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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