A 2-million-gallon aboveground reservoir built in 1980 with a 1-million-gallon counterpart in its service zone.
Coon and Wagner planned to have all three inspected by a diver. They hadn't contracted this type of service and couldn't find old records that would've helped them estimate the cost, so they settled on a budget of $50,000. When faced with initial estimates in the $135,000 range, they regrouped.
“We stepped back and asked ourselves what work we could do and what would require special services,” says Coon, who's worked with a zero-growth budget for several years.
While both aboveground reservoirs were visibly seeping, there was also a crack around the entire circumference of the reservoir built in 1980. He and Wagner felt a die test, which must be conducted while a reservoir is filled, would give them the clearest picture of the crack's extent and the asset's other vulnerabilities. That settled it: They'd contract one dive and prepare the other two reservoirs in-house for inspection by the dive contractor.
Like they do with other professional services, Coon and Wagner used qualification-based procurement to award the contract. Of the two firms they interviewed, only Stanley Consultants Inc. employed certified commercial divers who are also professional engineers. The other firm planned to subcontract the dive.
“That's a pretty tough combination to beat,” Coon says.
Once they selected Stanley Consultants, Coon and Wagner worked with Principal Civil Engineer Mark Jaster, PE, to narrow the project scope.
Stanley Consultants Structural Engineer-Commercial Diver Ryan Bell, PE, spent three days carefully pumping the bottom to avoid stirring up the sediment and resuspending microorganisms that could contaminate the water, clog filters, and use up chlorine residuals. Then, in accordance with Association of Diving Contractors International Inc. Standard 11-1999 developed with the American Water Works Association for potable water facilities, he combed every inch for cracks and spalls, debris in drains, corroded steel, and deteriorating seals, checking connections and anchors.
The system was isolated, meaning the valve to the asset's single pipe was closed and “locked and tagged out,” while he worked. An asset can remain on line during the process, but extreme care must be taken to avoid “Delta P,” where differential water pressure entraps divers so powerfully they can only be removed by extreme force. This is another reason to ensure a consulting firm doesn't send a scuba diver with limited air supply into storage tanks.
Consultants prefer to walk a site before providing a quote, but if that costs too much then provide as many pictures of the asset as possible.
“The asset's condition determines how long the assessment and cleaning take,” Bell says. “And if the structure's in bad shape, it takes a long time to document everything.”
Also provide maintenance records as well as any old reports that identified deficiencies. If you've established the asset's baseline condition, routine inspections take less time because the firm is confirming any change in previously documented items and recording new deficiencies.WEB EXTRA
For a step-by-step slideshow of how Rapid City's 2-million-gallon concrete reservoir was inspected, click here.