Environmental Engineering Reference
In-Depth Information
In the assessment of faecal contaminants and pathogens in water environments,
indicator organisms have been traditionally used. Total coliforms and
E. coli
are indi-
cator bacteria commonly used for regular monitoring in drinking water sources. Indicator
organisms used for parasites are intestinal enterococci and sulphite-reducing
clostridia and for viruses bacteriophages is used, which all tend to survive longer
in the water environment than
E. coli
making them more useful as indicators for
environmentally resistant pathogens
[9]
. Bacteriophages, of which coliphages are
the most common, are considered as model organisms of enteric viruses in water
[9]
, for example to assess the virus removal efficiency for water treatment facilities
such as in stormwater ponds.
This paper presents field measurements on the levels of stormwater contamina-
tion, and the relative removal of microbial, physical and chemical contaminants in
a traditional stormwater pond. Also a discussion on relative removal of virus par-
ticles in relation to the human health risk associated with pathogens in raw water
sources is included.
Experimental Method
The pond that has been studied in this paper is the Järnbrott stormwater pond situ-
ated 5 km from the city of Göteborg. It has been investigated in previous studies
[1, 10, 11]
, and is an off-stream stormwater pond with a permanent pool, and with
no constant inflow during dry periods. The pond is divided into three sections
with different bottom materials and with water depths between 0.6 and 1.5 m.
The catchment area consists of about 160 ha impervious surfaces and is a mix of
residential, industrial and traffic areas. For metals and PAH, the major source in
the catchment is expected to be the traffic, where an important highway is situated
within the catchment. Possible sources of microbial contaminants in the catchment
include commercial and residential settlements, where faecal bacteria may origi-
nate from domestic and wild animals. Since the catchment only include separate
sewer systems, household sewage will not contaminate the stormwater entering
the pond.
Three storm events during fall 2004 (22 October, 18 November and 24 November
2004) were sampled using two ISCO 6700 samplers that were installed at the inlet
and the outlet of the stormwater pond. The samplers were equipped with flow
meters which monitored the flow and triggered flow-weighted sampling during
the storm events. The inlet sampler was equipped with a velocity-height (V/H)
probe (ISCO 750 module) and the outlet sampler with a pressure probe (ISCO 720)
close to the outlet concrete weir. The samplers, equipped with 12 (1 L) plastic and
glass bottles, were programmed to take a subsample at every 800 m
3
of stormwater
passing the measuring point at the inlet and outlet respectively. Each sample was added
to a set of two bottles (totally six sets, each representing 4,800 m
3
of stormwater)
and were kept at ambient temperatures (0-10°C) in the sampler. The samples were
transported in cold to the laboratory for analysis. Characteristics of the three storm
