HomeMy Public PortalAboutADS Stormtech and Isolator Row 9-20-16Metropolitan
St. Louis Sewer
District
2350 Market Street
St. Louis, MO 63103-2555
(314) 768-6200
September 20, 2016
ADS
Attn: Mr. Mark Joersz
605 Dartmouth Crest Dr.
St. Louis, MO 63011
RE: Stormtech and Isolator Row
Dear Mr. Joersz,
The Metropolitan St. Louis Sewer District (MSD) has reviewed your July 5, 2016 analysis of the
ADS Stormtech/Isolator Row system as a standalone post -construction stormwater Best
Management Practice. MSD hereby grants approval of the Stormtech/Isolator Row system for
use on new development, redevelopment and highway/roadway improvement projects of any
size under the following conditions:
Properly sized Isolator Row chambers are provided as a measure of pretreatment at each location
where flow is injected into the Stormtech system. The sizing of the Isolator Rows shall be based
upon the Peak Discharge for the Water Quality Storm (Appendix D.10 of the 2000 Maryland
Stormwater Design Manual) tributary to each point of injection, and Table 1:
Table 1
Isolator Row — Flow Rates per Chamber
Chamber Model
Max Allowable Peak Discharge for the Water
Quality Storm / (cfs) per Chamber
SC-160
0.06
SC-310
0.10
SC-740
0.15
MC-3500
0.24
MC-4500
0.16
At a minimum, an equal number of non -Isolator Row chambers are required for each installation.
The Stormtech outlet shall be perched a minimum 6" and the infiltration bed area sized in
accordance with the attached Figure 1. With a perched outlet, and when sized in accordance
with Table 1 and Figure 1, the Isolator Row and Stormtech Chambers provide sufficient water
quality treatment for its tributary area. A runoff volume reduction credit of 0.45 may be entered
into "Item 11, Site Specific BMP" in the MSD MEP spreadsheets.
It is noted that Figure 1 was derived using an assumed underlying subgrade saturated hydraulic
conductivity of 0.05 in/hr. This may be the default assumption for all sites utilizing a 6"
perched outlet.
When configured with a greater than 6" but less than 18" perched outlet height, MSD will
require the following from a Professional Geotechnical Engineer licensed in Missouri: a) Onsite
geotechnical investigation to determine the actual saturated hydraulic conductivity of the
underlying soils beneath the Stormtech/Isolator Row System, b) assessment and recommendation
for pavement structural stability, c) assessment of possible impacts to adjacent structures due to
seepage, including recommended setback distances between those features and the
Stormtech/Isolator Row system.
In all instances, a minimum 2 feet separation is required between the bottom of the infiltration
bed and the seasonal high water table.
Integration with Channel Protection and Detention Design
Channel Protection storage, 2yr-24 hour and 100yr-24 hour detention storage may be managed
within the same system, with a properly configured, sized, maintenance -accessible, reinforced
concrete control structure. The footprint of the infiltration bed/chamber system shall be sized at
a minimum to manage Water Quality, and expanded as necessary to manage these additional
volumes as required on sites.
MSD reserves the ability to withdraw or modify this approval based on subsequent information,
including information indicating that the Stormtech and Isolator Row do not satisfy MSD rules,
requirements, or construction and material specifications.
Sincerely,
Jason T. Peterein, P.E.
Principal Engineer (BMP Committee Chairman)
Engineering / Planning - Development Review
Metropolitan St. Louis Sewer District
Attachment: Figure 1 — Stormtech Underground Infiltration Bed Area Sizing Graph
Infiltration Bed Area as Percentrage of Tributary Area (%)
50%
40%
30%
20%
10%
0%
Figure 1 - StormTech Underground Infiltration Bed Area Sizing Graph
0
rtm6" Underdrain Height
t12" Underdrain Height
41•8•018" Underdrain Height
10 20 30 40 50 60
Contributing Watershed Percent Impervious
70
80
90
100