248 ENVIRONMENTAL ENGINEERING
'Igble 11-7. Typical Pollutant Removal Efficiencies for BMPs
TSS TP TN Metals PathogensCatch basin
Catch basin + sand filter
Constructed wetlands
Grassed swale
Infiltration basidtrench
Porous pavement
Sand filters
Vegetated filter strip
Wet pond
60-97
70-90
50-90
20-40
50-99
60-90
60-90
40-90
50-90na
na
0-80
20-40
50-100
60-90
0-80
30-80
20-90~
na
30-40
0-40
10-30
50-100
60-90
20-40
20-60
10-90na
50-90
30-95
10-60
50-100
60-90
40-80
20-80
10-95~~
na
na
na
na
75-98
na
40
na
naFrom EPA 1993.CONCLUSIONControlling nonpoint source pollution in our waterways is currently one of the biggest
challenges facing engineers, regulators, and scientists. Many nonpoint pollutants orig-
inate from common, everyday human activities, like driving a car, putting in a new rose
bed, walking the dog, or building a house. Because of its widespread nature, nonpoint
source pollution is difficult to contain, even harder to eliminate, and costly to mitigate.
Source control through public education, community planning, and regulatory guide-
lines can be very effective, but often requires substantial changes in human behavior.
Technological approaches, such as storm water BMPs, can help reduce nonpoint source
pollution, but rarely if ever eliminate it entirely. Add to this, it is difficult to predict
whether a pollution reduction effort will be successful because of the large variability
in performances seen in the existing storm water treatment systems. Given the rapid
changes occurring in nonpoint source pollution treatment technology, it is important to
continue gathering information on what works, what does not work, and what factors
contribute to successful nonpoint source pollution reduction.
PROBLEMS11.1 Use Table 11-1 compare the relative concentrations of nonpoint source pol-
lutants coning from construction sites vs those from urban runoff. How would you
rank these same pollutants in terms of harm to the environment? Compare and discuss
both rankings.
11.2 Contact the Soil Conservation Service agent in your area and calculate the
soil loss from 500 acres of cropland using the USLE. Assume:-conventional tillage
-cornstalks remain in field after harvest