Abstract
Introduction
One of the major issues of urban wet weather pollution is the control of floatables
pollution. Many urban areas experience beach wash-ups and shore-line accumulations of
floatable materials such plastic, paper and styrofoam items. Studies conducted in New York
City have shown street litter to be a major contributor of floatables pollution to New
York Harbor. Several floatables control methods are being considered including increased
street sweeping, end of pipe treatment technologies, booming and skimming at CSO outfalls
and catch basin controls. Catch basins, which exist in most urban areas, offer a means of
controlling floatable material at the source. They are simple devices, which if properly
maintained, can be very effective in removing floatable material from stormwater. This
paper presents New York City's efforts in evaluating the effectiveness of catch basins,
outlines the City-wide program to inspect, map and hood all catch basins and presents data
which characterizes the effectiveness of the program.
Catch basin designs for most urban areas throughout the US are similar. The most important
aspect of this design, with respect to floatables removal, is the presence of a hood or
trap which is generally hung over the basin's outlet. The hood, which extends into the
water surface, provides a seal which prevents the release of sewer odors into the
surrounding neighborhood. The hood also acts as a baffle at the water surface which
prevents the release of floatable material to the sewer system. Several studies conducted
in New York City have shown hoods to be capable of retainng 70 to 90% of floatables
entering the catch basin.
New York City is implementing a City-wide catch basin hooding program as part of its CSO
control program. This effort includes inspection, inventory and mapping of all catch
basins. There are approximately 135,000 basins distributed over 190,000 acres in New York
City. Following the inspections, basins are cleaned and hoods are installed where needed.
The program was started in February 1996 and is expected to be completed by the end of
1999.
A database is being constructed from the information being collected during the
inspections which includes approximately 150 data items per basin. GIS mapping of the
basins is being integrated with the database to produce a comprehensive management tool
which will be used to direct future catch basin maintenance and repair activities. This
program, with periodic basin inspections, will provide a means of maintaining hoods on
catch basins and thereby ensure the effective use of catch basins as a floatables control.
The program is also very cost effective when compared to other floatable control
technologies. Figure 1 presents approximate costs of several technologies, ranging
from less that $100 per acre to approximately $10,000 per acre. As shown in the figure the
cost of catch basin hooding is significantly less than most other options. Catch basin
hooding also folds into existing catch basin maintenance programs very easily. New
equipment, procedures and training are generally not necessary to put a program in place.
New York City constructed floatables booms around several CSO outfalls as part of an
interim floatables control program. Following wet weather events, floatable material
captured by the booms is removed by skimmer boats and transported to roll-off containers.
This program was in place prior to the catch basin hooding program and offered a means of
assessing the effectiveness of the hooding program. Figure 2 presents a bar graph of
City-wide floatables loads captured in the City's booms between January 1997 and September
1998. During this period catch basin hoods were installed in over 60% of the boomed
drainage area. Concurrent to the hooding program a significant reduction in floatables
loads was observed. By September 1998 the load was reduced by approximately 70% from the
January 1997 levels. These loads will continue to be monitored as the hooding program
approaches completion through 1999.
Catch basin hoods are proving to be a very effective means of controlling floatables in
urban areas, both in terms of cost and capture efficiency. These devices control floatable
material as close to the source as possible. The residuals created by the device can be
collected during normal catch basin cleaning activities. They are simple low-tech devices
that do not require any extensive facilities, staff or specialized training. |
Authors:
- Gary M. Grey,
Associate
- HydroQual, Inc.
1200 MacArthur Blvd.
Mahwah, NJ 07430
(201) 529-5151
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- Frank Oliveri, P.E., Chief, Sewer Analysis
- Bureau of Water Supply & Wastewater Collection
New York City Department of Environmental Protection
59-17 Junction Blvd.
Corona, NY 11368-5107
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