United States
Environmental Protection
Agency
Off ice of Water
Washington, D.C.
EPA832-F-01-004
September 2001
Storm Water
Technology Fact Sheet
Baffle Boxes
DESCRIPTION
Baffle boxes are concrete or fiberglass structures
containing a series of sediment settling chambers
separated by baffles. The primary function of baffle
boxes is to remove sediment, suspended particles,
and associated pollutants from storm water. Baffle
boxes may also contain trash screens or skimmers
to capture larger materials, trash, and floatables.
Baffle boxes are located either in-line or at the end
of storm pipes. Figure 1 shows a typical baffle box
design.
The use of baffle boxes for pollutant removal is
based on the concept of slowing the flow velocity
through the box, thereby allowing solids and
associated pollutants to settle to the bottom of the
box. Storm water enters the box and begins to fill
the first chamber. As water encounters the baffles,
flow velocity decreases, allowing particles with a
settling velocity greater than the horizontal flow
velocity to settle to the bottom of the box. In
addition to decreasing flow velocities, the baffles
impede particle movement. As suspended solids
strike the baffles they begin to settle. Larger
particles usually settle out first and accumulate in
the first chambers while smaller particles usually
settle out in subsequent chambers.
ACCUMULATED
SEDIMENT
Source: Modified from Suntree Technologies, Inc., 2000.
FIGURE 1 SCHEMATIC OF A BAFFLE BOX
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APPLICABILITY
Baffle boxes have proven effective in removing
sediment from storm water runoff. They are mainly
utilized in areas where sediment control is a
primary concern, while other storm water Best
Management Practices (BMPs) may be more
effective in areas where additional storm water
pollutants, such as dissolved nutrients, oil and
grease, or metals, are prevalent.
Florida has used baffle boxes for several years. By
1998, Brevard County, Florida, had 42 baffle boxes
serving residential areas, collecting runoff from
lawns, driveways, and streets. Sediment
accumulation in the baffle boxes varies greatly and
depends on site characteristics such as drainage
area, land use, soil type, and slope. In addition,
non-wet weather flows, such as runoff from
domestic activities like washing cars or watering
lawns, can increase sediment contributions to storm
sewers.
Baffle boxes are ideally suited for retrofitting into
existing storm pipes. Baffle boxes for pipes up to
48 inches in diameter can be precast, making
installation quick and cost-efficient. Baffle boxes
can be used for pipes up to 60 inches in diameter,
but these boxes must be cast in place, making them
more expensive and time-consuming to install.
Baffle boxes are principally designed for sediment
removal, but trash racks, screens, or skimmers can
be installed to trap floatables and oil and grease as
well.
ADVANTAGES AND DISADVANTAGES
Baffle boxes are simple, inexpensive storm water
BMPs that effectively remove sediment and
suspended solids from storm water. A primary
advantage of baffle boxes is that they can be
retrofitted into existing storm lines, allowing
installation within existing rights-of-way. This is
especially important in areas where land is
unavailable or too expensive for other storm water
BMPs.
A major disadvantage of baffle boxes is that they
require significant maintenance to remove
accumulated sediment. If the boxes are not cleaned
regularly, subsequent storms may resuspend the
accumulated sediment and carry it out of the box,
reducing the overall pollutant removal efficiency.
Also, because many trash racks installed in baffle
boxes are hinged at the top to prevent damage from
high hydraulic pressure, they may release
accumulated trash during high flows. Based on
their experience with baffle boxes, officials in
Brevard County recommend checking and cleaning
them every two to three months during the dry
season, and every month during the wet season
(Bateman, et. al., 1998, and National Resources
Defense Council, 1999).
Another disadvantage is that baffle boxes are not
designed for nutrient removal, and may not be an
appropriate storm water BMP if nutrients are a
problem at a particular site. However, because
baffle boxes effectively remove suspended
materials, nutrients attached to sediments may
settle out in the box. In general, modeling results
show that baffle boxes are more effective at
removing larger particles and less effective at
removing smaller particles (Pandit and
Gopatakrishnan, 1996).
DESIGN CRITERIA
The design concept of a sediment [baffle] box is
similar to the design of a three-chamber water
quality inlet (also known as an oil/grit separator).
