The objectives of field monitoring water quality in drainage studies include:
• Analyzing the impact on receiving waters of (1) storm sewer discharges, (2) combined sewer overflows, (3) atmospheric fallout and urban activities, and (4) new facilities or treatment plants designed to reduce environment impacts.
• Identifying the contributions of various land uses to total pollution discharge, to optimize urban development and derive some regulations such as source control.
• Increasing existing treatment efficiency during wet weather in combined sewer systems.
• Analyzing of scour and deposit problems in sewers to define optimal cleaning sequences or to design facilities for better hydraulic conditions.
To fulfill these objectives, storm water discharges need to be sampled during dry-weather and wet-weather conditions. Water quality data gathered during dry weather provide a baseline and indicate point source impacts.
To trace contaminants and identify pollutant sources, a phased monitoring approach requires repeated investi gation of land use activities in a basin. The program is expected to be an iterative process, as several rounds of sampling are generally required. Precise data are essential for calibrating and verifying nonpoint source models.
Experience proves that water quality data collection programs can be costly. Collection procedures have high manpower requirements, as frequent site visits are required. The cost of analyzing collected samples may increase rapidly with the number and types of pollutants studied. It is important that the parameters to be studied are carefully selected and limited to the essentials.
This section presents an outline of water quality parameters important in studies on urban stormwater discharges, and reveals the main difficulties in obtaining representative samples. Also included is a brief discussion on data analysis.
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