urban toxic contaminants: removal by urban stormwater...
TRANSCRIPT
Urban Toxic Contaminants: Removal by Urban Stormwater BMPs
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Speaker Info
Tom Schueler, Executive Director
Cecilia Lane, Stormwater Coordinator
Today’s Agenda
1. Introduction
2. Definition of Urban Toxic Contaminants
3. The Dirty Dozen UTCs in Urban Watersheds
4. Effectiveness of Urban BMPs in Removing Them
5. Risk that UTCs Accumulate in BMP Sediments
6. Watershed Strategies for Reducing Toxics
7. Recommended Approach for Toxic TMDLs
8. Discussion and Resources
Why Worry About Toxics?
The N and P we deal with most often are not particularly cuddly, scary or photogenic
Toxins exert a real impact on both human health and harm aquatic life, fish and wildlife
The public is justifiably concerned about the presence of toxins in the environment
Most of the TMDLs in the country are for toxins
Rationale for industrial stormwater permits
Implications for long term maintenance for stormwater practices
Toxics and TMDLs in the US
Rank Pollutant # of TMDLs in US
1 Mercury 21,545
2 Pathogens 13,016
3 Metals (excluding Hg) 9,828
4 Nutrients 6,034
5 Sediment 3,922
11 Pesticides 1,233
13 PCBs 698
17 PAH and Toxic Organics 158Source: EPA OWOW Website, Accessed July 2015
Project Background
One year research synthesis project that evaluated 35 group of toxins generated by the ag, urban wastewater sectors
Goal: Investigate toxic reduction benefits associated with Bay BMP implementation for the TMDL, and give managers better data for local TMDLs to control toxic pollutants in the watershed
Scope: More than 400 papers reviewed
2. Criteria to Define Urban Toxic Contaminants
1. The toxin is primarily associated with urban land use, compared to other sectors in the watershed.
2. The toxin is either generated within the urban sector or is deposited from the atmosphere onto impervious surfaces and subsequently washed off.
3. Urban stormwater runoff is the predominant pathway for transporting it thru the watershed.
4. The toxin has "sediment-like characteristics" and can be removed by settling or filtering practices.
5. The toxin is generated or produced in an upland landscape position in the watershed where it can be effectively treated by an urban BMP that captures surface runoff.
6. Physical evidence exists that the toxin is captured and/or retained within an urban stormwater BMP.
3. The Dirty Dozen UTCs
PCBs
PAH
TPH
Mercury
UTM (Cd, Cu, Pb, Zn)
OTM (As, Cr, Fe, Ni)
Pyrethroid Pesticides
Legacy OC Pesticides
Legacy OP Pesticides
Plasticizers (Phthalates)
Flame Retardants (PBDE)
Dioxins
Urban Toxic Contaminants
Toxin Category
1. urban land use?
2. urban sources ?
3. stormwaterpathway ?
4. Sediment characteristics
5. Upland Position ?
6. Urban BMPRetention?
PCBs Y Y Y Y Y y
PAH Y Y Y Y Y Y
TPH Y Y Y Y y Y
Mercury Y Y Y Y Y y
UTM Y Y Y Y Y Y
OTM Y Y Y Y y y
UTM: Urban Trace Metals (Cd, Cu. Pb and Zn)OTM: Other Trace Metals (As, Cr, Fe and Ni)
Y = Yes, based on strong evidencey = Yes, supported by limited monitoring dataND = no data available to assess
Urban Toxic Contaminants (continued)
Toxin Category
1. urban land use?
2. urban sources ?
3. stormwater pathway ?