Many of the earliest baffle boxes were, in effect,
modified septic tanks (Pandit and Gopatakrishnan
1996). Typical baffle boxes are 3 to 5 meters (10 to
15 feet) long, 0.6 meters (2 feet) wider than the
pipe, and 2 to 2.7 meters (6 to 8 feet) high. Weir
height is usually 1 meter (3 feet). Weirs are usually
set at the same level as the pipe invert to minimize
hydraulic losses. Manholes are set over each
chamber to allow easy access for cleaning and
maintenance. Manholes should be located within
15 feet of a paved surface to allow access by
vacuum trucks for box maintenance.
The design of the baffle box can be modified to
promote easy cleaning and to prevent nutrient
leaching from accumulated biota. Some fiberglass
baffle boxes have been designed to include sliding
grates on both ends. These gates are closed during
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cleaning to block flow, allowing removal of
accumulated sediments and trash without
vacuuming up incoming or residual flows. These
baffle boxes also have rounded bottoms that cause
accumulated sediment to collect in the middle of
the box, making it easier to vacuum it out (Suntree
Technologies, Inc., 2000).
Baffle boxes can also be designed with aluminum
screens installed below the inflow pipe but above
the baffles. In this design, incoming flow drops
through the screen, trapping trash, yard waste, and
other debris away from the accumulating water
below. Leaching is reduced because this debris is
kept out of standing water. Therefore, there is less
chance of introducing nutrients into the outflow.
Trash deflectors are set at the outflow end of the
box, reducing the chance of carrying garbage out
with excess flow. Preliminary modeling by the
Florida Institute of Technology indicates that these
screens do not become clogged even under heavy
loads of debris (unpublished data reported by
Suntree Technologies, Inc., 2000).
As flow accumulates in the first chamber, it is
forced over a baffle into the next chamber. Flow
deflectors at the top of the baffle reduce the
possibility of sediment being carried from one
chamber to the next. Flow exits through the outlet
pipe (Suntree Technologies, Inc., 2000).
Possible modifications to a standard baffle box
design to accommodate site-specific conditions
include:
a two-chamber box for small pipes and
small drainage areas;
• a three-chamber box for larger pipes; and
• two multi-chambered boxes in a series.
These design modifications have not been fully
studied. However, the Florida Institute of
Technology used hydraulic scale-modeling to
evaluate box size and shape, along with baffle size
and placement, on pollutant removal efficiency
(Pandit and Gopatakrishnan, 1996). Using three,
four, and five-chambered baffle boxes, this study
evaluated the sediment removal efficiencies of fine
and coarse-grained sediments under several typical
flow rates and sediment concentrations. The
researchers also evaluated the effect of changing the
depth of the box and raising the height of the
baffles. The results showed that, in general, adding
more chambers to the box did not increase sediment
removal because each chamber became shorter, and
thus sediment did not settle out as efficiently.
Resuspension of sediments in the box was a
consistent problem because incoming flow
disturbed sediments that had already settled,
causing them to be resuspended and carried out of
the settlement chamber. The study suggested that
reducing resuspension in the box would increase its
overall efficiency, but this has not been
investigated.
A project to evaluate two baffle boxes in a series is
underway at Sunset Park in Indiatlantic, Brevard
County, Florida (Royal and England, 2000). This
site consists of 23.8 acres of medium-density
residential properties and 0.3 acres of highway.
One baffle box was installed on a 24-inch pipe in
1992. Flow entered the box at a 90-degree angle
relative to the length of the box and the weirs,
forcing the flow to turn before entering the second
chamber. This box removed approximately 8,490
pounds of sediment per year during the study
period. A second baffle box was installed upstream
of the original box in February 1998, with the goal
of removing more sediment from the system.
However, preliminary results indicate that overall
sediment removal efficiencies have not increased
(see Performance section below). While 5,639
pounds of sediment per year are currently being
removed by the upstream box, the downstream box
only removes an additional 715 pounds per year.
This slight increase in overall removal efficiencies
indicates that the addition of a second box in a
series is not a major design improvement for this
system.
