Launch Slideshow

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Marine masters

Marine masters

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    Divers locate trestle bridge piles for engineers who designed the replacement Hendrickson Dam in Punta Gorda, Fla. Photo: Stanley Consultants Inc.

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    A $600,000 project to extend a near-shore discharge pipe 300 feet into a river included $130,000 for planning, design, permitting, subconsultants, and construction contract administration including full-time, onsite observation and ive services. Photo: Matt Dodds

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    Structural Engineer Ryan Bell (pictured left) enters a digester to plug the discharge outlet so a valve can be installed in the sludge withdrawal pipe. Meanwhile, Diving Supervisor Hank Mann works the dive station where communication, video, and air supplied by the portable high-pressure cylinders are controlled. Photos: Matt Dodds

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    In addition to a condition assessment, the $81,000 professional services contract includes cleaning and preliminary design for repair options. Photo: Ben Boss


OPTION #3: Condition assessment

OWNER: Rapid City Water Division, Public Works Department

WHERE: South Dakota

Operations Management Engineer Dan Coon and Water Superintendent John Wagner's 55-square-mile service area in South Dakota's Black Hills houses 16 reservoirs in six pressure zones. One new reservoir is under construction and a second is being designed to provide a total potential storage capacity of 27 million gallons for Rapid City's 70,000 residents.

Thanks to clean, reliable water sources, sediment buildup is minimal. Employees can drain and clean a reservoir within two to three weeks. But to avoid interrupting drinking water service, reservoirs generally aren't taken off line unless employees see seepage on an exterior wall or the underground drain system detects a leak.

That was the situation in 2010 with three assets:

  • A 5-million-gallon belowground reservoir built in 1952 with two other reservoirs in its pressure zone
  • A 2-million-gallon aboveground reservoir built in 1963 with one additional 2-million-gallon reservoir in its zone
  • 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.