4. Sediment characteristics
5. Upland Position ?
6. Urban BMPRetention?
PP Y Y Y Y y y
OCP Y Y Y Y y y
OPP Y Y Y Y y ND
Plasticizer Y Y y Y y y
PBDE y Y y Y y y
Dioxins Y Y y Y ND ND
PP: Pyrethroid Pesticides, OCP: Organochlorinepesticides, OPP organophosphate pesticides.PBDE: Polybrominated diphenyl ethers
Y = Yes, based on strong evidencey = Yes, supported by limited monitoring dataND = no data available to assess
Polychlorinated Biphenyls (PCBs)
•Still detected in fish and wildlife tissues four decades after they were banned (although levels are gradually declining)
•PCBs moving through urban watershed as contaminated sediments are mobilized, deposited and re-suspended
•Older commercial and industrial watersheds are primary focus
Polychlorinated Biphenyls (PCBs)
Useful data on sources, generating sectors, and pathways
More limited data to establish levels in runoff and/or sediment and BMP removal rates
Most data collected outside of Chesapeake Bay
Meets UTC criteria and behaves like sediment
Should be removed along with sediment in urban BMPs
Polycyclic Aromatic Hydrocarbons (PAH)
Highest contributor to overall toxicity in urban creeks
Unique urban sources: coal tar sealants and vehicle emissions
First flush pollutant, behaves like sediment
BMP studies show high removal rates (80 to 90%)
Strong concern about PAH accumulation in pond sediments and possible toxicity
Total Petroleum Hydrocarbons (TPH)
Term for the oil, grease, gasoline and other hydrocarbons found in urban runoff (i.e., the oil sheen)
No numerical standards for TPH
TPH meets all 6 UTC criteria
Limited monitoring shows very high removal rates in most stormwater BMPs.
Microbes in bioretention media are especially effective in rapidly breaking down TPH
Mercury (Hg)
Hg is a global pollutant and is deposited from the atmosphere across all Bay land uses (including open water)
Hg accumulates in fish, birds of prey, and fish-eating mammals and humans
Hg is leading cause of water quality impairment in the Bay watershed and across the nation
Urban areas are a key source when Hg is deposited and washed off impervious surfaces or contaminated soils are eroded
Acts like a UTC. Limited monitoring data show high Hg removal by
stormwater BMPs
Hg Biomagnification
Mercury Methylation
Methylation is the process whereby Hg rapidly accumulates in fish tissue and becomes magnified up the food chain
The process is enhanced in anoxic and organic rich sediments of natural wetlands, estuarine sediments
Hg is the least treatable UTC due to methylation and air deposition over open waters
Limited data show that constructed wetlands also enhance methylation
Hg bioacccumulation in eagles and osprey is trending down in the Chesapeake Bay
Urban Trace Metals (UTMs)
Cd, Cu, Pb and Zn are detected in nearly 100% of urban stormwater samples, and soluble levels of these metals exceed aquatic life standards
Abundant research on EMC and BMP removal for all four metals
Unique urban sources: roofing materials, brake pads, tire wear, vehicle emissions and air deposition
Despite solubility, monitoring data generally show high to very high UTM removal by BMPs (especially bioretention).
Comparison of Urban Trace Metals
Factor Cadmium Copper Lead Zinc
Runoff EMC (ug/l) 1 16 17 115
Solubility (%) 45% 60% 10% 50%
Acute Toxicity (%) 50% 50% 18% 45%
Sediment Level (ug/g)
0.2 to 0.5 40-150 20-200 200-500
Removal Rates (%)
40 to 70% 40 to 60 50 to 90 55 to 75
Sediment Risk Low Mod. Low Mod.
