Environmental Engineering Reference
In-Depth Information
and changes in pollutant loads by comparing data collected in the past. Quantitative
data of pollutant load from road surface will provide planners of watershed man-
agement with basic information for establishing precise the CBPSW and deciding
the priority order of measures for controlling urban nonpoint sources (Table
1
).
Method
Surveys were conducted in four cities in Japan twice in each site in 2006-2007 by
sprinkling water. In each city, residential, commercial and industrial districts were
extracted, and survey was conducted at three mutually close points in each sites. All
the survey points were one-lane road each way and were set at where the nearby
land use was uniform and there were no other pollutant sources, such as greenery
and parks.
Equipment Used for the Survey
In the nationwide survey, mobile sprinkling equipment was prepared and used to
reproduce rainfall events. The equipment has nozzles at the top from which water
is sprinkled to reproduce rainfall artificially. Since pollutants are highly probable to
be unevenly distributed on road surfaces, pollutants on the entire lane were decided
to be collected. Thus, the sprinkling equipment was designed so as to change the
length according to the width of the road. In a preliminary test, the equipment was
verified to be capable of uniformly sprinkling water over road surface. The equip-
ment is shown in detail in Fig.
1
a and b. Moreover, the concentrations of the pol-
lutants in runoff water were found to be high soon after the start of sprinkling but
converged into certain values in 20 min after the start of spraying.
Methods of the Sprinkling Survey
The survey was conducted by first checking that the antecedent precipitation at the
target site had been zero over at least 4 days and then spraying water at 30 mm/h
for 60 min.
A preliminary test was also performed to compare data with that when the
artificial rainfall intensity was set at 50 mm/h, in which almost no difference was
shown. The runoff water from the road surface was collected in the street inlet and
was all pumped into a container using a small pump. Specimens were sampled
and subjected to quality analysis. Then, the road surface was scrubbed using a
nylon brush for 20 min while spraying water at 30 mm/h to wash out pollutants.
The scrubbing force was adjusted to be uniform in all survey points by installing metal
