The Plains sewer lagoons are increasingly vulnerable to the encroaching Clark Fork River.
Consulting engineer Shari Johnson, of Shari A. Johnson and Associates, encouraged Plains Town Council and Mayor Dan Rowan, at the March 5 meeting, to consider recent streambank changes as they evaluate options for ensuring the long-term viability of the town’s sewer treatment facility.
Johnson explained that at least some of the alternatives to protect the lagoons, presented in an earlier PER (preliminary engineering report) from another firm, are no longer possible. The PER was developed prior to the 2018 flood, which caused the bank to erode beyond where the proposed reinforcements would have been placed. In four days, Johnson showed, 47 feet of bank was lost — a third of the distance between the river and the lagoons, and flood waters reached the lagoon dams. Existing riprap (rock) bank stabilization areas were breached and eroded. While it is impossible to predict the speed with which the remaining bank will be eroded by the meandering river, it appears that any time within the next few years, there will likely be little or no bank left between the lagoons and the river.
Other alternatives in the PER included possibly moving the entire system to another location away from the river. Johnson suggested the town start planning for this scenario before it is “absolutely necessary,” while developing shorter-term plans for emergency pumping of effluent if needed. Moving the system would likely take years of preliminary work for such things as land acquisition, design, getting permits, and applying for and obtaining grants and loans.
Johnson showed that though it might be tempting to consider the protection alternatives 1 to 3 in the PER, estimated to cost between $1 million and about $3 million, these would likely be temporary fixes and the larger estimates of around $6 million or more to move the facility would still be necessary soon, on top of that expense. In addition, Plains still has debt on the existing lagoons. Johnson said that because of the new situation, granting agencies may be more willing to put money toward relocation than toward shorter-term bank protection.
The option of a mechanical treatment plant was expected to be much costlier. Other Montana municipalities have built such plants at construction costs of $7 million to as high as $18.5 million, and they cost at least three times as much for maintenance and operation as a lagoon system.
On a positive note, the two new police cars are nearly ready to be picked up in Great Falls. Also, the council voted unanimously to appoint Connie Foust as the first of three members to the new Police Commission. Montana code requires a commission if there are three or more police officers working for a municipality. Foust will serve a three-year term, with the other two positions to be appointed to two- and one-year terms so as to stagger term expiration dates.