Other Trace Metals (OTM)
Include Arsenic, Chromium, Iron and Nickel
For these metals, the potential risks are for drinking water contamination
Violations of water quality standards are quite rare, but operators must closely monitor them during storms
The source of OTMs are corrosion of urban landscape surfaces often by acid rain
Most urban BMPs appears to have a moderate to very high removal rate
Comparison of Other Trace Metals
Factor Arsenic Chromium Iron Nickel
Runoff EMC (ug/l)
3 7 700 3 - 8
Solubility (%) 48 35 15 45
Sediment Level (ug/g)
4 42 ND 37
Removal Rates (%)
15 to 30 35 to 65 50 to 80 40 to 60
Sediment Risk ? Moderate Moderate Moderate
Sources of Other Trace Metals in the Urban Landscape
Metal Urban SourcesArsenic Wood preservatives, pesticide formulations,
paints, dyes, semi-conductors and incinerator fly ash
Chromium Stainless steel, chrome-plating, paint and some wood preservatives
Iron Rust and corrosion of pipes, metal roofs and other iron surfaces
Nickel Automotive batteries, household and industrial appliances, fabricated metals, fuel and lubricating oil
Source: Gilbreath et al (2012) and other sources
Comparative Ability of Stormwater BMPs to Remove Selected Trace Metals
StormwaterBMP
Other Trace MetalsArsenic Chromium Iron Nickel
Bioretention -- H L LWet Pond M H H HWetland -- -- HSand Filter L M H MPermeable Pavers -- L -- HInfiltration -- H -- --Grass Channel M M L HGrass Filter L M L MDry Pond L M -- L
VH: Very High Removal (76% to 100%)H: High Removal (50% to 75%)
M: Moderate Removal (26% to 50%)L: Low Removal (0% to 25%)
Sources: Leisenring (2014) and Winer (2000)
Trends in Insecticides
The insecticides applied to crops and urban areas have changed over time, and are now less persistent in the environment and do not bioaccumulate in tissues.
However, they are still mobile in the environment and are deadly to aquatic invertebrates at the part per trillion level
Evolution in Insecticides Over Time
Era Insecticide Types Notes1940to1970
Organochlorines (OC)
DDT Banned in the 1970sDDD/DDE DDT degradation productsDieldrin Banned in 1985
1960to2000
Organophosphate (OP)
Chlordane Banned in 1978Chlorpyrifos Restricted in 2002Diazinon RestrictedDichlorvos Increased use after 2002
2000 topresent
Pyrethroids Bifenthrin Replacements for OCP and OPP
Permethrin Less toxic than bifenthrin2005topresent
Fipronil Fipronil Most aquatic life toxicity in recent surveys
Neonictinoids Imdiacloprid Emerging concerns about aquatic toxicity
Pyrethroid Pesticides
Pyrethroid pesticides include bifenthrin, permethrinand others
New class of insecticides introduced in the last decade
Non-persistent in the environment and unlikely to bio-accumulate in vertebrates
Extremely lethal to aquatic invertebrates in urban streams, even at part per trillion level
Routinely detected in urban creek sediments
Pyrethroid Pesticides
Meet criteria to qualify as an UTC, although some data gaps remain
Strong affinity for sediment and organic matter
BMP removal rates should be comparable to suspended sediment
More research needed on persistence and toxicity in BMP sediments.
Legacy Organochlorine Pesticides
Organochlorine (OC) pesticides include DDT, DDE and dieldrin that were banned decades ago but still persist in the environment. Classified as a UTC, but were also used on crops and for mosquito control.
Soils contaminated by OC pesticides more mobile in urban watersheds. Likely present in older pond sediments
Sharply declining trends in OC pesticide levels in urban runoff and creek sediments -- reduced bioaccumulation in fish, eagles and marine mammals.
Continued tracking of OC pesticides may be warranted for another decade or two.
Legacy Organophosphate Pesticides
Organophosphate (OP) pesticides include chlorpyrifos, diazinon and dichlorovos and were introduced 15 to 20 years ago to replace OC pesticides.
Relatively non-persistent but still very highly toxic to aquatic life in urban streams, most were banned by the turn of the century
Found in urban watersheds, are highly mobile, are carried by urban stormwater runoff and generally behave like a sediment particle.
No data on BMP removal or persistence in BMP sediment
Sharp declines in stormwater runoff and urban creek sediments since they were banned
Less persistent pesticides can be eliminated from the environment due to short watershed lag times.
