"%
NONPOINT SOIRCf SICCESS STOIY
Coordinated Efforts Reduce Polluted Stormwater Runoff, Improving
Water Quality in Lower Twin and Ryan Lakes
Waterbodies Improved
Nutrients in stormwater runoff led to eutrophic conditions
in Lower Twin Lake and Ryan Lake in the Minneapolis
metropolitan area. Because of these conditions, Minnesota added both lakes to its 2002 Clean
Water Act (CWA) section 303(d) list of impaired waters for failing to attain their aquatic recreation
designated uses. Implementing best management practices (BMPs) throughout the watershed
decreased nutrient runoff and improved water quality in the lakes, allowing Minnesota to remove
them from its impaired waters list in 2014.
Problem
Lower Twin Lake and Ryan Lake are in the Shingle
Creek watershed in the northwestern Twin Cities
metropolitan area in Minnesota (Figure 1). The lakes
are part of the Twin Lake chain of lakes, which includes
Upper Twin, Middle Twin, Lower Twin and Ryan
lakes. The chain of lakes flows into Shingle Creek and
ultimately the Mississippi River. The Shingle Creek
Watershed Management Commission (SCWMC) is the
local entity responsible for protecting the watershed's
lakes, streams and wetlands.
The SCWMC contains nine cities, 16 lakes, seven
streams and numerous wetlands. The majority of the
Shingle Creek watershed is developed, with industrial,
commercial and residential land uses present. The
Lower Twin and Ryan lake subwatersheds are fully
developed with single and multi-family residential land
uses. Together, the lakes drain more than 8 square miles
of land. The lakes are regularly used for recreational
activities such as canoeing and fishing.
Minnesota water quality standards for aquatic life and
recreation for shallow lakes in the summertime (June-
September) require that (1) the average total phospho-
rus (TP) concentrations are equal to or less than (<)
60 micrograms per liter (u.g/L), (2) chlorophyll-o (chl-o)
concentrations are < 20 u.g/L, and (3) Secchi disc (SD)
transparency is at least 1.0 meter (3.3 feet). For deep
lakes, the standards are more stringent, requiring
that the summertime average TP concentrations are
< 40 u.g/L, chl-o concentration are < 14 u.g/L, and SD
transparency is at least 1.4 meters (4.6 feet).
B
L
Lower Twin and Ryan Lakes
Shingle Creek Watershed
Data sources include *305(b) assessed lakes s
1 Miles
He, Watershedboundaiy •
"^ - I dataset, US. Census Bureau state map, and USGS Topo Basemap.
Figure 1. Lower Twin and Ryan lakes are in the Shingle
Creek watershed in eastern Minnesota.
Historical water quality trends indicated that the
lakes exceeded Minnesota Pollution Control Agency's
(MPCA's) water quality standards until the 2000s for
shallow lakes (i.e., Lower Twin Lake) and deep lakes
(i.e., Ryan Lake). On the basis of these data, MPCA
added the two lakes to the state's 2002 CWA section
303(d) list of impaired waters for excess nutrients/
eutrophication. In 2007 MPCA finalized a phosphorus
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120
100
Lower Twin Lake Water Quality (2000-2012)
•1
,1
O t— r*j
• Total Phosphorus
I Chlorophyll-a
I Secchi Depth
Figure 2. Data show that Lower Twin Lake has met all three
shallow-lake water quality standards since 2010.
total maximum daily load (TMDL) for the lakes and
developed a TMDL implementation plan. The TMDLs
indicated that to attain standards, phosphorus loads
must be reduced by zero to 65 percent in Lower Twin
Lake and by zero to 54 percent in Ryan Lake.
Project Highlights
Watershed stakeholders have cooperated on numer-
ous projects to reduce nutrients in runoff. In the
Lower Twin Lake watershed, the city of Robbinsdale
increased street sweeping to four times per year and
installed several rain gardens, stormwater ponds and
grit chambers beginning in 2004. Also since 2004,
Hennepin County and the Minnesota Department of
Transportation installed numerous BMPs as part of
highway reconstruction projects. In 2011 the city of
New Hope expanded a stormwater pond to maximize
the removal of sediment and phosphorus from runoff.
Similar efforts have occurred in the Ryan Lake
watershed. Since 2004, the city of Brooklyn Center
has installed five sump manholes that remove sus-
pended sediment from runoff. In 2004 the Victory
Neighborhood Association planted more than
6,000 native plants on an eroding shoreline, and then
partnered with the city of Minneapolis in 2013 to
install 15 rain gardens.
Both lakes have benefited from the ongoing efforts
(since 2004) of the SCWMC and local partners to reduce
phosphorus and improve water quality in upstream
impaired lakes. In 2013 the SCWMC updated the Shingle
Creek Watershed Management Plan and development
rules to require higher stormwater infiltration capacity.
Ryan Lake Water Quality (2000-2012)
140
120
100
80
60
40
20
'1
388
• Total Phosphorus
88888
I Chlorophyll-a • Secchi Depth
Figure 3. Data show that Ryan Lake has met all three deep-
lake water quality standards since 2008.
Results
Recent monitoring data indicate that water quality
has improved in both lakes: TP and Chl-o concentra-
tions have decreased, while SD transparencies (mean
June-September) have increased. Lower Twin Lake has
consistently met shallow-lake water quality standards
since 2010 (Figure 2). Ryan Lake has met deep-lake
water quality standards since 2008 (Figure 3). As a
result of these improvements, MPCA removed Lower
Twin Lake (MN27-0042-03; 30 acres) and Ryan Lake
(MN27-0058-00; 15 acres) from the list of impaired
waters in 2014.
Partners and Funding
The restoration of Lower Twin and Ryan lakes was
supported by many partners and funding sources.
Specific partners included SCWMC, the Minnesota
Board of Water and Soil Resources, the National Park
Service, Minnesota Department of Transportation,
Minneapolis' Victory Neighborhood Association, the
nonprofit Metro Blooms, Hennepin County, and the
cities of New Hope, Minneapolis, Robbinsdale and
Brooklyn Center.
Project funding included $6,200 in Hennepin County
Natural Resources Incentives for Critical Habitat funds,
$52,908 in SCWMC Capital Improvement Program
funds, $160,000 in Clean Water Legacy Grant funds,
$1,762 in funds from the city of New Hope, and $3,600
in National Park Service Challenge Cost Share funds.
SCWMC served as the lead on these projects and the
project manager was funded using CWA section 319
match funds.
I
9
U.S. Environmental Protection Agency
Office of Water
Washington, DC
EPA841-F-16-001E
February 2016
For additional information contact:
Judie Anderson
Administrator, SCWMC
judie@jass.biz • 763-553-1144
Rachel Olmanson
Watershed Project Manager, MPCA
rachel.olmanson@state.mn.us • 651-757-2473
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