Low Impact Development and the CT General Stormwater Permit Preparing for the NEXT BIG STORM SNEC of SWCS Willimantic, CT Copyright Trinkaus Engineering,

Low Impact Development Low Impact Development and the CT General and the CT General Stormwater PermitStormwater Permit

Preparing for the NEXT Preparing for the NEXT BIG STORMBIG STORM

SNEC of SWCSSNEC of SWCS

Willimantic, CTWillimantic, CT

Copyright Trinkaus Engineering, LLC

StevenSteven Trinkaus Trinkaus Invited presenter on LID in Taiwan, South

Korea and China, Consultant to Pusan National University,

Korean Water and Land & Housing Institute in South Korea for LID projects

Licensed Professional Engineer (CT) CPESC and CPSWQ certifications Over 31 years in the Land Development

Field with 14 years applying LID

What is Low Impact What is Low Impact Development?Development?

LID is an ecologically friendly approach LID is an ecologically friendly approach to site development and storm water to site development and storm water management that aims to mitigate management that aims to mitigate development impacts to land, water, development impacts to land, water, and air. The approach emphasizes and air. The approach emphasizes the integration of site design and the integration of site design and planning techniques that conserve planning techniques that conserve natural systems and hydrologic natural systems and hydrologic functions on a site.functions on a site.

LID is Not “NO IMPACT”LID is Not “NO IMPACT”

All development will have some impact All development will have some impact on our environment. The on our environment. The implementation of LID design implementation of LID design concepts and treatment systems can concepts and treatment systems can minimize the environmental impacts minimize the environmental impacts associated with development and will associated with development and will lead to development approaches lead to development approaches which are sustainable in the future.which are sustainable in the future.

The Old WaySource: University of Arkansas Community Design Center

The New WaySource: University of Arkansas Community Design Center

The General Stormwater The General Stormwater PermitPermit

Certification that development plans Certification that development plans are in compliance with following are in compliance with following Guidance Documents:Guidance Documents:

2002 Erosion Guidelines,2002 Erosion Guidelines,

2004 Storm Water Quality Manual2004 Storm Water Quality Manual

The General Stormwater The General Stormwater PermitPermit

Permit is not meant to be or implied Permit is not meant to be or implied to be a design document,to be a design document,

It is simply a requirement to ensure It is simply a requirement to ensure that development plans meet that development plans meet minimum erosion control and minimum erosion control and stormwater management standards stormwater management standards (one size fits all approach)(one size fits all approach)

Applicability of General Stormwater Permit

Development projects with site disturbance greater than 5 acre with local permitting,

Requires preparation of Stormwater Pollution Control Plan (SWPCP), Not correct terminology: we do not want

to control pollution, we want to PREVENT pollution (Stormwater Pollution Prevention Plan) [SWPPP – Industry Standard)

2002 Erosion & Sediment Control Guidelines

Guidance document to be referenced in local land use regulations to require preparation of plans conforming to this document,

Municipal agencies need to ensure erosion control plans are in compliance with the standards and specifications found in this document

2004 Storm Water Quality Manual

Purpose is to provide guidance and is intended to augment, rather than replace professional judgement in the design of stormwater management systems, focusing on addressing water quality,

LID & General Permit

Neither 2002 Guidelines, 2004 Manual or Appendices of 2011 contain design processes and methodologies for LID,

The Appendices discuss in general terms land use approaches for LID, but they are not requirements,

The requirements to consider LID conflict with many local land use regulations (home rule issue?)


Very few municipalities refer to 2004 Storm Water Quality Manual in their regulations,

Result is that applicants do not provide information on water quality, groundwater recharge & channel protection flow as part of their project


Several Technical definitions are not correct: Effective Impervious Area

Not defined by Rational method runoff coefficient

Runoff Reduction Practices Must be defined by a storm size and soil

conditions, not a one size fits all approach

Section 5 (b) of Permit

Estimate of average runoff coefficient has nothing to do with GP,

Calculations supporting the design of sediment and floatable removal controls (no equation for this requirement)

Section 5 (b) (v) of Permit

(v) Runoff Reduction: “quantified as total annual post-

development runoff volume reduced through canopy interception, soil amendments, evaporation, rainfall harvesting, engineering infiltration, extended infiltration or evapo-transpiration” Very few hydrologic models can determine and evaluate the losses associated with these items

