The presence of oil and gas wells in residential areas exposes communities to various environmental hazards, including air and water pollution, noise, and stress, increasing the risk of numerous health issues. Studies have shown a disproportionate exposure of racial and socioeconomically marginalized communities to these hazards. This disparity is hypothesized to be linked to historical racist policies, particularly redlining, which systematically disadvantaged certain neighborhoods through discriminatory lending practices and urban planning. Redlining, implemented by the HOLC in the 1930s, categorized neighborhoods into grades A through D, with D-graded neighborhoods (redlined) often characterized by the presence of minority populations. This study aims to determine whether a correlation exists between lower HOLC grades and increased exposure to oil and gas wells, thereby examining the potential role of historical redlining in shaping current environmental injustices.

Existing research has documented the adverse health effects associated with proximity to oil and gas wells, including respiratory problems, cardiovascular disease, and adverse birth outcomes. Studies also highlight the disproportionate burden of these risks on marginalized communities. The historical context of redlining and its lasting impact on residential segregation and health disparities is well-established. Previous studies demonstrate that redlined neighborhoods experience higher rates of various health problems, reduced access to environmental amenities, and increased exposure to environmental hazards. However, the direct link between redlining and the siting of oil and gas wells remained unexplored prior to this study. This paper builds upon this prior research to directly assess the connection between historical redlining and the current distribution of oil and gas wells.

This retrospective cross-sectional study utilized digitized HOLC appraisal maps and a national dataset of oil and gas wells. The study included 33 U.S. cities with urban oil and gas wells. The researchers assessed cumulative exposure to wells within a 100-meter radius of each HOLC-graded neighborhood. The primary analysis considered all wells, while secondary analyses examined wells drilled before and after HOLC appraisals. For a subset of 17 cities with 1940 census data, propensity score restriction and matching were employed to control for confounding due to sociodemographic differences between neighborhoods with varying HOLC grades. Propensity scores were estimated using an ensemble of machine learning algorithms. Pairwise comparisons were made between neighborhoods with adjacent HOLC grades (A vs. B, B vs. C, C vs. D). Targeted maximum likelihood estimation (TMLE) was used to analyze the association between HOLC grade and well exposure. Sensitivity analyses were conducted using alternative exposure metrics (wells within neighborhood boundaries, well density).

Across all cities, redlined (D-graded) neighborhoods had a significantly higher density of oil and gas wells (12.2 ± 27.2 wells/km²) compared to A-graded neighborhoods (6.8 ± 8.9 wells/km²). In propensity score-matched analyses, redlined neighborhoods had approximately two more wells than comparable neighborhoods with better grades. This association remained consistent across well types and was robust to sensitivity analyses. Analyses separating wells drilled before and after HOLC appraisals indicated that D-graded neighborhoods had more wells both before and after the appraisals. The higher density of wells was not solely attributable to neighborhood size, as analyses using well density as the exposure metric yielded similar results. Sociodemographic data showed that D-graded neighborhoods had disproportionately high populations of Black, non-White, and foreign-born residents, along with lower median home values and educational attainment.

The findings strongly suggest that historical redlining practices are associated with the current disproportionate siting of oil and gas wells in marginalized communities. This supports the hypothesis that structural racism embedded in federal policies has contributed to environmental injustices. The consistent association between redlining and well density across well types underscores the significance of this finding. These exposure disparities have significant implications for community health, given the established adverse health effects linked to oil and gas well proximity. The results align with previous research demonstrating that redlined neighborhoods often experience higher exposure to various environmental hazards. The study also notes the possible role of HOLC appraisers in Los Angeles considering the presence of oil and gas wells when assigning grades, potentially exacerbating the disparities.

This study provides compelling evidence linking historical redlining to the disproportionate siting of oil and gas wells in historically marginalized communities. The robust association observed, even after controlling for confounding factors, highlights the long-lasting consequences of structural racism on environmental justice. Further research is needed to explore the mechanisms driving this association in more detail and to assess the health consequences of this disproportionate exposure. Additionally, further investigation is needed into the role of other factors such as local zoning laws and the influence of industry practices in the placement of oil and gas wells.

The study's limitations include the availability of data. 1940 census data were not available for all cities included, potentially underestimating the association in regions with historically high levels of racial segregation. Data on well production dates were missing for a substantial number of wells, which could introduce bias, especially in pre-appraisal analyses. The study also did not consider other forms of housing discrimination beyond HOLC redlining and could not account for all potential confounding factors influencing well siting, including geological and geographical factors. The reliance on historical redlining maps as a proxy for long-term housing discrimination might also mask additional contributing factors.