18 August 2013
In two high-profile cases, efforts to block the flow of contaminated groundwater resulted in short-term relief – until water tables rose and leaks started popping up all over the place. It’s groundwater whack-a-mole.
Red and Bonita Mines
Near Silverton, CO, owners of a metallic mine with an acid mine drainage problem and state regulators reached a consent decree that was supposedly going to solve the problem. A tunnel access to the mine, which was sending metal and acid laden drainage to Cement Creek, a tributary of the Animas River, would be plugged to stop the flow.
Prior to plugging the tunnel, the mine company had been operating a treatment plant, which worked well but was apparently too expensive.
At first, the tunnel plug seemed to work, until the groundwater that once contributed to the drainage started backing up. Like a kitchen sink with the drain blocked and the faucet left running, the water table rose to levels where it started leaking out the side of the mountain.
From the Durango Herald:
At Red and Bonita Mine, the mountain opens like a wound, oozing a sticky, white, webbed lattice over red ground. There, especially after heavy rains, toxic amounts of metal gush out from within the mountain and bleed into Cement Creek.
The whole article is good and includes a video interview with Peter Butler of the Animas Stakeholders Group. This is an ugly situation in an otherwise gorgeous landscape.
At the crippled Fukushima nuclear facility, Tokyo Electric Power Company (Tepco) struggles with groundwater flowing from nearby mountains, pushed by a high hydraulic gradient. Estimates are fresh groundwater is seeping into the reactor buildings and mixing with contamination at the rate of 400 tonnes of water per day.
To stop or slow down the groundwater from entering the contaminated zone, Tepco is building what’s called a “slurry wall” by pumping cement into the ground to form an impermeable barrier. From Reuters:
Tepco has been injecting a chemical into the ground to build barriers to contain the groundwater. But the method is only effective in solidifying the ground from 1.8 meters below the surface, whereas data from test wells shows the contaminated water has risen to one metre below the surface, the Asahi said.
As radioactive water leaks over and through the slurry wall and into the ocean, Tepco is racing to build a pump and treat system to suck groundwater out and decontaminate it, or at least reduce the toxicity, before it reaches the bay.
Soil as a Filter
Over at LiveScience is an article discussing the status of the troubles at Fukushima, with some emphasis on fish contamination.
The article explains that, shortly after the meltdown, radioactive cesium was a major threat, but now, strontium and tritium are the more dominant radioisotopes in the contaminated water reaching the food web.
The point was made that cesium is “absorbed” by soil, which is true, but only to a point. The capacity of cesium, or any other cation, to be adsorbed (stuck to the surface) to soil particles depends on clay and organic matter content, and other soil solution factors. Eventually that capacity reaches a limit even under optimum conditions.