Combined Sewer System Long Term Control Plan - DC Water

Existing Conditions
Section 2
Existing Conditions
2.1 INTRODUCTION
This section discusses physical features and the framework of regulations that affect the development
and selection of the CSS Long Term Control Plan. Physical features that have the greatest impact on
the District receiving waters are their watersheds and the regional rainfall patterns. Governing
regulations are concerned with water quality and sensitive areas; and establish criteria upon which
the LTCP will be selected.
2.2 WATERSHEDS
The USEPA CSO Control Policy emphasizes the importance of the watershed approach in the
development of a Long Term Control Plan (LTCP) for CSOs. Of particular importance to CSO
control planning and management is the NPDES Watershed Strategy (USEPA, 1994). This strategy
outlines national objectives and implementation activities to integrate the NPDES program into the
broader watershed protection approach. The major advantage in using a watershed-based approach in
LTCP development is that it allows for the site-specific determination of the relative impacts of
CSOs and non-CSO sources of pollution on water quality (USEPA, 1995).
There are three principal waterbodies within the District. These are the Potomac River, Anacostia
River and Rock Creek. Figure 2-1 shows the watersheds of these waterbodies with drainage areas
extending across multiple states and/or jurisdictions. Both the Anacostia River and Rock Creek
watersheds include land area in Maryland and the District. The Potomac watershed includes land area
in Virginia, West Virginia, Maryland, Pennsylvania and the District. As shown in the Figure 2-1,
the Anacostia and Rock Creek are sub-watersheds of the entire Potomac River basin (EPMC-III,
1999c). The District encompasses only a small portion of each watershed. General information
about each of the three watersheds including physical characteristics and pollution sources is
summarized in Table 2-1 below.
Table 2-1
Watershed Characteristics
Characteristic Anacostia River Potomac River Rock Creek
Population Population – Slightly over
761,000
Population – the majority exist along the
river in the Washington Metropolitan area
Population – slightly over
408,000
Land Use Land Use – Primarily
residential, agricultural and
commercial/industrial
Land Use – Primarily agricultural and
forest land
Land Use – Primarily
residential, agricultural and
commercial/industrial
Topography
Generally flat within the
District, flat and rolling hills
upstream of the District
Upper Watershed – steep mountainous
terrain
Lower Watershed – rolling hills and flat
within the District
Generally moderate grades
within the District, rolling hills
upstream of the District
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