AWA braces for dam projects
Having just finished $65 million in renovations to its pair of sewer plants and having just begun $8.5 million in sewer line improvements in Pleasant Valley, the Altoona Water Authority faces the need to plan for an estimated $22.5 million in safety improvements to a pair of high-hazard dams.
Last week, to meet a deadline from the state Department of Environmental Protection, the authority authorized its staff to submit a schedule for replacement of the grievously undersized spillway on the Bellwood Dam, along with other work, to bring the dam into compliance with DEP’s recently upgraded safety requirements.
The authority will also need to replace the undersized spillway at Mill Run Dam, along with other work there.
“The system is old, and it has capital needs,” said Mark Glenn of Gwin Dobson & Foreman, the authority’s consulting engineer,
The work will need to be done even if the authority loses control of the water and sewer systems as a result of the City of Altoona’s plan to shop the systems for a big, upfront payment in exchange for a long-term lease, to help the city escape the state’s Act 47 program for distressed municipalities, Glenn said.
“Regardless what happens with the authority, [the capital needs are] not going away,” Glenn said.
Upon request of the DEP’s Division of Dam Safety, the authority evaluated the Mill Run Dam in 2010 and the Bellwood Dam in 2013, under the upgraded safety provisions, which require that dams be able to handle an “apocalyptic” maximum rainfall, which for this area is 32 inches in 72 hours, Glenn said.
The Bellwood Dam spillway can only handle 27 percent of the probable maximum flood, rendering it “seriously deficient,” according to Glenn.
The spillway is also deteriorated, and there is no intake control for withdrawing water, which creates treatment problems.
The Mill Run spillway can only handle 55 percent of the maximum flood, which renders it “inadequate,” according to Glenn.
Also, the Mill Run intake tower has mechanical problems and is inaccessible, due to rock falling from a hillside onto the spillway of the dam – a serious problem in and of itself.
Initially, the authority believed the Mill Run improvements would have priority, but the Bellwood evaluation showed that improvements there are more pressing, Glenn said.
After evaluating several options, Glenn recommended an $11.5-million project for Bellwood that includes construction of a “labyrinth” spillway, a new intake tower and access bridge, removal of silt deposited in the reservoir as a result of surface mining near Blandburg and replacement of the toe drain of the dam.
DEP reviewed the plan in May.
Labyrinth spillways provide greater capacity within a fixed width, because of its zig-zag configuration.
A spillover wall that is 100 feet long, because of the zig-zags, will allow more water to flow over, at a given depth or thickness – based on the reservoir level in relation to the top of the spillover wall – than would a straight line conventional spillover wall 25 feet long.
After evaluating several options for Mill Run, Glenn recommended an $11-million project that includes a labyrinth spillway, a new intake tower and access bridge, downstream seepage collection and a reassessment of the Allegheny Reservoir, which is downstream from the Mill Run dam.
The new spillway would be located towards the middle of the Mill Run Dam, eliminating the rock-slide problem.
DEP approved the Mill Run plan in 2011.
The authority would probably seek Pennvest funding for the projects, according to authority controller Gina DeRubeis.
The authority has 11 dams, seven of which have been upgraded in recent times.
Between 1984 and 1999, under mandates from DEP, the authority successively upgraded the Kittanning Point Dam, the Cochran Impounding Dam, the Kettle Dam, the Plane Nine Dam and the Lake Altoona dam, at a total cost of about $40 million, according to a presentation by Glenn.
The authority also repaired the Tipton and Blair Gap dams.
The Bellwood Dam schedule would need to include major milestones for the project, according to Glenn.
The authority will need to work out the details with DEP, he said.
He declined to predict how long the project would take to finish.
The 47-acre, 335-million gallon reservoir it created is a “key element” of the authority’s distribution system, according to Glenn.
Bellwood Borough uses water that is treated in the authority’s plant just downstream from the reservoir.
The Mill Run Dam was built in 1958.
At 100 feet high, it’s the tallest in the authority system.
The 44-acre reservoir behind it holds 426 million gallons.
Mirror Staff Writer William Kibler is at 949-7038.