What water well drillers should know about arsenic in groundwater
“The well industry is for the most part ignoring it,” says Roger Renner, MGWC, president of Minnesota-based drilling company E.H. Renner and Sons. “Arsenic is new to the industry as far as non-public water supply problems.”
Renner is a member of the Minnesota Department of Health’s Water Well Advisory Council and he’s also the former president of the National Ground Water Association (NGWA). He points out that while the U.S. Environmental Protection Agency (EPA) set the maximum contaminant level (MCL) for arsenic at 10 parts per billion (ppb) for public water supplies, privately owned wells aren’t regulated.
But that doesn’t mean there isn’t a problem. In fact, U.S. Geological Survey (USGS) data show almost 7 percent of roughly 2,100 domestic wells sampled nationally exceed the 10 ppb standard. And a recent study of Maine students exposed to arsenic in drinking water suggests even that standard may not be enough to protect children.
Some states have stepped in with additional testing requirements, even requiring special well-construction techniques for certain areas with high arsenic. These methods, while more expensive, may be adapted for use in other areas as experts begin to better understand the problem.
Who’s at Risk
Dr. Joseph Graziano of Columbia University recently led a study examining the effects of arsenic in drinking water on 272 Maine schoolchildren, the results of which have caused some serious concern among area residents.
“At fairly low arsenic concentrations you see a decline in child intelligence,” says Graziano. “In comparison to those children whose household water arsenic concentrations were less than 5 [ppb], those with more than 5 [ppb] lost an average of 5 IQ points.”
Graziano is quick to point out, however, that while the study has implications for child development, arsenic exposure carries risks for people of all ages — risks that include a range of cancer types, as well as cardiovascular disease.
“Let’s not lose sight of the fact that there are other killer health outcomes that people should be aware of,” Graziano says.
A Widespread Issue
In addition to agricultural and industrial pollution sources, arsenic occurs naturally in groundwater from weathering of bedrock containing iron oxide and sulfide minerals. According to the National Ground Water Association, geologic settings known to produce elevated arsenic include evaporite deposits like limestone and gypsum, oxide-rich sedimentary rocks including some shales, ore deposits containing sulfide minerals, and some volcanic settings.
Dr. Neil Dubrovsky is a researcher with the USGS National Water Quality Assessment (NAWQA) program, a long-term monitoring study aimed at understanding the health of national water resources. Dubrovsky notes that while local geologic conditions are highly variable, there’s a much higher chance of seeing elevated arsenic in groundwater of the western U.S.
“Between the change in climate and geology, you have more than twice the rate of arsenic concentrations above the drinking water limit in the western states,” says Dubrovsky.
Data mapping of more than 30,000 samples from private and public wells across the country show other regions with high arsenic concentrations. These include parts of the Midwest, areas of Texas and portions of the Northeast. A 2009 report from NAWQA states that arsenic exceeds the EPA’s MCL in 6.8 percent of private wells sampled nationwide.
Concentrations exceed the MCL in more than 10 percent of wells located in certain aquifers, including crystalline-rock aquifers in New England; basin-fill aquifers in California, Nevada, Arizona, New Mexico, Texas and Nebraska; and the Snake River basaltic-rock aquifers of Idaho.
The next phase of USGS research will focus on improving data resolution and developing better models to predict where arsenic is likely to be found in groundwater supplies.
“We will be doing that nationally over the next eight years, starting with the northern part of the country, where there are spotty but occasionally very high concentrations,” Dubrovsky says.
Arsenic is odorless and tasteless; its presence can be detected only by lab testing. In addition to EPA regulation of public water supplies, some states now require private-well testing in high-risk areas, often by way of a real estate transaction law.
For example, New Jersey’s Private Well Testing Act requires wells be tested for several contaminants, including arsenic, whenever someone buys or sells a home. New Jersey has also set the limit for arsenic in public water supplies at 5 ppb, notably stricter than the EPA limit.
“New Jersey has the most protective arsenic standard worldwide,” says Dr. Steve Spayd, a research scientist with the New Jersey Geological and Water Survey.
It’s not surprising, given that up to 15 percent of state residents use private wells, many in areas like the state’s Piedmont region where nearly half of wells sampled exceed the state standard.
“The Piedmont aquifers are definitely the highest risk, but when we looked at private-well testing data for all of north [New] Jersey, there wasn’t any aquifer that didn’t have at least one well at 16 [ppb] or higher,” says Spayd.
Highly variable local geology means there’s little drillers can do to avoid arsenic-bearing strata, but Spayd points to the state’s many outreach programs aimed at getting private owners to test for arsenic.
Where arsenic concentrations are high in private wells, options include using bottled water, drilling a new well (which may not necessarily solve the problem) or installing a treatment system, the most commonly recommended option. Point-of-entry systems that treat water for the whole house cost around $3,000 to install, while point-of-use systems that treat a single tap for drinking water use cost around $400.
Drilling Practices to Reduce Arsenic
Despite the fact that most states leave it to well owners to test for arsenic, Wisconsin has taken a more proactive approach to the issue. In 2004, special drilling regulations from the Wisconsin Department of Natural Resources (DNR) went into effect for that state’s Winnebago and Outagamie counties, where a sulfide cement layer had caused arsenic concentrations above the EPA limit in almost 20 percent of area wells.
“The specifications are aimed at reducing oxygen introduced into the system during well construction and development,” says Tom Riewe, a hydrogeologist with the Wisconsin DNR who helped write the drilling rules. “Once the oxygen gets in, it oxidizes arsenic and releases it to the groundwater,” he adds.
The special drilling requirements call for rotary mud-circulation or cable-tool methods, prohibiting rotary-air methods that would bring oxygen into the system. The water used to mix the drilling mud slurry must be treated with soda ash to keep the pH between 7 and 8.5, below which acidic conditions can trigger geochemical reactions that release arsenic.
Regulations for well construction in these areas also contain restrictions on grouting, requiring the use of bradenhead or grout shoe techniques and letting cement set for 24 hours to ensure the well is completely sealed off from the surrounding bedrock.
Not surprisingly, these methods significantly increase the cost of well construction. Although these restrictions did create some initial pushback, Riewe says, the program has been extremely successful in producing arsenic-free water — something well owners are now willing to pay more for.
“I think one thing that helps is that we give well owners an additional option to drill a shallow bedrock aquifer in certain areas,” says Riewe. “The fact that we try to provide a less expensive option shows we’re trying our best.”
In 2009, a team of experts at the National Ground Water Association (NGWA) included the Wisconsin DNR’s methods in a best practices document aimed at educating water well professionals about arsenic contamination.
Renner, who was involved in creating the guidance document, admits that the cost of drilling and developing a well without air means drillers are unlikely to use the methods except where required by law. However, he sees it as less a question of if, and more a question of when more drillers will have to adopt these types of techniques as the problem of arsenic in groundwater receives more attention.
In the meantime, it’s up to private well owners to test for arsenic and install treatment systems, an area where Renner sees a missed opportunity on the part of many in well construction.
“It’s a shame the well industry hasn’t woken up to the ability to sell treatment equipment,” Renner says. “Water treatment goes to another industry altogether, while we could be the natural choice as those licensed to deal with wells.”
Find out more...
The National Ground Water Association offers a publication titled “Reducing Problematic Concentrations of Arsenic in Residential Well Systems” free to members. Visit www.ngwa.org and search for “arsenic.”