Design of Effective Stormwater Treatment Systems for Water Quality

8/24/2010 Trinkaus Engineering, LLC

The Importance of Assessing The Importance of Assessing Pollutant Loads from Land Pollutant Loads from Land

Development Projects and the Development Projects and the Design of Effective Stormwater Design of Effective Stormwater

Treatment SystemsTreatment Systems

2010 Watershed Management2010 Watershed Management

ASCE/EWRIASCE/EWRI


Steven TrinkausSteven Trinkaus

�� Licensed Professional Engineer (CT)Licensed Professional Engineer (CT)

�� Certified Professional in Erosion and Certified Professional in Erosion and Sediment Control (CPESC)Sediment Control (CPESC)

�� Certified Professional in Storm Water Certified Professional in Storm Water Quality (CPSWQ)Quality (CPSWQ)

�� Over 28 years in the Land Development FieldOver 28 years in the Land Development Field

�� Expertise in the field of Stormwater, Water Expertise in the field of Stormwater, Water Quality Issues & Low Impact DevelopmentQuality Issues & Low Impact Development


Current Local Stormwater FocusCurrent Local Stormwater Focus

�� Peak rate control for large storm eventsPeak rate control for large storm events

�� No consideration of small frequent No consideration of small frequent stormsstorms

�� No evaluation of pollutants found in No evaluation of pollutants found in stormwaterstormwater

�� No evaluation of the effectiveness of No evaluation of the effectiveness of stormwater systems to remove stormwater systems to remove pollutantspollutants


Storm Water RunoffStorm Water Runoff


Storm Water Quality IssuesStorm Water Quality Issues


Water Quality IssuesWater Quality Issues


Water Quality ImpactsWater Quality Impacts

Results of Non-Point Source Pollutants

Connected Impervious Areas

Lawns to edge of water –Increased nutrient loads


How we design todayHow we design today

�� Stone Stone bermberm across level across level bottom of basin does NOT bottom of basin does NOT create a proper create a proper forebayforebay

�� This cell may trap some This cell may trap some coarse sediment but will coarse sediment but will NOT prevent NOT prevent resuspensionresuspension of of sedimentssediments

�� BermsBerms of modified riprap do of modified riprap do not function well at trapping not function well at trapping of fine sediments (void of fine sediments (void spaces are too large)spaces are too large)

�� Flows may “short circuit” Flows may “short circuit” parts of basin due to location parts of basin due to location of inlet & outlet structuresof inlet & outlet structures Forebay will not

trap sediments over long term

No provisions to ensure long flow paths in basin


What we see todayWhat we see today

Inadequate Forebay– No Depressed Sediment Storage -Lack of Maintenance

Outlet set too close to inlet – flows will short circuit –inadequate treatment for water quality

Riprap BermDoes Not create forebay


Why should we Assess Pollutant Why should we Assess Pollutant Loads?Loads?

�� Are permit performance standards being Are permit performance standards being met?met?

�� Will there be short or long term adverse Will there be short or long term adverse impacts to receiving waterways?impacts to receiving waterways?

�� Are the treatment systems designed Are the treatment systems designed correctly?correctly?


How do you Assess Pollutant Loads?How do you Assess Pollutant Loads?

SLAMMSLAMMSource Loading and Management Model Source Loading and Management Model

P8P8PProgram for rogram for PPredicting redicting PPollutant ollutant PParticle article PPassage through assage through PPits, its, PPuddles and uddles and PPondsonds

The Simple MethodThe Simple MethodEstimates pollutant loads for urban areasEstimates pollutant loads for urban areas


The Simple MethodThe Simple Method

�� Equation developed by Tom Equation developed by Tom SchuelerSchueler in in 1987 to estimate pollutant loads on an 1987 to estimate pollutant loads on an annual basisannual basis

�� Requires easily obtainable information Requires easily obtainable information to use:to use:�� Annual PrecipitationAnnual Precipitation�� Pollutant ConcentrationsPollutant Concentrations�� Percent Impervious Cover per land use typePercent Impervious Cover per land use type�� Watershed AreaWatershed Area


