Monday, September 23, 2019

Before Purchasing a Home-Test a Well for Nitrate

Before you purchase a home with a well, you should test it for more than the presence of bacteria. One of the contaminants you should test for is nitrate. The levels of nitrate in groundwater tend to increase over time from the presence of fertilizer and human and animal waste. The Safe Drinking Water Act maximum contaminant level (MCL) for nitrate in public drinking water supplies in the United States is 10 mg/L as nitrate-nitrogen (NO3-N). This concentration is slightly below the World Health Organization (WHO) guideline of 50 mg/L as NO3 or 11.3 mg/L NO3-N. The regulatory limit for nitrate in public drinking water supplies was set to protect against infant methemoglobinemia, but other health effects were not considered.

Dr. Mary Ward of the Occupational and Environmental Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute has lead several important studies comparing all the research on the health impacts from exposure to nitrate in water. The first review was of studies published before 2005. In 2018 Dr. Ward was lead author on a review of more than 30 epidemiologic studies on drinking water nitrate and health outcomes.

According to their study, the strongest evidence for a relationship between drinking water with elevated nitrate concentrations and adverse health outcomes (besides methemoglobinemia) is for colorectal cancer, thyroid disease, and neural tube defects. “Many of the studies observed increased health risks with ingestion of water nitrate levels that were below regulatory limits.” So, having nitrate concentrations below 10 mg/L is no protection against increased cancer risk or birth defects.

For example, Dr. Ward’s study found “Mothers of babies with spina bifida were twice as likely [to have ingested] ≥5 mg/day NO3 from drinking water than control mothers. Mothers of babies with limb deficiencies, cleft palate, and cleft lip were, respectively, 1.8, 1.9, and 1.8 times more likely to [have ingested] ≥5.4 mg/day of water NO3 than controls.”
Ward, M.H.; Jones, R.R.; Brender, J.D.; De Kok, T.M.; Weyer, P.J.; Nolan, B.T.; Villanueva, C.M.; Van Breda, S.G. Drinking Water Nitrate and Human Health: An Updated Review. Int. J. Environ. Res. Public Health 2018, 15, 1557.

In the United States, nitrates are present in most surface water and groundwater supplies at levels below 4 mg/l, with levels exceeding 20 mg/l in about 3% of surface waters and 6% of groundwater. “A recent nationwide study found that concentrations of nitrate over 1 mg/L nitrate indicate human activity (Dubrovsky et al. 2010).” According to the EPA levels of nitrate in groundwater have been increasing. The increasing use of artificial fertilizers, the disposal of wastes (both human and from animal farming) and changes in land use are the main factors responsible for the progressive increase in nitrate levels in groundwater supplies over the last 20 years. In Virginia the EPA estimates that on 2% of the state has groundwater nitrate concentrations >5 mg/L. Boiling water to concentrates the nitrate. A survey of bottle water sold in 42 Iowa and 32 Texas communities found varying but generally low nitrate levels. Nitrate concentrations ranged from below the limit of detection (0.1 mg/L NO3-N) to 4.9 mg/L NO3-N for U.S. domestic spring water purchased in Texas.

Dr. Ward concludes “To date, the number of well-designed studies of individual health outcomes is still too few to draw firm conclusions about risk from drinking water nitrate ingestion. Additional studies that incorporate improved exposure assessment for populations on PWS, measured or predicted exposure for private well users, quantification of nitrate-reducing bacteria, and estimates of dietary and other factors affecting nitrosation are needed.” The bottom line here is that if you, like 22% of Virginians get your water from a well you need to know the nitrate levels of your water; and if you are considering buying a home with a well test it for nitrates and bacteria before you buy the home. (Make sure your offer to purchase has a water quality contingency.).

The most common contamination problem for a well is an adjacent septic system. Research done in Duchess county New York identified density of septic systems as an easy indicator of nitrate contamination to groundwater. The Dutchess County study and another study performed in North Carolina found that overall average density of on-site waste disposal (traditional septic or alternative) should not exceed one unit per 2-3 acres for an average size house to ensure water quality and recharge in groundwater supplies. The controlling factor in minimum lot size requirements in the northeast appears to be maintaining water quality, not groundwater recharge. The measure they used to test water quality was nitrate level. Adequate dilution, soil filtration and time are necessary to ensure that the nitrate level did not rise. It is often surprising how close to a private well the recharge zone is.

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