Level of treatment	1988	1992	1996	1996 facilities design capacity	1996 population served
	number of facilities			mgd	millions	%
Non-discharge	1,854	1,981	2,032	1,421	7.66	2.9
< Secondary	1,769	868	176	3,054	17.18	6.5
Secondary	3,536	9,086	9,388	17,734	81.94	31.0
> Secondary	3,412	3,678	4,428	20,016	82.93	31.4
Total	15,591	15,613	16,024	42,225	189.71	71.8

Source:  U.S. Environmental Protection Agency, Office of Wastewater Management, 1996 Clean Water Needs Survey Report to Congress (Washington, DC, 1998), and earlier reports in this series.

Notes:  mgd = millions of gallons per day. Non-discharge = facilities that do not discharge effluent to surface waters (e.g., spray irrigation, ground water recharge). A secondary treatment level is defined as an effluent biochemical oxygen demand (BOD) of between 25 and 30 milligrams per liter.

Last Updated on 1/22/01