PERFORMANCE
Baffle boxes are an effective BMP to remove
sediments from storm water. Baffle boxes have
been shown to remove from 225 to 22,500
kilograms (500 to 50,000 pounds) of sediment per
month, depending on the sediment load feeding into
the baffle box. However, pollutant removal
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efficiencies (e.g., the percentage of pollutants
removed by the BMP) depend on factors such as
land use, drainage basin area, soil types, storm
water velocities through the box, and the frequency
and thoroughness of box cleaning. Limited data
exists on the pollutant removal efficiencies of baffle
boxes. Only one laboratory and one field
evaluation are complete, while several more field
tests are scheduled for the future. Results to date
are discussed below.
Sediment accumulation in baffle boxes varies
greatly depending on the season and the amount and
intensity of rainfall events. For example, Brevard
County, Florida, monitored baffle boxes in the
communities of Indiatlantic and Micco between
1992 and 1994 (Royal and Vanderbleek, 1994). In
a one month period between August 21 and
September 22, 1992, the Indiatlantic baffle box
removed 2,040 kilograms (4,500 pounds) of
sediment. This time of year (the summer season) is
characterized by high intensity, short duration
storms. However, in contrast, over a four-month
period from September 1992 through January 1993
(during the winter season of lower intensity, longer
duration storms), the box removed only 1,815
kilograms (4,000 pounds) of sediment.
Monitoring of the baffle boxes included both water
column and sediment samples. Measuring the
concentration of contaminants in samples at both
the inlet and outlet of the baffle box showed that the
concentration of contaminants was reduced from
the inflow to the outflow of the Indiatlantic box (see
Table 1). Analysis of this site indicated removal
rates of 71 percent Total Suspended Solids (TSS)
and 38 percent phosphorous. Analysis of BOD
removal on three dates showed an average of 39
percent removals for two dates, but a 25 percent
increase in BOD from inlet to outlet on a third date
(Royal and Vanderbleek, 1994).
Results from the Micco site baffle box were even
more inconsistent, showing an increase in
concentrations of some contaminants through the
box. The researchers suggest that these increases
may be due to inadequate cleaning and the
resuspension of accumulated contaminants.
Analysis of the sediments from the boxes, found
that larger particles (primarily coarse, large-grained
sand) were trapped in the first chamber of the baffle
box, while finer particles (primarily fine organic
and metals-rich sediments) settled out in subsequent
chambers (Vanderbleek and Royal, 1994). In
assessing these data along with removal
efficiencies, the researchers concluded that
resuspension of sediments from the second and/or
third chambers of the box could increase organic
materials and metals in the outflow from the box,
especially if the box had not been cleaned recently.
A scale model test at the Florida Institute of
Technology indicated that baffle boxes can remove
up to 90 percent of coarse sediments at pipe
velocities of 183 centimeters per second (6 feet per
second). Removal of smaller fly ash particles is
roughly 28 percent at the same velocities (Pandit
and Gopatakrishnan, 1996). The removal rate for
coarse sediments remained constant even as
sediment concentrations increased from 50 mg/L to
1000 mg/L. In contrast, removal efficiencies
increased for finer sediments as sediment
concentrations increased. This study also showed
TABLE 1 POLLUTANT REMOVAL EFFICIENCIES, INDIATLANTIC BAFFLE BOX
Date
Percent Reduction,
TSS
Percent Reduction,
Total Phosphorous
Percent Reduction, BODS
10/6/93
11/23/93
1/12/94
2/17/94
Total
89.8
79.2
57.1
56.4
70.6
87.6
67.4
-3.0
0.0
38.7
46.0
31.8
No Data
-25.0
17.6
Source: Modified from Royal and Vanderbleek, 1994.
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that an increase in the inflow rate decreased
removal efficiencies. For coarser sediments,
removal efficiencies declined slightly as the inflow
rate increased, while removal rates for finer
sediments decreased significantly as inflow rates
increased. Thus, the pollutant removal efficiency of
a baffle box may depend on both site-specific
conditions and the characteristics of individual
runoff events.
More studies are either planned or underway to
assess baffle box performance. Officials in
Jacksonville, Florida, plan to monitor the
performance of a baffle box installed on a 48-inch
pipe as part of the city's Storm Water Master Plan
(City of Jacksonville Department of Public Works,
2000). This baffle box should be installed by early
2001, with performance monitoring beginning soon
thereafter. The City of Gainesville, Florida, will
also begin performance monitoring of a baffle box
to gather information as part of their Storm Water
Phase II program. Brevard County plans to
continue monitoring the Sunset Park site, where
two baffle boxes were installed in a series (Royal
and England, 2000).
