MUNICIPAL WASTEWATER MANAGEMENT
FACT SHEETS:
STORM WATER BEST MANAGEMENT PRACTICES
Municipal Technology Branch (4204)
United States Environmental Protection Agency
401M Street, SW
Washington, DC, 20460
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PREFACE
This document is part of a series of municipal wastewater
management fact sheets. These fact sheets are intended to serve
a wide audience including: the consulting engineer who is looking
for basic technical information; the municipal engineer who must
understand these technologies well enough to evaluate the assets
>and limitations; the municipal official who must sell the
technologies as part of a comprehensive pollution prevention
program; the state regulator who must approve the technologies
used to'meet permit requirements; and ultimately the citizen who
must understand the importance of preventing pollution of the
Nation's waters. . . . ,
The material presented is guidance for general information only.
The document does^not provide sufficient information to design
BMPs, but does provided sufficient information to compair
alternatives. In some cases, the information represents new
technology or new application of existing technology and is base
oh very limited data. This information should not be used
without first obtaining competent advice, with respect to its
suitability to any general or specific application. References
made in this document to any specific method, product or process
does not constitute or imply an endorsement, recommendation or
warranty by the U.S. Environmental Protection Agency.
Municipal Wastewater Management Fact Sheets are divided into«
several sets:- Wet Weather 'Flow Management Practices; Innovative
.and Alternative Technologies; Biosblids Technologies ;and
Practices; Wet Weather Technologies; Water Conservation, etc.
Each set is published separately starting with Storm Water Best
Management Practices, September, 1993. This document
incorporates and superseeds previous storm water best management
practice fact sheets (EPA 832-F-93-013, September 1993 and
Addendum to EPA 832-F-93-013, September 1994) .'Updates to this
set of fact sheets and development of additional sets is;
.dependent upon continued resources being available.
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INTRODUCTION
Storm water runoff is part of a natural hydrologic process.
However, human activities, particularly urbanization, can alter
drainage patterns and add pollution to the rain water and snow
melt that runs off*the earth's surface and enters our Nation's
rivers, streams, lakes, and coastal waters. A number of recent
studies have shown that storm water runoff is a major source of
water pollution as indicated by a .decline in fish population and
diversity, beach closings or restrictions on swimming and other
water sports, bans on consumption of fish and shellfish and other
public health concerns. These conditions limit our ability to
enjoy many of the benefits that our Nation's waters provide. '
In response to this problem, the States and many municipalities'
have been taking the initiative to manage storm water more
effectively. In acknowledgement of these storm water management
concerns, the U.S. Environmental Protection Agency (EPA) has
undertaken a wide variety of activities, including providing
technical assistance to States and municipalities to help them
improve their storm water management programs. .
This document contains fact sheets on storm water best management
practices (BMPs). These fact sheets represent two types of BMPs:
pollution prevention and treatment. Pollution prevention BMPs
include both source controls and administrative practices.
Treatment BMPs include both in-line ans off-line applications.
However, many are not stand alone BMPs, but 'are most effective,
when combined with other BMPs in a comprehensive storm water
management plan. These BMPs are suitable for both municipal'and
industrial applications and can be used to supplement other EPA
guidance documents such as Storm water Management for Industrial
Activities; Developing Pollution Prevention Plans and Best
Management Practices (EPA 832-R-92-006) and Storm Water
Management for Construction Activities: Developing Pollution
Prevention Plans and Best Management Practices (EPA 832-R-92-005)
as well as other State or local guidance.
In order to better serve our customers and identify additional
information needs, a short questionnaire is included at the- end
of this document. Please take a few minutes to tell us if this
document was helpful in meeting your needs and what other needs
you have concerning storm water management. Responses can be
mailed to the Municipal Technology,Branch (4204), US EPA, 401 M
Street, SW, Washington, DC, 20460 or- faxed to (202) 260-0116.
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TABLE OF CONTENTS
Perface
Introduction ,
Fact SheetsStorm Water Best Management Practice
1. Airplane Deicing Fluid Recovery Systems
2. Bioretention
3. Catch Basic Cleaning
4. Coverings
5. Dust Control
6. Employee Training
7. Flow Diversion
8. Highway Ice and Snow Removal and Minization of
Associated Environmental Effects from These procedures
9. Handling and Disposal of Collected SolidsYResiduals from
Storm Water and Sediment Control Processes
10. Infiltration Drainfields
11. Infiltration Trenches
12. Internal Reporting
13. Materials Inventory
14. Non-Storm Water Discharges
15i Porous Pavement
16. Preventive Maintenance
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17. Record Keeping
18. Sand Filters
19. StromTreat System TM
20. Spill Prevention
21. Storm Water Contamination Assessments
22. Storm Water Wetlands
23. Vegetative Covers
24. Vegetative Swales
25. Visual Inspections
26. Vortex Solids Separtors
27. Water Quality Inlets
28. Wet Detention Ponds
Customer Questionnaire
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STORM WATER BMP:
AIRPLANE DEICSNG FLUID
RECOVERY SYSTEMS
Office of Wastewater Management
MUNICIPAL TECHNOLOGY BRANCH'
DESCRIPTION
Ethylene or propylene glycol recovery is accomplished by a three-stage process typically consisting
of primary filtration, contaminant removal via ion,exchange or nanofiltration, and distillation as shown in
Figure 1 below. The process technologies involved in glycol recovery have been proven in other industries
and are now being applied to spent airplane deicing fluid (ADD. '.''''
NNteXCHMMK
(HEMOVM.OF DISSOLVED MUDS)
WASTEWATCR
CMttMOOE FWEH
OOUICTION
SYSTEM
t>1t%QLYOOU
.COHCCMTHATH)
OLYCOL
FMMMY nUMTION
MLCF
1HMIW
NANOnUIUTION
fWUOVAL Of KUUERSj
TWO 8TAOE4N*nUATION
fCMOVALOFWATE*
SOURCE: Reft
FIGURE 1: TYPICAL AIRPLANE DEICING FLUID RECOVERY SYSTEM
The purpose of the primary filtration step is to remove entrained suspended solids from contact with
the aircraft and pavement from the used ADF. The suspended solids must be removed to avoid plugging of
downstream equipment and heat exchangers. Primary filtration is defined as the removal of solids greater
than 10 micron in size. Primary filters employed by ADF systems may be polypropylene cartridge or bag
filters. Ion exchange may be employed to remove dissolved solids such as chlorides and sulfates. Ion
exchange removes ions from an aqueous solution by passing the wastewater through a solid material (called
ion exchange resin) which accepts the unwanted ions, while giving back an equivalent number of desirable
ions from the resin. Nanofiltration may be employed to remove polymeric additives. Nanofiltration systems
are pressure-driven membrane operations that use porous membranes for the removal of colloidal material.
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Colloidal material and polymeric molecules with molecular weights in excess ,of 500 are normally removed by
nanofilters. The requirement to remove polymer additives is dictated by the specifications of the end user
of the recovered ADF product. .
The key process step in the overall ADF recycling system is distillation. Distillation is defined as the
separation of more volatile materials (in this case, water) from less volatile materials (glycol) by a process of
vaporization and condensation. Distillation is capable of recovering volatiles with little degradation, which
is an important advantage in this application where the recovered product can be sold or recycled; Product
purity of any desired level can theoretically be obtained by distillation, however in some cases the processing
costs may be prohibitive, la most ADF applications, the separation of water from either a water-ethylene
glycol or a water-propylene glycol mixture of ADF, employs a two stages of distillation process.. This will
typically, remove enough water to produce a recovered ADF with a minimum of a 50% glycol content. The
requirement glycol concentration is dictated by the specifications of the end user of the recovered ADF
product. -
* "'''- ' ' l ' '
COMMON MODIFICATIONS
The details of the distillation process that each vendor employs are proprietary. Design variables
include temperature; distillation column design (number of stages, type of packing, size) and reflux ratio.
Batch distillation systems are generally employed due to the variation in the composition of the influent and
the irregular supply of the feed. Secondary filtration and ion-exchange stages vary with the quality of the
influent feed and the specifications of the end-user. The temperature of distillation also varies between
ethylene glycol and propylene glycol recovery applications.
* . \ . '
/ '''...* .
CURRENT STATUS
This fact sheet contains general information only, and should not be used as the basis for designing
an airplane deicing fluid recovery system. While the basic technologies used to recycle ethylene and propylene
glycol are well established, actual operating experience in recycling airplane deicing fluids is limited. To
date, there is only one on-site application of ADF recovery operating hi the United States. This is a pilot-scale
operation conducted for Continental Airlines at the Denver Stapleton Airport. Another pilot-scale ADF
operation is currently being conducted in Canada at the LIB. Pearson Airport in Toronto. While, recovery
systems are proposed for the St. Louis, Missouri Airport and the Indianapolis, Indiana airport, these systems
are not in operation. There are also three ADF recovery systems in operation at airports in Europe: Lulea,
Sweden; Oslo, Norway; and Munich, Germany.
There are currently three vendors actively designing, testing or marketing ADF recovery systems for
use on-site at airports in North America: Deicing Systems (DIS), Glycol Specialists, Inc. (GSD, and Canadian
Chemical Reclaiming (CCR). There are also a number of chemical waste service companies that will provide
off-site processing for spent glycol for other industries. The technology and process applications of ADF are
evolving rapidly. The equipment manufacturers and the airport operators should be contacted for the current
state of the art information. .
APPLICATIONS
Ethylene or propylene glycol recovery systems are generally applicable at any airport that collects
ADF with a minimum concentration of approximately 15% glycol. Spent ADF mixtures with lower glycol
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content are generally Impractical to recover via distillation, without expensive preconceniration steps such as
reverse osmosis. Dilute streams are typically .discharged to municipal wastewater treatment plants, if
permitted, treated by oxidation to destroy the organics prior to direct discharge, or hauled away be a
chemical waste contractor. A number of other BMPs such as water quality inlets and pil\water separators
are being tested to demonstrate their ability and reliability to concentrate dilute streams.
LIMITATIONS
In order for the ADF to be recovered or regenerated,, it must first be collected at the airport. The
implementation of ADF collection must respond to the unique requirements of each airport. The feasibility
of glycol recovery is dependent on the ability of the collection system to contain a relatively concentrated waste
stream without significant contamination by other storm water components. Since distillation is an energy
intensive process, it is generally not cost effective to distill and recycle waste glycol solutions at low
concentrations (< 15%). However, individual airports may have to collect and recover lower concentrations
of waste glycol solutions to satisfy requirements of their storm water NFDES permit. Remote or centralized
deicing with the containment and collection of used glycol is one method for collecting a more concentrated
used glycol. However, centralized deicing systems may be impractical for all but the largest airport
operations due to their cost and physical size^ For established airports, a switch to centralized deicing systems
would present a number of operational and logistical problems. In lieu of a centralized facility, used glycol
can be collected via vacuum trucks and fluid collections containers that siphon glycol from runway aprons.
Roller sponge devices have been employed at the Toronto Airport with mixed results due to uneven surfaces.
Mixtures of ethylene and propylene glycols cannot be recovered effectively in a single batch process
because the technology currently available cannot cost effectively separate the two glycols. While there is a
market for either recovered ethylene glycol or propylene glycol, there is little demand for a recovered blend
of both glycols by end users. 'In order to recover either ethylene or propylene glycol from spent ADF, an
airport must use one or the other, or isolate application and runoff areas. Treated separately, each type of
water-glycol mixture can then be recovered effectively via the distillation process. ;
DESIGN CRITERIA v
There area number of important criteria that must be determined in order to properly design an ADF
system. Table 1 below list some of the key criteria. Storage and handling of process chemicals, energy
requirements, and disposal of spent chemicals and residuals generated in the recovery process must also be
carefully considered. Other factors such as site drainage, weather patterns, water quality requirements, state
and local restrictions, marketability of the recovered product, etc., will also influence the final design of the
. system, . - ' . . '-._.'.,-
Sodium hydroxide (NaOH) and hydrochloric acid (HCL) are required for regeneration of the ion
exchange process unit. As a part of the recertification process, wetting agent and a corrosion inhibitor must
be added to the recovered product prior to reuse as airplane deicing fluid. While recertification and reuse
od recovered airplane deicing fluids is practiced in Europe, the Federal Aviation Administration (FAA)
currently has no recertification guideline for reuse of recovered ADF in the United States. Care should be
taken when handling these chemicals to avoid contact with skin. Eye protection should also be worn.
For the most part, energy requirements are dependent on the waste stream glycol concentration of
the fluid to be recycled and the purity required by the end user. Recovery by distillation is energy-intensive,
with nominal energy requirements being about S.SlxlO5 to 2.79x10* J/kg of feed (250 to 1200 BTU/lb of feed).
As the technology is refined and as operating experience grows, these costs should decrease.Flush and spent
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TABLE 1: KEY"
SYSTEM
AN AIRPLANE DEICING FLUID RECOVERY
Deicing Fluid Data
- Type
- Concentration
- Total consumption per season
- Total consumption per peak-day
- Average consumption per aircraft
Airport Operations Data
- Flights per day
- Peak Traffic Periods
Length of deicing season
- Number of deicing days per season
- Future traffic extension plans
Spent Fluid Data
- Volume generated
- Glycol concentration
- Contaminants
Reuse Specifications ,
- Glycol concentration
- Acceptable impurities
SOURCE: References 10 and 11
wastewater are generated by recovery processes which employ ion-exchange .systems. These fluids may be
disposed of, after neutralization by addition of acids or bases, to the sanitary sewer. Spent filter cartridges
may be generated in some systems and may be disposed of to landfills. Distillation condensate, with less than
1.5% glycol, is also generated and may be reused or disposed. Currently discharges to the sanitary sewer
system may require permitting under local pretreatment programs.
PERFORMANCE
Three ADF recovery systems were evaluated using data provided by three vendors. In each ADF
recovery system investigated, the quality of the fluid recovered was dictated by the specification objective.
The data provided for the ethylene glycol recovery system" at the Toronto Airport shows that the process
reliably produced an effluent with a glycol content over 80%. The data from the ADF recovery system in
Denver showed that high purity (98.5% glycol) can be reliably produced., The process at the Munich Airport*
reliably produced an effluent with a glycol content over 50%, which meets the lower end-user requirements
in Europe.
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COSTS
Since there are no full-scale ADF systems currently operation in the U.S., it is difficult to determine
the actual construction costs. However, based on pilot study at the Denver Stapleton Airport, flie total capital
cost for the complete project, including deicing and anti-icing application equipment, collection piping, storage
facilities, and glycol recovery system has been estimated to be between $6 and $7 million dollars. The
construction costs for the ADF collection system, storage and handling facilities, piping, and recovery system
has been estimated at approximately $600,000 (GSI, 1993).
'The total capital cost for the new Denver International Airport, including deicing and anti-icing
application pads and equipment, drainage and collection piping, storage and handling facilities, and complete
glycol recovery system is currently estimated at between $20 and $25 million dollars. These costs are based
on a complete package including planning, engineering design, equipment, construction and installation, start-
up services and other contingencies. _The construction costs for the ADF collection system, storage and
handling facilities, piping, controls and instrumentation, and complete recovery system is currently estimated
at approximately $5 million dollars.
The major operating expense for all ADF systems is cost of energy used in the distillation process.
Other maintenance costs include flushing of filters and ion-exchange units, disposal of spent filter cartridges,
process and neutralization chemical, lubrication of pumping equipment, and inspection and repairs to the
distillation equipment and heat exchanger. The collection system and storage facilities will also require
periodic cleaning and maintenance. Based on vary limited operating data from the pilot study at the
Stapleton Airport, the cost for processing ADF with a 28 percent glycol concentration, is approximately 35
cents per gallon treated. However, this cost will vary depending on the volume treated and concentration of
glycol hi the waste stream. As the technology is refined and as operating experience grows, these costs
should decrease. ',
ENVIRONMENTAL IMPACT
While the potential for volatile-organic emissions to the air is considered small, the discharges of air
emissions from the distillation process through losses from condenser vents, accumulator tank vents, and
storage tank vents must be considered. Ion-exchange flush and spent wastewater are generated by recovery
processes may generally be discharged to the sanitary sewer. These spent byproducts may require
neutralization by addition of acids or bases before discharge. Currently discharges to the sanitary sewer
system may require permitting under local pretreatment programs. Spent filter cartridges may be generated
in some systems. In most cases these can be disposed,of in the local landfill.
' . " / "
Distillation condensate, with less than 1.5% glycol, is also generated and may be reused or disposed.
However, release of more than 1 pound of ethylene glycol to the environment must be reported under the
Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) requirements. The
FJPA currently has under review a proposal to raise the disposal limit to 5000 pounds. This proposal is
expected to be promulgated as a rule in calendar year 1995. A spill prevention control and countermeasure
(SPCC) plan should be developed for all ADF systems to address the handling, storage and accidental release
of chemicals, regenerated products anid waste byproducts.
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REFERENCES
I. American Association of Airport Executives. Conference on Aircraft Deicing, August, 1993.
Washington, D.C.
2. Comstock, C., 1990, as cited in Sills, R.D. and Blakeslee, P.A., 1992. "The Environmental Impact of
Deicers in Airport Storm Water Runoff", in Chemical Deicers in the Environment, ed. Frank M. D'ltri.
Lewis Publishers, Inc., Chelsea, MI.
3. FN-gP rv»iciilrtng and Engineering. 1993. Evaluation of the Biotic Communities and Chemistry of the
Water and Sediments in Sand Creek near Stapleton International Airport. Prepared for Stapleton
International Airport. Document Number. 6321-002. .
4. freeman, H.M., 1989. Standard Handbook of Farardmis Waste Treatment and Disposal. McGraw-Hill,
New York, N.YV
5. Federal Aviation Administration, 1991. Advisory Circular (150/5320-15): Management of Airport
Industrial Waste. U.S. Department of Transportation, Washington, D.C.
6. Federal Register Notice, Vol. 55, No. 222, page 48062, November 16, 1990. EPA Administered Permit
Programs; the National Pollutant Discharge Elimmation System. .
7. Federal Register Notice, Vol. 58, No. 222, page 491587, November 19, 1993. Fact Sheet for the Multi-
Sector Storm Water General Permit (Proposed).
8. Hartwell, S.I., D.M. Jordahl, E.B., May. 1993. Toxicitv of Aircraft Deicer and Anti-icer Solutions
to Aquatic Organisms. Chesapeake Bay Research and Monitoring Division, Annapolis, Maryland.
Document Number CBRM-TX-93-1.
9. Health Advisory, 1987. Ethvlene Glvcol. Office of Drinking Water, U.S. Environmental Protection
Agency. Document Number PB87-235578.
10. Kaldeway, J., Director of Airport Operations, 1993. L.B. Pearson International Airport, Toronto,
Canada. Personal communications with Lauren Ffflmore, Engineering-Science, Inc.
11. Legarreta, G.,Civil Engineer, 1993; Design and Operations Criteria Division, Federal Aviation
Administration. Personal communication with Lauren Fillmore, Engineering-Science, Inc.
12. Lubbers L., 1993. Laboratory and Field Studies of the Toricitv of Aircraft Deicing Fluids. Presentation
to the SAE Aircraft Ground Deicing Conference, Salt Lake City, Utah, June 15-17, 1993.
13. McGreevey, T!, 1990, as cited in Sills, R.D. and Blakeslee, P.A., 1992. "The Environmental Impact of
Deicers in Airport Storm Water Runoff', in Chemical Deicers in the Environment, ed. Frank M. D'ltri.
Lewis Publishers, Inc., Chelsea, MI.
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14. Morse, C., 1990, as cited in Sills, R.D. and Blakeslee, P.A., 1992. "The Environmental Impact of Deicers
in Airport Storm, Water Runoff', in Chemical Deicers in the Environment, ed. Frank M. D'ltri. Lewis
Publishers, Inc., Chelsea, ML
-15. NIOSHTIC101 Search Results - Ethylene Glycol, Propylene Glycol
16. Roberts, D., 1990, as cited in Sills, R.D. and Blakeslee, P.A., 1992. "The Environmental Impact of
Deicers hi Airport Storm Water Runoff', in Chemical Deicers in the Environment, ed. Frank M. D'ltri.
Lewis Publishers, Inc., Chelsea, Ml.
" 17. SAE International, May 17,1993. Unconfirmed Minutes of Meeting No. 37 of AMS Committee, Rome,
18. Sills, R.D. and Blakeslee, P.A., 1992. "The Environmental Impact of Deicers hi Airport Storm Water
Runoff', in Chemical Deicers in the Environment, ed. Frank M. D'ltri. Lewis Publishers, Inc., Chelsea,
ML ' ." - .- ". , '. ' ' , ''. " '..; ..'. .;'
"19. Transport Canada, 1985. State-of-the-Art Report of Aircraft Deicing/Anti-icing. Professional and
Technical Services, Airports and Construction, Airport Facilities Branch, Faculties and Environment
-Management. Document Number AK-75-09^129. (TypeI Fluid Only)
20. Verschueren, K., 1983. Wandhnnk of Environmental Data on Organic Chemicals. 2nd Edition, Van
Nostrand Remhold Co., New York, N.Y.
TOs BMP feet sheet was prepared by tteI*niJC5><>lTeduiol<^ Branch (4204), US EPA, 401 MStreet, SW, Wadungton, DC, 20460
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IMTB
Exeefcnce In conplanoe through
STORMWATER BMP:
BIORETENTION
MUNICIPAL TECHNOLOGY BRA N
DESCRIPTION
Bioretention is a recently developed best management practice (BMP) developed by the Prince
George's County, Maryland Department of Environmental Resources (PGDER). The BMP utilizes soils
and plants to remove pollutants from stormwater runoff. As shown in Figure 1, runoff is conveyed as
FIGURE 1 BIORETENTION AREA
EVAPO-TRANSPIRATION
TURF
PONDING AREA
GRASS
PAVEMENT ' TURF GRASS
PLANTING SOIL
SAND BED
IN-SITU MATERIAL N f f f INFILTRATION
Source: PGDER, 1993.
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sheet flow to the BMP, which consists of a grass buffer strip, sand bed, ponding area, organic layer
or mulch layer, planting soil, and plants. Runoff first passes over a sand bed, which slows the velocity
and evenly distributes the runqff over the ponding area. Runoff also infiltrates the sand bed, which adds
to the infiltration capacity of the bioretention area. After runoff passes over or infiltrates the sand bed
it enters the ponding area. The ponding area is formed by depressing the surface organic layer and/or
ground cover and the underlying planting soil, Water is ponded to a depth of 6 inches and gradually
infiltrates the bioretention area or is evapotranspired. The grading of the bioretention area is done so
that excess runoff is diverted away from the BMP. Stored water in the bioretention area planting soil
exfiltrates over a period of days into the underlying soils of the BMP.
COMMON MODIFICATIONS
1 ' ' - - ' I . -
The City of Alexandria, Virginia has modified the design to include an underdrain within the
sand bed to collect the infiltrated water and discharge it to a downstream sewer system. Underdrains
were required due to impervious subsoils and marine clays. This modified design makes the
bioretention area act more as a filter that discharges treated water than an infiltration device. The BMP
can also be modified to include or not include a sand bed. The benefit of using a sand bed is the
reduction in velocity arid infiltration achieved with the bed. Design modifications are also being
reviewed to potentially utilize both aerobic and anaerobic zones in the BMP. The anaerobic zone will
promote denitrification.
CURRENT STATUS
Bioretention has been used successfully at urban and suburban areas in Prince George's County,
Maryland (MD)., Montgomery County, MD, Baltimore County, MD, and Prince William County,
Virginia. The first system was installed nearly four years ago (1992). The BMP is planned for
installation hi Alexandria, Virginia and locations in North Carolina.
APPLICATIONS
Bioretention typically provides stormwater treatment for impervious surfaces at commercial,
residential, and industrial areas. Three prime locations where the BMP could be used 'are at median
strips, parking lot islands^ and in swales. They are usually best used at locations that are upland from
inlets that receive sheet flow from graded areas and at areas that will be excavated. Sheet flow should
be conveyed to the BMP to minimize erosive conditions and to maximize treatment effectiveness. Low
environmental impacts to a site are desired. Therefore, construction of bioretention areas best suited
to sites where grading or excavation will occur so that the bioretention area can be readily incorporated
hi the site plan. Bioretention areas should be used in stabilized drainage areas to minimize the -sediment
loading to the BMP. . ,
LIMITATIONS
Bioretention is not an appropriate BMP at locations where the water table is within 6 feet of the
ground surface and when the surrounding soil stratum is unstable. In cold climates there is the potential
for the soil to freeze and prevent runoff from infiltrating into the planting soil. The BMP is also not
recommended for areas with slopes greater than 20 percent or where mature tree removal will be
required. Clogging may be a potential problem, particularly if the BMP receives runoff with high
sediment loads.
PERFORMANCE
Stormwater pollutant removal in bioretention is attributed to physical and biological processes
that occur in the plants and soils of the BMP. These processes include adsorption, filtration, plant
uptake, microbial activity, decomposition, sedimentation arid volatilization.
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Adsorption is the process where pollutants attach to soil (e.g., clay) or vegetation surfaces.
Adequate contact time between the surface and pollutant must be provided for hi the design of the
system for this removal process to occur. Therefore, the infiltration rate of the soils must not exceed
those specified or pollutant removal may decrease. Pollutants removed by adsorption include metals,
phosphorus, and some hydrocarbons.
Filtration occurs as runoff passes through the bioretention area media, such as the sand bed,
ground cover and planting soil. The media trap participate matter and allows water to pass through.
The filtering effectiveness of the bioretention area may potentially decrease over tune. Common
particulates removed from stormwater include particulate organic matter and suspended solids.
i
Biological processes that occur in wetlands result in pollutant uptake by plants and
microorganisms in the soil. Plant growth is sustained by the uptake of nutrients from the soils.
Microbial activity within the soil also contributes to the removal of nitrogen and organic matter.
Nitrogen is removed by nitrifying and denitrifying bacteria and aerobic bacteria are responsible for the
decomposition of the organic matter (e.g., petroleum). Microbial processes require oxygen and can
result in depleted oxygen levels if the bioretention area is not adequately aerated.'
Sedimentation occurs in the swale or ponding area as the velocity slows and suspended solids
fall out of suspension. Volatilization also plays a role.in pollutant removal., Pollutants such as oils,
hydrocarbons, and mercury can be removed from the wetland via evaporation or by aerosol formation
under windy conditions. .
Data is not available on the removal effectiveness of bioretention; however, results from
performance studies for infiltration BMPs can be used due to the similarities hi the BMPs. The
microbial activity and plant uptake occurring in the bioretention area will likely result in higher removal
rates than those determined for infiltration BMPs, as shown hi Table 1. As shown, the BMP could
potentially have greater than 90 percent removal rates for total suspended solids, organics, metals, and
bacteria. Excessive pollutant loadings (e.g., suspended solids) may exceed the removal capabilities of
the bioretention area.
TABLE 1 ESTIMATED PERFORMANCE OF BIORETENTION (1)
Pollutant
Removal Rate
Total Suspended Solids
Total Phosphorus
Total Nitrogen
Organics
Metals
Bacteria
90 %
60 %
60 %
90 %
90 %
90 %
(1) Source: Schueler, 1987, 1992.
DESIGN CRITERIA ,
Design details have been specified by the Prince George's County DER hi a document entitled
Design Manual for Use of Bioretention in Stormwater Management (PGDER, 1993). The specifications
were developed after extensive research on soil adsorption capacities and rates, water balance, plant
pollutant removal potential, plant adsorption capacities and rates, and maintenance requirements. A case
study was performed using the specifications at three commercial sites and one residential site in Prince
George's County, Maryland. ' .
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Each of the components of the bioretention area is designed to perform a specific function. The
function of the grass buffer strip is to reduce incoming runoff velocity and filter particulates from the
runoff. The sand bed also reduces the velocity and provides some participate filtration, as well as
evenly spreading the flow over the bioretention area. Aeration and drainage of the planting soil is
provided by the 1 foot deep sand bed. The ponding area provides a temporary storage location for
runoff prior to its evaporation or infiltration. Particulates that had not been previously filtered out by
the grass filter strip or the sand bed settle within the ponding area. The organic or mulch layer also
filters pollutants and provides an environment conducive to the growth of microorganisms, which
degrade petroleum based products and other organic material. This layer acts as the leaf litter in a
forest and prevents the erosion and drying of underlying soils. Planted ground cover and mulch reduce
the potential for erosion, with mulch being slightly less effective than planted ground cover. The
maximum sheet flow velocity prior to erosive conditions is 1 ft/sec and 3 ft/sec for planted ground
cover and mulch, respectively. The clay in the planting soil provides adsorption sites for hydrocarbons,
heavy metals, nutrients and other pollutants. Storage of stormwater is also provided by the voids in the
planting soil. The stored water and nutrients in the water and soil are then available to the plants for
uptake.
The layout of the bioretention area is determined after site constraints such as location of utilities,
underlying soils, existing vegetation, and drainage are considered. The existence of utilities (e.g.,
electric or gas) which would be costly to relocate may limit the feasibility of a site. Sites with loamy
sand soils are especially appropriate for bioretention because the excavated soil can be backfilled and
used as the planting soil, thus eliminating the cost of importing planting soil. An unstable surrounding
soil stratum (e.g., Marlboro Clay) and soils with a clay content of greater than 25 percent may preclude
the use of bioretention, as would a site with slopes greater than 20 percent or a site with mature trees
that would be removed during construction of the BMP. Bioretention can be designed to be off-line or
on-line of the existing drainage system. The "first flush" of runoff is diverted to the off-line system.
On-line systems capture the first flush but that volume of water will likely be washed out by subsequent
runoff. .
The size of the drainage area for one bioretention area should be between 0.25 and 1 acre. Multiple
bioretention areas may be required for larger drainage areas. The maximum,drainage area for one area
is determined by the amount of sheet flow generated from the 10-year storm." Flows greater than 5 cfs
may potentially erode stabilized areas. In Maryland, a flow of'5 cfs generally occurs with a 10-year
storm at one-acre commercial or residential sites. The designer should determine the potential for
erosive conditions at the site. ,
The size of the bioretention area is a function of the drainage area and the runoff generated from
the area. The size should be 5 to 7 percent of the drainage area multiplied by the rational method
runoff coefficient, "c", determined for the site. The 5 percent specification applies to a bioretention
area that includes a sand bed and 7 percent applies to ,an area designed without the sand bed. An
example of sizing a facility is shown in Figure 2. Sizing specifications are based on 0.5 inches to 0.7
niches of precipitation over a 6-hour period, which is the mean storm event for the Baltimore-
Washington area, infiltrating into the bioretention area. Other areas with a different mean storm event
will need to account for that in the design of the BMP.
Recommended minimum dimensions of the bioretention area are 15 feet wide by 40 feet in length.
The minimum width allows enough space for a dense randomly distributed area of trees and shrubs to
become established that replicates a natural forest and creates a microclimate. This enables the
bioretention area to tolerate the effects of heat stress, acid rain, runoff pollutants, and insect and disease
infestations which landscaped areas in urban settings typically are unable to tolerate. The preferred
width is 25 feet, with a length of twice the width. Any facilities with widths greater than 20 feet should
have a length of twice the width; This length requirement promotes the distribution of flow and
decreases the chances of concentrated flow. ,
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FIGURE 2 BIORETENTION AREA SIZING
BIORETENTION AREA
SIZING- COMPUTATION
DEVELOPMENT
PAVEMENT
GRASS
AREA
FT.
23,800
10.100
"C"*
FACTOR
0.90
0.25
C x AREA
21.400
. 2.500
TOTALS
eiORETENTlON AREA SIZE
33,eoo
23,900
1. WITH SAND BED (5% SUM OF C x AREA) '
= .05 x 23.900 = 1.195 OR SAY 1.200 SQ.FT.
2. WITHOUT SAND BED (7% SUM OF C x AREA)
= .07 x 23,900 + 1,673 OR SAY 1.700 SO. FT.
-SEE CHAPTER IV, PRINCE GEORGES COUNTY STORMWATER MANAGEMENT MANUAL
Source: PGDER, 1993
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The maximum ponding depth of the bioretention area has been determined to be 6 inches. This
depth provides for adequate storage and prevents excessive periods of time for standing water. Water
left to stand for longer than four days restricts the type of plants that can be used due the water
tolerance of most plants. Mosquitoes and other insects may also start to breed if water is standing for
longer than four days.
The appropriate planting soil should be backfilled into the excavation bioretention area. Planting
soils should be sandy loam, loamy sand, or loam texture and have a clay content ranging from 10 to
25 percent. The soil should have infiltration rates greater than 0.5 inches per hour (in/hr), which is
typical of sandy loams, loamy sands, or loams. Silt loams and clay loams generally have rates of less
than 0.27 in/hr. The pH of the soil should be between 5.5 and 6.5. Pollutants (e.g., organic nitrogen
and phosphorus) can be adsorbed by the soil and microbial activity can flourish within this pH range.
Other requirements for the planting soil are a 1.5 to 3 percent organic content and a maximum 500 ppm
concentration of soluble salts. In addition, criteria for magnesium, phosphorus, and potassium are 35
Ibs/acre, 100 Ibs/acre, and 85 Ibs/acre, respectively. Soil tests should be performed for every 500 cubic
yards of planting soil with the exception of tests run for pH and organic content, which is only required
once per bioretention area.
A ihinimum planting soil depth of 4 feet should be used in a bioretention facility. This depth will
provide adequate soil for the plants root system to become established in and prevent plant damage due
to severe wind. Four feet of soil also provides adequate moisture capacity. To obtain the 4 foot depth,
most sites will require excavation. Depths of greater than 4 feet may require additional construction
practices (e.g., shoring measures). Planting soil should be placed in 18 niches or greater lifts and.
lightly compacted until the desired depth is reached.
The bioretention area should be vegetated to resemble a terrestrial forest community ecosystem, that
is dominated by trees and has discrete soil zones. A terrestrial forest community also has a mature
canopy and a distinct sub-canopy of uhderstory trees, a shrub layer and herbaceous ground covers.
Three species of both trees and shrubs are recommended at a rate of 1,000 trees and shrubs per acre.
For example, a 15' by 40' bioretention area (600 ft? or 1.4 percent of an acre) would require 14 trees
and shrubs. The tree to shrub planting ratio should be 2:1 to 3:1. On average, the trees should be
spaced 12 feet apart and the shrubs should be spaced 8 feet apart. In the metropolitan Washington,
D.C. area trees arid shrubs should be planted from mid-March through the end of June or from mid-
September through mid-November. Planting periods in other areas of the US will vary. Vegetation
should be watered at the end of each day for fourteen days following its planting.
, Native species "that are tolerant to pollutant loads and varying"wet and dry conditions should be used
hi the bioretention area. These species can be determined from several published sources, including
Native Trees, Shrubs, arid Vines for Urban and Rural America (Hightshoe, 1988). The designer should
assess aesthetics, site layout, and maintenance requirements when selecting plant species. Adjacent noil-
native invasive species should be identified and the designer should take measures (e.g., provide a soil
breach) to eliminate the threat of these species invading the bioretention area. Regional landscaping
manuals should be consulted to ensure that the planting of the bioretention area meets the landscaping
requirements established by the local authorities. ,
The optimal placement of vegetation within the bioretention.area should be evaluated by the
designer. Plants should be placed randomly to replicate a natural forest. Shade and shelter from the
, wind will be provided to the bioretention area if the designer places the trees on the perimeter of the
area. Damaging flows to trees and shrubs can be minimized if they are placed away from the path of
the incoming runoff. Certain species that are more tolerant to cold winds (e.g., evergreens) should be
placed hi areas of the site where these whids typically enter the site.
-------
After placing the trees and shrubs, the ground cover and/or mulch should be established. Ground
cover such as grasses or legumes can be planted during the spring of the year. There are no restraints
to the timing of mulch placement, except that it should immediately follow tree and shrub planting.
Two to three inches of commercially available fine shredded hardwood mulch or shredded hardwood
chips should be applied to the bioretention area to provide protection from erosion. Depths greater than
3 inches should not be applied because it would negatively impact the cycling of carbon dioxide and
oxygen between the soil and the atmosphere. The mulch should be aged for at least six months, (one
year is optimal), and applied uniformly over the site. v
MAINTENANCE
Recommended maintenance for a bioretention area includes inspection and repair or replacement
of the BMP components. Trees and shrubs should be inspected twice per year to determine their health
and remove and replace 'any dead or severely diseased vegetation. Diseased vegetation that can be
treated should be done on an as needed basis. Pruning and weeding may also be necessary to maintain
the appearance of the BMP.
Mulch replacement is recommended when erosive conditions are evident or when the aesthetics
of the bioretention area are declining. Spot mulching may be adequate when there are random void
areas; however, once every two to three years the entire area may require mulch replacement. This
activity should be performed during the spring. The previous layer of mulch should be removed prior
to application of the replacement mulch.
The application of an alkaline product, such as limestone, is recommended one to two times per
year due to increasing acidity of the soil that results from slightly acidic precipitation and runoff. Prior
to applying the limestone, the soils and organic layer should be tested to determine the pH and
determine the quantity of limestone required. Testing should also be performed to determine
concentrations of heavy metals and other toxic substances hi the soil. Forest buffers and grass swales,
which accept similar sources of runoff as the bioretention area, tend to accumulate toxins and heavy
metals within five years of installation. This suggests the possibility of a similar accumulation at a
bioretention area. Soil replacement may be required when toxic levels of heavy metals or other
pollutants are reached which impairs plant growth and the effectiveness of the BMP (PGDER, 1993).
COSTS
Construction cost estimates for a bioretention area are slightly greater than the required
landscaping for a new development. Recently constructed 400 ft2 bioretention areas in Prince George's
County cost approximately $500. These units are rather small and are on the low side for cost
estimation purposes particularly if a larger unit is required. The cost estimate includes the cost for
excavating 2 to 3 feet and vegetating the site with 1 to 2 trees and 3 to 5 shrubs. The estimate does
not include the cost for the planting soil. Purchasing soils will increase the cost for a bioretention area.
Retrofitting a site typically has higher costs with an average cost of $6,500 per bioretention area. The
higher costs are attributed to the demolition.of existing concrete, asphalt, and/or existing structures and
the replacement of fill material with planting soil. Plans for retrofitting a commercial site in Maryland
(Kettering Development) was estimated at $111,600, which included 15 bioretention areas. The final
costs for the retrofit were much lower due to only six bioretention areas being constructed.
The use of bioretention can decrease the cost for stormwater conveyance systems at a site. A
medical office building in Maryland was able'to reduce the required amount of storm drain pipe from
800 to 230 feet with the use of bioretention. The drainage pipe costs were reduced by $24,000 or 50
percent of the total drainage cost for the site (PGDER, 1993). Landscaping costs that would be required
at a development regardless of the installation of the bioretention area should also be considered when
determining the net cost of the BMP.
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The operation and maintenance costs for a-bioretention facility will be comparable to typical
landscaping required for a site. Costs beyond the normal landscaping fees will include the cost for
testing the soils.
ENVffiONMENTAL IMPACTS
Bioretention provides stormwater treatment that enhances the quality of downstream water
bodies. Runoff is temporarily stored in the BMP and released over a period of four days to the
receiving water. The BMP is also able to provide shade and wind breaks, absorb noise, and improve
an area's landscape.
REFERENCES
1. Prince George's County Department of Environmental Resources (PGDER), 1993.
Design Manual for Use of Bioretention in Stormwater Management. Division of Environmental
Management, Watershed Protection Branch. Landover, MD. ,
2. Bitter, S., and J. Keith Bowers, 1994. Bioretention as a Water Quality Best
Management Practice. Watershed Protection Techniques, Vol. l%No.3, Fall 1994, Silver Spring, MD.
3. Hightshoe, G.L., 1988. Native Trees, Shrubs, and Vines for Urban and Rural America.
Van Nostrand Reinhold, New York, New York. v
4. Reed, P.B., Jr, 1988. National List of Species That Occur in Wetlands: Northeast.
United States Fish and Wildlife Service, St. Petersburg, Florida.
' , ' - ' l , ~ , ' . , . .
5. Schueler, T.R., 1987. Controlling Urban Runoff: A Practical Manual for Planning and
Designing Urban Best Management Practices. Metropolitan Washington Council of Governments.
6. Schueler, T.R., 1992. A Current Assessment of Urban Best Management Practices.
Metropolitan. Washington Council of Governments.
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!MTB
STORM WATER BMP:
CATCH BASIN CLEANING
Office of Wastewater Erforcemert & Compfcrce J
MUNICIPAL TECHNOLOGY BRANCH
DESCRIPTION ,
Catch basins are chambers or sumps, usually built at the curb line, which allow surface water
runoff to .enter the storm water'conveyance system. Many catch basins have a low area below
the invert of the outlet pipe intended to retain sediment. By trapping coarse sediment, the catch
basin prevents solids from clogging the storm sewer and being washed into receiving waters.
Catch basins must be cleaned out periodically to maintain their sediment trapping ability. The
removal of sediment, decaying debris, and highly polluted water from catch basins has aesthetic
and water quality benefits, including reducing foul odors, reducing suspended solids, and
reducing the load, of oxygen-demanding substances that reach surface water.
CURRENT STATUS .
Catch basin cleaning is an easily implemented but often overlooked Best Management Practice.
Frequently, the cleaning procedures deal with removal of debris from grate openings but do hot
extend down into the catch basin itself. ',
APPLICATIONS . : .
Catch basin cleaning is applicable to any facility that has an on-site storm sewer system-which
includes catch basins and manholes.
UMTTATIONS ' '
Limitations associated with cleaning catch basins include:
. Catch basin debris usually contains appreciable amounts of water and offensive organic
material which must be properly disposed of.
Catch basins may be difficult to clean in areas with poor accessibility and in areas with
traffic congestion and parking problems. , . ,
. Cleaning is difficult during the winter when snow and ice are present. .,
PERFORMANCE , . ,'-.'.''
It is not possible, based on current data, to- quantify the water quality benefits to receiving
-waters of catch basin cleaning. The rate at which catch basins fill with debris, as well as the
total amount of material which can be removed by different frequencies of cleaning, are highly
variable and cannot be readily predicted. Past studies have estimated that typical catch basins
retain up to 57 percent of coarse solids and 17 percent of equivalent biological oxygen demand
(BOD). . . :
MAINTENANCE . ' .
* - : -
A catch basin should be cleaned if the depth of deposits are equal to or greater than one-third
the depth from the basin bottom to the invert of the lowest pipe or opening into or out of the
basin. Catch basins should be, at a minimum, inspected annually. If a catch basin is found
during the annual inspection to significantly exceed the one-third depth standard, it should be
inspected anil cleaned on a more frequent basis. If woody debris or trash is likely to accumulate
in a catch basin,'it should, at a minimum, be inspected and cleaned, if necessary, on a monthly
basis.
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In addition, data collected as part of a Nationwide Urban Runoff Program (NURP) project in
Castro Valley Creek, California indicated that a typical catch basin, which were cleaned once per
year or once every other year contained approximately 60 pounds of material each.
Catch basins, can be cleaned either manually or by specially designed equipment. These include
bucket loaders and«vacuum pumps. Material removed from catch basins is usually disposed of in
landfills. ' /,
, - . .). - - - - - .
COSTS
Catch basin cleaning costs will vary depending upon the method used, required cleaning
frequency, amount of debris removed, and debris disposal costs. Cleaning costs for catch basins
were estimated in three NURP program studies (Midwest Research Institute, 1982). These
estimates are summarized in Table 1 below.
TABLE 1. CLEANING COST PER CATCH BASIN
U)CATTON
METHOD
COST
Castro Valley, CA.-
Vacuum attached to street sweeper-
-$7.70
Salt Lake County, UT,-
Winston-Salem, NC
SOURCE: lUfernc* L
-Vacuum attached to street sweeper
-Vacuum attached to street sweeper
In communities equipped with vacuum street sweepers, a cleaning cost of $8 per basin cleaned
is recommended for budgetary purposes (Southeastern Wisconsin Regional Planning
Commission, 1991). Cleaning catch basins manually costs approximately twice as much as
cleaning the bdsins with a vacuum attached to a sweeper. Therefore, a cost estimate of $16 per
catch basin cleaned may be used for manual cleaning. It should be noted; that costs vary
depending on local market conditions.
ENVIRONMENTAL IMPACTS
Sediment and debris removed from catch basins must be disposed of in a proper manner to
avoid negative environmental impacts.
REFERENCES ' , ' ' "
1. Midwest Research Institute, Collection of Economic Data from Nationwide Urban Runoff
Program Projects-Final Report; Report to U.S. Environmerital Protection Agency, March,
." 1982. '- ''-...- '.' '. .- ' '' ' . --._.'..
2. Minnesota Pollution Control Agency. Protecting Water Quality in Urban Areas. 1989.
3. Southeastern Wisconsin Regional Planning Commission, Cost of Urban Nbnpoint Source
Water Pollution Control Measures. Technical Report No. 31, June, 1991.
4. U.S. EPA: Results of the Nationwide Urban Runoff Program. December. 1983.
5. U.S. EPA, Catch Basin Technology Overview and Assessment. May, 1977.
6. Washington State Department of Ecology, Storm Water Management Manual for Puget
Sound. February. 1992.
VS ETA. M H Sato. SW, WaM^m.DC, 10460.
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IMTB
STORM WATER BMP:
COVERINGS
Ofto rf Watewaor Erforcotmrt
MUNICIPAL
DESCRIPTION . . .
