A group of local officials tour the Duck River dam in September 2012, shortly after excavation work had begun.

Additional excavation work at the site of the Duck River dam has uncovered more clay at the construction site than engineers had originally anticipated, and the design team at engineer-of-record CH2M Hill will now spend the next three months looking at the plans to determine the best way to move forward.

While the specifics of the hybrid earth-fill/roller-compacted concrete dam are being considered, the Cullman Utilities Board has asked contractor Brasfield & Gorrie to move ahead with some ancillary work on a diversion around the dam structure site. Officials say the additional design work shouldn’t affect the construction timeline, but could increase the budget above the estimated $68 million.

“I don’t think we’ll be on budget,” CH2M Hill engineer Tom Harwell. “I don’t think it will come in the same as anticipated when we started.”

The potential cost increase comes because engineers may have to use more concrete than expected in the design of the dam, to compensate for the recently unearthed issues with the ground at the site. Depending on the final design, the cost of the dam could increase to an undetermined level.

The issues at the dam site were not uncovered until excavation had begun, and engineers say the findings were not evident in borings and core samples that had been taken in the past to survey the area.

To help keep costs closer to the original estimates, engineers plan to revisit the dam’s rating as a “high hazard” dam — a classification that was made more than a decade ago when the U.S. Army Corps. of Engineers was the primary engineer on the project.

The design team hopes to learn exactly why the dam was classified as “high hazard,” and see if the rating can be lowered. The classification levels are determined by dam location, as well as potential maximum flow charts for potential rainfall in the region and how much water flow the structure could handle. If the classification can be lowered, it would open up more design options for engineers when finalizing the dam specifications.

The utilities board had originally hoped to bid out phase II, the dam construction itself, by the end of the year. Mayor Max Townson said the setback is obviously frustrating, but noted the project remains on track and will still be a safe, positive addition to the county.

“We believe we are still within our existing time frame, and safety is of course our No. 1 priority,” he said. “We want this to be something to help the community for the next 100 years. We’re hoping any effect on the cost will be minimal, but we have to wait until the information comes back.”

The Cullman utilities board, with the cooperation of Cullman County and other area water systems, is creating a 640-acre lake with a 32-million-gallon-per-day capacity in northeast Cullman County. The dam will be approximately 2,000 feet wide. Once complete, the new lake will be used in conjunction with the area’s sole water source, Lake Catoma.

Trent Moore can be reached by e-mail at trentm@cullmantimes.com, or by telephone at 734-2131, ext. 220.