Nonpoint Source Success Story Florida Stormwater Retrofit Projects Help Reduce Nutrient Pollution in Lake Conine

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1 NONPOINT SOURCE SUCCESS STURY

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Nutrient Pollution in Lake Conine

Stormwater Retrofit Projects Help Reduce Nutrient Pollution

V\terbody |pppp,., Water quality impacts from nutrient loading and polluted

runoff from nonpoint sources led the Florida Department of
Environmental Protection (DEP) to add Lake Conine to Florida's Verified List and the Clean Water Act
(CWA) section 303(d) list of impaired waters for nutrients. In response, DEP developed a nutrient
total maximum daily load (TMDL) that was adopted by rule in 2018. Project partners implemented
nonpoint source pollution management strategies, including the Lake Hartridge Stormwater
Treatment Facility, the South Lake Conine Stormwater Treatment Project, and the implementation of
a community-wide educational campaign. As a result of these activities, chlorophyll a, total nitrogen
(TN), and total phosphorus (TP) levels have improved, demonstrating that these projects have had a
positive impact on water quality within Lake Conine.

Problem

Lake Conine (WBID 1488U) is in the Group 3 Sarasota
Bay- Peace - Myakka watershed in north-central
Polk County within the city of Winter Haven in cen-
tral Florida (Figure 1). It is a Class III Lake waterbody
designated for recreation and the propagation and
maintenance of a healthy, well-balanced fish and wild-
life population. The predominant land uses in the Lake
Conine watershed are 55% medium-density residen-
tial; 11% wetlands; 26% water; and 6% transportation,
communication, and utilities. Lake Conine has an area
of roughly 213 acres, and the surrounding watershed
drains an area of roughly 589 acres. The average depth
of the lake is 9.9 feet (3.0 meters), with a maximum
depth of 20.0 feet (6.1 meters).

In 2005, DEP placed Lake Conine on the state's Verified
List and the CWA section 303(d) list of impaired waters
for nutrients. There are no point sources within the
Lake Conine watershed; nonpoint pollution sources
include septic systems, surface water runoff, ground-
water seepage and precipitation. Additionally, the
Lake Conine watershed is within an area identified
as a disadvantaged community on the Council on
Environmental Quality's draft Climate and Economic
Justice Screening Tool.

In 2018 DEP wrote a nutrient TMDL for Lake Conine
that calls for a 36% reduction in the TN load and a 57%
reduction in the TP load entering the lake. One of the
primary sources of pollutants contributing to Lake
Conine's declining water quality is nonpoint source

Figure 1. Aerial view of Lake Conine and the adjacent
Lake Hartridge in central Florida. The two lakes are
connected by the Conine-Hartridge Canal (red circle).

pollution carried in stormwater runoff from a 328-acre
drainage area on the south side of Lake Conine. Based
on stormwater sampling, the runoff from this area has
a high concentration of nutrients.

Story Highlights

The City of Winter Haven was awarded CWA section
319(h) Fiscal Year (FY) 2002 grant funds to treat water
from an 89.02-acre drainage basin south of Lake
Hartridge, the northernmost lake in the hydraulically

Lake* Conine Wetland Treatment^Areas

Conine-'l-jSrtridge Canal

WBID 15211 - Lake Hartridge

Treatment'Arb,

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Lake Conine Chlorophyll-a Annual Geometric Means (|ig/L)

Year

•The red line indicates the generally applicable chlorophyll-a criteria for type 2 lakes, not to be exceeded
more than once in a three-year period.

Figure 2. Lake Conine chlorophyll a annual geometric
means (2007-2020).

connected Southern Winter Haven Chain of Lakes
that flows to the Peace River System. Lake Hartridge
is directly upstream of Lake Conine, and the two lakes
are connected to each other via the Conine-Hartridge
Canal. The project included construction of a sediment
sump, a 4-acre wetland detention area, and an outfall
skimmer to treat nonpoint source pollutant runoff. The
project also included public education signage about the
project's environmental benefits along the walking/jog-
ging trails. This system helped reduce TN and TP levels
from stormwater runoff by 93% and 97%, respectively.

In 2016 the City of Winter Haven was awarded legisla-
tive funds to design and produce a stormwater master
plan to outline capital improvement projects aimed
at performance enhancements for the Chain of Lakes.
The City was also awarded a CWA section 319(h) FY
2015 grant for a community education program to
guide development and implementation of green infra-
structure projects, including four community work-
shops for public and private stakeholders and five land
planning development reviews. These efforts resulted
in the creation of enhanced stormwater permit design
and management procedures being developed and
implemented to increase performance of stormwater
systems within the City of Winter Haven.

In 2018 the City of Winter Haven was awarded a grant
for the South Lake Conine Stormwater Treatment
Project, which included constructing stormwater treat-
ment ponds and a series of wetland marsh chambers
to treat runoff from the surrounding drainage network
before it enters Lake Conine. Work included selective
dredging of organic soils, creating berms, removing

invasive exotic vegetation, and establishing desirable
aquatic vegetation. Public education will be provided
about the project's environmental benefits with sig-
nage, kiosks, brochures, and post cards. The estimated
load reduction from this project for TN and TP are 65%
and 36%, respectively.

Results

The restoration projects have had a positive impact
on water quality. Nutrient concentrations within
Lake Conine have been reduced to below the state's
numeric nutrient criteria for type 2 lakes. Chlorophyll
a annual geometric means collected at two monitor-
ing stations show that concentrations decreased from
a maximum value of 46 micrograms per liter (|ig/L)
in 2007 to a value of 16 |ig/L in 2020 year (Figure 2).
Post-project annual geometric means have consis-
tently remained below state's impairment threshold of
>20 |ig/L since 2018. Similar improvements have also
been observed for TN and TP annual geometric mean
concentrations in Lake Conine. TN and TP levels have
declined from maximum values of 1.65 milligrams per
liter (mg/L) TN in 2011 and 0.07 mg/LTP in 2007, down
to post-project (2019) values of 0.91 mg/LTN and 0.02
mg/LTP.

Data show that the upstream Lake Hartridge is not yet
meeting water quality standards; however, chlorophyll
a concentrations are decreasing (31 |ig/L in 2013,
down to 25 |ig/L in 2019), which demonstrates a posi-
tive trend in water quality likely linked to watershed
restoration efforts.

Partners and Funding

The City of Winter Haven conducted water quality
monitoring and implemented projects that reduce
and treat nonpoint source pollution and educate the
public. Funding sources for these efforts included two
CWA section 319 grants in FYs 2002 and 2015 (total
of $424,250 with $980,250 local match from the City
of Winter Haven). Additionally, the State of Florida
provided legislative appropriation funding of $400,000
in FY 2016-2017. Finally, the State of Florida Nonpoint
Source Management Program provided a Water-
Quality Assistance Grant of $750,000 in FY 2015-2016,
with $750,000 in local matching funds provided by the
City of Winter Haven.

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U.S. Environmental Protection Agency
Office of Water
Washington, DC

EPA 841-F-24-001K
April 2024

For additional information contact:

Amanda Peck

Florida Department of Environmental Protection
850-245-2952 • Amanda.Peck@floridaDEP.gov

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