FRAC SAND MINING AND PUBLIC HEALTH CONSIDERATIONS IN MINNESOTA

Expanded oil and gas development in the US has driven demand for high-quality industrial silica sand (ISS), also called “frac” sand. Some of the largest, accessible deposits of such sands are found in lower Paleozoic formations in western Wisconsin and eastern Minnesota, often in areas with vulnerable groundwater supplies. The surge in proposed frac sand mining, processing and transport in Minnesota raised public concerns regarding possible human and environmental health implications. The Minnesota Departments of Health (MDH), Natural Resources, and Transportation, along with the Minnesota Pollution Control Agency (MPCA), and other state agencies collaborated to evaluate these concerns and provide information and guidance to local governments.

MDH evaluated potential human health risks from airborne respirable crystalline silica (4 microns diameter or smaller, or PM₄) and potential contamination of drinking water by chemicals (polyacrylamide and poly-diallyldimethylammonium chloride, or pDADMAC) used in the sand washing process. MDH established health-based guidance values of 3 µg/m³ for PM4 crystalline silica in air and 0.2 µg/L acrylamide in drinking water, which are used by MPCA in the permitting and monitoring of ISS mines. The MN Public Health Laboratory also developed an analytical method to detect acrylamide at trace levels (0.017 µg/L) in groundwater. Early data suggest best management practices are capable of achieving these air and water guidance values. MDH continues to evaluate potential health risks related to pDADMAC), which under certain conditions may lead to the formation of N-nitrosodimethylamine (NDMA), a likely carcinogen.