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Image: Myers 2010
WI Sources of Silica-Myers 2010


The Wisconsin Department of Natural Resources currently regulates public exposure to particulates using the National Ambient Air Quality Standards (NAAQS):

Particulate Matter (PM10)

150 µg/m3 24-hour average

Particulate Matter (PM2.5)

15.0 µg/m3 annual average and 35 µg/m3 24-hour average.

Other approaches that DNR uses are tests of pressure drops in a "baghouse" to see if this pollution-control device is effectively collecting small particles, whether a stack that emits pollutants has the proper temperature and flow rate ("stack testing") and if emissions look dark ("opacity").  This latter test is subjective and will not detect particles less than 10 µm (PM 10) since they are too small to be seen.


Crystalline Silica 

Crystalline silica is identified as a human carcinogen and meets the criteria of a hazardous air pollutant defined in NR 445.13. Enforcement of a limit for public exposure is consistent with NR 445.03 "Hazardous substances include but are not limited to the hazardous air contaminants listed in Tables A to C of s. NR 445.07."  However, silica is not currently "listed" as a pollutant and so not regulated.  In NR 445.14, the DNR was tasked with conducting studies on crystalline silica to "...evaluate the sources and amounts of emissions and alternative strategies for minimizing public health risks. The department staff shall report progress on the studies to the natural resources board by July 1, 2006."  A study on sources and regulation of silica was produced by DNR toxicologist Jeff Myers in December 2010 (  According to DNR Environmental Engineering Supervisor Jeff Johnson, this report along with public comments on the report will be submitted to the Natural Resources Board at the end of August 2011.

The Trempealeau County Environment and Land Use Committee (2010) recently set a goal for crystalline silica exposure in the Winn Bay Sand conditional use permit, based upon an estimate that 10% of PM10 emissions would be silica:

"Minimum of 3 scientific approved air quality monitors in active mining area available for staff review and data collection at all times. Type/brand of monitor will be pre approved by all parties including Winn Bay, staff and Dr. Pierce. 30 micrograms per cubic meter PM10 or lower shall be a personal goal for Winn Bay to achieve related to air quality monitoring."