Issue Date: September 21, 2009
Water And CO2 Shouldn't Mix
The Environmental Protection Agency has proposed to broaden the range of geological formations where coal-based electric utilities and companies that generate carbon dioxide may inject the greenhouse gas for sequestration. The Aug. 26 proposal allows CO2 injection and sequestration at shallower depths that are not necessarily below drinking water aquifers, contrary to what the agency proposed a year ago.
Capturing carbon dioxide and sequestering it underground is considered the only way the world can continue to burn coal and avoid the ravages of climate change. Coal supplies half of the electricity in the U.S., but it generates one-third of the 6 billion tons of CO2 the nation emits annually.
However, sequestering CO2 underground risks damaging drinking water aquifers, and for the past year, EPA has been wrestling with development of regulations that protect groundwater and allow carbon sequestration.
Water suppliers tell C&EN they don’t like EPA’s latest plan. They are worried that it won’t protect underground drinking water. If the agency finalizes the proposal, companies injecting and sequestering CO2 should be held liable for drinking water degradation “in perpetuity,” says Alan Roberson, director of regulatory affairs for the American Water Works Association, an organization of water professionals and utilities.
“This is a balance between energy production and water production,” Roberson notes. “If you ruin the water, you are not going to get it back.” He offers limited support for the original proposal but opposes the modified one.
According to EPA, ideally, CO2 will be injected under pressure in a supercritical state into geologic formations that are at least 2,500 feet deep. At that depth, pressure and temperature are sufficient to keep CO2 in a supercritical state, behaving like a liquid. CO2 would be trapped in low-permeability layers and immobilized in rock formation pores, avoiding escape into the atmosphere. Scientists hope that minerals in the geological formations will encourage precipitation of CO2 to solid carbonate minerals.
But CO2 carries impurities, can become mobile, and is corrosive. It forms a weak acid in the presence of water, which may cause leaching of naturally occurring elements found underground. These traits can encourage movement and contamination of groundwater.
EPA’s proposal of a year ago would allow CO2 injection only deep in the ground and below drinking water aquifers (C&EN, July 28, 2008, page 41). The modified proposal would allow states and EPA regional offices to waive deep-injection requirements and place CO2 in shallow reservoirs above or between drinking water aquifers.
Several state officials sought the modification because aquifers in their states are quite deep, in some cases more than 15,000 feet deep, making injection too costly and difficult, they say. In its proposal, EPA adds that depth flexibility is also needed to allow injection into volcanic rocks, such as flood basalts, and into depleted coal seams.
Determining when regulations can be waived would be left to state and EPA regional directors who oversee underground injection programs for other waste materials. These regulators would determine whether the impermeable layers above and below the injection site are sufficient to protect water sources.
At this time, however, EPA is simply seeking comments on how the government should eventually regulate underground injection of CO2, the agency stresses. The actual regulations are yet to come.
Research on underground injection of CO2 is also just getting started, EPA notes. The agency estimates that some 30 geological sequestration demonstration projects are operating in the U.S. Many more are planned in the global rush to find an inexpensive and safe way to capture and permanently sequester CO2.
Along with its modified proposal, EPA released a computer simulation by Lawrence Berkeley National Laboratory. It found that CO2 can cause leaching of naturally occurring trace elements such as arsenic, barium, cadmium, mercury, lead, antimony, selenium, zinc, and uranium from geological formations, but only arsenic could be released into water at levels exceeding drinking water standards.
Roberson wants drillers to go deeper, below aquifers. “However, if we lose this battle and water quality gets degraded, we expect the well’s owner and operators to pay for water treatment in perpetuity,” he says. “They have to understand they are taking a risk. This is going to be a pretty hefty ticket to consider.”
CO2 sequestration demonstration projects must include strong groundwater monitoring components, Roberson says, adding that, so far, CO2 migration studies have relied too strongly on modeling. Test data will just be coming in when EPA is finalizing the regulation, which Roberson expects in late 2010 or 2011.
“We want that regulation to be tough,” Roberson says. “EPA can always dial it back and make it less restrictive if the technology proves to work. But you can’t get water back if you have a problem.”
EPA would not comment beyond its documents.
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