Following years of contested regulatory procedures and court hearings, the San Luis Obispo County Air Pollution Control District (APCD) and the California Department of Parks and Recreation appear to have struck a deal on mitigating dust flows from the Oceano Dunes.

State parks has agreed to fence off about 100 acres to create islands of vegetation within the Oceano Dunes off-road vehicle riding area. Presently, there are already 186 acres of fenced vegetation islands, according to a map being circulated by the APCD.

Critics of the APCD allege the district is manipulating state parks into making more concessions. In order to advance its regulatory agenda, the APCD has in the past relied on contested studies concluding off-roading on the dunes is causing pollution on the Nipomo Mesa.

In 2011, the APCD adopted the Oceano Dunes dust rule, which required state parks to reduce the amount of particulate matter blowing from the Oceano Dunes off-roading area or face fines of $1,000 per day. The dust rule became the subject of a multi-year court battle, during which the APCD was barred from requiring state parks to obtain a permit to operate the riding area. The air pollution district and state parks have since been involved in talks on reaching a settlement.

Recently, the APCD and state parks agreed to a pollution abatement order. While state parks still denies that off-roading is causing the pollution on the Nipomo Mesa, the agency did agree to a host of conditions outlined in the abatement order.

The order requires state parks to begin fencing off areas by March 31 and finish erecting the fences by Sept. 28. The fencing would remain in place indefinitely.

Additionally, the agreement calls for state parks to draw up annual plans to achieve yearly 5 percent reductions in particulate matter emissions, starting in 2019 and continuing through 2024.

State parks has also agreed to restore vegetation to the fore dunes, or the part of the riding area near the ocean, in similar fashion to how it existed in the 1930s. Likewise, state parks agreed to continue crystalline silica testing and to publish the results of its tests in a comprehensive report.

Crystalline silica commonly appears in nature as quartz. Recently, Nipomo Mesa residents have complained that silica dust is polluting the air around their homes.

On Wednesday, the nonprofit Friends of Oceano Dunes, which sued the APCD over the dust rule, sent a letter to air district board members stating their agency was withholding information about crystalline silica levels on the Nipomo Mesa in order to manipulate state parks into closing more off-road riding area.

The APCD did not make public the findings of its 2017 samples of crystalline silica levels. Meanwhile, state parks’ tests have shown crystalline silica levels were below the detection limit, Friends of Oceano Dunes said in the letter.

In order for the agreement between state parks and the APCD to take effect, it must be approved by the air district’s hearing board. The APCD hearing board is a five-member body that is separate from the agency’s board of the directors. The hearing board will meet on March 21 at 9 a.m. in the San Luis Obispo City Council Chambers to discuss and possibly finalize the deal between the APCD and state parks.