ABSTRACT
In 1990, the last time the decennial census included a question on domestic drinking water source, it was estimated that private domestic water wells (PDWs) supplied household water to about 15.1 million housing units (15% of the population) in the United States (U.S.). PDWs are not regulated by the Safe Drinking Water Act, and with few exceptions, are not subject to the water quality testing required of public water suppliers. We expanded two methods in estimating housing units reliant on PDWs from an Oklahoma pilot study (Weaver et al. 2017), nationally. Both use 1990 census data on drinking water sources as a baseline. The first method uses housing unit change and private well drilling logs for 20 states. This allows for the rate of well use to change between 1990 and 2010 in these states. The second, based solely on housing unit change, assumes a constant rate of well use. Ordinary least squares regression demonstrated (R 2 = 0.78) that the methods yield similar estimates for nationwide well use. Using the housing unit change method, it is estimated that in 2010, 23 million housing units were reliant on PDWs (17% of the population). We provide these estimates at the census block group and census block resolution. This dataset will assist in a better understanding of the reliance on PDWs in the U.S., and position local, tribal, state, and national groups to better protect this water resource from contaminant sources. RESEARCH IMPACT STATEMENT: The work provides improved estimates of the spatial distribution of housing units reliant on private domestic wells in the United States and a foundation to protect this water supply at all levels of government.
ABSTRACT
For protecting drinking water supplies, the locations of areas with reliance on private domestic wells (hereafter referred to as "wells") and their relationship to contaminant sources need to be determined. A key resource in the U.S. was the 1990 Census where the source of domestic drinking water was a survey question. Two methods are developed to update estimates of the areal density of well use using readily accessible data. The first uses well logs reported to the states and the addition of housing units reported to the Census Bureau at the county, census tract and census block group scales. The second uses housing units reported to the Census and an estimated well use fraction. To limit the scope and because of abundant data, Oklahoma was used for a pilot project. The resulting well density estimates were consistent among spatial scales, and were statistically similar. High rates of well use were identified to the north and east of Oklahoma City, primarily in expanding cities located over a productive aquifer. In contrast, low rates of well use were identified in rural areas without public water systems and in Oklahoma's second largest city, Tulsa, each attributable to lack of suitable ground water. High densities of well use may be expected in rural areas without public water systems, expanding cities and suburbs, and legacy areas of well usage. The completeness of reported well logs was tested by counts from neighborhoods with known reliance on wells which showed reporting rates of 20% to 98%. Well densities in these neighborhoods were higher than the larger-scale estimates indicating that locally high densities typically exist within analysis units. A Monte Carlo procedure was used to determine that 27% of underground storage tanks that had at least one well within a typical distance of concern of 300m (1000ft).