Section 5 (b) (v) of Permit

(v) Runoff Reduction and LID Appears to be a requirement to provide

runoff reduction (but this is not a standard found in the 2004 manual),

This is in conflict with Appendix B of GP,

(v)(d) Does not define how infiltration tests are to be done, yet states you must use 50% of the field-measured infiltration rate

Section 5 (b) of Permit (h) Calculation illustrating retention of

WQV or 50% WQV (2004 manual does not mention 50% standard),

(i) The size of the storm for runoff reduction is not defined,

(C) stormwater measures designed & implemented in accord with 2004 Manual & DOT qualified list

Section 5 (b)(C) of Permit

Due to age of 2004 Manual (12+ yrs), design standard for Bioretention is not valid, No specification for soil media, No sizing criteria, Stated 3’separation to SHGW prevents

use except in deep well drained soils, If manual does not provide design

specifications, people will use the web (google it), not a good solution

Section 5 (b)(C) of Permit (a) requirement to retain 50% of WQV

for redevelopment projects is a “one size fits all approach” which is not feasible on many sites,

The GP is telling designers how to design their project (not intent of permit),

What is “Maximum Extent Achievable” Not defined in GP


(b) Only applicable to site with less than 40% effective impervious cover, Is arbitrary standard, One blanket standard with minimal

flexibility, (ii)(a) Requires Runoff Reduction & LID

to meet volume reduction requirements, yet Manual does not have volume reduction requirement


(ii)(b) Goal is 80% removal of TSS, How do you assess the annual load for

post-development conditions? How to you evaluate the effectiveness of

your treatment system(s) to meet or exceed this goal?

Only focusing on TSS does not mean there will not be adverse impacts on water quality

Issues with LID in PermitIssues with LID in PermitAppendix BAppendix B

Encouragement to use LID measures Encouragement to use LID measures to reduce impacts of development to reduce impacts of development and address stormwater quality and address stormwater quality issues,issues,

Encouragement of LID rarely results Encouragement of LID rarely results in the successful implementation of in the successful implementation of LIDLID

The result when LID is The result when LID is encouragedencouraged

1. Bioretention are infiltration systems – do the soils next to a wetland infiltrate?

2. Bottom of system is 6” above observed seasonal high groundwater level

3. Bottom of system is 2’ below ex. grade in wetlands

4. Treating parking lot runoff – require 3’ vertical separation to groundwater – not provided


1. Ponding more than 3 days AFTER a rainfall event

2. Very few plants

3. Site was not fully stabilized prior to installation of facility

4. No sizing computations S. Trinkaus Photo


1. Used outdated detail for construction,

2. Inappropriate soil media (too much topsoil)

3. Use of filter fabric (causes clogging, reduced or no infiltration

Detail used for system on prior slide

Bioretention moving to Bioretention moving to WetlandWetland

Bioretention moving to Bioretention moving to WetlandWetland


The result when LID is encouragedThe result when LID is encouraged

Rainfall Event on 9/2/12



1 week later – 9/9/12

Potential Problems:

-Poor Natural Soils

-Design Calculation in Error

-Incorrect Soil Mixture


1. Overflow grate set flush to soil surface, NO STORAGE VOLUME

2. Notch on left side has no function, parking pitches away from facility

3. 24” of soil media on top of Structural fill with no underdrains (Where would the water go if it could infiltrate?)

Target/Lowes – Southington, CT S. Trinkaus Photo


Target/Lowes – Southington, CT, S.Trinkaus photo

Design of bioretention systems were an ‘after thought’ in the design process – system is located on ‘graded ridge line in parking area’ – what water will enter system

Pitch


Ponding because system has no underdrain & soil media was placed on top of compacted structural fill


1. At low point is flush catch basin grate directly connected to hydrodynamic separator

2. No available storage for runoff

3. Balance of island is raised, not depressed, good plants are only positive

1. Runoff can only enter near low end of sloping facility

2. Runoff must make 90 degree turn into facility

3. Minimal storage around overflow grate

Staples – Branford, CT

CT DEP Photo

Evergreen Walk – Windsor, CT CT DEP Photo


Evergreen Walk – Windsor, CT S. Trinkaus Photo

Runoff will not make a 90 degree turn when flowing along a curb line

Runoff cannot enter facility with accumulated sediment blocking the way


Evergreen Walk – Windsor, CT S. Trinkaus Photo

Water will ALWAYS take the path of least resistance!!!

