Mesa’s plan to shut down nearly 25 percent of its wells to meet new arsenic limits in 2006 could jeopardize the city’s ability to cope with an emergency.
Right now, Mesa has enough wells to take up the slack if either of the city’s water treatment plants goes down.
But Mesa’s water system will lose that important safety feature when 25 percent of city wells close in 18 months.
"We don’t have somewhere else where we can turn real quick in an emergency," said Alan Martindale, the city’s water quality supervisor.
The two treatment plants produce about 85 percent of the city’s water, Martindale said. Wells account for 15 percent of the water supply.
Last year, when a power failure shut down one of the plants for eight hours, the city switched to wells and reservoirs without interruption, Martindale said.
Wells also take over when the plants are shut down for repairs, or while canals are being cleaned.
The city plans to drill 27 new wells by 2025, according to a water plan going through final revisions. But that won’t be in time for the new arsenic limit.
On Jan. 23, 2006, the arsenic limit for drinking water will change from 50 parts per billion — the standard since 1942 — to 10 parts per billion.
Mesa is aiming for 8 parts per billion to make sure it is under the limit. One part per billion equals a drop in a 10,000 gallon swimming pool.
The U.S. Environmental Protection Agency, which is forcing the change, has estimated it will prevent 21 to 30 deaths from cancer each year. Long-term exposure to arsenic in humans has been linked to various forms of cancer, along with diabetes, birth defects, neurological damage and other diseases.
Water high in arsenic typically comes from underground aquifers. By contrast, river water processed at Mesa’s water treatment plants is low in arsenic.
Chlorine is added to well water to remove bacteria. Otherwise, it is sent to Mesa homes untreated.
Of the city’s 37 active wells, 14 have arsenic levels that exceed 8 parts per billion. The city water plan calls for closing nine wells, installing equipment at three wells to remove arsenic, and diluting arsenic levels at two wells by blending in purer water. The cost is estimated at $20 million, said Bill Haney, an assistant utility director.
Previously, the city water utility said it would close 10 of 38 active wells. But, one of the wells has already been closed because of high nitrate levels, Martindale said. The nine wells targeted for closure can produce about 19.9 million gallons of water per day.
Altogether, the city’s 37 we lls can pump about 75 million gallons of water per day, Martindale said.
Mesa has commissioned another study, at nearly $1 million, to find the best way to have the rest of its wells comply with new arsenic levels.
One option Mesa is considering is building special treatment plants — called groundwater facilities — to remove arsenic from well water before it goes to homes.
This treatment method would cost about 69 cents per gallon, as opposed to $1.48 to $2 per gallon for treatment plants at individual wells, according to the water plan.
Mesa also plans to add pipelines and build a reservoir on the east side by 2006 to replace three of the wells being closed.
The cost to buy land, drill and equip a well is about $750,000, said Bill Haney, an assistant utility director.
Mesa uses an average of 80 million to 85 million gallons of water per day, with peaks of about 130 million to 140 million gallons per day in the summer, Martindale said. The city’s water system serves about 450,000 people.
Mesa, Chandler, Scottsdale, Gilbert, Phoenix and Peoria could spend a combined $124 million to reduce arsenic in drinking water by the federally imposed deadline. In addition, more than 200 small water systems in Arizona will pay $80 million to $150 million.
The U.S. Environmental Protection Agency has estimated it will cost about 4,000 water systems nationwide $180 million to $206 million per year to make the change. Martindale said the figures are too low, and don’t include the cost of replacing wells, among other things. Some agencies estimated the cost at more than $600 million per year.
"We feel strongly that the EPA has not adequately taken certain costs into consideration," said Tom Curtis, deputy executive director of American Water Works Association in Washington, D.C., a trade organization.