Journal of Geology and Geoscience

Anatomy of a Case of Elevated Chloride in the Shallow Black Hand Sandstone Providing Rural Drinking Water Supplies in North-Central Ohio, USA:Hydrogeological and Hydrochemical Characterization by Major and Minor Elements,and δ2H,δ18O,δ13C and Tritium Isotopes

Author(s): Michael D. Campbell, M. David Campbell, Roger W. Lee and Glen A. Collier

Elevated chloride concentrations (>250 mg/l) were reported to the Ohio State Environmental Protection Agency in the early 2000s by a rural resident using groundwater for domestic consumption from a private water well. An adjacent commercial oil and gas pipe yard had spread relatively small volumes of oilfield brines from 1998 through 2000 to control dust during summers and to de-ice on the property driveways, and county and state agencies used halite and other brines on surrounding rural county and state highways during the winter. There are multiple sources in the immediate area that might have contributed to local groundwater by varying degrees, resulting in elevated chloride concentrations reported in the samples from the on-site monitoring wells and from the neighborhood water wells over the years prior to 2004, the time of our investigations. 
An independent investigation was undertaken to characterize the local hydrogeological and geochemical conditions below and surrounding the pipe yard, which has the highest elevation in the area. Data collection to support the investigation consisted of: 1) the installation of nested groundwater monitoring wells (shallow and deep) located at six sites along the periphery and central part of the pipe yard, 2) stratigraphic core drilling, recovery and examination of 220 feet of core, 3) natural gamma and caliper logging of core hole, 4) groundwater sampling for geochemistry and periodic on-site measuring of water levels in each of the monitoring wells, surrounding off-site rural water wells, and up-gradient rural water wells. Formal interviews with residents concerned their use and management of water wells, and any water-softening and/or septic-tank systems’ operational histories, and 5) local reconnaissance of spring/seep sites around the area, and sampling a local stream. 
Our data were limited to one groundwater sampling period with only two samples filtered in the lab; all other chemical data were reported as total concentrations, which included adsorbed and particle constituents for the purpose of assessing the total hydrochemical load carried in the groundwater. Even with these limitations, we were able to conclude that the elevated chloride concentrations in groundwater from a few wells in the neighborhood, located to the north and adjacent to the subject property, likely resulted from: 1) the poor management of home water-softening systems, 2) the subsurface conditions making groundwater especially vulnerable to rapid recharge from waste releases at the surface, 3) the disposal of domestically generated brines from water-softening regeneration and septic tank effluents flowing into septic-tank leachfields constructed in a thin soil zone overlying a thin zone of glacial till, 4) the use of halite for deicing the county roads and state highways adjacent to the neighborhood water wells, and 5) the unfavorable geological and hydrogeological conditions in the area where shallow, heavily fractured and jointed sandstone receives vertical recharge to the local water table from above, which encourages rapid migration of chloride-impacted recharge sampled by the monitoring wells. 
Hydrochemical and stable and radioactive isotope data analyses of δ18O, δ2H, δ13C (DIC), and 3H in groundwater also confirmed that little mixing has occurred prior to 2004 between the industrial site and neighborhood locations. We concluded that in some instances the groundwater had been altered while migrating through the glacial till during recharge and while moving through the unsaturated zone downward through fractures as well as through the porous media, prior to reaching the water table. The brine spread on the industrial property could not have migrated into the groundwater supplies of neighborhood residents over the five or six years prior to 2004, and thus, these data confirm that the local chloride concentrations are attributable to neighborhood activities and to adjacent driveway and roadway activities of de-icing using halite brine during the winter months, with no apparent contribution from the commercial oil and gas pipe yard.

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