Delaware Estuary Case Study

The Mid-Atlantic Basin (Hydrologic Region 2), covering a drainage area of 111,417 square miles, includes some of the major rivers in the continental United States. Figure 7-1 highlights the location of the basin and the Delaware estuary, the case study watershed profiled in this chapter.

With a length of 390 miles and a drainage area of 11,440 square miles, the Delaware River ranks seventeenth among the 135 U.S. rivers that are more than 100 miles in length. On the basis of mean annual discharge (1941-1970), the Delaware ranks twenty-eighth (17,200 cfs) of large rivers in the United States (Iseri and Langbein, 1974). Figure 7-2 highlights the location of the Delaware estuary case study catalog units identified by major urban-industrial areas affected by severe water pollution problems during the 1950s and 1960s (see Table 4-2). This chapter presents long-term trends in population, municipal wastewater infrastructure and effluent loading of pollutants, ambient water quality, environmental resources, and uses of the Delaware estuary. Data sources include USEPA's national water quality database (STORET), published technical literature, and unpublished technical reports ("grey" literature) obtained from local agency sources.

The Delaware River, formed by the confluence of its east and west branches in the Catskill Mountains near Hancock, New York, on the Pennsylvania-New York state line, becomes tidal at Trenton, New Jersey (Figure 7-2). The first 86 miles of the tidal river are the Delaware River estuary, which flows by Trenton, New Jersey; Philadelphia, Pennsylvania; Camden, New Jersey; and Wilmington, Delaware. This major urban-industrial area has a tremendous impact on the water quality of the river. In this area, the Delaware River estuary flows along the boundary between the Piedmont Plateau and the Atlantic Coastal Plain. A large number of municipal and industrial wastewater facilities discharge to the Delaware River, with municipal water pollution control plants accounting for the largest component of BOD5 loading. In general, water quality is good at the head of the tide at Trenton (RM 134.3), but it begins to deteriorate downstream.

From the 1930s through the 1970s, water quality conditions were very poor. Depleted DO levels were recorded in the region from Torresdale (RM 110.7) to Eddy-stone (RM 84.0) as a result of wastewater loading from Philadelphia (RM 110-93). Since the mid-1980s, water quality conditions in the estuary have improved significantly.

Figure 7-1 Hydrologie Region 2 and Delaware estuary watershed.

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