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406 Chapter 12 Urban Runoff and Combined Sewer Overflow Management
12.3.3 Determine Existing Conditions

After initiating the program, the planning team must develop a greater understanding of
existing watershed characteristics and water resource conditions in order to:

1. Define existing conditions pertinent to the urban runoff management and control
program.
2. Identify data gaps.
3. Maximize use of existing available information and data.
4. Organize a diverse set of information in a usable way.
The required research is typically done by gathering existing available watershed in-
formation (e.g., environmental, infrastructure, municipal, and pollution source informa-
tion), as well as receiving-water data (e.g., hydrologic, chemical, and biological data, and
water quality standards and criteria). This information can be obtained from various data-
bases; mapping resources; and federal, state, and local agencies. The information can then
be used to develop watershed maps; to determine water, sediment, and biological quality;
and to establish the current status of streams, rivers, and other natural resources. Once
these data are gathered, the program team can organize the information into a coherent de-
scription of existing conditions and determine gaps in knowledge. In this way, the existing
conditions of the watershed and receiving waters can be defined.

12.3.4 Set Site-Specific Goals

Setting goals is a key aspect of the planning process, and refining goals is an ongoing con-
sideration. Projects that deal with multiple point and nonpoint sources require an inte-
grated urban runoff management program, including flood, drainage, and pollution pre-
vention and control. Successful implementation of these programs depends on establishing
clear goals and objectives that are quantitative, measurable, and flexible. Setting goals is a
process that moves from less to more specificity as additional information on the water-
shed and water resources is obtained. Figure 12.4 shows the iterative nature of setting pro-
gram goals as the planning process proceeds.
The two main types of urban runoff goals are water resource- and technology-based
goals. Water resource-based goals are based on receiving-water standards, which consist of
designated uses and criteria to protect these uses. For example, water resource-based goals
may include reducing the number of oxygen-demanding substances in a lake. In addition,
water resource-based goals can place numerical limits on the concentrations of specific
pollutants. Further, examples of water resource-based goals include no degradation, no sig-
nificant degradation, and meeting water quality standards. Applying water resource goals
to urban runoff problems, however, might be difficult because water quality standards
would need to be assigned to intermittent and variable events.
In contrast, technology-based goals require specific pollution prevention or control
measures to address water resource problems. They can be very general, such as “imple-
ment the nine minimum technologies for CSO control,” or very specific, such as “imple-
menting runoff detention at 50% of the industrial sites in a watershed.” A municipality
might be able to determine the effectiveness of implementing these goals without conduct-
ing future water quality monitoring. With most technology-based goals, implementing the
control measures is presumed to be adequate to protect water resources. Monitoring, how-
ever, is still essential after implementation to gauge the program’s effectiveness and to see
if the desired environmental results are being achieved.