The Simple MethodThe Simple Method

L = 0.226(P)(Pj)(Rv)(C)(A) where:L = 0.226(P)(Pj)(Rv)(C)(A) where:�� L = Pollutant Load in PoundsL = Pollutant Load in Pounds

�� P = Rainfall Depth (inches)P = Rainfall Depth (inches)

�� PjPj = Factor that corrects P for storms that produce no = Factor that corrects P for storms that produce no runoff, use runoff, use PjPj = 0.9= 0.9

�� RvRv = Runoff Coefficient, fraction of rainfall that turns to = Runoff Coefficient, fraction of rainfall that turns to runoff, runoff, RvRv = 0.05 + 0.009(I)= 0.05 + 0.009(I)

�� I = Site Impervious Coverage (percent)I = Site Impervious Coverage (percent)

�� C = Flow weighted mean concentration of pollutant (mg/l)C = Flow weighted mean concentration of pollutant (mg/l)

�� A = Area of Site (acres)A = Area of Site (acres)

�� 0.226 = Unit Conversion Factor0.226 = Unit Conversion Factor


Best Source of Pollutant Best Source of Pollutant ConcentrationsConcentrations

National Stormwater Quality Database National Stormwater Quality Database (NSQD), Version 1.1(NSQD), Version 1.1 –– ((MaestreMaestre & Pitt, & Pitt, 2005)2005)

Land Use Category TSS TP TNLand Use Category TSS TP TN

22--8 units/ac8 units/ac 60 0.38 2.160 0.38 2.1

8+ units/ac 60 0.38 2.18+ units/ac 60 0.38 2.1

Commercial 58 0.25 2.6Commercial 58 0.25 2.6

Industrial 80 0.23 2.1Industrial 80 0.23 2.1

Transportation 99 0.25 2.3Transportation 99 0.25 2.3

Forest Deciduous 90 0.1 1.5Forest Deciduous 90 0.1 1.5


Pollutant Concentrations for Metals & Pollutant Concentrations for Metals & Total Petroleum Hydrocarbons (TPH)Total Petroleum Hydrocarbons (TPH)

Land Use CategoryLand Use Category Zn Cu TPHZn Cu TPH

�� Medium Density Res. 0.176 0.047 0.344Medium Density Res. 0.176 0.047 0.344

�� High Density Res.High Density Res. 0.218 0.033 0.3440.218 0.033 0.344

�� Commercial 0.156 0.037 0.324Commercial 0.156 0.037 0.324

�� Transportation 0.156 0.037 0.375Transportation 0.156 0.037 0.375

Sources: Metals (NURP 1983, Horner 1994, Sources: Metals (NURP 1983, Horner 1994, Cave 1994); Cave 1994); TPH’sTPH’s –– UNHSC & NY Stormwater UNHSC & NY Stormwater Manual 2003Manual 2003


How do the Systems Work?How do the Systems Work?

�� LID Systems:LID Systems:�� Filtration thru soil columns, Filtration thru soil columns,

�� Uptake by vegetated biota, Uptake by vegetated biota,

�� Settlement due to slow flow velocities, andSettlement due to slow flow velocities, and�� Infiltration into underlying soils,Infiltration into underlying soils,

�� Biological and chemical reactions within the Biological and chemical reactions within the soil media and plants assimilation.soil media and plants assimilation.


