Effects of highway deicing chemicals on shallow unconsolidated aquifers in Ohio — Final report

Abstract

As a result of concerns about salt intrusion into drinking-water aquifers, the effects of highway deicing chemicals on shallow aquifers were studied at eight locations in Ohio from 1988 through 2003. Sites were selected along major undivided highways where drainage is by open ditches and ground-water flow is approximately perpendicular to the highway. Records of deicer application were kept, and apparent movement of deicing chemicals through shallow, unconsolidated aquifers was monitored by means of periodic measurements of specific conductance and concentrations of dissolved sodium, calcium, and chloride. The counties and corresponding sections of State routes monitored were the following: state Route (SR) 3 in Ashland County, SR 84 in Ashtabula County, SR 29 in Champaign County, SR 4 in Clark County, SR 2 in Lucas County, SR 104 in Pickaway County, SR 14 in Portage County, and SR 97 in Richland County. Routine ground-water sampling device was constructed and used. Other conditions monitored on a regular basis included ground-water level (monitored continuously), specific conductance, air and soil temperature, precipitation, chloride concentration in soil samples, and deicing chemical application times and rates. Evidence from water analysis, specific-conductance measurements, and surface-geophysical measurements indicates that three of the eight sites (Ashtabula County, Lucas County, and Portage County sites) were affected by direct application of deicing chemicals. Climatic data collected during the study indicate that cold weather, and therefore deicing chemical application rate, varied widely across the State. As a consequence, only minor traces of dissolved chloride (mean 24-43 mg/L) above background concentrations (mean 13-23 mg/L) were determined in ground-water samples from the Pickaway County, Clark County, and Champaign County sites. At the Ashland and Richland County sites, dissolved chloride concentrations increased above background concentrations only intermittently (mean background concentrations 4-41 mg/L), rising to a mean of 40-56 mg/L in downgradient wells). At the Lucas County, Portage county, and Ashtabula County sites, deicing-chemical application was consistent throughout the winter, and downgradient dissolved chloride concentrations (mean 124-345 mg/L) rarely returned to background concentrations (mean 7-37 mg/L) throughout the study period. Other factors that may affect the movement of deicing chemicals through an aquifer were precipitation amounts, the types of subsurface materials, ground-water velocity and gradient, hydraulic conductivity, soil type, land use, and Ohio Department of Transportation deicing priority.