HomeMy WebLinkAboutO - Stormwater Feasibility Analysis (SUFA) - Untitled VOL.
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City Ordinance : Stormwater
Upgrade Feasibility Analysis (SUFA)
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southburlington
VERMONT
South Burlington
Stormwater Utility
CITY CLERKS OFFICE
Received „IA 20 21 at I I:1-15VA
Recorded in Vol._MIALon page____ —
Of So. Burlington Land Records
Attest:
Donna S. Kinville,City Clerk
Vol Unit
STORMWATER UPGRADE FEASIBILITY ANALYSIS 2
Table of Contents
1. Background and Introduction 3
2. Installation of Stormwater Treatment Practices 3
3. Payment of Stormwater Mitigation Fee 4
4. Combination STP/Fee Method 5
5. Penalties/Enforcement 5
6. Severability 6
Appendix A. Method for Infiltration Testing 6
Appendix B. Submission Standards 7
City of South Burlington Ordinance
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STORMWATER UPGRADE FEASIBILITY ANALYSIS 3
The Council of the City of South Burlington hereby ordains:
1. Background and Introduction
The City of South Burlington is subject to multiple stormwater Total Maximum Daily Load (TMDL)
requirements established by the Vermont Agency of Natural Resources (ANR). Compliance with these
TMDLs is required by the City's Municipal Separate Storm Sewer System (MS4) permit, which is also
promulgated by ANR. The MS4 permit requires that the City develop a Flow Restoration Plan (FRP) for
each of the five stormwater impaired watersheds located in the City. In addition, the City's MS4 permit
requires that the City develop a plan to deal with properties covered by expired State of Vermont
Stormwater permits. On top of these requirements, all of South Burlington ultimately drains to Lake
Champlain.ANR and United States Environmental Protection Agency(EPA) have developed a phosphorus
TMDL for Lake Champlain. The MS4 permit contains a requirement that the City develop a Phosphorus
Control Plan (PCP)to reduce phosphorus loading to the Lake from stormwater discharges.
In order to meet the requirements of these State and Federal regulations it is necessary for the City of
South Burlington, and the properties located within its boundaries, to install Stormwater Treatment
Practices(STPs)capable of addressing the uncontrolled stormwater runoff that contributes to these water
quality impairments. The City's "Ordinance Regulating the Use of Public and Private Sanitary Sewerage
and Stormwater Systems" (Ordinance), which shall be incorporated by reference herein, provides the
opportunity for properties with existing or expired State stormwater permits,or properties subject to the
"three-acre site" requirement included in §1.3.D of the ANR General Permit 3-9050 to obtain valid State
stormwater permit coverage under the City's MS4 permit. The ability for the City to provide this permit
coverage was further clarified by the Vermont Department of Environmental Conservation when the MS4
Permit was reissued in 2018.
In order for a property to obtain coverage under the City's MS4 permit, it must provide a level of
stormwater treatment that will facilitate compliance with the State and Federal regulatory requirements
(MS4 permit and TMDLs)to which the City is subject.The goal of this document is to establish a procedure
by which an existing site can be evaluated for best practicable on-site treatment of stormwater runoff.
The standard is intended to be met through installation of on-site STPs.Alternatively, a site may elect to
pay a stormwater mitigation fee in lieu of installing STPs on their site.These funds will be utilized by the
South Burlington Stormwater Utility(SBSU)to construct the STPs necessary for the City to implement the
FRPs required by its MS4 permit. These funds may also be used to gain access to the land necessary for
the construction of large scale or regional STPs.
2. Installation of Stormwater Treatment Practices
(A) The goal of the SUFA is: (1)to reduce the volume of stormwater runoff and associated pollutants
leaving the site via pipe or overland flow, and (2) to ensure that a site complies with any water quality
plan (e.g. FRP, PCP, etc.)developed for the watershed in which it is located.At a minimum,the site must
install STPs capable of infiltrating the volume of stormwater runoff generated on site during the Water
Quality Volume (WQv) rain event as described in the Vermont Stormwater Management Manual, as
amended from time to time by the Agency of Natural Resources, (VSMM),which shall be incorporated by
reference herein. This volume of water must be infiltrated or reused on site using Tier 1 practices as
defined in the VSMM.
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(B) It is understood that some sites may contain constraints that make the site unsuitable for
infiltration of stormwater runoff.A list of acceptable site constraints is included below(Table 1).
Table 1.Constraints on Use of Infiltration Practices
1. Seasonally high or shallow groundwater(as defined in the VSMM).
2. Shallow bedrock(as defined in the VSMM).
3. Soil infiltration rates of less than 0.2 inches per hour(as demonstrated by infiltration testing
conducted in accordance with the procedure in Appendix A).
