HomeMy WebLinkAboutSP-23-027 - Supplemental - 0550 Dorset Street (5)STP Selection Matrix Project Name:
Version 5/8/2017 Discharge Point:
Step 1: Is the Water Quality Treatment Standard entirely managed with one or more of the following Tier 1 practices?
Infiltration Basins/ Trenches/ Chambers Simple Disconnection
Drywells Disconnection to Filter Strips and Vegetated Buffers
Bioretention (designed to infiltrate) Dry Swales (designed to infiltrate)
Filters (designed to infiltrate)Permeable Pavement1
Reforestation1
1 1. These practices do not require specific justification due to feasibility limitations
Step 2: Assess the feasibility of using Tier 1 Practices
Infiltration Basin/ Trench/ ChamberDrywellBioretention (infiltrating)Simple DisconnectionDisconnection to Filter Strips or Vegetated BufferDry Swales (infiltrating)Filters (infiltrating)Practice Availability for Water Quality Treatment?Yes Yes Yes Yes Yes Yes Yes
Response
Available Available Available n/a n/a Available Available
Available Available Available Available Available Available Available
Available Available Available Available Available Available Available
n/a n/a n/a Available Available n/a n/a
n/a n/a n/a Available n/a n/a n/a
n/a n/a n/a n/a Available n/a n/a
Available n/a Available n/a n/a Available Available
Available Available Available n/a n/a Available Available
Available Available n/a n/a n/a n/a n/a
Available n/a n/a n/a n/a n/a n/a
Tier 1 Practices are available to meet the Water
Quality Treatment Standard. If using one of these
practices, stop here. If additional site constraints
exist other than those listed here, proceed to Step 3.
South Burlington High School Basketball Court
S/N01
Complete the matrix below in its entirety for each drainage area.
Stop. No further
justification
needed.
Seasonal high water table or bedrock would be less
than 3 feet from the bottom of the practice.
Is the slope of the filter strip greater than 15%
Is the slope of the vegetated buffer greater than
8%
Are natural slopes where an infiltration trench or
basin could be sited greater than 15%
Bottom of practice would be below seasonal high
water table
Seasonal high water table or bedrock would be less
than 1 foot from the bottom of the practice.
Practice Availability Based on RestrictionsFeasibility Restriction
Do underlying soils have an infiltration rate of less
than 0.2 inches per hour, as confirmed by field
geotechnical tests or are classified as Hydrologic
Soil Group D according to the NRCS Soil survey?
Will runoff to the practice include discharge from a
hotspot landuse or activity?
Is the site a brownfield or contaminated site where
infiltration is restricted or where infiltration would
increase the threat of pollution migration, as
confirmed in writing by the Department’s Waste
Management and Prevention Division?
Is the slope of the vegetated buffer greater than
15%
Yes No
Yes No
Yes No
Yes No
Yes No
Yes
Yes No
No
Yes No
No
Yes No
Yes No
Yes
STP Selection Matrix - SN1 Page 1 of 2
Available Available Available n/a n/a Available Available
Available Available Available n/a n/a Available Available
Available Available Available n/a n/a Available Available
Available Available Available n/a n/a Available Available
Available Available Available n/a n/a Available Available
Available Available Available Available Available Available Available
Step 3: Other feasibility constraints for remaining Tier 1 and Tier 2 practices
2
Provide written feasibilty justification below or list attachments
Will the practice be located within 200 feet of non-
transient non-community groundwater source?
Will the practice be located within 75 feet down-
gradient of a wastewater disposal area system,
within 35 feet up-gradient or 75 feet down-
gradient of a wastewater disposal system?
Will the practice be located within 150 feet of a
drinking water source located in an unconfined
aquifer?
Will the practice be located within 100 feet of a
drinking water source located in bedrock or a
confined unconsolidated aquifer?
Will the practice be located within Zone 1 or Zone
2 of a public community groundwater source
protection area?
Provide written site specific justification below.
Tier 3 Practices may be used to meet the Water
Quality Treatment Standard.
