Arsenic is the 20th most abundant mineral in the earth’s crust. Its atomic symbol is As, and its atomic number is 33. There, the simplicity ends.
In February, the U.S. Environmental Protection Agency (EPA) finalized the Arsenic in Drinking Water Rule, reducing the maximum contaminant level (MCL) for arsenic in drinking water from 50 parts per billion (ppb) to 10 ppb. All public water systems must comply with the new standard by Jan. 23, 2006.
EPA estimates that approximately 5.5 percent, or nearly 3,000 of the nation’s 54,000 community water systems (CWSs, which serve at least 15 locations or 25 residents regularly, year-round), will need to take measures to meet the revised MCL for arsenic. Most of those systems rely on groundwater and are located west of the Mississippi River. While the highest concentrations of arsenic (i.e., those greater than 5 ppb) are found in groundwater in the westernmost states, communities in New Hampshire, North Dakota, South Dakota, Michigan and Minnesota also have reported high levels of arsenic in their groundwater.
In preparation for meeting the 10 ppb standard, CWSs are monitoring their systems and examining their options for compliance. They also are looking to Washington for assistance in meeting the latest water mandate.
Options for compliance
To determine whether a CWS complies with the Arsenic in Drinking Water Rule, a community must sample each point of entry to its distribution system. Samples should be taken for total arsenic (a combination of dissolved and particulate forms) after treatment and before water enters the distribution system. If laboratory results indicate concentrations greater than the MCL, the utility should re-test and evaluate treatment and non-treatment options accordingly.
For communities that are not in compliance, there are a variety of options for managing high levels of arsenic. Depending on the needs and resources of the communities, those options include:
blending high-arsenic source water with other low-arsenic source water,
modifying well operations and
abandoning the water source.
Treatment can be centralized, or it can target the point of entry or point of use. For small systems, arsenic-adsorbent media are the most cost-effective tools for removing arsenic from the source water. Systems that already employ conventional water treatment methods, such as coagulation and filtration, reverse osmosis and ion exchange, may find it most practical to remove arsenic by modifying existing processes.
Systems that do not treat water beyond disinfection also can use coagulation/filtration, ion exchange or activated alumina to remove arsenic. Although reverse osmosis is effective, implementation costs and residuals-handling requirements make it less attractive than other treatment options unless contaminants other than arsenic also need to be removed.
Exploring non-treatment strategies
The cost of arsenic removal is significant, both in initial capital investment and ongoing operations and maintenance (O&M). According to the American Water Works Association Research Foundation, based in Denver, the projected capital costs of treating a 1 million gallons per day water well range from $0.75 to $1.50 per gallon, depending on the raw water quality and the process used to treat it. Land acquisition, if needed, will add to that cost. Additionally, the annual O&M cost for the same facility is $100,000 to $180,000.
Cost was a paramount concern in Mesa, Ariz., which delivers water to 420,000 residents. Faced with removing arsenic in 21 of its 35 wells, the city could install arsenic-treating technology, requiring an initial capital investment of $30 million, or employ “non-treatment” strategies for significantly less money.
The city chose the latter option, and it is currently implementing a variety of non-treatment compliance measures. For example, it is:
modifying well construction to produce water from only low arsenic-bearing zones,
blending high-arsenic well water with low-arsenic surface water in reservoirs or at the well discharge to the distribution system,
limiting well operation and assigning an annual average exposure limit so the yearly arsenic concentration does not exceed a 10 ppb equivalent, and
abandoning three wells.
By implementing the non-treatment strategies, Mesa will spend less than $3 million on capital investments to meet the 10 ppb standard.
Blending water sources
Like Mesa, the Victor Valley Water District (VVWD) in Victorville, Calif., is exploring non-treatment strategies to alleviate high arsenic concentrations. (Half of the district’s 25 wells are affected by the new arsenic rule.) However, the community does not have an alternate surface water source to replace high-arsenic groundwater, and — situated in the high desert, northeast of Los Angeles — it cannot afford to abandon any water source.
As a result, VVWD, which serves 60,000 residents, is studying the feasibility of blending high-arsenic water from one well with low-arsenic water from another well. In conjunction with the California Regional Water Quality Control Board and the Department of Health Services, VVWD also is examining the feasibility of pumping high-arsenic water into a part of the aquifer containing low arsenic, blending the water in-situ and then withdrawing water that meets the new MCL.
Although the city can reduce arsenic levels in some wells using blending techniques, it will have to implement central treatment methods in others. For those wells, VVWD is conducting pilot tests to determine the most cost-effective treatment technology.
As part of those tests, VVWD is working with neighboring Baldy Mesa Water District to explore the use of arsenic-adsorbing media. Water from a well is pumped through a tank containing porous, iron-based media that chemically pulls the arsenic out of the water. When the media is exhausted, it is replaced with fresh media. If the treatment method is effective, it will save VVWD $5 million in up-front capital costs, compared to the cost of implementing more complex technologies such as ion exchange.
Home-based treatment systems
Centralized treatment of a town’s well(s) removes arsenic from all of the water pumped to customers. While large water systems can recoup some of the costs of centralized treatment by increasing water rates, small systems are less likely to have that option. For very small systems (i.e., those serving 500 people or less), home-based water treatment may be the most viable method of meeting the MCL.
Home-based arsenic removal is achieved by installing a treatment device at the point of use (e.g., under the sink) to treat drinking water only or at the point of entry to treat all water entering a home. A point-of-use device may incorporate distillation, reverse osmosis or a filtration cartridge with adsorbant media; a point-of-entry unit may employ one of those treatment methods or ion exchange. The cost of purchasing and installing an in-home treatment device ranges from $500 to $2,000, depending on the unit.
If used to meet the MCL for arsenic, home treatment systems must be monitored and maintained by a public water system. It is important to use units that are certified by the Ann Arbor, Mich.-based National Sanitation Foundation to ensure that they are effective for arsenic removal. Additionally, they should be certified and accepted by the primary state agent for regulatory compliance.
The result of more than 10 years of scientific and political debate, the Arsenic in Drinking Water Rule is, like most mandates, unwelcome. It comes at a time when cities and counties are strapped to fund infrastructure upgrades, facilities expansions and compliance with the Safe Drinking Water and Clean Water Acts.
With that in mind, Senators Harry Reid (D-Nev.) and Pete Domenici (R-N.M.) have co-authored a bill that would fund a five-year, $5 billion program to assist communities in meeting the arsenic mandate. (See “The Reid-Domenici plan” on this page.) The Senate passed that bill in May, and it has reauthorized the Water Investment Act of 2002 with additional provisions for arsenic compliance.
That is particularly good news for communities in New Mexico, where 25 percent of all water systems are affected by the arsenic rule. (The New Mexico Environment Department has estimated that compliance costs in the state will range between $400 million and $500 million in initial capital expenditures. Additional annual operating costs could reach $21 million.)
“This year’s drought in New Mexico and the West only underscores the necessity for this arsenic compliance grant program,” Domenici says. “Water costs are rising for virtually every community as [water] becomes harder and harder to access and deliver. Throwing arsenic compliance costs on top of that will only add to the water hardships we already face.”
As local governments await the outcome of this month’s Congressional budget battles, they have already begun assessing their water systems to determine their needs for arsenic compliance. Some, like Mesa and VVWD, are ahead of the curve. All have a variety of options — centralized treatment, non-treatment and in-home treatment — for customizing cost-effective solutions.
Tim Chinn is a vice president and national director for potable water for Omaha, Neb.-based HDR. He is based in Austin, Texas.