1996-10-23 Engineering EAW Reviewjohn Oliver ~r Associates, Inc.
Civil Engineering
Land Surveying 580 Dodge Avenue, Elk River, MN 55330
Land Planning (612) 441-2072 • Fox: 441-5665
October 23, 1996
Mr. Garrison Hale
City Administrator
City of Albertville
P.O. Box 4
5475 Main Avenue NE
Albertville, MN 55301
RE: MINNEAPOLIS FACTORY SHOPPES
Environmental Assessment Worksheet
Dear Mr. Hale:
This letter responds to the EAW comments dated September 19, 1996, by Lawrence Koshak of Hakanson
Anderson Associates, Inc. representing the City d'f Otsego.
Item 12
The north-south ditch which flows south into the north side of the Factory Shoppes site will be replaced
by a twin 36" pipe system to convey water through the site. Prior to entering the site this ditch flows
through a system of wetlands. We have constructed a TR20 model to represent the existing and proposed
conditions utilizing the wetlands as reservoirs. The pipe system proposed through the site will
accommodate the flow from the existing 100 year, 24 hour event, and does not connect with the proposed
ponds around Town Square.
The ditch entering the Factory Shoppes site from the west flows through existing wetlands, which are
proposed to be enlarged as part of the wetlands mitigation. The twin 3fi" pipe outlet for this ditch system,
located in the southwest corner of the Factory Shopper parking lot, is sized to allow the existing
downstream wetland and the existing wetlands proposed mitigation areas to the west of the site, to work
together for storm water storage.
The proposed ponds around Town Square are designed to control the rate of discharge from the Factory
Shoppes site to the 100 year, 24 hour historic event. All rates of discharge are in accordance with the
ultimate drainage plan for the Otsego Creek Watershed.
The existing culvert under County Road 19 is a 30 inch RCP culvert. This culvert controls the storm
water flows to School Lake, for the entire tributary area west of County Road ] 9, including the Factory
Shoppes site. No change is proposed for this culvert.
The net effect of the proposed ponds and pipes is that there is no increase in the existing 100 year 24 hour
event storm realized at the upstream end of the existing 30 inch culvert under County Road 19, as defined
by the ultimate drainage plan for Otsego Creek.
Page 2
October 23, 1996
Mr. Garrison Hale
Item 14
The project will be available for review by the joint Otsego Creek Authority. A formal review and
approval process currently does not exist for this watershed and a permit is not required.
Item 18
The proposed onsite water quality ponds adjacent to Town Square were designed in accordance with the
guidelines in Section 4.1 of "Protecting Water Quality In Urban Areas Best Management Practices for
Minnesota", by the Minnesota Pollution Control Agency Division of Water Quality. The ponds should
provide the following water treatment as given iu Figure 4.1-1 of the Best Management Practices Manual:
Target Pollutant Percent Removal
Suspended Solids 85-95
Oxygen Demand 50-90
Total Phosphorous 40-70
Dissolved Phosphorous 40-70
Nitrate Nitrogen 60-80
Kjeldaal Nitrogen. 20-40
Copper 60-80
Lead 80-95
Zinc 40-80
The runoff discharged from the water quality ponds will be additionally treated by the existing wetland
south. of the Factory Shoppes development. Wetland treatment in Section 4.5 states "wetland treatment
is very effective for removing sediment and pollutants associated with it (such as trace metals, nutrients,
and hydrocarbons), oxygen demanding substances, and bacteria from urban runoff'. The runoff from the
site will therefore be treated twice before reaching School Lake.
The guidelines set forth in the Best Management Practices Manual represents the current standards for
storm water quality treatment in the Twin City Metropolitan area. There are no special water quality
issues associated with the proposed Factory Shoppes development that would not be addressed by the Best
Management Practices Manual requirements.
S, INC.
File: 7253.10-OS
Sincerely,