Photo Credit: Bethany K. Kunz USGS
According to the U.S Department of Transportation, of the over 4.1 million miles of roads in the U.S., 34% of them are unpaved. These roads produce 47% of the annual airborne particulate matter emissions which can cause respiratory and cardiovascular issues, as well as put stress on vegetation. A recent study indicates the use of oil and gas (O&G) wastewaters from conventional drilling on roads to suppress dust may also cause health impacts.
In May, the Pennsylvania Deptment of Environmental Protection (DEP) no longer permitted these wastewater to be used on roads. It should be noted that wastewater from unconventional wells (those drilled below the Elk sandstone or its geologic equivalent where natural gas can’t be produced except by horizontal or vertical well bores stimulated by hydraulic fracturing) has never been permitted to be used on roads in PA, OH, CO, NY, and WV.
While there are close to 200 dust suppressants that can be used on roads, costs make many of these prohibitive for smaller municipalities. The free alternative in thirteen states has been to use O&G wastewater, taking advantage of the high salt content to retain road moisture for dust suppression and for deicing in the winter. These wastewaters have been known to have levels of salt, radioactivity and organic contaminants above drinking water standards.
A group of researchers from various disciplines at Penn State University worked together to determine:
- The states and regulations that use O&G wastewater on roads
- The trends of this activity in Ohio and Pennsylvania as case studies
- The chemical characteristics and mobility of contaminants after road application and rainwater leaching
- The aquatic and human toxicity potential
Through a variety of experiments simulating O&G wastewater application to roads, followed by simulated rain events, the majority of contaminants were found not to be retained in the road. The high salt concentrations are likely the major potential threat to aquatic toxicity, requiring up to 1600 times dilution to reach drinking water quality standards. Radium, a carcinogen, was found to be partially retained in the roads treated with the wastewater, but concentrations were found to plateau after multiple applications of wastewater.
The study suggested three means to reduce environmental impacts when using O&G wastewater on roads:
- Use only O&G wastewater treated at wastewater treatment facilities. The water would still be high in salt concentrations but can effectively remove radium, oil, grease and other trace metals.
- Develop chemical standards for the O&G wastewaters that can be spread on roads to reduce toxicity concerns.
- Develop affordable nontoxic dust suppressants affordable for townships with small annual budgets for road maintenance.
The full study may be found in Environmental Science & Technology.