4. Contaminated soils subject to review and approval of the Stormwater Superintendent.
5. The presence of a "stormwater hotspot" (as defined in the VSMM).
6. Other site constraints subject to the review and approval of the Stormwater Superintendent.
(C) If it is not possible to infiltrate the volume of stormwater runoff generated by the site during WQv
storm event due to one or more of the constraints listed above (Table 1), then this volume of water can
be detained on-site using Tier 2 practices as described in the VSMM.
(D) A site with existing retention/detention based STPs is allowed to evaluate retrofitting/expanding
these facilities in order to meet the detention requirement indicated above. Retrofit/expansion of these
facilities may be considered prior to evaluation of Tier 1 practices. Existing Tier 3 practices shall be
upgraded to Tier 2 practices, if used for water quality treatment.
(E) FRPs and PCPs for impaired watersheds in the City contain a preliminary assessment of the
stormwater treatment potential of some sites. If an FRP or PCP identifies an STP on a site, then the site
must install either the specified STP or an STP that provides equivalent or greater treatment. Properties
that choose to construct STPs must do so prior to the deadline established by the State's Agency of Natural
Resources, within 5 years of signing a Stormwater Improvement Agreement with the City, but no later
than November 1, 2028,whichever is sooner.
(F) All proposed STPs must be submitted to the Stormwater Superintendent for review. Standards
for these submissions are included in Appendix B.
3. Payment of Stormwater Mitigation Fee
(A) In lieu of installation of STPs as described above, the property owner may elect to pay a
stormwater mitigation fee. The mitigation fee for a property can be determined utilizing the following
equation, where IA is the impervious area on the site in acres and WQvT is the percent of the Water
Quality Volume treated on site:
Stormwater Mitigation Fee= IA x(1-WQvT)3 x$70,000
(B) Impervious Area (IA) is calculated by measuring the impervious surfaces located on the property
at the time of application. Applicants shall not include any publicly owned impervious area (e.g. public
roads within a City-owned ROW) in their calculation of IA.
(C) Payment of a stormwater mitigation fee does not prevent or exclude a site from being used for
stormwater treatment. If the site contains a project identified in a FRP as a regional stormwater treatment
facility then the City will require an Irrevocable Offer of Dedication to use the land for stormwater
treatment, if deemed feasible.
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(D) Stormwater mitigation fees must be paid in full upon signing an MS4 Permit Coverage Agreement
with the City. Alternatively,the property owner can elect to pay the fee over a 5-or 10-year term. If a 5-
year term is selected,the total value will be assessed at 3.5% interest over that period. If a 10-year term
is selected, the total value will be assessed at 5.5% interest over that period. Fees paid over a 5- or 10-
year term will be included in the property's stormwater fee for developed properties as established in the
Ordinance.
4. Combination STP/Fee Method
(A) Some sites may install STPs for a portion of the site and pay a stormwater mitigation fee for the
remaining portion of the site.When this method is used,the percent of the Water Quality Volume treated
on site(WQvT)will be factored into the equation.Property owners are encouraged to maximize treatment
on site to the greatest extent possible, as the greater the level of treatment provided on site, the lower
the cost per impervious acre for the portion of the Water Quality Volume not achieved.
5. Penalties/Enforcement
(A) This ordinance shall constitute a civil ordinance within the meaning of 24 V.S.A. Chapter 59. Any
Person who violates a provision of this Ordinance, including but not limited to failure to install a STP prior
to the deadline established by the State's Agency of Natural Resources or to pay the stormwater
mitigation fee when due, shall be subject to a civil penalty of up to $800 per day for each day that such
violation continues. Any law enforcement officer or the Director of Public Works, City Engineer, Deputy
Director of Public Works,or Stormwater Superintendent may act as an Issuing Municipal Official and issue
and pursue before the Judicial Bureau a municipal complaint for any violation of any provision of this
Ordinance.
(B) In addition to the enforcement procedures available before the Judicial Bureau,the City Manager
is authorized to commence a civil action to obtain injunctive and other appropriate relief, or to pursue
any other remedy authorized by law. Nothing herein shall be construed to limit other rights, remedies or
penalties available by law.
(C) An Issuing Municipal Official is authorized to recover civil penalties in the following amounts for
each violation:
First offense $160
Second offense $320
Third offense $480
Fourth offense $640
Fifth and subsequent offenses $800
(D) An Issuing Municipal Official is authorized to recover a waiver fee, in lieu of a civil penalty,
in the following amounts, for any Person who declines to contest a municipal complaint and pays the
waiver fee:
First offense $100
Second offense $250
Third offense $400
Fourth offense $550
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Fifth and subsequent offenses $700
Each day the violation continues shall constitute a separate violation.