A simple yet effective Best Management Practice (BMP) is covering. Covering is the partial or total
enclosure of raw materials, byproducts, finished products, containers, equipment, process operations, and
material storage areas which, when exposed to rain and/or runoff, could contaminate stormwater..
Tarpaulins, plastic sheeting, roofs, buildings, and other enclosures are examples of temporary or
permanent covering that are effective in preventing stonnwater contamination: The most prominent
advantage of covering is, that it is inexpensive in comparison to other BMPs.
CURRENT STATUS
A review of numerous NPDES group applications indicates that covering is a commonly implemented
BMP. As more facUities identify potential sources of stonnwater contamination, the use of coverings will
increase significantly due to its effectiveness from a performance and cost perspective.
APPLICATIONS
Covering is appropriate for loading/unloading areas, raw material, byproduct and final product outdoor
storage areas, fueling and vehicle maintenance areas, and other high risk areas. . .
LIMITATIONS . !
Limitations associated with covering as a BMP include:
Temporary methods such as plastic sheeting can become torn or ripped, :
exposing the contaminant to precipitation and/or stormwater runoff.
\ ' . ' '< :
Costs may prohibit the building of complete enclosures.
May pose health or safety problems for enclosures built over certain
materials or activities. , ".-'
Requires frequent inspection. . .
A structure with only a roof may not keep out all precipitation.
PERFORMANCE - . . .
It is difficult, based on data currently available, to quantify the mitigation of runoff contamination when
covering is used. However, significant runoff water quality benefits are expected by simply reducing the
contact between potential contaminants and precipitation or stormwater runoff. One source has
estimated that 80 percent of the environmental damage from de-icing chemicals is caused by inadequate
storage facilities.
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DESIGN CRITERIA
Evaluate the integrity and durability of the covering, as well as its compatibility with the material or
activity'being enclosed. When designing an enclosure, one should consider materials access, handling
and transfer. Materials that pose environmental and/or safety dangers because they are radioactive,
pathogenic, flammable, explosive, or reactive require special ventilation and temperature considerations.
Covering alone may. not protect exposed materials from stormwater contact. Placing material on an
elevated impermeable surface or building curbing around the outside of the materials may be required to
prevent contact with stormwater runoff from adjacent areas.
Practicing proper materials management within .an enclosure or underneath a covered area is essential.
For exainple, floor drainage within an enclosure should be properly designed and connected to a sanitary
sewer The local publicly owned treatment works should be. consulted to determine if there are any
pretreatm'ent requirements,restrictions, or compatibility problems' prior to discharge. .
MAINTENANCE "' '~ '_.'
"/.'.'-.' ' - : -
Maintenance invblves frequent inspection of the covering for rips, holes, and general wear. Inspecting
;coverings should be part of an overall preventive maintenance program. :
COSTS' .' . . t - , ';: '..;. ' "'
Covering costs vary in proportion to the degree of protection desired; and the required lifespan. The
most inexpensive covering is plastic sheeting, but it is not suitable where a high degree of protection is
desired for a long period. An enclosed building is the most expensive type of'covering when materials
for the structure, lighting, and ventilation are considered^ but it offers the highest degree of protection
for the longest period.
ENVIRONMENTAL IMPACTS "_:'_
The impact from a covered area depends on the degree of complexity in the; covering design. A simple
plastic sheeting can possibly have a stormwater diversion, and allow for disposal of uncontaminated
water to a storm sewer. A structure with a permanent roof may be.less effective, if the material inside is
not sufficiently protected from contact with runoff. An enclosed structure may need to have internal
drainage. If this is the case, it must hot be connected to the storm sewer, and may not be suitable
connection to a sanitary sewer, if the stored material is considered hazardous; the internal drains would
then need to be connected to some suitable containment area for later disposal.
REFERENCES
1. Minnesota Pollution Control Agency. Protecting the Water Quality in Urban Areas. 1989.
2.
3.
U.S; EPA. Stormwater Management for Industrial Activities: Developine Pollution Prevention
Plans and Best Management Practices. Pre-print. July 1992.'
' , ' ' ' ' . : ' . .."''
Washington State Department of Ecology, Stormwater Management Manual for Piteet Sound.
February 1992.
TVi BMPfaa **t wtr^pwrf tf Ac Mwc*»( T^malay BmA (12M), US EPA. «l M Sm* SW Wal*i*m. DC 30**
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JMTB
STORM WATER BMP:
DUST CONTROL
Oflkx/Wa&water Enforcement - ...
MUNICIPAL TECHNOLOGY BCANCH
.DESOUPTION
Dust controls are methods that prevent pollutants from entering stormwater discharges by reducing die
surface and air transport of dust caused by industrial or construction activities. Control measures can
prevent dust from spreading into areas of a facility where runoff may eventually transport the'material to
a storm sewer collection system or directly to a receiving waterbody. :
* *'» .
Dust control for industrial activities normally'involves mechanical systems designed to reduce dust
emissions from, in-plant, processing activities, and/or materials handling. These may include hoods,
cyclone collectors, bag-type collectors, filters, negative pressure systems, or mechanical sweepers. .
*-'.- '.. ' ..... .'"'.. :' '.'., . ' . ,,-
Dust control measures for construction activities include windbreaks, minimization of soil, spray-on
adhesives, tillage, chemical treatment^ and water spraying. .
COMMON MODIFICATIONS ,
There are a number of temporary alternatives for dust control. However, another consideration is to
eliminate the need for temporary dust control completely by permanent modification of the site. This
could include such measures as covering exposed areas with vegetation, stone, or concrete.
APPLICATIONS :.'_'"' -
Dust control measures may be'applied to any site where dust generation, can cause damage to the site or
adjacent properties.-. However, application of dust controls is especially critical in arid areas where
reduced rainfall levels expose soil particles for transport by air and runoff into water bodies. Dust
control measures should also be applied to any industrial activity where dust poses a threat of
contamination to water bodies. ' ,
LIMITATIONS
' ' '
Primary limitations of dust control include: , .
Some temporary dust controls must be reapplied or replenished on a regular basis.
Some controls are expensive (e.g., chemical treatment) and may be ineffective under ,
certain conditions.
Some controls may cause an increase in the amount of mud being tracked off-site.
Typical windbreaks are not as effective as chemical treatment or mulching and
seeding, and may require land space that might, not be available at all locations.
Industrial dust control is typically labor and equipment intensive and may not be
effective for aU sources of pollution (e.g. street sweepers).
More elaborate industrial dust control systems require'trained personnel to operate
them, an require the implementation of a preventive maintenance arid repair program
to ensure operational readiness.
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PERFORMANCE
"..-".' - "^ _ r . - \ *',' . ,
.The decision on which dust control measures to implement must take into consideration the
performance objectives sequired for a particular site. Some examples of performance objectives include:
' .'-'"" i
Prevent wind and water-ibased erosion of disturbed areas
;-. A reduction of employee respiratory problems. . ,
Rapid implementation at low cost and effort. -
Little or no impact on the environment.
' ' '. ' '' ; . ' - . . '..'''- ' ' ' .''*...
. Permanent control of the dust problem.
Based on the objectives simply sweeping the impervious .areas for larger particles on a routine basis may
provide an efficient and reliable method of dust control that can be quickly implemented. Other controls
might include vegetative windbreaks which would provide a much more permanent and environmentally
safe,alternative to chemical use: f* _' _':'-'-
' ' ' ' ''>,. -.*,.-
i ' - ' . ' ' ' , " S ',-",''
DESIGN CRITERIA . . ';.
The main goals of the dust-control project design is to limit dust generation and"reduce the amount of
/soil or dust particulate exposed. However this must also take into consideration the performance
objectives established for the particular project. Additionally, some project sites may require solutions to
both industrial and dust control problems. Realistically it may not be practical or possible to develop a
design that meets all of the project goals and objectives at one time. Therefore it may be more
appropriate to develop a phased design approach that utilizes^ combination of temporary, permanent, or
mechanical measures for dust control. .
TEMPORARY MEASURERS
Vegetative Coverings: Temporary seeding and mulching may be applied to
cover bare sofl and prevent wind erosion.
Adhesives:, Use spray-on adhesives according to Table 1 below. It is
recommended using these adhesives only if other methods cannot be used
as many of them are difficult to work with and form fairly impenetrable
surfaces. - . '. . -. .-. '''- ' ' .;.. '
Wetting: This is generally done as an emergency treatment. The site is
sprinkled with water until the surface is wet and repeated as necessary. If
this method is to.be employed, it is recommended that a temporary gravel
rock entrance be created to prevent carry-out of mud onto local streets.
Tillage: This practice roughens the soil and brings clods to the surface. It is
an emergency measure that'should be used before wind erosion starts.
Plowing should begin on the windward side of the site using chisel-type
plows spaced about 12 inches apart, spring-tooth harrows, or similar plows.
Barriers: Solid board fences, snow fences, burlap fences, crate walls,
bales of hay, and similar material can be used to control air currents and
soil blowing. .Barriers placed at right angles to prevailing currents, at
intervals of about 15 times' the barrier height are effective iri controlling
wind erosion.'
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Calcium Chloride: This material, is applied at a rate that will keep the surface
moist. Pretreatment may be necessary due to varying site and climatic conditions.
TABLE 1: DESIGN OF ADHESIVE MEASURERS
Type of Emulsion
Anionic Asphalt
Latex
Resin and Water
SOURCE: RtfacnaL
Water Dilution
Nozzle Type
Application Rate
(gallons per* acre)
7 to 1
12.5 to 1
4tol
Coarse
Fine
Fine
1,200
235
300
PERMANENT MEASURERS
Permanent Vegetation: Seeding and sodding should be done to .
permanently stabilize'exposed areas against wind erosion. It is
recommended that existing trees and large shrubs remain in place
to the greatest extent possible during site grading processes.
Stone: The purpose of this method is to place coarse gravel or crushed
stone .over highly erodible soils. . ' - -
Topsoilihg: This method is recommended when permanent vegetation
cannot be established on a site. Topsoiling is a -process in which less
erosive soil material is placed on top of highly erodible soils.
Cyclone Collectors. Cyclone collectors separate dry dust and paniculate
pollutants in the air by'centrifugal force:
Bag Collectors/Fabric Filters. Bag collectors or fabric .filters remove dust
by filtration. Storage of collected dust should be carefully considered so
that it does not become a source, of fugitive dust. .
Negative Pressure Systems. These systems minimize the release of dust
from an operation by maintaining a small negative pressure or suction tp
confine the dust to a particular operation.
Water Spraying. This temporary mechanical method confines and settles
the dust from the air by dust and water particle adhesion. Water is
sprayed through nozzles over the problem area.
Street Sweepers. Two kinds of street sweepers are common in mechanical
dust collection systems. The brush system has proven to be an efficient
method at an industrial facility generating dust on a daily basis. It has
proven to be extremely dependable and picks up the majority of the dust.
Vacuum swe'epers are presumed to be more efficient because the
pollutants typically associated with contaminating storinwater are the
smaller particles which may be left behind by a brush street sweeper.
However, no performance data are as yet available to verify that.
vacuum sweepers are more efficient than brush sweepers. " -.
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MAINTENANCE ,< .
Typically, all dust control measures require periodic and diligent maintenance. For example, mechanical
equipment should be operated according to the manufacturers recommendations and inspected regularly
.as part of an industrial site's preventive maintenance program. Temporary dust control measures, such
as chemical spraying, watering, etc. require periodic renewal. Permanent solutions such as vegetation,
wind barriers, impervious services also require upkeep and maintenance in'order to remain effective.
'COSTS ' '..'.. '',-". -.''. ", , '- . . . '
The costs associated with dust control measures are generally lower for vegetative and barrier methods,
and increases significantly for chemical and mechanical treatments. For example, an industrial facility
purchased a mechanical brush sweeper for approximately $35,000.
-.-.,"". ' ' '*. " ; ' . /
. ' ' - . ' . > . , ,' "
ENVIRONMENTAL IMPACTS
There are several negative environment impacts which are related to the dust control BMPs; These
include: '" .''
If over-application of a chemical treatment to control dust occurs, excess .
chemicals couldbe exposed to both wind and rain erosion with potential for
both surface and groundwater contamination. -'.-.'
Oil should never be used to control dust because of the high potential for
polluting stormwatef discharges. .
. When using mechanical measures such as street sweepers, disposal is a major
problem and could involve parameter testing of dust particulate. RCRA
regulations may be applicable to" this situation. '
REFERENCES- ' , ' "'."'".'
1 c.ity of Kagan. Minnesota. Erosion Control Manual. 1984 " , .
- - ' ~'
2. Hennepin County, Minnesota, Erosion and Sediment Control Manual. 1989.
3. Minnesota Board of Water and Soil Resources, Minnesota Construction Site Erosion and Sediment
Control Planning Handbook. November 1987.
4. U.S. EPA, NPDES Best Management Practices Guidance Document December 1979.
5. U.S. EPA. Stormwater Management for Industrial Activities: Developing Pollution Prevention Plans
and Best Management Practices. September 1992. , ,
JK* BHTfaa **t **,p*putd Jy Ac MinicfNii Ttdmaby Bmdi (4104). US EPA. 401 MStm*. SW., WaHKfm. DC, 20460.
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IMTB
STORM WATER BMP:
EMPLOYEE TRAINING
MUNICIPAL TECHNOLOGY KAMCH
DESCRIPTION
In-house training programs are designed and implemented to teach employees about stormwater
management, potential sources of contaminants, and.Best Management Practices (BMPs). Employee
training programs should instill all personnel with a thorough understanding of their Stormwater
Pollution Prevention Plan (SWPPP). This includes identification of BMP's, processes and materials they
are working with, safety hazards, practices for preventing discharges, and procedures for responding
quickly and properly to toxic and hazardous material incidents.
1 ' , " ~ " ' . ,f
CURRENT STATUS . .
Typically, most industrial facilities have an employee training programl Usually these address such
areas as health and safety-training, or fire protection. The effort required to modify, these programs to
include discussion of stormwater management and BMP implementations .should be reasonable.
APPLICATIONS . . . \
Employee training program implementation, can be achieved through posters , and bulletin boards
designed to raise awareness of stormwater management, potential contaminant sources, and prevention
of surface water runoff contamination. Field training programs where employees are shown areas of
potential stormwater contamination and associated pollutants, followed by a discussion of site-specific
BMPs by trained personnel, would also be beneficial for implementing the program.
UMTTATIONS
Limitations of an employee training program include:
Lack of employee'motivation
Lack of incentive to become involved m BMP implementation
Lack of commitment from senior management :
PERFORMANCE
Quantitative performance wfll vary between facilities because.performance is dependent on employee
participation and commitment from senior management to reduce .point and nonpoint sources .of .
pollution. Employee training programs that teach identification of potential sources, of contaminants, are
highly recommended for implementation at all. facilities. Support of these programs should given the
highest priority, by senior management.
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DESIGN CRITERIA
Specific design criteria for implementing an employee training program include: .
. Meetings should be held at intervals frequent enough to ensure adequate understanding
of SWPPP goals and objectives. ,
A strong commitment by, and periodic input from, senior management.
. Transmission of knowledge from past spill causes and .solutions to prevent future spills.
Making employees aware of internal reporting procedures relative to BMP monitoring and
spfli reporting procedures. - ,
. Operating manuals and standard procedures.
Implementation of spill drills to minimize potential contamination of stormwater runoff
- from toxic pollutants.
MAINTENANCE .
An employee training program should be an on-going yearly process'. There should be, at a minimum,
annual meetings to'discuss SWPPPs. These meetings could be held in conjunction with other training
programs. Figure 1 below illustrates a sample employee training tracking worksheet.
'' "
EMPLOYEE TRAINING
WackslMtt . '
THUr
Q*t** ' ° ' ... !_
' Inctructioni: Onctti* th» «motov»« man
iMponM. good houMkMpine
./
- SfdiPravwnionwdllMpanw'1
Good HottHkMpino
Oi
'
OthwToefca
.
SOURCE; Bifoaictl
ifef OMcripttan of TrtWnf
eeuTMl .
v
; f
schMkito far th* wining pro
«
SdwMilorTraMnt
OMi*MM>' .
" u
uwaprmMfen«nd
gram tat ta «
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.
FIGURE 1: SAMPLE WORKSHEET FOR TRAOONG EMPLOYEE TRAINING
-------
COSTS ; ; '; . ' . , ; ' \.
Costs for implementing an employee" training program are highly variable. It is anticipated that most
stormwater training program costs will be directly related to labor and associated overhead costs.
however, the example shown in Table 1 below can be used to estimate what the annual costs might be
for an in-house training program at your facility. Figure 2 can be used as a worksheet to calculate the
estimated cost for an employee training program, ..''".
TABLE 1: EXAMPLE OF ANNUAL EMPLOYEE TRAINING COSTS
, Estimated .
Yearly
Avg. Hours Est.
, Hourly Overhead* onSW Annual
Tide Quantity Rate ($) Multiplier Training Cost {$)
Stormwater Engineer 1 x 15 x 2.0 x 20.
Plant Management 5 x 20 x . 2.0 x 10
Plant Employees . 100 x 10 x 2.0 x 5
- TOTAL ESTIMATED ANNUAL COST
. ... . . . .
Note: Defined as a multiplier (typically ranging between 1 and 3) that
those costs associated with, payroll expenses, building expenses, etc.
SOUKE: EfA . " .
= 600
.« 2,000
= 10.000
$12^00
1 '
takes into account.
, Estimated
..-"' '.-'". . " Yearly,
Avg. Hours
Hourly Overhead onSW
Tide Quantity Rate ($J Multiplier Training
x. , ' « x ,., '
x' x ' ' x '
x ' x ' x '',,., =
* - -
x x . .._. x _, -
Est.
Annual
Cost($)
fA)
(B3
(0
(D)
TOTAL ESTIMATED ANNUAL COST
(Sum of A+B+C+D)
SOURCE: fefaaiaii
. FIGURE 2: SAMPLE ANNUAL TRAINING COST WORKSHEET
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REFERENCES ,. / ,
'' , '.*
1. U.S. EPA, NPDES BMP Guidance Document. December, 1979.
2. U.S. EPA. Stormwater Management for Industrial Activities: Developine Pollution Prevention
Plans and Best Management Practices. September, 1992. ,
JKtBHPfact AMwpfnpoitrfiy AeMuiicgnl Ttdaaloy Bmd, (CM). US EPA. 401 MSa^SW, VaMifaa. DC 30460.
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MTB
STORM WATER BMP:
FLOW DIVERSION
Office of Wa
Erfo
MVNlC/PAt. TECWNOLOar IIAMCH
DESCRIPTION , ' .
Structures which collect -and divert runoff (such as gutters, drains, sewers, dikes, berms, swales, and
graded pavement), are used in two ways to prevent the contamination of storm water and receiving
water bodies. First, flow diversion structures may be used to channel storm water away from industrial
areas so that storm water does not mix with on site pollutants. Second, they may also be used to carry
contaminated runoff directly to a treatment facility. :
Storm* water conveyance systems can be constructed from many different materials, including concrete,
clay tiles, asphalt, plastics, metals, rip-rap, and compacted soils covered with vegetation. The type;'of .
material used depends upon the design criteria used for conveyance of storm water runoff. These
conveyances can be temporary or permanent.
Some advantages of storm water conveyance systems used for flow diversion purposes are:
Direct storm water flows around industrial sites.
Prevent temporary flooding of industrial site. . , ,
Require low maintenance. . . ' . ,
. Provide erosion-resistant conveyance of storm water runoff.
Can typically Be installed at any time.
Provide long-term control of storm water flows.
COMMON MODIFICATIONS ' ,
Flow diversion structures can be modified by incorporating them with other pollution control best
management practices. For example, diverted flow can be fed into an infiltration drain field system,
diverted to an infiltration basin, diverted to a constructed wetland treatment facility, or diverted to an
onsite treatment facility for discharge under the NPDES program. Another common modification is to
construct a temporary flow diversion to determine its effectiveness. If the "diversion structure is proven
effective, it could then be converted to a permanent structure.
APPLICATIONS ,
Storm water diversions work" well at most industrial sites. Storm water can be directed away from
industrial areas by collecting it in a channel or drain system. Diversions can be used to collect storm
water from the site and direct it down slope where it can be kept separate from runoff that has not been
in contact with 'those areas. When potentially contaminated storm water is collected in a conveyance
system, it can be directed to a treatment facility. ' .
t ' .- ' \
A good example' of the utilization of a diversion structure is The Isle La Plume Wastewater Treatment
Plant in La Crqsse, WI The area immediately surrounding the facility has been regraded so mat storm
water runoff can be directed into.the process tanks where it is treated right along with other wastewater.
Figure 1 below illustrates this storm water runoff control method.
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PERFORMANCE , ,
- ' "'''- . ' \
Properly, designed storm water diversion systems are very effective in preventing storm water from being
contaminated. or in routing contaminated flows to' a proper treatment facility. For example, at the
Denver Stapleton International Airport, flow diversion techniques intercept 99 percent of the glycol used
and prevent its introduction; to Sand Creek, the local receiving waterbody. At the La Crosse, WI
Wastewater Treatment Plant, it is estimated that approximately one-third of the storm water runoff from"
the. facility is diverted into their, treatment process. -
DESIGN CRITERIA .
Planning for flow diversion structures should consider the typical volume and rate of storm water runoff
present. Also, the patterns of storm water drainage should be considered so that the channels may be
located to efficiently collect and divert the flow. When deciding on the type of material for the
conveyance structure, consider the resistance of the material to erosion, its durability and compatibility
with any pollutants it may carry. . ; , '.; ' .-
Diversion systems are most easily installed during facility construction. Existing grades should be .used
to limit costs. Positive grades should be provided to allow for continued movement of runoff through
the conveyance system. CNote: care must be exercised to limit velocities which could potentially
increase erosion.) A/typical diversion swale is shown in Figure. 2 Below.
Dyke
Dyke Top Width
2
Channel
Existing Grade
FIGURE 2: TYPICAL DIVERSION SWALE DETAILS
MAINTENANCE
A" maintenance program should be established to ensure proper functioning of the system. Storm water
' diversion systems should be inspected to remove debris within 24 hours after a significant rainfall event
since heavy storms may clog or damage them. Flow diversion structures should also be inspected on an
annual basis to ensure that-they meet their hydraulic design requirements for proper performance. .
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.^ ' Secondary Clanfier Wall
I 1 Secondary Clarifier Wall
Section AA
FIGURE 1: STORM WATER RUNOFF CONTROL MEASURERS
At the Denver Stapleton International Airport, the terminal area, aprons, and support facility areas (0.5
square miles), where activities resulting in storm water contamination are concentrated, .are served by
four individual large diameter .storm sewers which collect storm water, snow melt, fuel spills, de-icing
agents, and wash down flows. These storm sewers have hydraulic diversion structures in place which
convey storm water flows to a 9 mgd detention basin. The basin contents are pumped to a sanitary.
sewer interceptor where it is then transferred to a local treatment facility.
Another concept being adapted into the new regional airport in Denver is 'based on centralized de-icing
areas for use by all airlines. All de-icing area flows will be diverted to an bn-site glycol recovery system
or diverted to detention basins for discharge to the local treatment facility.
LIMITATIONS .
Storm water flow diversion structure limitations include: .
Once flows are concentrated, they must be routed through stabilized structures, or
treatment facilities in order to minimize erosion prior to discharging to receiving waters.
May increase flow rates.
May be impractical if there are space limitations.
May not be economical especially for small facilities or after a site has been constructed.
. May require maintenance'after heavy rains.
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COSTS . - '.- .."- . ' . .-: ' '.-.- ; '... ;. ' . _ : ._ ; . .- .;.
Costs vary depending of! the type of flow diversion structure used. For example, if vegetated swales are
to be used for flow diversions, the Southeastern Wisconsin Regional Planning Commission (SEWRPG)
reported that, in 1991, costs may vary between $8.50 to $50 per lineal foot, depending upon swale depth
in feet and bottom width. Capital costs for the Stapleton International Airport flow diversion system,
including basins, diversion structures in- each of the four main .storm sewers, and additional flow
diversion modifications made by airport staff, were $6 million in 1988. Clearly the cost will be
determined by the scope of the project and design requirements.. .
ENVIRONMENTAL IMPACTS , ;
Environmental impacts include: , ' .
Erosion problems due to concentrated flows.
Potential groundwater contamination if conveyance channels have high infiltration
capacities.
'', '''' ". : "-.' '.--. / . .. /
. Undersized water treatment facilities may result in discharges that have not been
adequately treated. / .
REFERENCES " .
1. James M. Montgomery, Consulting Engineers, Inc., SiteJ^itData, September 1992.
2. Minnesota Pollution Control Agency, Protecting Water Quality in Urban Areas, 1989.
3. Southeastern' ,Wf«"""""'" a »oinnal. Planning Commission. Costs of Urban Nonpdint Source
Water Pollution Control Measures; technical Report No. 31, June 1991?
- 4. . u.S. EPA, NPDES BMP Guidance Document. June 1981.
5. U.S..EPA, Storm water Management for Industrial Activities: Developing Pollution Prevention
Plans and Best Management Practices. September^ 1992. :
6. Washington State Department of Ecology, Storm water Management Manual for Puget Sound,
February 1992. ,
TMr BMffaa AM x> pxpatd by At Muu*ol Tmbulcv Bmn* (4ZH),US ERi. «1 M Soml. & Wajmfa*. DC 20*0.
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STORMWATER BMP:
HIGHWAY ICE AND SNOW " _'
REMOVAL AND MINIMIZATION
OF ASSOCIATED ENVIRONMENTAL
EFFECTS FROM THESE PROCEDURES
IMTB
Excellence h tompfanoe through optfmal technical
MUNICIPAL TECHNOLOGY
INTRODUCTION
The United States is critically dependent on the nation's road system to support the rapid, reliable
movement of people, goods, and services. The widespread expectation holds that even in the face of
winter storms, roads and highways will be maintained to provide safe travel conditions. In many states,
this requires substantial planning, training, manpower, equipment, and material resources to clear roads
and streets throughout the winter. ,
The dependency on deicing chemicals has increased since the 1940s and 1950s to provide "bare
pavement" for safe and efficient whiter transportation. Sodium chloride (salt) is one of the. most
commonly used deicing chemicals. Concern about the effects of sodium chloride on the nation's
environment and water quality has increased with this chemical usage. Automobile and highway bridge
deck corrosion has also become a concern. However, in most cases sodium chloride is the most cost
effective deicing chemical. Such concerns have led to major research efforts by the Strategic Highway
Research Program (SHRP), the highway community, industry, government, and academia. This ongoing
research is exploring many different areas in an effort to maintain the safest roads possible in the most
economical way while protecting the environment.
This fact sheet summarizes research addressing water pollution and associated effects from-deicing
chemicals, and describes the methods used to control snow and ice on roadways while minimizing impacts
on the environment. Due to the broad nature of this topic, sources for research and alternative methods
are listed and can be referenced for more detail. This fact sheet emphasizes methods and practices for
snow removal which are feasible and cost effective for local governments to implement consistent with
sound environmental quality goals. . ,
BACKGROUND
Salt was first used on roads in the United States for snow and ice control in the 1930s (Salt
Institute, 1994).. Beginning hi the late 1940s and 1950s, the "bare pavement" policy was gradually
adopted by highway agencies as the standard for pavement condition during inclement weather providing
safer travel conditions on roadways. The "bare pavement" policy became a useful concept for roadway
maintenance because it was a simple and self-evident guideline for highway crews. However, this policy
should be implemented with the application of the minimum amount of salt needed rather than the
maximum (Lord, 1988). A common perception that "more is bettef" led to practices of high application
rates of salt. Dispersion of city populations into suburbs, higher travel speeds, and growing dependence
upon automobiles for commuting and commerce increased the need for snow and ice removal for safer
roadways (Lord, 1988). In the 1960s, the use of salt as a deicing chemical became widespread in the
United States because it is readily available, it is effective on ice and snow, and it is the lowest cost
alternative (Salt Institute, 1994).
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In the late 1950's, damage to roadside sugar maples (a salt 'intolerant species) in New England
gave rise to concern about the widespread use of salt. Shortly thereafter, contamination to drinking water
from wells located near unprotected salt storage areas heightened this concern (Lord, 1988); Runoff of
road salts also became recognized as causing additional environmental damage in many areas. Other
adverse effects of the increased use of salt included the pitting and "rust out" of automobiles and
corrosion of highway structures, especially bridge decks (Lord, 1988).
These environmental concerns have spawned a number of research programs. The goal of this
research has been to minimize the environmental effects of deicing while still providing a cost effective
means of clearing roadways for safe travel conditions. Early in the 1960s, research began on alternative
deicing chemicals, reduced chemical use, improved operational practices, pavement heating, pavement
modification, and mechanical approaches (Lord, 1988). More recently, a "Snow and Ice Control" study
was conducted by the Strategic Highway Research Program (SHRP). SHRP is a unit of the National
Research Council that was authorized by Section 128 of the Surface Transportation and Uniform
Relocation Assistance Act of 1987 (SHRP-H-381, 1994). The show and ice control research included
five major initiatives: snowplpws, snow fences, road weather information systems, pretreatment, and
deicing chemicals (SHRP, 1991). '.-
INITIATIVES TO CONTROL SNOW AND ICE ON ROADWAYS WHILE MESIMIZIN&
ASSOCIATED ENVIRONMENTAL EFFECTS
Improved Operational Practices .
Clearing roadways after whiter storms accounts for-a. large portion of the highway maintenance
budget for many northern states. According to the Salt Institute's 1991 Snowftghters Handbook, snow
removal in 33 snow belt states accounted for 16.2 percent of total maintenance costs and 3.6 percent of
all highway expenditures (Salt Institute, 1991). To ensure public safety, minimize environmental effects,
and minimize costs, a well planned,and operated snow,and ice removal program is essential.
- ', > _ i
To aid highway management personnel hi improving operational practices, the Salt Institute
initiated a "sensible salting" program .in 1967 (Lord, 1988). These guidelines have evolved with
technology to include the following: planning; personnel training; equipment maintenance; spreader
calibration; proper storage; proper maintenance around chemical storage areas; and environmental
awareness (Salt Institute, 1994). Further information on the "sensible salting" program can be obtained
from the Salt Institute located in Alexandria, Virginia. While all of these guidelines reflect key concerns,
proper storage is considered one of the most effective in source control of deicing chemicals (EPA,
1974).
In a 1988 paper by Lord, the estimated annual loss of uncovered stockpiled salt in the United
States due to rainfall was 400,000 tons, which is approximately 5 percent of the 8 million tons of salt
used annually,in the United States. An estimate of $30 per ton of salt equates to a monetary loss of $12
million dollars each whiter (Lord, 1988). Rock salt may be purchased hi bulk for approximately $15 to
$20 per ton. Including transportation, these costs increase to $35 to $70 per ton (Lord, 1988). Monetary
loss calculations; by Lord used a unit cost estimate for salt of $30 per ton which is between estimates
including and excluding transportation. Guidelines for siting and design of deicing chemical storage
facilities are provided in the Manual for Deicing Chemicals: Storage and Handling (EPA-670/2-74-033,
1974), , / ,
Another source, the Regional Groundwater Center (1995), estimated that 10 million tons of salt
are used each whiter hi the United States to melt snow and ice on roads and surface streets (Regional
Groundwater Center, 1995, Salt Institute, 1994). The cost for salt is currently estimated at $17 to $20
per ton excluding transportation costs (Jesperson, 1995). To'minimize environmental impacts associated
with briny runoff due to rain and an uncovered stockpile of salt, proper storage facilities must be
implemented. , , .
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One of the most effective measures for reducing chemical application has been the use of a
calibrated spreader using the optimal application rate. Salt application rates range from 300 to 800
pounds per two-lane mile, depending on road, storm, and temperature conditions (Salt Institute, 1994).
Automatic controls on spreaders are recommended to ensure a consistent and correct application rate.
The spreader should be calibrated prior to and periodically during the snow season, regardless of whether
automatic or manual controls are used. Uncalibrated controls and poor maintenance are often responsible
for excessive salt use (Salt Institute, 1994). Guidelines for the calibration of spreaders and determination
of application rates are given in the Salt Institute's Snowfighters Handbook (1991) and in the EPA
document entitled Manual for Deicing Chemicals: Application Practices (EPA-670/2-74-045, 1974).
Road Weather Information Systems
The United States and Canada spend over $2 billion dollars each year on snow and ice control,
(SHRP, 1993). In an effort to reduce these costs and maximize efforts, the SHRP sponsored research
using road weather information systems (RWIS) for highway snow and ice control. Components of the
RWIS include meteorological sensors, pavement sensors, site-specific forecasts, temperature profiles of
roadway, other available weather information (including.a weather advisor), communications, and
planning (SHRP, 1993).
The RWIS can be used to maximize icing and plowing efforts by pinpointing and prioritizing
roadways which need attention.. It is also designed to eliminate unnecessary call-outs and provide better
scheduling of crews based on knowledge of the probable extent and severity of the whiter storms.
Research indicated that the use of the RWIS technologies can improve efficiency and effectiveness as well
as reduce the costs of highway winter maintenance practices (SHRP, 1993). It was concluded hi this
report that road weather information system technology has the potential' for improving service. This
conclusion led to the recommendation that every agency that regularly engages in snow and ice control
should consider acquiring some form of road weather information systems; at a minimum, forecast
services should be used. The SHRP also pointed out that additional research beyond the scope of the
original RWIS project would be helpful (SHRP, 1993). Additional information about RWIS and
intelligent and localized weather prediction are provided in the following SHRP manuals: Road Weather
Information Systems, Volumes land 2 (SHRP-H-350 and SHRP-H-351); and Intelligent and Localized
Weather Prediction (SHRP-H-333).
Alternative Deicing Chemicals
The most commonly used salts for deicing are sodium chloride (NaCl) and calcium chloride
(CaCl) (Salt Institute, 1994). Approximately 10 million tons of salt are used each year at a cost of
approximately $17 to $20 a ton (Jesperson, 1995). The eastern and north-central sectors of the country
use more than 90 percent of this salt each year (Lord, 1988). Salt has proven to be a very effective and
feasible deicing chemical. However, the importance of snow and ice removal programs, public safety,
economic concerns, and environmental factors have led to research utilizing alternative deicing chemicals.
An acceptable alternative to salt as a deicer must have an effective melting range similar to salt,
lack detrimental effects, and be cost-comparable. Some alternative deicers evaluated include formamide,
urea, urea-formamide mixture, tetrapotassism phosphate (TKPP), ethylene glycol, ammonium acetate,
and calcium magnesium acetate (Lord, 1988). The only alternative that warranted further consideration
was calcium magnesium acetate (CMA). CMA is made from delometric limestone treated with acetic
acid. While CMA does not overcome all the undesirable characteristics of salt, it is an effective deicing
chemical (although more material does need to be applied to result hi the same deicing achieved with
salt). Since CMA has less potential to effect the environment and is not as corrosive as salt, it is a
frequently used deicing chemical. However, the cost of CMA was estimated to exceed salt by a factor
of 10 to 20 (Lord, 1988). Efforts have been made to find a more effective production technology to
lower the cost of CMA, but these efforts have had limited success (Lord, 1988). Alternative deicers can
-------
cost anywhere from $200 to $700 a ton (Jesperson, 1995). Therefore, salt is still the most cost effective
deicing agent. Another study performed by the Michigan Department of Transportation also found salt
to be the most cost effective deicing agent of those evaluated. Those evaluated included sodium chloride
(road salt), GMA, CMS-B (also known as Motech), CG-90 Surface Saver (a patented corrosion-inhibiting
salt), Verglimit (patented concrete surface containing calcium chloride pellets), and calcium chloride
(MOOT, 1993).
In 1992, the SHRP published a handbook to standardize testing procedures for evaluating deicing
chemicals (SHRP, 1992), Parameters evaluated include fundamental properties (e.g., ice melting
potential, fundamental thermodynamic factors), physicochemical characteristics, deicing performance
(e.g., ice melting, ice penetration, ice undercutting), materials compatibility, and additional engineering
parameters. This handbook is a valuable tool for the on-going research and technology of evaluating
deicing chemicals. Additional information on these testing procedures is provided in the Handbook of
Test Methods for Evaluating Chemical Deicers(SBSP-R-332, 1992). >
Pretreatment
Limited experience (mainly hi Scandinavian and other European countries) has shown that
applying a chemical freezing-point depressant on a highway pavement prior to, or very shortly after, the
start of accumulation of frozen precipitation minimizes the formation of an ice-pavement bond (SHRP,
1994). Liquid salt solution has been practiced in Scandinavia and has proven successful for pretreatment
(SHRP, 1994). The anti-icing or pretreatment practice reduces the task of clearing the highway and
requires smaller chemical amounts than are generally required under conventional deicing practices (e.g.,
applying after snow or ice have begun to accumulate). When properly implemented, pretreatment
practices may reduce costs and be more effective than conventional practices. However, most state
highway agencies generally have not adopted pretreatment due to uncertainty regarding how to implement
this practice and which conditions most favor it. Other concerns with pretreatment practices include the
imprecision with which icing events can be predicted, the uncertainty about the condition of the pavement
surface, and the public's perception of wasted chemicals. Some early attempts to utilize pretreatment
practices hi the United States have failed because of these uncertainties (SHRP, 1994). . -
The technological improvements hi weather forecasting and hi assessment of pavement surface
conditions, as previously mentioned, offer the potential for successful implementation of pretreatment.
Research during the winters of 1991-92 and 1992-93 by the SHRP indicated that a 40 percent arid 62
percent reduction, respectively, in chemical usage was possible using pretreatment (SHRP, 1994). The
success of pretreatment depends on accurate RWIS, a technology which is still evolving. Development
of spreaders specifically designed or retrofitted to distribute prewetted solid material or liquid chemicals,
calibration and evaluation of spreaders, training of maintenance personnel, and effective communication
are also items that need further attention to ensure the success of a pretreatment program (SHRP, 1994).
Additional,information on pretreament is available in the SHRP manual entitled, Development of Anti-
Icing Technology(SHRP-H-385, 1994).
Mechanical and Design Approaches
Many mechanical and design approaches have been and are being evaluated hi an effort to
improve snow and ice control practices. Some of these attempts have been very successful, while others
have had limited success or need additional research. Pavement heating, pavement coatings, mobile
thermal deicing equipment, snow fences, and snowplows are examined in this section. This is not an
inclusive list of mechanical and design approaches to improve snow and ice control,procedures.
Pavement heating and pavement coatings are two approaches to snow and ice removal that have
had limited success due to cost or feasibility. Pavement heating, systems are costly to install, and
operational costs exceed salt on the order of 15 to 30 times (Lord, 1988). Mobile thermal deicing
-------
equipment has also been evaluated and determined to be impractical Pavement coatings involve using
hydrophobic or icephobic coatings to reduce the adhesion of ice and snow to the roadway. Pavement
coatings are required to weaken or prevent bonding, while not decreasing traction in no snow conditions.
They are also required to persist in extremely harsh conditions. Pavement coatings were generally
unsuccessful because they were unable to meet these goals (Lord, 1988 and EPA, 1976). A 1976 EPA
Manual, Development of a Hydrophobic Substance to Mitigate Pavement Ice Adhesion (EPA-600/2-76-
242) describes this research.
Snow fences minimize costs associated with'snow clearing, reduce the formation of compacted
snow, and reduce the need for chemicals. Mechanical snow removal costs approximately 100 times more
than trapping snow with fences (SHRP, 1991). However, the snow fence must be properly positioned
and designed. A 4 foot picket fence in contact with the ground and improperly positioned was common
20 years ago (SHRP, 1991). Properly designed and positioned, taller fences are more effective than the
traditional lowpicket fence. Lightweight plastics allow the construction of portable fences up to 8 feet
tall (SHRP, 1991). A 15 foot tall snow fence used at Prudhoe Bay, Alaska is shown in Figure 1., To
rninimize improper positioning and design of snow fences, the SHRP provided publications such as
Design Guidelines for the Control of Blowing and Drifting Snow (SHRP-H-381,1994), Snow Fence Guide
(SHRP-W/FR-91-106, 1991), and a 21 minute video entitled "Effective Snow Fences".
Snowplow designs in the United States have evolved empirically, with scant regard to physical
properties of the material being handled and with little consideration to aerodynamic and hydrodynamic
principles involved in the flow of fluidizing snow. Consequently, the energy expended in displacing snow
is disproportionate to the work performed, and the low cast distance requires unnecessary rehandling of
the snow (Lord, 1988). The SHRP funded research at two universities to improve development of plow
blade design and cutting edges for the plow blades (SHRP, 1991).
FIGURE 1. SNOW FENCE (15 FT TALL) LOCATED AT PRUDHOE BAY, ALASKA
Source:
Design Guidelines for the Control of Blowing and Drifting Snow, SHRP-H-381, 1994
-------
The first research project, conducted By the University of Wyoming Department of Mechanical
Engineering, focused on developing an improved snowplow blade. The objective of this design was to
produce a plow that minimizes energy needed to throw snow clear of the roadway. The plow design,
based on analytical methods and laboratory scale experiments, showed a 20 percent improvement in
efficiency over conventional plows. The plow underwent testing hi West Yellowstone, Montana during
the whiter of 1990-1991 (SHRP, 1991)! Research for additional technological advances in plow design
is ongoing.
Another research project, conducted by the University of Iowa Institute of Hydraulic Research,
evolved to improve snowplow efficiency by improving cutting edges of plow blades based on mechanics
of ice. cutting (SHRP, 1993). Laboratory tests were performed with a hydraulic ice cutting ram to
determine the effects of the geometry on the cutting edge of a snow plow blade ,on the force required to
.remove ice from a highway pavement surface. Results Of this research indicate that changes hi the cutting
edge geometry result hi substantially unproved ice cutting, although the cutting edge performance may
benefit from further studies (SHRP, 1993). An Iowa Department of Transportation "plowing track" is
shown in Figure 2. Figure 3 shows a plowing truck which is cutting ice. Additional information can
be obtained in the SHRP manual entitled, Improved-Cutting Edges for Ice Removal (SHRP-H-346, 1993).
FIGURE 2. PLOWING TRUCK USED BY THE IOWA DEPARTMENT OF TRANSPORTATION
Source: Improved Cutting Edges for Ice Removal, SHRP-H-346, 1993
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FIGURE 3. A PLOWING TRUCK CUTTING ICE
Source: Improved Cutting Edges for Ice Removal, SHRP-H-346, 1993
SUMMARY OF FINDINGS
The importance of snow and ice control in terms of public safety, environmental effects, and costs
have prompted significant breakthroughs in technology. Technological breakthroughs and on-going
research have increased and will continue to increase the effectiveness of snow and ice removal programs
across the United States. However, these advances should be supplemented by additional research and
testing in the future.
To date, one of the most important advances to these programs has been improving operational
practices. These operational practices include guidelines on the following: planning, personnel training,
equipment maintenance, spreader calibration, proper storage of deicing chemicals, proper maintenance
around chemical storage areas, and an increased environmental awareness. Using proper storage facilities
for deicing chemicals and proper application rates has significantly reduced improper and overuse of these
chemicals. Best management practices for snow and ice removal should implement unproved operational
procedures supplemented by technological advances if they are feasible and cost effective.
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REFERENCES j
roved Operational Practices
1. Environmental Protection Agency (EPA), 1971. Environmental Impact of Highway Deicing.
Water Quality Office, Edison, New Jersey, 11040 GKK 06/71.
2. v EPA, 1972. A Search: New Technology for Pavement Snow-and Ice Control. Office of
Research, and Development, Washington, D.C., EPA-R2-72-125.
3. EPA, 1974. Manual for Deicing Chemicals: Application Practices. Office of Research and
Development, Cincinnati, Ohio, EPA-670/2-74-045.
4. EPA, 1974. Manual for Deicing Chemicals: Storage and Handling. Office of Research and
, Development, Cmcinmti, Ohio, EPA-670/2-74-033.
5. EPA, 1976. An Economic Analysis of the Environmental Impact of Highway Deicing. Office
of Research and Technology, Cincinnati, Ohio, EPA-600/2-76-105. ,
6. EPA, 1978. Optimization and Testing of Highway Materials to Mitigate Ice Adhesion (Interim
Report). Office of Research and Development, Cincinnati, Ohio, EPA-600/2-78-035.
7. Jesperson; K., 1995. "Road Salt and Groundwater, Is It a Healthy Combination?", On Tap,
Spring 1995, Volume 4, Issue 2.
8. Lord, B.N., 1988. "Program to Reduce Deicing Chemical Usage", Design of Urban Runoff
Quality Controls, 1988.
9. Regional Groundwater Center, University of Michigan,, 1995. Water Fact listed in On Tap,
Spring 1995, Volume 4, Issue 2. .
10. Salt Institute, 1991. "The SnowFighter's Handbook". Alexandria, Virginia, 1991.
11. Salt Institute, 1994. "Deicing Salt Facts: A Quick Reference". Alexandria Virginia, 1994.
Road Weather Information Systems
1. Strategic Highway Research Program (SHRP), 1993. Intelligent and Localized Weather
Prediction. SHRP - National Research Council, Washington, D.C., SHRP-H-333, 1993.
2. SHRP, 1993. Road Weather Information Systems, Volume 1: Research Report. SHRP -
National Research Council, Washington, D.C., SHRP-H-350, 1993.
;3. SHRP, 1993, Road Weather Information Systems, Volume 2: Implementation Guide. SHRP-
National Research Council, Washington, D.C., SHRP-H-351, 1993.
