Water works: Bellwood dam project on tap
AWA authorizes bid ads for renovations
The Altoona Water Authority will advertise for bids to renovate the Bellwood dam and the water treatment plant below it — work that could cost about $26 million.
The “high-hazard” dam is “seriously deficient,” according to the state Department of Environmental Protection, because of a severely undersized spillway and issues with embankment stability and seepage control.
The plant is ready for improvements, especially now when it would be offline anyway for the dam work, said consulting engineer Mark Glenn of Gwin Dobson & Foreman.
Bid advertisements will go out for the $18.1 million dam construction within days, with bids to be opened Sept. 8, work to begin Nov. 1 and finish two years later, according to a timeline provided by Glenn.
Bid advertisements will go out for the $8.5 million treatment plant construction in mid-August, with work to begin April 1 and finish Oct. 1, 2023, according to the timeline.
The existing spillway of the dam is not only too small, but there are missing chunks of concrete, exposed aggregate and voids underneath that have been detected by ground-penetrating radar, according to Glenn.
The improvements to the dam, built in 1902 by the Pennsylvania Railroad, renovated in 1946 and acquired by the city in 1981, will include a new zig-zag or “labyrinth weir” spillway, plus a parapet wall along the top of the dam, that together with the spillway will provide capacity to handle the “probable maximum flood” caused by 26 inches of rain in 24 hours, Glenn said.
The design allows for greater flow capacity within a shorter stretch of the dam breast, because a zig-zag line from one point to another is longer than a straight line between those points.
The parapet wall on top of the dam will allow the reservoir to hold more water, before water would begin to flow — dangerously — over the dam breast.
Such an overflow would not happen unless the maximum flow is exceeded, Glenn said.
Building the parapet wall is actually a money-saving feature, Glenn said, as the alternative would have been widening the spillway to allow more water to escape more quickly, which would have been costlier.
The dam work will also include a new intake tower and tower access bridge, a new vault for outlet valves and removal of sediment from the reservoir bottom, if funds allow.
The intake tower setup will allow operators to draw water into the plant from various levels in the reservoir, which isn’t possible now.
That is important because the level at which the least turbid water resides varies according to conditions.
Removing the sediment would free up 28 million gallons of capacity and help alleviate the turbidity problem, officials said.
The sediment would be trucked to game lands above Blandburg, said General Manager Mark Perry.
The plant project will also include drilling and grouting to ensure the spillway side of the dam — the side farthest from Route 865 — is tied securely into the rock structure of the valley walls, Glenn said.
The 335 million-gallon reservoir on Bells Gap Run is fed by an 18.3-square-mile watershed, the largest in the authority system.
The treatment plant project will include installation of a filtration system with membrane filters that can remove “submicron” particles, including pathogenic cysts, bacteria and some viruses.
That will bring the plant into compliance with a DEP mandate to replace the current sand filtration system.
There will be similar replacements eventually in the authority’s other treatment plants.
The Bellwood plant project will add ultraviolet disinfection, a new control system and a mixing system in the reservoir to discourage algae formation.
The plant work will also include replacement of the ozonation system — although that is being funded as part of another project involving ozonation system replacements in several of the authority’s treatment plants.
The current ozonation systems are failing due to lack of parts and logic boards.
The Bellwood plant’s capacity is 4 million gallons a day, with an average output of 2.5 million gallons.
Mirror Staff Writer William Kibler is at 814-949-7038.