G-2. Lake Susan Preserve Spent Lime Reactor CITY OF MEMORANDUM
CIIAMISSI N TO: Todd Hoffmann,Park and Recreation Director
7700 Market Boulevard
PO Box 147 FROM: Terry Jeffery, Water Resources Coordinator
Chanhassen,MN 55317
DATE• April 28,2015
Administration
Phone 952 2271100 RE: Lake Susan Preserve Spent Lime Reactor
Fax 952 2271110
Building Inspections In 2010, Lake Susan was included on the Clean Water Act, Section 303(d)list as being
Phone 952.2271180 impaired for excess nutnents This listing is based upon the North Central Hardwood Forest
Fax 952 2271190
(NCHF) ecoregion shallow lakes standards
Engineering
Phone 952.2271160 Table 1 Lake Susan Water Quality Sununuty
Fax 952 2271170 Total Phosphorus Chlorophyl-a Secchi Deph(m)
Finance Existing conditions [75 µg/L [37 µg/L (0 7
Phone 952 2271140 NCHF Shallow Lakes [60 tg/L [20 µg/L (1.0
Fax 952 2271110 Standard
Park&Recreation In 2013, Chanhassen and the Riley Purgatory Bluff Creek Watershed Distnct updated the Use
Phone 952 2271120 Attainability Assessment(UAA) for Lake Susan. The UAA modeled the phosphorus budget
Fax 952 2271110 for Lake Susan and calibrated it with the 15 years of data collected by the watershed distract.
Recreation Center
Based upon this model, it was determined that the annual phosphorus load should be reduced
2310 Coulter Boulevard by 185 pounds
Phone 952 2271400 Table 2 Load Allocation Summary foi Lake Susan
Fax 952 2271404
Recommended Load
Source Existing TP Load t Target TP Loading Reduction
Planning& (lbs,'year) eat) (lbs;}ear)
Natural Resources Watershed 424 366 58 14%
Phone 952 2271130 Upstream Lakes 16 16 0 0%
Fax 952 2271110
Atmosphkre 21 21 0 0%
Internal Load 281 154 127 45%
Public Works TOTAL 742 557 185 25%
7901 Park Place 'Fxrstmg load is the average for the years 2004-2005 and 2008-2012
Phone 952 2271300
Fax 952 2271310 The UAA divided the watershed into five areas shown on the attached map; Figure 3-8 from
the UAA. In addition to an in lake, Aluminum-Manganese(Alum)treatment,the UAA
Senior Center identified four potential projects that could be implemented to address the external load to
Phone 952 2271125 Lake Susan with a relatively short horizon These projects are improvements to the pond
Fax 952 2271110
south of Target and north of TH 5, improvements to the pond northeast of Lake Susan in
Website Lake Susan Park, improvements to the pond just south of Lake Dnve West and west of
www ci chanhassen mn us Powers Boulevard and the construction of an iron-filing filter within the wetland in Lake
Susan Park Preserve This last project is the purpose of this memorandum
Chanhassen is a Community for Life-Providing for Today and Planning for Tomorrow
Mr.Todd Hoffman
April 28, 2015
Page 2
The Riley Purgatory Bluff Creek Watershed Distnct has allocated funds to make the improvements within
Lake Susan Park Preserve in 2015 Barr Engineenng,the District Engineer,has worked with the City on
the design of the system to assure that the finished project has the greatest removal efficiency in terms of
dollars spent per pound removed,has the least impact on tree removal and wetland and is in keeping with
the intended use of the preserve. To meet this objective,we evaluated a woodchip bioreactor in two
locations, an iron enhanced sand filter at two locations and a spent lime treatment system The spent lime
was second only to the spent lime system as shown in the UAA but at only a quarter of the cost and a
fraction of the footprint it was determined that the spent lime system made the most sense
Table 3 Summary of Lake Susan projects fi'onl Bari Engineering repoi I prepared foi RPBCWD
Estimated Wetland Upland Engineer's Annual Cost
Conceptual Design Annual TP Impacts Impacts Opinion of per Pound TP
Reduction Probable Cost Removed
(lbs/yr)1 (acre) (acre) (5) (S/lbs TP/yr)2
Conceptual Design $111,000-
Woodchip Bioreactor 32 <�.1 0.2 $150-$240
$194,000
(West Location)
Conceptual Design 2
Woodchip Bioreactor <0.1 03 $107,000- $150-$230
(East Location) $187,000
Conceptual Design 3 22 <0.1 0.2 $194,000 $350-$580
Iron-Enhanced Filtration $339,000
Conceptual Design 4 45 <0.1 0.1 $160,000- $140-$230
Spent-Lime Treatment System $280,000
Conceptual Design 5
4592,000-
Iron-Enhanced Filtration 53 -0.33 --0.13 $1,035.000 $400-$670
(2013 UAA Update Location)
1- Estimated annual total phosphorus(TP)reduction is the removal with the BMP the BMP perfomiance was evaluated over a 10-
year penod(2003-2012)Additional removals in the upstream wetland through settling or infiltration are not included
2- Based on a 30-year period Includes estimated costs for permitting engineering,and construction; and estimated annual
operation and maintenance costs of$1000/year
3- Approximate values based on available information.If this is the selected conceptual design,a wetland delineation is required
during the next design phase to determine the impacted area
The watershed distnct will pay for the cost of constructing the facility and the City will then assume
ownership of the facility and will be responsible for the maintenance of the spent lime system moving
forward. Upon final permit approval from the DNR and approval of the City,the distnct will finalize
plans and solicit bids. The city and distnct will enter into an agreement stipulating responsibilities and
the distnct will solicit bids for construction There will be some latitude given to the contractor regarding
when the work is to be performed although it is anticipated that it will be late fall or early winter and the
schedule must be communicated clearly to the city for approval The contractor is to keep the trail open
throughout the project unless they receive approval from the city otherwise The contractor will be
responsible for repainng the trail if it is shown that the work resulted in damage to the trail Grass pavers
will be used to provide access to the facility for maintenance while allowing for establishment of
vegetation consistent with the area A landscaping plan is being prepared that will provide screening of
the system and a cover has been designed to make the facility safe while allowing access for maintenance
The goal is to have a finished project that blends with the surroundings that improves the water quality of
Lake Susan—ultimately resulting in it being removed from the 3O3D list of impaired waters
Atachments
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