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St. Louis Sewer
District
2350 Market Street
St. Louis, MO 63103-2555
(314) 768-6200
June 2, 2008
Mr. John MacKinnon, P.E.
Regulatory Specialist
Hydro International
94 Hutchins Drive
Portland, ME 04102
RE: Downstream Defender®: St. Louis MSD Submission
Highway Use Level (HUL) and Redevelopment Use Level (RLTL) Approval within
District
Dear Sir:
The Metropolitan St. Louis Sewer District (MSD) has reviewed your application regarding the
Downstream Defender® for use as a Best Management Practice for stormwater management.
MSD is pleased to provide Highway Use Level (HUL) and Redevelopment Use Level (RUL)
approval for use of the Downstream Defender® as a stand-alone water quality BMP, subject to
the following provisions.
• The Downstream Defender® is only approved for use on public highway and roadway
projects and for redevelopment sites less than 5 acres. This approval is based compliance
with requirements listed in MSD's Proprietary Water Quality Products and the MSD's
Stormwater Management Program (Jan. 2008).
• The Downstream Defender® must be sized to capture all floatable trash and free oil, and
remove 80% of total suspended solids for the OK-110 particle size distribution at the site
water quality flow -rate (WOO. Procedures for calculating WQf are provided in Appendix
D.10 of the Maryland Stormwater Design Manual (2000). Table 1 provides a list of
approved models and their respective instantaneous peak treatment WQf.
Table 1: Downstream Defender® Approved Models and Peak WQf
System Model
Max Treatment Flow (cfs)
4 Foot Diameter
1.3
6 Foot Diameter
4.1
8 Foot Diameter
9.4
10 Foot Diameter
17.7
• Devices should be configured as off-line units. In most cases the BMP will be installed
without the need to store the water quality volume (WQ,) upstream of the unit.
• All devices shall provide a minimum sediment storage capacity of 10 ft3.
" C o n f i n e d s p a c e e n t r y s h a l l n o t b e a r e q u i r e m e n t f o r r o u t i n e m a i n t e n a n c e . N o s p e c i a l
t o o l s o r a t t a c h m e n t s s h o u l d b e r e q u i r e d t o p r o v i d e r o u t i n e m a i n t e n a n c e w i t h a v a c u u m
p u m p i n g t r u c k .
" A l l p r o p r i e t a r y l i d s a n d c o v e r s s h o u l d b e c a p t i v e c o m p o n e n t s . T h e m i n i m u m s i z e a c c e s s
h o l e i s 3 0 i n c h e s i n d i a m e t e r .
" P r o j e c t s p e c i f i c d e s i g n c a l c u l a t i o n s a n d m a i n t e n a n c e p l a n s f u r n i s h e d b y H y d r o
I n t e r n a t i o n a l m u s t b e i n c l u d e d w i t h i n t h e p r o j e c t '