4. SHRP, 1993. "SHRP Innovations - Snow and Ice Control". H-200 Series Contracts, No.20.
Video - 12:41 minutes, SHRP- National Research Council, Washington, D.C., 1993.
Alternative Deicing Chefticals '
1. Environmental Protection Agency (EPA), 1971. Environmental Impact of Highway Deicing.
Water Quality Office, Edison, New Jersey, 11040 GKK 06/71.
2. EPA, 1972. A Search: New Technology for Pavement Snow and Ice Control. Office of
Research and Development, Washington, D.C., EPA-R2-72-125.
3. EPA, 1974. Manual for Deicing Chemicals: Application Practices. Office of Research and
Development, Cincinnati, Ohio, EPA-670/2-74-045.
4. EPA, 1974. Manual for Deicing Chemicals: Storage and Handling. Office of Research and
Development, Cincinnati, Ohio, EPA-670/2-74-033. ,
5. EPA, 1976. An Economic Analysis of the Environmental Impact of Highway Deicing. Office
of Research and Technology, Crncinnati, Ohio, EPA-600/2-76-105.
6. EPA, 1978. Optimization and Testing of Highway Materials to Mitigate Ice Adhesion (Interim
Report). Office of Research and Development, Cincinnati, Ohio, EPA-600/2-78-035.
7. Jesperson, K., 1995. "Road Salt and Groundwater, Is It a Healthy Combination?", On Tap,
Spring 1995, Volume 4, Issue 2.
-------
8. Lord, B.N., 1988. "Program to Reduce Deicing Chemical Usage", Design of Urban Runoff
Quality Controls, 1988. ,
9. Regional Groundwater Center, University of Michigan, 1995. Water Fact listed in On Tap,
Spring 1995, Volume 4, Issue 2.
10. Salt Institute, 1994. "Deicing Salt Facts: A Quick Reference". Alexandria Virginia, 1994.
11. SHRP, 1992. Handbook of Test Methods for Evaluating Chemicals Deicers. SHRP - National
Research Council, Washington, D.C., SHRP-H-332. ,
12. SHRP, 1993. "SHRP Innovations - Snow and Ice Control". H-200 Series Contracts, No.20.
Video - 12:41 minutes, SHRP- National Research Council, Washington, D.C., 1993.
13. Michigan Department of Transportation (MDOT), 1993. The Use of Selected Deicing Materials
on Michigan Roads: Environmental and Economic Impacts. Lansing, MI.
Pyetreatment
1. EPA, 1976. Development of Hydrophobic Substance to Mitigate Pavement Ice Adhesion. Office
of Research and Development, Cincinnati, OhiOj EPA-600/2-76-242, 1976.
2. Lord, B.N., 1988. "Program to Reduce Deicing Chemical Usage", Design of Urban Runoff
Quality Controls, 1988.
3. SHRP, 1993. "SHRP Innovations - Snow and Ice Control". H-200 Series Contracts, No.20.
Video - 12:41 minutes, SHRP- National Research Council, Washington, D.C., 1993.
4. SHRP, 1994. Development of Anti-Icing Technology. SHRP - National Research Council,
Washington, D.C., SHRP-H-385, 1994.
Mechanical and Design Approaches
Office of
1. EPA, 1972. A Search: New Technology for Pavement Snow and Ice Control.
Research and Development, Washington, D.C., EPA-R2-72-125.
2. EPA, 1976. Development of Hydrophobic Substance to Mitigate Pavement Ice Adhesion. Office
of Research and Development, Cincinnati, Ohio, EPA-600/2-76-242, 1976.
3. Lord, B.N., 1988. "Program to Reduce Deicing Chemical Usage", Design of Urban Runoff
Quality Controls, 1988.
4. Salt Institute, 1994. "Deicing Salt Facts: A Quick Reference". Alexandria Virginia, 1994.
5. SHRP, 1991. Snow Fence Guide. SHRP - National Research Council, Washington, D.C.,
SHRP-W/FR-91-106, 1991.
6. SHRP, 1993. Improved Cutting Edges for Ice Removal. SHRP - National Research Council,
Washington, D.C., SHRP-H-346, 1993. . ...
7. SHRP, 1993. "SHRP Innovations - Snow and Ice Control". H-200 Series Contracts, No.20.
Video - 12:41 minutes, SHRP- National Research Council, Washington, D.C., 1993.
8. SHRP, 1994. Design Guidelines for the Control of Blowing and Drifting Snow. SHRP -
National Research Council, Washington, D.C., SHRP-H-381, 1994.
9. SHRP, 1994. Development of Anti-Icing Technology. SHRP - National Research Council,
Washington, D.C., SHRP-H-385, 1994.
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STORMWATER BMP:
HANDLING AND DISPOSAL
OF COLLECTED STORMWATER
AND SEDIMENT CONTROL
SOLIDS/RESIDUALS
!MTB
Excellence h compljnce through optfmaf technical seditions
MUNICIPAL TECHNOLOGY BRANCH
INTRODUCTION
The total watershed has become increasingly important in defining modern urban stonnwater
management. Not long ago, stormwater management programs often provided little more than local
storm drainage, with scant regard for downstream effects. Today, a broad range of "best management
practices" (BMPs) have evolved because of increasing concern about comprehensive watershed
protection, these practices are intended to protect aquatic and terrestrial habitat, wetlands and cultural
resources by preventing or controlling erosion, sedimentation, and pollution runoff.
As technology has evolved to afford better environmental protection, operations and maintenance
requirements have increased; Many modern stormwater BMPs are designed to capture and retain solids.
The continued effectiveness of such BMPs depends on periodic inspection and removal of these
"residuals". ..'..,
This fact sheet summarizes the nature of the residuals problem, discusses the regulatory
framework and presents the management options available, along with typical unit costs and practical
considerations. In addition to the available literature, the following draws on the experience of a
number of practitioners at both the state and local levels.
POLLUTION FROM URBAN RUNOFF
Urban runoff carries a wide variety of pollutants from many sources and activities. Oil and salt
on roads, automobiles, atmospheric deposition, chemicals used in homes and offices, erosion from
construction sites, industrial plants, pet wastes, wastes from processing and salvage facilities, and
chemical spills are all typical sources of pollutant runoff. The quality of runoff water tends to worsen
as urbanization increases. This is caused by an increase in the density of sources and a decrease in
natural systems for capturing pollutants. Urbanization reduces the coverage of trees and other
vegetation which once intercepted rainfall. Natural paths, such as stream banks, become channels. The
erosive conditions increase the amount of sediment carried by runoff. Natural dips or depressions that
had formed temporary ponds for rainwater storage may be lost by grading and filling for development.
As asphalt and concrete replace vegetation, the quantity of runoff increases and it reaches'surface water
faster. When the land loses its ability to absorb and store rainwater, the groundwater table drops and
stream flows decrease during dry weather.
Urban runoff can affect water quality hi various ways depending on the type of pollutant in the
runoff, the quantity and concentration of the pollutant, and the nature of the receiving waters. Some
of the major pollutants include sediment (organic and inorganic), nutrients, bacteria, oil and grease, and
heavy metals. Other activities, parameters, and pollutants which may affect water quality include the
disturbance of stream habitats due to construction and erosion; impervious surfaces, temperature, toxic
substances, chlorides, and trash/debris. Urban runoff can also cause loss of property and vegetation
through erosion. '
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URBAN BEST MANAGEMENT PRACTICES
BMPs are an integral part of an urban stormwater management program. For new development,
BMPs intended for an erosion and sediment controFplan during the site development stage can be
designed with long-term runoff management as part of the objective. Some BMPs are designed for
long-term control; others are retrofit projects intended to correct problems resulting from the lack of
stormwater management. Goals of a BMP are to reduce the erosive effects of runoff and minimize the
pollutants in urban runoff, including toxic pollutants which may effect downstream waters. Selection
of the proper BMPs or combination of BMPs is critical to achieve this goal. BMP selection criteria
include: the site's physical condition and development; runoff control benefits provided by each BMP
option; the pollutant removal capability of each BMP option under several design scenarios; the
environmental and human health advantages of each BMP option; the ultimate use of the receiving water
body; and the long-term maintenance cost of the BMP.
Urban BMPs can generally be grouped in the following categories: detention basins,
retention/infiltration devices, vegetative controls, and pollution prevention. Detention basins are widely
used and are very effective in reducing suspended solid particles by temporarily holding the stormwater
runoff and allowing the sediments to settle. Dry ponds, wet ponds, and extended detention dry ponds
are examples of detention basins. Detention basins can reduce suspended solids concentrations.by 50
to 95 percent. In addition, since detention basins delay the amount of runoff released into receiving
waters, downstream flooding and streambank erosion fromvhigh flows are reduced and stress on the
physical habitat is lessened.
Infiltration devices allow runoff to percolate into the ground, thereby reducing the amount of
pollutants released into the receiving water. Infiltration basins, infiltration trenches and dry wells, and
porous pavement are some examples of infiltration devices. The filtration and adsorption mechanism
traps many pollutants (e.g., suspended solids, bacteria, heavy metals, and phosphorus) in the upper soil
layers and prevents them from reaching groundwater. Infiltration devices can remove up to 99 percent
of some runoff pollutants, depending on the percolation rate and area, soil type, pollutants present, and
available storage volume. Retention devices are also used as pretreatment devices to treat runoff before
it enters the stormwater collection system or infiltrates into the ground. Sand filters and oil/grit
separators are examples of these devices. There has been limited success with some of these devices.
Negative aspects of oil/grit separators are their limited ability to remove pollutants caused by low
average detention times, and the resuspensipn and release of settled material during later storms.
Vegetative BMPs are used to decrease the velocity of stormwater runoff. This promotes
infiltration and settling of suspended solids and also prevents erosion. Basin landscaping, filter strips,
grassed swales, and riparian reforestation are examples of vegetative BMPs. Vegetative BMPs also
remove organic material, nutrients, and trace metals. For maximum effectiveness, vegetative, controls
should be used as a first line of defense in removing pollutants in combination with other BMPs.
Pollution prevention is a source reduction program usually classified as a non-structural BMP.
Local governments and industries establish pollution prevention programs to reduce the generation and
exposure of pollutants that accumulate on streets, parking lots, and other surfaces, and eventually wash
into streams and lakes. Examples of pollution prevention controls include land use planning, zoning
strategies, street sweeping, good housekeeping practices, public education/awareness, and community
involvement. A combination of a pollution prevention program and a structural urban BMP within the
framework of a watershed management plan is usually required.
OPERATION AND MAINTENANCE OF URBAN BMPS
Proper operation and maintenance (O&M) procedures for all structural BMPs are essential to
ensure their continued effectiveness. These O&M procedures may include the following: periodic
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inspections; pipe, pump, and structure maintenance; erosion control; nuisance control; general
housekeeping; and debris and sediment removal. Periodic inspections are important to ensure that the
structure, operates in the manner originally intended. Inspections of municipal BMPs are usually
performed by the local jurisdiction under stale inspection criteria. Ideally, these inspections occur
annually during wet weather to assess the BMP's effectiveness.
Erosion control may be necessary for some types of BMPs. Corrective measures such as
regrading and revegetation may be'necessary. Nuisance control is probably the most frequent
maintenance item demanded by the local residents. Control of insects, weeds, odors, and algae may
be needed with some BMPs. Some general housekeeping maintenance practices include grass,cutting,
vegetation control, and litter/debris removal.
For the BMP to achieve maximum pollutant removal it is necessary to periodically remove the
stormwater residuals and sediment solids from the system. The removal of collected stormwater and
sediment control solids/residuals is very site specific, However, it is possible to provide a general
discussion for each structural BMP category (i.e., detention basins, .retention/infiltration devices, and
vegetative controls). O&M procedures for removing and handling stormwater solids/residuals from
BMPs should be planned in the design stages of the BMP.
Detention Basins , ,
Wet ponds will eventually accumulate enough sediment to significantly reduce storage capacity
of the permanent pool. This loss of capacity can reduce both the appearance and the pollutant removal
efficiency of the pond. The best available estimate is that approximately one percent of the storage
yolume capacity associated with the two year design storm can be lost annually (MWCOG, 1987).
Even more storage capacity can be lost if the pond receives large sediment input during the construction
phase. A sediment clean-out cycle of 10 to 20 years is frequently recommended in the Washington,
D.C. metropolitan area (APWA, 1981; MWCOG, 1983b). According to the Center for Watershed
Protection, stormwater ponds should require sediment clean-out on a 1.5 to 25 year cycle (Schueler and
Yousef, 1994). Most ponds are now designed with a forebay to capture the majority of sediments
decreasing the solids load to the wet pond. A common forebay sizing criterion is that it should
constitute at least 10 percent of the total pool volume (Schueler and Yousef, 1994). This forebay could
lose 25 percent of its capacity within 5 to 7 years based on a 0.5 inch/year muck deposition rate and
the assumption that a forebay traps 50 percent of all muck deposited in the pond (Schueler and Yousef,
' 1994). However, using a forebay, the sediment removal frequency for the mam pond may be extended
to 50 years (Schueler and Yousef, 1994).
To clean out a larger wet pond, dragline or hydraulic dredge methods may be necessary.
Dipper, clamshell, or bucket dredges are mechanical dredge methods, which are sometimes used on
ponds which are not large enough to warrant a hydraulic dredge method. With smaller wet ponds, the
pond level may be drawn down to a point where the residuals can begin to dry hi place. After the-
material is dried, a front end loader can be used to remove it from the pond bottom. /
Dry ponds and .extended detention dry ponds also accumulate significant quantities of sediments
over tune. This sediment gradually reduces available stormwater management storage capacity within
me pond and also reduces pollutant removal efficiency. Sediment accumulation can make dry ponds
unsightly. In addition, sediment may tend to accumulate around the control device of the dry extended
detention ponds. This sediment deposition increases the risk that either the orifice or the filter medium
will become .clogged, and also gradually reduces storage capacity reserved for pollutant removal in the
lower stage. .Therefore, hi an extended detention dry pond it is recommended that sediment be removed
from the lower stage every 5 to 10 years (MWCOG, 1987). Sediment removal from these systems is
relatively simple if access is available for the equipment. /Therefore, it is essential that access be
included in the pond design. Front-end loaders or backhoes can be used to remove the accumulated
sediment.
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Retention/Infiltration Devices .
Infiltration basins are usually located in smaller residential watersheds that do not generate large
sediment loads or are equipped with some kind of sediment trap. Even when the sediment loads are
low, they still have a negative impact on the basin's performance. The sediment deposits reduce the
storage capacity reserved for exfiltration and may also clog the surface soils. Methods to remove
sediment are different from those utilized for detention basins. Removal should not begin until the basin
has thoroughly dried out, preferably to the point where the top layer begins to crack. The top layer
should then be removed using lightweight equipment, being careful not to unduly compact the basin
surface. The remaining soil can then be deeply tilled with a rotary tiller or disc harrow to restore
infiltration capacity. Vegetated areas disturbed during sediment removal should be revegetated
immediately to prevent erosion. .
Infiltration trenches require that the pretreatment inlets of underground trenches be checked
periodically and cleaned out when sediment depletes more than 10 percent of the available trench
capacity. This can be done using a vacuum pump or manually. Inlet and outlet pipes should also be
checked for clogging and vandalism. Dry wells should also be checked periodically for clogging.
Performance of sand filter systems may be sustained through frequent inspections and replacement of
the filter media every 3 to 5 years depending on the pollutant load. Accumulated trash and debris
should be removed from the sand filters every 6 months or as necessary. Sand filter systems are usually
cleaned manually (Parsons ES, 1995). Sediment is removed from porous pavement using vacuum
sweeping. It has been recommended that the porous pavement be vacuum swept four times per year,
followed by high-pressure jet hosing, to keep the pores open in the asphalt (MWCOG, 1987).
Ideally, oil/grit separators should be cleaned out after every storm event to prevent re-entry of
any residuals or pollutants into the storm sewer system during the next storm event. However, due to
the O&M costs and manpower requirements associated with this cleaning schedule, less frequent
cleaning usually occurs at a point when an oil/grit separator is no longer operating effectively. The
Metropolitan Washington Council of Governments recommends that oil/grit separators be cleaned out
at least twice a year (MWCOG, 1987). As with all BMPs, the cleaning frequency depends upon the
pollutant load which is site specific. Oil/grit separators can be cleaned out using several methods. One
method to clean an oil/grit separator is to pump out the contents of each chamber. The turbulence of
the vacuum pump in the chamber produces a slurry of water and sediment that can then be transferred
to a tanker truck., The other method involves carefully siphoning or pumping out the liquid from each
chamber (without creating a slurry). If needed, chemicals can then be added to help solidify the
residuals. The solidified solids/residuals can then be removed manually from the separator.
Vegetative Controls
Vegetative controls (basin landscaping, filter strips, grassed swales, and riparian reforestation)
rely on various forms of vegetation to enhance pollutant removal, habitat value, or appearance of a
development site. These controls should be used in combination with other BMPs. Some natural
systems require periodic sediment removal. For example, accumulated sediments deposited near the
top of a filter strip will periodically need to be removed manually to keep the original grade.
PROPERTIES OF STORMWATER SOLIDS/RESIDUALS
Stormwater solids/residuals have properties that are very site specific. It is difficult to precisely
estimate "typical" stormwater or sediment residual properties by the BMP employed or even.by site
classification such as residential, commercial, or industrial. A recent study by Schueler and Yousef
reviewed bottom sediment chemistry data from 37 wet ponds, 11 detention basins, and two wetland
systems, as reported from 14 different researchers. This research covered a broad range of geography,
although nearly 50 percent of the sites were located in Florida or the Mid-Atlantic states. These
-------
stormwater ponds Had been in use from 3 to 25 years. Sampling and analysis was restricted to mean
dry weight concentrations of the surface sediments that comprise the muck layer, which is usually the
top 5 centimeters (Schueler and Yousef, 1994). Properties of stormwater solids/residuals presented in
this 1994 study and hi three other technical papers, discussed hi the next paragraph, are presented in
the following sections. A summary of this data is presented in Table 1.
A1982 study performed at Marquette University, Milwaukee, Wisconsin, obtained urban runoff
'residuals from a field-assembled sedimentation basin hi Racine, Wisconsin, swirl and helical bend solids
separators in Boston, Massachusetts, and an in-line upsized storm conduit in Lansing, Michigan. The
residual samples from Racine and Boston were obtained from individual storm events, while the Lansing
samples represent a six month accumulation of residuals. All of the sample locations were primarily
residential (EPA - Marquette University, 1982). Results from the sampling are shown in Table 1, Also
shown hi Table 1 are the findings documented hi two other technical papers (EPA - Rexnord, Inc.,
1982, and Field and O'Shea, 1992).
In a 1994 paper on Pond Muck (pond sediment), Schueler and Yousef indicate that the
properties of the solids/residuals from all BMPs are similar except for oil/grit separators. Analyzed
properties mentioned hi the paper include the following: nutrients, trace metals (cadmium, copper,
lead, zinc, nickel, chromium), hydrocarbons, and priority pollutants. A noted exception, was that
grassed swale soils tend to have about twice as much phosphorus and lead as detention ponds. Only
one sand filter had been sampled, but these characteristics appeared similar to other BMPs (Schueler
and Yousef, 1994). Characteristics of solids/residuals from BMPs are discussed hi me following
sections, with the exception of oil/grit separators which warrant a separate subsection.
Solids
Solids from stormwater and sediment BMPs can consist of organic and inorganic material.
According to Schueler and Yousef (1994), the muck layer of a pond has a high organic matter content.
An average of nearly 6 percent volatile suspended solids was reported. Pond muck solids have a very
soupy texture with an average total solids content of 43 percent, although this parameter was reported
from Only 15 out of the 50 site locations. It was also described as having a distinctive grey to black
color. These residuals have a low density averaging approximately Ii3 g/cm3. These solids/residuals
also consist of poorly-sorted sands and silts dominating the muck layer (Schueler and Yousef, 1994).
According to a 1982 EPA study at Marquette University, total solids concentration of residuals
samples from a sedimentation basin hi Racine, Wisconsin ranged from 233 to 793 mg/1, with 104 to
155 mg/1 being volatile. Urban runoff residual samples from swirl and helical bend solids separators
hi Boston, Massachusetts ranged from a total solids concentration of 344 to 1,140 mg/1, with 107 to 310
mg/1 being volatile. The six month accumulated samples from the in-line upsized storm conduit in
Lansing, Michigan had a total solids concentration of 161,000 mg/1 with 25,800 mg/1 being volatile
(EPA - Marquette University, 1982). A 1992 paper by Field and O'Shea reported estimated annual
residual/sludge volumes for urban storm runoff hi the United States ranging from 27 to 547 million
cubic meters (35 to 715 million cubic yards) at an average total solids content'ranging from 0.5 to 12
percent (Field and O'Shea, 1992).
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Nutrients
The muck layer is enriched with nutrients. In the 1994 paper by Schueler and Yousef,
phosphorus concentrations were reported for 23 studies. The phosphorus concentrations ranged from
110 to 1,936 mg/kg, with an average concentration of 583 nig/kg. Nearly all of the nitrogen found hi
pond muck is organic hi nature. Total kjeldahl nitrogen (TKN) concentrations were reported for 20
studies and ranged from 219 to 11,200 mg/kg, with an average concentration of 2,931 mg/kg. Nitrate
was found to be present hi very small quantities. This either indicates that some denitrification is
occurring, hi the sediments or perhaps that less nitrate is initially trapped hi the muck layer. The
nitrogen to phosphorus ratio in this pond study averages 5 to 1. In comparison, the nitrogen to
phosphorus ratio for incoming stormwater usually averages about 7 to 1. Ponds appear to be more
effective hi trapping phosphorus than nitrogen. Another explanation for .the lower ratio is that the decay
rate for nitrogen hi the muck layer is thought to be more rapid than for phosphorus (Schueler and
Yousef, 1994). S
A 1982'EPA report and a 1992 paper by Field and O'Shea reported urban sludge nutrient
concentrations ranging from 502 to 1,270 mg/kg total phosphorus as P and 1,140 to 3,370 mg/kg TKN.
These nutrient concentrations were reported as being lower than nutrients found hi combined sewer
overflows (GSOs) and raw primary sludges (EPA - Rexnord, Inc., 1982 and Field and O'Shea, 1992).
Another 1982 EPA report presented the concentration of individual nutrients [total phosphorus, TKN,
ammonia-nitrogen (NH3), nitrite-nitrogen (NO^, and nitrate-nitrogen (NO3)] in stormwater sediment
samples from Boston, Massachusetts and Racine, Wisconsin as never exceeding 5 mg/1. Urban
stormwater sediment samples taken from Lansing, Michigan were between 0.3 and 2,250 mg/1 for
individual nutrients (total phosphorus, TKN, NH3, NO2, and NO3) (EPA - Marquette University, 1982).
Heavy Metals
According to the Northern Virginia Planning District Commission (NVPDC), sediment toxicity
has been measured and analyzed in the Northern Virginia area (Guliea, 1995). One of these studies by
Dewberry and Davis, 1990, is entitiled "Investigation of Potential Sediment Toxicity From BMP
Ponds". This report analyzed sediments from 21 ponds hi Northern Virginia under various land use
conditions. Many of these ponds are owned and maintained by a property owner or a homeowners'
association. Testing was performed for the presence of metals and to determine if the metals
concentration is classified as toxic._ The Extraction Procedure (EP) toxicity test was used by Dewberry
and Davis in the analysis. Conclusions of this report indicate that the stormwater sediments tested were
not hazardous and could be safely disposed of on-site or hi a landfill. Sediments should be tested
further for there use as backfill material or topsoil maintenance (Dewberry and Davis, 1990).
NVPDC had noted that while the 1990 study by .Dewberry and Davis determined the material
to be non-hazardous, characteristics of stormwater sediments are very site specific. In every jurisdiction
hi Northern Virginia, it is the responsibility of the owner/operator of the BMP to maintain and operate
the system. However, this may vary'from state to state. In addition, it is also recommended to plan
and design a BMP for on-site disposal of the material (Guilea, 1995).
Trace metal levels are typically 5 to 30 times higher hi the muck layer of a pond than in the
parent soil below the muck layer (Schueler and Yousef, 1994). Trace metal levels were also reported
to follow a relatively consistent pattern and distribution. The zinc concentration hi the muck 'layer was
the highest followed by lead. Zinc and lead concentrations were much greater than chromium, nickel,
and copper concentrations which were approximately equal. = Cadmium had the lowest concentration hi
the muck layer. In the 1994 Schueler and Yousef study, 50 ponds and wetlands were examined and
found to have zinc concentrations ranging from 6 to 3,171 mg/kg (dry weight). Lead and chromium
concentrations ranged from 11 to 748 mg/kg, and from 4.8 to 120 mg/kg, respectively. Nickel and
copper concentrations ranged from 3 to 52 mg/kg, and from 2 to 173 mg/kg, respectively. Cadmium
concentrations ranged from being non-detectable to 15 mg/kg (Schueler and Yousef, 1994).
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Field and O'Shea indicate that median concentrations of zinc, lead, copper, nickel, and
chromium in urban runoff sludges and residuals were reported as 316, 268, 263, 131, and 189 rag/kg,
respectively (Field and O'Shea, 1992). In the 1982 study at Marquette University, iron was found as
the highest concentration of metals in all of the samples ranging in concentration from 6.1 to 2,970
mg/1. Lead and zinc concentrations ranked second and third, respectively (EPA - Marquette University,
1982).
As with all pond parameters, trace metal concentrations are site specific. Ponds that primarily
service roadways and highways are enriched with trace metals which are presumably associated with
automotive loading sources (e.g., cadmium, copper, lead, nickel, and chromium). On the other hand,
stormwater ponds that service primarily residential areas have the lowest trace metal concentrations
(Schueler and Yousef, 1994). In general, the muck layer is highly enriched with metals; however, in
most cases it should not be considered an especially toxic or hazardous material. For example, none
of over 400 muck layer samples from any of the 50 pond sites examined in the referenced 1994 study
exceeded EPA's current land application criteria for metals (Schueler and Yousef, 1994).
Hydrocarbons
There is limited data on hydrocarbon and poly-aromatic hydrocarbon (PAH) concentration in
the muck layer of ponds. It was reported that the concentration of total PAH and aliphatic
hydrocarbons in the muck layer of a 120 year old London basin were 3 to 10 tunes greater,
respectively, than the base "parent" sediments. Minor degradation of the hydrocarbons trapped in the
muck layer appeared to have occurred in the basin in recent years. On the other hand, hydrocarbons
were rarely detected in the muck of Florida ponds. Hydrocarbon concentrations were reported for 2
out of the 50 sites in the 1994 report by Schueler and Yousef. These concentrations were reported for
a industrial and residential site as 12,892 and 2,087 mg/kg, respectively (Schueler and Yousef, 1994).
Bacteria
Urban stormwater solids may contain high levels of bacteria and viral strains, including fecal
streptococcus and fecal colifonn from animal and human wastes. These bacteria have the potential to
be spread from land application of stormwater residuals or landfill sites unless the proper precautions
are taken. Measures which reduce their concentration in the sludge and minimize any sludge-vector
contact include the following: stabilization of the solids; immediate covering of landfill trenches after
disposal of these solids; the treatment of these bacteria in the solids by pasteurization, heat treatment,
irradiation, etc; and public and animal access control away from the site (Field and O'Shea, 1992).
Other Pollutants
Other pollutants which may be toxic include pesticides and polychlorinated biphenyls (PCBs).
Toxic wastes may also be present in fertilizers, herbicides, and household substances such as paints and
cleaning materials. All of these pollutants may find then: way into stormwater solids/residuals. In the
1982 report from Marquette University, PCBs were observed hi measurable concentrations in the
Racine, Wisconsin and the Lansing, Michigan samples. These concentrations ranged from 0.19 to 24.6
pg/l. Of eight pesticides surveyed only three (DDT, DDD, and Dieldrin) were observed in measurable
concentrations (EPA - Marquette University, 1982).
Oil/Grit Separators
As previously mentioned, the stormwater and sediment solids collected by an oil/grit separator
contain unique characteristics compared to other stormwater BMPs. The metal content of trapped
sediments in an oil/grit separator may be 5 to 20 times higher than in other BMPs, especially if this
separator services a gas station. Priority pollutant and hydrocarbon levels are also much higher. These
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higher levels reflect the fact that most oil/grit separators service areas that may discharge higher
pollutant levels such as at gas stations or industrial sites, and are designed to trap lighter fractions of
oil which may not be trapped by other BMPs. Other BMPs, such as detention basins, usually drain
larger watersheds that dilute the influence of higher hydrocarbon or metal concentrations like those seen
from gas stations or industries. Therefore, it is doubtful if solids from other BMPs would approach
metal and hydrocarbon concentrations as high as those recorded with oil/grit separators (Schueler and
Yousef, 1994).
STORMWATER SOLIDS/SLUDGE HANDLING ALTERNATIVES
Centralized Treatment (Bleed/Pump Back To The Dry Weather Treatment Plant)
"-"''. / -' " '
Centralized treatment involves temporary storage of stormwater solids followed by its regulated
release into a sanitary sewer during dry weather flow conditions. Advantages of this residuals handling
alternative include the possible achievement of flow equalization through the timed addition of urban
storm runoff to the dry weather influent, and the use of a central, pre-existing treatment facility and
transportation system. Disadvantages of this system include: the deposition of large amounts of grit
in the sewer system; the potential for exceeding the capacity of the dry weather treatment facility; any
impacts to the treatment plant operation and efficiency which may arise due to differences in the
characteristics of sanitary wastewater and urban storm runoff residuals; and additional cost for treatment
(Field and O'Shea, 1992). The problems associated with bleed/pump back solids stonnwater/sediment
solids are similar to those evaluated with regard to CSO sludges.
Huibregste determined that "Centralized Treatment" was generally not practical (Huibregtse et
al, 1977). In addition to the disadvantages already listed, some problems which may be associated with
this type of system include: difficulties in effectively equalizing flow to the dry weather treatment plant
due to the high solids/low volume characteristic of sludges; and difficulties maintaining sludge quality.
Significant increases in heavy solids and toxic substance loadings will have an impact on treatment plant
operation and effluent quality. The addition of large amounts of gritty solids can grossly overload solids
handling facilities at treatment plants, and have a negative impact on overall sludge quality. Moreover,
the addition of these stormwater and sediment residuals to the treatment system will increase the
quantity of sludge which must be handled (Field and O'Shea, 1992). In a 1982 EPA report, -research
indicated that the riumb'er of days required for bleed/pump back of the residuals without overloading
'the dry weather treatment facility ranged from 2.8 to 3.9. This was considered an unacceptable
bleed/pump back period, considering the likelihood of overlapping rainfall events (Huibregste et al,
1977). . , ~
' , ; ' ~' - * '
Stormwater Solids Handling at Satellite Treatment Facilities
Another handling alternative for urban stormwater and sediment solids is treatment at a satellite
facility. Average characteristics of urban storm runoff differ substantially from those of sanitary
wastewater. For the treatment of stbrmwater runoff, biological processes are generally, not employed
due to its low organic and nutrient content as well as the intermittent and varying quantity and quality
of the storm flow. The major differences affecting treatment process design include urban runoffs high
grit content, low organic content, intermittent nature, and short flow duration (Field and O'Shea, 1992).
Evaluation of several CSO sludge handling processes by Huibregste found the most effective
unit processes to be: conditioning through chemical treatment; gravity thickening; stabilization through
lime addition; dewatering through vacuum or pressure filtration; and disposal through land application
or landfill (Huibregste et al, 1977). In a 1982 report by Huibregste a cost analysis was performed
specifically for the handling and disposal of urban storm runoff residuals. This cost analysis compared
the following six alternative sludge handling scenarios for either swirl or sedimentation concentrated
solids: (1) gravity thickening, vacuum filtration and landfill; (2) gravity thickening, vacuum filtration
and landspreading; (3) gravity thickening, pressure filtration and landfill; (4) gravity thickening,
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pressure filtration and landspreading; (5) gravity thickening and landspreading; or, (6) landspreading.
These cost estimates by. Huibregste et al, 1982, are presented in terms of dollars per acre for residuals
handling in an urban storm runoff area of 15,000 acres. These estimates were updated to July 1995
dollars and are presented in Table 2. As shown on Table 2, the most cost effective solids handling
scenario based on annual costs is lime stabilization, gravity thickening, pressure filtration, and
landfilling.
A 1982 EPA report from Marquette University concluded that of those options evaluated the
most cost-effective means for handling and disposal of urban stormwater runoff residuals is, gravity
thickening followed by lime stabilization and landspreading or landfilling (EPA - Marquette University,
1982). This conclusion was based on urban stormwater studies from Boston, Massachusetts, Racine,
Wisconsin, and Lansing, Michigan involving solids sampling, characterization, analysis, and treatability.
The characterization study included analyses for nine metals, eight pesticides and PCBs, solids,
nutrients, and organics. The treatability study included bench scale sedimentation tests, centrifugation
tests, lime stabilization tests and capillary suction tune tests (EPA - Marquette University, 1982). Other
bench scale studies were performed by Carr in 1982 that evaluated the effectiveness of three dewatering
alternatives for stormwater runoff residuals from sedimentation basins and swirl concentrators. These
dewatering alternatives were gravity thickening, centrifugation, and capillary suction. Data from these
studies indicated that the most effective method for concentrating urban stormwater runoff residuals was
gravity thickening (Carr et al, 1982).
These bench scale studies identified some effective treatment methods for urban stormwater
runoff residuals. However, characteristics of urban stormwater residuals are very site specific. Testing
and analysis may be necessary to determine what level of treatment is necessary to dispose of these
residuals.
On-Site Handling of Stormwater Solids/Sludge
The third alternative for handling/disposal of stormwater runoff residuals is on-site handling.
This option may be used after the residuals have been analyzed and determined to be a non-hazardous
material. During the design stage of a BMP, a dedicated area on the site should be set aside for land
application or land disposal of the residuals. The area for this material should be carefully selected to
prevent residuals from flowing back into the BMP during rainfall. On-site handling of this material is
usually very cost effective as it avoids transportation costs and landfill tipping fees.
The stormwater runoff residuals must first be removed from the BMP. Alternatives for
removing solids from various BMPs were discussed previously. After the solids are removed from the
BMP, they will usually require dewatering. Dewatering is accomplished by spreading the material out
on the ground and occasionally turning it. A front-end loader can be used for this. This material is
then either land applied or land disposed. Land application involves spreading the material to the land
at approved application rates. This material cannot be applied to a direct food chain crop and would
probably be applied to a meadow or vegetated area. There is very little nutrient value associated with
stormwater residuals. Land disposal consists of piling the material on an approved location at the site.
In some cases it may not be feasible to land apply or land dispose of the material on-site. This
may be due to limited space on-site initially or limited space due to the accumulation of material. In
any case, after the material is removed from the BMP it should be dewatered on-site if this is feasible.
This will cut down on the volume of material to be transported. The. material can then be loaded using
a front-end loader and transported to either a landfill or another site for land applicatibn.or land
disposal.
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TABLE 2
COST ESTIMATE ($/acre) FOR RESIDUALS HANDLING IN AN
URBAN STORMWATER RUNOFF AREA OF 15,000 ACRES (1)
Sludge Handling
Method
Sedimentation
Capital Q&M Annual
Swirl Concentration
Capital O&M Annual
Lime Stabilization 475 71
Gravity Thickening
Vacuum Filtration
Landfill ,
Lime Stabilization 507 . 76
Gravity Thickening
Vacuum Filtration
Landspreading
Lime Stabilization 492 60
Gravity Thickening
Pressure Filtration
Landfill
Lime Stabilization 522 64
Gravity Thickening
Pressure Filtration
Landspreading
Lime Stabilization
Gravity Thickening
Landspreading
Lime Stabilization 308 104
Landspreading .
134
171
124
156
186
507
531
550
569
394
1025
64
67
49
50-
87
856
130
155
117
139
166
1194
Note: (1) Huibregste et al, 1982; Costs have been updated to July 1995 dollars using the ENR
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REGULATIONS (CURRENT AND PENDING) AND LIABILITIES
Traditional point sources of water pollution are regulated by the EPA and individual states under
the National Pollutant Discharge Elimination System (NPDES) permit program. This program was
established by section 402 of the Clean Water Act, and establishes permit requirements for certain
municipal and industrial stormwater discharges. However, the regulations governing the handling and
disposal of stormwater runoff residuals is not as well defined. ,
Most states have regulations for runoff quality control. To adhere to these regulations, many
local governments have implemented drainage and flood control regulations. Some local governments
have also adopted localized stormwater quality and erosion/sediment control regulations which require
BMPs. To help local governments implement and properly operate these BMPs, states issue guidance
documents for local jurisdictions which are responsible for inspecting, maintaining, and ensuring proper
operation of stormwater BMPs. Some states will also periodically inspect a local jurisdiction's
stormwater management program.
In reality, many local jurisdictions do not have the manpower to inspect all BMPs regularly.
BMPs which are not maintained do not perform efficiently. If not maintained, pollutants removed by
the BMPs can be released back into the stormwater. An oil/grit separator is a good example of this.
Some BMPs, such as detention basins, were installed by local jurisdictions in the 1980s and are now
requiring or have not yet required cleaning/dredging for the first time. This is a learning experience
for many jurisdictions that have hot yet had to (or are doing it for the first time) dredge this.material
or handle/dispose of it. . :
Stormwater and sediment solids/residuals should initially be tested prior to disposal. If they are
not hazardous, they will usually require dewatering prior to disposal. Some disposal methods for this
material can be landfilling, land application, land disposal, and even incineration (e.g, non-hazardous
solids from oil/grit separators). Historically, and in most cases, the disposal of sediments removed from
BMPs has posed no special regulatory or legal difficulty. Many municipalities and industries have
disposed of such sediments hi the same way that they would have any uncontaminated soil (Jones et al,
1994). In fact, after drying, stormwater sediment has been mixed with other soil and reused as backfill
on construction projects (Jones et al, 1994) as well as cover for landfills (Cox, 1995).
If the residuals/solids from a BMP are determined to be hazardous, they must be managed
according to the Resource Conservation and Recovery Act of 1976 (RCRA) requirements. Wastes can
be defined by RCRA as hazardous because they either have certain characteristics or contain constituents
specifically listed in the RCRA regulations. Certain characteristics include ignitability, cor^ositivity,
explositivity, or toxicity. In nearly all cases involving stormwater BMP solids, sediments could be
classified as a hazardous waste because they contained listed chemicals rather than because the sediments
are hazardous by characteristic (Jones et al, 1994). Simply because a chemical regulated by RCRA is
detected in BMP sediments, does not render the sediment a hazardous waste. If no sample containing
greater than ten percent of the listed chemical (by volume), or if contact with precipitation/runoff is
unlikely, the sediment would not be classified as hazardous (Jones et al, 1994). Hazardous waste
material must be disposed or handled according to RCRA regulations which would either require
treatment to lessen the concentration of the hazardous constituent or disposal in a hazardous waste
landfill.
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EXAMPLES/CASE STUDIES
The following BMP residual management programs have been implemented by several
municipalities, states, and a company which cleans oil/grit separators for various clients. This section
is not inclusive, but is presented to illustrate how some states, municipalities, and industries manage the
solids/sediments from BMPs.
Waste Reduction, Disposal, and Recycling Services
A Baltimore, Maryland firm cleans oil/grit separators for many commercial areas and industries.
They use a three man crew and two trucks to clean these BMPs. A liquid tanker truck is used to pump
the oil and water out of the separator. This mixture is transported to their facility in Baltimore for.
treatment (Schorr, 1995).
The solids in the oil/grit separator are further solidified using chemical addition. Once the
material is solidified, it is shoveled put of the separator into 55 gallon drums. A composite sample is
taken from each drum. This material is analyzed for toxicity, ignitibility (flash test), and PCBs. If the
material is determined to be non-hazardous, the drums are taken back to their Baltimore facility. The
material is then loaded into roll-off dumpsters and transported to an incinerator where they receive a
certificate of destruction for the material (Schorr, 1995).
> As each cleaning and maintenance job is site specific,this firm charges by the hour. The cost
for cleaning is $202/hr for the three employees and two trucks. In addition, disposal of the liquid waste
is $0.35/gallon, charge for the chemical that aids in solidification is $9.95/bag, drum purchase cost is
$25/drum, drum disposal cost is $100, analytical charge is $145, and transportation charge is $250.
It was emphasized that these oil/grit separators should be cleaned periodically. Cleaning schedules of
oil/grit separators are site specific. For example, a typical commercial building may be cleaned one
time per year, whereas, an industry may have its oil/grit separators cleaned approximately every three
months (Schorr, 1995). .
If the material is determined to be hazardous, it is dealt with in an appropriate method
depending on the hazardous constituent of the waste. A copy of the analytical results are faxed to the
generator. Additional testing is usually required to determine what constituents) is present in the
sediment to classify it as a hazardous material (Schorr, 1995).
A hazardous material is handled on a case-by-case basis. Additional analytical testing and
handling of the hazardous material will increase costs. In most cases, treatment to lower the hazardous
chemical concentration to a non-hazardous level is preferred over landfilling in a hazardous waste
landfill. For example, a sediment that contained a high hydrocarbon content, which may occur at a
service station, would be spread out on an approved site for a period of time sufficient to allow the
concentration to decrease in the sediment (Schorr, 1995).
Prince George's County. Maryland ' , - ' ,
In Prince George's County, Maryland, BMPs such as wet ponds have been in service long
enough that they are just beginning to require dredging. In some cases, on-site disposal of the sediment
was planned for in the design of the BMP. However, if on-site disposal is not an alternative then
locating a site for disposal of the material is a major operation. Residual sand and gravel material from
the' BMP is transported to construction-sites for use or is disposed of on-site (Coffman, 1995).
Oil/grit separators are being phased out in Prince George's County for the following reasons
all of which pertain to residuals management: sometimes the landfill will not accept the material; they
require frequent maintenance and cleaning; the material is difficult to dewater; and the material is
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expensive to dewater, haul, and landfill (when the landfill accepts the material). In addition, the county
does not have the personnel to routinely inspect and enforce the cleaning of oil/grit separators. As an
alternative to this BMP, the county is focusing on pollution prevention and is also evaluating
bioretention (Coffinan, 1995).
Fairfax County, Virginia ,
Fairfax County has very few wet ponds. The wet ponds in the county are large lakes which
can properly function up to 100 years without dredging (Henry, 1995). The county has not dredged
a wet pond since 1991. A small mini-dredge is used for dredging wet ponds. For the smaller ponds,
the lake level is lowered and attempts are made to dry the sediment material. After this, a clamshell
or bucket dredge is used to remove the material. Material is either disposed of on-site or in a landfill.
Sediments from dry ponds are dried on-site and removed using a front-end loader. This material is
either landfilled or disposed of on-site (Henry, 1995).
Montgomery County. Maryland
Montgomery County has wet ponds and dry ponds, the majority of which have not required
dredging. The State of Maryland has determined that the sediment from these ponds are a non-
hazardous material. Thus, the material can be disposed of either on-site or hi a landfill. The state law
requires that BMPs be inspected annually. In practice, this typically does not occur because of resource
limitations. The county has recently hired two more people to help with these inspections, but there
are many BMPs in the county and. the county does not anticipate achieving the annual inspection goal
(Brush, 1995).
Typical oil/grit separators require much maintenance attention, and Montgomery County is
trying to phase them out. The county has many sand filters proposed to replace the oil/grit separators,
but information on then* maintenance is not available due to the limited experience with cleaning and
niarntaining these filters (Brush, 1995).
State of Florida ' .
The State of Florida does not have a specific regulation stating that each jurisdiction must
dredge or remove material from BMPs periodically. They have issued a "Guidance Manual" as a
supplement to the regulations which are considered inadequate for handling stormwater sediments for
BMPs. Most BMPs were implemented hi 1982, and are just to the point where they require dredging
(Cox, 1995).
The guidance manual recommends testing of all BMP sediments, using the Toxicity
Characteristics Leaching Procedure (TCLP), before disposal. The state has performed numerous
analytical studies on this material, and in no cases was BMP sediment from any location determined to
be hazardous. However, oil/grit separators were not tested as part of this study. Materials considered
to be non-hazardous must have the appropriate laboratory TCLP paperwork before most landfills in
Florida will accept it. Some cities and counties avoid this testing by .sending BMP residuals to
construction/debris landfills which are not as stringent. This practice is not supported by the state (Cox,
1995).
Even if a material is considered not hazardous using the TCLP test, the State of Florida also
has a clean soil criterion. This is to protect community exposure from a material with.elevated
concentrations of a material which might not be classified hazardous. If a material does not pass the
clean soil criterion, (e.g., if metal concentrations are high, but not hazardous) then it can only be used
in an area where public access is controlled. Material such as this can be used as a landfill cover
because public access is limited to most .landfills. If the material does pass the TCLP and clean soil
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criterion then it can be used or disposed of in any manner. A beneficial use of the material is to blend
it with soil as a conditioner (Cox, 1995).
Sediments from dry ponds in Florida are removed using a front-end loader and a dump truck.
It is then recommended that a TCLP test be conducted on this material before either disposing on-site,
landfilling, or disposing of hi another manner. Wet ponds are dredged, however, these ponds are
sometimes directly connected to a waterway so caution is taken to ensure solids are not resuspended in
this operation. This, material is usually spread out on the site to allow drying and disposed of on-site.