OPERATION AND MAINTENANCE
The key to the successful performance of a baffle
box is regular maintenance, including routine
inspection and cleaning. As sediment accumulates
in the box, the chance for resuspension of
accumulated material increases, and pollutant
removal efficiencies can decline. Standing water
that accumulates in the baffle box may become
stagnant, leading to odor problems (England, 1996)
and problems with mosquito breeding. It is
important to establish a routine schedule to check
the boxes and clean out accumulated sediment.
Boxes may accumulate anywhere from 225 to
22,500 kilograms (500 to 50,000 pounds) of
material per month (England, 1998b). The baffle
boxes installed in Florida require monthly cleaning
during the wet season and cleaning every two to
three months during the dry season. However,
maintenance schedules depend on individual site
characteristics, including typical sediment loads, the
size of the sewershed, flow rates, land use in the
area, and the size of the box. For example, a baffle
box in a small sewershed that does not receive
much runoff will probably not need to be inspected
as frequently as a baffle box serving a larger area.
The size of the box may also impact the
maintenance schedule. In general, the deeper the
box, the longer it can function before needing
maintenance.
Baffle boxes in Brevard County are cleaned by
vacuum trucks on a regular schedule of two to six
times per year (England, 1998a). Originally, a
private contractor performed the cleaning, but as the
number of baffle boxes increased, the County
determined that it was more cost effective and
efficient to purchase a truck and perform the
maintenance itself. Brevard County currently
divides the use of one its vacuum trucks between
pipe cleaning and baffle box clean out. During the
wet season, the truck is scheduled primarily for
baffle box maintenance; during the dry season,
baffle boxes do not accumulate as much sediment
and the truck is used primarily for pipe maintenance
(England, 1998a).
During a baffle box clean out, vacuum truck
operators access the chambers through manholes set
above each compartment. Boxes cannot be cleaned
out if base flow remains in the inlet pipes. To block
incoming flow, inflatable plugs or sandbags can be
placed in the inflow pipe or in the manhole
upstream. If the box is below the outfall level,
additional plugs will be needed to prevent backflow
(England, 1998b).
Residual material from baffle boxes is not
considered hazardous and, therefore, its disposal is
not problematic. In Brevard County, useable spoil
is dried and used on road projects, while unuseable
material is landfilled (England, 1998b).
COSTS
Installation costs for most precast baffle boxes run
between $20,000 and $30,000, depending on
utilities that must be relocated to accommodate the
box (England, 1996). Average costs are
approximately $22,000 (Bateman, et. al, 1998, and
National Resources Defense Council, 1999).
However, costs can be significantly higher for
individual installations. For example, pre-design
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estimates for installation of a cast-in-place concrete
baffle box for a 48-inch pipe in Jacksonville,
Florida, are approximately $250,000 (Saint John's
Water Management District, 2000).
Because baffle boxes are usually retrofit into
existing storm water sewers, costs are often
independent of the size of the drainage area served.
Most retrofit baffle boxes are about the same size,
making capital costs about the same. Good
examples of this come from two Brevard County
communities. A baffle box for the Cedar Lane
community, which serves 0.9 acres, cost $25,027,
while the Riverside baffle box, which serves 161
acres, cost $24,944 (Bateman, et. al, 1998, and
National Resources Defense Council, 1999). The
major cost differences for drainage areas of
different sizes usually result from an increase in
maintenance frequency for boxes in larger drainage
areas with increased runoff.
The average clean out cost for a baffle box is $450.
At an average of 1,925 kg/clean out, this is an
approximate cost of $0.23 per kg of sediment
removed (England, 1998a). An average vacuum
truck can clean two baffle boxes per day.
REFERENCES
Other Related Fact Sheets
Catch Basin Cleaning
EPA832-F-99-011
September 1999
Handling and Disposal of Residuals
EPA832-F-99-015
September 1999
Water Quality Inlets
EPA 832-F-99-029
September 1999
Other EPA Fact Sheets can be found at the
following web address:
http://www.epa.gov/owmitnet/mtbfact.htm
1. "Baffle Boxes Around a Lagoon," 1999.
