UC Berkeley

Oil and gas development (OGD) by the US petroleum industry spans decades in many states but concern about its potential health and equity impacts did not gain traction among researchers until the recent rapid uptake of hydraulic fracturing (HF). As of 2017, California was one of the top five producers of crude oil in the country and four of the ten largest US oil fields are in the San Joaquin and Los Angeles Basins. Oil recovered via conventional enhanced oil recovery methods accounted for 76% of the state’s oil production in 2009 while HF, an unconventional stimulation technique, accounted for 20% of CA’s oil production in the last decade. Due to the state’s unique geological formations, California’s OGD infrastructure and practices differ from other states. OGD production also occurs in both rural and urban settings. Despite growing evidence of health and equity implications from living near OGD, until now, no epidemiology studies had evaluated health endpoints or conducted spatial analyses characterizing population health risks in areas with intensive OGD in California.

To fill this major knowledge gap, I evaluated: 1) the relationship between prenatal exposure to conventional and unconventional OGD and fetal growth outcomes and preterm birth in California (Chapter 1), 2) the association between prenatal exposure to hydraulically fractured (HF—“fracked”) wells and fetal growth outcomes and preterm birth in Los Angeles and Kern County (Chapter 2), and 3) spatial relationships between OGD sites and drinking water systems (domestic wells and community water systems) reliant on groundwater in the San Joaquin Valley (Chapter 3). To address the first two aims, I conducted retrospective cohort studies. Outcomes included low birth weight, small for gestational age, term birth weight and preterm birth. Exposure metrics were based on production volume from active wells and count of inactive wells within 1 km of maternal residences during their pregnancies. The third aim hones in on potential drinking water threats, one of the main OGD exposure pathways that could impact human health. Here, I first identified vulnerable drinking water systems based on co-location of OGD infrastructure and domestic well areas and community water systems. I then determined socioeconomic and area-level predictors of these at-risk water systems via spatial regression techniques.

My work expands current literature with several major findings. Through the epidemiology analyses, I found that prenatal exposure to OGD is differentially associated with adverse birth outcomes among rural versus urban populations, with stronger effects in rural areas; greater oil and gas production volume can lead to stronger effects; birth outcomes may be impacted among pregnant women residing within 1 km of high production volume wells; and HF operations are associated with adverse birth outcomes beyond the hazards of actively producing wells. From the drinking water systems analysis, I discovered that system size matters when predicting the number of OGD wells and percolation pits nearby–since small systems are overwhelmingly inundated with high counts of OGD infrastructure sites–and different regression techniques should be applied when analyzing different water system types.

This work is timely as Californians and policymakers continue to discuss the expansion of the oil and gas industry in the state. Regulatory agencies should consider additional health and risk assessments, increased groundwater source monitoring in particular areas with intensive oil and gas extraction activities, and standardization of regulatory strategies for protecting drinking water sources from potential contamination across all OGD infrastructure.