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Theses and Dissertations
2012
Development of a method to compare storm waterbest management practices at The University ofToledoChristopher Michael WancataThe University of Toledo
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Recommended CitationWancata, Christopher Michael, "Development of a method to compare storm water best management practices at The University ofToledo" (2012). Theses and Dissertations. Paper 461.
A Thesis
entitled
Development of a Method to Compare Storm Water Best Management Practices at The
University of Toledo
by
Christopher Michael Wancata
Submitted to the Graduate Faculty as partial fulfillment of the requirements for the
Master of Science Degree in Civil Engineering
_________________________________________
Dr. Cyndee Gruden , Committee Chair
_________________________________________
Dr. Patrick Lawrence, Committee Member
_________________________________________
Dr. Ashok Kumar, Committee Member
_________________________________________
Dr. Patricia Komuniecki, Dean
College of Graduate Studies
The University of Toledo
December 2012
Copyright 2012, Christopher Michael Wancata
This document is copyrighted material. Under copyright law, no parts of this document
may be reproduced without the expressed permission of the author.
iii
An Abstract of
Development of a Method to Compare Storm Water Best Management Practices at The
University of Toledo
by
Christopher Michael Wancata
Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Master
of Science Degree in Civil Engineering
The University of Toledo
December 2012
Storm water runoff has become a concern in urban environments. Urban
environments have a very large percentage of impermeable area, creating large amounts
of surface runoff. This surface runoff carries contaminants (nutrients, sediments,
pathogens, oils and greases) into storm water collection systems, which drain directly into
natural waters. These contaminants degrade water quality, harming human health and
aquatic life. In order to address these concerns, storm water best management practices
(BMPs) have been developed to reduce flow rates and improve water quality. However,
many sites that require the use of the BMPs have no means of deciding which BMP is the
best fit for the site in question. To address this problem, a Storm Water BMP Model was
developed to analyze three different BMPs (porous pavement, bioswales, and rain
gardens) for effectiveness. A comparison is made using input parameters including water
quality information and permeable/impermeable areas, and potential. BMPs are ranked
iv
based on flow quantity reduction, pollutant reduction, and payback period. The payback
period includes capital costs associated with constructing the BMP as well as monetary
values associated with environmental gains from implementing the BMP. This model
provides the opportunity to see a side by side comparison of BMPs in a retrofit situation
and to evaluate their implementation based on cost and performance.
v
Table of Contents
Abstract .............................................................................................................................. iii
Table of Contents .................................................................................................................v
List of Tables ................................................................................................................... ix
List of Figures ......................................................................................................................x
List of Abbreviations ........................................................................................................ xii
1 Introduction .........................................................................................................1
2 Literature Review.....................................................................................................2
2.1 Storm Water Regulatory Context....................................................................2
2.1.1 The National Pollutant Discharge Elimination System ......................3
2.1.2 Municipal Separate Storm Sewer Systems .........................................5
2.2 Urban Storm Water ............................................................................................6
2.2.1 Combined Sewer Systems...................................................................7
2.2.2 Non-Point Source Pollutants ...............................................................8
2.2.3 The First Flush ....................................................................................9
2.3 Storm Water Pollutants and Their Sources ......................................................10
2.3.1 Physical Contaminants ......................................................................10
2.3.2 Chemical Contaminants ....................................................................12
2.3.3 Biological Contaminants ...................................................................15
vi
2.4 Issues with Heavy Flows in Storm Water ........................................................16
2.5 Local Storm Water Implications ......................................................................17
2.6 Local Storm Water Regulations .......................................................................22
2.7 Introduction to Urban Storm Water Controls ..................................................23
2.7.1 Hydraulic Controls ............................................................................24
2.7.1 A Flow Attenuation...............................................................24
2.7.1 B Reduction of Volume ........................................................25
2.7.2 Unit Processes ...................................................................................27
2.7.2 A Physical Treatment Processes ...........................................28
2.7.2 B Biological Treatment Processes ........................................30
2.7.2 C Chemical Treatment Processes..........................................30
2.8 BMP Design Type............................................................................................33
2.8.1 Structural BMPs ................................................................................33
2.8.2 Non-structural BMPs ........................................................................35
2.9 Criteria for BMP Selection ..............................................................................38
2.10 Selected BMPs ...............................................................................................42
2.10.1 Permeable Pavement ......................................................................43
2.10.2 Rain Gardens ...................................................................................46
2.10.3 Bioswales ........................................................................................47
3 Methods ........................................................................................................50
3.1 Water Quality Methods ....................................................................................50
vii
3.1.1 Nitrates ..............................................................................................51
3.1.2 Orthophosphates ...............................................................................51
3.1.3 Coliform/E.coli .................................................................................52
3.2 Calculation of Overall Flow Rate ....................................................................53
3.3 Site Specific Goals ...........................................................................................54
3.4 Developing Solutions for Storm Water Management ......................................55
3.4.1 Water Quality Inputs .........................................................................56
3.4.2 Drainage Areas..................................................................................56
3.4.3 Construction Cost..............................................................................58
3.4.4 Runoff and Pollutant Reduction........................................................60
3.4.5 Economic and Decision Analysis .....................................................62
3.5 Sensitivity Analysis .........................................................................................65
4 Experimental Results .............................................................................................67
4.1 Water Quality Results ......................................................................................67
4.2 Drainage Areas.................................................................................................68
4.3 Example 1 (Drainage Area A) ......................................................................69
4.4 Example 2 (Drainage Area H) .....................................................................75
4.5 Sensitivity Analysis .........................................................................................81
5 Discussion .......................................................................................................83
5.1 Example 1 (Drainage Area A) .....................................................................83
5.2 Example 2 (Drainage Area H) .....................................................................85
viii
5.3 Comparison to CNTs Green Values National Storm Water Calculator .........86
5.4 Sensitivity Analysis .........................................................................................87
6 Conclusion and Future Work ................................................................................89
References ..........................................................................................................................91
A Appendix A ............................................................................................................95
A.1 Overall Site Information at The University of Toledo ....................................95
ix
List of Tables
2.1 NPDES Monitored Pollutants ..................................................................................5
2.2 Origins of Nonpoint Source Pollutants ....................................................................9
2.3 Common Forms of Nitrogen and Phosphorus in Receiving Waters ......................14
2.4 Measure of Progress for the Great Lakes Restoration Initiative ............................21
2.5 Structural BMPs listed by Fundamental Process Category and Unit Operation ...32
2.6 Proprietary BMPs in Current Use ..........................................................................35
2.7 Non-structural BMPs .............................................................................................36
2.8 Groups of Pollutants and Relevant BMPs Listed Based on FPCs .........................37
2.9 BMP Objective Checklist ......................................................................................42
3.1 Summary of Nitrates Concentrations .....................................................................51
3.2 Summary of Orthophosphates Concentrations ......................................................52
3.3 Coliform/E.coli Results..........................................................................................53
3.4 Site Specific Storm Water Goals ...........................................................................55
3.5 Water Quality Analysis (1 of 2) .............................................................................56
3.6 Water Quality Analysis (2 of 2) .............................................................................56
x
List of Figures
2-1 Black Swamp Area ................................................................................................18
2-2 Demonstration of Water Infiltration through Permeable Pavement ......................44
2-3 Cross Section of Vegetated Swale .........................................................................48
3-1 Drainage Area Calculation .....................................................................................57
3-2 Construction Cost Calculation ...............................................................................58
3-3 Runoff and Pollutant Reduction.............................................................................61
3-4 Payback Period for Porous Pavement ....................................................................63
3-5 Results for Combined BMP Processes ..................................................................64
3-6 Percent of Water Quality/Quantity Goals Attained ...............................................64
3-7 BMP Ranking System ............................................................................................65
4-1 Nitrates/Phosphates Data for Sites A and H (2012) ..............................................68
4-2 Pathogen Water Quality Data for Sites A and H (2012) .......................................68
4-3 Proposed Area for Porous Pavement/Rain Gardens (A) ...................................69
4-4 Total Surface Runoff Calculations (A) .............................................................70
4-5 Construction Costs for Porous Pavement .............................................................71
4-6 Construction Costs for Rain Gardens ....................................................................71
4-7 Runoff and Pollutant Reduction Calculations .......................................................72
4-8 Payback Period Calculations for Porous Pavement ..............................................73
xi
4-9 Payback Period Calculations for Rain Gardens ....................................................73
4-10 Percentages of Goals Attained by Porous Pavement ............................................74
4-11 Percentages of Goals Attained by Rain Gardens ..................................................74
4-12 Decision Analysis Calculations for Drainage Area A .......................................75
4-13 Proposed Areas for Bioswale/Rain Garden (H) ................................................76
4-14 Total Surface Runoff Calculations (H) .............................................................77
4-15 Construction Costs for Bioswale/Rain Garden .....................................................77
4-16 Runoff and Pollutant Reduction Calculations (H) ............................................78
4-17 Payback Period Calculations for Bioswale/Rain Garden .....................................79
4-18 Percentages of Goals Attained by Bioswale/Rain Garden ....................................80
4-19 Decision Analysis Calculations for Drainage Area H .......................................80
4-20 Sensitivity Analysis for Porous Pavement .............................................................81
4-21 Sensitivity Analysis for Bioswales ........................................................................82
4-22 Sensitivity Analysis for Rain Gardens ...................................................................82
A-1 Water Quality Data for The University of Toledo .................................................95
A-2 Outfall Locations (West)........................................................................................96
A-3 Outfall Locations (East) .........................................................................................96
A-4 Map of The University of Toledo ..........................................................................97
xii
List of Abbreviations
EPA ............................Environmental Protection Agency
NPDES .......................National Pollutant Discharge Elimination System
1
Chapter 1
Introduction
In the past few decades, storm water has become an increasing concern.
