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Figure 2-9 Population served by POTWs nationwide for select years between 1940 and 1996 organized by wastewater treatment type. Sources: U.S. Public Health Service Municipal Wastewater Inventories and USEPA Clean Water Needs Surveys.

CWA), about 39 percent of the 140.1 million people were served by POTWs providing only raw or less than secondary wastewater treatment. By 1996 (24 years after the 1972 CWA), this percentage was reduced to about 9 percent; only 17.2 million people of the 189.7 million served by POTWs received less than secondary wastewater treatment.

• Stated another way, the U.S. population served by POTWs with secondary or greater treatment almost doubled between 1968 and 1996, from 85.9 million people in 1968 to 164.8 million people in 1996! [It is noted that 5.1 million of the 17.2 million people served by less than secondary facilities in 1996 were connected to 45 POTW facilities granted CWA Section 301(h) waivers (nine pending final waiver decision as of November 1998), which allow the discharge of primary or advanced primary effluent to deep, well-mixed ocean waters.]

• Although the number of people served by POTWs with secondary treatment remained fairly constant between 1968 and 1996 (a slight decrease of 3.7 million people or about 4 percent of the population), the number of people provided with greater than secondary treatment increased significantly (from 0.3 million people in 1968 to 82.9 million people in 1996). This is consistent with the trend since 1968 in increasing numbers of POTWs providing greater than secondary treatment, as shown in Table 2-4.

Trends in Influent BOD Loading to POTWs

Table 2-6 presents nationwide influent loading of CBOD5, CBODu, NBODu, and BODu organized by wastewater treatment type for select years from 1940 to 1996.

TABLE 2-6 Influent BOD Loading to POTWs by Wastewater Treatment Type, 1940-1996

Influent CBOD5 Loading (mt/day)

TABLE 2-6 Influent BOD Loading to POTWs by Wastewater Treatment Type, 1940-1996

Influent CBOD5 Loading (mt/day)

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