Pollutant Removal EfficienciesPollutant Removal Efficiencies

I.I. Event Mean Concentration (EMC)Event Mean Concentration (EMC)

II.II. Mass EfficiencyMass Efficiency�� EMC gives equal weight to large & small EMC gives equal weight to large & small

storms and averages incoming & outgoing storms and averages incoming & outgoing concentrations for all stormsconcentrations for all storms

�� Mass efficiency is affected by the Mass efficiency is affected by the volume of water in the system & losses volume of water in the system & losses that occur within the practice, such as that occur within the practice, such as evapotranspiration & infiltrationevapotranspiration & infiltration


Pollutant Removal EfficienciesPollutant Removal Efficiencies

2. 2. Mass EfficiencyMass Efficiency�� Mass efficiency is affected by the volume of Mass efficiency is affected by the volume of water in the system & losses that occur within the water in the system & losses that occur within the practice, such as evapotranspiration & infiltrationpractice, such as evapotranspiration & infiltration

�� Method is based upon a summation of incoming & Method is based upon a summation of incoming & outgoing loads and is considered the more accurate outgoing loads and is considered the more accurate methodmethod

�� Not easily applied for a proposed project due to Not easily applied for a proposed project due to lack of monitoring datalack of monitoring data


Caveats of “Removal Efficiencies”Caveats of “Removal Efficiencies”

�� Removal efficiency is closely related to Removal efficiency is closely related to influent quality. I.E. the “dirtier” the influent influent quality. I.E. the “dirtier” the influent water is higher the pollutant removal rate will water is higher the pollutant removal rate will likely be as a percent.likely be as a percent.

�� Removal efficiency rates may encourage Removal efficiency rates may encourage designs which do not address ‘source’ control.designs which do not address ‘source’ control.

�� A system which has a ‘high’ removal efficiency A system which has a ‘high’ removal efficiency rate may still be discharging high pollutant rate may still be discharging high pollutant concentrations in the effluent.concentrations in the effluent.



�� Many Best Management Practices have not Many Best Management Practices have not been monitored long enough to establish valid been monitored long enough to establish valid data to determine a supportable removal rate.data to determine a supportable removal rate.

�� Removal efficiency does not always account Removal efficiency does not always account for how much water is treated. If a system for how much water is treated. If a system is bypassed due to clogging, a stated removal is bypassed due to clogging, a stated removal rate is not likely to be valid.rate is not likely to be valid.



When using ‘median’ removal rates, it is When using ‘median’ removal rates, it is imperative to design the treatment system imperative to design the treatment system fully in accord with the specifications as fully in accord with the specifications as provided for in the State’s Water Quality or provided for in the State’s Water Quality or Storm Water Manual.Storm Water Manual.

I.E. A I.E. A forebayforebay for a Wet Extended Detention for a Wet Extended Detention Pond needs to be 4’ deep and contain 10% of Pond needs to be 4’ deep and contain 10% of the WQV within the the WQV within the forebayforebay. A 1’ deep . A 1’ deep forebayforebay does not work.does not work.


IRREDUCIBLE CONCENTRATIONSIRREDUCIBLE CONCENTRATIONS

�� ““If pollutant concentrations in the influent approach If pollutant concentrations in the influent approach the “Irreducible” concentrations noted below, then it the “Irreducible” concentrations noted below, then it is not possible to change the effluent concentrations is not possible to change the effluent concentrations very much (very much (SchuelerSchueler)”)”

Irreducible Pollutant Concentrations (CWP)Irreducible Pollutant Concentrations (CWP)Water Quality Parameter Irreducible ConcentrationWater Quality Parameter Irreducible ConcentrationTotal Suspended SolidsTotal Suspended Solids 20 to 40 mg/l20 to 40 mg/lTotal PhosphorousTotal Phosphorous 0.15 to 0.2 mg/l0.15 to 0.2 mg/lTotal NitrogenTotal Nitrogen 1.9 mg/l1.9 mg/lNitrateNitrate--NitrogenNitrogen 0.7 mg/l0.7 mg/lTKNTKN 1.2 mg/l1.2 mg/l


Pollutant Removal Efficiency Rates Pollutant Removal Efficiency Rates ––Conventional SystemsConventional Systems


Pollutant Removal Efficiency Rates LID Pollutant Removal Efficiency Rates LID SystemsSystems


Pollutant RemovalPollutant Removal

�� LID systems are most effective when LID systems are most effective when used as part of a “Treatment Train”. used as part of a “Treatment Train”. This is a system when more than one This is a system when more than one system is used in series to treat runoff.system is used in series to treat runoff.