Agricultural activities, stream channelization, and urbanization have caused degradation
of landscapes that had once slowed flow, acted as detention basins, and a means from
controlling sedimentation. For example, in the Maumee River Basin, 41% of the river
basin is considered impaired due to urbanization. (US Army Corps of Engineers, Buffalo
Division, 2011) Storm water has also been collected into combined sewer system, in
which storm water and sewage are combined in one sewer system. During large rain
events, wastewater treatment plants become over loaded, and raw sewage is bypassed
into rivers and streams, creating a hostile environment for aquatic life. In order to
separate these sewer structures, millions of dollars must be spent. Flooding due to large
rain events has also proven to be costly. Some storms in the Greater Toledo area have
caused damages estimated at over $1,000,000. In order to address developing storm water
concerns, a tool shall be developed that objectively compares potential BMPs using cost
and environmental benefits. (US Army Corps of Engineers, Buffalo Division, 2011)
2
Chapter 2
Literature Review
2.1 Storm Water Regulatory Context
The Clean Water Act (1972), initially written in 1948 as the Federal Water
Pollution Control Act, provides the basic principles for regulating pollutant discharge into
the water of the United States, as well as quality standards for surface waters. The United
States Environmental Protection Agency (EPA), under authority from the Clean Water
Act, has developed certain standards, such as pollution monitoring programs, which
provide guidelines for wastewater effluent for industries. Under the Clean Water Act, it is
illegal to discharge any pollutant from a point source directly into a water source, unless a
permit is obtained. The U.S. EPA enacted the National Pollutant Discharge Elimination
System (NPDES) in 1972, which further controls discharges into water sources.
Industrial, municipal, as well as other facilities need to obtain permits if any of their
discharges enter into surface waters. Individual homes connected to water collection
systems, use septic systems, or do not have a surface water discharge are not required to
obtain a permit. NPDES does not directly apply to storm water discharges; it applies to
surface and receiving waters in the United States. Storm water contributes to receiving
water pollution, which is why storm water pollution control is becoming more important.
(United States Environmental Protection Agency, 2012)
3
2.1.1 The National Pollutant Discharge Elimination System
More recent concerns, through the NPDES program, have focused efforts to
address storm water discharges. In 1987, the United States Congress amended the Clean
Water Act, which allowed the U.S. EPA to establish NPDES permits for storm water.
The initial permit established by the U.S. EPA focused regulations for storm water
discharges on industrial activity, as well as large separate storm sewer systems, typically
with a population greater than 100,000 people (NPDES Phase I). These permits establish
a means for monitoring pollutant discharge, as well as establish proper controls for
pollutants. (U.S. EPA, Department of Water, 1996)
The U.S. EPA has broadly defined the idea of industrial storm water discharge.
Any industrial activity that discharges storm water through a municipal storm sewer
system, or directly into a water source, must obtain a NPDES permit. Any discharge to
combined sewers or a Publicly Owned Treatment Plant (POTW) can be excluded from
permits. Included in industrial activities are the following: manufacturing plants,
construction sites greater than 5 acres, hazardous material, landfills, sewage treatment
facilities, recycling plants, power plants, mining, oil and gas facilities, airports, and other
transportation related operations. (U.S. EPA, Department of Water, 1996)
In terms of permits, municipalities and industries have three options for dealing
with storm water discharges. The options include the following: (i) individual permit; (ii)
group permits; or (iii) general permits.
4
Individual permitting can occur when facilities of industrial activity choose not to
participate in a group permit or do not receive permit under a general permit, in which the
information required by an individual permit must include a drainage map for the site,
site descriptions identifying pollutants that can be present at the site, as well as testing
data. Group permits can be used when industries of similar work require a permit.
Finally, general permitting can be done when an industry would like to be involved in a
permit that covers an entire area. (U.S. EPA, Department of Water, 1996)
In August 1995, the U.S. EPA developed regulations for Phase II of the NPDES
permit. Phase II of the NPDES program includes all storm water discharges not included
in Phase I. Phase II includes storm water discharges from small municipal separate storm
sewer systems, as well as commercial and industrial activities. Phase II has been designed
for discharges that the NPDES program, regulated by the U.S. EPA, has identified as
contributing to poor water quality or a significant addition to pollution to U.S. waters.
(U.S. EPA, Department of Water, 1996)
Protecting human life and aquatic habitats is the primary concern for the NPDES
permit. In order to do so, the NPDES permit program determines site specific effluent
standards, site specific management programs, and data reporting goals. If a site fails to
comply with these standards, the EPA can enforce fines. If the situation requires aid to
meet standards, the EPA will step in to offer assistance to meet NPDES requirements.
(U.S. EPA, Department of Water, 1996)
5
Each NPDES permit is valid for a period of 5 years. Renewal of the permit must
take place at least 180 days prior to the expiration date of the previous permit. For each
applicant, it becomes imperative to become familiar with the details of the NPDES
permit. The NPDES permit has data reporting and management standards that applicants
need to be aware of. Although each site has specific regulations, the pollutants generally
being regulated can be seen below:
Table 2.1: NPDES Monitored Pollutants
Monitored Pollutants
Conventional
Human wastes
Food from garbage disposals
Bath Waters
Fecal Coliform
Bacteria found in the digestive systems of
humans and animals; can lead to growth of
pathogens
Oils and Greases Can produce sludge solids that are difficult
to treat
Toxic Pollutants Organics, such as pesticides
Metals
Nonconventional Nutrients, such as phosphorus and nitrogen
(Pennsylvania Department of Environmental Protection)
2.1.2 Municipal Separate Storm Sewer Systems
Polluted storm water is frequently transported through Municipal Separate Storm
Sewer Systems, also known as MS4s. Through an MS4, untreated water is emptied
directly into a body of water. Operators of an MS4 must obtain a NPDES permit and
develop a feasible storm water management system to prevent pollutants from entering
into a sewer system. (United States Environmental Protection Agency, 2012) A MS4
6
permit is generally a system of conveyances that is state, city, town or village owned.
