Post on 07-Aug-2020
3/7/2019
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Managing Difficult Pollutants:PAHs, PCBs, and Other Trace Organics
NEBC Managing Stormwater in Washington 2019
Myles Gray
Introduction
• What makes pollutants challenging to manage?
• How to approach treatment of difficult pollutants
• Trace Organics: PAHs, PCBs, Dioxins, and Others
• Treatability and Treatment Case Studies
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What Makes Pollutants Difficult to Manage?Pollutants Limited
Treatment History
Challenging Removal Processes
Variable pollutant speciation
Extremely frequent O&M
Comments
Extremely high metals X X May require multiple treatment
mechanisms
Extremely high solids (TSS) X X Frequently requires active treatment
and frequent O&M
Organic TSS / BOD X X X Frequently requires active treatment
Trace Organics: PAHs, PCBs, Others X X X Trace organics frequently associated
with very fine particles
E. Coli X X Compliance often requires very high removal rates (e.g. >99.9%)
Dissolved nutrients X Especially nitrate
Data Availability and EffectivenessInternational BMP Database for Media Filters
1:1 line; removal vs. export
TSS:
Lots of data, good removal
E. coli:Nitrate:
Lots of data, poor removal Limited data, good removal; but not consistently below limits
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Speciation and Fractioning
Particulate‐bound: >0.45 micron
Coarse Settleable Solids
Finer Filterable Solids
Dissolved:
<0.45 micron
Colloidal (particles smaller than 0.45
micron)
Complexed (e.g., CuDOM)
True dissolved (e.g. ionic copper)
Cu2+
Often hardest to treat
Attached to sand, silt, organics
Management for Difficult Pollutants
Process-Based Approach:
• What types of treatment may be effective?
• Does available data support full-scale implementation?
• Is infiltration feasible?
• Would treatability and/or pilot testing reduce risk of poor performance?
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Infiltration: Pollutant Mass Reduction
Can you do it?• Does soil support infiltration?
– > 1” per hour rate usually suitable
– Soil maps, soil infiltration testing
Should you do it?• Are there other constraints?
– Geotechnical: slopes, liquefiable soils, etc.
– Groundwater quality and soil contamination
– Groundwater protection zones
– Utilities or structures
– High groundwater table
Treatability / Pilot Testing to Assess Effectiveness
Goal is to make sure treatment will work!Treatability / Pilot Testing Guidelines:• Use actual site stormwater• Include ageing periods or sample
over longer period• Collect minimum of three paired
influent/effluent samples per alternative
• Monitor flows to confirm proper function and assess clogging
• Document O&M, especially for filtration which can clog
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PAHs (Polycyclic Aromatic
Hydrocarbons)
PCBs (Polychlorinated Bi‐
Phenyls)Dioxin
Chemical Form
Solubility and fractioning
Very low solubility, typically associated with particulates
SourcesTar, asphalt, incomplete
combustion Many historic uses: caulking, paint, lubricants, transformers
By‐product of chemical production, trash burning
Regulatory Drivers
Not included in ISGP, but included in Superfund cleanup goals and some TMDLs
Treatability Data
Limited; some studies show good removal. May need to select treatment for fine particles and provide multiple treatment mechanisms to target different speciations.
Trace Organics: PAHs, PCBs, and Dioxin
Case Study: PAH Fractioning & TreatabilityProject Objective: Assess fractioning of PAHs in stormwater to inform treatment selection
Composite Sample ContainerLaboratory Filtered Samples
20 um 5.0 um 0.45 um
Whole Water Samples
TSS As PAH
Event Sample Bottles
Flow Weighted Composite Sampling Progressive Filtration and PAH Analysis
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Case Study: PAH Fractioning & TreatabilityBasin #2Basin #1
0
2
4
6
8
10
12
14
16
A C D E
Total PAHs (µg/L)
Basin M‐Control Basin M‐Control‐20 micron
Basin M‐Control‐5 micron Basin M‐Control‐.45 micron
Control
< 5 micron
< 20 micron
< 0.45 micron
0
0.5
1
1.5
2
2.5
A C D E
Total PAHs (µg/L)
Basin L‐Control Basin L‐Control‐20 micron
Basin L‐Control‐5 micron Basin L‐Control‐0.45 micron
Four Discrete Storm Events Four Discrete Storm Events
Control
< 5 micron
< 20 micron
< 0.45 micron
Likely requires removal of very fine particulates to meet targets• Further treatability testing to select treatment
Likely requires only limited filtration to meet targets
Water quality targets
LegendSampling PointLevel SensorGate ValveFlow DirectionUntreated PipingPrefiltered PipingTreated Piping
Proprietary Devices
Bypass Return (above ground) Treated Return
(above ground)
BSM Test Columns(indoor)
Bypass Returns Outlet Control Structures
Inlet Distribution Header
StormwateRx Aquip
½ HP Submersible Pump
High Flow Return
Contech StormFilters:Upper = Perlite media = PretreatmentLower = GAC media blend
Existing Basin M StormFilter Vault Forebay
Treatability Testing:
• Compared effectiveness of five passive treatment alternatives
• Conducted testing on site, using site stormwater
• Collected four long-duration multi-storm composite samples
• Monitored system flow rates and head loss changes over time to inform O&M
Case Study: PAH Treatability
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UntreatedPretreatedFully Treated
Case Study: PAH Treatability
Water Quality Targets = 0.018 µg/L
Engineered media was effective, but effluent still above targets
Consider treatment and infiltration to limit mass loading to receiving waters
Case Study: PAH Treatability
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Case Study: Regional PCB RemovalProject Objective: Assess a range of treatment options for broad application across Bay Area
Hydrodynamic separator
Tree Wells (Filterra)
Bioretention and Green Streets
StormFilter
Case Study: PCB Removal Results
Hydrodynam
ic
separator
Tree
Well #1
Tree
Well #2
Green
Streets #1
Storm
Filter
Bioretention #1
Bioretention #2
Bioretention #3
Influent
Effluent
Data are for single sites, so transferability to other sites may be limited
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Good Performance Marginal Performance Poor Performance
Tree WellsBioretention*
StormFiter Green StreetsHydrodynamic Separator
* Biochar addition may improve performance
Influent
Effluent
Side-by-side Bioretention Cells
With biocharWithout biochar
Case Study: PCB Removal Results
Trace Organics Summary
• Effective treatment exists, but can be expensive– Physical filtration for particulate-bound– Sorption for dissolved and more soluble compounds
• Treatment effectiveness data is limited– Few sites treat for these compounds– Cost of sample analysis inhibits investigations– Litigation
• Particle fractioning and speciation are dependent on pollutant and site characteristics
• Treatability testing and/or pilot testing are highly recommended
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Questions?
Myles GrayMgray@Geosyntec.com