If on-site disposal is not an alternative, then the sediments are usually transported to a landfill (Cox,
1995).
, " . ' J . - -
State of Delaware ,
The State of Delaware has followed Florida's lead as far as handling and disposal of stormwater
BMP residuals. The State of Delaware has not conducted testing of stormwater BMP sediments, but
considers the material as non-hazardous based on Florida's research and other research/reports. The
state also has a stormwater management program in which local jurisdictions are required to inspect
BMPs on an annual basis (Shaver, 1995),
The state's stormwater management plan includes BMP construction guidelines for ease of.
maintenance for the BMP and on-site disposal of the stormwater residuals. Oil/grit separators are not
a BMP alternative hi the State of Delaware. In addition to detention basins, sand filters are commonly
used. The cleaning schedule for a sand filter is site specific, but three to four times a year is a general
estimate. Three people are used to plean a "typical" Delaware Filter manually and shovel out the
material which takes approximately 4 hours. Labor cost to clean the filter is approximately $120. The
material is then transported to the landfill for disposal as this sediment was tested and not considered
a hazardous material (Shaver, 1995).
State of Maryland
The State of Maryland conducted a four year study on oil/grit separators with the Metropolitan
Washington Council of Governments. This study evaluated material from oil/grit separators in
Maryland to determine if it was hazardous. The study also evaluated maintenance of oil/grit separators,
as well as disposal of the residuals/solids from an oil/grit separator. Results from the study indicated
that the solids from oil/grit separators were not hazardous, therefore, this material could be disposed
of at a landfill after dewatering. However, as this material is site specific it was recommended that it
be tested prior to sending to a landfill (Pencil, 1995).
Inspections of BMPs are required of all local jurisdictions. Every three years, the state reviews
stormwater programs and procedures utilized by the local jurisdiction. The state has noted that many
BMPs are not being properly maintained. This is due to cost and manpower requirements associated
with regularly inspecting all BMPs by the local jurisdiction. Many homeowners' associations have
BMPs on their property. Maintenance of these BMPs is another area of concern for the state because
many homeowner's associations do not implement proper O&M procedures to maintain the BMP on
thehr property (Pencil, 1995). "
Sediments from Wet ponds and dry ponds, as long as they are not hazardous, are usually
dewatered and then disposed of on-site or landfilled. It is a pominon practice to spread this material
out on a site for use as a soil amendment (Pencil, 1995).
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SUMMARY OF FINDINGS
Data is available for solids content, nutrients, heavy metals, and other pollutants such as PGBs
for many urban stormwater BMP solids/residuals. However, the data on.stormwater residual's PAH
and hydrocarbon concentrations is limited. Additional sampling and analysis would be beneficial to
further examine these parameters.
Inspection and maintenance programs are the key to success for all BMPs. Guidelines for
inspection and frequency of inspection are provided by most states for local jurisdictions. However,
manpower requirements associated with enforcing the guidelines on the state level and inspection of
these BMPs on the local level do not seem to be adequate. BMPs located on private property are not
usually properly maintained or inspected. A possible solution to this lack of maintenance is to put a
maintenance requirement hi the deed for the land. This would require all owners of that property to
properly maintain the BMP.
Difficulties hi maintaining oil/grit separators and disposing of the residuals have resulted in
some jurisdictions phasing their use out. Oil/grit separators require frequent maintenance and cleaning,
the material is difficult to dewater, and the material is expensive to dewater, haul, and dispose of in a
landfill (when the landfill accepts the material). Also, if oil/grit separators are not properly maintained
then pollutants removed by the BMP can be released back into the stormwater. '
Since many wet ponds and dry ponds were implemented in the 1980's, they have not required
dredging or handling of the dredge material. Some local jurisdictions planned for oh-site disposal of
the material in the BMP design which is very cost effective because it avoids transportation charges.
Local jurisdictions which did not plan for on-site disposal in the design of these BMPs are searching
for disposal options for this material. Testing of stormwater sediment hi many studies have indicated
that this material is non-hazardous. Therefore, in most situations it can,be disposed of on-site (land
application or land disposal), hi a landfill, or in an incinerator.
REFERENCES
1. Brush, R., 1995. Personal communication with an employee from Montgomery County,
Maryland. '
2. Coffman, L., 1995. Personal communication with an employee from Prince George's County,
Maryland.
3. Cox, J., 1995. Personal communication with an employee from the State of Florida.
4. Dewberry and Davis, 1990. Investigation of Potential Sediment Toxicity from BMP Ponds;
Prepared for the Northern Virginia Planning District Commission, the Occoquan Policy Board,
and the Virginia State Water Control Board.
5. Environmental Protection Agency (EPA), 1978. Use of Dredgings for Landfill; Summary
Technical Report. Municipal Environmental Research Laboratory, Cincinnati, Ohio, EPA-
600/2-78-088a.
6. EPA, 1992. Storm Water Management for Industrial Activities: Developing Pollution
Prevention Plans and Best Management Practices. Office of Water, EPA 832-R-92-006.
7. EPA, 1993. Handbook: Urban Runoff Pollution Prevention and Control Planning. Office of
Research and Development, Washington, D.C. 20460, EPA/625/R-93/004.
8. Field, R. and O'Shea, M.L., 1992. "The Handling and Disposal of Residuals from the
Treatment of Urban Stormwater Runoff from Separate Storm Drainage Systems," Waste
Management & Research (1994) 12, 527-539. .'"'-.
9. Guilea, N., 1995. Personal communication with an employee from the Northern Virginia
Planning District Commission. - ( '
.10. Henry, W., 1995. Personal communication with an employee from Fairfax County, Virginia.
-------
lif Huibregtse, K.R., Morris, G1R., Geinopolos, A. and Clark, M.J., 19771 Handling and
Disposal of Sludges from Combined Sewer Overflow Treatment. Phase IT- Impact Assessment.
United States Environmental Protection Agency, EPA-600/2-77-053b, NTIS No. PB 280 309
12. Huibregste, K.R. and Geinopolos, A., 1982. Evaluation of Secondary Environmental Impacts
of Urban Runoff Pollution Control. United States Environmental Protection Agency, EPA-
600/2-82-045, NTIS No. PB 82-230 319
13._ Jones, J., et. al., 1994. An Enforcement Trap for the Unwary: Can Sediments that
Accumulate in Stormwater "Best management Practice" Facilities Be Classified as Hazardous
Wastes Under RCRA? A Practical Review for Engineers, Lawyers, and Drainage Facility
Owners. Report from Wright Water Engineers, Inc., Denver, Colorado.
14. Jones, J., et. al., 1995. "BMPs and Hazardous Sediment," PublicWorks, for May 1995, 51-
54- .'"' ..''''.-.'
15. Lee, G.F. and Jones-Lee, A, 1995. "Issues in Managing Urban Stormwater Runoff Quality,"
Water/Engineering & Management, May 1995, 51-53.
16. Leersnyder, Hugh, 1993. The Performance of Wet Detention Ponds for the Removal of Urban
! Stormwater Contaminants in the Aukland (NZ) Region. A thesis presented to the University
of Auckland in partial fulfillment of the requirements for the degree of Master of Science in
Environmental Science and Geography (University of Auckland).
17. Marquette University, 19821 Characteristics and Treatability of Urban Runoff Residuals.
Prepared for the EPA, Municipal Environmental Research Laboratory, Cincinnati, Ohio.
18. Metropolitan Washington Council of Governments (MWCOG), 1987. Control Urban Runoff:
A Practical Manual for Planning and Designing Urban BMPs.
19. Mineart, P and Singh, S., 1994. "The Value of More Frequent Cleanouts of Storm Drain
'-- Inlets," Watershed Protection Techniques,"'Volume 1, Numbers (Fall 1994).
20. Parsons Engineering Science, Inc. (Parsons ES), 1995. Navy Pollution Prevention Opportunity
Data Sheet (Sand Filters).
21. Pencil, K., 1995. Personal communication with an employee with the State of Maryland.
22. Rsxnotd, Inc., 1982. Evaluation of Secondary Environmental topacts of Urban Runoff
Pollution Control. Prepared for the EPA, Municipal Environmental Research Laboratory,
Cincinnati, phio. .
23. Schorr, S., 1995. Personal communication with an employee from All Waste-Clean America,"
. Inc. / ' -._/.'/ . ./' ';
24. Schueler, T and Yousef, YX., 1994. "Pollutant Dynamics of Pond Muck," Watershed
Protection Techniques, Volume 1, Number 2. Summer 1994.
25. Shaver, E., 1995. Personal communication with an employee from the State of Delaware.
26. Terrene'Institute, 1994. Urbanization and Water Quality: A Guide to Protecting the Urban
Environment. ;
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MTB
STORM WATER BMP:
INFOLrTRATION DRAINFIELDS
Offiot of Watewattr
MUNICIPAL TECHNOLOSr
DESCRIPTION ' '
Infiltration drainfidd structures are constructed to aid in stormwater runoff collection and are designed
to allow stormwater to infiltrate into the subsoils. Runoff is diverted into a storm sewer system which
passes through a pretreatment structure such as an oil .and grit separator. -The oil and grit .chamber
effectively removes coarse sediment, oils, and grease. Stormwater runoff continues through a manifold
system into the infiltration drainfield. The manifold system consists of perforated-pipe which distributes
the runoff evenly throughout the 'infiltration drainfield. The runoff then percolates through the
aggregate sand filter, the filter fabric and into the subsoils. A schematic of a typical system is illustrated
in Figure 1 below. . .
Perforated Pipe Manifold
Observation Wei
Top Sol
Washed Stone Reservoir
6%- 12" Sand Filer
SOURCE:
FIGURE 1: TYPICAL INFILTRATION DRAINFIELD SCHEMATIC
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COMMON MODIFICATIONS
Common design modifications include die installation of porous pavement surrounded by a grass filter
strip over the infiltration draiiifield or insertion of an emergency overflow pipe in the oil and grit
pretreatment chamber. The overflow pipe allows runoff volumes exceeding design capacities to
discharge directly to a trunk storm sewer system. > Infiltration drainfields are very similar to infiltration
trenches and basins.
CURRENT STATUS
Currently there is little information on infiltration drainfields. However, in .general the same principals
that apply to infiltration, basins and infiltration trenches will apply to design of infiltration drainfields.
The Environmental Protection Agency is currently evaluating the following issues, related to the design
and operation of infiltration drainfields: . : . .
.. ' . '''.' ">"-. ,,'.»".
. Is the oil and grit separator the most effective pretreatment system to protect infiltration
capacity? - . ' ' -. .
What is the pollutant removal capacity of infiltration drainfields 'with various pretreatment
' . systems? ' . ;'.. ' . , - . .-''''''.
Is the performance of infiltration drainfields. better than infiltration basins and trenches
during subfreezing weather and snow melt runoff conditions?
.What level of maintenance is required to ensure proper performance?
APPLICATIONS
.Infiltration drainfields are most applicable on sites with a relatively, s'mall drainage area (less than 15
acres). They can be used to control runoff from parking lots, rooftops, impervious storage areas, or
other land uses. Infiltration drainfields should not be used in locations that receive a large sediment
load that could dog a pretreatment system, which in turn, would plug the infiltration drainfield and
'reduce its effectiveness. :\ , .
Soils should have field-verified permeability rates of greater than 0.5 inches per hour and there should
be a 4-foot minimum clearance between the bottom of the system and;bedrock or the water.table.
LIMITATIONS . T.
The use of infiltration drainfields may be restricted in regions with colder, climates, arid regions, regions
with high wind erosion rates (increased windblown sediment loads), and areas where sole source
potable aquifers could be contaminated. Some specific limitations of infiltration drainfields include:
.. 'f High maintenance when sediment loads to the drainfield are heavy.
- High costs of excavation, fill material, engineering design, and
pretreatment systems. ; .
Short life span if not well maintained.
. Not suitable for use in regions with clay or silty soils. : , : .
, .'..,. Not suitable for use .in regions where groundwater is used locally for human consumption.
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Systems require sufficient time, between storm events, to allow the soil to dry out, or
anaerobic conditions may develop in'underlying soils which could clog the soil and
"reduce the capacity and performance of the system.
PERFORMANCE . . .
The effectiveness- of infiltration drainfields depends upon their design. When-runoff enters the
drainfield, many of the pollutants are prevented from entering surface water. -However, any water that
bypasses the pretreatment system and drainfield. will not be treated. Pollutant removal mechanisms
include absorption, straining, microbial decomposition in the soil below the drainfield, and trapping of
sediment, grit, and oil in the pretreatment chamber.
" f
Currently there is little monitoring data on the performance of infiltration drainfields. However, some
monitoring data is available on porous' pavements which incorporate many similar design'criteria as
infiltration drainfields. An estimate of porous pavement pollutant removal efficiencies range between 82
and 95'percent for sediment, 65 percent for total phosphorus, and 80 to 85 percent for total nitrogen.
Some key factors that increase performance and pollutant removal efficiencies include:
Good housekeeping practices in the tributary drainage area. ,.
s , t ' ' ' ' '
,. . Sufficient drying time <24 hours) between storm events.
Highly permeable soils and subsoils. . .
Pretreatment .system incorporated. . , : ,
Sufficient organic matter in subsoils. ,-
, . Proper maintenance. , ,
i * s '
Use of a sand layer on top of a filter, fabric at. the bottom of the drainfield. .
DESIGN CRITERIA '
Infiltration drainfields, along with most other infiltration BMPs (infiltration basins, trenches, etc.) have
' demonstrated relatively short life spans in the past. Failures have .generally been attributed to poor.
design, poor construction techniques, subsoils with low permeability and lack of adequate preventive.
maintenance. Some design factors which can significantly increase the performance and reduce the risk
of failure of infiltration drainfields and other infiltration processes are shown in Table 1 below. ,
MAINTENANCE .
Routine maintenance of infiltration drainfields is extremely important The pretreatment grit chamber
"should be checked at least four times per year and after major storm events. Sediment should be
cleaned out when the sediment depletes more than 10 percent of the available capacity. This can be
done manually or by vacuum pump. Inlet and outlet pipes should also be inspected at this time.
* ' (''-*'
The infiltration drainfield should contain an observation well. The purpose of the monitoring well is to
provide information on how well this system is operating. It is recommended that the observation well
be monitored daily after runoff-producing storm events. If the infiltration .drainfield does not drain after
three days, it usually means that the drainfield is clogged. Once the performance characteristics of the
structure have been verified, the monitoring schedule can be reduced to a monthly or quarterly basis.
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TABLE 1: INFILTRATION DRAINFIELD DESIGN CRITERIA
Design Criteria
Guidelines
Site Evaluation
Design Storm Storage Volume
Drainage Time Tor Design Storm
Construction
Pretreatment
Dispersion Manifold
Take soil borings 'to a depth of at least 4 feet
below bottom of stone reservoir to check fpr
soil permeability; porosity, depth to seasonally
high water table, and depth to bedrock.
Not recommended on slopes greater than 5
percent and best when slopes are as flat as
possible.
Minimum Infiltration rate 3 feet below, bottom
of stone reservoir: 0.5 inches per hour.
Minimum depth to bedrock and seasonally high
water table: 4 feet. ,
Minimum setback from water supply wells:
100 feet -.,'
Minimum setback from bui.ldtng-foundations:
10 feet downgradient, 100 feet upgradient.
Drainage area should be, less than 15 acres.
Literature values-suggest'this parameter is
highly variable and dependent upon regulatory
requirements. One typically recommended
storage volume Is the stormwater runoff*
volume produced In the tributary watershed by
the 6-month, 24-hour duration storm event.
Minimum: 12 hours.
*' . .
Maximum: 72 hours.
Recommended: 24 hours.
Excavate and grade with light equipment with
tracks or oversized tires to prevent soil
compaction..-'..''-.
As needed, divert stormwater runoff away from
site before and during construction.
A typical Infiltration cross-section consists of
the following: 1) a stone reservoir consisting of
coarse 1.5 to 3-Inch diameter stone (washed);
2) 6 to 12-inch sand filter at the bottom of the
drainfield; and 3) filter fabric.
Pretreatment is recommended to treat runoff
from all contributing areas.
A dispersion manifold should be placed 1n the
upper portions of the Infiltration dralnfield.
The purpose of this manifold is to evenly
distribute stormwater runoff over the largest
possible area. Two to four manifold extension
pipes are recommended for most typical
infiltration drainf leid applications.
SOURCE: Bjaaicti.
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COSTS
There is little infonna^on on the cost of infiltration drainfields. However, the construction costs for
installing an infiltration drainfield that is 100 feet long, 50 feet-wide, 8 feet deep and with. 4 feet of
cover can be estimated using the general information in Table 2 below.
TABLE 2: ESTIMATED COST FOR INSTALLING AN INFILTRATION DRAINFEELDS
Excavation Costs:
Stone Fill
Sand Fill
Filter Fabric
Perforated Manifold
and Inlet Pipe
Observation Well
Pretreatment Chamber
(2,220 cy) ($5.00/cy)
(1,296cyM$20.QO/cy)
(185cy)($10.00/cy)
$11,100
25,920
1,850
4,550
Top and Bottom - 10,000 sf
Sides = 1,600 * 800 - 2,400 sf..
Total - 12,400 Sf * 10?? - 13,640 Sf
(13,640 sf) (1 sy/9 sf) ($3.00/sy-)
75- * 4(40') * 235'
40'
(275)($10.00/ft)
1 at $500 ea
1 ,at $ 10,000
Miscellaneous
(Backfilling, overflow pipe, sodding, etc.)
2,750
500,
10,000
1,000
$57,670.
; SUBTOTAL
Contingencies (Engineering, administration, permits, etc.) * 25%_JA42P-
TOTAL , . $72,090 . '.
Note: Unit prices will vary greatly depending upon local market conditions.
SOURCE:
ENVIRONMENTAL IMPACTS : ,
One potential negative impact of infiltration drainfields is the risk of groundwater contamination.
Studies to date "do not indicate that this is a major risk. However, migration of nitrates and, chlorides
has been documented. " . , ,/
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REFERENCES ' -
1, Metropolitan Washington Council of Governments, Controlling Urban Runoff: A Practical Manual
. for Planning and Designing Urban' BMPs. 1987. -
2. Minn-"^ DftllnHon Control Agency. Protecting Water Quality in Urban Areas. 1989.
3. Cautfacartcm Wfcrw-'r n^r"' P^? <~"«sion- Costs of Urban Nonpoirit Source Water
Pollution Control Measures. Technical Report No. 31, June 1991.
4. TT.S. EPA. Stormwater Management for Industrial Activities: Developing Pollution Prevention Plans
Management Practices. Pre-print. July 1992.
. Stormwater Management Manual for the Puget Sound
, Basin. February 1992.,
,p*pa*dty**l*atapalT*****BmA(#M, VSEPA. *>1 HSamt.SW.WMnfaa,DC,20*&
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SMTB
STQRM WATER BMP:
INFILTRATION TRENCH
C*te of Wastevvater Management
.MUNICIPAL 'TECHNOLOGY BRANCH
DESCRIPTION ',..-..
Infiltration trenches are used to remove suspended solids, particulate pollutants, coliform bacteria,
organlcs and some soluble forms of metals and nutrients from storm water runoff. An infiltration trench,
as shown in Figure 1 below, is an excavated trench, 3 to 12 feet deep, backfilled with stone aggregate. A
small portion of the runoff, usually the first flush, is diverted to the infiltration trench, which is located either
underground or at grade. The captured runoff exits the trench by infiltrating into the surrounding soils.
filtration through the soil is the primary pollutant removal mechanism. Infiltration trenches also provide
groundwater recharge and preserve base-flow in nearby streams. '
FT.
CEOTEXTLE
nLTERFABKC
UOtSTUBED SOL
HMMUU WFtLTWOTOK KATE
OFO^OMCHPERHOUR
. 9 MCH SOUME STEEL FOOT PLATE
SOURCE: Reference*
I/I MCH OIAICTEK WBM ANCHOR
FIGJUREl: TYPICAL, INFILTRATION TRENCH
Infiltration trenches capture and treat, small amounts of runoff, but do not control peak hydraulic
flows. Infiltration trenches may be used in conjunction with another best management practice (BMP), such
as a detention pond, to provide both water quality control and peak flow control (Schueler, 1992, Harrington,
1989). Runoff that contains high levels of sediments or hydrocarbons (oil and grease) that may. clog the
trench are often pretreated with other BMPs. Examples of pretreatment BMPs include grit chambers, water
quality inlets, sediment traps, swales and vegetated filter strips (SEWRPC, 1991, Harrington, 1989).
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COMMON MODIFICATIONS
The infiltration trench can be modified by substituting pea gravel for stone aggregate in the top 1 foot
of the trench. The pea gravel improves sediment filtering and maximizes the pollutant removal in the top
of the trench. When the modified trenches become dogged, they can generally be restored to full
performance by removing and. replacing only of the pea gravel layer with out replacing the lower stone
aggregate layers. Infiltration trenches can also be modified by adding a layer of organic material (peat) or
loam to the trench subsoil. This modification appears to enhance the removal of metals and nutrient through
adsorption.
CURRENT STATUS
Infiltration trenches are often used in place of other BMPs where limited land is available.
Infiltration trenches are most widely used in wanner, less arid regions of the U.S. However, recent studies
conducted in Maryland and New Jersey on trench performance and operation and maintenance, have
demonstrated the applicability of infiltration trenches in colder climates (Lindsey, et al, 1991).
LIMITATIONS
The use of infiltration trenches may be limited by a number of factors, including type of soils,
climate, and location of groundwater tables. Site characteristics, such as the slope of the drainage area, soil
type, and location of the water table and bedrock, may preclude the use of infiltration trenches. The
surrounding area slope should be such that the runoff is evenly distributed in sheet flow as it enters the
trench. Generally, infiltration trenches are not suitable for areas with relatively impermeable soils such as
clayey and silty soils or in areas with fill. The trench should be located above the water table so that the
runoff can filter through the trench and into the surrounding soils and eventually into the groundwater. In
addition, the drainage area should not convey heavy levels of sediments or hydrocarbons to the trench. For
this reason, trenches serving parking lots should be preceded by appropriate pretreatment. Generally,
trenches that are constructed under parking lots are also difficult to access for maintenance.
As with any infiltration BMP, the potential of groundwater contamination must be carefully
considered, especially if the groundwater is used for human consumption or agricultural purposes; . In some
cases the infiltration trench may not be suitable for sites that use or store chemicals or hazardous materials.
In these areas other BMPs that do not interact with the groundwater should be considered. If infiltration
trenches are selected, hazardous and toxic materials must be prevented from entering the trench. The
potential for spills can be minimized by aggressive pollution prevention measures.. Many, municipalities and
industries have developed comprehensive spill prevention control and counter-measure (SPCC) plans. These
plans should be modified to include the infiltration trench and the contributing drainage area. For example,
diversion structures can be used to prevent spills from entering the infiltration trench.
An additional limitation is the climate. In cold climates, trench surface may freeze, thereby
preventing the runoff from entering the trench and allowing the untreated runoff to enter surface water.
The surrounding soils may also freeze reducing infiltration into the soils and groundwater. However, recent
studies indicate if properly designed and maintained infiltration trenches can operate effectively in colder
climates. By keeping the trench surface free of compacted snow and ice and by ensuring the part of the
trench is constructed below the frost line, will greatly improve the performance of the infiltration trench
during cold weather.
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PERFORMANCE
Infiltration trenches function similarly to rapid infiltration systems that are used in wastewater
treatment. Estimated pollutant removal efficiencies from wastewater treatment performance and modeling
studies are shown in Table 1 below. Based on this data, infiltration trenches can be expected to remove up
to 90 percent of sediments, metals, coliform bacteria and organic matter, and up to 60 percent of phosphorus
and nitrogen in the runoff (Schueler, 1987,1992). Biochemical oxygen demand (BOD) removal is estimated
to be between 70 to 80 percent. Lower removal rates for nitrate, chlorides and soluble metals should be
expected especially in sandy soils (Schueler, 1992).
TABLE 1: TYPICAL POLLUTANT REMOVAL EFFICIENCY
Sediment
Total Phosphorus
Total Nitrogen
Metals
Bacteria
Organic?
Biochemical Oxygen Demand
SOURCE: References 4 and 5
Typical Percent Removal Rates
90%
60%
60%
90%
90%
90%
70-
Pollutant removal efficiencies may be improved by using washed aggregate and adding organic matter
and loam to the subsoil. The stone aggregate should be washed to remove dirt and fines before placement
in the trench. The addition of organic material and loam to the trench subsoil will enhance metals and
nutrient removal through adsorption.
LONGEVITY
There have been a number of concerns raised about the long term effectiveness of infiltration trench
systems. In the past, infiltration trenches have demonstrated a relatively short life span with over 50 percent
of the systems checked, having partially or completely failed after 5 years. A recent study of infiltration
trenches in Maryland (Lindsey et al., 1991) found that 53 percent were not operating as designed, 36 percent
were partially or totally clogged, and another 22 percent exhibited slow filtration. Longevity can be increased
by careful geotechnical evaluation prior to construction. Soil infiltration rates and the water table depth
-------
should be evaluated to ensure that conditions are satisfactory for proper operation of an infiltration trench.
Pretreatment structures, such as a vegetated buffer strip or water quality inlet, can increase longevity by
removing sediments, hydrocarbons and other materials that may clog the trench. Regular maintenance
including the replacement of clogged aggregate, will also increase the effectiveness and life of the trench.
DESIGN CRITERIA
Prior to trench construction, a review of the design plans may be required by state and local
governments. The design plans should include a geotechnical evaluation that determines the feasibility of
using an infiltration trench at the site. Soils should have a low silt and clay content and have infiltration rates
greater than 0.5 inches per hour. Acceptable soil texture classes include sand, loamy sand, sandy loam and
loam. These soils are within the A or B hydrologic group. Soils in the G or D hydrologic groups should be
avoided. Sofl survey reports published by the Soil Conservation Service can be used to identify soil types and
infiltration rates. However, sufficient soil borings should always be taken to verify site conditions. Feasible
sites should have a minimum of 4 feet to bedrock in order reduce excavation costs. There should also be a
least 4 feet below the trench to the water table to prevent potential ground water problems. Trenches should
also be located at least 100 feet up gradient from water supply wells and 100 feet from building foundations.
Land availability, the depth to bedrock and the depth to the water table will determine whether the
infiltration trench is located underground or at grade. Underground trenches receive runoff though pipes
or channels, whereas surface trenches collect sheet flow from the drainage area.
In general infiltration trenches are suitable for drainage areas up to 10 acres (SEWRPC, 1991,
Harrington, 1989). However, when the drainage area exceed 5 acres, other BMPs should be carefully
considered (Schueler, 198? and 1992). The drainage area must be fully developed and stabilized with
vegetation before constructing an infiltration trench. High sediment loads from unstabilized areas will quickly
clog the infiltration trench. Runoff from unstabilized areas should be diverted away from the trench until
vegetation, is established.
The drainage area slope determines the velocity of the runoff and also influences the amount of
pollutants entrained in the runoff.. Infiltration trenches work best when the up gradient drainage area slope
js less than 5 percent (SEWRPC, 1991). The down gradient slope should be no greater than 20 percent to
minimize slope failure and seepage.
The trench surface may consist of stone or vegetation with inlets to evenly distribute the runoff
entering the trench (SEWRPC, 1991, Harrington, 1989). Runoff can be captured by depressing the trench
surface or by placing a benn at the down gradient side of the trench. Underground trenches are covered with
an impermeable geotextile membrane overlain with topsoil and grass.
A vegetated buffer strip (20 to 25 foot wide) should be established adjacent to the infiltration trench
to capture large sediment particles in the runoff. The buffer strip should be installed immediately after
trench construction using sod instead of hydroseeding (Schueler, 1987). The buffer strip should be graded
with a slope between 0.5 and 15 percent so that runoff enters the trench as sheet flow. If runoff is piped or
channeled to the trench, a level spreader can be installed to create sheet flow (Harrington, 1989).
During excavation and trench construction, only light equipment such as backhoes or wheel and
ladder type trenchers should be used to minimize compaction of the surrounding soils. Filter fabric should
be placed around the walls and bottom of the trench and 1 foot below the trench surface. The filter fabric
should overlap each side of the trench in order to cover the top of the stone aggregate layer (see Figure 1).
The filter fabric prevents sediment in the runoff and soil particles from the sides of the trench from clogging
the aggregate. Filter fabric that is placed 1 foot below the trench surface will maximize pollutant removal
within the top layer of the trench and decrease the pollutant loading to the trench bottom.
-------
The required trench volume can be determined by several methods. One method calculates the
volume based on capture of the first.flush, which is defined as the first 0.5 inches of runoff from the
contributing drainage area (SEWRPC, 1991). The State of Maryland (MD., 1986) also recommends sizing
the trench based on the first flush, but defines first flush as the first 0.5 inches from the contributing
impervious area. The Metropolitan Washington Council of Governments (MWCOG) suggests that the trench
volume be based on the first 0.5 inches per impervious acre or the runoff produced from a 1 inch storm. In
Washington B.C., the capture of 0.5 inches per impervious acre accounts for 40 to 50 percent of the annual
storm "runoff volume. The runoff not captured by the infiltration trench should be bypassed to another BMP
(Harrington, 1989) if treatment of the entire runoff from the site is desired.
Trench depths are usually between 3 and 12 feet (SEWRPC, 1991, Harrington, 1989); However, a
depth of 8 feet is most commonly used (Schueler, 1987). A site specific trench depth can be calculated based
on the soil infiltration rate, aggregate void space, and the trench storage time (Harrington, 1989). The stone
aggregate used in the trench is normally 1 to 3 inches in diameter, which provides a void space of 40 percent
(SEWRPC, 1991, Harrington, 1989, Schueler, 1987). . .
A minimum drainage time of 6 hours should be provided, to ensure satisfactory pollutant removal
in the infiltration trench (Schueler, 1987, SEWRPC, 1991). Although trenches may be designed to provide
temporary storage of storm water, the trench should dram prior to the next storm event. The drainage time
wfll vary by precipitation zone. In the Washington, D.C. area, infiltration trenches are designed to drain
within 72 hours. . ' . , .
'. ' ' ' - '
An observation well is recommended to monitor water levels in the trench. The well can be a 4 to
6 inch diameter PVC pipe, which is anchored vertically to a foot plate at the bottom of the trench as shown
in Kgure 1 above. Inadequate drainage may indicate the need for maintenance.
MAINTENANCE
/ '.
Maintenance should be performed as needed. The principal maintenance objective is to prevent
dogging, which may lead to trench failure. Infiltration trenches and any pretreatment BMPs should be
inspected after large storm events and any accumulated debris or material removed. A more through
inspection of the trench should be conducted at least annually. Annual inspection should include monitoring
of the observation well to confirm that the trench is draining within the specified time. Trenches with filter
fabric should be inspected for sediment deposits by removing a small section of the top layer. If inspection
indicates that the trench is partially or completely clogged, it should be restored to its design condition.
When vegetated buffer strips are used, they should be inspected for erosion or other damage after
each major storm event. The vegetated buffer strip should have healthy grass that is routinely mowed.
Trash, grass clippings and other debris should be removed from the trench perimeter. Trees and other large
vegetation adjacent to the trench should also be removed to prevent damage to the trench.
COSTS .
Construction costs include clearing, excavation, placement of the filter fabric and stone, installation
of the monitoring well, and establishment of a vegetated buffer strip. Additional costs include planning,
geotechnical evaluation, engineering and permitting. The Southeastern Wisconsin Regional Planning
Commission (SEWRPC, 1991) has developed cost curves and tables for infiltration trenches based on 1989
dollars. The 1993 construction cost for a relatively large infiltration trench (i.e., 6 feet deep and 4 feet wide
with a 2,400 cubic foot volume),ranges from $8,000 to $19,000. A smaller infiltration trench (i.e., 3 feet deep
and 4 feet wide with a 1,200 cubic foot volume) is estimated to cost from $3,000 to $8,500 (1993).
-------
Maintenance costs include buffer strip maintenance and trench inspection and rehabilitation.
SEWRPC (1991) has also developed maintenance costs for infiltration trenches. Based on the above examples,
annual operation and maintenance costs would average $700 for the large trench and $325 for the small
trench. Typically, annual maintenance costs are approximately 5 to 10 percent of the capital cost (Schueler,
1987). Trench rehabilitation, may be required every 5 to 15 years. Cost for rehabilitation will vary
depending on site conditions and the degree of clogging. Estimated rehabilitation cost run from 15 to 20
percent of the original capital[cost (SEWRPC, 1991).
ENVIRONMENTAL IMPACTS
Infiltration trenches provide efficient removal of suspended solids, particulate pollutants, conform
bacteria, organics and some soluble forms of metals and nutrients from storm water runoff. Infiltration
trenches also reduce the volume of runoff by providing a storage reservoir. The captured runoff infiltrates
the surrounding soils and increases groundwater recharge and base-flow in nearby streams.
Negative impacts include the potential for groundwater contamination. Fortunately, most pollutants
have a low potential to contaminate groundwater (Schueler, 1987). However, an EPA study (USEPA, 1991)
found that chloride and nitrate, which are very soluble pollutants, can migrate from infiltration trenches into
groundwater. In the future, federal or state agencies may require a groundwater injection permit for
. infiltration trench sites (Schueler, 1992). '
1. Harrington, B.W., 1989. Design and Construction of Infiltration Trenches in Design of Urban Runoff
Quality Control. American Society of Civil Engineers.
2. Lindsey, G., Roberts, L., and Page, W., 1991. Storm Water Management Infiltration
, Department of the Environment. Sediment and Storm Water Administration.
3. Maryland Department of Natural Resources, 1986. Minimum Water Quality Objectives and Planning
Guidelines for Infiltration Practices. Water Resources Administration, Sediment and Storm Water
Division.
I . - . . _ . r . 1 '. ,
4. Schueler, T.R. 1987. Controlling Urban Runoff: A Practical Manual for Planning and Designing Urban
Best Management Practices. Metropolitan Washington Council of Governments.
5. Schueler, T.R. 1992. A Current Assessment of Urban Best Management Practices. Metropolitan
Washington Council of Governments.
6. Southeastern Wisconsin Regional Planning Commission ([SEWRPC), 1991. Costs of Urban Nonpoint
Source Water Pollution Control Measures. Technical Report No. 31.
7. United States Environmental Protection Agency (USEPA), 1991. Detention and Retention Effects on
Groundwater. Region V.
8, Washington, State of, 1992. Storm Water Management Manual for the Puget Sound Basin (The
Technical Manual), Department of Ecology.
Tliis tact sheet was prepaid by the Municipal Tectaotogy Branch (420«, US EPA, 401M Slrwt, SWO, WaAitgtai, DC, 20460
-------
IMTB
Offict oT Wastewattr Btotwmrt 6 Ca^tsraf
MUNICIPAL TECHNOLOGY
STORM WATER BMP:
INTERNAL REPORTING
DESOUPTTON -.
Internal reporting provides a framework for "chain-of-command" reporting of stonnwater management
issues. Typically, a facility develops a Stonnwater Pollution- Prevention Team {SWPPT) concept for
implementing, maintaining, and revising the facility's Stonnwater Pollution Prevention Plan (SWPPP).
The purpose of identifying, a SWPPT ,is to clarify the chain of responsibility for stonnwater pollution
prevention issues and provide a point of contact for personnel outside the facility who need to discuss
the SWPPP. . '. '
CURRENT STATUS ' .
The U.S. EPA first identified internal reporting as a Best Management Practice CBMP) in the late 1970s.'
Currently, internal reporting has evolved into 'development of an SWPPT for facilities> implementing an
'SWPPP as part of their NPDES stonnwater discharge permit. This SWPPT concept/is a. new and
innovative part of the SWPPP.
IMPUEMENTATION - - '
The key to implementing internal reporting as a BMP is to establish a qualified SWPPT. Where setting
up an SWPPP is, appropriate, it is important to identify key people on-site who are most familiar with the
facility and -its operations, and to provide adequate structure and direction to the facility's entire
stormwater management program. Limitations involved in developing an internal reporting system are
' the potential lack of. corporate commitment in designating appropriate funds, inadequate staff hours
available for proper implementation, arid a potential lack of motivation from SWPPT members that could
inhibit the transfer of key stonnwater pollution information.
PERFORMANCE
The performance and effectiveness of an internal reporting system is highly variable and dependent upon
several factors. Key factors include:
- Commitment of senior management. ,
Sufficient time and financial resources. , .
Quality of implementation.
Background and experience of the SWPPT members. . , '
DESIGN CRITERIA . .
When establishing an internal reporting structure, it is important to select appropriate personnel to serve
on the team. Both team' and individual responsibilities should be designated with clear goals defined for
proper stormwater management. Internal reporting should be tied to other baseline BMPs such as
employee training, individual inspections, and record keeping to ensure proper'implementation. Figure 1
below illustrates an example SWPPT organization chart. _ , ,
-------
- ,' . Senior
"-.' Plant
Management
;: >
\ 1 .---t 1
Research ?, ;
Engineering | and ' .' \ Production
;: ' Development >
j «-g£^|; Maintenance)
.- ./- -1 .- :-___ ; L_
. .- 1 ' Material
Manufactunng | Storage
.Shipping and " .
. , Receiving
''..-' ' .... '-.'':. J . '
. SOURCE: Rfaaicti ' " V .' J ' ' " ' " ' ' ' -
HGURE 1: EXAMPLE SWPPT ORGANIZATION CHART
MAINTENANCE'' ' ' : ". ; '* '
To ensiire that an internal reporting system remains effective, the person or team responsible for
maintaining the SWPPP must be^ aware of any changes in plant operations or key team members to
determine if modifications must be--made; in the overaU execution of the SWPPP. -
..""' ' . ' ' . " * '
COSTS ' - - . , ' _ ' - - . . - . ..';'-,.,". ;
Costs associated with implementing an internal reporting system are those associated with additional
staff hours and related overhead costs. Annual costs can be estimated using the example shown in
Table 1 below. Figure 2 can be used as a worksheet to calculate ^the estimated costs for an internal
record keeping program. . , , ; .
TABLE 1: EXAMPLE OF ANNUAL INTERNAL REPORTING COSTS
, Tide
Stormwater Engineer
\
. Plant Management
Plant Employees
. SOURCE: EPA .
Note: Defined as a
those costs associated
,'"; ' ' . Avg.
"'.'. Hourly
Quaintly Ratt ($)
1 x 15
5 x 20..
100 x 10
Overhead*
Multiplier
x 2.0
x ,2.0
x 2.0
Estimated
'Yearly
Hours
onSW
Training '
x 20
x . . ' 10
x 5
TOTAL ESTIMATED ANNUAL COST
multiplier (typically, ranging between 1 and 3)
with payroll expenses, building expenses, etc.
that takes into
Est.
Annual
- 600
« 2,000
» 10.000
$12,600
account
-------
Estimated
Yearly
Avg. Hours
Hourly Overhead onSW
Tide . Quantity Rate (S) Multiplier Training
X X X , »
X X X .-
'x x x =
Est,
Annual
Cost($)
(BV
fO :
x x x ,m, (D)
TOTAL ESTIMATED ANNUAL COST
(Sum of A+B+C+D)
SOUKS: Rifemeti , .
FIGURE 2: SAMPLE ANNUAL INTERNAL REPORTING COST WORKSHEET
REFERENCES , ' ' / .. ,
1. IJ-S. EPA. NPDES BMP Guidance Document June 1981. .
2. TI.S. EPA, Storrrtwater Management for Industrial Activities: Developing Pollution Prevention Plans
and Best Management Practices, September,. 1992.
-------
%
MUNlCirAL.TECHNOL.Oar 1IANCH
STORM WATER BMP:
MATERIALS INVENTORY
DESCRIPTION , ''"-.,'
A materials inventory system involves the identification of all sources and quantities of materials that
may be exposed to direct precipitation or storm water runoff at a particular site. Significant materials
are substances related to industrial activities such as process chemicals, raw materials, fuels, pesticides,
and fertilizers. When these substances are .exposed to direct precipitation dr storm waiter runoff, they
may be carried to a receiving waterbody. Therefore, identification of these substances and other
materials helps to determine sources of potential contamination and is:the first step in pollution controj.
1 . / '
CURRENT STATUS .
Most facilities already have in place a materials inventory system. However, die inventory of significant
materials is not generally performed from a?, storm water contamination viewpoint. Modification of die
existing materials inventory program to include storm water considerations should be minimal. The
inventory should be incorporated into die Storm Water Pollution Prevention Plan (SWPPP).
APPLICATIONS
A materials inventory system is applicable to most industrial facilities. Inventory of exposed materials
should be part of a baseline administrative program and is direcdy related to botii record keeping and
visual inspection Best Management Practices (BMP).-
LIMITATIONS
Limitation of materials inventory system BMP include:
N " - .
It is an on-going process that continually needs updating.
Qualified personnel are required to perform die materials inventory from a storm
water perspective. :
Materials inventory records should be readily accessible.
PERFORMANCE
It is not possible to quantify water quality benefits to receiving waters of a materials inventory program
since die program is intended to prevent pollution before it occurs. However, it is anticipated that an
effective materials inventory program willresult in improved storm water discharge quality.
DESIGN CRITERIA ' .
Keeping an up-to-date inventory of all materials (hazardous and non-hazardous) on thie site will help to
limit material costs caused by overstocking, track how materials are stored and handled on site, and
identify which materials and activities pose die greatest risk to the environment.. The following basic
steps should be used in completing a materials inventory:
-------
Identify all chemical substances present in the work place; Walk through the facility and
review the purchase orders for the previous year. List all chemical substances used in the
work place and then obtain the material safety data sheets (MSDS) for each.
Label all containers to show the name and type of substance, stock number, expiration
date, health hazards, suggestions for handling, and first .aid information. This ,
information can usually be found "on the MSDS. Unlabeled chemicals and chemicals with
deteriorated labels are often disposed of improperly or unnecessarily.
Clearly mark on the inventory hazardous materials that require .specific handling, storage,
use, and disposal considerations. ,
Improved material tracking and inventory practices, such as instituting a shelf life program, can reduce
die wastes resulting from overstocking and the disposal of outdated materials. Careful tracking of all
materials ordered may also result in more efficient materials use. Figure 1 below illustrates,a simple
material-inventory tracking system. . , : - .
Based on your materials inventory, describe the significant materials that were exposed to storm water
during the past three years and/or are currently exposed. Other BMPs should then be evaluated and
implemented or constructed to eliminate exposure of theses materials to storm water or that provide
'appropriate treatment. before discharge to receiving waters. Figure 2 below illustrates a sample
worksheet for evaluating exposed materials. .-
MBOMBBBM
mwuatan*: Uft
\.
SOURCE: Rtfaaic
MATERIAL MVEHTCMY
ruLli.tn
cZ.
MM '
.,
-__
_
WocfcthMt .
D«»: ^^
nd vakwn'thM* IM
a umirrr"-"
3Y<0>
l»i»n<««i.imi i Hi n MI.
»-
To
U*
--
FIGURE 1: SAMPLE MATERIAL INVENTORY ,
-------
DESCRIPTION OFEXTOSEO SIGNIFICANT MATERIAL
WrOfflCMMttl . . f
jMBuctfem: Boid OB your mmM ktnmoiy. dMcrtM ttw lignHfcM mrariib «IM «» npewdanaimiMttrdurinaAcpMtttrMyMra
md/or ira Anntfy «>paMd. " '
e^S,1£3T''
'
SOURCE: Vtfanet
*M^<«
'ZZ
'
< rt
',., ...
-rjr=rsr
- . .*
-
. -
, '
.. '
i ., ' ; . . , ' . , , i
FIGURE2: EXPOSED MATERIAL WORKSHEET
MAINTENANCE
The key to a proper materials inventory system is continual updating, of records. Maintaining an up-to-
date materials inventory is an efficient way to identify what materials are handled on-site that may
contribute to storm water contamination problems. .
'COSTS * ' - . -...;.. , . V .'; ' . ' . /._''
The major cost of implementing a materials inventory system is the time required to implement a
program that places emphasis on storm water quality. Typically, this, is a small incremental increase if a
materials inventory program already exists at the facility. Keeping an up-to-date mventory. of aU
materials present on your, site will help to keep material costs down .by identifying waste and
overstocking. " ; '''
1 * ' ' ',.'- - i
REFERENCE "[ ' _ - . ,
1. U.S. EPA, NPDES Best Management Practices Guidance Document December. 1979.
2. U.S. EPA. Storm water Management for Industrial Activities: Developing Pollution Prevention
Plans and Best Management Practices. September, 1992.
7%tr BMPfoaJw* wpKpu*! bf At Mime**! Ta**aic# BmaA (4ZM). US EPA. *>l MSata. SW. WOngm, DC 2Mf&
-------
MTB
STORM WATER BMP:
NON-STORM WATER DISCHARGES
OfltoefWa
finfa
rt&
MUNICIPAL TECHNOLOGY BRANCH
DESCRIPTION .
Identifying and eliminating non-storm water discharges is an important,and very cost-effective Best'
Management Practice (BMP). Examples of non-storm water discharges include process water, leaks from
portable water tanks or pipes, excess landscape watering, vehicle wash water, and sanitary wastes. Non-
storm water discharges are typically the result of unauthorized connections of sanitary or process
wastewater drains that discharge to tie storm sewer rather than to the sanitary sewer. Connections of
non-storm water discharges to a storm water collection .system are common, yet often go undetected.
