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COUNCIL TO PURSUE AERATION APPROACH 4-7-10

The Salmon City Council has voted unanimously to conduct further research into an aerobic system to thoroughly oxygenate the sewer lagoons as a way of removing the 23 year build up of sludge.

The city is in the process of repairing and improving its sewer system comprised of underground delivery lines and holding lagoons. The engineering firm of Keller and Associates has produced a study identifying the system’s priority needs in order for it to meet Environmental Protection Agency and Idaho Department of Environmental Quality effluent regulations.

The first phase of repair will begin soon as city crews start replacing some of the old sewer delivery pipes. The project of installing liners in other sewer lines is scheduled to begin in the Fall.

The delivery line repair work is expected to greatly reduce the amount of extra water infiltrating the pipes and ending up in the lagoons. The additional inflow results in water having to be treated that is not sewage related.

The next phase of work concerns the lagoons themselves. The Keller study identified removal of the sludge build-up as being absolutely necessary for increasing lagoon capacity and efficiency. Both the EPA and DEQ agreed with that assessment. The recommendation was to remove sludge from the lagoon by dredging.

Retired biochemist Calvin Leman believes there is a much less expensive way to approach the sludge problem. There are currently 16 surface aerators on the two lagoons. Leman is proposing an aerobic system that would oxygenate all levels of the 12 foot deep lagoons. He said the oxygenation would activate the anaerobic microorganisms already present. The activated ‘bugs’ would then break down and digest all biodegradable materials in the sludge, possibly eliminating the need and expense of dredging. Leman said that without actual data he would have to guess approximately 70 percent of the lagoon sludge is organic.

Leman told the council the aerators would cost $21,000 and are easy to install. He said the total cost would not exceed $50,000.

Councilman Ken Gutzman said the proposal looks like it might be feasible however he would want the manufacturer to do the installation to prevent any possible warranty issues. He commented that if the proposed system works as well as it’s supposed to it could lower sewer rates and, if it doesn’t it could still be utilized in the lagoons.

City Administrator George Ambrose explained when water enters the lagoon system it is supposed to remain in each lagoon for 17 days so that the ‘bugs’ can digest the material. He said with 26,000 cubic yards of sludge displacing the water there isn’t room for the water to stay in the lagoons that long. Due to the extra inflow and infiltration from old sewer lines plus the amount of sludge occupying lagoon space the water moves on out in about nine days which doesn’t give enough time to complete the digestion process. Ambrose said, “So, if we take the sludge out, get rid of the sludge, it will leave us more retention time because the water isn’t being displaced by sludge in the ponds.”

Leman thinks the aeration system he is proposing will not only reduce the sludge it would bring the lagoon percentages of suspended solids into agency compliance.

The City Public Works Department, on the other hand, believes that if the sludge is not removed and bottom aerators are installed the sludge will be stirred up causing even more suspended solids in the effluent which will increase the total number of suspended solids violations, possibly for as long as one year. The department favors the Keller Associates and DEQ recommendation that dredging and a mechanical sand filter is the best way to achieve a long term solution for removal of suspended solids

During a public comment period Recorder Herald Assistant Publisher Shiela Johnson supported Leman’s plan. She said the newspaper has a small water system used in connection with the printing press. Prior to the installation of a machine that puts oxygenated water into the system the water had been emitting a very foul odor. She said the oxygenated system has totally removed the smell. Johnson told the council, “I think if you want to be heroes in this community…put this system in.”

Mayor John Miller said the council feels the $50,000 would be worth taking the chance an aerated system would fix lagoon suspended solids problems. He said even if it didn’t work the aeration would help the lagoons and, if it did break down the sludge there may be no need to dredge. He said prices on dredging will still be investigated however no dredging would take place until the work on sewer lines is finished. In answer to a request by Councilman Jim Baker for core samples of the sludge and oxygen tests of lagoon water at various levels, Ambrose said that information is available and will be provided.


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