These cities that discharge to U.S. waters require an MS4 that is to be designed to collect
storm water, and is not to be collected in a combined sewer situation. Finally, an MS4 is
not to be part of a Publicly Owned Treatment Works, otherwise known as a sewage
treatment plant. (United States Environmental Protection Agency, 2012)
City municipalities, along with guidance from the EPA, have developed these
regulations for many reasons. Heavy runoff flows are being seen in urbanized areas,
creating sediment transport and erosion problems. Contaminants are entering into the
ecosystem through runoff that enters into a citys storm sewer system. Ultimately,
NPDES and MS4 permitting has been developed to address urban storm water problems.
2.2 Urban Storm Water
Urban storm water runoff is created when water flows across lawns, streets, and
paved surfaces during and after a rain event. Surfaces can be classified into two
categories: permeable and impermeable. Permeable surfaces allow the movement of
water through a surface (soil, porous pavement, etc.), while impermeable surfaces forbid
movement of water through the surface (concrete, roofs, etc.). Impermeable surfaces
prevent storm water from naturally percolating through the ground, which filters water
prior to becoming ground water. During a rain event, water removes pollutants from the
air through which it falls, as well as collects debris, litter, and animal refuse from the
ground over which is travels. Storm water, in essence, carries pollution from one place to
another, without treatment. Storm water can have a huge environmental impact due to the
7
fact that all pollution washed away with storm water usually ends up in a water source
somewhere else. (The Pennsylvania State University Institute of State and Regional
Affairs, 1980)
2.2.1 Combined Sewer Systems
Typically, storm water runoff is a major concern in urban areas. Much of the area
taken up by an urban area is considered to be impermeable, or simply impassable, to rain
water trying to infiltrate the surface. In an urban setting, water flows across an
impermeable surface, in which it collects all pollutants it comes in contact with before
entering a storm sewer system. A municipality has two options for storm water:
combined sewer systems, in which wastewater and storm water are combined into one
sewer system, or separate sewers, in which storm water and wastewater have their own
systems, respectively. (The Pennsylvania State University Institute of State and Regional
Affairs, 1980)
Some cities, such as Toledo and Cleveland, have combined sewer systems that
carry sanitary waste from homes and storm water from streets and roofs. In the past, these
systems were beneficial. Storm water was captured and treated along with the sanitary
waste before re-entering the environment. However, as city population and density grew,
these systems became overloaded and high flows were untreatable. This problem has lead
to combined sewer overflows (CSOs), in which raw sewage and storm water is bypassed
directly into rivers and streams to avoid overflowing a treatment plant during a large rain
8
event. This has obvious environmental implications. Solving this problem has proven to
be expensive. The first option thought of was to separate the combined sewers into two
separate systems: sanitary and storm.
Other options have included constructing underground storage tunnels to store
combined sewer overflow. The City of Cleveland has one of these tunnels in operation
currently, and will begin constructing another segment that will run 3,000 feet under
Lake Erie in the next few years. The tunnel is again an expensive option, costing nearly
$198 million. (Scott, 2012)
2.2.2 Non-Point Source Pollutants
In past decades, water quality management had been directed towards point
source pollution (i.e. an individual source of pollution, such as a factory). In this case,
pollution sources are relatively easy to address once identified. However, recent studies
have shown that even though point source pollution is being regulated, storm water
quality is still of concern. A study performed by the Council of Environmental Quality
showed that 75% of urban areas were impacted by nonpoint source pollution. Some
factors that play into nonpoint source pollution can be seen in the table below:
9
Table 2.2: Origins of Nonpoint Source Pollutants
Nonpoint Source Pollutant Origins
Automotive Traffic Construction Air Quality Refuse
Heavy Metals Dirt Smokestack Debris Animal
Acid-Producing Substances Asphalt Coal Plant
Salts Paint Dirt Street Debris
Oil Trash
(The Pennsylvania State University Institute of State and Regional Affairs, 1980)
As seen in the table above, construction sites pose a large problem for overall
water quality in storm water. Due to loose, non-compacted materials, runoff rates from
construction sites can be up to one hundred times greater than that of a non-construction
site. (The Pennsylvania State University Institute of State and Regional Affairs, 1980)
2.2.3 The First Flush
Urban storm water runoff that is of the most concern usually occurs during the
first 30-60 minutes of an event. This is also known as the first flush, in which most
contaminants that will be collected in storm water runoff enter into the ecosystem. Even
though the first flush lasts for a short duration, storm water has a much larger impact on
the environment as compared to treated wastewaters. When compared to treated
wastewater, urban runoff contains much larger amounts of suspended solids (TSS),
metals, and nutrients that enter back into a water source during the storm event. Large
storm events, such as thunderstorms that last 15-30 minutes, contribute the largest
10
amount of pollution in urban runoff. Large amounts of rain lead to heavy runoff. The
heavy runoff can pick up any contaminant it can come in contact with, as well as
contribute to erosion. Erosion is of concern due to high velocities and flow rates through
man-made channels and storm sewer systems, as well as natural streams and rivers. (The
Pennsylvania State University Institute of State and Regional Affairs, 1980)
2.3 Storm Water Pollutants and Their Sources
Not only is water quantity an issue in understanding storm water runoff, water
quality is an issue as well. Decreased water quality hinders aquatic ecosystems and limits
the amount of use for humans. When contaminants are in storm water that is being
collected and released at high flow rates, the delivery of contaminants to waters can be
quite significant.
2.3.1 Physical Contaminants
Temperature
Storm waters can have fluctuating temperatures depending upon their source.
Temperature can be a big contributor to decreased habitat sustainability. Temperature
variations, especially those that increase water temperature, are detrimental to cold water
fish. Water temperature can affect the life cycle of fish, which survive best with water
temperatures of 14 C. Once the temperature of the water reaches 25 C, aquatic life
becomes almost inexistent. (Natarajan & Davis, 2010) Temperature variations can be
caused by cooling water from power plants, runoff from hot parking lots, which can be as
warm as 29 C, as well as the removal of shade from streams and rivers. (Anisfeld, 2010)
11
pH
Another contributor to water pollution is unbalanced pH levels. Typical pH ranges for
natural waters occur between 5 and 9. If a discharge, typically found from industrial
processes, of highly acidic (low pH) or highly basic (high pH) enters into a water source,
can create a toxic environment for aquatic life, as well as damage infrastructure.
(Anisfeld, 2010)
Turbidity/Total Suspended Solids
Turbidity and total suspended solids (TSS) measures the amount of sediment that
is suspended in a water sample. Sediment levels can vary from water source to water
source naturally, through storm events, as well as other sources. Human activities can
increase TSS, especially those activities involved with industrial discharges. TSS and fine
sediments can modify the physical and chemical qualities of rivers and streams.
