Carol Stream Water Storage Reservoir Repairs
The Village of Carol Stream reported apparent leakage and loss of water from the reservoir located at 124 Gerzevske Lane after draining and refilling of the tank for cleaning and routine maintenance. DN Tanks (formerly Natgun Corporation) constructed the 2.5 MG prestressed concrete water storage reservoir in 1985. Baxter & Woodman, Inc. teamed with DN Tanks to complete inspection, determine the cause of leakage, and prepare strategy for rehabilitation.
The tank was drained for the inspection allowing for a thorough observation of the interior tank roof, wall, and floor surfaces. A significant amount of cracking in the cast-in-place concrete floor slab and evidence of floor and pipe movement were observed. The pattern of cracking observed in the tank floor during the inspection indicated that the floor slab raised when subjected to an uplift load condition. Uplift occurs when a tank is empty and the ground water level rises above the floor elevation resulting in the hydrostatic pressure beneath the floor slab exceeding the floor slab weight. This commonly occurs for tanks designed with very thin non-structural base slabs during a major rain event when proper precautions are not taken to assure that ground water remains below the tank floor.
When the tank was refilled, the weight of the water within the tank lowered the concrete floor slab close to its original position. Complete failure of the floor slab was not observed, but the floor had lost the ability to be watertight because of excessive cracking. Baxter & Woodman recommended application of an elastomeric watertight coating over the entire tank floor and bottom four feet of the tank wall to seal the cracks.
The Village authorized Baxter & Woodman to prepare bidding documents and perform construction services for the repair work. The fast-tracked project construction was completed in less than two months.