Naturally occurring metals in unregulated domestic wells in Nevada, USA

Abstract

The dominant source of drinking water in rural Nevada, United States, is privately-owned domestic wells. Because the water from these wells is unregulated with respect to government guidelines, it is the owner's responsibility to test their groundwater for heavy metals and other contaminants. Arsenic, lead, cadmium, and uranium have been previously measured at concentrations above Environmental Protection Agency (EPA) guidelines in Nevada groundwater. This is a public health concern because elevated levels of these metals are known to have negative health effects. We recruited individuals through a population health study, the Healthy Nevada Project, to submit drinking water samples from domestic wells for testing. Water samples were returned from 174 households with private wells. We found 22 % had arsenic concentrations exceeding the EPA maximum contaminant level (MCL) of 10 μg/L. Additionally, federal, state, or health-based guidelines were exceeded for 8 % of the households for uranium and iron, 6 % for lithium and manganese, 4 % for molybdenum, and 1 % for lead. The maximum observed concentrations of arsenic, uranium, and lead were ∼80, ∼5, and ∼1.5 times the EPA guideline values, respectively. 41 % of households had a treatment system and submitted both pre- and post-treatment water samples from their well. The household treatments were shown to reduce metal concentrations, but concentrations above guideline values were still observed. Many treatment systems cannot reduce the concentration below guideline values because of water chemistry, treatment failure, or improper treatment techniques. These results show the pressing need for continued education and outreach on regular testing of domestic well waters, proper treatment types, and health effects of metal contamination. These findings are potentially applicable to other arid areas where groundwater contamination of naturally occurring heavy metals occurs.

Keywords: Drinking water; Heavy metals; Private well.

Figure 1:

Numerical breakdown of participants in this study. Blue numbers are number of participants.

Figure 2:

Bar graphs showing results of the Healthy Nevada Project well water survey. A) Responses to the question if homeowners previously had their well water quality tested. “No” is in green and “Yes” is in black. B) The year of the well water quality test by percent of those that have tested their well.

Figure 3:

Map of the study area. (A) Map of the United States showing the study area (red box). (B) Locations of homes that submitted a household water sample (red dots). Blue boundaries are the six-digit hydrologic unit classifications (HUC 6) for this region. Relevant HUC 6 basins are labeled in italics. Major cities are also shown.

Figure 4:

Histogram of household water elemental concentration. Households without water treatment (A, grey) and with water treatment (B, blue). Results are plotted as Log₁₀ of the concentration, with the red line indicating the guideline value from Table 1.

Figure 5:

Box and Whisker plots showing elemental concentration pre-water treatment (green) and post-water treatment (blue) from the same household. Whiskers represent 5/95 percentile. Red lines denote guideline value.

Figure 6:

Concentration of metals pre-treatment and post-treatment from the same well water system. Pre-treatment concentrations above guideline values are shown. Black line indicates no reduction in concentration, green dotted line a 50% reduction, and light green line a 90% reduction. Black dots are households with one treatment type (One), red dots are households with multiple treatment types (Multi), orange dots have multiple treatments including a Reverse Osmosis (RO) system (Multi-RO), and yellow dots are households with RO systems only. Copper is not shown as all pre-treatment concentrations were below the guideline value.