Invertebrates and other aquatic life can be affected by suspended particles that affect food
and habitats. Also, suspended solids decrease the amount of light entering the water,
which directly hinders the amount of photosynthetic activity that can occur. (Izagirre, et
al. 2008) Turbidity is usually measured in nephelometric turbidity units, otherwise known
as NTUs. Turbidity can be measured by determining the degree to which light is
scattered by particles in a water sample. Total suspended solids are a measurement based
on mg/L of sediment in a water sample. (Anisfeld, 2010)
12
2.3.2 Chemical Contaminants
Conductivity
Conductivity, which is the ability of water to conduct a current, measures the
amount of dissolved material in water. Higher conductivity goes hand in hand with higher
amounts of dissolved materials. High levels of conductivity can be caused by mineral
weathering (natural cause) as well as sewage discharge (human cause). (Anisfeld, 2010)
Dissolved material, commonly referred to as dissolved organic carbon (DOC), indicates
that there is a potential pollution source found in the water. This dissolved organic carbon
is the most common occurring form of organic matter found in water, easily digested by
bacteria found in the same waters. This process by bacteria then limits the amount of
oxygen in the water source, making it difficult to sustain aquatic life. (Moitra, 2012)
Dissolved Oxygen
The next contributor to water pollution is dissolved oxygen (DO). It is imperative
for organisms in a stream or river to have an adequate amount of dissolved oxygen in
order to sustain its life. Physical, as well as biological, processes can control oxygen
levels. Good aeration, or contact between air and water, typically results in 100% oxygen
saturation. The 100% saturation of oxygen in water represents a balance between air and
oxygen in the water. The level of saturation is dependent on a few factors: temperature
and salinity. At high temperatures and salinity, DO can be as low as 6mg/L; at low
temperatures and salinity, DO can be as high as 14 mg/L. Although saturation levels can
depict a certain percentage of oxygen, biological processes can cause a significant
13
difference in actual oxygen levels in water. Respiration, otherwise known as the
consumption of oxygen, is a leading problem found in a water source with high levels of
organic matter. This organic matter is consumed by bacteria, which use DO found in the
water. This scenario can lead to hypoxia (DO levels with less than 3 mg/L), in which
aquatic life will be unable to sustain life. (Anisfeld, 2010)
Biochemical Oxygen Demand
Biochemical oxygen demand (BOD), chemical oxygen demand (COD), and total
organic carbon (TOC) reflect the amount of organic matter found in a water sample, and
can be a sign of wastewater present. Organic matter will consume oxygen needed by
living organisms in the receiving waters. (Anisfeld, 2010)
Nutrients (Nitrates and Phosphates)
Nutrients, specifically nitrogen and phosphorus, are required by plants and algae
to grow. However, high levels of these nutrients lead to eutrophication, which leads to
increased rates of photosynthesis. This increased rate can cause algae blooms, which can
then lead to hypoxia in the water source. Agricultural activities, fossil fuel combustion
and sewage lead to increased nutrient levels. The following are the typical forms of
nitrogen and phosphorus found in surface waters:
14
Table 2.3: Common Forms of Nitrogen and Phosphorus in Receiving Waters
Dissolved Inorganic Nitrogen (DIN)
includes forms of nitrogen that include
NH4+ (ammonium), NH3 (ammonia), and
NO3- (nitrates). All of these forms are
typically used by plants during
photosynthesis
Total Nitrogen
includes both DIN and organic nitrogen.
Organic nitrogen reflects the amount of
nitrogen that has entered into organic
matter through photosynthesis
Dissolved Inorganic Phosphorus (DIP) commonly found as an orthophosphate
(PO43-
)
Total Phosphorus includes DIP and organic phosphorus
(Anisfeld, 2010)
Nitrates are of concern in urban storm water runoff. High levels of nitrates can
lead to eutrophication. Eutrophication (also an implication of high phosphorus and carbon
levels) can lead to algae blooms, which deplete oxygen levels in rivers, streams, and
lakes, making it difficult for fish and other aquatic life to exist. Due to health concerns,
nitrate levels in drinking water can be no more than 10 mg/L. Consequently, it is
important to limit the amount of nitrogen entering a water supply. (Kim, Seagren &
Davis, 2003)
Phosphorus is found naturally in receiving waters in the form of phosphates.
(Geosyntec Consultants, Inc. & Wright Water Engineers, Inc., 2010) Phosphates are also
another source of storm water pollution. Phosphorus can enter into storm water through
the use of fertilizers and other home use. Like nitrates, phosphates can lead to
15
eutrophication. To limit eutrophication, phosphate concentrations should be limited to 0.1
mg/L. (Pretorius & De Villiers, 2000) Also excess phosphorus concentrations can lead to
hindered water clarity, odors, and loss of aquatic habitats. Excess phosphorus can also
indicate the presence fecal indicator bacteria. (Geosyntec Consultants, Inc. & Wright
Water Engineers, Inc., 2010)
Metals
Metals and other organic contaminants, also known as toxic micro pollutants, are
found at much lower concentrations than other pollutants. Metals, although naturally
occurring, are widely used in human activities. Synthetic compounds are emerging as a
leading pollutant under this category as well. There are more than 100,000 different
synthetic compounds today, which is why minimal information exists about them. These
compounds are typically found in sediments, in a process known as sorption, as well as in
organisms, through bioaccumulation. Human exposure to these harmful metals typically
occurs through the consumption of fish and animal products. (Anisfeld, 2010)
2.3.3 Biological Contaminants
Bacteria
Bacteria in a water source are the biggest concern to human health. Human and
animal waste, found in a water source can indicate the presence of pathogens that can be
detrimental to human health. In order to determine the presence of pathogens, certain
indicators can be used that, by themselves, are not harmful but tend to coexist with
pathogens. When these indicators reach a certain concentration, the water is deemed
16
unsafe for human use. Indicators include total coliform, fecal coliform, Escherichia coli
(E. coli), and enterococci. All of the above bacterial indicators indicate the possibility for
the presence of pathogens, and require further water testing to confirm the extent to
which the water quality is contaminated. (Anisfeld, 2010)
2.4 Issues with Heavy Flows in Storm Water
Although contaminants polluting watersheds cause issues for an ecosystem, heavy
flow rates due to large amounts of urban storm water runoff also wreak havoc on an
ecosystem. Although stream and river velocities vary over time due to increased sediment
and water flows from upstream locations, urbanization has drastically increased the rate
as to which this occurs. (Bledsoe, 2002) In an ever-changing urban environment, river
and stream sizes are enlarging. Due to increased runoff caused by impermeable surfaces,
and a decrease in sediment travel, stream and river reliability is diminishing. Damage to
the integrity of river/stream banks and ecosystems are occurring due to structural/shape
changes to channels, changes in channel materials, increase in TSS, and loss of habitats
due to increased flow rates.
Increase of flow rate is becoming a concern to urban watersheds. With an increase
in impermeable material, due to roofs and asphalt, more water is being collected in storm
water systems. Many times, the flows enter directly into a river or stream. An increase in
impermeable surface increases quantity of flow, and subsequently a higher flow rate of
water through a system. (Bledsoe, 2002) A study done in an urban Alabama city shows
17
that from 1990-2002, the amount of impermeable surfaces increased from 73.62 acres to
148.28 acres. This amount of impermeable surface has more than doubled over the past
12 years, which is a direct indication that the amount of runoff has increased by the same
amount. As a result of urbanization, impermeable surfaces are increasing in cities
nationwide. To minimize flow rate, best management practices such as permeable
pavement, detention/retention basins, as well as any other practice that can improve the
infiltration rate of storm water, can be selected to improve the effect of heavy flows on an
ecosystem. (Bledsoe, 2002)
2.5 Local Storm Water Implications
The Greater Toledo area is comprised of land included in the lower Maumee
watershed (approximately 692,000 acres). Activities in the area are primarily agricultural,
accounting for 85% of the land usage. Included in the lower Maumee watershed is 2,150
miles of stream, of which 41% is considered impaired. Agricultural activities, stream
channelization, erosion, and urbanization have degraded much of the landscape that once
slowed flow of storm water, acted as a detention facility, and help control sedimentation
downstream. (US Army Corps of Engineers, Buffalo Division, 2011)
Before the area became urbanized, the area made up a portion of the Black
Swamp. This swamp was once one of the largest wetlands in the United States, until it
was officially drained in the late 1800s. The area initially was settled in the 1850s, after
which the State of Ohio began efforts to drain the area to improve roadway quality.