Another form of non-storm water discharge is wash water discharge to a storm drain. Typically these
discharges are significant sources of pollutants, and unless regulated by an NPDES permit, are illegal.
CURRENT STATUS . ,
Identifying and eliminating non-storm water discharges as a BMP have rarely been used at industrial
facilities. Part of the problem is educational. Many facility operators are unaware of what constitutes a
non-storm water discharge, and tie potential "impact The new NPDES permit requirements for the
presence of .non-storm water discharges will greatly improve the implementation of this BMP.
APPUCATIONS
Identification of potential non-storm, water discharges is applicable to almost every industrial facility that
has not been tested or evaluated for the presence of such non-storm water discharges.. Generally, a non-
storm discharge evaluation includes: .
Identification of potential non-storm water discharges locations.
Results of a physical site evaluation for the presence of non-storm water discharges.
The evaluation criteria or test method used.
The date of testing and/or evaluation. . .
The on-site drainage points that were directly observed during die test and/or evaluation.
LIMITATIONS ' '-.'..
Possible problems in identifying non:storm water discharges include:. ,
The possibility .that a non-storm water discharge may hot occur on the date of s
the test'or evaluation. .
The method used to test or evaluate the discharge may not be applicable to the
situation. . .
Identifying an illicit connection may prove difficult due to the lack of available data on
. the location of storm drains and sanitary sewers, especially in older industrial facilities.
-------
PERFORMANCE
The question of whether or not the elimination of non-storm water discharges is an effective BMP is
answered by evaluating the environmental impact of these discharges. If a significant loading of
pollutants is common from these, discharges, then their elimination will be an effective BMP.
Several studies exist on the contents of non-storm water discharges. Pitt and Shawley (1982) reported
that non-storm water discharges were found to contribute substantial quantities of many pollutants* even
though the concentrations.'were not high. The long duration of the base flows offset the lower
concentration leading to a substantial loading of pollutants. Gartner, Lee and Associates, Ltd. (1983)
conducted an extensive survey of non-storm water discharges in the Humber River watershed (Toronto),
Out of 625 outfalls, about 10 percent were considered significant .pollutant sources. Further
investigations identified many industrial and sanitary non-storm water discharges into the storm
.drainage system. For example, problems found in industrial areas included liquid dripping from animal
hides stored in tannery yards and washdowns of storage .yards at meat packing facilities. Therefore, it is
anticipated tiaat elimination of non-storm water discharges wm be a Wghly effective BMP.
DESIGN CRITERIA, '.." r
Key program criteria includes the identification and location of .non-storm water entries into storm
drainage systems. It is important to note that for any effective investigation of pollution within a storm
water system, all pollutant sources must be included. For many pollutants, storm water may contribute
the smaller portion of .the total pollutant mass discharged, from a storm drainage system. Significant
pollutant sources may include dry-weather entries occurring during both warm and cold months and
snowmelt runoff, in addition to conventional storm water associated with rainfall, consequently, much
less.pollution reduction benefit will occur if only storm water is.considered in a control plan for
controlling storm drainage discharges. The investigations may also identify illicit point source outfalls
that do not carry storm water. Obviously, .these outfalls also need to be controlled and permitted.
Figure 1 below can be used as a sample worksheet to report non-storm water discharges.
NON-STORM WATER DISCHARGE
Dauo<
.Test or.
' . . . -
'-. SOURCE-
Outfall Oiractfy
ObMrwd During dw
T««t Hin»(» m n*i«l< «'
: .
' f . . '
Rifatncfi.
Method UMd to
T«a or EvihiM
pneturg*
'
%
WorkshMt
Camptettd tan
TM.:
Oat*:
Dnerite Route from Tot tar
IIMJ PTMMWS or Moft*Stonn
Watw DiKitarg*
Ilia ill if II BkWMM^ri
fOvnUTy (vdnBHI
.SiflnifiCBHt Sourest
. -
N«n* of Pmon Ww
Conductid jOw TMt or
EvabiMian
!* ',
-------
There are four primary methods for investigating non-storm water discharges. These methods include:
"Sanitary and Storm Sewer Map Review. A review of a plant schematic is a simple, way to
'determine if'there are any unauthorized connections to the storm water collection system.
A sanitary or storm sewer map, or plant schematic is a map of pipes and drainage
systems used to carry process wastewater, non-contact cooling water, and sanitary wastes.
These maps (especially as-built plans or record drawings of the facility) should be
reviewed to verify that there are no unauthorized connections. A common problem is
that sites often do not have accurate or current schematics or plans.
Visual Inspection. The most simple method for detecting non-storm water connections in
the storm water collection system is to observe all discharge points during periods of dry
weather. Key parameters to look for are the presence of stains, smudges, odors, and other
abnormal conditions. , ? ,
' Sampling and Chemical Analysis. Sewer mapping and visual inspection are also helpful in
identifying locations for sampling. Chemical tests are needed to supplement the visual or
'physical inspections.- Chemical tests can help, quantify the approximate components of
the mixture at the outfall or discharge point. Samples should be collected, stored, and
analyzed in accordance with standard quality control and quality assurance (QA\QC)
procedures. Statistical analysis of the chemical test results can be used to estimate the
' , . relative magnitude of die various flow sources. In most cases, non-storm water
discharges are made up of may separate sources of flow (such as leaking domestic water
systems,' sanitary discharges, ground water infiltration, automobile washwater, etc.). Key
parameters that can be hdpM m identifying the source of the no-storm water flows
include, biochemical, oxygen demand (BOD), chemical oxygen demand (COD), total
organic carbon (TOC), specific conductivity, temperature, fluoride, hardness, ammonia
ammonium; potassium, surfactant fluorescence, pH, total available chlorine, and toxicity
screening. It may be possible to identify the source of the non-storm water discharge by
examining the flow for specific chemicals. . " .
Just as high levels 6f pathogenic bacteria are usually associated .with a discharge from a
sanitary, waste water sources, the presence of certain chemicals are generally associated
with specific industries. Table 1 below includes a listing of various chemicals that may
be associated with a variety of different activities. . -
Dye Testing. Another method for detecting improper connections to the storm water
collection system is dye testing. A dye test can be performed by simply releasing a dye
(either pellet or powder) into either the sanitary or process wastewater system.
' Discharge.points from the storm water collection system are them examined for color
. change.
MAINTENANCE, , .
A maintenance program consists of annual inspections for non-storm water discharges, even if previous
tests have been negative. New processes, building additions, and other plant changes, if they are not
carefully reviewed during design, may result in future unauthorized connections to the storm water
conveyance system. ' ,' , ' . "
-------
TABLE"!: CHEMICALS COMMONELY FOUND INDUSTRIAL DISCHARGES
Chemical:
Acetic acid
Alkalies
Ammonia
Arsenic
Chlorine
Chromium
Cadmium
Citric add
"Copper
Cyanides
Fats, oils
Fluorides
Formalin
Hydrocarbons
Hydrogen peroxide
Lead . .
Mercaptans
Mineral adds
Nickel
Nitro compounds
Organic adds
Phenols
Silver
Starch
Sugars . ,
Sulfldes
Suintes
Tannic acid
Tartaricadd
Zinc-
Industry; '
Acetate rayon, pickle and beetroot manufacture
Cotton and straw tiering, cotton manufacture, mercerizing, wool
scouring, laundries ,
Gas and coke manufacture, chemical manufacture '
Sheep-dipping, felt mongering ,
Laundries, paper mills, textile bleaching
Plating, chrome tanning, aluminum anodizing '
Plating
Soft drinks and dtrus fruit processing
Plating, pickling, rayon manufacture
Plating, metal deaning, case-hardening, gas manufacture
Wool scouring, laundries, textiles, oil refineries
Gas and coke manufacture, chemical manufacture, fertilizer plants,
transistor manufacture, metal refining, ceramic plants, glass etching
Manufacture of synthetic resins and penicillin .
Petrochemical and rubber factories
Textile bleaching, rocket motor testing ....: ..
Battery manufacture, lead mining, paint manufacture, gasoline
manufacture -
Oil refining, pulp mills
Chemical manufacture, mines, Fe and Cu pickling, brewing, textiles,
photoengraving, battery manufacture ' .
Plating '- '''
Explosives, and chemical works .
Distilleries and fermentation plants
Gas and coke manufacture, synthetic resin manufacture, textiles,
tanneries, tar, chemical, and dye manufacture, sheep-dipping
Plating, photography
Food, textile, wallpaper manufacture
Dairies, foods, sugar refining, preserves, wood process
Textiles, tanneries, gas manufacture, rayon manufacture
Wood process, viscose manufacture, bteaching
Tanning, sawmills . . .
Dyeing, wine, leather, and chemical manufacture :
Galvanizing, plating, viscose manufacture, rubber process
SOURCE Rtft**c*7.
-------
COSTS . '.... . -
The above methods are,mostly time-intensive and their cost are dependent on the amount of effort and
level of expertise employed. Visual inspections are the least expensive of, the three. Dye testing may be
.more cost effective for buildings that do not have current schematics of their sanitary and storm sewer
systems. The cost of disconnecting illicit discharges from-the storm water system will vary depending on
the type and location of the connection and die type of corrective action needed.
The Full use of all of the applicable procedures is most likely necessary to successfully identify pollutant
sources. Attempting to reduce costs, for example, by only examining a certain class of outfalls, or using
inappropriate testing procedures, will significantly reduce the utility of the testing program and result in
inaccurate conditions. , .
" ' '-.'/'
ENVIRONMENTAL IMPACTS '
Eliminating non-storm water discharges can have significant impacts on improving water quality in the
receiving waters. . '
REFERENCES'
1 Pin-, Robert-, and Field. Richard. Non-Storm water Discharges into Storm Drainage Systems.
NTiS Report No. PB92-158559, 1992. ' . ,
^ . , : x . ' T '.
2. Pitt, R. and Shawley, G., A Demonstration of Non-Point Pollution Management on Castro Valley
Creek Alameda County Flood Control District (Hayward, California) and U.S. EPA,
Washington, DC, June 1982. :
3. fiat-mir, T.»» and Associates. Ltd.. Toronto Area Watershed Management Strategy Study.
Technical Report No. 1. Humber River and Tributary Drv Weather Outfall Study. Ontario Ministry
of the Environment, Toronto, Ontario, November 1983. '' .
4. U.S. EPA. Storm water Management For Industrial Activities; Developing Pollution Prevention
Plans and Best Management Practice; September 1992. ;
e; Washington State Department of Ecology. Storm water Management Manual for the Puget ;
Sound Basin. February 1992.
6. raiifami-a PmrirnnTnpntal Protection Agency. Staff Proposal for Modification to Water Quality.
Order No. 91-13 DWO Waste Discharge Requirements for Discharges of Storm water Associated:
with Industrial Activities.' Draft, August 1992.
7. Pitt, Robert, Barbe, Donald; Adrian, Donald, and Field, Richard, Investigation of Inappropriate
Pollution Entries Into Storm Drainage Systems - A Users Guide. US EPA, Edison, New Jersey, 1992.
p*»«i**'*'**>' TtcMep »«* «ZM). US ETA. «U MSt~* SW, WUnfa*. DC, WtO.
-------
STORM WATER BMP:
POROUS PAVEMENT
IMTB
MUNICIPAL TECHMOtOOT »»ANCM
DESCRIPTION
Porous, pavement is a specially designed and constructed pavement which allows stormwater to pass
through it. The purpose of porous pavement is to reduce the speed and amount of runoff from a site,
and to filter potential pollutants from the stormwater. There are two principal types of porous
pavement: porous, asphalt pavement; and pervious concrete pavement. Porous asphalt, pavement
consists of an open graded coarse aggregate bound together by asphalt with sufficient interconnected
voids to provide a high rate of water percolation. Pervious concrete consists of specially formulated
mixtures of Portland cement,.uniform open graded coarse aggregate, and water. When properly handled
and installed, pervious concrete has a high percentage of void space which allows rapid percolation of
liquids through the pavement
The porous pavement surface is typically placed over a highly permeable layer of open graded gravel and
crushed stone. The void spaces in the aggregate layers provide a storage reservoir for runoff. A filter
fabric is placed Beneath the gravel and stone layers to prevent the movement of fine soil particles into
these layers. Figure 1 below illustrates a common porous asphalt pavement installation.
Berm Keeps Off-site
Runoff arid Sadiment Out.
Provides Temporary .
Asphalt is Vacuum Swept.
Followed by Jet Hosing.to
Keep Pores Free
Site Posted to Prevent
Resurfacing and Use of
Abrasives, and to Restrict
; Truck Parking
everse Perforated Pipe O
Discharges When 2 Year
Storage Volume Exceeded
Stone Reservoir Drains in 48-72 Hours or Less
Overflow Pipe
Filter Fabric Lines
Sides of Reservoir
to Prevent
Sediment Entry
Observation Well
Gravel Course or
6 Inch Sand-Layer
Undisturbed Spite with an Ic > 0.27 inches/Hour
Preferably 0.50 Inches/Hour or More
SOURCE.-
FIGURE 1: TYPICAL POROUS PAVEMENT INSTALLATION
Porous pavement offers a number of advantages including:
Provides water quality improvement by removing pollutants.
-------
Reduces the need for curbing and storm sewer installation.- . .
Improves road safety by increasing skid resistance. {Tests have shown that there
is up to*15 percent less hydro-planing and skidding on porous pavement surfaces.)
Provides recharge to local aquifers. .-' ' ,
COMMON MODIFICATIONS
A common modification for porous pavement design systems consists of varying the amount of storage to
be provided in the stone reservoir located directly beneath the pavement, and' adding perforated pipes
near the top of the reservoir to discharge stormwater runoff after the reservoir has been rilled to design
capacity. Stone reservoirs .may be designed to accept the first flush of stormwater runoff or provide
enough storage to accommodate runoff from a chosen design storm for infiltration through the
underlying subsoil. Pretreatmeht of off-site runoff is highly recommended., Another variation of pervious
concrete is the use of a concrete block or brick system with individual blocks separated by a pervious
material; -
.CURRENT STATUS ; ,
Currently there is little information on porous pavement. However, in general information about
infiltration trenches and basins also applies to porous pavement. The following concerns are
currently being evaluated by the EPA.' ,
Can pavement porosity be maintained over the long term,
particularly with .resurfacing needs and snow removal?.
What is the pollutant removal capability of porous pavement
during subfreezing weather and snow removal conditions?
What are the optimal relationships between porous pavement, -
groundwater, sandy soils, vand high water table conditions?
What are the costs of maintenance and rehabilitation options .
for restoration of porosity? . .
APPLICATIONS , . -'...
Porous pavement is applicable as a substitute for conventional pavement'on parking areas and low traffic
volume roads, provided that the grades, subsoils, drainage characteristics, and groundwater table
conditions are suitable. Slopes should be very, gentle to flat. Soils should have field-verified
permeability rates of greater than 0.5 inches per hour, and there should be a 4-foot minimum cleararice
from the bottom of the system to bedrock or the water table. Additional areas for use of porous
pavement include fringe overflow parking areas and taxiway and runway shoulders at airports.
UMITATIONS
The use of porous pavement may be restricted in regions with extremely cold climates, arid regions or
regions with high wind erosion rates (increased windblown sediment loads) and areas where sole source
potable aquifers.could be contaminated. The use of porous pavement is highly constrained, requiring
deep permeable soils, restricted traffic, and adjacent land uses. Some specific disadvantages of porous
pavement include:.
-------
The lack of experience with this technology with most pavement .
engineers and contractors.
Porous pavement has a tendency to become clogged if improperly
installed* or maintained. ,
The high failure rate of porous pavement sharply limits the
ability to meet watershed stormwater quality and quantity goals.
: Slight to moderate .risk of grouridwater contamination depending
on soil conditions and aquifer susceptibility.
Possible transport of hydrocarbons from vehicles and leaching '
of toxic chemicals from asphalt and/or binder surface.
Some building codes may not allow for the installation of porous
pavement. " , "'.' : . '.'.' ' .' ' '
The possibility exists that anaerobic conditions may develop in
:. underlying soils if the sofls, are unable to dry out between storm
events. '.'';;: ' : ;
PERFORMANCE .
.Traditionally, porous pavement sites have had a high failure rate (75 percent). Faflure has been
attributed to poor design, inadequate construction techniques, low permeability sofls, heavy '_
vehicular traffic, and resurfacing with nonporous pavement materials.
Porous pavement pollutant removal mechanisms include absorption, straining, and microbiological
decomposition in the soil underlying the aggregate chamber and trapping of paniculate matter
within the chamber. An estimate of porous pavement pollutant removal efficiency is provided by
twoi long-term monitoring studies. These studies indicate long-term removal efficiencies of . ' ,-
between 82 and 95 percent for sediment, 65 percent for total phosphorus, and 80-85 percent of
total nitrogen. They also indicated high removal rates for zinc, lead, and chemical oxygen
demand. Sonie'key factors to increase pollutant removal and prevent failure include:
.. Routine vacuum sweeping and high pressure washing.
Maximum'recommended drainage time of 24 hours.
Highly permeable sofls. ,
Pretreatment of off-site runoff.
. Inspection and enforcement of specifications during construction.
. Organic matter in subsofls. .
Clean-washed aggregate.
Use only in low-intensity parking areas.
. Restrictions on use by heavy vehicles.
Limiting useiof de-icing chemicals and sand. .
-------
DESIGN CRITERIA
Porous pavement, along with other infiltration BMPs (infiltration basins, trenches, etc.) have
demonstrated relatively short life spans in the past. Failures have, general been attributed to poor
design, poor'construction techniques, subsoils with low permeability, and lack of adequate preventive
maintenance. Key design factors that can significantly increase the performance and reduce the risk of
failure of pprous pavements and other infiltration BMPs" is shown in Table 1 below.
TABLE 1: DESIGN CRITERIA FOR POROUS PAVEMENT.
Design Criteria
Guidelines
Site Evaluation
Traffic Conditions'
Take son borings to depth of at least 4 feet
, below bottom of stone reservoir to check for
soil permeability, porosity, depth to seasonally
high water table, and depth to bedrock.
Not recommended on slopes greater than 5
percent and best with slopes as flat as possible;
Minimum infiltration rate 3 feet below bottom of
stone reservoir 0.5 inches per hour.
Minimum depth to bedrock and seasonally high
water table: 4 feet
Minimum setback from water supply wells: 100
feet. -'. '.,-.,..-.'
Minimum setback from building foundations: 10
feet downgradient, 100 feet upgradient.
Not recommended .in areas where wind erosion
supplies significant amounts of windblown
sediment. .
Drainage area should be less than 15 acres.
Use for low volume automobile parking areas
and lightly used access roads.
Avoid moderate to high traffic areas and
significant truck traffic
SOURCE:
-------
TABLE 1: DESIGN CRITERIA FOR POROUS PAVEMENTS.
.'. (CONTINUED)
Design Criteria
Guidelines
Design Storm Storage Volume
Drainage Time for Design Storm
Construction
While the standard porous pavement design is
believed to withstand freeze/thaw, conditions
normally encountered in most regions of the
country, the porous pavement system is sensitive to
dogging during snow removal operations. Therefore,
the area should be posted with signs to restrict the
use of sand, salt, and other deicing chemicals
typically associated with snow cleaning activities.
Literature values suggest this parameter is highly
variable and dependent upon regulatory '
requirements. One typically recommended
storage volume is the stprmwater runoff volume
produced in the tributary watershed by the
produced in the tributary watershed by the
6-month, 2£>hour duration storm event.
Minimum: 12 hours.
Maximum: 72 hours.
Recommended: 24 hours.
\ .,--__
Excavate and grade with light equipment with
tracks or oversized tires to prevent soil
compaction. .
As needed, divert stonnwater runoff away from
planned pavement area to keep runoff and
sediment away from site before and
during construction." ., .
A typical porous pavement cross-section consists
of the following layers: 1) porous asphalt course,
2-4 inches thick; 2) filter aggregate course; 3)
reservoir coarse of 13-3-inch diameter stone; and
4) filter fabric.
Porous Pavement Placement.
Pavement temperature: 240-260' F.
Minimum air temperature: 50* F.
Compact with one or two passes of a 10-ton
roller.
Prevent any vehicular traffic on pavement for at
least two days. ' , ''.
SOURCE:
Pretreatment*Pretreatment is recommended to
treat runoff from all off-site areas. An example
would be a 25-foot wide vegetative filter strip
placed around the perimeter of the porous
pavement where drainage flows onto the
pavement surface. .
-------
MAINTENANCE . ' .
Routine maintenance of porous pavements is extremely-important. Maintenance should include vacuum
sweeping at least four times per year, followed by high-pressure hosing to limit sediment dogging in, the
pores of the top, layer. «Potholes and cracks can be filled with typical patching mixes unless more than
10 percent of the surface area needs repair. Spot-clogging may be fixed by drilling half-inch holes
through the porous pavement layer every few feet.
The pavement should be inspected several times during the first few months following installation and
then annually thereafter. Inspections after large storms are necessary to check for pools of water. These
pools may indicate clogging. The condition of adjacent pretreatment facilities should also be inspected.
r * .
COSTS .'.-.; :
' "\ ' » ,
The costs of developing a porous pavement system 100 feet by 50 feet and with a 4 foot deep storage
area can be estimated using the example in table 2 below.
Estimated costs for an average annual maintenance program of a porous pavement parking lot are
approximately $200 per acre -per year. This cost assumes four inspections, vacuum sweeping and jet
hosing treatments per year. - ' .
TABLE 2: ESTIMATED COSTS FOR A POROUS PAVEMENT SYSTEM
1. Excavation Costs:
2. Filter Aggregate/Stone Fill
3. Filter Fabric
4. Porous Pavement
S. Overflow Pipes
6. Observation Well
7. Grass Buffer
8. Erosion Control
740 cy x $5.00/cy
740 cy x S20.0b/cy
760 sy x S3.00/sy
556 sy x S13.00/sy
200 ft x S12.00/ft
laiS200ea
833 sy x $1.50/sy
Sl,000/lump sum
SUBTOTAL .. $32,858
9. Contingencies (Engineering, Administration, etc.) = 25% 8,215
TOTAL* $41,073
SOURCE: Rjatnct*.
* Costs for traditional pavement, including any storm sewers, curb and gutter should be
subtracted from this amount to reflect the difference in total cost for implementing a
porous pavement system. Unit costs will vary according to local market conditions.
-------
ENVIRONMENTAL IMPACTS ,
One potential negative impact of porous pavement is the risk of groundwater contamination. Pollutants
(such as nitrates and cSlorides) riot.easily trapped, absorbed, or reduced may continue to move through
the soil profile and into groundwater. This is not a desirable condition, as it could lead to
contamination of drinking water supplies. Therefore, until more scientific data is available, it is
advisable not to site porous pavement near groundwater drinking, supplies.
REFERENCES .'"' .
1. A Current Assessment of Best Management Practices: Techniques for Reducing Nonooint Source
Pollution in a Coastal Zone. December 1991. . .
2. Field. 'Richard *et al.. An Overview of Porous Pavement Research. Water Resources Bulletin, Volume
18, No. 2, pp. 265-267, 1982.
3. Metropolitan Washington Council of novemments. Controlling Urban Runoff: A Practical Manual for
. Planning and Designing Urban BMPs. 1987. ;
4. Southeastern Wisconsin Regional Planning Commission. Costs of Urban Nonpoint Source Water
Pollution Control Measures. Technical Report No. 31-, June 1991.
* * ' -.
5. U.S. EPA. Best Management Practices Implementation Manual. April 1981. -.-..;
6. ILS. EPA, Stormwater Management for Industrial Activities: Develooine Pollution Prevention Plans
and Best Management Practices. September 1992. , -
of Ecology.' Stormwater Management Manual for the Puget Sound
7. wa AiTigfnn grato
Basin. February 1992.
m> BMP f<*
tp*t~>ibt *t ttaidt* Tcdmeioff B^aA (420Q. VS EPA. «1 MSa*. SV, Wati*0OK, DC 20100.
-------
STORM WATER BMP:
PREVENTIVE MAINTENANCE
Oftecf WaUMaarBfcroanent&Cuiifa"6^
MUNICIPAL TECHNOLOQr IIANCH
DESCRIPTION "'"'..''
Preventive maintenance involves the regular inspection and testing of plant equipment and operational
systems. These inspections should uncover-conditions such as cracks or slow leaks which could cause
breakdowns or, failures that result in discharges of chemicals to surface waters either,by direct overland
flow or through storm drainage systems. The purpose of the preventive maintenance program should be
to prevent breakdowns and failures by adjustment, repair, or replacement of equipment before a major
breakdown or failure can occur. .
Preventive maintenance has been practiced predominantly in those industries where excessive down time
is extremely costly. As a storm water best management practice BMP, preventive maintenance should be
used selectively to eliminate or minimize the spill of contaminants to receiving waters. For many.
facilities this would simply be an extension of the current plant preventive maintenance program to
include items to prevent storm water runoff .contamination. , .
For sites that have storm drainage facilities, proper maintenance is necessary to ensure that they serve
their intended function. Without adequate maintenance, sediment and other debris can quickly clog
facilities and render them useless. Typically, a preventive maintenance program should include
inspections of catch basins, storm water detention areas, and water quality treatment systems.
CURRENT STATUS :
Most plants already have preventive maintenance programs that provide some degree of environmental
protection. This program could be expanded to include stormwater considerations, especially the upkeep
and maintenance of storage tanks, valves, pumps, pipes, and storm water management devices.
APPLICATIONS ' . V :
Preventive maintenance procedures-and activities are applicable to. almost, every industrial facility.
Preventive maintenance should be part of a general good housekeeping program designed to maintain a
clean and orderly work ^environment. Often the most effective first step towards preventing storm water
pollution from industrial sites simply involves good common sense to improve the facility .preventive
maintenance and general good housekeeping methods. .
LIMITATIONS
Primary limitations of implementing a preventive maintenance program include:
Additional costs. . _ _ ,
Availability of trained preventive maintenance staff technicians.
. ' Management direction and staff motivation in expanding the preventive
maintenance program to.include storm water considerations. .
-------
PERFORMANCE . ".'.',
Quantitative data is not available on the effectiveness of preventive maintenance as a best management
practice. However, it is clear that an effective preventive maintenance program can result in'improved
storm water discharge quality. , . - . .-' , ' , .
DESIGN CRITERIA : ^ :
Elements of a good preventive maintenance program should include:
Identification of equipment or systems which may malfunction and cause spills, leaks, or
other situations that could lead to contamination of storm water, runoff. Typical
equipment to inspect include pipes, pumps, storage tanks and bins, pressure vessels,
pressure release valves, process and material handling equipment, and storm water
management devices. . .
Once equipment and areas to be inspected have been identified at the facility, establish
; schedules and procedures for routine inspections.
Periodic testing of plant equipment for structural soundness is a key element in a
...,'. / preventive maintenance program. ' .
; ' ' x .-.'-''. '-".' '.' ' '
Prompdy repair or replace defective equipment found during inspection and testing.
Keep spare parts for equipment that need frequent repair. " .
* It is important to include a record keeping system for scheduling tests and documenting
inspections in the preventive maintenance program.
Record test results and follow up with corrective action taken. Make sure records are
complete and detailed. These records should be kept with other visual inspection records.
MAINTENANCE RECORDS '''
The key to properly tracking a preventive maintenance program is through the continual updating of
maintenance records. Records should be updated immediately after preventive maintenance, or when
any repair has been performed on any item in the plant. An annual review of these records should be
conducted to evaluate the overall effectiveness of the preventive maintenance program. Refinements to
the preventive maintenance procedures and tasking should be implemented as necessary.
COSTS
, The major cost of implementing a preventive maintenance program that places emphasis on storm water
quality is the staff time required to implement the program." Typically, this is a small incremental
increase if a preventive for training and maintenance program already exists at the facility.
-------
REFERENCES v
1. U.S. EPA, NPDESJ?est management practice Guidance Document. June 1981.
2. U-S. EPA. Storm water Management for Industrial Activities; Developing Pollution Prevention Plans
and Best Management Practices. September, 1992. .
3. Washington State Department of Ecology. Storm water Management Manual for Puget Sound.
February 1992. . : ,
J** w*f*pmllytitNiuidr*T*Mc0Bm* (1204), OS ETA. 401M Sum. SW, WtMitfo*. DC 2M6H
-------
STORM WATER BMP:
RECORD KEEPING
Office oT Wastewatar Errtrommt &
MUNICIPAL TECHNOtOar
DESCRIPTION
A record keeping system should be implemented for dooimenting spills, leaks, and other discharges such
as hazardous substances. Keeping record* and reporting events that occur on-site are effective ways of
tracking title progress of pollution prevention efforts and waste-minimization. Analyzing records of past
spills can provide useful information for developing improved Best Management Practices (BMPs) to
prevent future spuis. Record keeping represents a good operating practice because it can increase the
efficiency of a facility by reducing down time and increase die effectiveness of other prevention and
treatment BMPs. Typical record keeping items include reported incidents and follow-up on results,of
inspections, and reported spills, leaks, or other discharges.
IMPLEMENTAnON ' ' \
Record keeping as a BMP should be an integral part of a BMP implementation program and should be
incorporated into Stormwater Pollution Prevention Plans tSWPPP).If a separate record keeping system for
tracking BMPs, monitoring results, etc., is not currently in place at a facility, existing record keeping
structures could be easily adapted to incorporate this data. An ideal tool for implementation is the
record keeping procedures laid out in an SWPPP. In many cases the. record keeping system can be
maintained on a personal or desk top computer .using standard spreadsheet or data base management
software. '.. ; - . ' - . ' ' . . "
UMTTATIONS
Limitations associated with a record keeping system are: .
It is an on-going process that continually needs updating.
Qualified personnel required to complete the record keeping forms.
. . Accessible of records.' .
Security of confidential information.
PERFORMANCE
Record keeping .performance as a BMP is highly variable. It depends on the time and commitment
dedicated to implementing an effective system. The benefit of an effective record keeping system being
incorporated into an overall SWPPP is improved stormwater discharge leaving facility grounds. The
effectiveness of the record keeping system is often dependent on the following:
The commitment of seniqr management to implementing and maintaining an effective
record keeping system. .
. The quality of the record keeping .program. . ,
. The background and experience of the assigned record keeping team.
-------
DESIGN CRITERIA . / ''.;., .
7 ' "' ' . .
Record keeping and reporting procedures for spills, leaks, inspections, maintenance, and monitoring
activities should include the following, 'a sample worksheet for keeping records' of spills and leaks is
shown in Figures 1 below. . ,- .
The date, location, and time of material; inventories, site inspections, sampling
observations, etc.
The individual (s) who performed site inspections,, sampling observations, etc.
. . . , " ' f'
The date(s) analyses were performed and the time(s) analyses were initiated, the '
individual or individual(s) who performed die analyses, analytical, techniques or methods.
used, and results of such analysis. ' . ' '
' '. t
Quality assurance/quality control results. , . ,
The date, time, exact location,and complete characterization of significant spills or leaks.
Visual observation and sample collection exception records.
All calibration and maintenance records of instruments used in stormwater monitoring.
All original strip chart recordings for continuous monitoring equipment.
UST OF SIGNIFICANT SPILLS AND LEAKS
Diractfcm: Itaosrt Mow * «ignific»* tpOi «nd *
>«f»ctlv< Oa» at B» ptirnk.
Ml tav» eccunW nitw f«*W * **«
SOURCE: Refrmxi
HGURE 1: SAMPLE.WORKSHEET FOR TRAC30NG SPILLS AND LEAKS
-------
MAINTENANCE . - «.
The key to a proper maintenance program for record keeping is continual updating. Records should be
updated with the correct name and address of the facility, name and location of receiving waters,
number and location of discharge points, principal product and significant changes in raw material
storage outside, and reports of monitoring results and spills at the site. It is recommended that all
reports be maintained - for a period of at least five years from the date of sample observation,
measurement, or spill report Some simple techniques used t<> accurately document and report results
include: .
Field notebooks . . '.'','.' .
, . Timed and dated photographs . '
. . * . .'
, . Videotapes s
. ..;.' Drawings and maps . . ',.'.'
. . Computer spreadsheet and database programs .
'COSTS- - : ;" '''. '' ' '-' .- :'".. ,; '-..-.. ' - .
v ' .".''< ", '. '''..; 'I'-..'"'..-;'.""
Costs associated with implementing a record keeping system are th&se-associated with additional staff
hours to initially develop the system and to keep records up to date, along with related overhead costs.
Annual costs can be estimated using the example shown in Table 1 below. Figure 4 can be used as a
worksheet to calculate the estimated annual cost for a record keeping system.
TABLE 1: EXAMPLE OF ANNUAL RECORD KEEPING COSTS
Tide
Stonnwater Engineer
Plant Management
Plant Employees
Avg.
Hourly
Quantity Rate ($}
. i: . x 15 x:
5 x 20 x.
100. x 10 x
Overhead*
Multiplier
V
2.0 x
2.0 x
2.0 x
Yearly
Hours
onSW
Training
'.
20 -
10 - -
5 -
TOTAL ESTIMATED ANNUAL COST
Note: Denned as a multiplier (typically ranging between 1 and 3)
those costs associated with payroll expenses, building expenses, etc.
SOURCE: ETA
Est. .
Annual '
Cost($)
600
2,000
10.000
$12,600
that takes into account
-------
TMe
Avg.
Hourly
Quantity Rate ($)
Overhead
Multiplier
x
X
,x '
X .
X
"X-
X
X
Estimated
Yearly
Hours
onSW
Training
Est
Annual
Cost($)
x
X
X
X
TOTAL ESTIMATED ANNUAL COST
(Sum of A+B+C+D)
SOURCE: tofeml
(A)
(B)
_ (Q
(D)
HGURE 2: SAMPLE ANNUAL RECORD KEEPING COST WORKSHEET
REFERENCES ' . , ' .
\
1: California Environmental Protection Agency, Staff Proposal for Modification to Water Quality
Order No. 91-13 DWO Waste Discharge Requirements for Dischargers of Stormwater
Associated with Industrial Activities. Draft Wording. Monitoring Program and Reporting
Requirements. August 17, 1992. . , . .
2. U.S. EPA. NPDES BMP Guidance Document. Jurie^ 1981. ,
3. U.S. EPA. Stormwater Management for Industrial Activities: Developing Pollution Prevention
Plans and Best Management Practices. September. 1992. . '-.
77* JWff/«»*«< ««jwjwrfiy *rM«K*»t Tethwloy Ban* (4204). US EPA. HIMSomt SW. WtMnfOK. DC 2M66.
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STORM WATER BMP:
SAND FILTERS
Offlce of Wastewater Manaoanert TO*
MUNICIPAL TECHNOLOGY BRANCH
DESCRIPTION
Sand fUtere are most often designed for storm water quality control and generally provide limited
storm water quantity management. A typical sand filter system consists of at least two chambers or basins
with one designed for sedimentation and one for filtration. The first chamber, the sedimentation chamber,
removes floatables and heavy sediments. The second chamber, the nitration chamber, removes additional
pollutants by filtering the runoff through a sand bed. The treated filtrate normally is discharged through
an underdraih system to a storm drainage system or directly to surface waters. Sand (filters can achieve high
removal efficiencies for sediment, biochemical oxygen demand (BOD) and fecal conform bacteria. However,
total metals removal is moderate and nutrient removal is often low.
There are three mam sand filter designs currently in common use: the Austin sand filtration system
(Figure la), the Washington, D.C. sand filter (Figure Ib) and the Delaware sand filter (Figure Ic). The
primary differences in these designs are location (i.e., underground or surface and on-line or off-line),
drainage area served, filter surface areas, land requirements, and quantity of runoff treated.
to .Stormwatef
Detention Basin
RfenfeoflBttin
A
> Stormwater Channel
Drop Met
filtered Otfflow
Sione
flpRap
WeirToAetwye
Uniform Discharge
Channel Sloped to
Facilitate Sediment
Transport into
Sedunematon Basin
SOURCE: Reference 2
Perforated Riser
vim Trash Rack
ELEVATION A-A
t
Undardrain Piping System
FIGURE la: TYPICAL AUSTIN SAND FILTER DESIGN
COMMON MODIFICATIONS ,
Modifications that may improve sand filter design and performance are being tested. One
modification is the addition of a peat layer hi the filtration chamber. The properties and characteristics of
the peat may increase the microbial growth within the sand filter and improve pollutant (e.g., metals and
nutrients) removal rates. Another design variation, which is included in the Washington, D.C. sand filter
design, includes an uhderdrain that is extended above the sand filter layer. This allows for backwasbing of
the filter when it becomes clogged.
-------
30" MANHOLE
FRAME 6 COVER
StfMANHOLE 2
-------
APPLICATIONS
I v . , " ,,',.'
In general, sand filters are preferred over infiltration practices, such as infiltration trenches, when
groundwater contamination is of concern due to high ground water tables or hi areas where underlying soils
are unsuitable. In most cases, sand filters can be constructed with impermeable basin or chamber bottoms
to collect, treat, and discharge runoff to a storm drainage system or directly to surface water without the
contaminated[runoff coming into contact with the groundwater.
The selection of the type of sand filter depends largely on the drainage area characteristics. For
example, the Washington, D.C. and Delaware sand filter systems are well suited for highly impervious areas
where land availability for structural controls is limited. Both the Washington, D.C. and Delaware sand filter
designs are intended for underground installation. These sand filters are often used to treat runoff from
parking lots, driveways, loading docks, service stations, garages, airport runways/taxiways, and storage yards.
The Austin sand filtration system is more suited for larger drainage areas with both impervious and pervious
surfaces. This system is located at grade and is often used at transportation facilities, large parking areas
and commercial developments. -
All three types of sand filters can generally be used as alternatives for water quality inlets, which are
more frequently used to treat oil and grease contaminated runoff from drainage, areas with heavy vehicle
usage. In climatic zones where evaporation exceeds rainfall, the Austin sand filtration systems can also be
used as an alternative to wet ponds for treatment of contaminated storm water runoff. In high evaporation
zones, wet ponds will not likely be able to maintain the required permanent pool unless there is adequate
baseflow from the groundwater.
LIMITATIONS
The size and characteristics of the drainage area as well as the pollutant loading will greatly influence
the effectiveness of the sand filter system. In some cases other best management practices (BMPs), such as
wet ponds, may be less costly for sites with large drainage areas and should also be considered if removal of
nutrients and metals is required. Drainage areas with heavy sediment loads may result in frequent clogging
of the filter. The lack of maintenance to the clogged filters will limit the performance. Certain climatic
conditions may also limit the performance of the filters. For example, it is not known how well sand filters
will operate in colder climates where sustained freezing conditions are encountered.
PERFORMANCE .
Particulates are removed by both sedimentation in the sedimentation chamber and by. filtration in
the filtration chamber. The City of Austin has. estimated pollutant removal efficiencies (Austin, 1988) based
on preliminary findings of the City's storm water monitoring program. The estimates shown hi Table 1
below, are average values for various sand filters serving several different size drainage areas.
As shown in Table 1, no removal of nitrate was observed in the preliminary findings. The removal
of other dissolved pollutants was not monitored. -Additional monitoring is currently being performed by the
City of Austin to supplement the preliminary estimates.
LONGEVITY c
There have been a number of concerns raised about the long term effectiveness of sand filter systems.
Proper design and maintenance are critical factors hi maintaining the useful life of any filter system. The
life of the filter media may be increased by a number of methods including: stabilizing the drainage area so
that sediments loadings in the runoff are minimized; placing a sedimentation chamber that removes sediments
prior to the filtration chamber; providing adequate detention times for sedimentation and filtration to occur;
and frequently inspecting and maintaining the sand filter to ensure proper operation. In some cases,
replacement of the filter media may be required every 3 to 5 years. The useful life of the media will depend
on the pollutant loading to the filter and the design and maintenance of the system.
-------
TABLE 1: TYPICAL POLLUTANT REMOVAL tKWClENCY
Pollutant
Fecal Coliform
Biochemical Oxygen Demand (BOD)
Total Suspended Solids (TSS)
Total Organic Carbon (TOC)
Total Nitrogen (TN)
Total Kjeldahl Nitrogen (TEN)
Nitrate as Nitrogen (NO3-N)
Total Phosphorus (TP)
Iron (Fe)
. Lead(Pb)
Zinc(Zn)
SOURCE: Reference 4
Typical Percent Removal
76
70
70
48
21
46
0
33
45
45
45 . '
DESIGN CRITERIA
Typically the Austin sand filter system is designed to handle runoff from drainage areas up to 50
acres. The collected runoff is first diverted to the sedimentation basin, where heavy sediments and floatables
are removed. There are two designs for the sedimentation basin: the full sedimentation system, as shown in
Figure la, and a partial sedimentation system, where only the initial flow is diverted. Both systems are
located off-line and are designed to collect and treat the first 0.5 inch of runoff. The partial system has the
capacity to hold only a portion (at least 20%) of the first flush volume in the sedimentation basin, whereas
the full system captures and holds the entire flow volume. Equations that are used to determine the
sedimentation basin surface areas (A^ in acres are shown in Table 2 below.
TABLE 2: SURFACE AREA EQUATION FOR
THE AUSTIN SAND FILTER SYSTEM
Partial Sedimentation
= (An)(H)/10
Full Sedimentation
A,
A,
Note: , .
D, (feet) = depth of the sedimentation basin;
H (feet) = depth of rainfall, 0.042 ft (0.5 inches); and
Ap (acres) = impervious and pervious areas that provide
contributing drainage.
SOURCE: Reference 4 .
-------
* Flow is'conveyed from the sedimentation basin either through a perforated riser, gabion wall, or
berm to the filtration basin. The filtration basin consists of an 18-inch layer.of sand 0.02 to 0.04 inch in
diameter that may be underlain with a gravel layer. Equations that are used to determine the filtration basin
surface areas (A,) in acres are also shown in Table 2. The filtrate is discharged from the filtration basin
through underdrain piping 4 to 6 inches in diameter with 3/8-inch perforations. Filter fabric is placed around
the underdrain piping to prevent sand and other particulates from being discharged. ,
. Typically the Washington, B.C. sand filter system is designed to handle runoff from completely
impervious drainage areas of 1 acre or less., The system, as shown in Figure Ib, consists of three chambers:
a sedimentation chamber, a filtration chamber, and a discharge chamber. The reinforced concrete chambers
are located underground. The sand filter system is designed to accept the first 0.5 inch of runoff. Coarse
sediments and flpatables are removed from the runoff within the sedimentation chamber. Runoff is
discharged from the sedimentation chamber through a submerged weir, where it then enters the filtration
chamber. The filtration chamber consists of a combination of sand and grave layers totaling 3 feet in depth
with an underdrain system wrapped in filter fabric. The underdrain system collects the filtered water and
discharges it to the third chamber, where the water is collected and discharged to a storm water channel or
sewer system. An overflow weir is located between the second and third chambers to bypass excess flow.
The Washington, D.C. sand filter is often constructed on-line, but can be constructed off-line. When the
system is off-line the overflow between the second and third chambers is not included.
The Delaware sand filter, as shown in Figure Ic, is similar to the Washington, D.C. sand filter; both
utilizing underground concrete vaults. However, the Delaware sand filter has two chambers: a sedimentation
chamber and a filtration chamberr A 1-inch design storm was selected for the sizing of the sedimentation
basin because it is representative of most frequent storm events. In Delaware, 92% of all storms are less than
1 inch in depth. Runoff enters the sedimentation chamber through a grated cover and then overflows into
the filtration chamber, which contains a sand layer 18 inches in depth. Gravel is not normally used in the
filtration chamber, although the filter can be modified to include gravel. Typical systems are designed to
handle runoff from drainage areas of 5 acres or less. A major advantage of the Delaware sand,filter is its
shallow structure depth of only 30 inches, thereby reducing excavation requirements.
' . . ._ . ' :-' ; ' ' - ' I ' " .' '
MAINTENANCE . s
; All filter system designs must provide adequate access to the filter to perform the required inspection
and maintenance. The sand filters should be inspected after all storm events to verify that they are working
as designed. Since the D.C. and Austin sand filter systems can be relatively deep, they may be designated
as confined spaces, therefore, require compliance with confined space entry safety procedures.
\ ' . - ,
Typically, sand filters begin to experience clogging problems within 3 to 5 years (NVPDC, 1992).
Accumulated trash, paper and debris should be removed from the sand filters every 6 months or as necessary
to keep the filter clean. A record* should be kept of the dewatering times for all sand filters to determine if
maintenance is necessary; Corrective maintenance of the filtration chamber includes removal and
replacement of the top layers of sand, gravel and/or filter fabric that have become clogged. The removed
media may usually be disposed of in a landfill. The City of Austin has tests then* waste media before disposal.
Results thus far indicate that the waste media is not toxic and can be safely landfilled (Schueler, 1992). Sand
filter systems may also require the periodic removal of vegetative growth.
\
COSTS
The construction cost for an Austin sand filtration system is approximately $17,750 (1993 dollars)
for a 1-acre drainage area. The cost per acre decreases with increasing drainage area. For example the cost
for a 15-acre site is approximately $3,300 (1993 dollars) per acre for a total of $49,500 (Austin, 1990b). The
cost for precast Washington, D.C. sand filters with drainage areas of less than 1 acre ranges between $6,300
and $10,500. This is considerably less than the cost for the same size cast-in-place system of approximately
$26,400 (D.C., 1992). Costs for the Delaware sand filter are similar to that of the D.C. system, except the
excavation costs are generally lower, because of the filters shallower depth.