If the the use of a Tier 1 or Tier 2 Practice is infeasible for reasons beyond those listed in Step 2 of the STP Selection Matrix, a designer may
submit site specific detailed feasibility justification that such practices are not feasible following the guidance in Section 2.2.4.1 of the 2017
VSMM. Only after completion of the STP Selection Matrix and determination that Tier and Tier 2 Practices are infeasible shall a designer
consider Tier 3 Practices or existing stormwater infrastructure for meeting the Water Quality Treatment Standard (WQTS) on the project
site.
Is the Water Quality Treatment Standard
entirely managed with Tier 2 Practices?
If, following completion of Step 2 of the STP Selection Tool there are no Tier 1 Practices available for use on the project site, designers shall
consider the use of Tier 2 practices for treatment of the Water Quality Treatment Standard.
Will the practice violate any restrictions of the
Vermont Wastewater and Potable Water Supply
Rules, or their replacement?
Yes
Yes
Yes No
Yes No
Yes No
Yes
Yes
No
No
No
No
STP Selection Matrix - SN1 Page 2 of 2
Vermont Operational Stormwater Permit - Standards Compliance Workbook
The name above will appear on all the discharge point tabs
Site Summary
Total SN1 SN2 SN3 SN4 SN5 SN6 SN7 SN8 SN9
New 0.12 0.12 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Redeveloped 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Existing 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Previously
Authorized 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Total 0.12 0.12 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Site Area 0.20 0.20 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
44.45347 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000
-73.17436 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000
Receiving Water
Wetland
Tributary
to Potash
Brook
0 0 0 0 0 0 0 0
Recharge
Total SN1 SN2 SN3 SN4 SN5 SN6 SN7 SN8 SN9
Required 0.0060 0.0060 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
Provided 0.0098 0.0098 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
Standard met?Yes Yes n/a n/a n/a n/a n/a n/a n/a n/a
Notes:
Water Quality
Total SN1 SN2 SN3 SN4 SN5 SN6 SN7 SN8 SN9
Required 0.0098 0.0098 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
Provided 0.0098 0.0098 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
Standard met?Yes Yes n/a n/a n/a n/a n/a n/a n/a n/a
Notes:
A minimum WQ V of 0.2" (P*R V ) is required for sites with low impervious (<16.67%). This calculation has not been incorporated
into this workbook. Designers should check that the minimum WQ V has been met for their site.ImperviousProject Name
Do not fill this tab out, apart from the project name and notes. It will auto-populated based on the values on the discharge point
tabs. Discharge points (SN) will only show on the summary if an area has been entered on that tab. Areas listed below are those
seeking permit coverage.
South Burlington High School Basketball Court
Latitude
Longitude
Last Updated 8/28/2018 Summary: Page 1 of 3
Vermont Operational Stormwater Permit - Standards Compliance Workbook
Channel Protection
Total SN1 SN2 SN3 SN4 SN5 SN6 SN7 SN8 SN9
Standard Applies?Yes Yes Yes Yes Yes Yes Yes Yes Yes
Waiver n/a n/a n/a n/a n/a n/a n/a n/a n/a
Method Extended
Detention
Hydrologic
Condition
Method
Hydrologic
Condition
Method
Hydrologic
Condition
Method
Hydrologic
Condition
Method
Hydrologic
Condition
Method
Hydrologic
Condition
Method
Hydrologic
Condition
Method
Hydrologic
Condition
Method
HCV 0.0166 0.0166 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
TV Provided 0.0098 0.0098 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
Notes:
Overbank Flood Protection
SN1 SN2 SN3 SN4 SN5 SN6 SN7 SN8 SN9
Standard Applies?Yes Yes Yes Yes Yes Yes Yes Yes Yes
Pre-Dev Q (cfs)0 0 0 0 0 0 0 0 0
Routed, Post-Dev Q (cfs)0 0 0 0 0 0 0 0 0
Waiver n/a n/a n/a n/a n/a n/a n/a n/a n/a
Notes:
Extreme Flood Protection
SN1 SN2 SN3 SN4 SN5 SN6 SN7 SN8 SN9
Standard Applies?Yes Yes Yes Yes Yes Yes Yes Yes Yes
Pre-Dev Q (cfs)0 0 0 0 0 0 0 0 0
Routed, Post-Dev Q (cfs)0.1 0 0 0 0 0 0 0 0
Waiver n/a n/a n/a n/a n/a n/a n/a n/a n/a
Notes: Modeling the pre-development site as "woods in good condition" results in no discharge, however
the peak discharge from the post-development site is negligible.
