunshine Canyon, we drove to the worksites past congestion at the base of Mount Sanitas, following the same route some miners must have taken over 100 years ago.

While we drove, MacHamer explained that mines and their waste had mostly receded from the public’s psyche before the Fourmile Canyon Fire in 2010 — the landscape having covered its wounds with vegetation and put yawning man-made caves to use as habitats for bats and other dark-dwellers. 

“I don’t think there was an awareness of the negative environmental impacts or the safety issues,” she said.

But the Fourmile Fire burned vegetation that held waste piles in place, allowing heavy metals to begin leaking into nearby waterways. The landscape has not recovered as it should in the 12 years since the fire, according to MacHamer. Few trees grow in the burned area except some ponderosa pines on waste piles: It seems they like more acidic soil. What the area needs, she speculated, is several consecutive wet springs for seeds to take hold, which it has not enjoyed.

There was also concern, as MacHamer said, for firefighters “falling down mineshafts.” In the mid 1800s to early 1900s prospectors simply dug as far as they wanted and then defected — leaving many of the foothills around Boulder pock-marked with openings to tunnels whose depth and breadth are undefined. 

This fear of falling firefighters started an endeavor by the Colorado Division of Reclamation, Mining and Safety to map and close the mines. Sometimes this meant backfilling shafts (which are holes that go straight down) with dirt, or putting grates over adits (mines that burrow horizontally into a mountainside).

These mines, which many in the City of Boulder can go a lifetime without considering, are a part of daily life for those living in the foothills. MacHamer, who grew up on nearby Sugarloaf Mountain, said she played on mine waste piles and went into the mines themselves as a kid.

“There just wasn’t that worry back then,” she said.

“That worry” is that mines collapse: a former hazard of the job and current hazard for anyone exploring the old tunnels. But that doesn’t stop many from using the mines on their property for wine cellars, bread proofers, or a place to hide food from bears.

And some still maintain the hopes of prospectors who came before. MacHamer spoke of an owner who refused to let the Boulder Watershed Collective move waste piles near his house because “he thinks there’s still stuff in [the piles] and if he could just haul all the sediment out and reprocess it, he thinks he could find something,” MacHamer said. “But that’s super expensive.”

We turned off the main road and started down a gravel side street where houses, built after the fire, backed up against large piles of what looked like sand. “That’s mine waste,” MacHamer said. She explained that it could have detrimental health effects “not immediately, but if breathed in day after day.”

Past meets present

The first worksite we toured was Sweet Home Gulch, where the Boulder Watershed Collective is beginning preliminary waste sampling for levels of heavy metals and working with consultants to design restorations. The gulch is an ephemeral drainage: ephemeral meaning water only flows there during the spring thaw or after a heavy rainstorm, and drainage being any geological structure that collects water into a stream or river. A gulch is a steep-sided ravine, and a Sweet Home is a pleasant place to return at the end of the day, though perhaps not when it’s a barren ravine.

Having taken care of the higher-priority waste and tailings that interact with Fourmile Creek, MacHamer and the Collective are now turning their attention to lower-priority gulches.

We hiked downward over mine waste that made up the bottom of the gulch. Partway down the drainage a metal rod stuck out of the ground surrounded by dried tree trunks and shifted rock. “That’s a mine shaft that was closed,” MacHamer said. She explained that there was a date on top of the rod stating when the mine was backfilled, but I probably shouldn’t get close enough to read it. “It was closed before the 2013 floods and all this debris was brought down on it, so we don’t know how stable the ground around it is.”

Channels carved in the mine waste showed where water had carried some of the earth’s innards down to greater rivers below. The goal for MacHamer and her team at the Boulder Watershed Collective is pulling waste out of the bottom of such gulches so it no longer interacts with passing water.

“There’s good vegetation growing on it,” MacHamer said, gesturing to the shrubbery on the waste piles. “That’s a good sign. If there were a lot of heavy metals or very toxic compounds we probably wouldn’t see that.”

