The survey, which was led by the University of Iowa (UI) Center for Health Effects of Environmental Contamination, also reveals that a high percentage of wells statewide were contaminated with arsenic.
"The nitrate and bacteria results were expected despite efforts to address contamination in ground water sources. The arsenic results were something we did not expect," says Peter Weyer, Ph.D., the study's lead investigator and associate director of the UI Center for Health Effects of Environmental Contamination. "Nearly half the wells sampled had some level of arsenic, and 8 percent of those had a level that could be considered a health concern.
"On a more positive note, the levels of the commonly used herbicide atrazine seem to be trending downward from what past studies have shown," Weyer adds.
The survey, conducted from 2006 to 2008, sampled 473 wells statewide for bacteria, nutrients, metals, common-use herbicides and insecticides, and herbicide degradates. This study was a follow-up effort to the original Statewide Rural Water Well survey, known as SWRL, that was conducted from 1988 to 1989.
Additional findings from the sampled wells in the latest study include:
- 43 percent of the samples had total coliform bacteria, 19 percent had enterococci and 11 percent had E. coli.
- 49 percent had nitrate, with 12 percent having more than 10 parts per million of nitrate-N, which is the Safe Drinking Water Act standard for public water supplies.
- 48 percent had arsenic, with 8 percent having arsenic above the Safe Drinking Water Act standard for public water supplies.
- 8 percent had atrazine at very low concentrations, and 2 percent had metolachlor.
- One or more of the pesticides acetochlor, alachlor and trifluralin were detected in less than 1 percent of wells.
- Analysis of herbicide degradates (breakdown products of the parent compound) included the finding that 11 percent of water samples had desethylatrazine, 11 percent had acetochlor ESA (ethane sulfonic acid), 27 percent had alachlor ESA, 33 percent had metolachlor ESA and 8 percent had metolachlor OXA (oxanilic acid).
Degradates generally are believed to be less toxic than the parent compound.
This new study was a joint effort among many statewide organizations, including Iowa private well owners and Iowa county public/environmental health departments. A full report of the latest survey is available for download through the UI Center for Health Effects and Environmental Contamination Web site at http://www.cheec.uiowa.edu/research/SWRL2.html.
Owners of private drinking water wells in Iowa are eligible for free testing for nitrate and bacteria through the statewide Grants-to-Counties Program. They can visit http://www.uhl.uiowa.edu/services/wellwater/gtc.xml, or contact their respective county public health department for further information.