PRAIRIE CITY - City residents may be noticing a little less chlorine aroma when they turn on the tap these days.
City officials two weeks ago put their new slow sand filter (SSF) water system into operation, and it provides natural filtering that allows them to reduce the amount of chlorine needed to treat the domestic water supply.
Prairie City Mayor Stan Horrell was pleased to see the system go on line.
"I feel good about it," he said. "It's working well. As far as I'm concerned, we're going to have good quality water now, and plenty of it."
The change-over was the culmination of several years of wrangling about what to do with the city's aging water treatment system, marked by public debate over whether to build a deep well system or the SSF filtration plant.
Doing nothing was not an option, as the state cracked down on the city for surface water impacts on the quality of its domestic water. The city had repeated orders from the state to upgrade the system, and was facing stiff penalties if it didn't act soon to comply with federal safe drinking water standards.
The city council in October 2007 finally decided to push ahead with the SSF option.
The city's engineers, Anderson Perry & Associates, designed the SSF system and Boise-based Bodiford Construction began the work last summer. The city obtained a $2 million loan for the project through the Oregon Economic and Community Development Department's safe drinking water revolving loan fund. The loan originally carried a 4.11 percent interest rate, but the city was able to renegotiate that term to 1.8 percent.
Residents and businesses are repaying the loan through their water bills. In order to qualify for the loan, the city was required to raise its water rates to $41 per 7,500 gallons of usage.
The rate hike would have been required, no matter which option the city chose for its new system, officials said.
The new filtration plant sits along Dixie Creek about three miles north of town. The system doesn't draw from the creek itself, but from subsurface infiltration galleries nearby. The water is collected and piped into two galleries - concrete pools, with multiple layers of sand and other aggregrate - that were built adjacent to the control building.
The water moves slowly through galleries' sand layer, which foster the growth of helpful bacteria and other natural agents that consume organic impurities in the water. According to the National Drinking Water Clearinghouse, SSF systems can produce exceptionally good drinking water, with bacterial reduction of 90 to 99 percent.
As the sand filters collect more material over time, the top layer of the sand will need to be scraped to improve the flow and reduce turbidity. The water level is lowered for that process, and then the tank is slowly refilled, from the bottom, and put back to work.
Georgia Patterson, city public works director, said the city probably won't need to do that often, and it won't interrupt water supply or usage. Since the system has two filter basins, one can be offline while the other is serving the community.
The water is piped from the filters through the control building and into a clear well - a large covered basin adjacent to the building. From there, the water is piped to the city's existing reservoirs, including the million-gallon tank, and on to the water users throughout the city.
The city still chlorinates the water as it goes from the control building to the main transmission lines, Patterson said, but the SSF process has greatly reduced the amount required. Under the old system, the city was up to eight pounds of chlorine gas a day; now the rate is down to 1.5 pounds per day.
"It's a big change," said Patterson.
The city will continue to test the water for coliform bacteria twice a month, although the testing has been more frequent during the start up. So far, she said, the test results have been very good.
The city is still putting the finishing touches on parts of the system, but once the work is done, there will be an open house so residents can get a closer look at how the system works, Patterson said.
David Wildman, the project engineer for Anderson Perry, noted that SSF combines "a treatment technology that's been in use for thousands of years with some modern technology" to provide city with a water supply that's both high-quality and reliable.
"The slow sand filter system is a great way for city to naturally treat the water that's been serving the community for decades," he said.