Chapter 7 of Stormwater Strategies:
Community Responses to Runoff Pollution,
National Resources Defense Council.
Principal Authors: P. Lehner, G. Clarke, D.
Cameron, and A. Frank. Internet site at
http://www.nrdc.org/nrdcpro/storm/stoinx.
html, accessed April 2000.
2. Bateman, M., E. Livingston, and J. Cox,
1998. "Overview of Urban Retrofit
Opportunities in Florida." Proceedings of
the National Conference on Retrofit
Opportunities for Water Resources
Protection in Urban Environments.
3. England, G., 1996. "Stormwater
Retrofitting Techniques for Water Quality
Benefits." Internet site at http://
www.stormwater-resources.com/library.
htm#BMP's, accessed April 2000.
4. England, G, 1998a. "BaffleBoxes andlnlet
Devices for Stormwater BMPs." Internet
site at http://www.stormwater-resources.
com/ library.htm#BMP's, accessed April
2000.
5. England, G., 1998b. "Maintenance of
Stormwater Retrofit Projects." Internet site
at http://www.stormwater-resources.com/
library.htm#BMP's, accessed April 2000.
6. Florida Department of Environmental
Protection, 2000. Eric Livingston, Florida
Department of Environmental Protection,
personal communication with Parsons
Engineering Science, Inc.
7. City of Gainesville, Florida, Department of
Public Works, 2000. Stewart Pearson,
Department of Public Works, personal
communication with Parsons Engineering
Science, Inc.
8. Indian River Lagoon Program, 2000. R.
Day, personal communication with Parsons
Engineering Science, Inc.
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9. City of Jacksonville Department of Public
Works, 2000. J. Cunningham, personal
communication with Parsons Engineering
Science, Inc.
10. Pandit, A., and G. Gopatakrishnan, 1996.
"Physical Modeling of a Stormwater
Sediment Removal Box." Final Report
submitted to Brevard County, Florida, and
the National Estuary Program.
11. Royal, J., and R.D. Vanderbleek, 1994.
"Stormwater Monitoring Program, Brevard
County, Florida." Final Report, Sediment
Control Project Assessment for Indialantic
Basin and Micco Basin, Brevard County,
Florida. Prepared for St. John's Water
Management District and Indian River
Lagoon National Estuary Program.
12. Royal, J., and G. England, 2000. "Final
Report, Indiatlantic Area Baffle Boxes."
Prepared for Florida Department of
Environmental Protection, Contract
WM651.
13. St. John's Water Management District,
2000. D. Busby, personal communication
with Parsons Engineering Science, Inc.
14. "Stormwater and the Environment," 2000.
Internet site at http://www.alachua.fl.us/
acepd/stormwat/storm w2.htm, accessed
April 2000.
15. Suntree Technologies, Inc., 2000. H.
Happel, personal communication with
Parsons Engineering Science, Inc., and
internet sites at http://suntreetech.com and
http://bafflebox.com, accessed May 2000.
ADDITIONAL INFORMATION
Brevard County, Florida
Gordon England
Surface Water Improvements
Department of Public Works
2725 Judge Fran Jamieson Way, Suite A203
Viera, FL 32940
Florida Department of Environmental Protection
Eric Livingston
2600 Blairstone Rd.
Tallahassee, FL 32399
City of Gainesville Department of Public Works
Stewart Pearson
P.O. Box 490, Mail Station 58
Gainesville, FL 32602-0490
Indian River Lagoon Program
St. John's River Water Management District
Bob Day
1900 South Harbor City Blvd., Suite 109
Melbourne, FL 32901
City of Jacksonville Department of Public Works
Jeff Cunningham
220 East Bay Street, 8th floor
Jacksonville, FL 32202
St. John's River Water Management District
P.O. Box 1429
Palatka, FL 32178
Suntree Technologies, Inc.
Henry Happel
720 Mullet Rd., Suite H
Cape Canaveral, FL 32920
The mention of trade names or commercial
products does not constitute endorsement or
recommendation for use by the U.S. Environmental
Protection Agency.
For more information contact:
Municipal Technology Branch
US EPA
1200 Pennsylvania Ave, NW
Mail Code 4204M
Washington, DC 20460
MTB
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