Engineering Comments 2-7-05
,.
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
Fax: 952.227.1110
Park & Recreation
Phone: 952.227.1120
Fax: 952.227.1110
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:
Bob Generous, Senior Planner
FROM:
Matt Saam, Assistant City Engineer M~
February 7, 2005
DATE:
SUBJ:
Preliminary Plat Review for Hidden Creek Meadows
LUR No. 04-16
Upon review of the plans dated January 14, 2005, prepared by Ryan Engineering, I
offer the following comments:
GRADING, DRAINAGE & EROSION CONTROL
The plans propose to grade about 75% of the site for the 21 new house pads, proposed
street ending with a cul-de-sac, and a storm water pond. The proposed grading will
prepare the site for full basement, lookout, and walkout-type dwellings. The plan
proposes a retaining wall in the back yard of Lot 7, Block 1. It appears the wall will
be approximately six feet in height. The applicant should be aware that any retaining
wall over 4 feet will require a building permit and must be designed by a Minnesota
Registered Professional Structural Engineer. Also, the retaining wall must be 20 feet
off the back of the building pad to provide adequate area for a backyard and deck.
The existing site drains to a wetland along the south side of the parcel. Under
developed conditions, the street, front yards and most of the house roofs and rear yard
drainage will be conveyed via storm sewer to a proposed storm water pond for
treatment prior to discharging to the existing wetland. The proposed development
will be required to meet the existing stormwater runoff rates for the 10- and 100-year,
24-hour storm events. The applicant has done a good job of attempting to preserve
the existing drainage pattern of the wetland on the site through the use of a storm
sewer culvert. Where the proposed street has bisected the wetland, the culvert will
act as a conduit and allow the water to flow as it would under existing conditions.
According to the City's Surface Water Management Plan (SWMP), the proposed
culvert must be a minimum size of 36-inches in diameter to facilitate proper drainage
through the site. The developer is proposing a 42-inch diameter culvert under the
road, which exceeds the minimum size requirement. By oversizing the culvert, the
developer is being conservative and helping to ensure that the drainage will flow
freely through the site.
There is an area in the rear yard of Lot 9, Block 1 that will need to be revised to
prevent trapping water behind the curb. Either a catch basin will need to be added or
the area will have to be regraded with a minimum slope of 2% to drain from the
The City 01 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
February 7, 2005
Page 2
rearyard to the street. Also, staff recommends that the existing culvert across the
street from Lot 9, Block 2 be incorporated into the storm sewer for Pipewood Lane.
Staff has received drainage calculations for the development and only minor revisions
are necessary. The proposed pond is required to be designed to National Urban
Runoff Program (NURP) standards. The storm sewer will have to be designed for a
lO-year, 24-hour storm event. Drainage and utility easements will need to be
dedicated on the final plat over the public storm drainage system including the pond,
drainage swales, and wetlands up to the 100-year flood level. The minimum utility
easement width must be 20 feet wide.
To help address concerns raised at the initial Public Hearing for this development, the
applicant has submitted a drainage exhibit for the area in and around the
development. This exhibit shows topography and critical HWL (high water level)
elevations for the ponds and wetlands on the development site and
upstream/downstream of the site. The HWL of the wetlands on the exhibit are from
the City's SWMP plan. Most importantly, the exhibit shows the HWL of the wetland
on the south side of TH 7. This wetland is upstream of the development site and was
one of the areas of concern raised by the public at the last Public Hearing. The
exhibit lists the HWL of the wetland as 943.4 which, based on the topography on the
exhibit, is 4+ feet lower than any of the adjacent homes. In order for any of these
homes to flood, the stormwater in the wetland would have to rise up past elevation
948 which would also begin to flood Minnewashta Parkway.
The applicant has included silt fence around the grading perimeter. Adjacent to the
pond and wetlands, silt fence type II must be used. A 75-foot minimum rock
construction entrance has been shown at the street entrance to the site. In addition, an
erosion control blanket will be required for the steep slopes along the north property
line of the site. The applicant should be aware that any off-site grading will require
an easement from the appropriate property owner. All disturbed areas must be
sodded or seeded and mulched within two weeks of grading completion.
UTILITIES
Municipal sewer and water service is available to the site from existing mains, which
run along the eastern property line and from Pipewood Lane on the southwest comer
of the parcel. The applicant is proposing to extend sewer and water lines along the
proposed streets to service the proposed lots. The watermain will be looped through
the site to avoid stagnant water issues.