Emerging Toxins of Concern
Flame retardants (PBDE)
Plasticizers (pthalates)
Dioxins
Very limited monitoring data available -- most of which was collected in Europe or west coast
Municipal wastewater and biosolids may also be very significant sources of these emerging toxins of concerns
Plasticizers (pthalates)
Plasticizers are emitted from flexible PVC products, coatings and sealants
Pthalates suspected of being endocrine disruptors but no human health standards yet issued
Widely detected in urban rain, surface water, stormwater runoff and urban sediments at low levels
Also detected in wastewater
Only one study looked at pthalate removal in BMPs and indicated high removal rates
Flame Retardants (PBDE)
PBDE used in many house hold and electronic items
Compounds are very persistent, lipophilic and hydrophobic
Bio-accumulate in tissues of fish and marine mammals….emerging concern for osprey in urban watersheds of the Chesapeake Bay
Detected in urban stormwater in San Francisco Bay at 50 ng/l level
Limited European monitoring (3 Studies) suggests BMPs are effective in removing PBDE
Dioxins
Legacy industrial discharges, but also detected in urban watersheds at ng/l levels
Environmental risks of dioxins are poorly understood
Unintended consequence of fuel combustion and incineration (even fireworks)
Primary sources are air deposition onto impervious surfaces and erosion of older contaminated soils
No monitoring data to establish BMP removal rates or persistence in BP sediments.
UTCs and Watershed Lag Times
Environmental benefits of reducing toxins may not be fully realized for several decades
Long lag time between when they are first deposited on watershed surfaces or soils and cycle through the stream network to ultimately reach the Chesapeake Bay.
Researchers suggest long lag times for the following UTCs:
PCBs
PAH
Mercury
UTMs
DDT and Chlordane
Questions and Answers
4. Capability of Stormwater BMPs to Remove UTCs
Urban BMPs are Very Effective at Removing UTCs
Most UTCs have sediment-like properties, so they are effectively trapped by most urban BMPs before they get to local waterways and the Bay.
UTC Treatability
Review of Sediment Removal Rates
Summary of Trace Metal Removal Rates
Suspended sediment and UTCs
Share many characteristics
UTCs bind, adsorb or otherwise attach to sediment particles
UTCs are hydrophobic, have very limited solubility and often have a strong affinity for organic matter.
Both are also relatively inert, persistent, and not very bio-degradable.
Both are often associated with fine and medium-grained particles that are easily entrained in stormwater runoff.
Both are subject to high removal rates simply through gravitational settling in the water column and/or filtering through sand, soils, media or vegetation.
BMP Treatability for Urban Toxic Contaminants
ToxinCategory
BMP RemovalRate?
Measured or Estimated?
Behaves likeSediment?
BMPRetention?
SedimentToxicity Concern?
PCBs TSS E Y Y Mod
PAH > TSS E Y Y High
TPH > TSS M Y Y Low
Mercury > TSS E Y Y Mod
UTM < TSS M Y Y Mod
OTM < TSS M Y Y Mod
BMP Treatability for Urban Toxic Contaminantscontinued
ToxinCategory
BMP Removal
Rate?
Measured or Estimated?
Behaves likeSediment?
BMPRetention?
Sediment
Toxicity Concern?
PP TSS E Y y High
OCP > TSS E Y y Low
OPP < TSS E Y ? Low
Plasticizers < TSS E Y Y ?
PBDE < TSS E Y Y ?
Dioxins < TSS E Y ? ?
Comparative Ability of Stormwater BMPs to Remove Urban Trace Metals
Stormwater BMP Urban Trace MetalsCadmium Copper Lead Zinc
Bioretention H VH VH VHWet Pond M H H HWetland M H M MSand Filter H M VH HPermeable Pavement L M VH VHDry Swale L H -- VHGrass Channel M L L MGrass Filter L M L MDry Pond L L M MVH: Very High Removal (76% to 100%) H: High Removal (50% to 75%)M: Moderate Removal (26% to 50%) L: Low Removal (0% to 25%)
Summary of Trace Metal Removal by Bioretention
Trace Metal
Research Studies (N)
Removal Rate (%)
Cadmium 2 66-90
Copper 10 43-98
Lead 12 75-98
Zinc 11 62-99
Source: LeFevre et al (2014)
Comparative Removal by ST and RR Practices
LID practices are effective in filtering UTCs where they are trapped in the media and tightly bound to particles. Microbes in the aerobic media are effective at biodegrading many UTCs . While there is some tisk of of media breakout , frequent media removal should minimize this risk
Ponds are effective environments to settle out UTCs. They tend to accumulate in bottom sediments. Anoxic conditions make it hard to degrade the compounds, so they can persist and even accumulate over time
Classification of BMPsRunoff Reduction
Practices (RR)
Stormwater Treatment
Practices (ST)
Bioretention Constructed Wetlands
Dry Swale Sand Filters
Infiltration Wet Swale
Permeable PavementWet Ponds
Green Roof
5. Risk of UTC Accumulation in BMP Sediments
UTC Accumulation In BMP Sediments
Persistent UTCs accumulate in BMP sediments over many decades at levels that trigger sediment toxicity guidelines.