Where the gully opened to a broader vista, a wash of green contrasted the barrenness of the waste piles. “This is my favorite spot,” MacHamer said. She pointed out two apple trees and a pipe that fed them a trickle of water. “There was probably a house here,” she said. “This water wasn’t just for the miners. Someone was cultivating their space.”

Remnants of whatever structure once stood there lay blackened in the undergrowth. An adit opened behind. The trickling water — loud against the silence — came through the pipe from deep in the mine. MacHamer led me to the opening of the hole into the earth.

Cold air came in a continuous stream from within. Beyond the grate, darkness quickly grew complete. I urged my sight into the void, hoping to see — I don’t know. An insight, maybe, into the thoughts of those long-dead who were once as alive as any of us today. Were they afraid as they entered the blackness? Or did the hope of discovering riches crowd out fear?

“Very cool,” I said, stepping back and taking a picture. “Very cool stuff.”

Walking back up to the car, MacHamer noted that, for this gulch, the Watershed Collective was hoping to work with someone who could manage the mine waste using only hand tools and horses. Though there were old mining roads carved into the hills around us, she said that because this was a smaller project, they really wanted to have a “light footprint,” as building larger roads to get in excavators can sometimes heighten erosion problems.

A finished project

“They must be showing this property because this gate isn’t normally open,” MacHamer said as we drove to Ingram Gulch, where the Boulder Watershed Collective has completed their mine reclamation work. “This’ll cut down our walk.”

Driving down what looked like a driveway, we continued to the end of pavement and turned onto a path spotted with rocks the size of cinder blocks. MacHamer buzzed by these stones while I waited for something to puncture the oil tank or disconnect the engine. “This was an old mining road,” she said over the rattle. “We used it to get excavators down here.”

I had to imagine excavators had more clearance than a Subaru.

The contrast between the finished gulch and Sweet Home showed mostly in its lushness. Because the mine waste in this worksite wasn’t excessively toxic, MacHamer and her team were able to move it to a “high and dry” location — out of the bottom of the gully and up the walls where water couldn’t reach — and then cap the piles. When waste is overly toxic, it must be moved to a hazardous waste landfill.

Mine waste is “capped” with layers of gravel, topsoil, soil amendments (such as lime, which makes the soil less acidic), native grass seed and an erosion control fabric that decomposes in sunlight. The two mounds in this gully could be seen clearly with their uniform vegetation, but a few bushes were already beginning to peck at the perimeters, sending branches as scouts onto the piles.

“Hopefully all the native plants will spill in,” MacHamer said. 

A tiny stream of water ran in the bottom of the gully that MacHamer pointed to. “It’s amazing that just that small amount of water is feeding all this life,” she said, gesturing to the plethora of green mobbing the water. 

Mines responsible for the waste watched from the walls of the gulch as we climbed back to the car.

MacHamer started her Subaru and we began our ascent back to the main road. Ahead of us rose the rocky path built by miners so many years ago. I hadn’t appreciated its steepness on our way down: I’d been too focused on the rocks with car-crippling ambitions. With gravity turned from friend to foe, however, the incline gained all my attention. The car moaned. “Oh come on,” MacHamer said as we stalled out.

We drifted backwards for a moment before MacHamer started the car again and gave it gas. A burning smell permeated. “I’m burning my clutch,” she said.

She declined my offer to get out and push, saying all we needed was a flat area to gain some momentum. I feigned unflappability while entertaining thoughts of being stranded in a sweltering canyon with the day approaching its hottest. Maybe I could shelter in a mine.

MacHamer backed almost to the bottom of the gulch. “Alright,” she said. “Here we go.”

We hustled up the incline. The Subaru clanked and groaned but cruised past where it stalled before. “There we go,” MacHamer said as we crested the hill. She looked over at me. “Sorry I scared you.”

I assured her I had not been scared. She shook her head and grinned. “I don’t know,” she said. “You were awfully quiet.”

Looking into the mine earlier, I’d wondered if I could’ve entered the darkness if I’d lived so long ago — wondered if I’d have had the guts. As we drove back to town, I realized I had my answer.