ABSTRACT Unconventional natural gas development (UNGD) has dramatically expanded since 2000 along with its chemical, physical, and psychosocial hazards as well as more general community impacts. While UNGD has been of public concern for over a decade, no study yet has evaluated the relationship between UNGD and mental health outcomes in adolescents, despite the recognition that children may be the most vulnerable population for the adverse effects of environmental exposures. Identifying factors associated with depression and anxiety is of high importance because these disorders can lead to disability, decrease quality of life, and require high expenditures for clinical care and public health. Prior research implicates two primary pathways from UNGD activity, air quality and stress, both of which can impact the mental health of children. My hypothesis is therefore that UNGD activity is contributing to increased odds of new onset internalizing disorders in adolescents. We propose to test this hypothesis using electronic health records (EHRs) from the Geisinger health system in Pennsylvania, conducting an epidemiologic study of the association between UNGD activity (assigned individually to patients using existing metrics which incorporate spatial and temporal information on UNGD by well phase, size, and gas production, and the patient’s residence), and new onset internalizing disorders, classifying our outcome using combinations of diagnosis codes and medication orders, in an adolescent population of approximately 35,000. For my sub-aims, analysis will be directed toward effect modification of this association, specifically by sex, receipt of Medical Assistance, prescription of antidepressants, and residential greenness. My second aim proposes to examine the association of UNGD activity with depressive symptoms among approximately 28,000 adolescents, using scores from Patient Health Questionnaires (PHQ-9). Using PHQ-9 data will enable us to evaluate a broader range of shorter-term depressive symptoms with higher sensitivity, while diagnoses and medication orders will identify more severe anxiety and depression disorders with higher specificity. In sub-aims, I will assess if the association strengthens when the UNGD activity metric is limited to specifically the drilling and hydraulic fracturing phases (because of higher reported truck traffic) and if it strengthens when limiting the symptoms evaluated to those regarding sleep and concentration. The proposed studies will be the first to investigate UNGD activity in relation to adolescent mental health. By utilizing EHR data with a large sample size in a region with extensive UNGD activity, these studies can advance the state of knowledge on potential health impacts of UNGD. Through a comprehensive training plan and close mentorship, the PI will receive training in the subject area of adolescent mental health, the use of analytic methods for environmental epidemiology, and the communication of resear...