Radial Collector Well Said to be First for a Rural Water Utility

The Le-Ax Water District in southeastern Ohio recently put a new radial collector well on line. A Ranney collector well, installed for the District by Hydro Group, Inc. near the community of The Plains, has added about 3 million gallons per day (mgd) of capacity to the water utility's supply. The well was installed for a capital cost of $770,000, and will help the District serve the growing water needs of its customer base, presently around 15,000. Describing the system, Le-Ax General Manager John W. Collins said: "To the best of our knowledge, this is the first radial collector well installed by a rural water company. We believe it will be a good long-term investment."

The decision to install a Ranney collector well as opposed to five or six conventional vertical wells to deliver the same levels of water production was based on several factors. Although capital costs would have been about the same for each alternative, the system selected is expected to have 30 to 40 percent lower annual operating costs. Primary reason for this projection is the effect of the high mineral content of the raw water in the District's groundwater source. Iron is one of the minerals present and tends to create wear in the pumps and clog the well screens. Because the entrance velocity of the water entering the larger screen area of a Ranney collector well is about 1/6th that of a conventional vertical well, maintenance is anticipated to be significantly lower for this reason alone. In addition, there are fewer pumps and well screens to maintain, and fewer pumps to operate, which reduces energy costs.

The District's engineering firm, Sieco Consulting Engineers, Inc., had carried out a present-worth 20-year capital and operating cost evaluation to determine the economics of the new collector well. According to Richard L. Sanson, Sieco's Ohio Services vice president, other advantages of one collector well versus a five or six vertical well arrangement are less environmental impact as a result of less land use, and a consolidation of the facilities.

A Ranney collector well consists of a steel-reinforced concrete, cylindrical caisson sunk into the ground. Lateral well screens project horizontally and radially from near the bottom of the caisson out into the aquifer. By comparison a conventional vertical well projects a single well screen vertically into the aquifer.

The new Le-Ax well has a caisson with an inside diameter of 9 ft and a vertical length of 63.5 ft. Three 8-in. diameter laterals project horizontally from the caisson at a depth of 41.5 ft below grade. Distributed among the laterals is a total of 432 ft of 8-in.-diameter wire-wound, stainless steel screen. Site of the well is approximately 140 yards from the bank of the Hocking River, which contributes about ten percent to aquifer recharge, depending on the weather and season.

A recent 24-hr pump test at 3999 gallons per minute (gpm), produced an observed draw-down in the collector of only 11.28 ft, for an apparent specific capacity of approximately 355 gpm/ft. Lateral flow analysis showed a relatively even flow distribution among the three laterals with screen entrance velocities ranging from 1.08 to 1.18 feet per minute. Yield calculations indicated that the collector well is capable of producing a long term sustained yield of over 3530 gpm under average conditions.

Hydro Group, Inc. specializes in water supply development, treatment and geotechnical construction. Headquartered in Bridgewater, New Jersey, the company can be contacted at: Tel. 908-704-8880; Fax. 908-704-9522.

Edited by Ian Lisk