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Vermont Operational Stormwater Permit - Standards Compliance Workbook
General Notes
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Vermont Operational Stormwater Permit - Standards Compliance Workbook
General Discharge Point Information
Project name
Discharge point serial number (e.g. S/N 001)
Name of receiving water
Latitude (decimal degrees to five decimal places)
Longitude (decimal degrees to five decimal places)
Precipitation Data NOAA Atlas 14
Storm WQ Storm 1 yr, 24 hr 10 yr, 24 hr 100 yr, 24 hr
Precipitation (inches) 1.00 1.88 3.22 4.80
Drainage Area Information
Landuse A B C D Total
Grass 0.000 0.000 0.000 0.000 0.000
Meadow 0.000 0.000 0.000 0.000 0.000
Woods 0.200 0.000 0.000 0.000 0.200
Existing Impervious 0.000 0.000 0.000 0.000 0.000
Impervious previously authorized under 2002 VSMM (not included in calculations)0.000
Total Pre Site Area 0.200
%
Landuse A B C D Total
Grass 0.080 0.000 0.000 0.000 0.080
Meadow 0.000 0.000 0.000 0.000 0.000
Woods 0.000 0.000 0.000 0.000 0.000
New Impervious 0.120 0.000 0.000 0.000 0.120 60.0%
Existing for Permit
Coverage (Treated to New
Standards)
0.000 0.000 0.000 0.000 0.000 0.0%
Existing Impervious Not for Permit Coverage 0.000 0.0%
Redeveloped Impervious 0.000 0.0%
0.000
Total Site Area 0.200
Total Impervious for Permit Coverage 0.120
Net Reduced Impervious 0.000 0.0%
Reduced Existing Impervious (for redevelopment)0.000 0.0%
Average
Catchment
Slope, Y (%)
Hydraulic
Length, l (ft)
Pre Development 2.2 134.00
Post Development 1.8 200.00
Pre Development Land Use (acres)
Wetland Tributary to Potash Brook
44.45347
-73.17436
* Preciptation values shall be obtained from
South Burlington High School Basketball Court
S/N1
Post Development Land Use (acres)
Information for Calculating TC by the
Watershed Lag Method
Impervious previously authorized under 2002 VSMM
Last Updated 8/28/2018
SN1: Page 1 of 4
Vermont Operational Stormwater Permit - Standards Compliance Workbook
Runoff Calculations 1 yr, 24-hr 10 yr, 24-hr 100 yr, 24-hr
0.0000 0.0000 0.0000
0.0166 0.0299 0.0467
Tier 1/Runoff Reduction Practices
Practice TV (ac-ft) TV (ac-ft)
Disconnection to FS/VB 0.010
Runoff Reduction Calculations
Standard Re WQ CP QP10 QP100
TV Required (ac-ft)0.0060 0.0098 0.0166 0.0299 0.0467
TV Provided (ac-ft)0.0098 0.0098 0.0098 0.0098 0.0098
TV Remaining (ac-ft)0.0000 0.0000 0.0068 0.0201 0.0369
Standard met with HCM?Yes Yes No No No
Post-Development CN n/a 95 90 85 81
CNadj n/a 69 78 77 74
Pre-Development CN n/a n/a 52 38 30
Groundwater Recharge Standard (Re)1
Standard Applicable?
ReV 0.0060
Standard met with Tier 1
Practices?
Yes
Recharge Notes:
List all Tier 1 practices below with the associated treatment volume (TV ). The T V will be applied to all treatment standards,
except for Green Roofs, which do not receive recharge or water quality credit. Please include the appropriate STP
worksheet(s) with the application.