18
Draining of the Black Swamp was done primarily through the use of clay tiles. Figure 2-1
shows the Black Swamp area:
Figure 2-1: Black Swamp Area
(US Army Corps of Engineers, Buffalo Division, 2011)
In recent years, strong storms have traveled through the area, dumping rainfall
amounts as high as 7.25 inches during one rain event. Due to improper flood controls,
damages caused were estimated as high as $1,000,000. These storms have drastically
overwhelmed drainage ditches, as well as the storm sewer system in Toledo. These
overflows are creating a situation in which wastewater treatment plants, which are part of
the combined sewer network, must bypass overflowing raw sewage into the Maumee
River, as well as local streams in the surrounding area. The raw sewage is leading to E.
coli concerns for the surrounding waters. Aquatic life is becoming hindered and algae
blooms are starting to also become of concern. (US Army Corps of Engineers, Buffalo
Division, 2011)
19
Studies performed by the US Army Corps of Engineers are now being done to assess the
current state of the watershed in Northwest Ohio. The assessment will develop a means
for assessing the situation, as well as cost breakdown and project management. (US
Army Corps of Engineers, Buffalo Division, 2011)
Outside of the Maumee River Basin, the Great Lakes, as a whole, are
experiencing large water quality issues. The demands placed on the Great Lakes have
resulted in severe levels of stress on the ecosystem, and the ecosystem simply cannot
keep up with the demands that are being placed on it. It is becoming imperative that not
only harm be minimized, but to be proactively restoring the ecosystem of the Great
Lakes. (U.S. Environmental Protection Agency, 2010)
In order to achieve this goal, President Barack Obama and the U.S. EPA proposed
a $475 million proposal that would execute the Great Lakes Restoration Initiative. The
initiative is intended to operationalize the intentions made by the Great Lakes Restoration
Initiative. The Great Lakes Regional Collaboration Strategy (GLRC Strategy) provides
the backbone for the Action Plan. This Action Plan points out which factors contribute to
ecosystem problems, as well as combine efforts to address these problems. (U.S.
Environmental Protection Agency, 2010)
The Action Plan focuses on five specific areas of concern. These areas include the
following: toxic substances and areas of concern, invasive species, near shore health and
nonpoint source pollution, habitat and wildlife protection and restoration, and finally
accountability, education, monitoring, evaluation, communication and partnerships. With
20
these five factors in place, the Action Plan then develops measurable goals for the
ecosystem. This plan is intended to further enhance the work that has already been done
by the states surrounding the Great Lakes. Overall, the goals behind the initiative are
simple and are as follows: the fish need to be safe to eat, the water needs to be safe to
drink, beaches and waters need to be safe for recreational activities, native species and
habitats are being protected, and finally, no community will suffer from the effects of
pollution. President Obama has also implemented a measure of progress that can be seen
in the table below:
21
Table 2.4: Measure of Progress for the Great Lakes Restoration Initiative
Measures of Progress for GLRI Project
Measure Baseline 2010 2011 2012 2013
2014
Cumulative
Target
Number of Areas of
Concern in the Great
Lakes where all
management actions
necessary for delisting
have been implemented
1 AOC 1 AOC 1 AOC 3
AOCs
4
AOCs 5 AOCs
AOC BUI (Beneficial
Use Impairments)
Removed
11 BUIs 20
BUIs
26
BUIs
31
BUIs
41
BUIs 46 BUIs
BUI delisting project
starts at AOCs
30 national
and bi-
national
projects
60
projects
80
projects
110
projects
140
projects
170
projects
Cubic Yards (in millions)
of contaminated sediment
remediated
5.5 million 6.3
million
7.0
million
7.2
million
8.6
million 9.4 million
Pollution (in pounds)
collected through
prevention and waste
prevention projects
0 10
million
15
million
25
million
35
million 45 million
Cumulative percentage
decline for the long term
trend in average
concentrations of PCBs in
fish
0% 34% 37% 40% 43% 46%
(U.S. Environmental Protection Agency, 2010)
This initiative is the starting point for reducing pollution in the Great Lakes
region. Using this initiative as a basis for information, smaller areas such as the Greater
22
Toledo area can implement smaller treatment solutions to reduce flow and contaminants
entering into the Great Lakes receiving waters. (U.S. Environmental Protection Agency,
2010)
2.6 Local Storm Water Regulations
Although there arent any specific standards for storm water effluents, the State of Ohio
has certain criteria all surface waters must comply with. The surface waters must meet
the following standards:
Waters added through human activity must be free of suspended solids that could
potentially cause sludge deposits
Waters must be free of debris, oil, and scum that can be considered unsightly
Free from materials causing odor or color change
Waters must be free of toxic substances that could cause harm to human, animal,
or aquatic life
Waters must be free of nutrients that could lead to the growth of aquatic weeds
and algae
Waters must be free of substances associated with raw sewage.
Public health issues occur when the following conditions are met: water samples
that contain five thousand fecal coliform counts per one hundred milliliters in two or
more samples when five or less samples are taken, or in more than twenty percent when
more than five samples are taken, are potential concerns to public health. Similarly, water
23
samples that contain 576 E. coli counts per one hundred milliliters in two or more
samples when less than five are taken, or more than twenty percent when more than five
samples are taken, are also deemed issues to public health. (Ohio EPA, 1998)
Following the actual water quality restraints, a few restraints on testing are also
included in the Ohio EPA code. The collection of samples must adhere to the following:
Samples are to be collected when conditions specify steady state conditions
Samples must be collected at least 2 hours apart
Sample collection must not exceed 30 days
(Ohio EPA, 1998)
The above restraints to surface waters took effect in 1998, and have been
reviewed in 2007, as well as in 2012. (Ohio EPA, 1998)
2.7 Introduction to Urban Storm Water Controls
Control of water quantity (controls for flow and volume) will always be the front-
runner in storm water management since pollutant concentrations will always be
dependent upon flow quantity. Pollutant removal using best management practices
follows the same routines found in conventional water and wastewater treatment, which
use physical, chemical, and biological principles to treat water. Best management
practices not only treat water, but also involve the storage, filtration, and education
behind storm water issues. (Transportation Research Board, 2006)
24
2.7.1 Hydraulic Controls
Hydraulic controls are a significant factor in determining a best management
practice to implement. Flow alteration is the leading idea behind hydraulic controls. The
goals of hydraulically controlling runoff are to reduce volume, reduce peak flows, and to
create uniform flow rates at all times. Hydraulic controls can be broken into two different
ideas: flow attenuation and volume reduction, and are discussed below. (Transportation
Research Board, 2006) Flow alteration solutions include practices such as runoff,
infiltration, detention, storage, and evaporation.
2.7.1.A Flow Attenuation
Flow attenuation aims to reduce peak flow discharge quantities, and can be
broken down into interception, conveyance, and detention. Interception of storm water
occurs when a drop of water is temporarily stored in a leaf, stem or branch. Throughfall,
or water that drips from a leaf to the ground, accounts for the majority of intercepted
storm water. A small portion of this intercepted water is retained on the surface area of
plants and is lost through evaporation. The amount of water that can be intercepted varies
depending on the density of vegetation, but percentage of rainfall intercepted can be as
much as 20%. The idea of conveyance deals with the transport of runoff over the entirety
of a flow path for a single drop of water. In a typical collection system, conveyance aims
for efficiency in collecting runoff. However, with a best management practice,
conveyance is provided, as well as the increase of infiltration, improves water quality,
increases travel time for runoff, also known as time of concentration (Tc). These controls
25
are becoming increasingly important with the idea of treatment trains, or a system of best
management practices that aim to increase water quality and reduce flow. Finally,
detention temporarily stores excess amounts of storm water until can be released over a
determined period of time. A commonly mistaken term is known as retention (part of
volume reduction), in which water is never released after capture. No matter how the
water is stored (either through ponded water or contained in soils), storm water enters
into the storm sewer system. Detention systems are designed to release collected storm
water and release it back into the sewer system so that flooding will not occur.
(Transportation Research Board, 2006)
2.7.1 B Reduction of Volume
The second concept of hydraulic controls deals with the idea of reduction of
volume. Reduction of volume can occur through any of the following ideas: retention,
infiltration, or evapotranspiration. Retention, introduced earlier, captures storm water and
never releases it back into a storm sewer system. Retention can occur when runoff is
captured through interception, evaporation, transpiration and reuse. Evapotranspiration
(ET), which is the combination of evaporation and transpiration, can occur in many
different scenarios. Transpiration aims volume reduction for the root zone of soil.
