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1 NONPOINT SOURCE SUCCESS STURY

Neighborhood-Scale Green Infrastructure Improves Water Quality in
Marsh Creek in the City of Sandy Springs
Waterbody Improved Afour-mile segment of Marsh Creek is not supporting the
designated use of fishing due to excess fecal coiiform (FC)
bacteria. In response, the City of Sandy Springs installed a wetland detention/bio retention green
infrastructure (Gl) area and a stormwater pond in a headwater tributary 3 miles upstream of the
impaired segment to treat stormwater runoff from the highly urbanized subwatershed. Pre- and
post-installation monitoring of the systems showed that the project goal of 20 percent bacteria
reduction was surpassed. Geometric means from continuous in-stream sampling of the impaired
segment show FC reductions of greater than the 60 percent requirement in the 2008 revised total
maximum daily load (TMDL).
Problem
The Marsh Creek watershed (HUC-10 #0313000111)
is in Sandy Springs, about 15 miles north of Atianta in
the Chattahoochee River Basin (Figure 1). The impaired
segment (Headwaters to Chattahoochee River) was
reported in Georgia's 2002 Clean Water Act (CWA)
Section 305(b)/303(d) Integrated Report based on
bacteria data collected in 1992-1996. A geometric
mean of 5,623.41/100 milliliters (mL) from 38 in-
stream samplings collected by Georgia Environmental
Protection Division (EPD) and Fulton County at the
Georgia EPD listing site (Brandon Mill Road) qualified
the segment as impaired for FC.
A 2008 revised TMDL for fecal coiiform required a
60 percent reduction in bacteria loadings to restore
compliance with state water quality standards: 1,000
per 100 mL (geometric mean November-April) and
200 per 100 mL (geometric mean May-October). The
2008 revised TMDL, which had replaced a 2002 study,
indicated multiple sources of FC from urban runoff,
domestic animals, leaks and overflows from sanitary
sewer systems, illicit discharges of sanitary waste,
leaking septic systems, runoff from improper disposal
of waste materials, and leachate from operating and
closed landfills.
A 2004 TMDL implementation plan further assessed
the causes of impairment with a land cover chart,
visual field survey, maps and photographs. In 2010
the City of Sandy Springs Fecal Coiiform Watershed
Figure 1. Marsh Creek is in northern Georgia's
Chattahoochee River watershed.
Improvement Plan ranked the Marsh Creek
Headwaters Project as the highest scoring new
solution to stormwater control among prioritized
watershed improvement recommendations.
Story Highlights
The City of Sandy Springs was awarded a Fiscal Year
(FY) 2013 Clean Water Act section 319(h) grant to
install the Marsh Creek Headwaters Project. Now
called the Marsh Creek Rain Garden Park, the regional
stormwater systems are at 100 Johnson Ferry Road
and heip protect the downstream channel and manage
Marsh
Creek

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Figure 2. The bioretention area filters and treats the
first flush of urban stormwater runoff.
stormwater runoff from the upstream 14-acre City
Springs mixed-use center. A Gi wetiand/detention
pond and a permanent pool provide storage volume
and outlet control for extreme flood event protection,
while also diverting and infiltrating runoff from a drain-
age basin measuring approximately 32 acres with 69%
impervious surface (Figures 2 and 3). In addition to
reducing bacteria loadings (as required by the TMDL),
the systems meet 88% of the channel protection
volume required for 100% redevelopment and provide
the required water quality treatment volume of 94,475
cubic feet (as required by Sandy Spring's National
Pollutant Discharge Elimination System permit).
Additionally, landscaping on the site features a
preserve with educational signage where the City of
Sandy Springs continues to host tours to showcase
GI projects in the southeast. The City has built on the
success of these stormwater infiltration technologies
with further "greening" activities upstream. The new
City Springs complex (2018) incorporates parks, trees,
green space and a rainwater harvesting system to
further reduce the impact of impervious surfaces.
Results
As monitoring continues to show water quality
improvement in the impaired segment, the City of
Sandy Springs is evaluating remaining sources of
bacteria with the goal to remove Marsh Creek from
Georgia's impaired waters list for FC. In 2017 Georgia
EPD approved the City of Sandy Spring's Sampling
Figure 3. The main pool provides storage volume for
water quality/channel protection and outlet control.
and Quality Assurance Plan to qualify monitoring data
for 305(b)/303(d) listing assessments. Post-installation
sampling of the project's stormwater systems showed an
average FC reduction of 84.5%. In-stream FC monitoring
conducted at the Georgia EPD listing site shows water
quality improvement in the impaired segment. All FC
sampling data is computed as geometric means, and
they have surpassed the 60% load reduction targeted
in the 2008 TMDL since the project was completed.
Data collected during the first two quarters in 2020
at the sampling site immediately downstream of the
stormwater BMP show FC geometric means (counts/100
mL) of 125 and 48, respectively. In 2019 the City of Sandy
Springs hosted site tours for various groups as part of
a GI certification course and for U.S. Environmental
Protection Agency Region 4 Earth Day Week.
Partners and Funding
WK Dickson & Co, Inc.; Wrecking Corp of America, LLC
(a minority-owned business); and Tri Scapes, Inc. (a
woman-owned company) partnered as contractors
with the City of Sandy Springs to provide engineering
logistics and water quality monitoring, demolition and
construction. The original grant budget was based on
preliminary estimates of $387,747 in federal award and
$437,247 in local match, totaling $824,994. The final
total cost of $2,129,843 reflected change orders for
nonfederal matching funds in the additional amount of
$1,304,849 to cover modifications such as a concrete
wall to support an earthen embankment and removal
of additional rock revealed by soil borings.
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U.S. Environmental Protection Agency
Office of Water
Washington, DC
EPA 841-F-20-0Q1KK
December 2020
For additional information contact:
Mary E Gazaway
Georgia EPD Watershed Protection Branch
404-651-8522 • mary,gazaway@dnr.ga.gov

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