-------
Annual costs for maintaining sand filter systems averages about 5 percent of the initial construction
cost (Schueler, 1992). Media replacement is performed as needed. Currently the sand is being replaced in
the D.C. filter systems about every 2 years. The cost to replace the gravel layer, filter fabric and top portion
of the sand for B.C. sand filters is .approximately $1,600 (D.C. 1992). The City hopes that improved
maintenance procedures will extend the life of the filter media and reduce the overall maintenance costs.
ENVIRONMENTAL IMPACTS
The three types of sand filters achieve high removal efficiencies for sediment, BOD and fecal coliform
bacteria and generally require less land than other BMPs, such as ponds or wetlands. Sand filters
constructed with impermeable basin liners limit the potential for groundwater contamination. Sand fitters
generally do not provide storm water quantity control and, therefore, do not prevent downstream stream
bank and channel erosion. Sand filters may also be of limited value in some applications because of their
traditionally low nutrient removal and metals removal capabilities. Waste media from the filters does not
appear to be toxic and is environmentally safe for landfill disposal. !
REFERENCES
1. Shaver, Earl, 1991. Sand filter Design for Water Quality Treatment. Delaware Department of Natural
Resources and Environmental Control. ' . . . .
2. Schueler, T.R. 1992. A Current Assessment of Urban Best Management Practices. Metropolitan
Washington Council of Governments. ,:
3. Troung, H. 1989. The Sand filter Water Quality Structure. District of Columbia.
4. City of Austin, Texas, 1988. Design Guidelines for Water Quality Control Basins. Environmental Criteria
Manual. , " ' ,
5. City of Austin, Texas, 1990. Removal Efficiencies of Storm Water Control Structures. Environmental
Resource Division, Environmental and Conservation Services Department.
6. City of Austin, Texas, 1990b. Memo from Leslie Tull, Water Quality Management Section (June 20,1990).
7. Northern Virginia Planning District Commission (NVPDC), 1992. Northern Virginia BMP Handbook.
8. Washington, D.C. (DC), 1992. Personal Communication.
9. Galli, John, 1990. Peat Sand filters: A Proposed Storm Water Management Practice for Urbanised
Areas. Metropolitan Washington Council of Governments.
Ufc BMP fcct jbeet w» prepared by the Ufanidpal Tedmologr Branch (42W), US EPA, «1 M Street, SW, Washington, DC, 2M«
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STORMWATER BMP:
STORMTREAT SYSTEM
Excellence ,ln complanee through optfma technical
MUNICIPAL TECHNOLOGY BRANCH
DESCRIPTION
; The STORMTREAT System (STS), developed in 1994, is a stormwater treatment technology
consisting of a series of sedimentation chambers, and constructed wetlands which are contained within
a modular, 9.5-foot diameter recycled-polyethylene tank. The STS is shown in Figure 1. Influent is
piped into the sedimentation chambers where pollutant remoyal processes such as sedimentation and
filtration occur. Stormwater is conveyed from the sedimentation chambers to a fringing constructed
wetland where it is retained for five to ten days prior to discharge. Unlike most constructed wetlands
for stormwater treatment, the stormwater is conveyed into the subsurface of the wetland and through
the root zone. It is within the root zone that greater pollutant attenuation occurs through processes such
as filtration, adsorption, and biochemical reactions. ;.
FIGURE 1 STORMTREAT SYSTEM
Source: StormTreat Systems, Inc.
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COMMON MODIFICATIONS
The STS design allows for modifications when the system is installed in areas with high
groundwater levels or in areas tidally affected. In areas with high groundwater, modifications to the
discharge .pipe work can be made so that runoff is discharged to a remote downgradient area with a
lower water table level. In tidally influenced areas, a check valve can be installed to prevent flow from
reentering the unit from its discharge -point after the flow has discharged and allow discharge only
during mid to low tide conditions. The valve would.be adjusted for higher than normal flow velocities
(those velocities used with a non-tidally influenced unit) so that the system maintains an average holding
time of five to ten days.
The manufacturers of the system indicate that the STS could be used throughout the US, with
only minor modifications to the system to make it effective in different geographical areas. In cold
climates, where the 4 foot height unit would be installed above the frost line, modifications may be
necessary to prevent the water within the tank from freezing. Adding a greenhouse to cover the system
or insulating the subgrade tank may prove to be effective.
ii . - ' . ' ''
Modifications may also be necessary in an arid region due to insufficient water to support the
wetland vegetation. In these areas the unit could be modified to discharge the flow at a slower rate
which would increase the water retained hi the bottom of the unit. Soils that retain water more
efficiently could also be used. Alternately, the unit could have an alternate water supply for the
extended dry periods.
CURRENT STATUS
An STS has been installed hi Kingston, Massachusetts (MA) and has been operational since
November 1994. The need for a stormwater treatment system in this area became evident as increased
bacteria levels caused the closing of shellfish beds hi the Jones River. Additional systems are planned
for installation hi Gloucester, MA, Harwich, MA, and Waltham, MA. Two systems will be installed
in Gloucester to help mitigate impacts to the downstream shellfish beds which have also been identified
as having high counts of fecal coliform bacteria. The system planned for installation in Harwich will
treat polluted runoff from the town landing prior to discharge to Wychmere Harbor, a scenic boating
harbor on Cape Cod. A system will be installed at GTE in Waltham during the Fall of 1995. The
industrial complex is located hi a sensitive watershed. The system will collect rooftop runoff and runoff
from a parking lot. If these installed systems prove to be cost effective, there are additional needs in
Massachusetts where 40 percent of the shellfish beds have been closed due to high levels of metals and
bacteria.
APPLICATIONS
The STS has applications in a wide range of settings. The system's size and modular
configuration make it adaptable to a wide range of site constraints and watershed sizes. Designers of
the system indicate that the system can be used to treat runoff from highways, parking lots, airports,
marinas, and commercial, industrial and residential areas. The ST.S is an appropriate stormwater
treatment technology for both coastal and inland areas.
LIMITATIONS
As discussed previously, the STS is relatively new and untested in different geographical
locations. There may be possible limitations hi these areas. Soil types surrounding the modular unit
will not limit the system's effectiveness nor will high water tables.
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PERFORMANCE
Preliminary monitoring results from four sets of samples collected in November 1994,
December 1994, and February 1995 indicate removal rates df 94% for total coliform bacteria, 83% for
fecal coliform bacteria, 95% for total suspended solids, and 90% for total petroleum hydrocarbons, as
shown in Table 1. Preliminary nutrient removal rates have been determined to be 44% for total
dissolved nitrogen, 89 % for total phosphorus (TP), and 32% for ortho-phosphorus. Total nitrogen (TN)
performance data are not available at this time; however, the manufacturer of the system indicates that
they should be high based on the results of other wetland systems where particulates, and therefore TN,
are removed. Removal rates are anticipated to increase as the wetland vegetation becomes more
established and during warmer months. The pollutant removal rates achieved by the system for other
pollutants are as follows: 65% for lead, 98% for chromium, and 90% for zinc.
TABLE 1 STORMTREAT MONITORING RESULTS
Pollutant
Total Coliform Bacteria
Fecal Coliform Bacteria
Total Suspended Solids
Chemical Oxygen Demand
Total Dissolved Nitrogen
Total Phosphorus
Ortho-phosphorus
Total Petroleum Hydrocarbons
Lead
Chromium
Zinc . '
Percentage Removed
94
83
95
" ' ''.". ' 75
44
89
. 32 ' ' . ;-
-90
'- ' ' 65 > ' ... :
i
98 ' . '.
90
DESIGN CRITERIA
The STS is a modular, 9.5-foot diameter recycled-polyethylene tank containing a series of
sedimentation chambers and constructed wetlands. The sedimentation chambers are in the inner ring
of the tank, which has a diameter of nearly 5.5 feet. The 9.5 feet diameter outer ring, which surrounds
the sedimentation chambers, contains the wetland. The tank walls and bulkheads, which separate the
sedimentation chambers, have a height of 4 feet. ,
The STS tanks are designed to withstand the hydrostatic pressures that result from the saturated
soils surrounding the tanks. The STS unit connects to existing catch basins with PVC piping. Influent
is conveyed through the PVC piping to the first of six internal sedimentation chambers. The 4 inch
diameter inlet pipe is covered with a burlap sack that traps larger particles and debris. Synthetic screens
and woven geotextiles placed within the bulkheads filter the flow as it passes into the succeeding
chamber. Flow is conveyed through larger mesh sizes in the first series of'sedimentation chambers,
followed by smaller mesh sizes in the remaining sedimentation chambers. In addition to the filter
screens, skimmers have been installed in the tanks. Skimmers replace the previously used screens and
combination of screens and skimmers. The screens and skimmers perform the same pollutant removal
mechanism; however, the screens require more maintenance than the skimmers. The skimmers float
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on the water surface within each chamber and have an opening 6 inches below the surface through
which flow is conveyed to the following tank. Sediments which collect in the bottom of the chamber
remain in that chamber until the unit is maintained. The skimmers prevent sediment from being
conveyed to the subsequent chamber. The bulkhead separating the last two sedimentation chambers is
fitted with an inverted elbow which traps oil and grease within the fifth chamber. The elbow is located
approximately 10 inches from the chamber bottom.
Flow is conveyed from the sedimentation chamber through four, 4 inch diameter, PVG, slotted
outlet pipes int6 the wetland portion of the STS. Stormwater flows subsurface through the length of
the wetland, which has a length of 23 feet, width of 2.4 feet, and contains 3 feet.of gravel and sand.
The gravel used at the Kingston facility is 1/4 inch rice stone and 3/8 inch Milestone. The weight of
the gravel provides the force that counteracts the buoyancy forces that would be present at a high water
table site. The wetland has an approximate storage capacity of 760 gallons. The entire system has a
capacity of 1,390 gallons.
Vegetation within the wetland will vary depending on the local, naturally occurring wetland
vegetation and the maximum expected root depth of the plant. Bulrush and burreeds have been used
in Massachusetts and have maximum root depths of 2.6 and 2 feet, respectively (USEPA, 1993). Mature
vegetation should have roots that extend into the permanent 6 inches of water in the bottom of the tank.
Insufficient root depth may result in a lack of water supply to the plants during the periods between
storm events.
Effluent from the wetland is discharged through a 2 inch diameter pipe that is controlled by a
valve. Flow rates and holding times can be varied by manipulating the outlet control valve. At the
Kingston facility, the control valve is adjusted to provide for a recommended discharge rate of 0.2
gal/nun, and a 5-day holding time in the wetland. The valve has an added benefit that in the event of
an upstream toxic spill the valve can be closed and the pollutants will be trapped in the STS.
Tanks are available in one size but multiple tanks can be installed at a site to capture the volume
of runoff from the site. The size of the tank was selected so that the prefabricated tanks could be
transported without requiring conformance to oversized load regulations. The determination of the
number of tanks needed for a site is based on three factors:
Area of impervious drainage surfaces; .
Design storm to be treated; and
Detention storage prior to the STS tanks.
\
To capture and treat the first 0.25 inches of runoff from a one acre, completely impervious
drainage area, the designers of the system estimate that two tanks would be required when preliminary
detention is provided and five tanks when it is not. For a design storm of 0.5 inches, four tanks are
required with preliminary detention and ten tanks without preliminary detention. Preliminary detention
may be provided hi the drainage pipes and catch basins which convey flow to the STS. In some
instances, settling tanks may be located upstream that detain the runoff. A typical site would require
100 ft? per tank, which includes sufficient space for the tank and access to the tank for maintenance.
MAINTENANCE
Anticipated maintenance of the STS is minimal. The system should be observed at least once
a year to be sure that it is operating effectively. At that time the burlap sack that covers the influent
line should be removed and replaced. If the system installed uses filters, these should be removed,
cleaned, and reinstalled. Sediment should be removed from the system once every 2 to 3 years, unless
the system has higher than normal sediment loads. After six months of operation the unit installed in
Kingston, MA was found to have 2 inches of accumulated sediment. The sediment can be pumped from
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the tank by septic haulers or by maintenance personnel responsible for sediment removal from
catchbasins. It is not anticipated that the sediment will be toxic and may be safely landfilled. However,
sediment toxicity will depend on the activities in the contributing drainage area and testing of the
sediment may be required to determine if it should be considered hazardous.
COSTS
The STS is a prefabricated unit that is easily installed in most locations. Installation time for
a normal site (i.e., bedrock not encountered) is approximately four man-days. This time includes both
site preparation and installation. The estimated cost for one installed tank is $3,600 to $4,000, which
includes the site work, tank, skimmers, gravel, wetland plants, external PVC piping, and installation
by the manufacturer. Costs of systems that have been installed or are planned for installation have been
lower that the estimated costs due to the municipalities providing the site preparation at no charge. The
higher end of the cost range may be encountered if complications with site preparation occur. Capital
and installation costs decrease as the number of units on a site increases. The cost for a system installed
by the manufacturer and consisting of four tanks is approximately $15,000. The four tank system
would effectively treat a one acre, completely impervious drainage area with preliminary detention
desigried to capture the first 0.5 inches of runoff. ,
The estimated maintenance cost for removal of sediment from one tank ranges from $100 to
$150. This cos.t is incurred every two to three years when sediment removal is necessary. Costs have
not been determined for an annual site inspection and removing any debris and leaves from the wetland
area. However, mese costs should be mmimal (i.e., one day of labor for one person). ~
ENVIRONMENTAL IMPACTS
' " ' - - / -, - ' - ' . -, '
Systems have been installed in Massachusetts due to the increased bacteria levels resulting in
the .closing of shellfish beds. -Regulators and environmental groups in Massachusetts are concerned over
the closing of 40 percent of the shellfish beds in the state and are utilizing stormwater management
practices, including the STS, to improve the water quality in the downstream beds. The STS also
protects the groundwater by removing pollutants prior to infiltration. The STS has shown high TPH,
TP, metals, and suspended solids removal rates, which improves water quality. An additional benefit
of the STS is the system's spill containment feature which results in capture of an upstream release, and
therefore, lessens the impact from the spill on the environment.
REFERENCES
1. StormTreat Systems, Inc.., date unknown. Technical Data for STORMTREAT System.
Barnstable, Massachusetts (relocated to Hyannis, MA).
2. StormTreat Systems, Inc., 1995. STORMTREAT Systems Newsletter. Barnstable,
Massachusetts (relocated to Hyannis, MA).
3. Horsley, Scott W. and Winfried Platz, January 4, 1995. Progress Report: Water Quality
Monitoring at Elm Street Facility, Barnstable, Massachusetts (relocated to Hyannis, MA).
4. Horsley, Scott W., June 15, 1995. The STORMTREAT System ,- A New Technology for
Treating Stormwater. ,
5. Horsley &, Witten, Inc., 1995. Fact Sheet - Modeling of Water Flow Through the
STORMTREAT System.
6, USEPA, July 1993. Subsurface Flow Constructed Wetlands for Wastewater Treatment: A
Technology Assessment. EPA 832-R-93-001. -
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IMTB
STORM WATER BMP:
SPILL PREVENTION PLANINO
Wasswster
TECHNOboar
DESCRIPTION '
A Spill Prevention Plan .identifies areas where spills can occur on site, specifies materials handling
procedures, storage requirements, and identifies spill clean-up procedures. The purpose of this plan is to
establish standard operating procedures, and the necessary employee training to minimize the likelihood
of accidental releases of pollutants that can contaminate stormwater runoff. Spill Prevention is prudent
from both an economic as well as environmental standpoint because spills increase operating costs and
lower productive ,
Storm water contamination assessment, flow division, record keeping, internal reporting, employee
training, and^ preventive maintenance are associated BMPs that should be incorporate into a
comprehensive Spill Prevention Plan.
N ' - ' '. ' .' . '"'. '
CURRENT STATUS .
Typicallyi most businesses and public agencies that generate hazardous waste and/or produce, transport,
or store petroleum products are required by state and federal law to prepare spill control and cleanup
plans. Therefore, a Spill Prevention and Response Plan may have already been developed in response to
other environmental regulatory requirements. Existing- plans should ber re-evaluated and- revised if
necessary to address stormwater .management issues.
APPLICATIONS . . .
A Spill Prevention Plan is applicable to facilities that transport, transfer, and store hazardous materials,
petroleum'products, and fertilizers that can contaminate stormwater runoff. An important factor of an
effective spill prevention plan is.quick notification of the appropriate emergency response teams. In
some plants each area or process may have a separate team leader and team of experts. Figure 1 below
illustrates a sample spill prevention team roster for quick identification of team leaders and their
responsibilities. .
UMTTATIONS ' .
Spfll Prevention Planing can be limited by the following:
Lack of employee motivation to implement plan.
Lack of commitment from senior management. .
Key individuals identified in the Spfll Prevention Plan may not be properly
trained in the areas of spill prevention, response, and cleanup.
PERFORMANCE - ., " . ., ., '
Past experience has shown that the single most important obstacle to an effective Spill Prevention Plan is
its implementation. Qualitatively, implementation of a well prepared Spill Prevention Plan should
significantly decrease contamination of stormwater runoff.
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POLLUTION PREVENTION TEAM
MEMBER ROSTER
Worksheet
Completed by:
Titla:
Data: '
leader:
R«»pon«ibiliti««:
Members:
(1)
Responsibi'rties:
(2)
Responsibilities:
(3)
Responsibilities:
Title:
Office Phone:
Trie:
Office Phone:
Title:
Office Phone:
Title:
Office Phone:
SOURCE: Sternal. .
FIGURE 1: SAMPLE SPILL PREVENTION TEAM ROSTER
DESIGN CRITERIA. . . . ' ,
General guidelines for the preparation of a Spill Prevention Plan include: " ;
. The first part of the plan should contain a description of the facility including the owner's
name and address, the nature of the facility activity, and die general types of chemicals
used in the facility.
. The plan shoidd contain a site plan showing die location of storage areas for chemicals,
location of the storm drains, tributary drainage-areas with drainage arrows, and the.
location and description of any devices to stop spills from leaving die site such as . ,
collection basins.' '- , . ,
The plan should describe notification procedures to be used in die event of a spill such as
phone numbers of key personnel, arid appropriate regulatory agencies such as local
Pollution Control Agencies and die local Sewer Authority.
. The plan should .provide specific instructions regarding cleanup procedures.
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The owner, through an internal reporting procedure, should have a designated person
with overall responsibility for spill response. Through an employee training program, key
personnel should be trained in the use of this plan. All employees should have basic
knowledge of spill control procedures.
A summary of the plan should be written and posted at appropriate points in the building
(i.e., lunch rooms, cafeteria, and areas with a high spill potential), identifying the spill
cleanup coordinators, location of cleanup kits, and phone numbers of regulatory
agencies to be contacted in the event of a spill.
Cleanup of spills should begin immediately. No emulsifier or dispersant should be used.
In fueling areas, absorbent should be packaged in small bags for easy use and small
drums should be available for storage of absorbent and/or used absorbent Absorbent '
materials shall not be-washed down the floor drain'or into the storm sewer.
Emergency spill containment and cleanup kits should be located at the facility site. The;
contents of the kit should be appropriate to the type and quantities of chemical or goods
. stored,at the facility. ' '
Some structural methods to consider when developing a Spill Prevention Plan include:
Containment diking- Containment dikes are temporary or permanent earth or concrete
berms or retaining walls that are designed to hold spills. Diking can be used at any
industrial facility, but'is most common for controlling large spills or releases from liquid
. storage and transfer areas. Diking can provide one of the best protective measures against
the contamination of stormwater because it surrounds the area of concern and-holds tie
spill, keeping spiH materials separated from the stormwater outside of the diked area.
' , * ,";'-
Curbing- Like containment diking, curbing is 'a.barrier that surrounds an area of concern.
Because curbing is usually-small-scale,' it cannot contain large spills like diking can.
However, curbing is common at many facilities and small areas where liquids are handled
and transferred. . ,
. ." Collection basins. Collection basins are permanent structures where large spills or
contaminated stormwater are contained and stored before cleanup or treatment.
Collection basins are designed to receive spills, leaks, etc., that may occur and prevent
these materials from being released to the environment. Unlike containment dikes,
collection basins can receive and contain materials from many locations across a facility.
* * * " ' i
Once a hazardous material spiH occurs and is contained, the material has to be cleaned up and disposed
of to protect plant personnel from potential health and fire hazards, and to prevent the release of the
substance to surface waters. Methods of cleanup, recovery, treatment, or disposal include:
Physical. Physical methods for cleanup of dry chemicals include the use of brooms,.
shovels, sweepers, or plows. .
Mechanical. Mechanical methods for cleanup include the use of vacuum cleaning systems
and pumps. .
Chemical. Chemical cleanup of material can be accomplished with the use of sorbents,
gels, and foams. Sorbents are compounds that immobilize materials by surface
absorption or adsorption m the sorbent bulk.* Gelling agents interact, with the spilled
chemicalCs) by concentrating and congealing to form a rigid or viscous material more
conducive to mechanical cleanup. Foams are mixtures of air and aqueous solutions of
proteins and surfactant-based foaming agents. "The primary purpose of foams is to reduce
the vapor concentration above the spill surface thereby controlling the rate of
evaporation.
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Create a map of the facility site to locate pollutant sources and determine
stormwater management opportunities. This site map should include all
surface'waterbodies on or next to the site, and should also identify, if any
that are in place. Tributary drainage areas with identification of flow direction
should also bed identified during this mapping phase. Table 1 contains a list of
features that should be indicated on the site map.
Conduct a material inventory .throughout the facility.
Evaluate past spills and leaks.
Identify non-stormwater discharges and non-approved connections to
stonnwater facilities. . ' .
Collect and evaluate stonnwater quality data.
Summarize the findings of this assessment . . .
: TABLE 1: CRITERIA FOR DEVELOPING A SITE MAP.
DEVELOPING A SITE MAP
Worksheet
Competed by:
Title: '
Date: ]
Instructions: Draw a map of your site including a footprint of all buildings, structures, paved areas/and
parking lots. The information below describes additional elements
All outfalls and storm water discharges
Drainage areas of each storm water outfall
Structural storm Water pollution control measures, such as:
- Flow diversion structures ' ..
- Retention/detention ponds
- Vegetative swales , . -
- Sediment traps
Name of receiving waters (or if through a Municipal Separate Storm Sewer System)
Locations of exposed significant materials , ' '
Locations of past spills and leaks .
Locations of high-risk,-waste-generating areas and activities common on industrial sites such as:
- Fueling stations '
- Vehicle/equipment washing and maintenance areas :
- Area for unloading/loading materials -
- Above-ground tanks for liquid storage
- Industrial waste management areas (landfills, waste piles, treatment plants, disposal areas)
- Outside storage areas for raw materials, by-products, and finished products
- Outside manufacturing areas
- Other areas of concern (specify: )
SOURCE: Rcfatxal. ' -
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MAINTENANCE ' _ ' . . ' ..'''
A facility Spill Prevention Plan should be reviewed at least annually and. following any spills to evaluate
the Spill Prevention plan's level of success and how it can be improved. Other times for significant
review of the plan should be when a'new material is introduced, to the plant as a result of a processing
modification, or when a change has occurred in a materials handling procedure. .
COSTS
'. " i - ' ' ''
If a'facflity already has a Spill Control and Cleanup Plan in-place, modifications, to address stormwater
contamination concerns, will require minimal cost. If a facility will be developing a Spill Prevention Plan
for the first time, initial cost will depend on the type of materials at die facility, facility size, and other
related parameters. Costs for structural containment devices will also need to be identified for each
facility. , . ' " . . ' .
ENVIRONMENTAL IMPACTS
Preventing or containing spills, especially toxic or hazardous materials, is important in reducing storm
water contamination and in maintaining the water quality of the receiving water;
REFERENCES - .."'/
1. U.S. EPA. Stormwater Management for Industrial Activities: Developing Pollution Prevention Plans
and Best Management Practices. September 1992. .
2. Washington State Department of Ecology. Stormwater Management Manual for Puzet Sound.'
February 1992. - ,'
, WaKHfat. DC. 20*60.
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IMTB
STORM WATER BMP:
CONTAMINATION ASSESSMENT
Office of Wartowattr Erforcemo* 6 Canpfax*^**
MUNlC ,
.'-.. A corporate commitment must exist to reduce the contamination
sources once discovered. - :
. Assessments need to be periodically updated.
PERFORMANCE
It is not possible, based on currently, available data, to quantify the water quality benefits to' receiving
waters of a stormwater contamination assessment program. Results are entirely based on the severity of
the contamination uncovered, and die corrective actions taken. Qualitatively, implementation of a
program that identifies areas of high pollutant concentrations and eliminate or reduces their potential
pollutant capabilities will result in positive water quality benefits..
DESIGNCRITERIA
A SWCA program should include the following key activities:
Assess potential pollutant sources and associated high risk activities such
as loading and unloading operations, outdoor storage activities, outdoor
manufacturing or processing activities, significant dustor particulate^generating
activities; and on-site waste disposal practices.
-------
Once you have completed the above steps in your pollutant source assessment, you* have enough
information to determine which areas, activities, or materials are a risk towards contributing pollutants
to stormwater runoff from your site. An important benefit is that by using this information, you can
effectively select other cost-effective BMPs to prevent or control pollutants. ,
IMPLEMENTATION
In addition to identifying problems within the storm sewer system, it is even more important to prevent
problems from developing at alii and to provide an environment in which future problems can be
avoided. Thus, an effective stormwater assessment program should include implementation activities to
insure success and follow-up activities to measure results. Keys to a successful implementation program
should include: . .
, . Public education, on organized systematic program of disconnecting commercial and ,
industrial stormwater entries into the storm drainage system.
. Tackling the problem of widespread septic system failure. .
Disconnecting direct sanitary sewerage connections.
Rehabilitating storm or sanitary sewers to abate contaminated
water infiltration. .
* "-,'
Developing zoning and other ordinances. . . .
In extreme cases, it may be 'that while it was thought that a community had a separate sanitary sewer
system and a separate storm sewer system, in reality the storm sewer system .is acting as a combined
sewer system, hi these cases, consideration should be given" to .the economic and practical advantages of
designating the storm sewer system a combined sewer, and applying end^of-pipe treatment to the entire
system. -..'."
"-. & '
A SWCA program needs to be periodically updated. Updating is especially important upon the
introduction of new raw materials or changes in processes at the site.
It is also important to establish parameters for measuring the. success of the correction .program. If
results do not meet expectation, then reassessment and appropriate changes to the correction program
should be made. ; ' . . , . .
COSTS
Costs'for the initial assessment may be high. However, by pinpointing high potential areas or activities a
SWCA program may reduce overall costs associated with a complete BMP implementation program. The
costs associated with an assessment program for stormwater are small when compared to or a part of a
larger overall hazardous waste site assessment.
ENVIRONMENTAL IMPACT
A comprehensive SWCA program can eliminate pollution sources that can significantly impair receiving
water quality. . '
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REFERENCES
1. U.S. EPA, Stormwater Management for Industrial Activities: Developing Pollution Prevention Plans
and Best ManaeemSnt Practices. September 1992. - - . . .
2. U.S. EPA. NPDES Best Management Practices Guidance Document. June 1981. >
3. .Pitt, Robert, Barbe, Donald; Adrian, Donald, and Field, Richard, Investigation of Inappropriate
Pollutant Entries into Storm Drainage System - A User's Guide. U.S. EPA, Edison, New Jersey, 1992.
mctcyBnM* (4204). US EPA. 401 MSara. SW.WiMtfe*. DC, 20*6
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IMTB
STORMWATER BMP:
STORMWATER WETLANDS
Bcedtenee h compftnoe through opOmat technical
MUNICIPAL TECHNOLOGY
DESCRIPTION
Wetlands are those areas that are typically inundated with surface or ground water and support
plants adapted to saturated soil conditions. A typical shallow marsh wetland is shown hi Figure 1.
Wetlands have been described as "nature's kidneys" due to the physical, chemical, and biological
processes that occur hi wetlands which result hi transformation of some elements (e.g., nitrogen,
sulfate) and filtration of others (Hammer, 1989). The natural pollutant removal capabilities of wetlands
have brought increased attention to then- usage as a stormwater best management practice (BMP).
FIGURE 1 SHALLOW MARSH WETLAND
25% of pond perimeter open grass
^^^~^C\.'
Maintenance
Bench
*oozxa0r
^gate valves provide
flexibility in depth control
N\
25 toot wetland buffer landscaped O
wiih native trees/shrubs for habitat /
₯
/
use of wetland mulch
to create diversity
Source: MWCOG, 1992.
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Wetlands used for stormwater treatment can be constructed, incidental or natural. Incidental
wetlands are those that were created as a result of previous development or human activities. The use
of natural wetlands for stormwater treatment is discouraged by many and may not be an option. Some
states, however, allow their usage but pnly in very restricted circumstances. For example, the State
of Florida allows the use of natural wetlands that have been severely degraded or wetlands that are
intermittently connected (flows when groundwater rises above ground level) to other waters (Livingston,
1994). Conversion of natural wetlands to stormwater wetlands are done on a case-by-case basis and
require the appropriate state and federal permits (e.g., 401 water quality certification and 404 wetland
permit).
Two types of constructed wetlands have been used successfully for wastewater treatment: the
subsurface flow (SF) and the free water surface (FWS) constructed wetland. In the.FWS wetland runoff
flows through the soil lined basin at shallow depths. The wetland consists of a shallow pool planted
with emergent vegetation (vegetation which is rooted in the sediment but the leaves are at or above the
water surface). The SF wetland also has a basin, however, the basin contains a suitable depth of rock
or gravel, through which the runoff is conveyed. The water level hi a SF wetland remains below the
top of the rock or gravel bed. Studies have indicated that the SF wetland is well suited for the diurnal
flow pattern of wastewater, however, the peak flows from stormwater or combined sewer overflows
(CSO) may be several orders of magnitude higher than the average flow. The cost for a gravel bed to
contain the peak storm event would be very high, and therefore, preclude the use of SF wetlands for
stormwater or CSQ treatment. The remainder of this factsheet addresses the FWS constructed wetland
or natural and incidental wetlands. r
COMMON MODIFICATIONS
There are four basic designs of constructed wetlands; shallow marsh, pond/wetland system,
extended detention (ED) wetland, and pocket wetland. The wetland designs, as shown in Figure 2,
.store runoff in a shallow basin vegetated with wetland plants. The selection of one design over the
other will depend on various factors, including the land availability, level and reliability of pollutant
removal, and size of contributing drainage area. The shallow marsh design requires the largest amount
of land and a sufficient baseflow to maintain water within the wetlands. The marsh can be modified
to include extra vertical runoff storage. This modified marsh system, known as the ED wetland,
attenuates flows and relieves downstream flooding.
Another variation, the pond/wetland system, has two separate cells: one being a wet pond and
the other a shallow marsh. The wet pond traps sediments and reduces velocities prior to runoff entry
into the wetland. Land requirements for a pond/wetland system are less than for the shallow marsh
system. Areas with insufficient land area for construction of a larger wetland system, may be
appropriate sites for the fourth wetland design, a pocket wetland. Pocket wetlands have contributing
drainage areas of 1 to 10 acres and usually will require excavation down to the water table in order to
provide a reliable water source to the wetland. Unreliable water sources and fluctuating water levels
result in low plant diversity and poor wildlife habitat value (MWCOG, 1992).
' ' . ' \ - .'
CURRENT STATUS
In the past the use of natural treatment processes occurring within wetlands has generally
focused on the the treatment of wastewater. Wetlands for stormwater treatment have gained attention
in recent years and many systems are now operational. Studies are ongoing to determine the
effectiveness of wetlands, design modifications that improve their performance, and required
maintenance to sustain their performance.
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FIGURE 2 COMPARATIVE PROFILES OF,
FOUR STORMWATER WETLAND DESIGNS
A. SHALLOW MARSH
normal pool elevation
f W^ftf-.
forebay
micropool
B. POND/WETLAND SYSTEM
v normal pool elevation
pond
wetland
C. ED WETLAND
. ED zone
S~ ' 7
max ED limit
\ .....
normal pool elevation
micropool
D. POCKET WETLAND
seasonal highwater table
normal water table
Cross-sectional profiles of the four stormwdter wetlands are not drawn to scale., In Panel A, the majority of the
shallow marsh is devoted to shallow depths that support.emergent wetland plants. The pondfroetland system (Panel
B) is composed of deep and a shallow pool. In ED wetlands (Panel C), the runoff storage of the wetland is
augmented by temporary, vertical ED storage. Pocket wetlands (Panel D) are excavated to the groundwater table
to provide a more or less constant water elevation.
Source: MWCOG, 1992.
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APPLICATIONS
Wetlands provide the benefit of stormwater quality control, with the option of achieving quantity
control (e.g., extended detention wetland). Wetlands are one of the more reliable BMPs capable of
removing pollutants and are adaptable to most locations in the US. Locations with existing wetlands
used for stormwater treatment include, but are not limited to,Washington, California, Minnesota,
Michigan, Illinois, Florida, Maine, Maryland, and Virginia. They haye^een used to treat runoff from
agricultural, commercial, industrial, and residential areas.
LIMITATIONS
Urban settings and established communities may preclude the use of wetlands due to the large
land requirement for the systems. The presence of trout, sculpins and other temperature sensitive fish
species or aquatic insects located hi downstream waters may also preclude the use of wetlands due to
the stream warming that could occur within a wetland, especially during,the warmer months.
Communities may be opposed to a wetland due to their preconceived notion that wetlands will result
in an infestation of mosquitoes and other nuisances. Communities may also be opposed due to the
appearance of the wetlands. Wetlands, however, can be designed to be attractive and features (e.g.,
morphology, fish, and vegetation) can be added to decrease, if not eliminate, a problem with mosquitoes
and other nuisances. .
Limitations in pollutant removal may be experienced during the non-growing season and in
localities with lower temperatures. Decreases hi pollutant removal efficiency have been observed when
wetlands are covered with ice or receive snowmelt runoff . ,
i - . ' . -_ . '
PERFORMANCE
Stormwater pollutant removal in wetlands is attributed to the physical, chemical, and biological
processes that occur within the wetland. Chemical and physical assimilation mechanisms include
sedimentation, adsorption, filtration, and volatilization. Sedimentation is the primary removal
mechanism for pollutants such as suspended solids, paniculate nitrogen, and heavy metals. The settling
of the particulates is influenced by the velocity of the runoff through the wetland, the particle size, and
turbulence. Sedimentation can be maximized by creating sheet flow conditions, slowing the velocities
through the wetland, and providing morphology and vegetation conducive to settling. The vegetation
and its root system will also decrease the resuspension of settled particles. ' ' _
Adsorption is the process where pollutants attach to surfaces of suspended or settled sediments
and vegetation. Adequate contact time between the surface and pollutant must be provided for in the
design of the system for this,removal process to occur. Pollutants removed by adsorption include
metals, phosphorus, and some hydrocarbons.
Wetland plants act as filters for pollutants such as trash, debris, and other floatables. Filtration
can be enhanced by slow velocities, sheet flow, and sufficient quantities of vegetation. The plants also
increase the pollutant removal achieved through sedimentation, adsorption, and microbial activity by
providing for an increased detention and contact time and a surface for microbial growth.
Volatilization plays a minor role hi pollutant removal from wetlands. Pollutants such as oils,
hydrocarbons, and mercury can be removed from the wetland via evaporation or by aerosol formation
under windy conditions.
^Biological processes that occur in wetlands result in pollutant uptake by wetland plants arid
algae. ^Emergent wetland plants uptake settled nutrients and metals through then: roots. The process
creates new sites hi the sediment for pollutant adsorption. During the fall the above ground parts
-------
typically die back and the plants may potentially release the nutrients and metals back into the water
column (MWCOG, 1992). Recent studies, however, indicate that most pollutants are stored in the roots
of aquatic plants, rather than the stems and leaves (CWP, 1995). Additional studies are required to
determine the extent of pollutant release during the fall die back.
Microbial activity contributes to the removal of nitrogen and organic matter. Nitrogen is
removed by nitrifying and denitrifying bacteria and aerobic bacteria are responsible for the
decomposition of the organic matter. Microbial processes require oxygen and can result in depleted
oxygen levels in the top layer of wetland sediments. The low oxygen levels and the decomposed
organic matter contribute to the immobilization of metals. . ' "
Soluble pollutants such as phosphorus and ammonia are partially removed by planktonic or
benthic algae. The algae consume the nutrients and convert it into biomass. The biomass settles to the
bottom of the wetland.
Evaluation of the removal effectiveness of wetlands is ongoing and limited data are currently
available; however, some conclusions can be drawn from available preliminary data. The projected
long term pollutant removal rates for constructed wetlands in the Mid-Atlantic Region as reported by
MWCOG (1992) and Strecker (1995) are presented in Table 1. As shown, total suspended solids (TSS)
and lead removal rates are anticipated to approach 75 percent. Lower removal rates are expected for
nutrients and organic carbon. The removal rates will vary with the loadings to die wetland. Excessive
pollutant "loadings (e.g., suspended solids) may exceed the wetlands removal capabilities.
TABLE 1 PERFORMANCE OF STORMWATER WETLANDS (1)
Pollutant
Removal Rate
Total Suspended Solids
Total Phosphorus
Total Nitrogen
Organic Carbon
Cadmium (2)
Copper (2)
Lead
Zinc
Bacteria
75 %
45 % ,
25 %
15 %
70%
40%
75%
50%
2 log reduction
(1) Source: MWCOG, 1992 '...,.
(2) Source: Strecker, 1995
Conclusions have been determined from studies performed on wetlands with regard to their
effectiveness compared to other BMPs and construction practices that affect performance. Data indicate
that the pollutant removal achieved with wetlands is similar to that achieved with conventional pond
systems. Studies also indicate that constructed stormwater wetlands achieve higher pollutant removal
rates than natural wetlands. This is likely due to the intricate design of the constructed systems and the
continued monitoring and maintenance of the systems (MWCOG, 1992). The effectiveness of the
wetland seems to improve after the first few years of use as the vegetation becomes established and
organic matter accumulates hi the wetland. During construction and excavation, many constructed
wetlands lose organic matter in the soils. The organic matter provides exchange sites for pollutants,
and therefore, plays an important role in pollutant removal. Replacing or adding organic matter after
construction improves performance. s
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LONGEVITY
Well designed wetlands can function as designed for 20 years or longer. Accumulated
sediments will gradually cause a decrease in storage and performance, and therefore, should be removed
as necessary or the water level in the wetland should be raised (e.g., adjust outlet to increase discharge
.elevation). Sediment forebays will decrease the accumulation of sediments within the wetland .and
increase the wetlands longevity. .
DESIGN CRITERIA
Required local, state and federal permits should be established prior to wetland design with the
appropriate regulatory authorities. Required permits and certifications may include 401 water quality
certifications, 402 stbrmwater NPDES permit, 404 wetland permits, dam safety permits, sediment and
erosion control plans, waterway disturbance permits, forest clearing permits, local grading permits, and
land use approvals. .
Prior to construction, a site should be selected that is appropriate for a wetland. The site must
have an adequate water balance and appropriate underlying soils. This requires that the baseflbw from
the drainage area or groundwater is sufficient to maintain a shallow pool in the wetland and support the
vegetation. Certain species are more susceptible to damage during dry periods. Underlying soils that
are type B, C, or D will have relatively insignificant infiltration losses. High infiltration rates may be
experienced at sites with type A soils or at sites underlain by karst, limestone, or fractured bedrock.
These sites may require geotextile liners or a 6 inch layer of clay. After any necessary excavation and
grading of the wetland at least 4 inches of soil should be applied to the site. This material may be the
soil previously excavated or sand and other suitable material. The soils are needed to provide a
substrate that the vegetation can become established in and anchor to. The substrate should be soft for
ease of insertion of the plants. ,
The Metropolitan Washington Council of Governments (MWCOG) has made recommendations
for the design of wetlands that require the designer to meet several basic sizing criteria. The volume
of the wetland is determined as the quantity of runoff generated by 90 percent of the runoff producing
storms. This volume will vary throughout the US due to the different rainstorms experienced. In the
Mid-Atlantic Region, for example, the 1.25 inch storm is used as the sizing criterion. The
imperviousness of a watershed will impact the runoff volume generated. The following equations are
used to determine the treatment volume (Vt):
(1) Rv = 0:05 + 0-009 (I)
where:
Rv =; storm runoff coefficient
I = percent site imperviousness ,
(2) Vt = [(1.25)(Rv)(A)/12](43,560)
where: , -. ,
Vt = treatment volume (ft3)
A = contributing area (acres)
Sizing criteria for wetlands vary with some states having their own methods. For example,
shallow wetland basins .constructed in Maryland are designed to maximize the surface area. The surface
area should be a minimum of 3 percent of the area of the watershed draining'to it. The preferred design
would include extended detention, the volume of which is determined by detaining the 1-year storm for
24 hours. The Washington State Department of Ecology sizes wetlands using the runoff generated from
the 6-month, 24-hour rainfall event.
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Criteria are also established by MWCOG for the water balance, maximum flow path, allocation
of treatment volume, minimum surface area, allocation of the surface area, and extended detention. The
water balance, as discussed previously, must be adequate during dry weather to provide a basefiow and
maintain the vegetation. The flow path should be maximized to increase contact time between the plants
and sediments and the runoff. The recommended length to width ratio is 2:1. A ratio of greater than
1:1 should prevent short circuiting where runoff escapes treatment. Suggested allocation of treatment
volumes, as shown in Table 2, are provided to improve removal efficiency. The minimum surface area
requirement for shallow marshes established by MWCOG is that the wetland to watershed area ratio
be greater than 2 percent. The remaining three wetland designs can have wetland to watershed ratios
greater than 1 percent.
TABLE 2 GUIDELINES FOR ALLOCATING WETLAND SURFACE AREA AND
TREATMENT VOLUME
Target Allocations
Shallow Marsh
Pond/Wetland
ED Wetland -
Pocket Wetland
Percent of Surface ,
Area (%) .
Forebay
Micropool
Deepwater
Low Marsh
High Marsh
Semi-Wet
5
5
5
40
40
'5
0
5
40
25
25
5
5
5
0
40
40
10
0
0
5
50
40
5
Percent of ,
Treatment (%)
Volume . ' , -
Forebay
Micropool
Deepwater
Low Marsh
High Marsh
Semi-Wet
10
10
10
45
25
0
0
10
60
20
10
0
10
10
0
20
10
50
o
0
20
55
25
0
Source: MWCOG, 1992
Deepwater-1.5 to 6 feet below normal pool , ,
Low Marsh - 6 to 18 niches below normal pool - ;
High Marsh - 0 to 6 niches below normal pool
Semi-Wet - 0 to 2 feet above normal pool (includes ED)
The wetland*surface area is allocated to four different depth zones: deepwater (1.5 to 6 feet),
low marsh (18 to 6 niches below normal pool), high marsh (up to 6 inches below normal pool), and
semi-wet areas (above normal pool). The allocation to the various depth zones will create a complex
internal topography. This is important because various wetland plants have different depth
requirements, therefore the internal complexity should maximize plant diversity and increase pollutant
removal. Allocation guidelines established by MWCOG are shown in Table 2. The State of Maryland
requires that 75 percent of the shallow marsh should have depths less than 12 inches and the remaining
25 percent should have depths ranging from 2 to 3 feet.. The 75 percent portion is additionally broken
down so that 25 percent ranges from 6 to 12 niches and the remaining 50 percent is 6 niches or less.
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Extending detention within the wetland increases the time for sedimentation and other pollutant
removal processes to occur and also provides for attenuation of flows. Up to 50 percent of the wetland
treatment volume can be added into the wetland system for extended detention. The ED elevation
should not, however, exceed 3 feet above the normal pool elevation. This will prevent large
fluctuations in the water level that could potentially harm the vegetation. The ED volume should be
detained between 12 and 24 hours. ".'
Sediment forebays are recommended to decrease the velocity and sediment loading to the
wetland. The forebays provide additional benefits of creating sheet flow, extending the flow path, and
preventing short circuiting. The volume of the forebay should be at least 10 percent of the wetland
treatment volume and have a depth of 4 to 6 feet. The State of Maryland recommends a depth of at
least 3 feet. The forebay is typically separated from the wetland by gabions or an earthen berm
(MWCOG, 1992).
Flow from the wetland should be conveyed though an outlet structure that is located within the
deeper areas of the wetland. Discharging from the deeper areas using a reverse slope pipe prevents the
outlet from becoming clogged. A micropool can be constructed where the outlet structure is to be
located that will also prevent outlet clogging. The micropool should contain approximately 10 percent
of the treatment volume and be 4 to 6 fetet deep. An adjustable gate controlled drain capable of
dewatering the wetland within 24 hours should be located within the micropool. A typical dram niay
be constructed with an upward facing inverted elbow with its opening above the accumulated sediment.
The dewatering feature eases planting and follow-up maintenance (MWCOG, 1992).
Vegetation can be established by one of five methods: mulching, allowing volunteer vegetation
to become established, planting nursery vegetation, planting underground dormant parts of a plant, and
seeding. Donor soils from existing wetlands can be used to establish vegetation within a wetland. This
technique, known as mulching, has the advantage of quickly establishing a diverse wetland community.
