Letter to John Knoblauch 05-17-201313 -12-
MY OF May 17, 2013
CgA NSEN
7700 Market Boulevard
PC Box 147
Chanhassen, MN 55317
Administration
Phone: 952.227.1100
Fax: 952.227.1110
Mr. John Knoblauch
J & S Ventures 1, Inc.
1450 Knob Hill Lane
Excelsior, MN 55331
Re: The Preserve at Rice Marsh Lake
Building Inspections
Dear Mr. Knoblauch:
Phone: 952.227.1180
Fax: 952.227.1190
Staff has reviewed your submittal for The Preserve at Rice Marsh Lake project
Engineering
and finds that certain elements are missing that will prevent staff from making
Phone: 952.227.1160
a
favorable recommendation. The critical items that are missing appear in bold in
Fax: 952.227.1170
the attached document.
Finance
Phone: 952.227.1140
There are three options before us:
Fax: 952.227.1110
1. Provide the information requested by June 30, 2013 in order for staff to
Park & Recreation
process the application.
Phone: 952.227.1120
Fax: 952.227.1110
2. If not, the request can move forward as submitted without a favorable
Recreation Center
recommendation from staff.
2310 Coulter Boulevard
Phone: 952.227.1400
3. Withdraw the application, address all the issues that appear in bold, and
Fax: 952.227.1404
resubmit the application.
Planning &
Natural Resources
Staff wishes to work with you and ensure that this development is successful.
y P
Phone: 952.227.1130
Please let me know your intended course of action.
Fax: 952.227.1110
Sincerely,
Public Works
7901 Park Place
Phone: 952.227.1300
Fax: 952.227.1310
Sharmeen Al -Jaff
Senior Center
Senior Planner
Phone: 952.227.1125
Fax: 952.227.1110
SAJ:k
Web Site Enclosure
www.d.chanhassen.rnfl.us
gAplan\2013 planning cases�2013 -02 preserve at rice lake concept pud\lmoblauch letter 5- 17- 13.docx
Chanhassen is a Community for Life - Providing forTodayand Planning forTomorrow
The Preserve at Rice Marsh Lake- Preliminary comments
May 15, 2013
Below are the plan review comments from Alyson Fauske, Assistant City Engineer and WSB & Associates
(City's consultant). Items in bold denote critical information that is required to determine the adequacy
of the preliminary plat request (which could affect the number of lots and layout of the subdivision) and
determine if the proposed development will adversely affect adjacent properties
Stormwater Management and Modeling Comments from WSB (the City's consultant) based on the April
19. 2013 plan submittal and the Mav 19 2013 drainage calculations
1. Additional information is needed to determine the extent that the proposed development is
able to meet City requirements. In particular, the applicant should present the following
information in the stormwater management and construction plans:
a. All Hydrologic Analysis items defined in Article VII- Surface Water Management
Section 19 of the City Code
Sec. 19 -143. - General elements (b) Peak discharge rates.
(1) Peak stormwater discharge rates and storage volumes from any drainage area,
watershed, subwatershed, detention basin, wetland or conveyor shall be consistent with the
values shown in this plan for the 100 -year storm event.
(2) No increase in peak discharge rate may result from the proposed project for the 1- or 2-
year storm, the 10 -year storm and the 100 -year storm event. Variances may be allowed if
computations can be provided which demonstrate no adverse downstream effects will result
from the proposed system. Cumulative storm depths for the required events are:
a. 2 -Year = 2.8 inches.
b. 10 -Year = 4.2 inches.
c. 100 -Year = 6.0 inches.
Sec. 19 -144. - Major facility design elements. (a) Facility design criteria.
(1) For design or modification of stormwater facilities, the following criteria shall be followed:
d. Outlet structure designs shall provide rate controls that limit post - project rates to
not exceed existing rates for 1- or 2 -year, 10 -year, 100 -year events and 100- year /10-
day snowmelt.
(2) The facility design shall provide adequate live storage to provide protection from the
design storm, consistent with lowest building elevation standards. Lowest building floor
elevation is defined as the lowest slab elevation for a home or building, including basements
and crawl spaces. The lowest building floor elevation for structures adjacent to wetlands and
water bodies shall be an elevation three feet above the 100 -year high water level.
b. Storm sewer design calculations
Sec. 18-40. - Same —Data required. Unless waived by the city because of the limited size and
nature of the proposal, the following shall be furnished with a preliminary plat:
(4) Supplementary information:
c. A drainage plan for the area indicating the direction and rate of natural stormwater
runoff and those unaltered areas where stormwater collects and percolates into the
ground. A proposed drainage plan for the developed site indicating the direction and
rate of runoff, the path of all stormwater discharge to the public stormwater
infrastructure and those areas where stormwater will collect and percolate into the
ground shall also be included. Stormwater management shall be consistent with the
city's surface water management plan.
