SPATIAL AND TEMPORAL GROUNWATER THERMAL ANOMALIES IN A WELLFIELD IN OHIO: IMPLICATIONS FOR DETERMINATION OF RIVER-AQUIFER CONNECTIVITY USING TEMPERATURE DATA

An anomalous spatial and temporal distribution of groundwater temperatures has been observed in a production well field in Ohio. Historical temperature data of groundwater extracted ~45-65 feet below the ground surface indicate substantial deviation from the mean annual air temperature (MAAT) expected at this depth.

This study implemented a seasonal survey of six production wells in the study area and grab samples from the adjacent Muskingum River. Monthly samples of nitrate NO₃^- and water isotopes (δ²D and δ¹⁸O) were evaluated alongside temperature measurements to determine thermally disparate areas and ultimately the likely heat source providing anomalous temperatures. Data from two wells (W-3 and W-9) yielded RMSD values <2.5°C when regressed against mean weekly air temperature (MWAT) at lags between 54-93 and 106-129 days, respectively. Other wells (W-6 and W-12) displayed near-constant temperatures ~1 to 2°C above local MAAT. Isotope data also linked W-3 and W-9 as having similar provenance, displaying seasonal progression toward lighter compositions from summer to winter, mirroring trends observed in precipitation and the river. Nitrate was detected at <0.10 to ~5.5 mg/L in groundwater samples throughout the well field, with slightly higher concentrations in the river. The river was determined to be the likely heat source, as it was found to be losing to the aquifer allowing transmission of seasonal air temperatures to W-3 and W-9. Increased shear stress on the riverbed caused by an artificially narrowed reach immediately upstream of these wells is suggested as the mechanism to remove clogging fine particles and allow infiltration into the aquifer. The lack of temperature disturbance in the south portion of the study site is attributed to the re-establishment of a clogging layer adjacent to W-6 and W-12.