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The 64,000,000 gallon question
A large building constructor was contracted by Washoe County to construct a multi-level parking garage at the Reno Tahoe International Airport. The twenty seven million dollar contract included relocating a large sewer transmission line.
The sewer pipe was to be laid at a depth of eighteen feet in a region below the groundwater table. Hydrocarbons and aviation gasoline contaminated the water complicating the ditch de-watering program. To maintain a dry working environment in the ditch, the groundwater had to be continually pumped out and then treated to remove the hydrocarbon contamination before it could be discharged into the storm drain. The geological consultant estimated a flow rate into the ditch to be about 600 gallons per minute.
Clear Creek Systems, Inc. proposed an equipment package to reduce the hydrocarbon contamination to below acceptable discharge limits, before pumping the clean water into the storm drain.
Shortly after the trench was opened and work began, the estimated flow rate increased from 600 gpm to 2,000 gpm. Clear Creek Systems, Inc. responded to the prime contractors request to immediately increase the capacity with a proposal for the equipment to treat the additional 1,400 gpm.
For heavy sediment removal and storage, the 600 gpm system consisted of six 18,100 gallon weir tanks and five 21,000 gallon storage tanks. In order to increase the capacity another 1,400 gpm to meet the revised flow rate, three 18,100 gallon weir tanks, and one 21,000 gallon storage tank were added.
Clear Creek Systems, Inc. installed a seven chamber, 600 gpm rated, 20 micron bag filter and two 10,000 pound Granular Activated Carbon filter vessels. To accommodate the increased flow of 1,400 gpm, the bag filter was replaced with a 2,000 gpm 20 micron string wound filter assembly and a 45,000 pound Granular Activated Carbon filter vessel was added to the two pressure vessels already installed.
The equipment pumped and treated all of the water as required throughout operation. The project was completed and the water quality passed all of the tests performed by the environmental consultant.
In all, the system treated and discharged over 64,000,000 gallons of water. The complete setup, treatment system, monitoring, operating, material, and dismantling of this system cost the contractor less than a penny a gallon.
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