�� As you can observe on the prior tables, As you can observe on the prior tables, by using multiple treatment systems, by using multiple treatment systems, significant pollutant removal rates can significant pollutant removal rates can easily be achieved.easily be achieved.


Pollutant RemovalPollutant Removal

�� After const., the goal is met by the After const., the goal is met by the utilization of LID systems to trap utilization of LID systems to trap sediment as many other pollutants are sediment as many other pollutants are attached to soil particles.attached to soil particles.

�� Proper design and construction is very Proper design and construction is very important, especially for infiltration important, especially for infiltration systemssystems


BioretentionBioretention

-Designed to provide groundwater recharge & water quality

- Infiltrate runoff into underlying soils

- Set ponding depth per soil type to fully drain within 24 hrs.

- Max. drainage area = 5 acres

- Gravel layer with raised underdrain can provide addl. storage in system


““Rain Garden/Bioretention”Rain Garden/Bioretention”Rain Garden at Sibley Residence - Newtown, CT

Designed & Constructed by Homeowner


Residential Rain Garden (dry)Residential Rain Garden (dry)


Residential Rain Garden (wet)Residential Rain Garden (wet)


Infiltration SystemsInfiltration Systems

-3’ separation from bottom of system to SHGW

- Native soils must have < 20% & 20-40% silt/clay

- Native soils must have in-situ infiltration rate of 0.5”/hr

- 25% of WQv to be provided by pretreatment

- Must be installed “off-line)

- Install on slopes < 15%

- Basin to fully infiltrate WQvthrough bottom of basin only


Infiltration BasinInfiltration BasinMulvaney Subdivision – Ridgefield, CT

Very sandy soils – has never discharged via overflow pipe


Extended Detention Shallow Extended Detention Shallow WetlandsWetlands

- Min. drainage area = 10 ac.

- Maximize flow paths by use of high & low marsh area, islands

- Required forebay with 10% WQv

- Surface area of system = 1.5% of drainage area

- 65% of area shall have a depth < 18”

- 35% of area shall have a depth < 6”

- Deep water areas (>4’) shall contain 25% of WQv

- Min. L:W ratio = 3:1


““Subsurface Horizontal Flow Subsurface Horizontal Flow Gravel Wetlands”Gravel Wetlands”

Deep Forebay & Two Treatment Cells

UNHSC


Subsurface Gravel WetlandsSubsurface Gravel Wetlands

�� Required Design ElementsRequired Design Elements�� ForebayForebay –– 10% 10% WQvWQv, 4, 4--6’ depth6’ depth

�� Two treatment cells, each holding 45% of Two treatment cells, each holding 45% of WQvWQv

�� Minimum length of treatment cell Minimum length of treatment cell –– 15’ 15’ (longer is better)(longer is better)

�� Water quality outlet pipe to maintain Water quality outlet pipe to maintain saturated condition just below soil surfacesaturated condition just below soil surface



�� Required Design ElementsRequired Design Elements�� Surface layer Surface layer –– 8” wetland soil8” wetland soil

�� Filter layer Filter layer –– 3” pea gravel3” pea gravel

�� Treatment layer Treatment layer –– 24” of 1” clean crushed 24” of 1” clean crushed stone (washed, no fines)stone (washed, no fines)

�� Appropriate wetland plants to be used to Appropriate wetland plants to be used to survive inundation depth to provide survive inundation depth to provide WQvWQv. . (larger cells, less depth of (larger cells, less depth of pondingponding better)better)


Pond / Wetland SystemPond / Wetland System

Min. drainage area = 25 ac.

Forebay required – 10% WQv

Create long flow paths within system by using high & low marsh areas

Surface area of system must be a min. of 1.5% of drainage area

Outlet pool must contain 10% WQv

35% of surface area must be shallow marsh (<6”)

50% of surface area must be less than 18” in depth


Wet SwalesWet Swales

Max. slope = 4%

Max. drainage area = 5 ac.