According to the City's Finance Department records, there is a remaining assessment
balance of $25,477.05 on the parcel. This balance is required to be paid at the time of
final plat recording. Since the developer will be responsible for extending lateral
sewer and water mains, the sanitary sewer and water connection charges will be
waived. However, the sanitary sewer and water hookup charges will still be
applicable for each lot. The 2005 trunk hookup charge is $1,458 for sanitary sewer
Bob Generous
February 7, 2005
Page 3
and $2,955 for watermain. Each of these charges is based on the number of SAC
units calculated by the Metropolitan Council. Sanitary sewer and watermain hookup
fees may be specially assessed against the parcel at the time of building permit
Issuance.
Public utility improvements are required to be constructed in accordance with the
City's latest edition of Standard Specifications and Detail Plates. Detailed
construction plans and specifications must be submitted at the time of final plat for
staff review. The applicant is required to finance all of the proposed improvements.
The applicant will also be required to enter into a development contract with the City
and to supply the necessary financial security in the form of a letter of credit or cash
escrow to guarantee installation of the improvements and the conditions of final plat
approval. Permits from the appropriate regulatory agencies must be obtained,
including but not limited to the MPCA, Department of Health, MnDOT, etc.
STREETS
The plans propose to extend Pipewood Lane, as the main road, approximately 1300
feet within the site. The public streets are shown within a 60-foot right-of-way, as per
City ordinance along with street pavement widths of 31-feet back-to-back and a 45.5-
foot radius on the cul-de-sac. Due to the long length of the proposed cul-de-sac and
the practice of having two connections int%ut of developments, staff is
recommending that the existing gravel road known as Cartway Lane be connected to
the proposed cul-de-sac at the eastern border of the site. This will be an interim
connection until the properties to the north develop and Cartway Lane is vacated.
RECOMMENDED CONDITIONS OF APPROVAL
1. Prior to final plat approval, a professional civil engineer registered in the State of
Minnesota must sign all plans.
2. Prior to final platting, storm sewer design data with a drainage map will need to
be submitted for staff review. The storm sewer will have to be designed for a 10-
year, 24-hour storm event. The pond is required to be designed to National Urban
Runoff Program (NURP) standards. Drainage and utility easements will need to
be dedicated on the final plat over the public storm drainage system including
ponds, drainage swales, and wetlands up to the 100-year flood level. The
minimum utility easement width shall be 20 feet wide.
3. Type II silt fence must be used adjacent to all ponds and wetlands. In addition, an
erosion control blanket is requi~ed for the steep slopes along the north property
line of the site. The applicant should be aware that any off-site grading would
require an easement from the appropriate property owner. All disturbed areas
must be sodded or seeded and mulched within two weeks of grading completion.
Bob Generous
February 7, 2005
Page 4
4. The remaining utility assessment due payable to the City at the time of final plat
recording is $25,477.05. In addition, the sanitary sewer and water hookup charges
will be applicable for each of the new lots. The 2005 trunk utility hookup charges
are $1,458 per unit for sanitary sewer and $2,955 per unit for water. Each of
these charges is based on the number of SAC units calculated by the Metropolitan
Council.
5. Public utility improvements will be required to be constructed in accordance with
the City's latest editions of Standard Specifications and Detail Plates. Detailed
construction plans and specifications will be required at the time of final platting.
The applicant will also be required to enter into a development contract with the
City and supply the necessary financial security in the form of a letter of credit or
cash escrow to guarantee installation of the improvements and the conditions of
final plat approval. Permits from the appropriate regulatory agencies must be
obtained, including but not limited to the MPCA, MNDOT, Department of
Health, etc.
6. A registered structural engineer must design any retaining walls in excess of four
feet in height. This will also require a building permit.
7. Show all of the existing and proposed easements on the plans.
8. Show all of the existing utilities on the plans.
9. The proposed development is required to meet the existing storm water runoff
rates for the 10- and 100-year, 24-hour storm events.
10. The walk-out elevation of the proposed homes must be a minimum of 3 feet
higher than the adjacent pond or wetland high-water-level.
11. Show the proposed storm manhole rim and invert elevations on the utility plan.
12. Show all emergency overflow elevations on the grading plan.
13. The existing temporary pavement turnaround for Pipewood Lane just south of this
site must be removed when Pipewood Lane is extended. Any disturbed area must
be sodded and restored.
14. The retaining wall in the rearyard of Lot 7, Block 1 must be 20 feet off the back
of the building pad.
15. Revise the rearyard grading of Lot 9, Block 1 to prevent trapping water behind the
curb. Either a catch basin will need to be added or the area will have to be
regraded with a minimum slope of 2% to drain from the rearyard to the street.
Bob Generous
February 7,2005
Page 5
16. The existing gravel road known as Cartway Lane must be connected to the
proposed cul-de-sac at the eastern border of the site.
17. The existing culvert across the street from Lot 9, Block 2 be connected to the
storm sewer for Pipewood Lane.
c: Paul Oehme, Public Works Director/City Engineer
Mak Sweidan, Engineer
g:\eng\projects\hidden creek meadows\revised ppr.doc