Infiltration occurs when water enters through the soil and recharges ground water. In a
setting such as a meadow or forest, this movement of water is quite easy. However, in an
urban setting soil becomes very compacted, and infiltration is restricted. Soil moisture
content determines how much volume can be reduced. The volume able to be captured is
26
a direct correlation to a soils field capacity. Field capacity can be defined as the point
where drainage of water through gravity stops and water is then collected in soil through
capillary action. Any water that enters after this point typically requires under drains that
will move storm water back into a system. Infiltration rate can be affected by soil type,
amount of vegetative cover, as well ground water conditions. Infiltration can be increased
through the use of the following BMPs:
Porous pavement
Lawns, which increase green area and promote runoff infiltration
Green roofs
Bioswales/rain gardens
Finally, the combined idea of evaporation and transpiration, or evapotranspiration,
reduced water in vegetated areas. Water found in the root zones of soils are taken up
through the root systems of plants and them becomes transpired through the leaves of the
plants. The removal of water by the root systems of plants may remove excess
contaminants, especially nutrients such as phosphorus and nitrogen. ET is typically the
dominant volume control once excess water is removed through infiltration and under
drains, and field capacity is once again achieved. The following equation reflects the total
volume that can be removed by ET:
27
where:
V = transpired volume
Dr = root depth
A = surface area of soil
FC = field capacity
WP = wilting point
The wilting point can be defined as the point in which the soil loses the amount of suction
force required to draw more amounts of water from the ground. The difference between
field capacity and wilting point produce the amount of moisture available for
transpiration. Systems such as rain gardens have low field capacities (the amount of water
stored by capillary action once drainage by gravity has concluded), which maximize
drainage potential and filtration of pollutants. (Transportation Research Board, 2006)
2.7.2 Unit Processes
The second way of characterizing best management practices involves unit
processes. FPCs (fundamental process categories) depict the efficiency of pollutant
removal for certain best management practices. FPCs deal with both unit operations (an
actual force removes contaminants) and unit processes (a biological or chemical process
performs contaminant removal). Similar to wastewater treatment technologies, some
BMPs can be considered both a unit operation and a unit process. Certain variables can
determine the effectiveness and practicality of each BMP, and are known as static and
state variables. Static variables deal with design parameters of a given system, which
28
include volumes and dimensions, location, size, slope, state of permeability, amount of
vegetation, and soil type. State variables take into account rainfall volumes and
intensities, detention times, season, vegetation, and maintenance. (Transportation
Research Board, 2006)
2.7.2 A Physical Treatment Processes
Sedimentation. Sedimentation occurs in two phases: settling of storm runoff
during harsh conditions, followed by longer sedimentation times during non-storm
conditions. Sedimentation aims at removing contaminants that include TSS and heavy
metals. Dynamic removal and particle settling are dependent upon factors that include
hydraulic loading rate and particle size. As a general rule, sedimentation is a highly
effective removal option with high pollutant concentrations (anything greater than 400
mg/L) and large particle size (anything greater than 50 ). Sedimentation is the leading
treatment system used in detention/retention ponds, as well as wetlands and biofilters.
(Transportation Research Board, 2006)
Filtration. Filtration is a contaminant removal process in which certain media are
able to remove contaminants from storm water as the water moves through the media
through gravity. Sorption refers to the combined processes of absorption and adsorption.
Absorption occurs when one substance is assimilated into another substance of a different
state. Adsorption occurs when one substance adheres chemically to the outside structure
of another substance. These processes aim to remove contaminants associated with
roadways. The absorption process aims to remove petroleum byproducts, while
29
adsorption focuses on nutrient, metal, and organic removal. The media used in BMPs that
deal with filtration and sorption can have a broad range. Media used can range anywhere
from vegetation and compost to activated carbon and engineered media. The extent of
filtration is determined by particle size and media type. The chemical process involved in
sorption is a little more complex. Chemical removal through sorption involves ion
exchange between water and media, absorption and adsorption. These processes can
remove dissolved contaminants such as metals nutrients and hydrocarbons. The sizing
and media selection must be based on the contaminants one is trying to remove. The
contaminants will control which media is used, and how often the media will need to be
replaced. Filtration and sorption are commonly associated with BMPs such as bioswales,
sand filters and ponds. These filters need to constantly remain in an aerobic state. If the
filter becomes anaerobic, the redox state will change, causing all sorbed metals to be
released. Dissolved contaminants are much more difficult to remove compared to solids,
which tends to lead to higher contaminant removal when solids concentrations are much
higher. (Transportation Research Board, 2006)
Flotation. Flotation tends to act in an opposite way compared to sedimentation.
Flotation takes advantage of differences in densities in contaminants and water. Flotation
is common when dealing with oils and greases, as well as trash, found in storm water.
Water has a specific gravity of 1.0. Anything having a specific gravity less than 1.0 is
less dense than water, causing the contaminant to float to the surface of the water. The
difference in specific weights determines the rise rate for the contaminant, allowing
30
someone to be able to design a proper size and depth for a removal mechanism. Oil-water
separators use this idea to remove contaminants from storm water. (Transportation
Research Board, 2006)
2.7.2 B Biological Treatment Processes
Biological processes use organisms such as plants, algae, and microbe to remove
organic and inorganic pollutants found in storm water. Biological treatment processes can
be broken down into two categories: microbially mediated transformations and uptake
and storage. Microbially mediated transformations involve chemical processes performed
by bacteria and algae in which pollutants are removed from a water source. Uptake and
storage involves processes in which plants are able to remove contaminants from a water
source through nutrient uptake and bioaccumulation. (Transportation Research Board,
2006)
2.7.2 C Chemical Treatment Processes
Chemical processes target the following problems commonly found in storm
water: pH, alkalinity, hardness, redox conditions, organic carbon, and ions. Typically,
treatment options from a chemical standpoint involve sorption, coagulation, or chemical
disinfection.
Sorption. Sorption involves the combined processes of absorption and adsorption.
Absorption involves a process in which a substance in one state is integrated into another
substance. Adsorption occurs when one substance is linked to the surface of another
substance, but is not integrated into the second substance. In storm water treatment,
31
sorption is commonly used, especially in treatment of highway runoff. Absorption is used
to treat hydrocarbons and byproducts of petroleum, and adsorption is used to treat
contaminants such as metals, nutrients, and pesticides. (Transportation Research Board,
2006)
Coagulation. Coagulation aims to form larger particles of contaminants by
destabilizing the particles so that they can grow. Ultimately, the particles will eventually
become large enough so that standard filtration can remove the contaminants. Usually,
this process can occur naturally, but in order to be efficient for storm water treatment, the
process must be sped up with the addition of chemicals. One negative impact of
coagulation is that large amounts of sludge can form, which will need to be removed to
keep treatment running efficiently. (Transportation Research Board, 2006)
Chemical disinfection. Chemical disinfection removes pathogens found in storm
water using chemicals such as chlorine and ozone. At times, chemical disinfection can be
cheaper than natural disinfection. Chemical disinfection has an added benefit, in which
residual from disinfection prevents the re-growth of pathogens and helps to treat water
downstream. (Transportation Research Board, 2006)
Table 2.5 shows how many processes overlap in the various types of contaminant
removal:
32
Table 2.5: Structural BMPs listed by Fundamental Process Category and Unit
Operation
Fundamental Process Category
(FPC) Unit Operation or Process BMPs
Hydrologic Operations
Flow/Volume Attenuation
Extended detention basins
Retention/detention ponds
Wetlands
Tanks/vaults
Equalization basins
Volume Reduction
Infiltration/exfiltration trenches
Permeable pavement
Bioretention cells
Dry swales
Dry well
Extended detention basins
Physical Treatment Options
Particle Size Alteration Comminutors
Mixers
Physical Sorption
Nutrients, metals, petroleum,
compounds
Engineered media, activated carbon,
and sands
Size Separation
Screens/bars/trash racks
Biofilters
Permeable pavement
Infiltration/exfiltration trenches
Manufactured bioretention systems
Engineered media
Hydrodynamic separators
Catch basin filters
Density, Gravity, and Inertial
Separation
Extended detention basins
Retention/detention ponds
Wetlands
Settling basins
Tanks/vaults
Swales with check dams
Oil-water separators
Hydrodynamic separators
Aeration and Volatilization
Sprinklers
Aerators
Mixers
Physical agent disinfection Shallow detention ponds
33
Ultraviolet systems
Biological Processes
Microbiotically Mediated
Transformation
Metals, nutrients and organics
Wetlands
Bioretention systems
Biofilters
Retention ponds
Engineered media
Uptake and Storage
Metals, nutrients and organics
Wetlands/wetland channels
Bioretention systems
Biofilters
Retention ponds
Chemical Processes
Chemical Sorption Processes
Subsurface wetlands
Engineered media
Infiltration/exfiltration trenches
Coagulation/flocculation
Detention/retention ponds
Coagulant/flocculent injection
systems
Ion Exchange Engineered media
Chemical Disinfection Custom devices for mixing chlorine
or aerating with ozone
(Transportation Research Board, 2006)
2.8 BMP Design Type
The final way to categorize a best management practice is based on the design of
the treatment system. The three options for categorization are structural BMPs, which are
constructed at the site of the problem, proprietary, which are pre-engineered solutions,
and non-structural BMPs, which involve source controls to reduce contaminants.
