Water pollution in the Delaware estuary reached its peak in the 1940s. The source of the pollution was raw sewage (350 mgd from Philadelphia alone), along with untreated industrial wastewater of all kinds. In response to steadily increasing pollution, the Interstate Commission on the Delaware River Basin (INCODEL) launched a basinwide water pollution control program in the late 1930s. Following a delay due to the war, the abatement program was finally completed by the end of the 1950s. During that time, the number of communities with adequate sewage collection and treatment facilities rose from 63 (approximately 20 percent) to 236 (75 percent) (Albert, 1982). Concurrent success was not achieved in abating industrial pollution.
The first generation of water pollution control efforts, largely completed by 1960, resulted in secondary treatment levels at most treatment plants above Philadelphia. Primary treatment was considered adequate in the estuary downstream of Philadelphia. Although most areas built the required facilities, some treatment facilities from the first-generation effort were not completed until the 1960s or 1970s.
In 1961 INCODEL became incorporated into a more powerful interstate regulatory agency, the Delaware River Basin Commission (DRBC). The DRBC, created as a result of federal and state legislation, has broad water resources responsibilities, including water pollution control. The Commission developed a clean-up program based on a 6-year $1.2 million Delaware Estuary Comprehensive Study (DECS), conducted by the U.S. Public Health Service. Nearly 100 municipalities and industries were found to be discharging harmful amounts of waste into the river. Using a water quality model (DECS), the DRBC calculated the river's natural ability to assimilate oxidizable wastewater loads and established allocations for each city and industry (Thomann, 1963; Thomann and Mueller, 1987). The objective of the DRBC wasteload allocation program and the corollary programs of Pennsylvania, New Jersey, Delaware, and the federal government, was to upgrade the somewhat improved water quality of 1960 to more acceptable levels.
For the purposes of water quality management, the Delaware estuary has been divided into six water quality zones. Zone 1 is upstream of the fall line at Trenton, New Jersey. Zones 2 through 6 are in the tidal Delaware, which is water quality-limited. Here, more stringent effluent limits are required, based on allocations of assimilative capacity, to achieve water quality standards. Based on the DECS water quality model, the DRBC, in 1967, adopted new, higher water quality standards, and then in 1968, issued wasteload allocations to approximately 90 dischargers to the estuary. These required treatment levels were more stringent than secondary treatment as defined by USEPA in the 1972 Clean Water Act.
IMPACTS OF WASTEWATER TREATMENT Pollutant Loading and Water Quality Trends
The Delaware River from Trenton, New Jersey, to Liston Point is one of the most heavily industrialized sections of a waterway in the United States. Four major cities and a large number of oil refineries and chemical manufacturing plants are located along the river. The effect of the DRBC wasteload allocation program and the related water pollution control programs of Pennsylvania, New Jersey, Delaware, and the federal government on the Delaware Estuary is best demonstrated by the substantial reduction of ultimate CBOD loading from municipal and industrial dischargers that has been achieved since the late 1950s (Figure 7-6). Ultimate CBOD loadings to the estuary have been reduced by 89 percent, from 515.4 metric tons/day (mt/day) in 1958 (Patrick et al., 1992) to 58.2 mt/day by 1995 (HydroQual, 1998). Major waste-water treatment facilities that upgraded to secondary treatment and better in order to meet the wasteload allocations include Philadelphia NE (1985), Philadelphia SE (1986), Philadelphia SW (1980), CCMUA (1989), Trenton (1982), Bordentown MUA (1991), and Lower Bucks MUA (1980). A complete listing of the 34 municipal and 26 industrial point sources discharging to the Delaware estuary between Trenton and Liston Point is presented in HydroQual (1998). In addition to reductions of pollutant loading from direct dischargers to the estuary, the cleanup of major tributaries to the Delaware has also contributed to water quality improvements in the Delaware estuary (Albert, 1982).
Since implementation of the 1972 CWA, reductions in point source loads of oxi-dizable materials have been achieved as a result of technology- and water quality-based effluent controls on municipal and industrial dischargers in the Delaware River watershed. Nonpoint source runoff, driven by the land uses and hydrologic characteristics of the watershed, also contributes a pollutant load that must be considered in a complete evaluation of the impact of regulatory policy and controls on long-term
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