2. Kerber Park Water Quality Treatment Project 08-01
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
;1
MEMORANDUM
TO:
Todd Hoffman, Parks Director
Terry Jeffery, Water Resources coordin~
March 18,2008
FROM:
DATE:
SUBJ:
Kerber Park Water Quality Treatment - Project No. 08-01
REQUESTED ACTION
The Engineering Dept. is requesting direction from the Park & Rec Commission on how
to proceed with the water quality project within Kerber Pond Park as an alternate bid
item to the Laredo Drive Street Reconstruction Project No. 08-01.
BACKGROUND
Laredo Drive is scheduled to undergo reconstruction during the summer of 2008.
Currently, the stormwater runoff from the elementary school runs into Lotus Lake
without any treatment, rate control or volume reduction. Lotus Lake is listed as
impaired for nutrients and Mercury. Under Section 303d of the Clean Water Act, any
permitted dischargers to the lake are required to make efforts to improve the water
quality of the lake to a non-impaired state. The 998 acre Lotus Lake watershed is fully
developed with limited opportunities for stormwater treatment. Most of the
development within the Lotus Lake watershed occurred prior to 1988 when the National
Urban Runoff Program (NURP) recommendations went into effect.
Additionally, the City is a Permittee under the National Pollution Discharge Elimination
System (NPDES) and is part of the select Municipal Separate Storm Sewer System (MS4)
cities required to develop and implement a Nondegradation plan. The City is known to
not meet the Nondegradation requirements for stormwater volume and needs to look
for methods to reduce stormwater runoff through infiltration of stormwater into the
ground and interception of rainwater before it reaches the ground.
The current design for the Laredo Drive reconstruction calls for the installation of three
environmental manholes along the storm sewer route. These structures will reduce the
total suspended solids delivered to Lotus Lake. These structures only act to capture
large particulate matter and do not sequester any of the nutrients which are delivered
to Lotus Lake. The City, in cooperation with the Lotus lake Watershed Quality
Organization, the Metro SWCD, and the Riley-Purgatory-Bluff Creek Watershed District,
began looking for alternative locations for stormwater treatment.
Because of the narrow right-of-ways, the minimal building setbacks, the placement of
utilities and other considerations, it was determined that there are minimal
opportunities for retrofitting storrnwater features within the corridor. It was
determined that as much as 9.65 acres of watershed could be diverted to the trail
heading to Kerber Park Pond from Laredo Drive to treat a significant amount of
stormwater prior to discharging into Kerber Pond and ultimately into Lotus Lake.
The City 01 Chanhassen . A growing community with clean lakes, quality schools, a channing downtown, thriving businesses, winding trails, and beautitul parks. A great place to live, work, and play.
Todd Hoffman
March 18, 2008
Kerber Park Water Quality Treatment
Page 2
Staff will be present at the March 25, 2008 meeting to discuss in more detail and to
answer any specific questions you may have.
OPTION #1 - PREFERRED PLAN
The proposed water quality treatment features in Option #1 involve the construction of
two stormwater treatment features within the trail corridor and a stormwater pond to
be constructed below the hill adjacent to Kerber Pond. The linear features adjacent to
the trail will be constructed with a porous growing medium to promote infiltration, a
granular bedding of washed aggregate below this for storage of stormwater and an
underdrain to ensure that these features are drained within 48 hours and, in the case of
feature #2, have no more than 18 inches of inundation. This design will also reduce
stormwater volume by promoting infiltration of stormwater into the soils.
Placement of the water quality features within the trail corridor will require the
realignment of the trail. Where the trail originates at Laredo Drive, the trail will need to
be moved nearly to the eastern property line before it meanders back to the west. (We
are currently working to redesign the stormwater profile to decrease the pond size and
lessen the need to realign the trail.)
The alignment after the meander to the west will be approximately six feet closer to the
western property line than the current alignment but will still be approximately 10 to 12
feet away from the western property line. This alignment will elevate the trail by an
average of 2 feet from its current profile. This should result in a drier trail as it has been
prone to inundation in the past.
The construction of these features will require the removal of 56 trees and or shrubs
along the trail. Where possible to do so, some of these may be spaded to an alternate
location. These stems will be replaced with native trees and shrubs which will be
planted between the property lines and the water features to ensure the trail is well
screened and privacy is maintained. In addition, the features themselves will be
landscaped to provide for aesthetics as well as water quality and rate control.
Water will be conveyed from these linear features and from a portion of Laredo Drive to
a stormwater pond located below the hill and adjacent to Kerber Pond. This pond will
provide additional rate control and water quality treatment before the water is
discharged into Kerber Pond.
The construction of this pond will result in the removal of just under 0.9 acres of trees.
These trees are predominately box elder with a few American elm and cottonwood
scattered throughout. There are numerous snags within the area and several of the
elms show signs of Dutch Elm Disease in the form of egg galleries for the American elm
beetle. The plan would involve reforesting 0.6 acres with red oak, burr oak, red maple,
and basswood. The areas to be planted include those portions graded for the pond
which are outside of the normal water level as well as those areas within the park which
were previously cleared by adjacent land owners. Some silver maple and black willow
G:\ENG\PUBLlC'-2008 Projects\08-012008 Street Improvements\THoffman_32508Parks_Kerber Park Pond.doc
Todd Hoffman
March 18, 2008
Kerber Park Water Quality Treatment
Page 3
may be planted immediately adjacent to the normal water level of the pond as these
species are more tolerant of periodic inundation.
OPTION #2
In Option #2, the linear water quality features adjacent to the trail would be eliminated
and only the pond adjacent to Kerber Pond would be constructed. This plan would not
offer as much water quality benefit as would Option #1 but would not require any
realignment of the trail and tree removal adjacent to the trail would be limited only to
that required for the placement of the storm
sewer conveyance system. The creation of the pond would still require the removal of
0.9 acres of trees. The pond may be increased in size by extending to the northeast
which would result in some additional tree removal. Total tree removal under this
design would increase to approximately 1.0 acres. The size of the watershed treated by
this system would be significantly less than what could be treated in Option #1. The
hydrologic model has not yet been finished but it is anticipated that as much as 1/3 of
the watershed would need to be diverted north along Laredo Drive.
RECOMMENDATION
Staff is seeking guidance from the Park & Rec Commission as to which option should be
advanced to the City Council for their review. Given the need for demonstration project
showing alternate water treatment, the need for maximizing water quality treatment in
the Lotus Lake Watershed and the need for reducing stormwater volume to meet the
City's MS4 Nondegradation requirements, Option #1 is the preferred option of the
Water Resources Department. Either option of the Kerber Pond Water Quality project
would be an alternate bid item within the Laredo Drive reconstruction Project No. 08-
01.
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