Following the precedent established by these earlier before-and-after assessments of changes in water quality that can be attributed, in part, to the effluent control regulations of the CWA, a number of freshwater and estuarine waterbodies were selected as case studies for this report. Criteria for the selection of case study sites included the following:
• The major river or estuarine system was identified in the 1960s as having gross water pollution problems.
• The major river or estuarine system lies in a major urban-industrial region.
• Municipal wastewater is a significant component of the point source pollutant load to the system.
• Water quality models were available to evaluate the water quality impact of simulated primary, secondary, and actual effluent scenarios for municipal dischargers.
• Historical data were readily available.
Table 4-1 provides the 1996 population for the Metropolitan Statistical Areas (MSAs) and counties included in the case study, and the types of data and information compiled for each river or estuarine waterbody selected as a case study. The population of the case study MSAs (43.2 million) accounted for 16 percent of the nation's total population in 1996 (265.2 million) (USDOC, 1998). Figure 4-1 shows the location of the case study watersheds. In contrast to some of the other case study assessments discussed previously, the case studies in this report were specifically selected because they represent large cities located on major waterways known to have been plagued by serious water pollution problems during the 1950s and 1960s (Table 4-2). Many of the case study waterways either were the sites of interstate enforcement conferences from 1957 to 1972 or were listed by the federal government as being potential waterways to convene state-federal enforcement conferences in 1963 (Zwick and Benstock, 1971) (see Appendix A). Two of the case studies, the Ohio River and tributaries to New York Harbor (Passaic River and Arthur Kill), were identified by the federal government in 1970 in a list of the top ten most polluted rivers (Zwick and Benstock, 1971). The Department of the Interior identified all the estuarine case study sites as waterways suffering from either low oxygen levels or bacterial contamination in a national study of estuarine water quality (USDOI, 1970). All but two of the case study areas were the subject of water quality evaluation reports prepared for the National Commission on Water Quality (NCWQ) to provide baseline data to track the effectiveness of the technology-based effluent controls required under the newly enacted 1972 CWA (see Mitchell, 1976). With the exception of the James River, enforcement actions were initiated by the Federal government for all the case study rivers (see Appendix A-4).
For all the case studies, data have been compiled to characterize long-term trends (more than 50 years) beginning in 1940 for population, upgrades to municipal waste-water facilities, effluent loading, water quality, environmental resources, and recreational uses. Additional data have been obtained from validated water quality models for the Upper Mississippi River, Potomac estuary, Delaware estuary, and James estuary to quantify improvements in water quality achieved by municipal upgrades from primary to secondary or advanced treatment levels. Data sources include published scientific and technical literature, USEPA's STORET database, and unpublished technical reports ("grey" literature) prepared by consultants and state, local, and federal agencies.
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