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WASHINGTON — The number of new enforcement actions by the Environmental Protection Agency has fallen significantly over the past year, according to data released Thursday by the Trump administration.

The EPA initiated 20 percent fewer civil cases against polluters for violating environmental laws from the beginning of September 2016 to end of September 2017, as compared to the previous fiscal year, according to the EPA’s latest enforcement numbers.

The EPA also opened 30 percent fewer criminal enforcement cases during the same time period.

The past fiscal year marked a historic low for enforcement actions across the board: The number of new civil and criminal cases, defendants charged, and federal EPA inspections and evaluations all reached their lowest levels in at least a decade, according to the data.

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The EPA said the declining numbers were not a sign of lax enforcement.

"EPA is focusing on finding efficient ways to deter noncompliance and return facilities to compliance with the law," said EPA spokesperson Liz Bowman. "EPA is increasing the deterrent effect of EPA’s enforcement program through criminal enforcement actions to address the most egregious cases."

But environmental advocates say the new data makes it clear that EPA administrator Scott Pruitt and the Trump administration are letting polluters off the hook.

"The drop-off in actions is very worrying," said Andrew Rosenberg of the Union of Concerned Scientists, an advocacy group. "It shows across the board a lack of desire to hold polluters accountable and that means the public health risks are greater."

EPA enforcement actions had already been on a downward trend during President Barack Obama’s second term. The previous administration said the drop in enforcement numbers was partly due to declining budgets, according to its 2016 analysis. Under both President Donald Trump and Obama, the EPA has stressed that it is prioritizing more complex, high-impact cases.

The Trump administration touted the rise in total criminal fines, administrative and civil judicial penalties, and Superfund cleanup commitments over the past year. "A strong enforcement program is essential to achieving positive health and environmental outcomes," EPA’s enforcement chief Susan Bodine said in a statement.

But Cynthia Giles, the former head of EPA enforcement under Obama, points out that the biggest environmental fines and penalties had been initiated and secured under the previous administration, not the current one.

For example, of the $2.98 billion in total criminal fines in fiscal year 2017, $2.8 billion came from Volkswagen’s penalties for cheating on emissions tests, which the company agreed to shortly before Trump took office. "Nearly all of the large cases included in EPA’s annual enforcement report were essentially over before the new administration arrived at EPA," Giles said.

The EPA said that it was not trying to take credit for the work of the previous administration.

"Large enforcement cases always span multiple years. Today’s announcement is about the accomplishments of the agency, including the great work the enforcement staff has performed throughout FY 2017," Bowman said.