Environmental health researchers, practitioners, advocates, and policy-makers are increasingly concerned about the origins and persistence of health disparities in California. Scientific research indicates that the inequitable distribution of health is linked to environmental and social conditions combined with underlying vulnerability factors that put people at "risk of risks" (Phelan et al., 2010). This combination of environmental hazard exposures and socioeconomic stressors has been described as a form of double jeopardy (Institute of Medicine, 1999) that disproportionately impacts vulnerable groups, particularly communities of color and the poor, immigrants and linguistically isolated groups. Although the importance of cumulative impacts may be theoretically obvious, the task of measuring and quantifying these impacts is challenging because data on interactions among these exposures are unavailable, information on place- and population-specific exposures is lacking, and validated models relating exposure to health effects for multiple chemicals and nonchemical stressors do not exist (Sexton, 2012). However, spatial screening allows decision-makers to identify areas that are over-burdened with environmental hazards and that are socially vulnerable so that communities might be targeted for regulatory and policy action to improve environmental conditions and protect public health. The Environmental Justice Screening Method (EJSM) facilitates such mapping of cumulative impacts using multiple health, environmental and social vulnerability measures organized along diverse categories. This project extended the original EJSM to create additional metrics, including indicators of climate change vulnerability, and increased cumulative impacts screening coverage from its initial focus on Southern California and the San Francisco Bay Area, to all California regions. In addition, we integrated our work with OEHHA on drinking water into our final maps, which are presented here. Methodological improvements include data updates, corrections of facility and sensitive land use locations in data provided by CARB, a more streamlined method for developing the land use base maps, and an approach to assessing area-level proximity to environmental hazards that reduces data processing time and enhances flexibility for implementing different buffers and scoring approaches.

We present maps of the EJSM scores for eight California regions, including intermediate scores for each category of cumulative impact (e.g. hazard proximity and sensitive use; health risk and exposure; social and health vulnerability; climate change vulnerability; drinking water quality) and total cumulative impact. Comparisons of cumulative impact scores derived using regional versus state quintile distributions indicate that different geographic definitions for deriving scores affect screening results. Although the EJSM is flexible enough to allow for comparisons of cumulative impact scores across different study areas (e.g., within regions or across the state) we favor a regional application of scoring because generally land use planning, industrial and transportation development, and environmental regulation are regionally rooted and require regionally specific interventions to reduce hazard exposures or to address social and health vulnerability factors. In addition, statewide scoring can mask important within-region inequities. Nevertheless, there may be certain policy and decisionmaking contexts when statewide distributions for scoring may be appropriate for larger scale impacts such as climate change vulnerability.

Spatial screening methods such as the EJSM are critical tools that can help decision-makers advance environmental justice goals by more efficiently targeting efforts and resources to remediate cumulative impacts, environmental inequities, and focus regulatory action at the neighborhood level. As environmental health science develops a better understanding of cumulative impacts, standard approaches in risk assessment may need to change and be harmonized with cumulative impact screening methods to assure the protection of public health.