Environmental Engineering Reference
In-Depth Information
determined, it would allow the determination of characteristic “unit loads” for specified
land use practices, which are expressed as the mass of pollution constituents per unit area
for a specified time, e.g. kg SS/ha.year. Unit loads include background pollution loads.
They are basic parameters for the application of models for pollution assessment and
abatement, which forms part of the WAC regulatory concept. However, EMCs are site
specific and depend on a variety of factors, and their determination should be carried on
for each specific case as an individual exercise. Some examples of basic types of land use
practice in agricultural areas are croplands, pastures and forests. In urban areas the
different types of land use patterns are described in Chapter 1.
It should be noted that EMCs from agricultural areas might vary extremely, even
within a geographic boundary, while EMCs in urban areas show a better correlation with
the corresponding type of land use practice (Novotny 2003). For this reason, the
monitoring network design should give more emphasis on urban areas, and the frequency
of sampling should be event-orientated towards typical storm events with a low return
period, which generates runoff. Also, the provision of discharge-integrated sampling is
imperative. The selection of parameters depends on each specific case, but the basic
recommended ones are: pH, DO, EC, turbidity, TS, TDS, TSS, general organic material
(BOD, COD or TOC), different forms of nutrients, toxic metals and other listed
compounds, which might be suspected to be present in the runoff.
In general, the EMCs of runoff are much lower compared to different types of
wastewater. To illustrate this, Table 2.1 presents data from a nation wide regression
analysis of urban runoff pollution in the USA, for different types of urban land use
practice. However, the large volumes of untreated runoff result in a considerable
pollution load to water bodies, which could have a substantial impact on the environment
and public health and needs to be considered in the integrated assessment of water
resources management.
Table 2.1. USA median values of runoff
concentrations from different land use practices (in
mg/l).
Pollutant
Residential
Mixed
Commercial
Natural open area
BOD
10
7.8
9.3
COD
73
65
57
40
TSS
101
67
69
70
Lead (total)
0.14
0.11
0.10
0.03
Copper (total)
0.03
0.03
0.03
Zinc (total)
0.13
0.15
0.23
0.19
TKN
1.90
1.30
1.18
0.97
Nitrate + Nitrite
0.74
0.56
0.57
0.54
Phosphorous (total)
0.38
0.26
0.20
0.12
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