However, the types of species that grow within the wetland is unpredictable with mulching. Another
unpredictable technique is allowing the species to voluntarily become established. Wind and waterfowl
provide volunteer species to wetlands. Volunteer species are usually well established within 3 to 5
years. Wetlands established with volunteers are usually characterized by low plant diversity with
monotypic stands of'exotic or invasive species. A higher diversity wetland can be established when
nursery plants or dormant rhizomes are planted. Planting of the vegetation from a nursery should take
place during the growing season and not during late summer and fall. Planting during the growing
season gives the vegetation time to store up food reserves hi the underground parts for the dormant
period. Underground parts of vegetation are planted during the plants dormant period, usually October
through April, but the months will vary in the US due to local climate. Another planting technique,
the spreading of seeds^ has not been very successful, and therefore, is not widely practiced as a
principal planting technique.
Selection of plant types will vary for different locations and climates. The designer of the
wetland should select five to seven plants that grow native to the area and design the depth zones in the
wetland to be appropriate for the type of plant and its associated maximum water depth. Approximately
half of the wetland should be planted. Of the five to seven species selected, three should be aggressive
plants or those that become established quickly. Examples of aggressive species used in the Mid-
Atlantic Region include softstem bulrush (Scirpus validus) and common three-square (Scirpus
americanus). Aggressive plants as well as other native wetland plants are available from numerous
nurseries. Most vendors require an advance order of 3 to 6 months.
After wetland excavation and grading the wetland should be inundated and allowed to stand until
planting. Six to nine months later, the wetland is typically surveyed, drained, and staked. The wetland
is surveyed two weeks prior to planting to ensure that depth zones are appropriate for plant growth.
Revisions may be necessary to account for any depths different from that originally excavated. Staking
-------
the site ensures that the planting crew spaces the plants within the correct planting zone. Planting zones
are used to avoid mixing species and creating competition within the planted areas. The State of
Maryland recommends planting two aggressive or primary species in 4 monospecific areas and planting
an additional 40 clumps (one or more individuals of a single species) per acre of each primary species
over the rest of the wetland. Three secondary species are planted close to the edge of the wetland at
an application rate of 10 clumps of 5 individual plants per acre of wetland, for a total of 50 individuals
of each secondary species per acre of wetland. At least 48 hours prior to planting, the wetland should
be drained. At the completion of planting and within 24 hours the wetland should be re-flooded.
The wetland design should include a buffer to separate the surrounding land uses from the
wetland. Buffers may alleviate some of the potential nuisances associated with the wetland, such as
accumulated fioatables or odors. MWCOG recommends a buffer of 25 feet from the maximum water
surface elevation, plus an additional 25 feet when wildlife habitat is of concern. An enhanced wildlife
habitat can be obtained if during construction the removal of existing forested areas is minimized. If
removal is necessary, the buffer area should be reforested. The reforestation also decreases the potential
for a goose pond due to their preference for open areas. ,
MAINTENANCE '..-.'
The use of wetlands for stormwater treatment is relatively new, and therefore, specific
guidelines on their maintenance have not been established. The wetlands will require monitoring,
reinforcement planting, sediment removal, and possibly plant harvesting. Access should be incorporated
in the design to facilitate these maintenance activities. Monitoring the wetland during the first three
years is crucial to the performance of the wetland. Inspections should be conducted twice per year for
the first three years, and* on an annual basis thereafter. Reinforcement planting may be required during
this time period if the original plants do not flourish in the wetland. The inspector should determine
sediment accumulation within the wetland and also take note of the species distribution/survival, water
elevations, and outlet condition. Water elevations can be raised or lowered by adjusting the outlet's gate
valve, if it is determined that plants are not receiving an appropriate water supply. The forebay will
likely require sediment clean-out every three to five years. The design of the forebay should allow for
it to be drained so that a skid loader or backhoe can be used to remove the accumulated deposits
(MWCOG, 1992). Mowing of the embankment and maintenance bench should occur twice per year.
Other areas surrounding the wetland will not require mowing. . -
Numerous studies have been performed to determine the toxicity of pond sediments and whether
landfilling or land application can be accomplished without having to meet hazardous waste
requirements. Studies to date have not found sediments to be hazardous. Therefore, on-site land
application of the sediments away from the shoreline will most likely be the most cost effective disposal
method. On-site disposal is preferred over off-site disposal due to the cost savings associated with
transportation and off-site disposal fees!. Wetlands that receive flow from a drainage area containing
industry and activities .associated with hazardous waste may contain toxic levels in the sediments and
testing may be required for these sediments prior to land application.
COSTS
Costs incurred for stormwater wetlands include those for permitting, design, construction and
maintenance. The permitting costs vary depending on state and local regulations, but it has been
estimated that permitting and design costs are between 15 and 25 percent of the construction cost.
Construction costs for an emergent wetland range from $12,000 to $20,000 per acre of wetland and for
a forested wetland range from $20,000 to $40,000 per acre of wetland. These costs include the costs
for clearing and grubbing, erosion and sediment control, excavating, grading, staking, and planting.
The cost for constructing the wetland is largely dependant upon the amount of excavation required at
a site. Maintenance costs are estimated ait 10 to 15 percent per year of the construction costs (Bowers,
1995). , ....'
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ENVIRONMENTAL IMPACTS
Benefits associated with stonnwater wetlands include increased downstream water quality,
wetland creation, enhancement of wildlife habitat, and flood attenuation. Water quality is improved due
to the partial removal of suspended solids, metals, nutrients, and bacteria. The creation of wetlands
is typically looked upon as positive, particularly when the nation has lost considerable acres of wetlands
within the past century. The wetlands provide an environment attractive to wildlife, such as sandpipers
and herons. ED wetlands also attenuate runoff and alleviate downstreanl flooding.
Potential adverse impacts attributed with stormwater wetlands can occur upstream, in the
wetland, and downstream of the wetland. There is potential for stormwater wetlands located hi a large
watershed (> 100 acres) to experience degradation of upstream headwaters, since they receive no
effective hydrologic control (MWCOG, 1992). The wetland designer can incorporate upstream
modifications to relieve this negative impact.
Concerns within the wetland are the potential for a fish barrier, habitation by undesirable
species, and groundwater contamination., A fish barrier may be created by the wetland, which prohibits
fish access to the full length of the stream. This may result in a lowering of fish diversity in the stream.
Geese and mallards may become year round residents of the .wetland if structural complexity is not
included in the wetland design. Geese and mallards favor deep and open water areas. Forested buffer
areas and a reduction of grassy areas will also deter the geese and mallards. The geese and mallards
will increase the nutrient and coliform loadings to the wetland and will also likely be a nuisance to local
residents. The issue of groundwater contamination resulting from migration of polluted sediments to
the groundwater has been considered a potential negative environmental impact. However, studies to
date indicate that there is little risk of groundwater contamination (MWCOG, 1992).
'Stormwater wetlands can act as a heat sink, especially during the summer, and discharge
warmer waters to downstream water bodies. The increased temperatures can negatively impact sensitive
fish species and aquatic insects located downstream. Avoidance of the use of wetlands with temperature
sensitive downstream species is recommended. Regardless of the sensitivity of downstream species, the
designer should still take precautions kL.the-design.of. wetlands to reduce the magnitude of wanning in
the wetland. The adverse impact can be minimized through careful design. Several possible remedies
to each of the negative impacts (e.g., upstream degradation, stream warming^ etc.) described are
suggested hi the publication Design of Stormwater Wetland Systems (MWCOG, 1992).
REFERENCES
1. Maryland Department of the Environment (Water Management Administration), 1987. Wetland
Basins for Stormwater Treatment: Discussion and Background. Baltimore, MD.
2. ~ Maryland Department of the Environment (Water Management Administration), 1987.
Guidelines for Constructing Wetland Stormwater Basins. Baltimore, MD.
.-'''. !'' - .
3. Metropolitan Washington Council of Governments (MWCOG), 1992. Design of Stormwater
Wetland Systems. Washington, DC
4. Streckler, Kersnar, Driscoll, and Horner, 1992. The Use of Wetlands for Controlling
Stormwater Pollution.
5. Strecker, Eric, 1995. The Use of Wetlands for Stormwater Pollution Control. Presented at the
National Conference on Urban Runoff Management, March 30 to April 2, 1993, Chicago, EL.
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6. Homer, Richard, 1995. Constructed Wetlands for Urban Runoff Water Quality Control.
Presented at the National Conference on Urban Runoff Management, March 30 to April 2,
1993, Chicago, IL.
7. Livingston, Eric, 1994. Water Quality Considerations in the Design and Use of Wet Detention
and Wetland Stormwater Management Systems.
8. Hammer, D.A. (ed), 1989. Constructed Wetlands for Wastewater Treatment. Lewis
Publishers, Chelsea, MI.
9. US Environmental Protection Agency (EPA), 1993. Subsurface Flow Constructed Wetlands
for Wastewater Treatment: A Technology Assessment. EPA832-R-93-001. Office of Water.
10. Bowers, J. Keith, August 14, 1995. Personal communication. Biohabitats, Inc., Towson,
Maryland.
11. Center for Watershed Protection (CWP), 1995. "Pollutant dynamics Within Stormwater
Wetlands: I. Plant Uptake." Techniques, Vol. 1, No. 4. Silver Spring, Maryland.
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IMTB
STORM WATER BMP:
VEGETATIVE COVERS
Oflfct rf Watiwabr
.MUNICIPAL
DESCRIPTION '.,-
This Best Management Practice (BMP) involves preserving existing vegetation or revegetating disturbed
soil as soon as possible after land disturbance activities in order to control erosion and dust Vegetative
covers include sod, temporary. and permanent seeding and other vegetative covers, as well as
preservation of existing vegetatipn. Sod is a strip of permanent grass cover placed over disturbed areas
to provide an immediate and permanent turf that both stabilizes the sod surface and eliminates sediment
due to erosion, mud, and dust. Temporary vegetative cover involves planting grass seed immediately
after rough grading to provide protection until establishment of final cover. Permanent vegetative cover
is die establishment of perennial vegetation in disturbed areas. Preservation of natural vegetation
(existing trees, vines, bushes, and grasses) provides a natural buffer zone during land disturbance
.activities.. -
Vegetative covers provide dust control and a reduction in erosion potential- by increasing infiltration,
trapping sediment, stabilizing the soil, and dissipating the energy of hard rain. Application of mulch
may be required for seeded areas. Mulch is the application of plant residues or ojther suitable materials
to the soil surface to protect the soil surface from rain impact and the velocity of stormwater runoff.
APPLICATIONS
Vegetative covers are applicable to all land uses. Soils, topography, and climate will be determinants in
the selection of appropriate tree, shrub, and'grpund cover species. Local climatic conditions determine
the appropriate time of year for planting. Temporary seeding should be performed on areas disturbed by
construction left exposed for several weeks or more. Permanent seeding and planting is appropriate for
any graded or cleared area where long-lived plant cover is desired. Some areas where permanent
seeding.is especially important are filter strips, buffer areas, vegetated swales, steep slopes, and stream
banks. Design criteria for vegetative covers is included in Table 1 below.
LIMITATIONS . .
Limitations of vegetative covers as a BMP'include:
The establishment of vegetative covering must be coordinated with climatic
conditions for proper establishment For example, cold climate areas have
limited growing seasons and arid regions require careful selection of species.
The key to proper performance is implementation of a maintenance program to
ensure healthy vegetative covering. ,
PERFORMANCE ,
Qualitatively, vegetative covers are dearly effective in controlling dust and erosion when properly
implemented. The amount of runoff generated from vegetated areas is considerably reduced and is of
better quality than from urivegetated areas. However, it is not possible, based on data currently
available, to quantify the water quality benefits of the vegetative coverings as a BMP.
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TABUS 1; DESIGN CRITERIA FOR VEGETATIVE COVERS
Measure
Temporary
Seeding
Permanent
Seeding
t : '
iOMKX:
Extent and
Material
- Place topsoil as
needed to
enhance plant
growth. A loamy
soil with an
organic content
of 1.5 percent or
greater .is
preferred. Use
rapid-growing
annual grasses,
small grains, or
legumes. Apply
seeds using a
cyclone seeder,
drill, cultipacker
seeder, or
hydroseeder.
Place topsoil as
needed . to
enhance plant
growth. A loamy
soil, with an
organic- content
,. of 1.5 percent or
' greater is
preferred.
Where possible,
use low
local plant
species. Apply
seeds using a
cyclone seeder,
drill, cultipacker
seeder, ' or
hydroseeder..
fkfatncxl.
Dimensions
Place topsoil,
where needed,
to a TT"1""1"1"
compacted
depth of 2
inches on 3:1
slopes or
steeper; and of
4 v inches on
flatter slopes.
Apply mulch to
slopes 4:1 or
steeper, if soil is
sandy or clayey
or if weather ia
excessively hot
or dry. Place
topsoil where
needed.
Hydraulic
Divert :
channelized flow
away from-
temporarily
seeded areas to
prevent erosion
and scouring.
Divert
. channelized flow
away from
seeded areas to
prevent erosion
and scouring.
Avoid
Heavy clay .or
organic soils as
topsoil. Hand-
broadcasting of
seeds ' (not .
uniform), except
in very small
.areas. Mowing
'temporary
vegetation.
High-traffic
areas.
r
-,
Heavy clay or
organic soils as
topsoil.- Hand-
broadcasting Of:
seeds (not
uniform), except
in very small
areas. High
traffic areas.
'
Miscellaneous
Use where
vegetative cover
is needed for less
than 1 year. Use
chisel plow . or
tiller to loosen
compacted soils.
As needed, apply
water, fertilizer,
lime,' and mulch.
Incorporate' lime
and fertilizer
into top 4-6
inches of soil.
Plant small
grains ' 1 inch
deep. Plant
grasses and
legumes 1/2-inch
deep. .
Use chisel plow
or taller to loosen
compacted soils.
As needed, apply
water, fertilizer,
lie,- and mulch.
Incorporate lime
and, fertilizer
into top 4-6
inches of soil.
Plant small
grains 1 inch
deep. Plant
grasses and
legumes 1/2-inch
«^AAVI
deep.
'
-------
TABLE 1: DESIGN CRITERIA FOR VEGETATIVE COVERS
(Continued)
Measure
Extent and
Material
Dimensions
Hydraulic
Avoid
Miscellaneous
Mulching
Prefer' Organic
mulches such as
straw ' (from
wheat or oats),
wood chips, and
shredded bark.
Commercial.
mats and fabrics
may also be very
effective.
Chemical . soil
stabilizers or
binders are less
effective, but
may be used to
tack wood fiber
mulches.
Application
rates (per acre):
straw, one. to.
.two.'tons; wood
chips, five to six
tons; wood
fiber, 0.5 to one '
ton; bark, 35
cubic yards;
asphalt (spray),
0.10 gallon per
square yard.
After spreading
much, less than
25 percent of
the ground
surface should
be visible.
Mulch may be
applied by
machine or by
hand.. Chemical
'mulches and
wood fiber
mulches, when
used alone, often
1 do not provide.
. adequate - soil
protection. Use
nets or mats in
.areas subject to
water flow."
Anchor mulch by
punching into
soil, . or by
applying.
chemical agents,
nets, or mats.
?Secure nets and
mats with 6
inches or longer.
No. 8 gauge or
heavier, wire
staples pieced at
3-foot intervals
SOURCE: AfccncxJ.
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TABLE 1: DESIGN CRITERIA FOR VEGETATIVE COVERS
(Continued)
Measure
Extent and
Material
Dimension* Hydraulic
Avoid
Miscellaneous
Sodding
Sod should be
machine-cut at a
uniform
thickness of 1/2
to 2 inches.
In waterways, Gravel or nonsoil
select, plant surfaces.
types able to Unusually wet or
withstand design dry weather.
flow velocity. Frozen soils.
Mowing for at
. least two to three
weeks.
Preservation 'of Careful planning Wherever
Natural , is required; prior- possible,
Vegetation to start of nmtntain
construction. fflrifiting
contours.
Maintain.
existing
hydraulic
characteristics.
Activities within
the drop line of
trees.
Concentrating
flows at new
locations.
Prior to. laying
sod, clear soil .
surface of debris,
roots, branches,
and stones
bigger than 2
inches in
diameter. Sod
should be
harvested,
delivered, 'and
installed within
36 hours. Lay
sod with
staggered joints
along .the
.contour. Lightly
irrigate soils
before sod
placement
during dry or hot
periods. After
placement, roll
sod and wet soil
to a depth of 4
inches. On
slopes steeper
than 3:1, secure
sod with stakes.
In waterways,
lay sod
perpendicular to
water flow.
Secure sod with
stakes, wire, or
netting.'
Preservation of
vegetation
should be
planned before
any site
' disturbance
begins. Proper
maintenance is
vitally
important.'
Clearly mark
areas to be
preserved. '
SOUKCE:
-------
MAINTENANCE . - , "*
Areas should be checked following each rain to. ensure that seed, sod,, and mulch haye not been
displaced. Staking the sod or netting for seeded areas may be required.
Newly sodded areas need to be inspected frequently for the first new months to ensure the sod is
maturing. Failures may be due to improper conditioning of the subsoil,, lack of irrigation, improper
staking, or improper placement of sod pieces. ..,--.
Newly seeded areas need to. be inspected frequently for the first few months to ensure the grass is
growing at a proper rate and density. If the seeded area is damaged, determihe the cause of the damage
before repeating seed bed preparatioh-and seeding procedures.
Once a vegetative cover has been established, it is important to water the sod. frequently and uniformly.
If the grass is* to be. mowed, keep grass to a height appropriate for the species selected and the intended.
use. Occasional soil tests should be collected and analyzed to determine if the soil is appropriately
fertilized. Weed control should only be done if absolutely required. Spot seeding should be 'done to
small and damaged areas, :
COSTS
Cost estimates for sodding, seeding, and mulching are provided;in Table 2 below. These costs were
developed by the Southeastern Wisconsin Regional Planning Commission (1991). Please note that costs
very depending on local conditions.
TABLE 2: INSTAUATION COSTS
Description
. Equip-
Unit Material Labor m'ent '
Indirect
Cost
Total
Cost
Year of
Cost
Comment*
Level
>400 square yards Square yard $0.98 $0,85
100 square yards Square yard -1.36 .1.07
50 square yards Square yard 1.95 1.14
Slopes ,' ' ' ' .
400 square yards - Square yard 1.03 1.19. . 0.24 0.72
$0.17 $0.56 .
0.22 0.70
0.23 0.80'
$2.56 January
3.35 1989
4.12
3.18 . ;
Mechanical Seeding
Fine Grade/Seed
Push Spreader
Grass Seed
Limestone
Fertilizer
Level Areas
Sloped Areas
Acre ' $410.00 $435.00 $165.00 $290.00 '$1.300.00 January
.Squareyard 0.08 0.09 0.03 0.06 .'0.26 1989
Square yard 0.15 0.85 0.17 0.48 1.65 ' Includes
. : -. ', fertilizer
. . , - . , and lime
J.OOO square
feet
1.000 square
feet ;.
1.000 square
feet .
Acre
Acre
$8.60
2.05
$0.67' $0.26 $1.22
$10.75 January
1989
0.67
0.26
0.58
5,40 0.67 0.26. ' 0.'92
578.21 149.30 S0.63 251.00
578.21 238.88 129.00 328.75
.3.56
7.25
1,059.14
1,274,84
Mid-1988
Hay ' Acre $255.76 $74.65 $40.31 $118.50 $489.22 Mid-1988
Squareyard ''- " - - . 0.58 1983 Average
. . 0.25-1.00 . Typical
: . ~ .. range
NOTE: Total cost includes operation and maintenance, taxes, insurance and bdier contingencies.
90O1KZ.- Modified from Refcreoce 4. . > ,
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ENVIRONMENTAL IMPACTS
None for proper installation of vegetative covers. However, care must betaken to avoid contamination
of run off and ground Tvater from over use of fertilizers, weed control herbicides and other hazardous
chemicals. '
REFERENCES ,''..
1. Hennepin Conservation District, Minnesota, Erosion and Sediment Control Manual, 1989.
2. Metropolitan Washington Council of Governments, Controlling Urban Runoff: A Practical
Manual for Planning and Designing Urban BMPs. 1987.. .
3. Minnesota Pollution Control Agency, Protecting Water Quality in Urban Areas. 1989.
4. Southeastern Wisconsin Regional Planning Commission, Costs of Urban Nonpoint Source
Water Pollution Control Measures; Technical Report No. 31, June 1991. .
5. .U.S. EPA, Stormwater Management for Industrial Activities: Developing Pollution
Prevention Plans and Best Management Practices. September,1992.
1 6. . Washington State Department of Ecology, Stormwater Management
Sound Basm. February 1992. '
for the Puget
TH, SMTfta
f^aml ly Ac Mmic^t T***clct, Bm»d. (420ft, OS EM, 4l>ltlSu~.SW.Wi*i*
-------
IMTB
STORM WATER BMP:
VEGETATE1D SWALES
Offa of Watfawatnr Erforament & Cui|fa>Jt'
MUNICIPAL TECHNOLOdT
DESCRIPTION
Vegetated swales are. natural or man made, broad, shallow channels with a dense stand of vegetation
covering the side 'slopes and main channel. Vegetated swales trap paniculate pollutants (total suspended
solids and trace metals), promote infiltration,,and reduce the flow velocities of stormwater runoff.
Figure 1 below illustrates an example of a vegetated swale.
Vegetated swales can serve as an integral part of an area's minor stormwater drainage system by
replacing curbs .and gutters and storm sewer-systems in low-density residential, industrial, and
commercial areas. The swale's advantages over a storm sewer system generally include reduced peak
flows, increased pollutant removal, and lower capital costs. However, vegetated swales typically have a
limited capacity to accept runoff from large storm, since high velocity flows can cause erosion of the
swale or damage the vegetated cover. .
CftttkDwnto
InntiiM Uriitoaaon
SOURCE: Reference 1.
FIGURE 1: EXAMPLE OF A VEGETATED SWALE
COMMON MODIFICATIONS ,
The effectiveness of vegetated swales can be enhanced by adding check dams approximately every 50
feet to increase storage, decrease flow velocities, and promote paniculate settling. Structures to skim off
floating debris may also be added. -Incorporating vegetated filter" strips parallel to the top of the channel
banks can also help to treat sheet flows entering the swale.
CURRENT STATUS
Vegetated swales are relatively easy to design and incorporate into a site drainage plan. While -swales
are not generally used as a stand alone Stormwater Best Management Practice. (BMP), they are very
effective when used in conjunction with other BMP's such as wet ponds, infiltration strips, wetlands, etc..
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APPLICATIONS . ..
Vegetated swales can be used in all regions of the country where climate and soils permit the
establishment and maintenance 'of a dense vegetative cover. The suitability of a vegetated swale at a
particular site depends on the area, slope, and imperviousness of the contributing water shed, as well as
the dimensions, slope,«end vegetative covering employed in the swale system.
The limitations of vegetated swales include:
Vegetated swales are generally impractical in areas with very flat grades, steep
topography, or wet or poorly drained soils. ,
Swales provide minimal water quantity and quality benefits when flow volumes and/or
velocities are high. : '
*. ' - . . .
Swales may pose a potential drowning hazards, create mosquito breeding .areas, and cause
odor problems. . . -" - ' . ; .
. ' The use of vegetated swales may be limited by the availability of land.
' '. Many local municipalities prohibit the use of vegetated swales if peak discharges exceed
five cubic feet per second (cfs) or flow velocities
Vegetative swales are generally impractical in areas with erosive soils or where a dense
vegetative cover is difficult to maintain. . "
Certain quantitative aspects of vegetated swales are not known at this time. These
include whether pollutant removal rates of swales decline with age, the effect of slope on
the nitration capacity of vegetation, the benefit of check dams, and the degree to which
design factors can enhance die effectiveness of pollutant removal.
PERFORMANCE
Conventional vegetated swale designs have achieved mixed results in removing paniculate pollutants,
such as suspended solids and trace metals. For .example, three grass swales in the Washington, DC^area
were monitored by the Nationwide Urban Runoff Program (NURP). NURP found no significant
improvement in urban runoff quality for the pollutants analyzed. However, the weak performance of
these swales was attributed to the high flow velocities in the swales, soil compaction, steep slopes, and
short grass height A Durham, NC, project monitored the performance of a carefully designed artificial
swale that received runoff from a commercial parking lot The project monitored 11 storm and
concluded that participate concentrations of heavy metals (Cu,Pb,Zn, and Cd) were reduced by
approximately SO percent However, the swale proved largely ineffective for removing soluble nutrients.
A conservative estimate is that properly designed vegetated swales may achieve a 25 to 50 percent
reduction in particulate pollutants, including sediment and sediment-attached phosphorus, metals, and
bacteria. Lower removal rates (less than 10 percent) can be expected for dissolved pollutants, such as
soluble phosphorus, nitrate, and chloride.-
.. :f * - ' . ' .
The literature suggest that vegetated swales represent a practical and potentially effective technique for
control of urban runoff quality. While limited quantitative performance data exists for vegetated swales,
some known positive factors for "pollutant removal are check dams, flatter slopes, permeable soils, dense
grass cover, longer contact time, and smaller storm events. Negative factors include compacted sods,
short runoff contact time, larger storm events, frozen ground, short grass heights, steep slopes, and high
runoff velocities and discharge rates. . -
-------
the useful life of a vegetated swale system is directly proportional to the effectiveness and frequency of
maintenance. If properly designed and regularly maintained, vegetated swales can last an indefinite
period of time. , . . . - -.. ,
DESIGN CRITERIA . , .
Although specific quantitative performance data for vegetated swales is limited, design criteria have been
established for implementation of the vegetated swales'and is presented below.
. Location. Vegetated swales are typically located along property boundaries, although they
can be used effectively wherever the site provides adequate space; Swales can be used in
place of curbs and gutters along parking lots.
Soil Requirements. Gravelly and coarse sandy soils that cannot easily support dense
vegetation should be avoided. If available, alkaline soils and subsoils should be used to'
promote the removal and retention of metals. Soil infiltration rates should be greater
than one^half inch per hour, therefore, care must be taken to avoid compacting the soil
during construction. . '
. Vegetation. Fine, close-growing, water-resistant grass should be selected for use in
vegetated swales. Dense vegetation maximizes water contact, improving the effectiveness
of the swale system. The vegetation should be selected on the basis of pollution control
objectives and the ability to thrive in the conditions present in the conditions present at
the site. Some examples of vegetation appropriate for swales include reed canary grass,
grass-legume mixtures, and red fescue. ;
. ' ' , *>.-*.
General Channel Configuration. It is recommended that a parabolic or trapezoidal
cross-section with side slopes no steeper than.3:l be used, maximizing the wetted,
channel perimeter. Recommendations for longitudinal channel slopes vary within the
existing literature. For example, Shuler (1987) recommends a vegetated swale slope as
close to zero as drainage permits. The Minnesota Pollution Control Agency (1989)
recommends that the channel slope be less than 2 percent. The Stormwater Management
Manual for the Puget Sound Basis (1992) specifies channel slopes between 2 and 4
percent; slopes of less than 2 percent can be used if drain tile is incorporated into the
design, and slopes greater than 4 percent can be used if check dams are placed in the
channel to reduce flow velocity. :
Drainage Area. The maximum flow rate" (Q) to the swale can be calculated using the
Rational Formula, depending on the size of the drainage area (A), the percentage of the ,
drainage area that is impervious (C) and the rainfall intensity 0) for the design storm.
- ' . ' -['_-.-'.' Q = CiA ".."'
A typical design storm used for sizing swales is a six-month frequency, 24- hour storm
event The exact intensity must be calculated for your location and is generally available :
from the US Geological Survey (USGS). Swales are generally not used where the
, ' . maximum flow rate exceeds 5 cfs.
.Sizing Procedures. The width of the swale can be calculated using various forms of the
Manning equation. However, this methodology can be simplified to the following rule of
thumb: the total surface area of the swale should be 500 square feet for each acre that
, drains to the swale.
' Unless a bypass is provided, the swale must be sized as both a treatment device and' to
pass the peak.hydraulic flows. But to be most effective as a treatment device, the depth
.of the stormwater should not exceed the height of the grass in the swale.
-------
Design Parameters. Based on limited research, swales can generally be designed using the
following parameters: , ;
1. Minimum grass height of 6 inches (Figure 2).
2. Maximum depth of stormwater during the design storm of 4 inches
(Figure 2).
3. Maximum flow in the swale of 5 cfs. '-,':
4. Maximum velocity in the swale of 3 fps.
5. Channel slope between 2 and 5 percent.
- Slopes of less than. 2 % can be used if the swale is drained jo
prevent ponding (Figure 2).
- Slopes of more than 5. % can be used if check dams are placed
in the swale to maintain channel velocity below 3 fps
. '. (Figure 2).
6. to provide maximum long term treatment effectiveness, the swale width
" should be calculated using a design flow of 0.2 cfs per acre of area '
draining into the swale. However, the minimum width is 18 inches.
7. If a by-pass is not provided, the channel width and/or height should be
increased, if needed, to pass peak hydraulic flowsi '
8.. In order to provide adequate treatment, the swale should have a
minimum length of 200 feet. If a shorter length must be used, the
width should be .increased proportionally'to maintain a treatment
surface area of at least 500 square feet, as discussed above.
However, the minimum length is 25 feet \ _
SOURCE: Reference 3.
HSF*
FIGURE 2: DESIGN PARAMETERS
-------
Construction. The subsurface of the swale should be carefully constructed to avoid
compaction of the soil. Compacted soil reduces the infiltration and inhibits growth of the
grass. Damaged areas should be restored immediately to ensure that the desired level of
treatment is maintained and to prevent farther damage due to erosion of exposed soil.
Check Dams. Check dams can be installed in swales to promote additional infiltration,
increase" storage, and reduce velocities. The check dam may be a railroad tie embedded
.into .the swale with riprap placed on the downstream side of the tie to prevent a scour
hole from forming. Earthen check dams are not recommended because of their potential
to erode. Check dams should be installed every 50 feet if longitudinal slope exceeds 4 .
percent. " ' , '
MAINTENANCE
The primary swale maintenance objectives are to maintain the hydraulic efficiency of the channel and
maintain a dense, healthy grass cover. Maintenance activities should include periodic mowing (with
grass never cut shorter than the design flow depth), Weed control, watering during drought conditions,
reseeding bare areas, and clearing of debris and blockages. Cuttings should be removed from the
channel and disposed in £ local composting facility. Accumulated sediment should be removed
periodically. Application of fertilizers arid pesticides should be minimal, if required:
Research has not yet identified proper mowing strategies. However, mowings during the spring and
"summer should keep the grass at the 6" design height In some commercial applications Where 6" may
cause an aesthetic problem .the grass can be cut to 4" but the last mowing of the season should not be
below 6": Mowing encourages growth thereby improving the removal of soluble pollutants. The filial
mowing should occur near the end of the growth season. Failure to remove the growth before the
dormant season will cause a loss of pollutants back to the storinwater.
/ .,'.'- -'"" -'-''. ' ' " . - ",
1 . r ,','-.',.' '' .
Any damage to the channel such as rutting must be repaired with suitable soil, properly tamped and
seeded. The grass cover should be thick; if it is not reseeding as necessary.
Any standing water removed during the maintenance operation must be disposed to a sanitary sewer at
an approved discharge location. Residuals (ie, silt, grass cuttings, etc.) must be disposed of in
accordance with local or state requirements.
COSTS
Vegetated swales typically cost less to construct than curbs and gutters or underground storm sewers.
Shuler (.1987) reported that costs may vary from $4.90 to $9.00 per lineal foot for a 15-foot wide
channel (top width). : ' ' '. ' .
The Southeastern Wisconsin Regional Planning Commission (SEWRPC) reported that costs may vary
from $8.50 to $50.00 per lineal foot depending upoii swale depth and bottom width (1991). The
SEWRPC cost estimates are higher than other published estimates because they include the cost.of
activities such as clearing, grubbing, leveling, filling, and sodding, which, may not be included in many
of the reported costs. Construction costs depend on specific site considerations and local costs for labor
and materials. The Table 1 below shows estimates capital cost of a vegetated swale.
Annual costs associated with maintaining vegetated sWales are approximately $0.58 per lineal foot for a
1.5-foot deep channel, according to SEWRPC (1991). Estimated average annual operating and
maintenance costs of vegetated swales can be estimated using Table 2 below. .
-------
TABLE 1: ESTIMATED CAPITAL COSTS
S to
z
I
SOURCE: Reference 4,
SWALE DEPTH INFECT
TABLE 2: ESTIMATED O & M COSTS
1.10
SOURCE: Beference.4.
-------
ENYEIONMENTAL IMPACTS
Negative environmental impacts of vegetated svrales may include:
Leaching from culverts and fertilized lawns may increase the presence of trace
metals and nutrients in the runoff. "
. Infiltration through the swale may affect local groundwater.quality.
Standing water in vegetated swales can result in potential safety, odor, and
mosquito problems. . , - .
REFERENCES
1. U..S. EPA, A Current Assessment of Best Management Practices; Techniques for Reducing Nonpoint
Source Pollution in the Coastal Zone. December 1991. .
2. Minnesota Pollution Control Agency, Protecting Water Quality in Urban Areas. 1991;
3. Shuler, Thomas R., Controlling Urban Runoff. A Practical Manual for Planning and
'Designing Urban BMPs. July 1987. - -
4. Southeastern Wisconsin Regional Planning, Commission, Cost of Urban Nonpoint Source '
Water'Pollution Control Measures. Technical Report No. 31. 1991.
5. U.S. EPA, Stormwater Management for Industrial Activities: Developing Pollution Prevention
Plans and Best Management Practices. September 1992.
6. U;S. EPA. Results of the Nationwide Urban Runoff Program. December 19831 ,
7. Washington State Department of Ecology, Stormwater Management Manual for the Puget Sound
Basin. Februaru 1992. , - '.
, WMosgnn DC ZM60.
-------
MTB
STORM WATER BMP:
VISUAL INSPECTIONS
rErtfa
rtt
MUNICIPAL TECHNOLOOr BBANCH
DESCRIPTION
Visual inspection is the process by which -members of a Stormwater Pollution Prevention Team (SWPPT)
visually inspects stormwater discharge from material storage and outdoor processing areas to'identify
contaminated Stormwater and its possible sources.
S . 'i . . . . . ' ". ' "
An example of a visual inspection is examination within the first hour of a. storm event that produces
significant stormwater runoff for the presence of floating and suspended materials, oil and grease,
discolorations, turbidity, odor, or foam. Another example would be to examine a raw materials storage
area where materials'are stored in 55-gallon drums and look for leaks, discolorations, or other
abnormalities that may cause a pollutant to contaminate stormwater runoff. .
CURRENT STATUS, .
The U.S. EPA has recognized visual inspections as a baseline Best Management Practice (BMP) for over
10 years. Its implementation across the country, however, has been sporadic. Stormwater Pollution
Prevention Plan CSWPPP) development will increase implementation of visual inspections in the future .as
facility management recognizes it to be an effective BMP from a water quality and cost savings
perspective. ... . '.''"'
- ' ' ' ' *
LIMITATIONS
Limitations associated with, visual inspections include:
Inspections are limited to those areas clearly visible to the human eye
Visual inspections need to be performed by qualified personnel
Lack of-a corporate commitment to actively implement inspections on a
, routine basis ' .
Inspectors need to be properly motivated to perform a thorough visual
inspection. , '
PERFORMANCE
The performance of visual inspections'as an effective tool in reducing stormwater runoff contamination
is highly variable and dependent upon site-specific parameters such as industrial activity occurring at the
facility, maintenance procedures, and employees. Currently there is no quantitative data regarding the
effectiveness of visual inspections as a BMP.. , .
DESIGN CRITERIA
Visual inspections should be-performed routinely for the presence, of non-stormwater discharges. Flows
during a dry period should be. observed to determine the presence of any dry weather flows, stains,
sludges, odors, and other abnormal conditions.
-------
Visual inspections shouid be made of all stormwater discharge outlet locations during the first hour of a
storm event that produces a significant amount of stormwater runoff. In geographic.locations with a
high frequency of storm .events, inspections should be performed at least.once per month. Inspection for
the presence of floating and suspended materials, oil arid-grease, discolorations, turbidity, foam, and
odor should be performed.' . " '
1 . . - ' '*'.<* ' * . .
' - ' ^ - : " ' x ~
, The inspection frequency interval is a key design criterion in a visual inspection program. To determine
the inspection frequency, experienced personnel should evaluate the causes of previous incidents and
assess the probable risks for occurrence in the future. Conditions in the stormwater discharge permit
may also dictate inspection frequency. '
Another key design criterion is proper record keeping of an inspection. .Record keeping should include
the date of the inspection, the names of the personnel who performed the inspection, and the
observations made during the inspection. Records should be forwarded to appropriate personnel
through an internal reporting system. Remedial modifications to a racility can then be implemented
based on documented inspections. ; .
.-,-. - " 1- .'" '
Visual inspections of a facility should focus on the following key areas: , . .
Storage facilities
. . . Transfer pipelines .
- Loading and unloading areas . ';--' , \
. Pipes, pumps, valves, and fittings . -
. Internal and external inspection for tank corrosion
Wind blowing of dry chemicals . .
. - Tank support or foundation deterioration , .
.... Deterioration of primary or secondary containment facilities
_ . Damage to shipping containers
' .. Wind, blowing of dry chemicals and dust particles
.... Integrity of stormwater collection system . . .
Leaks, seepage, and overflows from sludge and waste disposal sites -
IMPLEMENTATION
A visual inspection BMP program should be .incorporated" within the facility's record keeping and internal
reporting BMP structure. Estimates of outfall flow rates, and noting the presence of oil sheens,
floatables, coarse solids, color, odors, etc. will probably be the most useful indicators of potential
problems. Specific parameters to look for in completing a visual inspection include:
Odor~The odor of a discharg'e can vary widely and sometimes directly reflects the source
of contamination. Industrial discharges will often cause the flow to smell like a
particular spoiled product, ofl, gasoline, specific chemical, or solvent As an
example, for'many industries, the decomposition of organic wastes in the discharge
will, release sulfide compounds into the air above the flow in the sewer, creating an
intense smell of rotten eggs: In particular, industries involved in the production of
meats, dairy products, arid the preservation of vegetables or fruits, are commonly ,
found to discharge organic materials into storm drains. As these organic materials
-------
spoil and decay, the sulfide production creates this highly apparent and
unpleasant smell. Significant sanitary wastewater contributions will also cause
pronounced and distinctive odors. . .
Color-Color is another important indicator of inappropriate discharges, especially from
industrial sources. Industrial discharges may be of any colorv Dark colors, such as
brown, gray, or black, are most common. For instance, the color contributed by
meat processing industries is usually a deep reddish-brown. Paper mill wastes are
also brown. In contrast, textile wastes are varied. Other intense colors, such as
plating-mill wastes, are often yellow. Washing of work areas in cement and stone
working plants can s\cause cloudy discharges. Potential sources-causing various
colored contaminated waters from industrial areas can include process waters (slug
or continuous discharges), equipment and work area cleaning water discharged to
floor drains, spills during loading operations (and subsequent washing of the
material into the storm drains). . ,. - f
Turbidity-Turbidity of water is often affected by the degree of gross contamination.
Industrial flows with moderate turbidity can be.cloudy, while highly turbid flows can be
" opaque. High turbidity is often a characteristic of undiluted industrial discharges, such as
those coming from some continual flow sources, or some intermittent spills. Sanitary
wastewater is also often cloudy in nature. , .
Floatable matter-A contaminated flow may also contain fipatables (floating solids or
liquids). Evaluation of floatables often leads to the identity of the source of industrial or
sanitary wastewater pollution, since these substances are usually direct products or
byproducts of the manufacturing process, or distinctive of sanitary wastewater. Floatables
of industrial origin may include substances such as animal fats, spoiled fppd products,
oils, plant parts, solvents, sawdust, foams, packing materials, or fuel, as examples.
Deposits and Stains-Deposits arid stains (residue) refer to any type of coating which
remains after a non-stormwater discharge has .ceased. They will cover the area
surrounding-the stbrmwater discharge and are usually of a dark color. Deposits and
stains often will contain fragments of floatable substances and, at times, take the form of
a crystalline or amorphous powder. These situations are illustrated by the grayish-black
'deposits that contain fragments of animal flesh and hair which often are produced by
leather tanneries, or the white crystalline powder which commonly coats sewer outfalls
due to nitrogenous fertilizer wastes. '
Vegetation-Vegetation surrounding a stormwater discharge may.show the effects of the
wastewater. Industrial pollutants will often cause a substantial alteration in the chemical
composition and Ph of the discharge water. This alteration wOl affect plant growth, even
when the source of contamination is intermittent. For example, decaying organic
materials Doming from various food product wastes would cause an increase in.plant life.
In contract, the discharge of chemical dyes and inorganic pigments from textile mills
could noticeably decrease vegetation, as these discharges often have a very acidic Ph. In
either case, even when the cause of industrial pollution is gone, the vegetation
surrounding the discharge will continue to show the effects of the contamination.
In order to accurately judge if the vegetation surrounding a discharge is normal, the
observer must take into account the current weather conditions, as well as the time of
year in the area. Thus, flourishing or inhibited plant growth, as well as dead and
decaying plant like, are all signs of pollution or scouring flows when the condition of the
vegetation-just beyond the discharge disagrees with the plant conditions near the
discharge. It is important not to confuse the adverse effects of high stormwater flows on
vegetation with highly toxic flows. Poor plant growth could be associated with scouring
flows occurring during storms. . -
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'. . . Structural Damage--Soructural damage is.another readily visible indication of industrial
. discharge contamination. Cracking, deterioration, and spalling of concrete or peeling of
. .surface paint, .occurring at an outfall are usually caused by severely contaminated
discharges, usually of industrial origin. These contaminants are usually very acidic or
basic 'in nature. For instance, primary metal industries have a strong potential for
causing structural damage because'-theirbatch, dumps are highly acidic. Poor.
; construction, hydraulic scour, and old age may also adversely affect the condition of -
.'.'.., structures. ...... - : " . .'...'
Implementation of visual inspections should be assigned to qualified staff such as maintenance personnel
/ or environmental engineers. Figure "1 provides a-sample visual evaluation worksheet which can be used
to record the results of the inspections. -
Outfall #.
location:
Photograph #.
Date:
Weather: air temp.:. ?C rain: Y N sunny cloudy
Outfall flow rate estimate: jL/sep
Known industrial or commercial uses in drainage area?. Y» N
describe: ' ' ' .. .
PHYSICAL OBSERVATIONS:
".'".' " * \ *
Odor: none sewage sulfide oil gas rancid-sour other:.
Color: none yellow .brown green red gray other:_
Turbidity: none cloudy opaque .
Floatabies: none petroleum sheen sewage other:.
Deposits/stains: none 'sediment oily describe:
. (collect sample)
(collect sample)
Vegetation conditions: normal excessive growth inhibited growth
' extent: . ' ' - ' .- -
Damage to outfall structures: . .
identify structure:
damage: none / concrete cracking / concrete spalling / peeling paint /
'corrosion .
other damage: ;
extent: / ' "' '. _
SOURCE: Reference 4.
HGURE1: VISUAL INSPECTION WORKSHEET
MAINTENANCE
Maintenance involved with visual inspections as a BMP include developing a schedule for performing .
visual inspections and follow-up to make sure the inspections are performed on schedule. Continual
record updates need to be performed with each inspection, and properly routed through the internal
reporting structure of a SWPPT. , ; .
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COSTS
Costs are those .associated with direct labor and overhead costs for staff hours. Annual costs can- be
estimated using the example in Table. 1 below. Figure 2 can be used as a worksheet to calculate the
estimated annual cost^or implementing a visual inspection program. .
TABLE 1: - EXAMPLE OF'ANNUAL VISUAL INSPECTION PROGRAM COSTS .
TMe
Stonnwater Engineer
Plant Management *
Plant Employees
\
Quantity.
1
5 ' '
100
Avg.
Hourly
Rate($)
x 15 x
x 20 x
x 10 x
Overhead*
Multiplier
2.0 .x
2.0 x
2.0 x
Estimated
Yearly
Hours
onSW
Training
20
10 «
. 5
TOTAL ESTIMATED ANNUAL COST
Note: Denned as a
those costs associated
SOURCEiEPA
multiplier, (typically ranging between 1. and
with payroll expenses, building expenses, etc
Est.
Annual
Cost($)
600
2,000
10.000
$12,600
3) that takes into account
. ,
' * , i .'.',''-
Estimated
. \ Yearly
Avg. Hours
Hourly Overhead onSW
TMe Quantity Rate ($) Multiplier Training
. ' x '' ' x ; x ' . ='
. x x ' x *
'X - '-X X =
x ' ,x . - x =
Est
Annual
Cost($)
fAl
ffl)
K3
035
TOTAL ESTIMATED ANNUAL COST
(Sum of A+B+C+D)
SOURCE: Reference 3. ' % ' . .' .. .
HGURE 2: SAMPLE ANNUAL-VISUAL INSPECTION PROGRAM COST WORKSHEET.
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ENVIRONMENTAL IMPACrS
Visual inspections is an effective way to identify a variety of problems. Correcting these problems can
have a significant impact on improving water quality in the receiving water.
REFERENCES
1. California Environmental Protection Agency, Staff Proposal for Modification to Water Quality
Order No. 91-13 DWO Waste Discharge Requirements for Dischargers of Stormwater Associated
with Industrial Activities. Draft Wording. Monitoring Program and Reporting Requirements. .
