06-03 Approval LetterFebruary 28, 2006
Mr. Mike Condon
Minnetonka Public Schools
5621 County Road 101
Minnetonka, MN 55345
Re: Interim Use Permit – Minnetonka Middle School West
Planning Case #06-03
Dear Mr. Condon:
This letter is to confirm that on February 27, 2006, the Chanhassen City Council
approved Interim Use Permit #06-03 to permit the grading of approximately 3,400
cubic yards for an infiltration basin and drainage swales, plans prepared by Larson
Engineering of Minnesota, dated December 19, 2005 subject to the following
conditions:
1.The applicant shall provide the City with a cash escrow or letter of credit in the
amount of $5,600.00 to guarantee erosion control measures and site restoration
and compliance with the interim use permit.
2.Verify the existing 24-inch culvert has sufficient capacity before replacing the
private drive entrance.
3.The applicant must provide a proposed haul route for review and approval.
4.If fill is coming from and/or going to another site in Chanhassen, a separate
grading permit will be required for the other property.
5.All disturbed areas as a result of construction are required to be reseeded and
mulched within two weeks of site grading.
6.An erosion control blanket must be installed on all sides around the infiltration
basin. All disturbed areas as a result of construction are required to be sodded
or reseeded and mulched within two weeks of site grading.
7.Submit a full size drainage area map.
8.Add City Detail Plates Nos. 3101, 3102, 3103, 5300, 5301 and 5302.
9.Show rock construction entrance per Detail Plate No. 5301. The applicant
shall construct and maintain a rock construction access to the site. Access to
the site shall be restricted to this access point only.
Minnetonka Public Schools
February 28, 2006
Page 2 of 3
10.The applicant shall obtain and comply with all permit requirements of the Watershed District
and MnDOT.Revise the existing storm sewer flow direction in all plans to match.
11.The applicant shall supply the City with a mylar as-built survey prepared by a professional
engineer upon completion of filling and/or excavation to verify the grading plan has been
performed in compliance with the proposed plan.
12.A plumbing permit must be obtained before installing the storm sewer piping.
13.The applicant shall provide a cross section for the filtration area showing the elevation of the
draintile and the trenches, as well as a cross section of the trench and details of the material
used. The draintile trenches shall be lined with drainage fabric (4% to 6% open space) and
filled with pea rock at a depth of at least 18 inches and 3 feet wide. The bottom of the entire
filtration basin shall be backfilled with a mixture of 50% coarse clean sand, 25% compost, 25%
loamy topsoil for a minimum depth of 6 inches (from approximately 1034.5 to 1035.0). The
rest of the area shall be top-dressed with native topsoil. CB-1 shall be revised to be an open
beehive inlet at an approximate elevation of 1037 for handling large storm event runoff if the
calculations for rate control work out to avoid overwhelming the filtration area and having long
periods (greater than 72 hours) of ponding.
14.Erosion control blanket/turf reinforcement mat (MnDOT Category 5) shall be used for
restoration of the exposed slope from the emergency overflow to the ditch along Highway 41
within 7 days of final grade. The blanket shall be specified and a detail provided. Erosion
control blanket shall be installed on any exposed soils south of the private drive within 24 hours
of final grade.
15.A seed mix for shaded, wooded areas shall be specified in the plan, along with the proposed rate
of application. A seed mix for the filtration area and slopes shall also be specified.
16.The rip rap at the flared-end section at the south end of the 24-inch pipe south of the private
drive shall be replaced.
17.Runoff from the storm sewer system from the school shall be controlled during construction.
The water shall be conveyed through a non-erosive means to the Highway 41 ditch through the
job site.
18.Erosion control blanket category 2 or 3 shall be installed within the filtration area within 24
hours of connecting the 18-inch PVC to the basin. The blanket shall be applied following a
seeding. Remaining exposed soils on site shall be mulched and seeded or sodded within 14
days of final grade.
19.The silt fence used shall be a City of Chanhassen type 1 silt fence; monofilament silt fence with
metal T-posts, 6 foot maximum spacing and 3 plastic zip ties in the top 8 inches of the fabric.
The silt fence specified for the filtration area shall be labeled as “Installed after drain tile
installation.”
20.A rock construction exit pad shall be installed from the bituminous edge 40 to 50 feet long into
the job site.
Minnetonka Public Schools
February 28, 2006
Page 3 of 3
21.Street sweeping shall be completed within 24 hours should soil be tracked upon paved surfaces.
22.Catch basin inlet control shall be provided for the catch basins adjacent to the school building if
tracking of soil becomes a problem on the paved surfaces.
Please submit a cash escrow or letter of credit in the amount of $5,600.00 as security for
compliance with the permit. If you have any questions or need additional information, please
contact me at (952) 227-1131 or Alyson Fauske, Assistant City Engineer, at (952) 227-1164.
Sincerely,
Robert Generous, AICP
Senior Planner
c: Mike Murphy, Larson Engineering
ec: Alyson Fauske, Assistant City Engineer
Lori Haak, Water Resources Coordinator
Steve Torell, Building Official
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