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The Altoona Water Authority has lowered the level of its Plane 9 reservoir by seven feet for safety, as it investigates the cause of water collecting under the spillway -- as indicated by a greatly increased rate of flow from the dam's underdrain, coupled with a faster-than-expected drop in the reservoir level prior to the recent drawdown.
It's not clear how much it may cost to repair whatever problem led to water building under the spillway, which led to an increase in the flow from the underdrain system to three million gallons a day.
The new reservoir level isn't ideal, but enough water remains to allow the treatment plant below the dam to continue to operate -- and Hollidaysburg Borough's Muleshoe Reservoir water is available as a supplementary source, according to authority officials.
Authority consulting engineer Gwin Dobson & Foreman and the state Department of Environmental Protection's Division of Dam Safety is involved in the investigation, according to staff engineer Jim Potopa.
Repairing the problem is likely to require an injection of grout below the concrete of the spillway, according to authority General Manager Mark Perry.
The authority hopes to finish that prospective repair by the end of the year, Perry said.
The underdrain releases were a red flag, but also shows that the underdrain system is "doing its job," by removing water, so that it doesn't "tunnel through" the dam breast, according to Potopa.
If the level of the reservoir rises due to rain, there still wouldn't be a threat, Perry said.
The authority is trying to keep the water level below the apron to the weir of the spillway, Perry said.
That new water level is about 30% down from normal, according to Potopa.
"Keep us abreast of what's going on," Neugebauer said.
Mirror Staff Writer William Kibler is at 814-949-7038.