2005-09-19_Chanhassen west business park 2Carver County Water Management – Department of Planning & Zoning
Government Center – Administration Building
600 East 4th Street
Chaska, Minnesota 55318
Phone: (952)361-1820
Fax: (952)361-1828
www.co.carver.mn.us/water
Memo
To: Pat Minger
From: Paul Moline, Carver County Water Management
Date: 9/19/2005
Re: Chanhassen West Business park County Water Project WP20050038
cc. Lori Haak, City of Chanhassen
Jerry Backman, Schoell-Madson
Aaron Mlynek, Carver SWCD
Robert Generous, City of Chanhassen
Enclosures: SWPPP Comments
Carver County Water Management has received plans (dated 8/25/05), SWPPP and hydrologic calculations
(dated 8/26/05) for the Chanhassen West Business Park project in the City of Chanhassen. The following
comments include review by the County, the SWCD and Wenck Associates:
Stormwater Issues:
1. The calculations for existing conditions should be resubmitted and show the effects of ponding in the
northeast wetland. The submitted calculations use sheet flow runoff from 35.74 acres to the southwest
wetland, which is not representative of the Existing Drainage figure. The increase in runoff may have
impacts on downstream and water quality treatment on site.
2. Water Quality calculations need to be submitted for review.
3. Proposed CNs for greenspace should be raised to C type soils to account for the affect of compaction.
4. Downstream capacity of the southwest wetland (Outlot A) should be submitted.
5. The outlet of the northwest wetland (Outlot B) should be submitted.
6. Rainwater Gardens/Infiltration - Additional details are needed including:
• Documentation should be submitted for the volume provided for infiltration. Several basins are
noted on the plans, but no calculations are provided.
• Soils used (sand fill or rock fill, 50% clean sand, 25% loamy topsoil, 25% compost)
• Cross-sections
• Erosion control blanket and type
• Timing of installation (after contributing area is stabilized).
• To reduce initial degradation of basins, It is recommended plugs, shrubs and grasses are used
in addition to the ‘rainwater garden seed mix’.
Erosion and Sediment Control: (please contact Aaron Mlynek at the Carver SWCD at 952.442.5101 for
questions or assistance on this section)
Erosion Control
1. Stable EOF’s are needed for the proposed pond on site. The EOF should be clearly labeled on the
plan and a detail is needed. The EOF can be stabilized with a turf re-enforcement mat or fabric and
riprap.
2. Erosion control blanket should be specified in the swale from the FES to the wetland along the west
boundary of the site. The blanket specified should adequately protect the area from designed velocity
and depth of flow. The blanket and seed in the swale should be installed within 24 hours of culvert
installation. All blanket on the plan should be shown as a shaded area.
3. Erosion control blanket is recommended for the pond slopes from around 952 to 942 contours. All
blanket on the plan should be shown as a shaded area.
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4. Erosion note number 5 should include 2 tons of mulch per acre with seed for stabilization; seed alone is
not considered stabilization.
5. All curb cuts need riprap and fabric or sod installed within 24 hours of curb installation.
Sediment Control
1. Temporary sediment basins are needed prior to disturbing upslope areas. The areas of temporary
sediment basins should be labeled on the plan. A temporary outlet is needed for the pond; details
should be provided. A temporary outlet could consist of a perforated riser and rock cone. Temporary
basins are needed in the area of the proposed permanent stormwater pond; the SE corner of the site
prior to discharging to the culvert under Galpin.
2. The Wimco inlet control detail proposed will work for all curbside inlets. Any and all area inlets or drop
inlets in paved areas will need alternate controls / Wimco details. The engineer should check on
alternate designs for Wimco-type inlet controls to fit the various type of inlets.
3. Additional inlet controls may be needed for adjacent inlets on Galpin and Street A.
4. Silt fence will be needed around Outlot A along the east side between the pond the wetland.
5. Silt fence needed for Lot 5, Outlot B.
6. Silt fence needed north of berm in Lot 6 as there is a FES taking water north off site.
7. Silt fence needed south of Lot 1.
8. Each building site will need perimeter controls once the streets are paved and rock exits will be needed
as each lot is built-out.
9. Type 1 and Type 2 silt fence locations need to be specified on the plan. Type 2 should be installed
around all wetland areas and in the SE corner of the site to protect the culvert under Galpin. The SF
should be extended along the South side to close the gap in the SF.
SWPPP
A SWPPP review has been completed; any items not marked with an ‘x’ or ‘n/a’ need attention.
If you have any questions, please feel free to contact me. A follow up meeting may be of benefit.
___________________
Paul Moline
952.361.1825
pmoline@co.carver.mn.us