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BACKGROUND: Hydraulically fractured wells produce 2-14 million liters of wastewater, which may contain toxic and radioactive compounds. The wastewater is predominantly disposed of using Class II injection wells.

OBJECTIVE: Our objective was to evaluate the relationship between sociodemographic characteristics and injection well locations in Ohio.

METHODS: Using state and federal data sources, we classified Ohio census block groups by presence of injection wells, number of hydraulically fractured wells, sociodemographic factors (median household income, % white, population density, % >= high school education, median age, voter turnout), and geographic information (land area, water area, situated over shale). We modeled the odds of having at least one injection well within a block group with respect to all covariatcs using three multivariable models incorporating different spatial components to account for similarities in neighboring block groups.

RESULTS: In bivariate analyses, block groups with injection wells (n = 156) compared with those without (n = 9,049) had lower population density (71 vs. 2,210 people/mi(2) or 27 vs. 854 people/km(2)), larger median area (43.5 vs. 1.35 km(2)), higher median age (42.8 vs. 40.2 y), and higher % white (98.1% vs. 92.1%). After adjustment using a spatial logistic regression model, the odds of a block group containing an injection well were 16% lower per $10,000 increase in median income [oddsiratio(OR) = 0.837; 95% credible interval (CE: 0.719, 0.9611 and 97% lower per 1,000 people/mi(2) (or per 386 people/km(2)) increase (OR = 0.030; 95% CI = 0.008, 0.072). Block groups on shale and those containing fewer hydraulically fractured wells were more likely to include an injection well. Percentage white, median age, % >= high school education, and % voter turnout were not significant predictors of injection well presence.

CONCLUSION: In Ohio, injection wells were inversely associated with block groups' median incomes after adjusting for other sociodemographic and geographic variables. Research is needed to determine whether residents in census blocks with injection wells face increased risk of chemical exposures or adverse health outcomes.