HomeMy WebLinkAboutSD-23-11 - Supplemental - 1200 Dorset Street (17)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
2 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?Not
Feasible
Not
Feasible
Not
Feasible Yes Yes
Not
Feasible
Not
Feasible
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
Not
Feasible
Not
Feasible
Not
Feasible n/a n/a
Not
Feasible
Not
Feasible
Not
Feasible
Not
Feasible n/a n/a n/a n/a n/a
Not
Feasible 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.
Heald Subdivision - Lot 6
S/N 001
Complete the matrix below in its entirety for each drainage area.
Proceed to Step
2
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
1
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?
Stop. No further justification is needed.
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