The studies conducted at the six projects varied from simple two-test studies to more comprehensive evaluations. The studies and their main findings are described briefly below; Table 5-1 provides further details.

In 1980, the U.S. Army Corps of Engineers began a two-year testing program of the Potomac Estuary Experimental Water Treatment Plant (EEWTP). Influent to the EEWTP was a 1:1 blend of estuary water and nitrified secondary effluent from the Blue Plains Wastewater Treatment Plant, which treats municipal wastewater from Washington, D.C. The blended water received further treatment by aeration, coagulation, flocculation, sedimentation, pre-disinfection, filtration, carbon adsorption, and post-disinfection.

Short-term in vitro tests (specifically, the Ames Salmonella/microsome test and a mammalian cell transformation test) were run on the EEWTP's blended influent, its effluent, and product water from three local conventional water treatment plants. For the toxicological parameters measured, the study found the EEWTP product water comparable to the finished waters from the local water treatment plants (James M. Montgomery, 1983). However, a National Research Council review panel (NRC, 1984) did not concur with this conclusion, because of the limited toxicological tests that were conducted.

The only toxicological study conducted to date on an operating indirect potable reuse project was performed as part of a five-year health-effect study, initiated in 1978, that evaluated possible effects resulting from surface spreading of reclaimed water in the Montebello Forebay area of Los Angeles County, California. Since inception of the potable reuse project in 1962, reclaimed water has been blended with local storm water and river water prior to percolation. At the time of the study, reclaimed water supplied about 16 percent of the total inflow to the ground water basin. Disinfected secondary effluent was used for recharge from 1962 to 1977, at which time dual-media filtration was added to the three wastewater treatment plants producing the product water. The toxicological study sought to detect, isolate, characterize, and if possible, trace