2007-05-03 Engineering Review Response LetterMarch 5, 2007
Mr. Alan Brixius
. Northwest Associated Consultants
4800 Olson Memorial Highway, Suite 202
Golden Valley, MN 55422
Westwood
Re: Albertville Market Place
Engineering Review
Response Letter
Westwood Project No. 20051047.01
Dear Alan:
Westwood Professional Services
7699 Anagram Drive
Eden Prairie, MN 55344
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www.westwoodps.com
This letter is in response to the City of Albertville Engineering Review
Memorandum, prepared by Lani Leichty of Bolton & Menk, Inc., on September 7,
2006 for the Albertville Market Place project.
A summary of the issues identified are listed below. Responses to specific items are
shown in italic font. The responses noted below were referenced or included in the
revised Civil Site Development Plans plan, dated 3/01/07.
1) It appears that the H/C stalls will have a difficult time meeting the 2% minimum
grades for those stalls in Lot 1.
A maximum of 2% slope is shown for all stalls along the front of Retail A and B.
2) Show proposed ditch improvements and culverts for drainage that will be directed
toward the east on the south side of County Road 37.
The ditch area on the south side of County Road 37 will drain east to a proposed
storm sewer pipe, and be directed south to the existing wetland, as shown on
Sheets S (Grading, Drainage and Erosion Control Plan) and 6 (Utility Plan).
3) Ponding will not be allowed in the County right-of--way.
The ditch area will be graded to provided positive drainage to the eas as noted in
comment 2.
4) Provide a pair of catch basins on the south side of the radius PC on Street A to
catch runoff and route it to Pond 1 via storm sewer.
Catch basins were added to Street A south of the proposed Bank exist drive.
... TWIN CITIES/METRO ST. CLOUD BRAINERD
March 5, 2007
Page 2
5) Design the stormwater pond to NURP standards for dead storage, which is a 2.5"
T rainfall over the entire site that drains to the pond. Provide a copy of the
calculations.
The stormwater Swale and pond system is designed to provide dead storage
~t~stwaod equivalent to a 2.5 "rainfall over the site development area. Refer to the Storm
Water Management Plan for Albertville Market Place, dated February 27, 2007.
6) Provide calculations showing how the time-of-concentrations were calculated in
the proposed condition, or use the Lag/CN Method to be consistent with the
existing condition model.
A minimum of IO minute time-of-concentration was used for proposed conditions.
7) Show the EOF elevation for Pond 1 on the grading plan.
The EOF elevation for Pond 1 is shown on Sheet 5, Grading, Drainage and
Erosion Control Plan.
8) Indicate on plans the projected overland flow path for all of the infiltration basins.
Filtration Basin EOF elevation and direction are shown on Sheet S, Grading,
Drainage and Erosion Control Plan.
9) Provide and detail a stabilized emergency overflow for the stormwater pond. The
overflow should be sized to convey to 100-yr flow rate at a depth no greater than
6" with a minimum of 6" of freeboard above emergency overflow water surface.
The top berm should be a minimum 1-ft above the 100-yr HWL.
Information is shown on Sheet S, Grading, Drainage and Erosion Control Plan.
The top of Berm is 1 ft- above the Pond EOF.
10) The post-development drainage map symbols do not match the area symbols in
the calculations. Correct the map so that they match each other.
The post-development drainage area labels (symbols) are consistent with the
HydroCAD model.
11) The HWL for the Swale and Pond 1 exceeds the top contour for these basins.
Adjust so that the 100-yr elevation is below the top contour (see #12).
Pond HWL is 952.1, Top of Berm elevation is 953.1 as noted on Sheet S, Grading,
Drainage and Erosion Control Plan.
12) The skimmer structure detail for Pond 1 does not match what is shown in the
HydroCad calculations. Revise the detail accordingly.
Skimmer structure detail was revised to be consistent with the HydorCAD
calculation.
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March 5, 2007
Page 3
13)Use abroad-crested weir as an overflow for Pond 4P: FB-4. The calculations
T show the 100-yr HWL reaching 958.8, which isn't possible.
Pond 4: FB-4 is renamed to Basin 1. Peak elevation calculated at 956.1 S.
~~~`""""~ 14) Provide the required wetland buffer signage per the City ordinance.
Wetland buffer signage will be provided per the City ordinance.
15) Provide the city with a copy of the Application for General Stormwater Permit for
Construction Activity (MN R100001) and a copy of the check for the required
application fee.
Application for the NPDES, General Stormwater Permit for Construction Activity
will be submitted a minimum of 7 days prior to commencing construction
activities on site. The contractor is yet to be determined.
16) Provide conveyance calculations, utilizing the rational method (CIA), for the
Stormwater conveyance piping system. The conveyance piping system should be
sized for the 10-yr, 24-hr event producing 4.1" of rainfall. Include subcatchment
basin areas, pipe segment velocities, individual pipe segment and total
subcatchment time of concentration, pipe capacity and max flow for given
conditions, structure size and casting information.
A copy of the Storm Sewer Design Calculation worksheet is attached for your
review.
Please contact me if you have any questions.
Sincerely,
WESTWOOD PROFESSIONAL SERVICES
~ ,~
~~~~
Shari Ahrens, P.E.
Project Engineer
Cc: City of Albertville
Phil Morris
George Daniels, Boulder Properties, Inc.
Linda Fisher, Larkin Hoffinan Daly & Lindgren Ltd.
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