United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-83-043 Aug. 1983
Project Summary
Evaluation of Catchbasin
Performance for Urban
Storm water Pollution Control
Gerald L Aronson, David & Watson, and William C Pisano
Data were collected in the field to
evaluate the performance and utility of
catchbasins in controlling pollution.
The project had three phases. The first
two were field data collection efforts
and the third involved data reduction
and analysis.
In the first phase of field work, three
catchbasins in the West Roxbury sec-
tion of Boston, Massachusetts, were
selected from more than 40 sites
throughout the city. The catchbasins
chosen illustrated a diversity of land
use, traffic situations, and design types.
First, each basin was cleaned using
traditional methods; then four runoff
events were monitored at each catch-
basin to evaluate performance. Influent
effluent sump liquid, and sump sedi-
ment were monitored.
Catchbasin suspended solids re-
movals varied widely, from a minus 10
percent (discharging before sump ac-
cumulations) to a positive 90 percent
On the whole, catchbasins were quite
effective for reducing solids (on the
order of 60 to 97 percent). Catchbasin
removals of associated pollutants such
as chemical oxygen demand (COD) and
biochemical oxygen demand (BOD)
were also significant (on the order of
10 to 56 percent and 54 to 88 percent
respectively).
The second phase of work involved
the addition of an inlet strainer to each
of the catchbasins according to Euro-
pean practice. The inlet strainers con-
sisted of a number 8 mesh (0.0937
in./2.36 mm) brass screen permanently
mounted on an aluminum backing plate.
Runoff for an additional three events
was monitored at each site during this
phase of work Inlet strainers provided
a marginal increase in catchbasin pol-
lutant removal (up to 10 percent).
This Project Summary was developed
byEPA's Municipal Environmental Re-
search Laboratory. Cincinnati. OH. to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information
at back).
Introduction
Purpose of Study
Control of stormwater runoff is a signifi-
cant problem in the field of water quality
management Over the past 70 years,
catchbasins have been used extensively
to remove coarse materials from storm-
water runoff. Yet their effectiveness (in
removing pollutants) has not been evalu-
ated in depth.
In a recent report by J.A Lager et a/.,
entitled "Catchbasin Technology Overview
and Assessment" (USEPA report number
EPA-600/2-77-051 (NTIS order number
PB 270 092)), it was recommended that
monitoring programs be undertaken to:
(1) determine the impact of best manage-
ment practices in reducing solids and
other pollutant loads in surface runoff that
must be collected from urban areas and
introduced to the sewer through catch-
basins, (2) evaluate the effectiveness of
closely monitored catchbasin cleaning pro-
grams with respect to the impacts of
cleaning frequency and techniques on
solids carryover as well as general pollution
abatement and (3) determine the extent
to which solids deposition can be mitigated
by properly designed and functioning
catchbasins.
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These recommendations were based on
an analysis of catchbasin pollutant re-
moval that used secondary data from a
variety of sources. Direct and concurrent
measurement of influent and effluent
pollutant characteristics had not been pre-
viously performed. Prior measurements
included either street surface pollutant
characteristics or spot grab sampling of
catchbasin sump liquor.
The basic purpose of this study was the
careful, simultaneous monitoring of in-
fluent and effluent characteristics for
several catchbasins m the Boston, Mas-
sachusetts, metropolitan area The primary
emphasis was to characterize the pollution
load attenuation characteristics of a catch-
basin. A secondary goal was to examine
the pollutant reduction effectiveness of
strainers inserted into several catchbasins
within the study area. These devices are
used in Europe and have been shown to be
effective for removing gross f loatables and
settleable solids such as cigarette butts,
leaves, lawn clippings, and paper.
Background
A catchbasin is a chamber or well,
usually built at the curbline of a street for
the admission of surface water to a sewer
or subdrain; at its base is a sediment sump
designed to retain coarse solids and de-
tritus below the point of overflow. Because
some communities call any device that
receives stormwater a catchbasin, a distinc-
tion is made between those devices that
intentionally trap sediment and those that
do not In this report the device that traps
sediment is referred to as a catchbasin.
Stormwater runoff in urban areas normally
flows for a short period of time in the
gutter and is diverted by an inlet structure
leading to an underground conduit or
open channel for transportation to a receiv-
ing body of water. The underground
conduit either a storm or combined sewer,
may be protected from clogging by catch-
basins built in conjunction with inlets.
Catchbasins serve two main purposes:
to prevent sewer gases from escaping
through the inlet gratings, and to prevent
heavy or large solid matter and floatables
from the street from entering the sewers.
The trapping of sewer gases is accomplished
by a water seal. The retention of solids is
achieved by providing a sump or settling
basin in which the heavy solids settle to
the bottom and the light solids float on top.
Water drains to the sewers through the
outlet of the catchbasin, which is generally
a few inches below the water surface to
retain floatables and provide a water seal.