(Transportation Research Board, 2006)
2.8.1 Structural BMPs
Structural BMPs rely on the idea of a treatment train, which involves two or more
processes to effectively remove contaminants from storm water. Selection of structural
BMPs depends on a few factors, including which BMPs can be used, site constraints, and
34
percentage removal of contaminants needed. The most commonly found structural BMPs
include the following:
Wet ponds
Retention ponds
Infiltration trenches
Wetlands
Bioswales and filter strips
Oil-water separators
Sand filters
Proprietary systems may also be part of a treatment train for contaminant removal. These
systems are popular in urban settings, since most processes are compact in design. The
table below shows commonly used BMPs, as well as product names for these devices:
35
Table 2.6: Proprietary BMPs in Current Use
Proprietary BMP Product Name
Wet Vaults
StormCeptor
BaySaver
StormVault
ADS Retention/Detention System
Constructed Wetlands StormTreat
Hydrodynamic/Vortex Separators
Vortechs
Aquafilter
V2B1
Downstream Defender
Continuous Deflective Separation (CDS) Unit
Sorptive Media Filters StormFilter
Flow Splitter StormGate
Modular Pavement Various
(Transportation Research Board, 2006)
2.8.2 Non-structural BMPs
The last of these options include non-structural BMPs, which include source
controls to limit the amount of contamination entering into storm water. These controls
attempt to install educational programs in order to reduce the amount of pollution coming
from human activities. These educational programs help people make more
environmentally-friendly decisions. These best management practices see the highest rate
36
of success when an entire community becomes involved, and is aware of the issues at
hand. Below is a list of non-structural BMPs that can be implemented with little or no
cost to reduce storm water contamination:
Table 2.7:Non-Structural BMPs
Non-Structural BMP Type
Source Control/Maintenance
Street sweeping
Catch basin cleaning
Covering of stockpiles
Safer construction materials, herbicides, and road
salts
Material storage control
Reduce vehicle use
Used oil recycling
Vehicle spill control
Above ground spill control
Illegal dumping control
Vegetation control
Storm drain flushing
Roadway and bridge maintenance
Detention and infiltration device maintenance
Litter control
Litter pickup
Public Education and Participation Newspapers, brochures
37
Land use planning
Adopt-a-Highway
Integrated pest management
Storm drain system signs
Other
Curb elimination
Reduction of runoff velocity
(Transportation Research Board, 2006)
Overall, the selection of the BMP should be based on treatment goals for an
individual site. The following table depicts which BMPs can target which pollutants:
Table 2.8: Groups of Pollutants and Relevant BMPs listed based on FPCs
Pollutant BMPs
Gravity
Settling/Flocculation
Filtration/Sorption Infiltration Biological Chemical Other
Particulates Sediments
Solids
Metals
Organics
Nutrients
Retention Ponds
Detention Ponds
Wetlands
Tanks/Vaults
Biofilters
Media Filters
Compost Filters
Wetlands
Trenches
Basins
Porous
pavement
Swales
Biofilters
Biofilters
Wetlands
Flocculation Wet vaults
Vortex
separators
Modular
wetlands
Solubles Metals
Organics
BOD
Nutrients
Media Filters
Compost filters
Wetlands
Retention ponds
Trenches
Basins
Porous
pavement
Biofilters
Wetlands
Precipitation
Flocculation
Activated
carbon
StormFilter
Trash/Debris Trash
Debris
Screening Vortex
separators
Skimmers
Floatables Oil
Greases
Retention ponds
Wetlands
Hooded catch basins
Catch basin
inserts
Vault filters
Compost filters
Biofilters
Wetlands
Oil/water
separators
Absorptive
media
filters
(Transportation Research Board, 2006)
38
2.9 Criteria for BMP Selection
In order to properly select a best management practice to incorporate into a storm
water management plan, proper storm water goals must be in place, such as flow
reduction percentage and water quality goals. Pollutants of concern (nitrates, phosphates,
coliform, E.coli) must be addressed. If the overall pollutants are addressed, quality of
effluent and percent capture can be designed to meet NPDES standards. The following
process should help any entity plan and install the proper BMP system for a site.
(Transportation Research Board, 2006)
1. Problem Definition
Before any solution can be designed, a quality understanding of the pollutant and
runoff issues (i.e. high flow, high concentrations of pollutants) associated with the site
must be defined. The end result for the storm water plan must also be determined, so that
a proper system can be designed. The problem statement should have all criteria needed
for the project to be specified (i.e. strictly retrofitting and new construction). All
objectives for the project also need to be listed and ranked based on importance to the
project. Also accompanying these objectives should be specific goals the project is
required to meet (reduction of volume by a certain percentage, removal of pollutants).
39
2. Site Characterization
The next step in selecting a best management practice is to characterize the site in
question. It is imperative to know all site conditions and constraints before the design
process even begins. This step can initially eliminate some options that simply are not
feasible for a given site. Hydrologic and soil conditions also help narrow down which
BMPs will work at the given site. Infiltration rates of certain soil types are imperative for
the success of BMPs. High infiltration rates allow BMPs to handle a higher quantity of
flow, thus allowing for more effective treatment of runoff.
3. Identification of Fundamental Process Categories
Once site conditions and constraints, as well as initial water quality, are
documented, certain processes need to be evaluated and ranked based on how well they
can reduce flow and treat contaminants. Soil types and infiltration rates are a key factor in
this step, simply because these factors depict how well a BMP can operate given the site
conditions. As discussed earlier, these FPCs can be divided into hydrologic, physical,
biological, and chemical operations. The selection of the best available process should be
done based on the types of pollutants found, and specific site goals for effluent storm
water quality.
40
4. Selection of BMPs and Other Treatment Options
Once the overall unit processes available to the site are specified, specific best
management practices can be identified and selected. A general understanding behind
how certain BMPs work (i.e. hydrological, chemically, biologically) is key to selecting
the proper solution. The goal should be to select a BMP that addresses all issues on site.
However, if one solution does not address all issues, multiple solutions may need to be
bundled together to create a treatment train. Once feasible solutions are addressed, the
next step is to analyze the solutions to see if one BMP works better given site constraints
than any other potential solution.
5. Practicability of Proposed Treatment Systems
Once certain BMPs are selected as potential solutions for storm water runoff
issues, the practicality of each solution needs to be evaluated. The evaluation process is
based on the following criteria:
Performance for target pollutants
Hydrology and hydraulics
Space availability, both above surface and subsurface
Maintenance
Economics
Aesthetics
41
Other factors go into the practicality of each solution, including downstream impacts,
health effects, climate, and overall budget for the project. This process should once again
narrow down which BMP would be most effective for the problem at hand.