August 17. 1992. ., ' V -'./
' ' '. ' ' ^ .''<
2. U.S. EPA. NPDES BMP Guidance Document. June 1981. ',
3. U,S. EPA. Stormwater Management for Industrial Activities: Developing Pollution Prevention .
Plans and Best Management Practices." September 1992. ; -.
4. :Pitt, Roberr, Barbe, Donald; Adrijan, Donald, and Field, Richard. Investigation of Inapprot?riate
Pollutant Entries into Storm Drainage Systems A users guide.-U. S. EPA. Edison. New Jersey.
-1992; ' ' v ' '>, ' '.'''.'.
TJm BMP fact J*a M» p*pa*J by, Ac ttuoofol Tedmateff OmA (4204). US EPA. 401H Soot SfT. WMaifa*. DC 20*&
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MTB
STORM WATER BMP:
VORTEX SOLIDS SEPARATOR
Office of Wastewater Management <*«^
MUNICIPAL TECHNOLOGY BRANCH
DESCRIPTION ,
A vortex solids separator is a wastewater treatment technology with no moving parts which lises
velocities imparted from vortex swirling to assist the settling and removal of concentrated solids. During a
storm event, flow enters the cylindrical unit tangentially and induces a swirling vortex which concentrates
solids in the underflow and reduces then* concentration in the clarified liquid. A general view of the vortex
solid separator and liquid flow paths is shown in figure 1 below. .
Floatable Solids
Outer Vessel Wall
SetUMtrii Solids
SOURCE: Reference 19
FIGURE 1: GENERAL VIEW OF THE VORTEX SOLID SEPARATOR
Vortex units are most often applied to combined sewer overflow (CSOs), but can also be used to treat
storm water runoff. In CSO treatment applications, the concentrated solids are removed from the bottom
of the unit and conveyed via the sanitary sewer to a wastewater treatment plant (WWTP). In separate storm
water applications, the concentrated underflow would likely go to a holding tank or pond. Effluent exits the
top of the unit and is discharged to the receiving water. Vortex units may be used on-line or off-line, and1
in combination with other Best Management' Practices (BMPs) such as storage tanks or detention ponds.
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CURRENT STATUS " . ,
This fact sheet contains general information only, and should not be used as the basis for designing
a vortex solids separators for storm water applications . While the basic vortex separator technologies used
for CSO applications are well established, actual operating experience for storm water applications is limited.
The three types of vortex solids separators currently being actively marketed in the United States are listed
below. While all three types use the same basic principal, this fact sheet will discuss some of the differences
in design and performance of the different units. The technology for storm water applications is evolving"
rapidly. The equipment manufacturers and the municipal operators should be contacted for the current state
of the art information. .
The EPA Swirl Concentrator.
TheFluidsep.
The Storm King.
The design specifications for the EPA Swirl Concentrator were developed by the U.S. Environmental
Protection Agency (EPA) in the early 1970s. Currently, there are 20 full-scale EPA Swirl Concentrator units
in the U.S. and four in Japan (EPA, 1977). All of these units were designed for CSO treatment. However,
the EPA Swirl Concentrator design was extensively tested during a study for separated storm water treatment
in West Roxbury, Massachusetts in the early 1980s (EPA, 1982,1984).
Fluidsep is a patented design that is licensed by a German firm, but is available in the U.S. There,
are 13 full-scale Fluidsep units operating in the U.S. and Europe, with additional units planned for
construction. Fluidsep has been consistently used for CSO applications and has not,been tested on separated
storm-sewer systems. .
Storm King, a patented unit, is available in the U.S. from H.I.L. Technology, Inc. There are no full-
scale Storm King units in operation in the U.S. at this time. However, there are more than 100 Storm King
treatment units in operation in Europe and Canada, almost exclusively on CSOs. Full-scale Storm King units
have been selected by the City of Columbus to treat CSOs. Storm water treatment by the Storm King has
been limited to a pilot study in Bradenton, Florida and a full-scale unit in Surrey Heath, England.
APPLICABILITY
Vortex separators are most effective where the separation of gritty materials, heavy particulates or
floatables from wet-weather runoff is required. The technology is particularly well suited to locations where
there is limited land availability which may preclude the use of other BMPs such as settling basins or
detention ponds. Vortex separators can also be applied as satellite units to treat smaller subareas of the
collection system, minimizing the high cost of conveyance systems heeded for centralized treatment facilities.
Units can be designed to remove solids and capture floatables. However, solids with poor settleability are not
effectively removed in vortex solids separators.
LIMITATIONS
The use of vortex solids separators as a wet-weather treatment option may be limited by the poor net
solids removal (10-34 percent). In some cases this level of solids removal may not meet the treatment
objectives for a potential location. There is even less information on-the ability of vortex soaids separators
to remove pollutants other than solids. Pollutants such as nutrients and metals that adhere to fine particulates
or are dissolved will not be significantly removed by the vortex separator.
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Site constraints, including the availability of suitable land, appropriate soil depth and stability to
structurally support the unit, may also limit the applicability of the vortex separator. The slope of the site
or collection system may dictate the use of an underground unit, which can result in extensive excavation.
For above-ground units, pumping may be required. Maintaining and operating these pumping facilities will
increase the capital costs as well as the energy, operations and maintenance cost of the vortex solids separator.
, i . / , .
DESIGN
Regardless of the type of vortex separator selected, the type and quantity of pollutants to be removed
must first be determined. The settleability characteristics and the quantity of flow to be treated will then
established for proper design to achieve the desired treatment level. The settling characteristics of particulates
anticipated in the influent are the basis of the design of all unit types.
The performance of each unit is based on the vortex separation mechanism. Each unit type has its
own design criteria to achieve solids/liquids separation. The design of the EPA Swirl Concentrator is based
on settleabffity studies developed in the 1970s. This information is available in the public domain from EPA
design manuals (USEPA, 1977). Design of the Storm King units is based on pilot-scale treatability studies.
Pilot-scale testing is conducted at each installation to select the appropriate full-scale unit design that best suits
the intended application. The Fluidsep design is based on modeling of participate settleability determined
during site-specific studies, including flow gauging and rainfall measurements.
PERFORMANCE .
Vortex separators designed primarily for removing grittier material, may have difficulty removing
the less settleable solids often found in storm water runoff. For CSO applications, average total mass solids
removals varied between 38%, at the EPA Swirl Concentrator facility in-Washington, B.C., to 61%, at the
Storm King pilot-study facility in Columbus, Georgia. For storm water runoff applications, average total
mass solids removal was observed to be approximately 26%, at the pilot-scale Swirl Concentrator
demonstration test in West Roxbury, Massachusetts. Average performance characteristics for the three
different types of separators in shown in Table 1 below. This data is for CSO applications only.
Solids are removed in the underflow by flow splitting even if there is no concentration of particulates
in the underflow from the vortex unit. The removal of solids in the underflow may account for a large
portion of the total mass solids removed in the unit. To discount the solids removed by the underflow without
concentration by the unit, net solids removals were determined. Net solids removals exclude from the total
solids removal, the solids removed by the underflow by flow-splitting. Net solids removals for CSO
applications, as shown in Table 1, were observed to a low of 7% for Tengen, Germany and a high of 34%,
for Columbus, Georgia. The average net mass solids removal for separate storm water applications was
observed to be a high of 17% for the EPA Swirl Concentrator tested at West Roxbury, Massachusetts and
a low of 12% for the Storm King unit tested at Bradenton, Florida. However, the data for storm water
runoff applications is not considered sufficient to allow for the evaluation of performance between unit designs
and is not included in Table 1. ,
MAINTENANCE
Vortex separators do not have any moving parts, and are therefore not maintenance intensive.
However, wash downs are required following every CSO event to prevent odors. To accomplish this, some
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TABLE 1: AVERAGE VORTEX PERFORMANCE CHARACTERISTICS
FOR CSO APPLICATIONS
Unit Type Location Effluent Hydraulic
Flow (MOD)
Swirl Washington, DC 10 .
Fhiidsep Tengen, Germany 11
Storm King James Bridge, UK 7.5
Storm King Columbus, GA 4.3
SOURCE: References 10, 11,20, and 21 -
Total Net
Solids Solids Treatment
Reduction Removal Removal Factor
24 38 12 1;7
47 54 7 1.2
39 53 14 1.7
23 61 34 2.6
units have been designed to be self-cleansing.
applications. Pretreatment
This may not be necessary for storm water treatment
BMPs such as bar screens or -street sweeping can be used to decrease the quantity of wastes reaching the
vortex separators, but it is not required. Maintenance would be required for pretreatment and pumping
equipment.
COSTS \
The capital cost for vortex solids separator treatment facilities are dependant on site-specific
characteristics. Commonly, vortex solids separators are used with other treatment technologies such as
automatic bar screens, and disinfection. The capital cost for vortex solids separator treatment facilities in
the U.S. varies between $3,000 and $5,250 per acre of drainage basin (1993 dollars). Typically the capital
cost for installed vortex solids separator units without pretreatment is approximately $4,900 per million
gallons of flow treated (1993 dollars).
Total costs of vortex units often include predesign costs, capital costs and operation and maintenance
(O&M) costs. Foe example, predesign study costs for the Storm King are typically $20,000 (1993 dollars).
Predesign costs for the Fluidsep, range between $25,000 and $100,000 (1993 dollars), there are no predesign
study costs associated with the EPA Swirl Concentrator, because published settleability curves are used for
the basis of design. ,
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Vortex solids separator units do not generally require significant energy expenditures unless pumping
is required. Operating expenses primarily include labor for wash down or energy costs for automatic wash
down or bar screens. However some installations such as the Storm King unit hi Surry Heath, England, do
not have a sanitary or foul sewer line for disposing of collected solids. These facilities must collect its
residuals in a collection zone or holding tank. The frequency for pumping out the collected residuals will be
dependent on the amount of material collected per storm, the number of storm events and the size of the
holding zone or tank. The Surry Heath facility is estimating the holding zone will require pump out every
2-3 years. The cost for periodic emptying and disposal of the collected residuals is estimated to be between
$300-450 per cleaning (1993 dollars).
ENVIRONMENTAL IMPACTS
Improvements can often be observer in water quality or in the health of the ecosystem. For example,
the Washington, D.C. CSO Abatement Program, .which includes EPA Swirl Concentrators and upstream
storage, has resulted in decreased oxygen demands in the receiving water. Fish have returned to the once
oxygen-depleted water. Much of the unproved receiving water quality is attributable due to a combination
of the upstream storage, and the bar screens, disinfection, and operation of the vortex units.
For CSO applications the vortex solid separators must be washed down after each storm events to
prevent objectionable odors. Odor control for some storm water applications and for residual storage
facilities may also be required. Collected residuals from storm water applications have not evaluated.
However, collected residuals should be evaluated for toxicity and metals content before disposal.
REFERENCES
1. American Public Works Association, 1978. The Swirl Concentrator as a CSO Regulator Facility. U.S.
EPA Report Number EPA-430/9-78-006.
2. Boner, M., 1993. Personal communication. . .
3. Brombach, H., 1992. Solids Removal from CSOs with Vortex Separators. Novatech 92, Lyori, France,
pp 447-459.
.4. Drysdale, 1993. Personal communication. '
5. Engineering-Science, Inc. and Trojan Technologies, Inc., 1993. Modified Vortex Separator and UV
Disinfection for CSO Treatment. Prepared for the Water Environment Research Foundation,
Alexandria, VA.
6. Engineering-Science, Inc., 1993. Trip Report for Work Assignment 1-09 EPA Contract No. 68-C2-0102.
7. Hedges, P.D., Lockley, P.E., and Martin, J.R., 1992. A Field Study of an Hvdrodvnamic Separator
CSO. Novatech 92, Lyon. France.
8. H.I.L. Technology, 1993. Informative brochures and memos.
9. NKK Corporation, 1987. Solid-Liquid Separation by Swirl Concentration. Brochure.
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10.
11.
12.
O'Brien and Gere, 1992. CSO Abatement Program Segment 1: Performance Evaluation. Prepared for
the Water and Sewer Utility Administration, Washington, D.C..
Pisano, William C., 1992. Survey of High Rate Storage and Vortex Separation Treatment for CSO
Control. For the Daly Road High Rate Treatment Facility Demonstration Project, Cincinnati, Ohio.
Pisano, William C., 1993a. Summary: The Fluidsep Vortex Solids Separator Technolc
Marketing Brief, Belmont, MA.
WKInc.
13. Pisano, William C., 1993b. Personal communication.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
Purcell Associates, 1975. Pollution Abatement Plan. Newark. New Jersey. Prepared for the City of
Newark, Department of Public Works.
Randall, Clifford W., Ellis, Kathy, Grizzard, Thomas J., and Knocke, William R., 1983. "Urban
Runoff Pollutant Removal by Sedimentation." Proceedings of the Conference on Storm Water Detention
Facilities. American Society of Civil Engineers. New York, NY.
Smith and Gillespie Engineers, Inc., 1990. Engineer's Study for Storm Water Management
Demonstration Project No. 2 for Evaluation of Methodologies for Collection. Retention. Treatment and
Reuse of Existing Urban Storm water. S&G Project Number 7109-133-01.
Sullivan, R.H., et al., 1974. The Swirl Concentrator as a Grit Separator Device. EPA Report Number
EPA-670/2-74-026.
Sullivan, R.H., et al., 1974. Relationship Between Diameter and Height for the Design of a Swirl
Concentrator as a CSO Regulator. EPA Report Number EPA-670/2-74-026.
US EPA, 1977. Swirl Device for Regulating and Treating CSOs. EPA Technology Transfer Capsule
Report. EPA Report Number EPA-625/2-77-012;
US EPA, 1982. Swirl and Helical Bend Pollution Control Devices. EPA Report Number
EPA-600/8-82-013. .
US EPA, 1984. Swirl and Helical Bend Regulator/Concentrator for Storm and CSO Control. EPA
Report Number EPA-600/2-84-151.
' J " : ' - _ ' . -
Water Environment Federation, Manual of Practice, MOP FD-20, 1992. Design and Construction of
Urban Storm Water Management Systems. Water Environment Federation, Alexandria, VA; American
Society of Civil Engineers, New York, NY.
Washington, D.C., undated. CSO abatement program.
Washington, D.C., July 22, 1993. Site visit to the D.C. Swirl Concentrator.
Whipple, W., and Hunter, J.V., 1981. "Settleability of Urban Runoff Pollution." Journal of the Water
Pollution Control Federation. Vol. 53. No. 12. Water Environment Federation, Alexandria, VA.
The BMP fact sheet was prepared by the Municipal Technology Branch (4204), US EPA, 401 M Street, SW, Washington, DC, 20460
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STORM WATER BMP:
WATER QUALITY INLETS
IMTB
S^IClESa^CHilSLOOV .RANCH*
DESCRIPTION
Water quality inlets (WQIs) consist of a series of chambers that allow sedimentation of coarse
materials, screening of larger or floating debris, and separation of free oil (as opposed to emulsified or
dissolved ofl) from storm water. They capture only the first portion of runoff for treatment and are generally
used for pretreatment before discharging to other best management practices (BMPs). A typical WQI, as
shown in Figure 1 below, consists of a sediment chamber, an oil separation chamber and a discharge
chamber. WQIs are also commonly called oil/grit separators or oil/water separators. WQIs can be purchased
as a pre-manufactured unit or can be constructed on site.
efefBlgi^i^i^fto
SOURCE: Ref
FIGURE 1: PROFILE OF A TOPICAL WATER QUAIJTY INLET
COMMON MODIFICATKMJS
The design of WQIs can be modified to improve their performance. Possible modifications include
(I) an additional orifice and chamber that replace the inverted pipe elbow, (2) the extension of the second
chamber wall up to the top of the structure, or (3) the addition of a diffusion device at the inlet. The
diffusion device is intended to dissipate the velocity head and turbulence and distribute the flow more evenly
over the entire cross-sectional area (API, 1990). Suppliers of pre-manufactured units (i.e., Highland Tank
& Mfg., Jay R. Smith Mfg., etc.) can also provide modifications of the typical design for special conditions.
CURRENT STATUS
WQfe are widely used in the U.S.; however, recent studies indicate that the lack of regular
maintenance adversely affect their performance. There is also some concern that, because the collected
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residuals contain hydrocarbon by-products, the residuals may be considered too toxic for conventional landfill
disposal. Maintenance requirements and residual disposal, should be carefully evaluated in selecting a WQI.
Possible alternatives to the WQI include sand filters, oil absorbent materials, and other innovative BMPs (i.e.,
Stormceptor System). .
APPLICATIONS
WQIs are often used where land requirements and cost prohibit the use of larger BMP devices, such
as ponds or wetlands. WQIs are also used to treat runoff prior to discharge to other BMPs. WQIs can be
adapted to all regions of the country (Schueler, 1992), and are typically located hi small, highly impervious
areas, such as gas stations, loading areas or parking areas. Sites with high automotive related uses can be
expected to have higher hydrocarbon concentrations than other land uses (MWCOG, 1993). Increased
maintenance and residual disposal, due to these higher hydrocarbon concentrations from these .areas, must
be carefully evaluated before selecting a WQI for these applications.
LIMITATIONS
Two major constraints limit the effectiveness of WQIs. Theses constraints are (1) the size of the
drainage area and (2) the activity within the drainage area. WQIs are generally recommended for drainage
areas of 1 acre or less (Berg, 1991, NVPDC, 1992). Construction costs often become prohibitive for larger
drainage areas. High sediment loads interfere with the ability of the WQI to effectively separate oil and
grease from the runoff. Therefore, WQIs should not accept runoff from disturbed areas unless the runoff
has been pretreated to reduce the sediment loads to acceptable levels.
- -..,.- > i
WQIs are also limited by maintenance requirements and pollutant removal capabilities. Maintenance
of underground WQIs can be easily neglected because the WQI is often "out of sight and out of mind."
Regular maintenance is essential to ensuring effective pollutant removal. Lack of maintenance will often
result in resuspension of settled pollutants. WQIs are most effective in removing heavy sediments and floating
oil and grease. WQIs have demonstrated limited ability to separate dissolved or emulsified oil from runoff.
WQIs are also not very effective at removing pollutants such as nutrients or metals, except where the metals
are directly related to sediment removal.
PERFORMANCE ,
More than 95 percent of all WQIs operate as designed during then: first 5 years. Very few
structural or clogging problems or problems with the separation of the pollutants and water are experienced
during that period. However, WQIs have a very poor record of pollutant removal due to a lack of regular
clean-outs and the resuspension of the sediments (Schueler, 1992). The efficiency of oil and water separation
in a WQI is inversely proportional to the ratio of the discharge rate to the unit's surface 'area (API, 1990).
Due to the small capacity of the WQI, the discharge rate is typically very high and the detention time is very
short, which can result in minimal pollutant settling. The average detention time in a WQI is less than 0.5
hour (MWCOG, 1993).
The WQI achieves slight, if any, removal of nutrients, metals and organic pollutants other than free
petroleum products (Schueler, 1992). Grit and sediments are partially removed by gravity settling within the
first two chambers. A WQI with a detention time of 1 hour may expect to have 20 to 40 percent removal of
sediments. .-
' - - , '.'". "' " ' - f ' . , " '
The Metropolitan Washington Council of Governments (MWCOG) performed a long-term study to
determine WQI performance and effectiveness. Monitoring of more than 100 WQIs indicated that less than
2 inches of sediments (mostly coarse-grained grit and organic matter) were trapped in the WQIs.
Hydrocarbon and total organic carbon (TOC) concentrations of the sediments averaged 8,150 and 53,900
mg/kg, respectively. The mean hydrocarbon concentration in the WQI water column was 10 mg/L. The
study also indicated that sediment accumulation did not increase over time, suggesting that the sediments
become re-suspended during storm events (MWCOG, 1993). Although the design of the WQI effectively
separates oil and grease from water, re-suspension of the settled matter appears to limit removal efficiencies.
Actual removal occurs when the residuals are removed from the WQI (Schueler1992). ,
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DESIGN CRITERIA. ' .' ! , ' ' '
Prior to WQI design, the site should be evaluated to determine if another BMP would be more cost-
effective in removing the pollutants of concern. WQIs should be used where no other BMP is feasible. The
site should be near a storm drain network so that flow can be easily diverted.to the WQI for treatment
(NVPDC, 1992). Construction activities within the drainage area should be completed and the drainage area
should be revegetated so that the sediment loading to the WQI is minimized. Upstream sediment control
measures should be installed to decrease the sediment loading. .
WQIs are most effective for small drainage areas. Drainage areas of 1 acre or less are often
recommended. WQIs are typically used in an off-line configuration (i.e., portions of runoff are diverted to
WQI), but they can be used as an on-line unit (i.e., receive all runoff). Generally off-line units are designed
to handle the first 0.5 inches of runoff from the drainage ares. Upstream isolation/diversion structured can
be used to divert the water to the off-line structure (Schueler, 1992). On-line units receive higher flows that
will likely cause increased turbulence and resuspension of settled material; thereby reducing WQI
performance. , ,
Chflmhcr Design ,
Structural loadings should be considered hi the WQI design (Berg, 1991). WQIs are available
in pre-manufactured units or can be cast-in-place. Reinforced concrete should be used to construct below-
grade WQIs. The WQIs should be water tight to prevent possible ground water contamination. The first
and second chambers are generally connected by an opening covered by a trash rack or by a PVC or other
suitable material pipe (Berg, 1991). If a pipe is used it should also be covered by a trash rack or screen. The
opening or pipe between the first and second chambers should be designed to pass the design storm with out
surcharging the first chamber (Berg, 1991). The design storm will vary depending on geographical location
and is generally definite by local regulations. , ,
When the combined length of the first two chambers exceeds 12 feet, the chambers are typically
designed with the length of the first and second chamber being 2/3 and 1/3 of the combined length
respectively. Each of the chambers should have a separate manhole to provide access for cleaning and
inspection. , .
f " t ' ' ' '
The State of Maryland design standards indicate that the combined volume of the first and second
chambers should be determined based, on 40 cubic feet per 0.10 acre draining to the WQI. In Maryland, this
is equivalent to capturing the first 0.133 inch of runoff from the contributing drainage area. The combined
volume includes the volume of the first and second chamber up to the top of the ulterior walls and the volume
of the permanent pool (Berg, 1991).
Permanent pools within the chambers help prevent the possibility of sediment resuspension. The first
and second chambers should have permanent pools with 4-foot depths. If possible, the third chamber should
also contain a permanent pool (NVPDC, 1992). .
In the standard WQI, an inverted elbow is installed between the second and third chamber. The
elbow should extend a minimum of 3 feet into the second chamber's permanent pool in order to retain oil
(NVPDC, 1992). The elbow should be capable of passing the design storm to prevent frequent discharge of
accumulated oil. The size of the elbow or number of elbows can be adjusted to accommodate the design flow
(Berg, 1991).
MAINTENANCE
WQIs should be inspected after every storm event to determine if maintenance is required. At a
minimum each WQI should be cleaned at the beginning of each change in season (Berg, 1991). The required
maintenance will be site-specific due to variations hi sediment and hydrocarbon loading. Maintenance should
include clean-out and disposal of the sediments and removal of trash and debris. The clean-out and disposal
techniques should be environmentally acceptable and in accordance with local regulations. Since WQI
residuals contain hydrocarbon by-products they may require disposal as a hazardous waste* Many WQI
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o-vmers contract -with -waste haulers to collect and dispose of these residuals. Since WQIs can be relatively
deep, they may be designated as confined spaces. Caution should be exercised to comply with confined space
entry safety regulations in the event that entry' into the WQI is required.
COSTS .' . ,''..'.'./. '''..'-. ' . ..'.'.
The construction costs for WQIs will vary greatly depending on the size and depth required. The
construction costs (in 1993 dollars) for cast-in-place WQIs range from $5,000 to $16,000, with the average
WQI costing around $8,500 (Schueler, 1992). For the basic design and construction of WQIs, the pre-
manufactured units are generally less expensive than those cast-in-place (Berg, 1991).
Maintenance costs will also vary greatly depending on the size of the drainage, the amount of the
residuals collected, and the clean-out, and disposal methods available (Schueler, 1992). The cost of residuals
removal, analysis and disposal can be major maintenance expense, particularly if the residuals are toxic and
are not suitable for disposal in a conventional landfill.
: <=- .'-,..'' '-'. ' "
' ' ' ' '.- ! '-'''
ENVIRONMENTAL IMPACTS
WQIs can effectively trap trash, debris, oil and grease, and other floatables that would otherwise be
discharged to surface waters (Schueler, 1992). The 1993 MWCQG study found that pollutants in the WQI
sediments were similar to those pollutants found in downstream receiving water sediments (the tidal Anacostia
River).. This information suggests that downstream sediment contamination is linked to contaminated runoff
(MWCOG, 1993). A properly designed and maintained WQIs can be an effectively BMP for reducing
hydrocarbon contamination in receiving water sediments. . .
WQIs generally provide limited hydraulic and residuals storage. Due to the limited storage, WQIs
do not provide adequate storm water quantity control. The WQI residuals require frequent removal and may
require disposal as a hazardous waste. The 1993 MWCOG study found that the residuals from WQIs
typically contain many priority pollutants, including polyaromatic hydrocarbons, trace metals, pthalates,
phenol, toluene, and possibly methylene chloride (MWCOG, 1993). During periods of high flow, the residuals
may be resuspended'and released from the WQI to surface waters. x
REFERENCES ' .-.
1. Fibresep Limited, not dated. Informative literature on the Stormceptor System. Oakville, Ontario,
Canada. ;
2. Schueler, T.R. 1992. A Current Assessment of Urban Blast Management Practices. Metropolitan
Washington Council of Governments. . '
3. Berg, V.H. 1991. Water Quality Inlets (Oil/Grit Separators); Maryland Department of the Environment,
Sediment and Storm Water Administration.
4. American Petroleum Institute (API) 1990. Monographs on Refinery Environmental Control - Management
of Water Discharges (Design and Operation of Oil-Water Separators). Publication 421, First Edition.
5. Northern Virginia Planning District Commission (NVPDC) and Engineers and Surveyors Institute, 1992.
Northern Virginia BMP Handbook.
6. Metropolitan Washington Council of Governments (MWCOG), 1993. The Quality of Trapped Sediments
and Pool Water Within Oil Grit Separators in Suburban Maryland. Interim Report.
This BMP feet shea was prepared by the Municipal Technology Branch(4204), US EPA, 401 M Stteet, SW, Washington, DC, 20460
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3MTB
STORM WATER BMP:
WET DETENTION PONDS
Office of Wastewater Management
MUNICIPAL TECHNOLOGY
BRANCH
DESCRIPTION .
Wet "detention ponds provide both retention and treatment of contaminated storm water runoff. A
typical wet detention pond is shown in Figure 1 below. A.wet detention pond maintains a permanent pool
of water where pollutant removal is achieved through physical, biological and chemical processes. Storm
water runoff is detained in the pond until runoff from the next storm event mixes with and displaces some
of the treated water before discharge to receiving waters. Discharge from the pond is controlled by a riser
and an inverted release pipe. ' " ,. , .
Principal Release Hpe
S* on Negative Stope
to Prevent dogging
Riser wan Trash Rack
Emergency
Spittway
Riprap
Cutoff Trench
SOURCE: Reference 2
D««p Water Zone tor
Gravity Settling
Emergent Aquatic
Plants
Riprap for Shoreline
Protection
Sediment Forebay
Concrete LOW Row Drain tor Pond Maintenance
(Should b*d»sigcMd to pnwid*MsyaecM*«ndB
void doflging by tafipM MdntMHK.)
FIGURE 1: TYPICAL LAYOUT OF A WET DETENTION POND
Wet detention ponds remove sediment, organic matter and metals by sedimentation and remove
dissolved metals and nutrients through biological uptake. Effective pollutant removal can be achieved if the
pond is properly designed and maintained (SEWPRC, 1991).
COMMON MODIFICATIONS
A typical wet pond may be enhanced with the addition of a sediment forebay, as shown in Figure 1,
or by constructing shallow ledges along the edge of the permanent pool. Runoff passes through the sediment
forebay where the heavier sediments drop out of suspension, while additional removal of lighter sediments
occurs in the permanent pool. The shallow, peripheral ledges contain aquatic plants that trap pollutants as
they enter the pond. Biological activity also increases due to the aquatic plants, and results in increased
nutrient removal. Perimeter wetland areas can also be created that will aid in pollutant removal. Theledges
also act as a safety precaution from accidental drowning and provide easy access for maintenance to the
permanent pool. ,
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Treatment within a pond can be enhanced through extending the detention lime in the permanent
pool. This allows for a more gradual release of collected runoff from a design storm over a specified time
(Hartigan, 1988). This results in increased pollution removal as wen as control of peak flows.
CURRENT STATUS
Wet detention ponds have been widely used throughout the U.S. for many years to treat of storm
water runoff. Many of these ponds have been monitored to determine their performance. EPA Region V
is currently performing a study on the effectiveness of 50 to 60 wet detention ponds. Other organizations,
such as the Washington, D.C., Council of Governments (Wash COG) have also conducted extensive
evaluations of wet detention pond performance (Schueler, 1992). Wet detention ponds provide the benefit
of both storm water quantity and quality control. In general, a higher level of nutrient removal and better
storm water quantity control can be achieved in wet detention ponds than can be achieved with other best
management practices (BMPs), such as infiltration trenches or sand filters. However, proper maintenance
is essential to maintaining these higher levels of treatment.
LIMITATIONS
Wet detention ponds must be able to maintain a permanent pool. Therefore, ponds should not be
constructed in areas where there is insufficient precipitation or on soils that are highly permeable. In wetter
regions, a small minimum drainage area may be adequate, where as, in more arid regions, a larger drainage
areas may be required in order to ensure sufficient water to maintain the permanent pool. In some cases,
soils that are highly permeable may be compacted or overlaid with clay blankets to make the bottom less
permeable. Land constraints, such as small sites or highly developed areas, may also preclude the use of a
pond. In addition, the local climate (i.e., temperature) may affect the biological uptake hi the pond. With
out proper maintenance, the performance of the pond will drop off sharply. Regular cleaning of the forebays
is particularly important. Maintaining the permanent pool is also important in preventing the resuspension
of trapped sediments. In most cases no specific limitations have been places on disposal of sediments removed
from wet detention ponds. Studies to date indicate that pond sediments are likely to meet toxicity limits and
can be safely landfilled (Schueler, 1992). Some states have allowed sediment disposal on-sfte, as long as the
sediments are deposited away from the shoreline, preventing their reentry into the pond.
PERFORMANCE
The primary pollutant removal mechanism in a wet detention pond is sedimentation. Suspended
pollutants, such as metals, nutrients, sediments, and organics, are partly removed by sedimentation. Other
pollutant removal mechanisms include algal uptake, wetland plant uptake and bacterial decomposition
(Schueler, 1992). Dissolved pollutant removal occurs as a result of biological and chemical processes
(NVPDC, 1992).
The removal rates of conventional wet detention ponds (i.e., without the sediment forebay or
peripheral ledges) are well documented and are shown in Table 1 below. The wide range in the removal rates
is a result of varying hydraulic residence times (HRTs), which is further discussed in the Design Criteria
section. Increased pollutant removal by biological uptake and sedimentation is correlated with increased
HRTs. Proper design and maintenance also affect pond performance.
Studies have shown that more than 90 percent of the pollutant removal occurs during the quiescent
conditions (i.e., the period between the rainfall events) (MD, 1986). However, some removal occurs during
the dynamic period (i.e., when the runoff enters the pond).
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TABLE 1: REMOVAL KtMClENCIES FROM WET DETENTION PONDS
Parameter
Total Suspended Solid
Total Phosphorus
Soluble Nutrients
Lead
Zinc
Biochemical Oxygen Demand or
Chemical Oxygen Demand
1 hydraulic residence time varies
2 hydraulic residence time of 2 weeks
SOURCE: Reference 1
SOURCE: Reference!
Percent Removal
Schueler. 1992* Hartigan. 19882
50-90 80-90
30-90
40-80 50-70
70-80
40-50
20-40
DESIGN CRITERIA
Well designed and properly maintained ponds can function as designed for 20 years or more.
Concrete risers and barrels have a longer life than corrugated metal pipe risers and barrels and are
recommended for most permanent ponds (Schueler, 1992). The accumulation of sediments in the pond will
reduce the storage capacity and cause a decline in performance. Therefore, the bottom sediments in the
permanent pool should be removed every 2 to 5 years or as necessary. The design of the pond should allow
easy access to the forebays for frequent sediment removal. .
, . ' j
All local, state and federal permit requirements should be established prior to starting the pond
design. Depending on the location of the pond, required permits and certifications may include wetland
permits, water quality certifications, dam safety permits, sediment and erosion control plans, waterway
permits, local grading permits, land use approvals, etc.(Schueler, 1992). Since many states and municipalities
are still in the process of developing or modifying storm water permit requirements, the applicable
requirements should be confirmed with the appropriate regulatory authorities.
Prior to designing the pond, a site should be selected that is able to support the pond environment.
The cost effectiveness of locating a pond at that site should also be carefully evaluated. The site must have
adequate base-flow from the groundwater or from the drainage area to maintain the permanent pool.
Typically, underlying soils with permeability between 10"5 and 10"* cm/sec will be adequate so that a
permanent pool can be maintained. In addition, the pond should be located where the topography, of the site
allows for maximum storage at minimum construction costs (NVPDC, 1992). Land constraints to avoid,
include existing utilities (e.g., electric or gas) that would be costly to relocate and excavation of bedrock that
would require expensive blasting operations.
The design of wet detention ponds should serve two functions: storm Water quantity control and
storm water quality control. Storm water quantity requirements are typically met by designing the pond to
control post-development peak discharge rates to pre-development levels. Various routing models (i.e., Soil
Conservation Service TR-20 or EPA SWMM) can be used to calculate the required storm water storage.
Usually the pond is designed to control multiple design storms (e.g., 2- and/or 10-year storms) and safely pass
the 100-year storm event. However, the design storm may vary depending on local conditions and
requirements.
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J
Storm water quality control is achieved in the permanent pool, which is designed by either the
eutrophication method or the solids settling method (Hartigan, 1988). Several models are available for both
methods. The solids settling method accounts for pollutant removal through sedimentation, whereas the
eutrophication method accounts for dissolved nutrient removal that occurs as a result of biological processes.
Equations for the Walker eutrophication model are shown in Table 2 below. Hie solids settling method
indicate that two-thirds of the sediment, nutrients and trace metal loads are removed by sedimentation within
24 hours. Theses projections are supported by the results of theEPA's 1993 National Urban Runoff Program
(NURP) studies. However, other studies indicate that a hydraulic residence time (HRT) of 2 weeks is required
to achieve significant phosphorus removal (MD, 1986). This longer HRT is similar to the HRT determined
, by the eutrophication method. In some cases, tne HRTs calculated by the eutrophication method are up to
three times greater than HRTs calculated by the solids settling method. These longer HRTs appear to be due
to the slower reaction rates associated with the biological removal of dissolved nutrients. This results in a
permanent pool that is approximately three times larger than the permanent pool calculated by solids settling
models (Hartigan, 1988): Other design methods, such as sizing the permanent pool to collect a specific
volume of runoff from the drainage area, have been tried with varying degrees of success, and are not
described in this fact sheet.
TABLE 2: WALKER EUTROPHICATION MODEL
K2 = (0.056XQS)
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One way to increase the HRT is to increase the depth of the permanent pool. However, the
permanent pool depth should not exceed 20 feet. The optimal depth ranges between 3 and 9 feet for most
regions, given a 2 week HRT (Hartigan, 1988). Ponds with shallower depths will have shorted HRTs. It is
important to maintain a sufficient permanent pool depth in order to prevent the resuspension of trapped
sediments (NVPDC, 1992). Conversely, thermal stratification and anoxic conditions in the bottom layer might
develop if permanent pool depths are too great. Stratification and anoxic conditions may decrease biological
activity. Anoxic conditions may also increase the potential for the release of phosphorus and heavy metals
from the pond sediments (NVPDC, 1992). , ,
In general, pond designs are unique for each site and application. Ponds should always be designed
to complement the natural topography (NVPDC, 1992). The pond should be constructed with adequate slopes
and lengths. While, a length-to-width ratio is usually not used in the design of wet detention ponds for storm
water quantity management, a 2:1 length-to-width ratio is commonly used when water quality is of concern.
In general, high length-to-width ratios (greater than 2:1) will decrease the possibility of short-circuiting and
enhance sedimentation within the permanent pool. Baffles or islands can also be added within the permanent
pool to increase the flow path (Hartigan, 1988). Shoreline slopes between 5:1 and 10:1 are common and allow
easy access for maintenance, such as mowing and sediment removal (Hartigan, 1988). In addition, wetland
vegetation is difficult to establish and maintain on slopes steeper than 10:1. Ponds should be wedge-shaped
so that flow enters the pond and gradually spreads out. This minimizes the potential for zones with little or
no flow (Urbonas, 1993). .
*
The design of the wet pond embankment is another key factor to be considered. Proper design and
construction of the embankments will prolong the integrity of the pond structure. Subsidence and settling
will likely occur after an embankment is constructed. Therefore, during construction the embankment should
be overfilled by at least 5% (SEWPRC, 1991). Seepage through the embankment can also affect the stability
of the structure. Seepage can generally be minimized by adding drains, anti-seepage collars and core
trenches. The embankment side slopes can be protected from erosion by using minimum side slopes of 2:1
and by covering the embankment with vegetation or rip-rap. The embankment should also have a minimum
top width of 6 feet to ease maintenance.
Normal flows will be discharged through the wet.pond outlet, which consists of a concrete or
corrugated metal riser and barrel. The riser is a vertical pipe of inlet structure that is attached to the base
with a watertight connection. Risers are typically placed in or adjacent to the embankment rather thanJn
the middle of the pond. This provides easy access for maintenance and prevents the use of the riser as a
recreation spot (e.g., diving platform for kids) (Schueler, 1988). The barrel is a horizontal pipe attached to
the riser that conveys flow under the embankment. ' .'
Typically, flow passes through an inverted pipe attached to the riser, as shown in Figure 1, with
higher flows will pass through a trash rack installed on the riser. The inverted pipe should discharge water
from below the pond water surface to prevent floatables from clogging the pipe and to avoid discharging the
warmer surface water. Clogging of the pipe could result in overtopping of the embankment and damage to
the embankment (NVPDC, 1992). Flow is conveyed through the near horizontal barrel and discharged to the
receiving stream. Rip-rap, plunge pools, or other energy dissipators should be placed at the outlet to prevent
scouring and minimize erosion. Rip-rap also 'provides a secondary benefit of reaeratioh of the pond
discharges.
. i
The design and construction of the riser and barrel should consider the design storm and the material
of construction. Generally, the riser and barrel are sized to meet the storm water management design criteria
(e.g., to pass a 2-year or a 10-year storm event). In many installations the riser and barrel are designed to
convey multiple design storms (Urbonas, 1993). The riser and barrel should be constructed of reinforced
concrete rather than corrugated metal pipe to increase the life of the outlet. The riser, barrel and base should
also have sufficient weight to prevent flotation (NVPDC, 1992).
In most cases, emergency spillways should be included in the pond design.' Emergency spillways
should be sized to safely pass flows that exceed the design storm flows. The spillway prevents pond water
levels from overtopping the embankment, which could cause structural, damage the embankment. The
-------
emergency spillway should be located so that downstream buildings and structures will not be negatively
impacted by a spillway discharges. The pond design should include a low flow drain, as shown in Figure 1.
The drain pipe should be designed for gravity discharge and should be equipped with an adjustable gate
valve. ;'". - , . . .''.'. ' ' - .;. '.-._ ' '
MAINTENANCE
. Wet detention ponds function more effectively when they are regularly inspected and maintained.
Routine maintenance of the pond includes mowing of the embankment and buffer areas and inspection for
erosion and nuisance (e.g., borrowing animals, weeds, odors) problems (SEWFRC, 1991). Trash and debris
should be routinely removed to maintain an attractive appearance and also to prevent the outlet from
becoming clogged. In general, wet detention ponds should be inspected after every storm event. The
embankment and emergency spillway should also be routinely inspected for structural integrity, especially
after major storm events. Embankment failure could result in severe downstream flooding. .'
' . " " ' / - ,
When any problems are observed during routine inspections, necessary repairs should be made
immediately. Failure to correct minor problems may lead to larger more expensive repairs or even pond
failure. Typically, maintenance includes repairs to the embankment, emergency spillway, inlet and outlet,
removal of sediment and control of algal growth, insects and odors (SEWFRC, 1991). Large vegetation or
trees that may weaken the embankment should be removed. Periodic maintenance may also include the
stabilization of the. outfall area (e.g., add rip-rap) to prevent erosive damage to the embankment and the
stream bank. In most cases sediments removed from wet detention ponds are suitable for landfill disposal.
However, where available, on-site disposal od removed sediments will reduce maintenance costs.
, '"" ' --'',. .- . "' I .''- ' " ---
costs
The total cost for a pond includes permitting, design and construction and maintenance costs.
Permitting costs may vary depending on state and local regulations. Typically, wet detention ponds are less
costly to construct in undeveloped areas than retrofitting into developed areas. This is due to the cost of land
and the difficulty in finding suitable sites in developed areas. The cost of relocating of pre-existing utilities
or structures is also a major concern in developed areas. The construction costs for wet detention ponds in
1989 for undeveloped areas are shown in Figure 2 below. These costs include mobilization and demobilization
of heavy equipment, site preparation (e.g., clearing and excavation), site development (e.g., seeding and inlet
construction) and contingencies (e.g., engineering and legal fees) (SEWPRC, 1991). Several studies have
shown the construction cost of retrofitting a wet detention pond into a developed area may be 5 to 10 times
the cost of constructing the same size pond in an undeveloped area. : .
Operation and maintenance costs in 1989 are presented in Figure 3 below (SEWPRC, 1991). Annual
maintenance costs can generally be estimated at 3 to 5 percent of the construction costs (Schueler, 1992).
Maintenance costs include the costs for regular inspections of the pond embankments, grass mowing, nuisance
control, debris and liter removal, inlet and outlet maintenance and inspection, and sediment removal and
disposal. Sediment removal costs can be decreased by as much as 50 percent if an on-site disposal areas are
available (SEWPRC, 1991).
ENVmONMENTAL IMPACTS
Wet detention ponds provide both storm water quantity and quality benefits. Benefits obtained from
the use of wet detention ponds include decreased potential for downstream flooding and stream bank erosion.
Water quality is also unproved due to the removal of suspended solids, metals, and dissolved nutrients. In
general, the positive impacts from a wet detention ponds will exceed any negative impacts from a pond,
assuming the pond is properly designed and maintained.
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TABLES: CONSTRUCTION COOTS (1989)
.1. .
JUSMOUT&T
IUXTENANCE'
PAOCMM
kOUIMSTMnON
INSPECTION
U9NM.E-
NUUNTEMAMCE;
SOURCE: Kef trace 4
ETKTEHTHNaASMmTBI VOLUME MTOOUS/yOS OF CMC FEET
TABLE 4: OPERATIONS AND MAINTENANCE COSTS (1969)
WOO
--I-
__L_H^rur
-^ I:
:'..- i U
1 J>!
"*ft^:.lt^±1JW:
-XT
x ;
SOURCE: KeferoKc4
"» «>
WET DrrENTKM BASIN WKTEK VOLUME M
I >
4 i-H-4
OF Owe FEET
IOOO
However, wet detention ponds that are improperly designed, sited or maintained may have potential
adverse affects on water quality, groundwater, cold water fisheries, or wetlands. Improperly designed or
maintained ponds may result in stratification and anoxic conditions that can promote the resuspension of
solids and the release of nutrients and metals from the trapped sediments. During construction, precautions
should be taken to prevent damage to wetland areas. Ponds should also not be sited in areas where warm
water discharges from the pond will adversely impact cold water fishery. The potential groundwater
contamination should be carefully evaluated. However, studies to date indicate that wet detention ponds do
not significantly contribute to groundwater contamination (Schueler, 1992).
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REFERENCES . ' '''"'' - '.. -'' . '. .
1. Schueler, T.R., 1992. A Current Assessment of Urban Best Management Practices. Metropolitan
Washington Council of Governments. . ' . , ,
2. Maryland, Department of the Environment (MD), 1986. Feasibility and Design of Wet Ponds to Achieve
Water Quality Control. Sediment and Storm Water Administration.
3. Hartigan, J.P, 1988. "Basis for Design of Wet Detention Basin BMPs" in Design of Urban Runoff
Quality Control. American Society of Engineers.
4. Southeastern Wisconsin Regional Planning Commission (SEWPRC), 1991. Costs for Urban Nonpoint
Source Water Pollution Control Measures. Technical Report No. 31. .
5. Northern Virginia Planning District Commission (NVPDC) and Engineers and Surveyors Institute, 1992.
Northern Virginia BMP Handbook.
6. Urbonas, Ben and Peter Stahre, 1993. Storm Water Best Management Practices and Detention for Water
Quality. Drainage.'and CSO Management.' FIR. Prentice Hall, Englewood Cliffs, New Jersey..
B
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3MTB
Office of Wastewater Management
MUNICIPAL TECHNOLOGY BRANCH
MUNICIPAL WASTEWATER MANAGEMENT
FACT SHEETS - '
STORM WATER BEST MANAGEMENT PRACTICES
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STAPLE HERE
FOLD HERE
Municipal Technology Branch (4204)
United States Environmental Protection Agency
401 M Street, SW
Washington, DC, 20460
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