About 100 residents packed the South County Regional Center in Arroyo Grande on Wednesday night to hear a technical report on pollution caused by off-roaders on the Oceano Dunes — in some case expressing fears that the study will lead to the recreational sport being banned.
Larry Allen, pollution control officer for the county’s Air Pollution Control District, insisted that he and his fellow scientists merely conducted a study and were not recommending that off-road activity end. That is a political decision that others will have to consider, he said.
Allen took an opportunity before the meeting began to respond to a key question for many in the crowd: Did the county conduct the study so it could justify shutting down off-roading at the Dunes? The answer, he said, was no.
Nonetheless, many off-roaders, some of whom have been riding their quads and other vehicles for years at the Oceano Dunes State Vehicular Recreation Area, said they worried that the end might be coming for their favorite sport.
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The meeting, which included a panel of experts, was intended to be informational, and no action was taken.
The study, released last month, concluded that break-up by off-highway vehicles of a natural crust that forms on sand dunes and a lack of vegetative cover in areas where OHVs are ridden are the primary causes of high particulate air pollution being blown from the park to populated areas of the Nipomo Mesa.
“All of these act to increase the ability of winds to entrain sand particles from the Dunes and carry them to the Mesa,” the report said.
The study further concluded that exhaust emissions from OHVs and the fact that they can kick sand into the air are only lesser causes of the air pollution. Farming operations and oil refining at the Conoco-Phillips plant are also lesser factors.
“OHV activity in the SVRA is a major contributing factor to high PM (particulate matter) concentrations observed on the Mesa,” the study’s executive summary said.
Particulates are microscopic bits of dust and other airborne substances that can lodge deep into lungs. For that reason, particulates are a significant health hazard, the federal Environmental Protection Agency has said.
The report does not contain any recommendation about how the problem can be minimized. The Air Pollution Control District board of directors may begin discussing that when it meets March 24 to be briefed on the study.
The Wednesday night workshop was intended to outline the study and answer questions.
The study is based on air monitoring conducted over a year that compared ambient particulate levels to levels of particulates coming off the OHV park. More than 2 million data points were generated.
The main conclusions of the study are:
• Particulate matter on the Mesa does not originate from an offshore source.
• Neither petroleum coke piles at the ConocoPhillips refinery nor agricultural fields are a significant source of particulates.
• The bulk of the particulate matter is fine sand blown onto the Mesa by strong winds.
• The primary source of these sand particles is the open sand areas of the Dunes.
• Open sand dunes where OHVs are ridden “emit significantly greater amounts of particulates than the undisturbed sand sheets at the study control sites under the same wind conditions.”
• Vegetative areas do not emit wind-blown particles.
The study can be obtained at the air district’s Web site, www.slocleanair.org.