ARTICLE VII. - SURFACE WATER MANAGEMENT Sec. 19 -143. - General
elements.
(a) Hydrologic analysis.
(3) Minor drainage systems (storm sewer) shall be analyzed and
designed to protect for the 10 -year frequency rainfall, and shall be
evaluated for the 100 -year frequency rainfall. Full pipe flow analysis shall
be used unless special conditions can be demonstrated to consider
pressure flow.
c. Groundwater evaluation to verify freeboard requirements /allowable low floor
elevations
Sec. 18 -40. - Same —Data required. Unless waived by the city because of the limited size
and nature of the proposal, the following shall be furnished with a preliminary plat:
(4) Supplementary information:
c. A drainage plan for the area indicating the direction and rate of natural stormwater
runoff and those unaltered areas where stormwater collects and percolates into the
ground. A proposed drainage plan for the developed site indicating the direction and
rate of runoff, the path of all stormwater discharge to the public stormwater
infrastructure and those areas where stormwater will collect and percolate into the
ground shall also be included. Stormwater management shall be consistent with the
city's surface water management plan.
d. A proposed grading plan shown at contour intervals appropriate to the topography
or spot elevations indicating the relationship of proposed changes to existing
topography and remaining features.
2. The preliminary and final grading plans must be 50 scale or larger. The
grading plan must comply with the following design standards as well as the
requirement of chapter 7 of the Chanhassen City Code:
L The lowest floor elevation must be minimum three feet above the
highest known groundwater elevation and must meet the minimum
requirements set forth in subsection 20- 481(e)(1).
d. 10 -day snowmelt analysis
See Code information under la.
e. Stormwater treatment calculations
See Code information under la.
f. Any other data needed to demonstrate that the development is able to meet City
standards
g. Storm Water Pollution Prevention Plan (SWPPP)
h. The proposed design does not account for approximately 22 acres of runoff that drains
through the site from the west. The drainage system design and associated high
water elevations cannot be considered valid if the upstream drainage area is not
included in the analysis. The discharge summary, high water elevations, and other
relevant items in the plans will need to be revised to account for this change.
See Code information under 1a.
2. Stormwater modeling for Pond Pl's outlet control structure should include all of the pipe inlets,
outlets, weir walls, and orifices. Modeling input should be consistent with an outlet control
structure that will provide skimming of floatables as required by the City standards.
3. The outlet pipe from the wetland in the west central portion of the site (Basin W1.1) is a 12"
pipe. Given that the runoff enters this basin from the project site and from offsite areas
through a much larger pipe (21 "), there is concern that the overflow leaving this basin could
be prone to significant erosion during a major rainfall. The applicant should evaluate the need
for a stabilized emergency overflow at this location and /or incorporate an outlet control
structure into the design at this location.
4. The emergency overflow from Wetland W1.4 (the wetland on the western edge of the site)
across the new road (at an approximate elevation of 898) should be evaluated to determine if
it meets the major facility design elements outlined in City code and if adequate freeboard is
provided for existing buildings located upstream.
5. Pond P3 (east pond) modeling input should match the information provided in the plans. The
outlet pipe is modeled as a 15" diameter pipe, while the utility plan shows a 12" pipe. High
water elevations shown in the model are also different than indicated on the plans.
6. The post development drainage areas and curve numbers in the HydroCAD model do not
correspond with the Drainage Area and Curve Number Table. Revise the HydroCAD model
input and table to match.
7. The storm sewer system design must be performed consistent with City code and calculations
should be provided for review.
8. Directly connected impervious areas should be modeled separately rather than included in the
composite Curve Number computation.
Sheet 1: Existing Conditions- City Comments
1. Show ground shots to verify topography
2. Topographic information shall extend 100' beyond the entire property
3. Show the MVEC line as flagged in the field and any easement associated with the utility
Sheet 2: Preliminary Plat- City Comments
1. The front yard drainage and utility easements shall be 15'. This was the concession for reducing
the ROW to 50'.
2. The street width shall be 31' beginning at the western edge of Lot 1, Block 1.
3. A 10' side yard drainage and utility easement is required on each side of the common lot line
between Lots 10 and 11, Block 1 for the proposed storm sewer.
4. A 10' side yard drainage and utility easement is required on each side of the common lot line
between Lots 2 and 3, Block 2.
Sheet 3: Utility Plan- City Comments
1. Show the lowest floor elevations on all lots.
2. Show the drainage and utility easements on the plan.
3. The proposed sanitary sewer connection is shallow: only 3' of cover. The additional topographic
information that the developer will be providing will be used to determine how much additional
cover can be provided over the proposed sanitary sewer connection. Any portion of the sanitary
sewer within the frost zone must be insulated with 4" of closed cell polystyrene, 4' wide
(centered on the pipe).
