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NONPOINT SOURCE SUCCESS STORY
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Planning and Partnerships Improve Water Quality in McCoy Creek
Waterbody Improved
As a result of impacts from urban arid agricultural runoff, McCoy
Creek was listed on Missouri's Clean Water Act (CWA) section
303(d) list of impaired waters for low dissolved oxygen (DO) in 2012. To address the impairment and
concerns about future urban growth, partners completed a nine-element watershed-based plan
(WBP) for the Dry Branch Creek watershed (a subwatershed of McCoy Creek) and implemented
green infrastructure projects. Best management practices (BMPs) were also applied in agricultural
areas within the watershed. Water quality data collected in 2016 showed that all DO concentrations
met the state's water quality standard (WQS), resulting in a segment of McCoy Creek being removed
from the CWA section 303(d) in 2018.
Problem
McCoy Creek, in northwestern St. Charles County,
is a tributary of the Cuivre River. The upper reaches
of McCoy Creek drain the unincorporated rural and
agricultural areas of St. Charles County, while the
middle and lower reaches drain portions of the cities
of Flint Hill (to the north) and Wentzville (to the south).
The three main tributaries of McCoy Creek receive
runoff from agricultural and forested areas, as well as
the urbanized areas of Wentzville, Interstate 70, and
State Highway 40/61 (Figure 1).
In 2012, a 1.9-mile segment of McCoy Creek (WBID
0214) was listed on Missouri's CWA section 303(d) list
of impaired waters for low DO due to unknown rea-
sons. As the population of Wentzville grew from 6,896
in 2000 to 29,070 in 2010, a greater percentage of the
rural landscape changed to urban to accommodate
the growing numbers. The percentage of impervious
surfaces, stream flow and its erosive power, and the
amount of nonpoint source (NPS) pollution trans-
ported into the surrounding waterways increased.
Increases in stream temperatures, excessive algal
growth, and sediment loads commonly contribute to
low DO and negatively impact aquatic life.
Story Highlights
The City of Wentzville completed a nine-element WBP
for the Dry Branch Creek watershed (a subwatershed
of McCoy Creek) in 2013 and implemented a variety of
retrofit enhancements between 2011 and 2015. The
Figure 1. McCoy Creek is in eastern Missouri.
St. Charles Soil and Water Conservation District (SWCD)
provided cost-share dollars to implement cover crops on
107 acres of agricultural area within the McCoy Creek
watershed to reduce soil erosion, increase water infiltra-
tion, and improve water quality and soil health. Retrofits
were completed at existing urban retention basins on
commercial properties and in residential subdivisions in
partnership with property owners. A number of green
infrastructure BMPs were constructed in the McCoy
Creek watershed. A car wash detention basin was
expanded and reconfigured as a rain garden to filter
stormwater runoff. Rain gardens and native shoreline
plantings were added to a subdivision's common ground
area to pretreat high-temperature runoff from 20 acres
(Figure 2). A series of green infrastructure pilot projects
Lincoln
McCoy Creek Watershed
Location of the
McCoy Creek
Watershed
Legend
® MoDNR Water Quality Monitoring Sites selection
2018 303(d) Delisted Segment
McCoy Creek Watershed
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fife
Figure 2. Native plants were planted along the
shoreline of a basin in the Huntsdale Subdivision.
(e.g., vegetated bioswales, pervious pavements, ripar-
ian areas, and native plantings) were implemented at
a city park. A forebay was constructed at the inlet of a
regional detention lake to capture and trap sediment and
nutrients from a 472-acre drainage area. Partners also
installed parking lot bioswales; athletic field biofilters/rain
gardens; three different types of pervious pavements;
wetlands; riparian areas; and over 2,500 trees, shrubs
and native plants. Additionally, educational shelters
and interpretive signage were constructed throughout
the park and along an educational trail system.
confluence of Dry Branch Creek to bracket inputs
related to NPS pollution and the wastewater treatment
plant (WWTP). Low DO levels were noted both above
the WWTP (site 1, NPS inputs) and below the WWTP
(sites 2 and 3, WWTP input): a total of 46 percent of
the DO levels exceeded the state WQS. The sampling
event was repeated in 2016. The results showed
improved conditions.
The water quality improvements upstream of the
WWTP (site 1) can be attributed to the implementa-
tion of on-the-ground practices to address NPS runoff
through the 319 NPS project efforts, the City of
Wentzvilie's Clear Stormwater and Green Parks initia-
tive and community outreach efforts, implementation
of a countywide stream buffer ordinance, and cost-
share practices implemented through the St. Charies
SWCD. Water quality improvements at site 2 and 3 can
be contributed to upgrades occurring at the WWTP.
From the 2016 sampling event, all the DO data met or
exceeded state water quality criteria (Figure 3).
Partners and Funding
Results
In 2012, 15 water quality monitoring events occurred
on McCoy Creek at three locations twice a day during
the early morning and late afternoon hours. The sites
were located on McCoy Creek, downstream of the
McCoy Creek Diurnal Dissolved Oxygen (D.O.) Concentrations
D.O. (mg/l)	Water Quality Standards
2012:46% Exceedance Rate
2016:0% Exceedance Rate
'Duplicate sample
2 2 5 5
Figure 3. A comparison of the 2012 and 2016 dissolved oxygen exceedance
rates in the morning (AM) and late afternoon (PM) at three instream
monitoring sites show improvement.
Partners involved in the project included the City
of Wentzville; the Wentzville Stormwater Advisory
Committee; St. Charles SWCD; Wentzville School
District; Oasis Kwik Car Wash; Huntsdale Subdivision
Homeowner's Association; SCI Engineering, Inc.; Water
Resources Solutions; Shockey Consulting; Teklab, Inc.;
Landesign, LLC; Bernardin, Lochmueller & Associates;
Demien Construction; Greenway Network, Inc.; the
	| City of Flint Hill; St. Charles County;
and the Missouri Department of
Natural Resources. The total cost
of the Dry Branch Watershed
Clean Stormwater and Green Parks
Section 319 NPS Grant Project
and partner contributions was
$1,248,015 for the completion
of a nine-element WBP. water
quality monitoring, demonstration
nfiltration projects at four sites,
and a citywide educational outreach
campaign and stream-naming
contest. Since 2012, the St. Charles
SWCD provided $3,424 in state
cost-share dollars to implement
cover crops on 107 acres within the
McCoy Creek watershed.
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©
U.S. Environmental Protection Agency
Office of Water
Washington, DC
EPA 841-F-19-001WW
December 2019
For additional information contact:
Jamie Paige, City of Wentzville
636-639-2055 • jamie.paige@wentzvillemo.org
Trish Rielly, Missouri Department of Natural Resources
573-526-4662 • trish.rielly@dnr.mo.gov

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