Linear applications are best

Pretreatment is required and must contain 10% WQv


Wet SwaleWet Swale

�� Swale side slopes shall be 3:1, Bottom width Swale side slopes shall be 3:1, Bottom width shall be min. of 8’, with a maximum shall be min. of 8’, with a maximum pondedpondeddepth of 12”depth of 12”

�� NonNon--erosive velocities must be provided for 1erosive velocities must be provided for 1--yr, 24 hr storm eventyr, 24 hr storm event

�� Swale shall handle flow rate from 10Swale shall handle flow rate from 10--yr, 24yr, 24--hr storm event on contributing drainage areahr storm event on contributing drainage area


Water Quality SwalesWater Quality SwalesDry Bioswales – High

Point – Seattle, WA

Wet Swale – G&F

Rentals – Oxford, CT


Grass Filter StripGrass Filter StripLedgebrook Lane – Southbury, CT


Filter StripsFilter Strips

Maximum slope = 6%

Stone trench or raised concrete lip – very important to achieve overland flow

Generally –berms are not needed or desired as concentration flow can develop


Sediment Sediment ForebaysForebays

Forebay needs to have 3:1, L to W ratio to promote residence time and settlement

Forebay must hold as a fixed volume – 10% WQv

Ideal depth is 4-6’ to promote settlement and sediment storage

WQv


Wet Extended Detention PondWet Extended Detention Pond

Most important features:

- Forebay

- 6-8’ permanent pool

- Aquatic shelf around pond

- Appropriate plants for hydrologic conditions

Pond system must be designed in accord with state manual to be effective

8/24/2010 Trinkaus Engineering, LLCCopyright Trinkaus Engineering, LLC

How not to apply LIDHow not to apply LID

Failed Bioretention: No sizing calculations, out of date soil mixture, too few plants, soil compaction



Failed Bioretention: water can enter from one side only, 2’ of soil mix on top of compacted structural fill with no underdrain, overflow grate set flush to bottom of facility, no sizing calculations



Failed Bioretention: Overflow grate set flush to bottom of facility, no storage volume, no plants


Commercial SiteCommercial Site

�� GoodhouseGoodhouse Flooring Flooring –– Newtown, CTNewtown, CT

�� 1+ acre 1+ acre –– Open Meadow in Industrial ParkOpen Meadow in Industrial Park

�� Soils consist of Hinckley, excessively well drained Soils consist of Hinckley, excessively well drained sand (Class A)sand (Class A)

�� Slight slope (average 3%)Slight slope (average 3%)


Existing ConditionsExisting Conditions

Slight slope –south to north

Hinckley Soils

Ex. Conventional drainage


Commercial SiteCommercial Site

�� Revised Building Program (LID)Revised Building Program (LID)

�� Building: 8,000+ with parking/loading for commercial Building: 8,000+ with parking/loading for commercial flooring companyflooring company

�� Stormwater: Grade paved surface direct all runoff to one of Stormwater: Grade paved surface direct all runoff to one of eight eight bioretentionbioretention facilitiesfacilities

�� Stormwater storage: Bioretention will fully infiltrate all Stormwater storage: Bioretention will fully infiltrate all storm events up to 100storm events up to 100--yr (7.2yr (7.2””/24hr)/24hr)

�� Stormwater treatment: 85%+ removal of TSS, TPH & Stormwater treatment: 85%+ removal of TSS, TPH & metals, roughly 50% removal of TPmetals, roughly 50% removal of TP


Proposed ConditionsProposed Conditions8 Bioretention systems will treat & infiltrate WQv f or entire site

Site is graded to direct runoff to one of the bioretentionsystems

NO STRUCTURAL DRAINAGE

Approx. cost saving vs. conventional drainage & galleries = $ 95,000


THE ENDTHE END

Design of Effective Stormwater Treatment Systems for Water Quality

Technology

Transcript of Design of Effective Stormwater Treatment Systems for Water Quality