Improve private well testing outreach efficiency by targeting households based on proximity to a high arsenic well.

Research into precautionary action suggests outreach with personally-relevant risk information may help overcome optimistic biases, which have been shown to impede voluntary testing for arsenic by at-risk private well households. Since 2002, New Jersey's Private Well Testing Act (PWTA) has required testing for arsenic during real estate transactions. The PWTA database of over 35,000 geocoded well arsenic tests offers a unique opportunity to evaluate the efficacy of targeted outreach to neighbors living in proximity to a known high arsenic well with variable risk messaging to motivate testing. In this study, residents of properties (n = 1743) located within 500 ft and between 500 and 1000 ft of a known high arsenic well (>5 μg/L, New Jersey's drinking water arsenic standard) were mailed a notice of the high arsenic result in their neighborhood and offered a free water test. Overall 274 households (16%) requested a test kit and 230 (13%) ultimately submitted a water sample; with significantly higher participation rates among those told their neighborhood well had an arsenic concentration "over 5 times higher" than the standard, compared to those told the concentration was "above." Overall, 25% of wells tested (n = 230), and 47% (n = 66) of non-treated wells located within 500 ft of a well with >25 μg/L arsenic, exceeded the standard for arsenic. Both the arsenic concentration and distance to the neighboring well were significant predictors of exceedance. Given the high proportion of previously untested wells (70%) and their owners' lack of awareness of arsenic in their area (80%), this targeting approach succeeded not only in identifying a much higher proportion of at risk wells than blanket testing by town or county, but also in motivating testing among households unreached by prior awareness-raising activities. In conclusion, geographically and personally-relevant risk targeted messaging and outreach are both efficient and effective.