5.1. SR 03-14-2011ITEM 5. I .
ver
TO: City Council
MEMORANDUM
FROM: Rebecca Haug, Environmental Administrator
DATE: March 14, 201 I
SUBJECT: 2010 NPDES Permit Update/Annual Meeting
^ SWCD Pond Update
The City of Elk River was required by the Minnesota Pollution Control Agency (MPCA) to apply for the
National Pollutant Discharge Elimination System General Storm Water (NPDES) Permit in 2003. This
permit requires the city to hold annual public meetings regarding the Best Management Practices and
measurable goals achieved for the year. The permit identifies six goals. They are:
1. Public Education and Outreach
2. Public Participation/Involvement '
3. Illicit Discharge Detection and Elimination
4. Construction Site Runoff Control
5. Post-construction storm water management in new development and redevelopment
6. Pollution Prevention/Good Housekeeping
In 2010, the city was able to meet goals in each of the six measures. Following are some examples:
^ Articles in the "Current" regarding storm drain stenciling to educate the public of where the water
ends up that is put down the storm drain and two articles informing residents about the Elk River
Watershed and the new wetland rules
^ Staff presented to Elk River students about the 3R's of water (Reduce, Reuse, Recycle) where
stormwater runoff was discussed
^ Website link to storm water related information
^ Continuance of licensing lawn care professionals
^ Inspections of building sites to ensure proper erosion control measures are being taken
^ Inspections of storm drains (20% required each year)
^ Environmental administrator sits on the Minnesota Stormwater Steering Committee Board through
the League of MN Cities
^ Staff training by Bonestroo in May
^ Stormwater BMP installed at corner of Main Street and Highway 169 through the partnership with the
Sherburne Soil & Water Conservation District (SWCD)
^ Staff has studied 10 +/- areas for possible installation of additional BMP's
In 2011, staff will continue to partner with the SWCD on stormwater measures. Staff will continue to educate
the public about sormwater issues.
Attachments
Elk River Subwatershed ERO4W: stormwater Retrofit Assessment (Assessment Area and Executive
Summary)
SWCD/Elk River Chamber of Commerce Rain Garden Proposal
Elk River Subwatershed ER04W: Stormwater Retrofit Assessment Page 1
Assessment Area
Elk River Subwatershed ER04W: stormwater Retrofit Assessment Page 2
Executive Summary
Subwatershed ER04 as delineated in Elk River's MS4 permit Non-degradation plan was selected
by the City for retrofit assessment. Modeling results for ER04 as reported in the Non-
degradation plan showed relatively high phosphorus and total suspended solids loading to the
Mississippi River, a priority surface water resource.
For practical reasons the City and SWCD decided to narrow the scope of this assessment. The
subwatershed was subdivided to the areas east and west of U.S. Hwy 169. These two areas are
not hydraulically connected with the exception of periods of extremely high precipitation. The
subwatershed west of U.S. Hwy 169, ER04W, is the focus of this assessment.
Based on existing stormwater system maps and City staff knowledge of the system, ER04W was
divided into 12 catchments. The 12 catchments were subdivided into a total of 30 sub-
catchments based on significant differences in land use or drainage to existing stormwater
treatment BMPs. During desktop review and field reconnaissance we identified additional un-
mapped stormwater system pipes and re-drew some flow boundaries. After re-evaluating the
data, we determined that for modeling, the 30 sub-catchments should be re-grouped into 8
catchments based on common outflow points. When present, an existing treatment basin was
used as the common outflow point. For this report, "catchment" will refer to one of these 8
catchments.
Five sub-catchments were not modeled or assessed for treatment options for the following
reasons. Two drained to land locked wetlands that were not connected to the stormwater
system (7B and 8A). One consists of low density development and steep topography not well
suited to installing BMPs (1J). One consisted of a high percentage of open space and modeling
showed that it exports a relatively small amount of phosphorus and TSS (2B). One industrial
area has been tentatively identified for redevelopment (5B).
Catchments ER04W6, ER04W7 were modeled but not assessed for treatment options because
modeling showed that the existing treatment ponds and wetlands were capable of effectively
treating runoff from these catchments.
List of Catchments and Sub-catchments
Catchment Sub-catchments
ER04W1 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H, 11, 1J
ER04W2 2A, 2B
ER04W3 3A, 3B, 3C, 3D, 3E
ER04W4 4A, 4B, 4C
ER04W5 5A, 5B
ER04W6 6A, 6B, 6C, 6D, 6E
ER04W7 7A, 7B
ER04W8 8A
Elk River Subwatershed ER04W: Stormwater Retrofit Assessment Page 3
The following table ranks retrofit projects identified in this report. In ranking projects, a number of
factors were considered including the level of treatment, the cost per pound of phosphorus treated and
the projected feasibility of doing the project. Feasibility included a subjective estimate of the level of
participation of private land owners and the estimated total cost of the project. The percent TP
reduction reflects a percent reduction for the catchment. Because catchment areas range from 13 to
238 acres, the percent TP reduction is not useful for comparing the level of treatment between
catchments. For that reason, the Ibs/yr of TP reduced was used to compare water quality benefits
between projects. Not all treatment options listed in the catchment profiles are ranked. The treatment
options selected for ranking were based on site constraints for sites identified, an estimate of public
participation and also total project cost.