Predevelopment runoff volume (ac-ft)
Pre-routed, post development runoff volume (ac-ft)
Practice
Yes No
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Vermont Operational Stormwater Permit - Standards Compliance Workbook
Water Quality Treatment Standard (WQ)1 1
(ac-ft)Apply Reduction?
WQV - New & Existing 0.0098 0.0%
WQV - Redevelopment 0.0000 0.0%
Total WQV 0.0098
WQV met with Tier 1
practices 0.0098 2
WQV to be met with Tier 2
and/or Tier 3 practices N/A
WQV Provided
(ac-ft)Tier
Total WQV Provided (ac-ft)0.0000 ac-ft
Is the WQV Standard met?Yes
Water Quality Notes:
Channel Protection Standard (CP)2 1
Standard Applicable?
Standard Met with HCM?No
Provide Extended
Detention for:0.007 ac-ft
Warm or Cold Water
Fishery?→Provide:
FALSE
Extended Detention STP:
CNAdj 78 7.0 (Watershed
Lag Method)
Channel Protection Notes:
Detention Trench
Tier 2 & 3 Water Quality Practice
Is all impervious treated by
disconnection?
% Net Reduction
% Removed Existing
Impervious (Redevelopment)
See the Vermont Water Quality Standards for warm and
cold water designations
Detention is provided in the trench with no overflow for the 1 year storm event.
Post Development TC (min)
Modeling Info: When demonstrating CP compliance with extended detention in a hydrologic model, use the CN and TC
below if the practice being modelled is not a Tier 1 practice. The CN Adj takes into account the reduction in runoff volume
achieved through Tier 1 practices. The T C is calculated by the watershed lag method using CNAdj as CN'.
OR
The Alternative Extended Detention
Method (§2.2.5.4) is being used.
24 hours of extended
detention
The channel protection standard has not been fully met. Either increase Tv
credit to fully meet HCM or provide extended detention.
Yes No
Cold
Warm
No
Yes (WQv met)
No Yes
No Yes
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Vermont Operational Stormwater Permit - Standards Compliance Workbook
Overbank Flood Protection (QP10)1
Standard Applicable?
Standard Met with HCM?No
STP used:
Pre-development peak discharge rate (cfs)0.00
Pre-routed, post-development peak discharge rate (cfs)
Routed, post-development peak discharge rate (cfs)0.00
Pre-Development CN (Flow-
weighted composite)38 9.6
CNAdj 77 7.2
Overbank Flood Notes:
Extreme Flood Protection (QP100)1
Standard Applicable?
Standard Met with HCM?No
STP used:
Pre-development peak discharge rate (cfs)0.00
Pre-routed, post-development peak discharge rate (cfs)
Routed, post-development peak discharge rate (cfs)0.10
Pre-Development CN (Flow-
weighted composite)30 9.6
CNAdj 74 7.8
Extreme Flood Notes:Modeling the pre-development site as "woods in good condition" results in no
discharge, however the peak discharge from the post-development site is negligible.
Post Development TC (min)
Post Development TC (min)
Pre Development TC (min)(Watershed
Lag Method)
Pre Development TC (min)
Modeling Info: When demonstrating Q P100 compliance in a hydrologic model, use the following CN and T C below, if the
practice used to meet QP100 is not a Tier 1 practice. The CN Adj takes into account the reduction in runoff volume achieved
through runoff reduction practices. The T C is calculated by the watershed lag method using CN Adj as CN'.
Detention Trench
The extreme standard has not been fully met. Provide additional STPs to
ensure post development peak runoff does not exceed pre development
peak runoff for the 100 yr, 24 hour storm event.
Modeling Info: When demonstrating Q P10 compliance in a hydrologic model, use the following CN and T C below, if the
practice used to meet QP10 is not itself a Tier 1 practice. The CN Adj takes into account the reduction in runoff volume
achieved through Tier 1 practices. The T C is calculated by the watershed lag method using CNAdj as CN'.
(Watershed
Lag Method)
The QP10 standard has not been fully met. Provide additional STPs to ensure
post development peak runoff does not exceed pre development peak runoff
for the 10 yr, 24 hour storm event.
Detention Trench
Yes No
Yes No
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