The added regulations would have prevented the vast majority of the accidents that occurred before the late 1980s, EPA officials contend.
"The requirements weren't as rigorous, the testing wasn't as rigorous and in some cases the shallow aquifers were contaminated," Kobelski said. "The program is not the same as it was when we first started."
Today's injection program, however, faces a new set of problems.
As federal regulators toughened rules for injecting hazardous waste, oil and gas companies argued that the new standards could drive them out of business. State oil and gas regulators pushed back against the regulations, too, saying that enforcing the rules for Class 2 wells – which handle the vast majority of injected waste by volume -- would be expensive and difficult.
Ultimately, the energy industry won a critical change in the federal government's legal definition of waste: Since 1988, all material resulting from the oil and gas drilling process is considered non-hazardous, regardless of its content or toxicity.
"It took a lot of talking to sell the EPA on that and there are still a lot of people that don't like it," said Bill Bryson, a geologist and former head of the Kansas Corporation Commission's Conservation Division, who lobbied for and helped draft the federal rules. "But it seemed the best way to protect the environment and to stop everybody from just having to test everything all the time."
The new approach removed many of the constraints on the oil and gas industry. They were no longer required to conduct seismic tests (a stricture that remained in place for Class 1 wells). Operators were allowed to test their wells less frequently for mechanical integrity and the area they had to check for abandoned wells was kept to a minimum – one reason drilling waste kept bubbling to the surface near Chico.
Soon after the first Chico incident, Texas expanded the area regulators were required to check for abandoned waste wells (a rule that applied only to certain parts of the state). Doubling the radius they reviewed in Chico to a half mile, they found 13 other injection or oil and gas wells. When they studied the land within a mile – the radius required for review of many Class 1 wells – officials discovered another 35 wells, many dating to the 1950s.
The Railroad Commission concluded that the Chico injection well had overflowed: The target rock zone could no longer handle the volume being pushed into it. Trying to cram in more waste at the same speed could cause further leaks, regulators feared. The commission set new limits on how fast the waste could be injected, but did not forbid further disposal. The well remains in use to this day.
In late 2008, samples of Chico's municipal drinking water were found to contain radium, a radioactive derivative of uranium and a common attribute of drilling waste. The water well was a few miles away from the leaking injection well site, but environmental officials said the contaminants discovered in the water well were unrelated, mostly because they didn't include the level of sodium typical of brine.
Since then, Ed Cowley, the public works director, said commission officials have continued to assure him that brine won't reach Chico's drinking water. But since the agency keeps allowing more injection and doesn't track the cumulative volume of waste going into wells in the area, he's skeptical that they can keep their promise.
"I was kind of like, ‘You all need to get together and look at the total amount you are trying to fit through the eye of the needle,'" he said.
When sewage flowed from 20 Class 1 wells near Miami into the Upper Floridan aquifer, it challenged some of scientists' fundamental assumptions about the injection system.