Catchment
or Pond ID Retro
Type Qty of
100 ft3
BMPs TP
Reduction
(%) TP
Reduction
(Ib/yr) Volume
Reduction
(ac-ft/yr) Overall Est.
Cost' O&M
Term
(years) Total Est.
Term
Cost/Ib-
TP/yr2
ER04~'V1' PM NA 1% 1.8 0.0 $2,250 30 $42
ER04W2 RG 25.3 30% 13.4 12.5 $33,084 30 $224
ER04W4 RG 17.8 1590 8.2 7.8 $24,173 30' $:261.
ER04W3 RG 15.6 16% 7.0 6.3 $21,474 30 $269
ER04W5 RG 2.1.9 ~ 30% 6.2 4.8 $29,013:.: 30 $421
ER04W5 RG,
IF 28.2 36% 7.5 5.8 $48,534 30 $595
ER04W1" FtG 24.4 2% ' 3.2 7.5 $32,009 30 .$905
ER04W1 PM 4,086 4% 10.9 0.0 $211,638 30 $931
RG= Rain Gardens (eioretention, infiltration and/or filtration)
IF =Underground filter and infiltration (tree planter infiltration boxes)
F=Filtration (sand curtain, surface sand filter, sump, etc)
IR =Impervious (cover] Reduction
PM = Pond Modification (increased area/depth, additional cells, forebay, and/or outlet
modification)
PS =Permeable Surface (infiltration and/or filtration)
VS =Vegetated Swale (wet or dry)
WD = New wet] Detention or Wetland creation
lEstimated overall costs include design, contracted soil core sampling, materials, contracted labor,
promotion and administrative costs (including outreach, education, contracts, grants, etc), pre-
construction meetings and installation oversight.
ZThe total estimated term cost/Ib-TP/yr includes overall cost plus a 30 years of operation and
maintenance cost divided by 30 years of treatment.
Sherburne Soil and Water Conservation District
Elk River Chamber of Commerce Rain Garden Proposal
Location: Chamber of Commerce on U.S. Hwy 10
Funding: State of Minnesota Clean Water Fund Grant 75%
City of Elk River 25%
Budget:
Total cost estimate: $4,600
Grant Funds: $3,450
City of Elk River: $1,150 (cash or in-kind)
A raingarden is a landscaped garden in a shallow depression that
receives rainwater runoff from nearby impervious surfaces such
as roofs, parking lots or streets. The purpose of a raingarden is to
reduce peak runoff flows, increase groundwater recharge and
improve water quality in our lakes, streams and wetlands.
Rain Gardens for Water Quality
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OF COMMER BUILDING
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PARKING AREA
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US HIGHWAY 10
GREAT RIVER ENERGY AR
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BIOINFILTRATtONRREA: POLLUTION REDUCTION MODELING (WinSLAMM): VEGETATION CONSIDERATIONS:
DRAINAGE AREA - 46,610 (519'o IMPERVIOUS)
BASIN AREA - 1000 SOET TSS (Ib/yr): - 589.00 (90% REDUCTION) With relatively shallow slopes of 15%, the pretreatment and
MAX PONDING DEPTH -.33 FT TP (Ib/yr): -,93 (88% REDUCTION) bioinfiltration areas can be vegetated with turf grass (or use
SIDE SLOPE AVERAGE- 15°k a no-mow fescue blend) or be planted predominately with
PRETREATMENT BASIN AREA - 27 SOFT (TURF GRASS) a native plant palette suitable for both drought and shallow
OVERFLOW - 6 FT WIDE (REINFORCED) ponding conditions. The pretreatment area should only be
EXCAVATED DEPTH -.S FT planted with turf grass to allow easier removal of sediment
SOIL AMENDM ENTS - .17 FT (COMPOST) buildup.
r
0 20 40 Feet
PROPERTY LINE
-;cx
CURB -CUT BIOINFILTRATION AREA:
CONCEPT DESIGN
Client: Sherburne SWCD /Elk River
Chamber of Commerce
509 US Highway 10 NW
Elk River, MN
District: Sherburne County Soil and Water
Conservation District
Date: 12.30.11
Designer: Sherburne County SWCD in
association with the Metro
Conservation Districts
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