These basins are normally built under the
inlet grating or openings, either under the
gutter or just behind the curb. Occasionally,
one catchbasin serves two or more stand-
ard inlets.
In American practice, a standard catch-
basin appears to be nonexistent Attempts
at uniformity within individual cities show
varying degrees of success. The effective-
ness of the water seal gas trap is an
important issue in American practice In
addition, organics that are allowed to ac-
cumulate in the catchbasin may decom-
pose with time and contribute odors similar
to sewer gases even if the water seal has
not evaporated.
Catchbasin sizes vary in Europe, but
they have been standardized in Germany.
Two types of catchbasins are used: a
simple depository type and one generally
called a selective catchbasin, in which a
bucket sieve or some means is used to
select and separate various solid materials.
The latter type varies greatly in different
countries and cities. The buckets provide
and easy and rapid method for cleaning by
street crews.
During the second phase of this study,
inlet strainers were fabricated and installed
in three monitored catchbasins to assess
their pollutant removal effectiveness, thus
simulating the European practice.
Procedures
During the period November 1979
through January 1980, seven runoff
events were monitored at each of three
catchbasin sites, yielding a total of 21
monitored runoff events. All of the catch-
basins were located in the West Roxbury
section of the city of Boston. Analyses
were conducted for total suspended solids
(TSS), volatile suspended solids (VSS),
chemical oxygen demand (COD), bio-
chemical oxygen demand (5-day) (BOD),
total Kjeldahl nitrogen (TKN), total phos-
phorus (TP), sediment particle sizing, and
percent volatiles. Special analyses were
conducted to assess the sump liquid and
solids conditions before and after the
runoff events. Inlet strainers similar to
those used in Europe were specially fabri-
cated, installed in the catchbasins, and
monitored over three runoff events to
assess their impact on overall performances.
Conclusions
1. Catchbasins were very effective in
removing suspended solids-related storm-
water pollutants from influent waste streams
Pollution mass reductions of 60 to 97
percent TSS, 48 to 97 percent VSS, 10 to
56 percent COD, and 54 to 88 percent
BOD were observed for relatively low
intensity storms during December and
January. No data were obtained for sum-
mer type storms.
2. The limited data collected indicated
that catchbasins do little with respect to
nutrient removal.
3. Though the total mass of the influent
to the catchbasins varied widely, the con-
centration profiles of both the influent and
effluent with time were very consistent
4. Sieve analyses of catchbasin sump
sediment samplings (taken 21 times over
the course of the evaluation program)
yielded results consistent with those found
in the literatura
5. Sump sediment was highly organic--
on the order of 60 to 90 percent depending
on particle size range.
6. Inlet strainers were designed, fabri-
cated, and installed on the three test
catchbasins for three runoff events each.
The strainers consistently retained signifi-
cant dry weather accumulations ranging
from 150 to 500 g of dry solids per day.
7. Accumulation of dry weather solids
in the catchbasin inlet strainers seemed to
be primarily a function of degree of vehicular
traffic at each location.
8. Inlet strainers offered a slight gain in
overall pollutant removal efficiency of catch-
basins, but they would not be functional
on a large scale. These devices are effective
for the removal of coarse material that
could cause visual upsets. Problems with
clogging and potential for decomposition
and ultimate discharge of pollutants negated
their value unless weekly (or more frequent)
maintenance was employed.
Recommendations
1. If maintained, catchbasins are an
efficient pollutant reduction/maintenance
tool and should continue to be used.
2. Monitoring studies such as those
conducted in Boston should be done in
other geographic areas to substantiate the
findings of this study. Regions recom-
mended are the midwest south, and west
because of their difference in climate,
hydrology, and system characteristics.
3. Since energy dissipation is of prime
importance to the function of catchbasins,
further research should be conducted into
simple ways of reducing influent energy.
4. Field-scale demonstration of closely
monitored, concurrent street sweeping,
catchbasin cleaning, and sewer maintenance
programs should be conducted in varying
terrain for both separate and combined
sewerage systems to investigate the
optimal mix of best management practices
for maintenance and pollution control. The
main emphasis of the studies should be
the careful monitoring of the separate and
joint effectiveness of these techniques
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and an assessment of the impacts of
cleaning frequency, solids carryover mech-
anisms, general pollution abatement and
associated costs.
5. Additional monitoring studies should
investigate the effectiveness of catchbasins
for removing heavy metals as well as oil
and grease.
The full report was submitted in fulfill-
ment of Grant No. R-804578 by North-
eastern University under the sponsorship
of the U.& Environmental Protection Agency.
GeraldL Aronson, DavidS. Watson, and William C. Pisanoare with Environmental
Design & Planning, Inc., Boston, MA 02134.
Richard Field is the EPA Project Officer (see below).
The complete report, entitled "Evaluation of Catchbasin Performance for Urban
Stormwater Pollution Control," (Order No. PB 83-217 745; Cost: $11.SO,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati. OH 45268
*US GOVERNMENT PRINTING OFFICE' 1983-659-017/7142
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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