More than 300 unlined oil wastewater pits are being used in Kern County, California, without proper permits.
Local water officials have just completed a survey which revealed that more than one-third of the region's active disposal pits are operating without permission, the Los Angeles Times reported.
The pits are used by oil producers to dump chemical-laden wastewater left over after fracking and other oil drilling activities.
According to the newspaper, there are concerns that these previously unidentified waste sites could harm water quality at a time when California faces one of the most severe droughts on record and protecting groundwater supplies is paramount.
However, initial tests have found no evidence that groundwater has been tainted.
The possible existence of the unpermitted pits emerged when water officials compared their list of pit operators to a list compiled by the Division of Oil, Gas and Geothermal Resources. They found that the oil regulator's list contained at least 300 more waste pits than water officials had permitted.
Inspections of the wastewater sites began last spring and were completed this week.
The Central Valley Regional Water Quality Control Board will take action to address the problem, according to Clay Rodgers, assistant executive officer of the water board's Fresno office. He told the Times that the unregulated pits were a "significant problem" and the agency expects to issue around 200 enforcement orders.
In pits located near clean water sources, operators will be required to install monitor wells to test water quality.
In the long term, the water board will require remediation of some abandoned pits so that contaminants left behind don't pollute the air.
And more generally, the agency will publish a series of orders to more tightly control the operation of wastewater pits.
The aim is to protect water quality, Rodgers explained. "Our goal is not to shut anybody down, but by the same token, they do not own the waters beneath them. Those waters are for the public good."