6. Sizing the Conceptual BMP
Once the selection process is complete, a conceptual design for the BMP needs to
be completed. This conceptual design not only needs to meet projects criteria, it also
needs to be designed within the restraints of EPA. Typically, the conceptual design is
based on hydrology, in which the BMP is designed for flow attenuation, volume
reduction, or flow duration. The sizing of the BMP can be done using factors such as
design storms, rainfall frequency analyses, and continuous runoff models.
7. Development of Performance Monitoring and Evaluation
Once design is completed, a long-term evaluation plan must be developed. This
plan should aim to address management, regulatory and research goals. These goals are
based on the success of project objectives, which includes hydraulics and water quality.
This monitoring plan, like the rest of the project is based upon cost and time available.
Overall, it is important to get long-term data to effectively analyze the performance of the
BMP selected and installed. (Transportation Research Board, 2006)
Overall, the selection of the correct best management practice can seem like an
open-ended question. Multiple solutions could potentially work just as well as another
42
solution. As a general guideline, the following criteria should be taken into account,
which is shown in the BMP objective checklist table below:
Table 2.9: BMP Objective Checklist
Category Typical Objectives for Urban Runoff
Hydraulics Manage flow characteristics
Hydrology Eliminate flooding while improving runoff quality
Water Quality
Reduce pollutants loads downstream
Improve downstream temperature impacts
Obtain desired pollutant concentrations
Remove trash and other debris
Toxicity Reduce acute and chronic toxicity of runoff
Regulatory
Comply with NPDES permitting
Comply with local, state, and national water quality
regulations
Implementation Function within management structure
Cost Minimize life-cycle costs
Aesthetics Improve appearance of site while reducing odors
Maintenance Operate within maintenance and repair schedule
Design BMP to allow for future retrofitting
Longevity Allow for long-term functionality
Resources
Improve downstream aquatic life/erosion control
Improve wildlife habitats
Achieve multiple use functionality
Safety, Risk, Liability
Function without significant risk or liability
Minimize environmental risk downstream
Contain any spills
Public Perception Help the public understand the importance of runoff
quality, quantity, and impacts on receiving waters
(Transportation Research Board, 2006)
2.10 Selected BMPs
There are many best management practices available used to treat storm water
runoff issues. Of these BMPs available, much focus has been put on permeable
pavement, bioswales, and rain gardens, due to their ability to effectively reduce volume
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and contaminants simultaneously. These various BMPs also have well documented
performance data, specifically flow reduction ability, contaminant reduction potential, as
well as cost information. Local stakeholders also have interests in these BMPs. Since this
information is needed to carry out a comparison that includes environmental benefits,
these BMPs were the focus of this work.
2.10.1 Permeable Pavement
Storm water quantity has become one of the largest areas of concern as
urbanization has occurred. (Brattebo & Booth, 2002) More and more surfaces are
becoming impermeable, creating larger quantities of runoff, flooding, channel erosion,
destruction of aquatic habitats, and landslides. (Booth & Leavitt, 1999). These surfaces
increase stream loadings, causing channel erosion, bank erosion, and sediment
movement. Impermeable surfaces reduce infiltration, causing a lack of groundwater
recharge, while increasing pollutant concentrations. Due to urbanization, significant
portions of permeable material (grasses, forests) have been destructed. This area had
acted as a large reservoir, capable of infiltrating and storing large amounts of water
runoff. This reservoir was capable of holding water for an extended period of time, but
now that it is gone, water is rapidly moving through urbanized areas causing significant
damage. One solution to this effect of urbanization is to seamlessly find a way to store all
of the excess water that is running off from impermeable surfaces. However,
retention/detention ponds capable of storing that amount of water are quite ineffective.
These ponds would have to be immense, which is virtually impossible in an urban
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environment. The solution to this problem involves permeable pavement. (Booth &
Leavitt, 1999)
Much of these surfaces, however, are used for light/medium traffic (parking lots,
driveways, road shoulders, etc.). These surfaces are design to allow for peak loading
conditions, which occur infrequently. One solution that offers infiltration benefits is
permeable pavement. Permeable pavement is set up in a web-like structure with voids,
filled with material such as sand or soil. These voids allow water to percolate through the
surface and re-enter into the ground water. Permeable pavement can be constructed with
numerous materials, such as asphalt, concrete, or plastics. The image below depicts how
water can infiltrate through the pavement (Brattebo & Booth, 2002):
Figure 2-2: Demonstration of Water Infiltration through Permeable Pavement
(Kujac, 2009)
Various studies have been completed that have tested the usefulness and
effectiveness of permeable pavement to reduce runoff quantity and pollutant
concentrations. In a study performed by the Civil Engineering Department at the
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University of Washington, a study was completed that tested water quality and quantity
performance of 4 different permeable pavement systems. The systems tested include
Grasspave, which is a plastic grid system filled with sand, then planted with grass,
Gravelpave, which is the same as Grasspave, except with gravel instead of sand,
Turfstone, made up of concrete blocks, and UNI Ecostone, made up of smaller concrete
blocks. Three questions were to be answered by this study: Are these surfaces durable
enough to withstand long-term use? Do these systems remain permeable, or do they clog
up over time? Finally, what is the water quality after the water infiltrates the system?
(Brattebo & Booth, 2002)
Overall, all permeable pavement systems tested well in terms of durability,
infiltration capacity, and improved water quality when compared to standard asphalt
systems. Turfstone and UNI Eco-Stone held up as well as an asphalt system during daily
loading. The highest rate of precipitation seen during this test was 7.4 mm/h, in which
each system was able to infiltrate all runoff. The site had positive drainage
characteristics, which increased the amount of water able to infiltrate. Under drains are
recommended to be installed with these pavement systems if soil conditions are less than
favorable to provide positive infiltration. Particulates, such as sand, dirt, and other debris
can clog this system over time, and is recommended to be flushed and swept with a street
cleaning system once per season. (Brattebo & Booth, 2002)
In conclusion to this study, it is apparent that permeable pavement can
significantly reduce the amount of runoff that is channeled into rivers and streams,
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minimizing damages such as erosion and pollutant travels. Permeable pavement also
reduces pollutant concentrations through the process of filtration. Specifically, nutrients
(nitrates and orthophosphates) are removed through adsorption of storm water solids.
Nutrients are often adhered to the outside structure of solids found in storm water runoff.
(Brattebo & Booth, 2002)
Another study testing the same 4 permeable pavement systems, performed by the
Center for Urban Water Resources Management, compared surface runoff from
permeable pavement systems to that of traditional asphalt surfaces. A storm with a
maximum rainfall of intensity of 4mm/hr was tested, in which 0.1% of the total rainfall
was considered runoff, and was mainly attributed to leaks in the gutter collection system
used to test the various pavements. In essence, all water was infiltrated through the
permeable pavement system, eliminating surface runoff, and as a result, damages caused
by rapid storm water runoff. (Booth & Leavitt, 1999)
2.10.2 Rain Gardens
Rain gardens are an effective tool used to reduce or remove pollutants from urban
storm water runoff. These gardens are typically shallow (approximately 2-3 deep), and
are planted with trees, shrubs and other plants, and covered with mulch. These gardens
allow water to infiltrate through the garden material, effectively recharging groundwater
and reducing large flow quantities of storm water runoff. Rain gardens are also effective
in pollutant removal, using processes such as adsorption and decomposition to remove
pollutants. (Dietz & Clausen, 2005) As such, rain gardens function as both a hydraulic
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control and unit process BMP. Rain gardens aim to infiltrate surface runoff diverted to
the system. Once surface runoff enters into a rain garden, runoff quantity, as well as
pollutant concentrations are reduced through plant uptake and storage.
Prince Georges County, MD, was the first area to recommend rain gardens as an
effective storm water treatment option. Prince Georges County published the
Bioretention Design Manual in 1993 to aid in the design and implementation of rain
gardens. However, it is still quite vague as to how to size certain rain gardens, as well as
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