It can be hard to put a price on the value of being a good neighbor, but in the case of the Orange County Water District, it comes to about $266 million. That is about half the cost of the district's Groundwater Replenishment System, being paid for by the Orange County Sanitation District. Its centerpiece is a 70-million-gallon-per-day advanced treatment plant.

OCSD

On schedule for completion next year, it will take secondary-treated effluent from OCSD's adjacent Plant 2 and send it through microfiltration tanks, reverse-osmosis membranes and ultraviolet disinfection. The resulting product, treated beyond safe drinking water standards, will be used for a dual purpose. A portion will be injected into a barrier to halt saltwater intrusion into the district's underground water supply and a 13-mile pipeline will transport about 35 mgd to district percolation ponds to help augment existing supply.

Presently, the district draws 75% of its 549,000-acre-ft demand from groundwater. Most of the remainder comes from federal and state allocations from the Colorado River Aqueduct and the State Water Project. But the district's allotment from both of those sources is expensive, and being reduced. Reclaiming wastewater effluent now discharged into the ocean provides another source to handle annual demand for the northern portion of Orange County, projected to increase to 634,000 acre-ft by 2025.

Designed by Cambridge, Mass.-based CDM, the plant will send flows through batteries of advanced treatment processes. The first is microfiltration, to remove any remaining pathogens and bacteria from the wastewater. Flows then move at 150 to 200 psi through reverse osmosis membranes to remove salts, viruses and other organics before undergoing ultraviolet disinfection. The purified water actually will reduce minerals in the system when it mixes with naturally occurring groundwater.

The system doesn't come cheap. Operations and maintenance costs are expected to be $22.9 million per year. Electricity costs, tied mostly to the energy-intensive reverse-osmosis system, are about $11.5 million per year, says Michael Markus, OCWD assistant general manager.

J.F. Shea Construction Inc. landed the plant's contract in 2004 with a $292-million low bid that was $39 million above the engineer's estimate. About $29 million of the difference was tied to an almost 60% jump in steel prices between the time the job was estimated, in summer 2003, and the March 2004 bid opening, and uncertainty over costs during the project, say district officials.

Now about 80% complete, the job is on schedule to finish next summer and begin producing water by September.

The project builds on the district's acclaimed 30-year-old Water Factory 21, which has been treating 14-mgd secondary flows to slightly lesser standards, then mixing the product with almost 9 mgd of water drawn from deep wells and injecting the mix into a barrier to halt seawater intrusion.