The original rules, issued in April 2012, instituted the first federal standards to reduce air emissions at hydraulic fracturing wells, among other measures.
The rules also included measures to regulate the storage tanks, which can emit toxic air pollutants and ozone-forming volatile organic compounds, mandating they control those compound emissions by 95 percent.
After issuing the rule, however, outside groups petitioned the agency to reconsider aspects related to the large tanks and containers used to store oil and gas liquid before it is sold or moved to a pipeline.
The agency received petitions from both industry and environmental groups, including heavyweights like the American Petroleum Association, the American Natural Gas Association and the Gas Processors Association. A coalition of environmental groups including the Natural Resources Defense Council and the Sierra Club also petitioned the agency.
The EPA's proposed revision would adjust the requirements for existing tanks, streamline some monitoring requirements and propose an alternative standard for storage vessels that have proven able to control their emissions.
The agency admits in the proposal that it had underestimated the number of affected storage tanks. Because it predicts there will not be enough control equipment available for companies to meet the compliance deadline of Oct. 15, 2013, the new rule would push that date back.
The proposed rule would also narrow the container definition so as not to unintentionally include fuel tanks and similar vessels, just those holding crude oil and hydrocarbon liquids.
According to agency analysis, there are about 970 storage tanks installed every month, and more than 20,000 constructed or modified since August 2011.