The Other Paper Thursday, June 26, 2008
The Work Behind Clean Water
By Colin Ryan, staff writer
Part 2 of a 3-part series.
When it comes to its 68,000 customers, spread out over twelve municipal water systems throughout Chittenden County, the Champlain Water District’s Peter L. Jacob Water Treatment Facility on Queen City Park Road has one mission.
“The whole point of this municipality is to provide safe drinking water to its members,” explains Mike Barsotti, director of Water Quality & Production. “We’re a commission-directed water supplier, chartered by the state of Vermont. We’re not a private company or a corporation we’re governed by a board of directors publicly elected from the towns they serve.”
Each year since 1999, following an extensive annual review process, the facility has received the “Excellence in Water Treatment Award.” The honor is awarded under the National Partnership for Safe Water program, of which the United States Environmental Protection Agency (USEPA) is a partner agency. CWD has maintained this “pinnacle of excellence” status each year since 1999. At this time, only four other water treatment facilities across the country have attained this public health protection optimization level.
The primary focus of the CWD is the Shelburne Bay Watershed. In the 1970’s, the CWD installed a large, u-shaped intake pipe 2500 feet off shore at a depth of 75 feet in the underwater canyon of Shelburne Bay. Barsotti calls it “the best spot in Shelburne Bay, where we can draw the coldest, cleanest water.” Any higher, and the warmer water would be more at risk of contamination. Any lower, and the pipes would draw in the metallic element iron manganese.
As the water travels the pipe, it mixes with a pumped-in natural preoxidant called potassium permanganate, which makes the water easier to treat. Also, baby zebra mussels are averse to the permanganate, which prevents their colonization at the mouth of the intake pipe deep in the bay.
CWD then uses disinfection as required by USEPA and the Vermont Water Supply Division as an additional public health protection barrier. At the pumping station on the shore, the water enters two stages of disinfection: primary disinfection with free chlorine and secondary disinfection with monochloramines.
The primary disinfectant, free chlorine, serves to ensure that the occasional, unlikely virus, bacteria and/or protozoa are inactivated immediately. The secondary disinfectant, monochloramines, enhances the benefits of the primary free chlorine by inactivating microbes, and eliminating the continual formation of disinfection-by-products (DBPs) produced with the reactive free chlorine. These disinfection-by-products are regulated by USEPA and must be kept to a minimum because of their potential to cause carcinogenic and reproductive problems.
The pretreated water is then filtered via a state-of-the-art treatment process using an adsorption clarifier to remove 60-80 percent of the natural clay and diatoms from the source water, and then a deep-bed multi-media filtration. Treatment efficiency is continuously measured by on-line laser particle counting technology. In addition, approximately 40 percent of the natural organic material, such as plankton, is also removed during filtration, as measured continuously by on-line analyzers.
The remainder is then reconstituted back into the environment, using a settling lagoon, a clearing pond, and long troughs where excess water thickens over a long period of time from 3 percent solid to 90 percent solid, which can be used as a compost amender.
“We’ve just done a paper with the American Waterworks Association Journal, looking at the advantage of this material to tie up excess phosophorous,” Barsotti relates. “The idea is that if you mix 5-10% of this material with manure, you convert it to a point where it has the perfect amount of nitrogen, and the perfect amount of phosphorous. That’s just one long-term project, amidst our ongoing purpose, which is to provide 68,000 people with safe drinking water.”
Next: The Controversy over Chloramine a look at both sides of the concern over the Champlain Water District’s use of monochloramines in its disinfection process.