COM 0865.001 1996-1998 - Laserfiche WebLink

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Draft Environmental Assessment June, 1998 Old Hilo Wastewater Treatment Plant Page 4 Clarifiers Two clarifiers on-site remain as the most visually identifiable structures of the sewage treatment function. These substantial structures are 80 feet in diameter, and constructed of 12-inch thick concrete with footings and piers up to 24-inch thickness. Although they are more than 10 feet deep, only one-third of the tank bodies are above the ground. Each clarifier has approximate 375,000 gallons of storage capacity. The sludge scrapers inside and the catwalks on the top are corroded and close to collapse. The two clarifiers are proposed to be converted into two large outdoor aquaculture tanks, one for seawater organisms and the other for freshwater organisms. The scrapers, the catwalks and the clarifier center well will be dismantled and removed, and the tanks cleaned. Some of the inlet and outlet features may be modified in anticipation of the requirements of their new use. Digestion Tanks The anaerobic digestion tanks are two 60-foot-diameter concrete cylinder tanks located makai of the primary clarifiers. Approximately two-thirds of the tank structures, which are about 29 feet deep, are above ground. Both tanks have sludge, supernatant and gas piping systems, and floating . covers. Each tank was able to contain approximately 300,000 gallons of sludge and supernatant. Significant amounts of sludge still remain inside the digesters. Following sludge removal and tank emptying, demolition will include dismantling and removal of the covers, piping systems, and tank internals. The empty tanks will be thoroughly cleaned in preparation for their modification. Sludge disposal will follow DOH approved practices. Chlorination Building and Chlorine Contact Tank The chlorination building is located immediately makai of the administration building. It is primarily an open concrete structure with a chlorinator room attached, and a concrete crane-rail supporting frame crossing the driveway. The enclosed areas of the structure can be adapted to provide storage space and the covered area is to be converted into an outdoor classroom after the walls and roof are refurbished. The machinery inside will be removed except the existing 2-ton rail crane which may be retained for the Center's use. The exterior rail of the crane and its support columns will be dismantled and removed as they are on the land to be retained for Pua Street Pump Station (Figure 3). The open chlorine contact tank outside the chlorination building is a channelized concrete box, 50-foot long and 40-foot wide with two concrete sluices inside. The structure is below the ground, and has a capacity of approximately 60,000 gallons. A broken flume is left in the tank, and vegetation has grown at the bottom of the tank. The tank is proposed for use as a fish waste treatment unit. The sluices and the flume will be dismantled and removed, and the vegetation cleaned out in preparation for refurbishing the tank for its new function.