4. The fully- executed easement agreement, including an executed Mortgage Holder Consent (if
applicable) for the proposed sanitary sewer connection must be submitted with the final plat
submittals.
5. The estimated operating pressure on the 2nd floor of the homes within the development is
between 58 and 60 psi, which is acceptable per the 10 States Standards. The developer may
want to consider installing private boosters within the homes to increase the operating
pressure.
Sheet 3: Utility Plan- WSB Comment
1. Outlet control structure details consistent with City standards should be provided in the plans.
The configuration and elevation of the outlet control device should be consistent with the
information provided in the model.
Sheet 4: Grading Plan- City Comments
1. The existing 894' contour on the east side of the street connection at Tigua Lane does not
appear to tie in to a proposed contour.
2. The existing 896' contour on the west side of the street connection at Tigua Lane (at Tree #101)
does not tie in.
3. There is no cover shown over the proposed pipe within Outlot B that outlets from the low point
of the street (Station 3 +91.59).
4. The distance between the inlet and outlet for the pond within Outlot B shall be increased to
prevent short- circuiting.
S. The pond in Outlot B must be adjusted so that the adjacent retaining wall will not be inundated
during the 100 -year event.
6. The proposed wall from Station 4 +50 to 5 +20 must be engineered.
7. A MNDOT permit is required for the proposed noise wall and the proposed grading within the
MNDOT right of way.
8. Provide a lot bench detail for the proposed home styles
9. Due to the 10' clear zone requirement around fire hydrants, the driveway to lot 11, Block 1 will
be relatively narrow (about 15' wide) at the street.
10. Note the storm sewer elevations on the grading plan.
11. The storm sewer from STMH 1 to the FES to the pond within Outlot A does not have adequate
cover. (see also Sheet 4: Grading Plan- WSB Comments #3)
12. The developer submitted a soils report from January, 2012 that includes 5 soil borings.
Groundwater was not encountered with the borings, however staff remains concerned about
groundwater for the following reasons:
a) The borings were completed during the winter following a below- average precipitation
year.
b) Carver County soils information identifies areas on the parcel where the groundwater
elevation is between 1' and 3' below the ground surface. Unfortunately it appears that
the soil borings were located outside of this area.
According to the developer's soils report the groundwater elevation is likely at the wetland
elevation. The elevation of the western portion of the wetland within Outlot A is 902'. The City
requires 3' separation between the groundwater and the LFE of a home, therefore it appears
that Lot 1, Block 2 shall be a lookout lot, and Lots 2 and 3, Block 2 shall be slab -on -grade homes.
Sheet 4: Grading Plan- WSB Comments
1. Emergency overflow elevations and dimensions must be clearly indicated on the plans so that
these features can be constructed and maintained as designed.
2. The low floor elevations of Lots 2, 3 and 4, Block 2 are not 3' above the high water elevations of
Wetland W3 (896.5') and Pond 3 (896'). The low floor of these buildings should be placed at
least 3' above the high water elevations.
3. The storm pipe in the rear yard of Lot 11, Block 1 does not have adequate cover. The pipe will
be exposed on the west side of Pond 3. Revise the grading plan to provide 2' of ground cover at
a minimum.
4. The plans should account for grading and storm sewer necessary to install the future trail across
Wetland W3 in the southeast corner of the site. It is expected that the trail would be raised
across the wetland to minimize standing water on the trail Alternately, a board walk or similar
feature may be an option to consider. Modeling should also account for this trail crossing.
S. The design criteria for the trail should be determined to ensure that clear zones and grades
adjacent to ponds can accommodate trail design standards.
6. The high water elevation indicated on plans for Wetland W1.1 (890.8') does not correspond to
the high water elevation shown in the modeling. The high water elevation should be updated
and low floor elevations of Block 1 should be revised to conform to City freeboard requirements.
7. The grading plan should account for soil corrections that are necessary to construct
infrastructure.
8. The applicant must document seasonal high groundwater elevations and set building low floor
elevations to meet City freeboard requirements.
9. Berms for major facilities should be lined with clay and anti - seepage collars must be included on
major storm sewer culverts to avoid stormwater migration under the roadway. Details for these
devices should be incorporated into the plans.
Sheet 6: Site Plan
1. The building pad for Lot 3, Block2 must be adjusted so that it doesn't encroach in to the 10' side
yard drainage and utility easement.
Based on the house plan provided Lot 3, Block 1 will not have any additional buildable area once
the home is built.
G: \ENG \PROJECTS \Klingelhutz north of 212 \05 -15 -2013 prelim plan comments.doc