As many as 8 UTCs pose a risk for sediment toxicity: PCB, PAH, Hg, Ni, Cr, Cu, Cd, and Zn
Most research on older stormwater pond sediments
PAH and Pond Sediments
Percent of MD Stormwater Ponds withPotential PAH Sediment Toxicity
Individual PAH TEC PECNapthalene 3% 0%Flourene 12% 1%Phenanthrene 46% 12%Anthracene 15% 1%Flouranthene 34% 13%Pyrene 34% 15%Benzo[a]anthracene 24% 7%Chrysene 34% 10%Benzo[a]pyrene 38% 7%Dibenz[a,h]anthracene 44% NASource: Gallagher et al, 2010
Managing the BMP Sediment Toxicity Risk
Are BMP sediments an acceptable place to trap toxics in the urban landscape ?
Where is the next place that sediments should go when they are cleaned out from BMPs ?
Is UTC sediment accumulation only a concern for older stormwater ponds in highly urban/industrial watersheds ?
What is the real risk to aquatic life and human health in the stormwater pond environment versus the LID environment ?
Not a Bad Place, After All ?
Toxicity risk to aquatic life in the stormwater pond environment may be limited:
Simplified food webs and low species diversity reduce bio-accumulation in urban fish and wildlife tissues.
Not much of a benthic community in pond sediments
Ponds appear to be effective at retaining UTCs over time
UTC levels are also high in other non-BMP sediments (e.g., urban creeks, rivers and estuaries).
Extremely limited fish consumption from ponds and recreational contact with sediments is non-existent
New LID practices (e.g., bioretention) do not create aquatic habitat and removal of surface sediments is frequent
Implications for BMP Maintenance
6. Watershed Strategies for Toxic Reductions
1. Stormwater Treatment and Retrofits
2. Targeted Street and Storm Drain Cleaning
3. Industrial and Municipal Pollution Prevention
4. Bans and Product Substitution
Industrial and Municipal Pollution Prevention
Potential Reduction By Pollution Prevention Practices
No data on impact of pollution prevention practices in reducing toxins required under industrial and municipal stormwater permits.
The potential effect of these practices could be considerable, given that:
2,700 industrial sites have stormwater permits in Bay watershed (25,000+ acres of impervious cover)
1,000 MS4 facilities and public works yards are subject to the same regulations.
Bans and Product Substitutions
Past bans and/or product substitution have worked
Lead
PCB
DDT and Diazinon
New bans and product substitution
coal tar sealant for PAH
brake pads and rotors for UTMs
more sustainable roofing materials for UTMs
Improved recycling and disposal (batteries, thermostats, fluorescent light bulbs, etc).