6. Severability
If any portion of this Ordinance is held to be invalid by a court of competent jurisdiction,such finding shall
not invalidate any other part of this Ordinance.
Appendix A. Method for Infiltration Testing
(A) The following requirements apply to any required infiltration testing:
(1) Testing must be performed under the supervision of a qualified professional (i.e.,
registered engineer, site designer licensed in the State of Vermont, a qualified soil scientist, a
qualified geologist, a qualified hydrogeologist, or other person approved in advance by the
Stormwater Superintendent).
(2) Infiltration test methods must assess the saturated hydraulic conductivity under "field-
saturated" conditions (see ASTM D5126-90 Standard Guide for Comparison of Field Methods for
Determining Hydraulic Conductivity in the Vadose Zone).
(3) Infiltration test locations shall correspond to the proposed Stormwater Treatment
Practice (STP) locations, and infiltration tests must be conducted at a minimum depth of the
bottom of the proposed STP.
(4) Design infiltration rates shall be determined by using a factor of safety of 2 from the field-
derived value.
(5) Percolation tests are not acceptable in place of testing for saturated hydraulic
conductivity, as they overestimate saturated hydraulic conductivity values. Acceptable tests
include:
i. Guelph permeameter-ASTM D5126-90 Method
ii. Falling head permeameter—ASTM D5126-90 Method
iii. Double ring permeameter or infiltrometer - ASTM D3385-09, D5093-152, D5126-90
Methods
iv. Amoozemeter or Amoozegar permeameter—Amoozegar 1992
(6) The following information must be documented for any infiltration testing:
i. Date and time of testing.
ii. Name and qualifications of the person conducting the testing.
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STORMWATER UPGRADE FEASIBILITY ANALYSIS 7
iii. Location of infiltration testing.
iv. Method utilized during testing.
v. Results of infiltration testing in inches/hour.
(7) A qualified professional may establish seasonal high groundwater depth in test pits based
on redoximorphic features.
(8) Verify depth to bedrock (if within 4 feet of proposed STP bottom) via test pits or solid
auger probes.
Appendix B. Submission Standards
(A) The following information must be included with a submission:
(1) Complete application form.
(2) A brief written narrative describing the proposed Stormwater Treatment Practice (STP)
and how it meets the SUFA standard.This includes a description of how the proposed STP matches
or differs from what is indicated in any approved Flow Restoration Plan (FRP).
(3) A written description of the ongoing maintenance needs for the drainage system and
proposed STP.
(4) A map delineating the drainage area flowing to each STP. This must include any off-site
areas flowing to the STP.
(5) Site plan and construction details for all proposed STPs.The site plan must include:
i. Location,type,and size of all impervious surfaces.
ii. Location,type, size, elevations, and specifications for all proposed STPs.
iii. Stormwater collection and conveyance systems including swales,culverts, and piping.
iv. Length, diameter, and material for all piping and culverts.
v. Topographic survey and natural resource delineations.
vi. Soil type and/or hydrologic soil group.
vii. The location and results of any infiltration testing conducted.
viii.Tree canopy and changes to landscaping.
(6) Modeling results that show the existing and post-development hydrographs for the storm
events indicated below. Any TR-55 based model shall be suitable for this purpose. Modeling
methods utilized shall be in accordance with the best practices utilized by the State of Vermont
Stormwater Management Section and described in the VSMM.
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STORMWATER UPGRADE FEASIBILITY ANALYSIS 8
i. The Water Quality Volume (WQv) storm event as described in the VSMM.
ii. The one year,twenty-four hour rainfall event as described in the VSMM.
iii. The twenty-five year, twenty-four hour rainfall event (currently 4.0 inches) as described
in the most recent version of the City's Land Development Regulations.
(7) Applications submitted under the Combined Method must include a stormwater
mitigation fee calculation. The site plan, listed under item 5 above, must indicate the portion of
Impervious Area (IA) being utilized in the stormwater mitigation fee calculation.
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STORMWATER UPGRADE FEASIBILITY ANALYSIS 9
Adopted at South Burlington, Vermont this 6 day of LIi_(/ , 2021, and to be effective
upon adoption.
SOUTH BURLINGTON CITY COUNCIL
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Helen Riehle,Chair Matt Cota
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Meaghan Emery,Vice Chair Thomas Chittenden
Tim Barritt, Clerk
Received and recorded this ; day of , 2021.
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Donna Kinville, City Clerk
City of South Burlington Ordinance
END OF DOCUMENT