BOX 1-2 Water Factory 21 in Orange County, California

The Orange County Water District (OCWD) has been injecting high quality reclaimed water into selected coastal aquifers to establish a salt water intrusion barrier. Seawater intrusion was first observed in municipal wells during the 1930s as a consequence of basin overdraft. Overdrafting of the ground water continued into the 1950s. Overpumping of the ground water resulted in seawater intrusion as far as 5.6 km (3.5 miles) inland from the Pacific Ocean by the 1960s.

OCWD began pilot studies in 1965 to determine the feasibility of injecting effluent from an advanced wastewater treatment (AWI) facility into potable water supply aquifers. Construction of an AWT facility, known as Water Factory 21, began in 1972 in Fountain Valley, and injection of the treated municipal wastewater into the ground began in 1976.

Water Factory 21 accepts activated sludge secondary effluent from the adjacent County Sanitation Districts of Orange County wastewater treatment facility. The 5.7 x 107 liter/day (15 x 106 gal/day) water reclamation plant processes consist of lime clarification for removal of suspended solids, heavy metals, and dissolved minerals; recarbonation for pH control; mixed-media filtration for removal of suspended solids; activated carbon absorption for removal of dissolved organic compounds; reverse osmosis for demineralization and removal of other constituents; and chlorination for disinfection and algae control (National Research Council, 1994).

Prior to injection, the product water is blended 2:1 with deep well water from an aquifer not subject to contamination. The blended water is chlorinated in a blending reservoir before it is injected into the ground. Depending on conditions, the injected water flows toward the ocean, forming a seawater barrier; inland to augment the potable ground water supply; or in both directions. On average, well over 50 percent of the injected water flows inland. It is estimated that this injected water makes up no more than 5 percent of the water supply for area residents who rely on ground water.

sources of drinking water supply. (The removal of particular chemical and microbiological constituents of concern is discussed in more detail in Chapter 2.)

History of Planned Potable Reuse and Its Motivation

Direct potable reuse is not currently approved for use in U.S. water systems. The only documented case of an operational direct potable reuse system is in Windhoek, Namibia, in southern Africa. For 30 years, this facility has been used intermittently to forestall water emergencies during drought conditions (Harhoff and van der Merwe, 1996; see Box 1-3). While direct potable reuse is not practiced in the United States,

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