Selection of Water Quality Parameters

Water quality parameters included in urban hydrological studies may be divided into seven groups. Those parameters, relating to a specific drainage problem, are listed in Table 9.22.1, along with their detection limits, precision level of analysis, and study objectives. In most cases, only biochemical oxygen demand (BOD), chemical oxygen demand (COD), and total suspended solids (TSS) are initially studied, but if these parameters show high values, some other parameters can be taken into account (i.e. Kjeldahl nitrogen, total phosphorous, and volatile suspended solids [VSS]). As the program continues, some special investigation should be made on trace elements and other special parameters mentioned in Table 9.22.1.

Solids are good indicators of urban water quality, as they may contain pollutant materials. Suspended solids are closely related to other pollutant concentrations. In fact, sample uniformity is not easily achieved. Suspended solid concentrations are affected by the flow level, which is not taken into account by manual or automatic sampling. The sampler itself may also introduce effects that can modify the gradient profile of suspended solids. Conditions at the sampler intake cannot be adapted to the flow variations encountered in storm sewers or combined sewers during high flows.

If the sampler cannot be precisely measured in the collected samples, sample uniformity can be questionable. In most cases, suspended solids are regarded as a rough indicator of water quality, so this should be among the parameters selected.

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