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Controlling Nonpoint Source Pollution from Agricultural and
Residential Areas Restores Stockley Branch
Waterbody Improvsd Run°ff from agricultural arid residential areas caused high bacteria
levels in Delaware's Stockley Branch. As a result, the Delaware
Department of Natural Resources and Environmental Control (DNREC) added Stockley Branch to
the 1996 Clean Water Act (CWA) section 303(d) list of impaired waters for bacteria and nutrients.
Watershed stakeholders provided technical assistance and installed agricultural best management
practices (BMPs) in the watershed, causing bacteria levels to decline in the stream. As a result,
DNREC removed the Stockley Branch from the state's 2008 list of impaired waters for bacteria.
Problem
Stockley Branch is in the 28,676-acre Cow Bridge
Branch watershed, which is in the Indian River basin
in southeastern Sussex County, Delaware (Figure 1).
Primary sources of nonpoint source pollution in the
watershed likely include runoff from agricultural
activities (e.g., fertilizer and manure application),
concentrated areas of animal production and urban
activities. Monitoring data collected in the late 1990s
indicated that Stockley Branch failed to meet the
state's enterococcus bacteria numeric criterion, which
requires the annual geometric mean to be less than
100 colony-forming units (cfu) per 100 milliliters (mL).
Stockley Branch did not support its freshwater primary
contact designated use, prompting the state to add it
to Delaware's 1996 CWA section 303(d) list of impaired
waters for bacteria and nutrients.
In 1998 and 2006 the U.S. Environmental Protection
Agency developed total maximum daily loads (TMDLs)
to address the nutrients and bacteria loading,
respectively, throughout the Indian River watershed.
The 1998 TMDL required an 85 percent reduction in
nitrogen and a 65 percent reduction in phosphorus
loadings to achieve TMDL targets and meet water
quality standards. The 2006 TMDL required that the
overall bacteria loading be reduced by 42 percent from
the 2000-2005 baseline levels in fresh water regions
of the Inland Bays Drainage Basin, which includes the
Indian River basin.
WATERSHEDS
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Chesapeake Bay
Inland Bays
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Figure 1. Stockley Branch flows into Cow Bridge Branch,
which is in the headwaters of Delaware's Inland Bays
Drainage Basin.

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Story Highlights
The Sussex Conservation District (SCD) offered techni-
cal assistance to the farming community by providing
nutrient management planning and cost-share funding
for agricultural BMPs. The SCD also partnered with
the U.S. Department of Agriculture's (USDA's) Natural
Resources Conservation Service (NRCS) to develop
conservation plans and Environmental Quality
Incentive Program (EQIP) contracts. Watershed part-
ners worked with landowners to enroll 11,000 acres
of cover crops over 5 years and implement nutrient
management plans on approximately 9,228 acres.
In addition, several BMPs were installed on poultry
operations within the watershed, including 26 manure
storage structures, 11 poultry carcass composters,
84 heavy use area protection pads and the transfer of
7,492 tons of manure. SCD planning staff continue to
work with farmers throughout the watershed, provid-
ing ongoing technical assistance to ensure improved
water quality. Delaware's USDA Conservation Reserve
Enhancement Program (CREP) was established in
1999 to protect and enhance environmentally sensi-
tive land and waters in the coastal plain geographic
areas of the Delaware, Chesapeake and Inland Bays
watersheds by establishing voluntary land retire-
ment agreements with agricultural producers. In
1999, to assist in CREP program development and
implementation, Delaware's Nonpoint Source Program
committed CWA section 319 funds to create a full-time
Delaware CREP Program Coordinator position. The
CREP Program Coordinator helped install 1 acre of
grass buffers, 9 acres of riparian buffers, 10.2 acres of
wetland restoration, 17.3 acres of wildlife plantings,
and 219.4 acres of hardwood trees in the Cow Bridge
Branch watershed, which includes Stockley Branch.
Continued water quality implementation efforts
between 2011 and 2016, including the installation of
the following urban practices, have helped maintain
water quality in Cow Bridge Branch: (1) adding a
retrofit dry stormwater pond to a bioretention facility
with the use of biochar on 1.6 acres and (2) restoring
1,000 feet of impaired stream that treated 30 acres.
:

Figure 2. Stockley Branch water quality has improved,
thanks to watershed restoration efforts.
Results
Bacteria levels have decreased in response to the
more than 10 years of water quality protection
and restoration efforts in the Cow Bridge Branch
watershed (Figure 2). DNREC collected monitoring
data at STORET Station 308281 in Stockley Branch
between September 2002 and August 2007. The
geometric mean of the 31 samples collected over the
5-year period was 59 cfu/100 ml. This was well below
Delaware's fresh water bacteria water quality standard
maximum of 100 cfu/100 mL, so DNREC removed the
8.23-mlle segment of Stockley Branch (DE-140-006)
from the state's list of impaired waters in 2008 per its
Assessment and Listing Methodology.
Partners and Funding
Key partners included SCD, NRCS, Delaware Center for
the Inland Bays and the Delaware Nonpoint Source
Program. Approximately $1.1 million in federal CWA
section 319 funds supported the costs of restora-
tion in the Stockley Branch and Cow Bridge Branch
watersheds. Additional funding came from the USDA
(through EQIP and CREP) and Delaware's Conservation
Cost Share Program, which was provided through
the SCD.
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©
U.S. Environmental Protection Agency
Office of Water
Washington, DC
EPA 841-F-19-001W
October 2019
For additional information contact:
Mark Hogan
Delaware Department of Natural Resources and
Environnmental Control
302-739-9922 • Mark.Hogan@delaware.gov

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