Targeted Street Cleaning in Older Watersheds with a lot of Legacy industrial land use
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Pollutant Reductions Associated with Different Street Cleaning Practices
Practice #
Description 1 ApproxPasses/Yr 2
TSS Removal(%)
TN Removal(%)
TP Removal(%)
SCP-1 AST- 2 PW ~100 21 4 10
SCP-2 AST- 1 PW ~50 16 3 8
SCP-3 AST- 1 P2W ~25 11 2 5
SCP-4 AST- 1 P4W ~10 6 1 3
SCP-5 AST- 1 P8W ~6 4 0.7 2
SCP-6 AST- 1 P12W ~4 2 0 1
SCP-7 AST- S1 or S2 ~15 7 1 4
SCP-8 AST- S3 or S4 ~20 10 2 5
SCP-9 MBT- 2PW ~100 0.7 0 0
SCP-10 MBT- 1 PW ~50 0.5 0 0
SCP-11 MBT- 1 P4W ~10 0.1 0 0
AST: Advanced Sweeping Technology MBT: Mechanical Broom Technol0gy1 See Table 15 for the codes used to define street cleaning frequency2
Street Dirt is Highly Contaminated
Trace Metal Content of Street Sweeper Waste (mg/kg)
Study STATE Copper Lead Zinc
Sorenson, 2012 MA 72 62 146
Sorenson, 2012 MA 47 111 169
SPU, 2009 WA 49 103 189
CSD, 2011 (1) CA 92 23 136
CSD, 2011 (2) CA 157 204 210
Walch, 2006 DE 64 81 208
MEAN 80 97 176
Urban Soils (Pouyat et al, 2007)
35 89 91
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Source: Expert Panel Report
Other Street Dirt Toxins
ToxicContaminant
Sediment Concentration
Petroleum Hydrocarbons
Diesel range: 200 to 400 mg/kgMotor Oil: 2,200 to 5,500 mg/kg
PCB's 0.2 to 0.4 mg/kgPAH Total: 2,798 ug/kg
Carcinogenic 314 ug/kgPthalates 1,000 to 5,000 ug/kgPesticides Pyrethroids presentChloride 980 mg/kgMercury 0.13 mg/kgBased on 3 West Coast Studies of street dirt and/or sweeper waste contamination. Source: Expert Panel Report
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7. Recommended Approach for TMDLs
Step-wise Approach
1. Decide Whether to Split Urban Land Uses
2. Estimate Loading Rates w/ Simple Method
3. Use TSS Removal Rates as a Benchmark
4. Estimate TSS Removal Rates for Current and Future BMPs
Adjustor Curves
CBP Removal Rates
Estimating Existing BMP Coverage in the Watershed
5. Assess Impact of Other Toxin Reduction Strategies (e.g., Pollution Prevention and Street Cleaning).
1. Split Urban Land Uses ?
Highest UTC levels are generated in older urban watersheds, especially those with extensive industrial, commercial or high ADT transport land uses.
Some UTCs can estimated using impervious cover (IC)
Consider non-urban toxic sources (ag and wastewater)
2. Compute Urban Toxic Loads
Limited monitoring data for most UTCs
Some unit area loading rates have been done
Event Mean Concentrations (EMCs) can also be developed or estimated, to use in the Simple Method
More sophisticated models not recommended unless supported by monitoring data
Check the Appendices of CSN UTC report for data summaries
3. Use TSS Removal as a Benchmark
Linking UTCs to a benchmark TSS removal rate
Allows users to project UTC removal rates based on known TSS removal rates
Can calculate reductions based on much larger CBP database on sediment removal by urban BMPs
More precise removal estimates using expert panel adjustor curves
TSS Removal Rates for Urban BMPs
Urban Stormwater Practices Removal Stormwater Retrofits 2 45 to 85%New Runoff Reduction (RR) Practices 3 45 to 80%New Stormwater Treatment (ST) Practices 4 40 to 75%Wet Ponds 60Constructed Wetlands 60Dry Extended Detention Ponds 60Infiltration 95Filtering Practices (Sand Filters) 80Bioretention C & D w/UD 55
A & B w/ UD 80A & B w/o UD 90
Permeable Pavement C & D w/UD 55A & B w/ UD 70A & B w/o UD 85
Grass Channels C & D w/o UD 50A & B w/o UD 70
Bioswale aka dry swale 80Street Cleaning 6 0 to 30
Urban BMP Coverage in Bay Watershed
Urban BMPs now cover 30% of urban land in the watershed – most of any region in the nation
BMP coverage could increase to 40 or 50% by 2025 due to TMDL compliance in the urban sector
UTC removal by nearly all urban BMPs is moderate to very high
Questions and Answers
Resources
CSN Report on Urban Toxic Contaminants
Archived Webcasts on Industrial Stormwater
Industrial Stormwater Benchmarking Tool
Upcoming Webcast on Street Cleaning Expert Panel Report – coming soon
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