Photo: M. Rickel Pelletier

Since water is already ponding on the soil surface, this would not be a good location for a rain garden. It appears that plants were just added to this area with no use of an appropriate bioretention media that would encourage infiltration.

Classical Magnet School – Classical Magnet School – HartfordHartford

Photo: CT DEP

More ponded water at far end, does not bode well for future infiltration of runoff

Classical Magnet School – Classical Magnet School – HartfordHartford


Incorrect terminology (LID is not Incorrect terminology (LID is not intended to maintain pre-intended to maintain pre-development hydrology (what size development hydrology (what size storm, not stated), storm, not stated),

A goal of LID is to mimic pre-A goal of LID is to mimic pre-development hydrology for small development hydrology for small frequent rainfall events)frequent rainfall events)


Refers to 2004 Manual and Appendix to provide guidance on implementing LID,

Neither document is a LID design manual,

States roof runoff is clean and can be infiltrated via dry wells, roof runoff is not clean (40% of nitrogen & phosphorous loads come from atmospheric deposition)


Direct discharge to groundwater of stormwater without pre-treatment is considered a Class V Injection Well which requires permit from EPA,

States that infiltration could be considered in historically industrialized areas. (In the LID community, infiltration is prohibited for this type of land use)

LID in Areas with High LID in Areas with High Seasonal Water Table or Seasonal Water Table or

Hardpan LayerHardpan Layer Language in this section implies a Language in this section implies a

“one size fits all approach” to dealing “one size fits all approach” to dealing with the soil condition,with the soil condition,

LID is a performance based approach LID is a performance based approach to stormwater management and can to stormwater management and can be applied on all types of soils, but be applied on all types of soils, but the design of the system must be the design of the system must be adjusted to reflect soil limitationsadjusted to reflect soil limitations


Hardpan LayerHardpan Layer A longer travel time through the soil A longer travel time through the soil

does not equate to improved water does not equate to improved water quality treatment (quality treatment (this is a valid this is a valid statement for on-site sewage disposal statement for on-site sewage disposal systems, but not for stormwater systems, but not for stormwater management systemsmanagement systems),),

More than infiltration tests are More than infiltration tests are necessary for the design of LID necessary for the design of LID systemssystems


Hardpan LayerHardpan Layer ““bioretention systems should be bioretention systems should be

planted with water tolerant/wetland planted with water tolerant/wetland plants” if located in areas with a high plants” if located in areas with a high seasonal groundwater table”, seasonal groundwater table”, if you if you do this, the bioretention system will do this, the bioretention system will fail as the language in the permit is fail as the language in the permit is telling you that water will pond for telling you that water will pond for extended periods of time and thus extended periods of time and thus only wetland plants will be able to only wetland plants will be able to grow here.grow here.

ConclusionConclusion

The incorporation of LID information The incorporation of LID information and requirements in the CT GP are and requirements in the CT GP are not appropriate,not appropriate,

They will not lead to the proper They will not lead to the proper implementation of LID,implementation of LID,

Can place applicants in a Catch 22 Can place applicants in a Catch 22 between local stormwater between local stormwater requirements and the GPrequirements and the GP

ConclusionConclusion

The Construction General Permit is The Construction General Permit is not the correct format to have LID not the correct format to have LID strategies implemented in CT,strategies implemented in CT,

LID is more than stormwater LID is more than stormwater management and by focusing in on management and by focusing in on stormwater alone, does not lead to stormwater alone, does not lead to the creation of sustainable projectsthe creation of sustainable projects

Contact InformationContact Information

Steve Trinkaus, PE, CPESC, CPSWQSteve Trinkaus, PE, CPESC, CPSWQTrinkaus Engineering, LLCTrinkaus Engineering, LLC114 Hunters Ridge Road114 Hunters Ridge RoadSouthbury, CT 06488Southbury, CT 06488203-264-4558 (phone & fax)203-264-4558 (phone & fax)Email: Email: [email protected]: Website:

http://www.trinkausengineering.com

THE END – Questions?THE END – Questions?
