Pumps provide flexibility

Maui County, Hawaii, is comprised of the three islands of Molokai, Lanai and Maui. The main island, Maui, is visited by 2.5 million tourists annually. This visitor loading, along with a doubling of the resident population over the past two decades, has taxed the island’s wastewater infrastructure. Wastewater collection, treatment and disposal presents some unique challenges due to three distinct population centers on the main island: topographic features, the warm sub-tropical climate and peak versus off-peak flows.

In the late 1970s, three secondary treatment plants, and related collection/transmission systems, were constructed with partial effluent reuse facilities and injections wells. No direct ocean outfalls ate utilized either for normal plant effluent or contingency disposal. These facilities replaced a cesspool-based system.

In the late ’80s, a construction program of plant expansions and improvements was begun in response to additional capacity demands and forecasts. The ’90s have brought another set of challenges, including system bottlenecks, degradation of unlined concrete trunk sewers from hydrogen sulfide attack and pump station equipment reaching the end of its economic life. Capacity and infiltration studies have identified problem areas.

Beginning in 1991, after a partial trunk sewer collapse, all concrete sewers were inspected, and a program for rehabilitation was begun. A project undertaken by a neighboring county revealed the high potential costs f6r shipping and rental of bypassing equipment. This, coupled with the growing concern about pump station serviceability, maintenance, repairs and backup systems, started a search for equipment to fill the needs of reliability, portability, ease of operation and broad pump performance characteristics. A market search led to the purchase of two English-designed vacuumprimed, 8-inch pumps and 1,600 feet of quick-disconnect piping from Godwin Pumps, Bridgeport, N.J. The pumps served for bypassing during the county’s first programmed sewer replacement project and now provide backup at numerous county wastewater pump stations.

The pumps’ performance during the initial project convinced county engineers and operations personnel of the suitability of such equipment. The portable pump fleet, which has supported two plant expansions, six pump station renovations and four sewer rehabilitation projects and helped avoid several major spills, is now comprised of 13 units and 2,500 feet of quick disconnect pipe.

Units are available to bypass each pump station on the island.

To date, savings over the contractor-provided equipment, which would have accrued on various division projects, have offset about half the purchase price, and full payback is expected within five years. In addition, the inventory provides flexibility and support of miscellaneous operations, such as wetwell cleaning and tank transfer and plays an important role in the zero spill goal of the division.