Memo from Alyson Fauske 11-21-06
CITY OF
CHANHASSEN
7700 Market Boulevard
PO Box 147
Chanhassen, MN 55317
Administration
Phone: 952.227.1100
Fax: 952.227.1110
Building Inspections
Phone 952.227.1180
Fax: 952.227.1190
Engineering
Phone: 952.227.1160
Fax: 952.227.1170
Finance
Phone: 952.227.1140
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Park & Recreation
Phone: 952.227.1120
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Recreation Center
2310 Coulter Boulevard
Phone: 952.227.1400
Fax: 952.227.1404
Planning &
Natural Resources
Phone: 952.227.1130
Fax: 952.227.1110
Public Works
1591 Park Road
Phone: 952.227.1300
Fax: 952.227.1310
Senior Center
Phone: 952.227.1125
Fax: 952.227.1110
Web Site
www.ci.chanhassen.mn.us
MEMORANDUM
TO:
Robert Generous, Senior Planner
Alyson Fauske, Assistant City Engineer ~
November 21,2006
FROM:
DATE:
SUBJECT:
Interim Use Permit Application- Independent School District 112
Planning Case 06-35
Independent School District 112 has submitted a grading plan for the proposed
Chanhassen High School site in the northwest comer of Audubon Road and Lyman
Boulevard. The railroad lies to the north of the site and Bluff Creek lies to the east.
The high point of the site currently runs south of the railroad and bisects the site. There
is between 20 and 50 feet of fall from the high area to Lyman Boulevard. Bluff Creek
lies approximately 80 feet below the high area. A gas pipeline bisects the site as it runs
east-west along the property from the intersection of the railroad and Lyman Boulevard;
the surface grade over the pipe varies approximately 80 feet.
The proposal is to grade 230,000 cubic yards of material to prepare a building pad for the
future high school. ISD 112 is not proposing to grade the site according to the
development plans at this time due to the winter construction start.
ISD 112 proposes to disturb the central third of the site and stockpile material south of
the railroad and west of the wetland. ISD 112 does not propose to grade within the gas
pipeline easement under the interim use permit. The school district has indicated that the
final grading plan does not propose cut or fill over this easement, either.
Due to the large gradient within the property and the restraints associated with the
existing gas pipeline through the site, the project will likely require mass grading almost
the entire site.
ISD 112 proposes to construct a "walk-out" style building; the lowest floor elevation of
the west side of the building will be 19.5 feet higher than that of the east side of the
building. This proposed building style compliments the topography of the site.
Material must be excavated for the proposed building pad. The west side of the building
will require between two and 34 feet of cut; the east side will require between two and 42
feet of cut. A large construction staging area is proposed west of the building pad and
will be relatively flat.
The proposed slope from the building pad towards the wetland will require up to 10 feet
of cut. ISD 112 proposes to construct a berm along the eastern boundary of the grading
to divert runoff to proposed Temporary Sedimentation Basin No.2. The proposed berm
will lie on top of the existing trunk sanitary sewer that lies west of Bluff Creek. During
The City of Chanhassen . A growing community with clean lakes, quality schools, a charming downtown, thriving businesses, winding trails, and beautiful parks. A great place to live, work, and play.
Bob Generous
Page 2 of 2
final grading of the site, the height of this berm should be reduced to the maximum extent practicable,
otherwise additional drainage and utility easements may be required.
ISD 112' s engineer indicates up to 20 feet of fill is proposed over this sanitary sewer. Based on the as-
built information for the sanitary sewer, the type of pipe and pipe bedding, the proposed fill will not
collapse the pipe. The developer is required to televise the section of sanitary sewer over which grading
operations will occur before and after construction to determine if the site grading damaged the pipe. ISD
112 shall be responsible for repairing any sections of sanitary sewer damaged during construction. The
developer must place sanitary sewer manhole sections on the existing manhole to bring the top of
manhole up to the existing grade. No more than one foot of rings is allowed.
Excess dirt generated from the building pad preparation is proposed to be stockpiled on the north side of
the site. The top of the proposed stockpile will be approximately 38 feet higher than the current grade, or
approximately 50 feet higher than the elevation of Lyman Boulevard at that location. Up to 50 feet of
temporary fill will be placed at this location. The top of the temporary stockpile will be approximately 87
feet higher than the wetland that lies between Temporary Sediment Basins 3 and 4. The majority of the
temporary stockpile will be a 3H: 1 V slope.
Staff is concerned with the proposed height of the temporary stockpile and its proximity to the wetland
which flows to Bluff Creek. Unfortunately, it does not seem feasible to stockpile any of this material at
any other location on the site, therefore it is critical that the development team articulate to the contractor
the necessity of properly installing and maintaining, on a regular basis, the erosion control practices.
Recommended Action: Staff recommends approval of the Interim Use Permit for 1425 Bluff Creek
Drive, staff recommends that the recommendation include the following conditions:
1. During final grading ofthe site, the height ofthe berm over the sanitary sewer shall be reduced to
the maximum extent practicable, otherwise additional drainage and utility easements may be
required.
2. The developer is required to televise the section of sanitary sewer over which grading operations
will occur before and after construction to determine if the site grading damaged the pipe.
3. ISD 112 shall be responsible for repairing any sections of sanitary sewer damaged during
construction.
4. The developer must place sanitary sewer manhole sections on the existing manhole to bring the
top of manhole up to the existing grade.
5. No more than eight inches of rings is allowed on the sanitary sewer manhole.
G:\ENG\IUPs\ISD 112 grading 11-21-06.DOC