Shirley E. Clark, Ph.D., P.E., D. WRE
Robert Pitt, Ph.D., P.E., D. WRE, BCEE
Example Site: Pollutants on Permit
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Oil and grease
Chloride
Sulfate
Ammonia
NO2 + NO3
Total Copper
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Total Zinc
Total Mercury
Total Lead
Total Thallium
Dioxin (TCDD)
Perchlorate
Challenge: Determine which pollutants are likely to
exceed permit limits.
• Probability plots used to estimate probability of
exceedance of site runoff concentration.
Site Stormwater Characteristics and
Permit Limits
90th percentile
historical conc.
3
Permit Limit
15
Exp. Exceedence (% >
limit if untreated)
5
Chloride (mg/L)
30
150
0.1
Sulfate (mg/L)
100
250
<<0.01
Ammonia (mg/L as N)
NA
10.1
SMALL
NO2+NO3 (mg/L as N)
8
8
10
Total Zinc (µg/L)
140
159
10
Total Copper (µg/L)
15
14
10
Total Mercury (µg/L)
0.15
0.13
15
Total Lead (µg/L)
25
5.2
40
Total Thallium (µg/L)
ND
2
UNK
5x10-6
2.8x10-8
40
1.5
6
0.1
Analytes on Permit
Oil and grease (mg/L)
TCDD (µg/L)
Perchlorate (µg/L)
Pollutants Used to Guide Media Selection
 Potential for Exceedence in 40% of Storms
 Dioxin (TCDD)
 Total Lead
 Potential for Exceedence in 15% of Storms
 Total Mercury
 Potential for Exceedence in 10% of Storms
 Total Copper
 Total Zinc
 NO2+NO3
 Potential for Exceedence in 5% of Storms
 Oil and Grease
Lead by Particle Size and Source Area
Pollutant Size Associations
Reference:
Morquecho 2005
Suspended Solids
Turbidity
Total-P
Nitrate
Cadmium
Copper
Lead
Zinc
Percent Pollutant Reductions after Removing all Particulates Greater
than Size Shown
20 µm
5 µm
1 µm
0.45 µm
76
81
98
100
43
68
0
20
26
41
64
55
82
0
22
34
62
70
92
89
12
22
34
76
70
96
92
17
22
37
82
72
• Lead typically heavily associated with
particulate fraction.
• But need to plan to reduce 25 µg/L
(90th percentile) to < 5 µg/L (slightly
below permit limit).
• Minimum 75% removal (assuming
concentration reduction is linear).
• Requires treatment to between 1 – 5 µm
(sedimentation efficient to 5 – 20 µm).
Anticipated Physical Filtration
Performance (assume sediment forebay)
Need (bio)chemically-active media to remove some pollutants
Design Information for Organics Removal
Pollutant
Kow (preference for
organic matter)
Ks (water solubility)
Dioxin (TCDD)
106.8
0.1 mg/L for
monochloro
isomers; 10-9 for
octochloroisomers
Perchlorate
10-5.8
2 x 10-5
Dimethyl Mercury
~2 x 102
1,000 mg/L
Oil & Grease
Not quantifiable but
many are PAHs;
therefore, expected
to be high
Not quantifiable but
many are PAHs;
therefore, expected
to be high
Analytes on Permit Treatment Technology Options
NO2+NO3
Total Zinc and Total
Copper
Total Lead
TCDD
Total Mercury
Oil and grease
Ion-exchange or plant uptake (potential
denitrification? Other problems with denitrification)
Chemically-active filtration (organic media
sorption/ion-exchange) after pre-settling
Physical filtration of larger particulate-associated lead
after pre-settling. Chemically-active filtration (organic
media sorption and potential ion-exchange)
Chemically-active filtration with strong organic
sorption (GAC) after pre-settling. Other organics
potential elevated parent material contamination.
Chemically-active filtration with sorption for MeHg &
ion-exchange for inorganic mercury and complexes.
Chemically-active filtration with strong organic
sorption component (GAC) after capture of freefloating material if concentrations are high and visible.
Peat and compost also possible.
Lead Treatability from Industrial Source Area
Selecting the Media Mixture from a Set of Potential
Components: “Dissolved” Copper Example
•
•
•
•
Model prediction: 25% +2 valence, 10% +1 valence, 65% 0 valence charge.
Sand with modification: prefers ion exchange (+2 charge)
Zeolite (SMZ) ion exchange resin (+2 charge)
GAC and peat moss have multiple types of exchange/adsorption sites – good for all
valence charges; GAC performing better for filtered copper but EXPENSIVE
Selecting the Media Mixture from a Set of Potential
Components: “Dissolved” Copper Example
• Modified sand and zeolite mixture – best removal 50%, but generally poor removal.
• GAC and peat moss were better than sand and zeolite; GAC performing better for
filtered copper, but may not support plant life
• Adding small amount of peat moss as organic matter for plant life support only
slightly reduced performance.
Dioxin Control Observations
Kow = 106.8
Ks = ranges from 0.1 mg/L for monochloro
isomers to 10-9 mg/L for octochloro isomers.
2.8 X 10-8 µg/L permit
limit
These samples
less than the
detection limit
Treatment Train Concept: Devices in Series
• Final Effluent Quality Controlled by Effluent of Device B.
• Device A generally has no impact on final water quality,
unless substantial reductions in pollutant concentration
needed to prevent damage to Device B (sediment forebay,
for example)
Combining Treatment: Devices in Parallel
• Final Effluent Quality Controlled by Weighted Average of
Performance of Two Devices (weighted by flow rates through
each device).
• Suggested applications would be providing treatment to some
portion of flow to reduce concentrations without providing
treatment to entire flow stream.
Other Design Considerations
 Clogging
 Kinetics of pollutant removal
 Media Capacity
 Nutrient Releases from Organic Component of Media
due to Changes in Porewater Chemistry
 Nutrient and Water Uptake by Biomass
 Maintenance Intervals
Conclusions and Questions
 Conclusion: Treatment can be tailored to address specific
pollutant problems.
 Conclusion: Removal function of influent water quality,
pollutant associations with particle size, and, for filtration,
media chemistry
 Knowledge rich and data poor on water quality chemistry and
speciation.
 For infiltration/filtration, media specs beginning to address
fundamental media characteristics.
 Limited understanding of bacterial effect on pollutant removal.
 Question: Improve/develop models for predicting media
effectiveness and lifespan of treatment devices? (define
breakthrough/maintenance criteria to permit limit or slightly
below)
 Question: How to improve media specs to reduce variability
in treated water concentrations?
 Question: And many more…….