Approval Letter 01-26-2011January 26, 2011
Mr. Cliff Buhman
CITY OF Inspec
CHMII jj��Tjj�(� 5801 Duluth Street
ASSFN Minneapolis, MN 55422
7700 Market Boulevard Re: Minnetonka Middle School West Interim Use Permit
PO Box 147 Planning Case # 11 -01
Chanhassen, MN 55317
Dear Mr. Buhman:
Administration
Phone: 9522271100 This letter is to confirm that on January 24, 2011, the Chanhassen City Council
Fax: 952.2271110 approved the interim use permit to permit site grading for the tennis courts at
Building Inspections Minnetonka Middle School West subject to the following conditions:
Phone: 952.227.1180
Fax: 952.227.1190 1. Adequate sediment and erosion control practices must be installed prior to any
earth - disturbing activities.
Engineering
Phone: 952.227.1160 2. All silt fence. shall use metal t -posts and shall be consistent with City Detail
Fax: 952.227.1170 Plate No. 5300. Include detail on sheet 5.
Finance
Phone: 952.227.1140
3.
Rock construction entrance locations shall be shown on the p lan and should be
p
Fax: 952.227.1110
placed such that construction traffic does not cross the proposed infiltration
areas. Rock construction entrances shall be consistent with City Detail Plate
Park & Recreation
No. 5301. Include detail on sheet 5.
Phone: 952.227.1120
Fax: 952.227.1110
4.
Infiltration areas shall be protected from sediment deposition and compaction
Recreation Center
resulting from construction equipment throughout construction. This must be
2310 Coulter Boulevard
noted on the plans along with all other areas to be protected.
Phone: 952.227.1400
Fax: 952.227.1404
5.
Category 3 erosion control blanket shall be used on all disturbed slopes with
positive flow to the pond unless sod is to be placed and staked.
Planning &
Natural Resources
6.
The applicant is responsible for procurement of the NPDES General Permit to
Phone: 952.227.1130
Fax: 952.227.1110
Discharge Stormwater Associated with Construction Activity prior to any
earth- disturbing activities. A full SWPPP will need to be prepared and
Public Works
submitted to the City for review and approval prior to any earth- disturbing
1591 Park Road
activities. The SWPPP must include all components identified in Parts III and
Phone: 952.227.1300
IV of the permit.
Fax: 952.2271310
7.
Redundant erosion control measures shall be included at the two new inlets to
Senior Center
Phone: 9522271125
the pond. Floating silt curtain should be used at the more southerly inlet but a
Fax: 952.227.1110
second line of silt fence may be adequate at the other new inlet.
Web Site 8. The infiltration design and maintenance shall be consistent with the 2008
wm.ci.chanhassen.mn.us Minnesota Stormwater Manual; in particular Chapter 12 and Appendix D.
Chanhassen is a Community for Life - Providing for Today and Planning for Tomorrow
Mr. Cliff Buhman
January 26, 2011
Page 2
9. Protection must be provided to assure that construction equipment is not tracked over the
proposed infiltration areas, materials are not stockpiled in these areas and sediment
deposition does not occur in these areas. This is most commonly accomplished through the
use of silt fence. Further, this should be noted on the plan set, in the SWPPP and within the
project specifications manual.
10. Infiltration features must be separated from the ground water by a minimum of three feet.
Provide boring data to confirm this separation.
11. As the infiltrometer tests were performed approximately 60 feet west of the proposed
infiltration area and the infiltration rates are under the optimal conditions, and likely to
decline over time, a margin of safety shall be built into the design to account for a diminished
infiltration.
12. To assure that the area drains in 48 hours or less, the system shall be designed with an
underdrain and coarse aggregate storage as depicted in Appendix D of the Minnesota
Stormwater Manual — ` Bioretention /Infiltration/Filtration Facility ", page 723 of 885. This
would likely satisfy the above condition.
13. CBMH 1 shall be moved northerly on the site and lowered so that the rim elevation is below
1060 feet.
14. The applicant shall relocate to proposed drain tile outlet for the four most easterly tennis
courts. The new outlet shall be between the most southerly court and the next most southerly
court. This shall then be connected to CBMH 2 and the outlet for this manhole shall then be
sized accordingly.
15. A stable emergency overflow shall be provided from the easterly basin to the pond.
16. The applicant shall demonstrate how the filtration swales are to be vegetated. At a minimum,
fescues and/or other deep- rooted grasses should be used to promote infiltration.
17. The new outlet elevations are shown to be 1046 feet. It appears that the ordinary high water
level (OHW) is at 1045.4 and the normal water level (NWL) is at an unknown elevation but
likely at or around 1043.5. The newly proposed outlet shall be set at the NWL.
18. The applicant or their consulting engineer shall develop an operations and maintenance
manual for the infiltration /filtration features and that this includes some type of vegetative
filter to provide pretreatment of the water entering the system.
19. The applicant shall provide a security in the amount of $4,000 to guarantee erosion control.
20. The applicant shall verify that the tennis courts are outside any easements and meet the 15
foot side yard setback.
Mr. Cliff Buhman
January 26, 2011
Page 3
A security in the amount of $4,000 for erosion control must be submitted before site grading can
commence. Additionally, all erosion control measures and tree protection fencing must be
installed and inspected prior to the City authorizing grading operations. Should you have
additional questions or need more information, please feel free to contact me at (952) 227 -1131
or bgenerous @ci.chanhassen.mn.us
Sincerely,
Robert Generous, AICP
Senior Planner
Mr. Mike Condon,Minnetonka School District, ISD# 276
ec: Kate Aanenson, Community Development Director
Alyson Fauske, Assistant City Engineer
Todd Gerhardt, City Manager
Terry Jeffery, Water Resources Coordinator
g: \plan \2011 planning cases \approval letter.doc