SILVER SPRINGS/RIVER POLLUTION REDUCTION PROJECT –
IMPROVING THE WATER QUALITY OF THE SILVER SPRINGS
ECOSYSTEM
Jonathan Steflik, PE – JEA (Formerly Black & Veatch)
Bruce Phillips, PE PLS, Tom Young, PE – City of Ocala
Rafael Frias III, PE, Kenny Blanton, PE – Black & Veatch
The Silver River is an Outstanding Florida Waterbody located in the heart of Marion
County. The river is the largest tributary of the Ocklawaha River and forms as the result
of the discharge of Silver Springs, a first-magnitude spring that flows at an average rate
of 795 cubic feet per second. Additional contributions to the Silver River’s base flow
come from Half Mile Creek and from shallow groundwater seepage along the river’s sixmile stretch. During storm events, the Silver River receives surface runoff discharge
from a 13,000-acre watershed, which includes the City of Ocala.
A portion of the watershed, identified as the State Road 40 (SR 40) drainage basin, was
significantly developed prior to the existence of any state regulations requiring storm
water treatment for water quality protection. Consequently, untreated urban runoff
discharges directly into Half Mile Creek and ultimately into the Silver River,
approximately one-half mile downstream from the Silver Springs head, impacting its
water quality.
Increasing public awareness and regulations regarding discharges to improve and protect
local water resources have grown since development has occurred in the SR 40 drainage
basin. In addition, recent water quality deterioration in the Silver Springs and Silver
River resulted in increased public concerns. This prompted the development of the Silver
Springs/River Pollution Reduction Project. This Project was a prime opportunity for local
and state agencies to work cooperatively to provide direct water quality and biological
improvements to the Silver River ecosystem. The City of Ocala participated in the Project
by implementing storm water improvements along the Silver Springs Boulevard (SR 40)
corridor within the city limits.
The Silver Springs/River Pollution Reduction Project included construction of a new
storm water conveyance system, upgrades to the existing storm water retention and
detention facilities, upgrades to the existing storm water pumping station, and a new offline detention system to collect and treat the “first flush” of pollutants from the SR 40
drainage basin.
Black & Veatch conducted a preliminary design study to consider several potential
design alternatives and develop design recommendations for improvements to the SR40
system. Previous to this project, the existing storm water treatment system did not meet
the St. Johns River Water Management District (SJRWMD) water quality standards and
had a high potential for flooding.
Black & Veatch utilized eXPert Storm Water Management Model (XPSWMM) software
to model the hydraulics and hydrology of the existing and proposed conditions. The GIS
data was collected and analyzed to determine land use, soil types and impervious areas.
This information was then used in the NRCS curve number method to determine the
model input parameters for the hyrdrologic conditions.
Model parameters for the hydraulic analysis such as pipe size, shape, length, material
type and invert elevations were imported directly from ArcGIS into XPSWMM. The
model developed in XPSWMM was then refined manually to reflect additional features
such as weirs, control structures and other non-standard components of the conveyance
system. Two versions of the model – one for existing conditions, another for proposed
conditions – determined the amount of flow contained and treated in the system for 10year and 25-year storm events. A node diagram of the SR40 system in XPSWMM is
shown in Figure 1.
Figure 1 - Node Diagram of SR40 in XPSWMM
The existing SR40 storm water treatment system consisted of four interconnected ponds
(Pond 1, Pond 2, Pond 3 and Pond 4) along the State Road 40 corridor.
Pond 1, the pond most upstream in the SR40 system, does not represent a true dry
retention or wet detention treatment system. Pond 1 does not have an overflow structure
or other means to control flow out of the pond. The pond could be more fairly described
as a “wide spot” in the system, utilized to capture reduce flooding potential. The
preliminary design study considered alternative design scenarios for Pond 1. One
alternative suggested routing runoff from Pond 1 to a series of three neighboring ponds at
the municipal golf course. This concept was quickly abandoned due to an unknown
upstream flow entering one of the golf course ponds. The drainage well with an
unknown capacity at the outfall further reduced the feasibility of this design
consideration. Because the addition of any type of control or overflow structure would
have increased the flooding potential already present in this area, treatment volume was
not addressed in Pond 1.
Pond 2, located immediately downstream from Pond 1 in the SR40 system, is a dry
retention system which receives flow from overland runoff and overflow from Pond 1 via
gravity flow. Prior to improvements to the system, Pond 2 had a storage capacity of
approximately 29 acre-feet and a treatment volume capacity of approximately 11 acre-
feet. Based on results from the XPSWMM model, the preliminary design study
recommended expanding Pond 2 to increase storage and treatment capacity as well as
increasing the capacity of the conveyance system from Pond 2 to Pond 3.
Because the potential for flooding in the SR40 system
was highest near Pond 2 and Pond 3, the preliminary
design study recommended the creation of a new
storm water detention facility. Pond 3A was designed
and constructed to retain and treat excess runoff
between Pond 2 and Pond 3. Pond 3A is a wet
detention storm water treatment facility which adds
approximately 59 additional acre feet of storage and
approximately 15 acre feet of treatment volume to the
SR40 system.
Figure 2 - Pond 3A Construction
Pond 3 is a wet detention storm water treatment facility capable of storing approximately
26 acre-feet of runoff. Pond 3 has a treatment volume of approximately 10 acre-feet. Due
to wetland conditions present at the facility and limited space for expansion, no additional
improvements to Pond 3 were recommended.
Excess storm water from Pond 3 is pumped to Pond 4 via an existing 16-inch ductile iron
force main. Per design recommendations, a redundant pump was installed to the existing
pump station to reduce the potential for flooding should the existing pump need service
during a storm event.
Pond 4 is a dry retention pond that prior to the
improvements to the SR40 system had a storage
capacity of approximately 18 acre-feet. Similar to
Pond 1, because Pond 4 did not possess a control
structure to attenuate outfall flow, the system could not
claim any treatment capacity. Design study
recommendations suggested that Pond 4 be expanded
and a control structure added to treat runoff prior to
discharge into Half Mile Creek and ultimately the
Silver River.
Figure 3 - Pond 4 Control Structure
Substantial completion of construction for the Silver Springs/River Pollution Reduction
Project was completed in August of 2009.
The City of Ocala was able to secure public funding from the Saint Johns River Water
Management District (SJRWMD), Florida Department of Environmental Protection
(FDEP) and the Florida Legislature for approximately 80 percent of the project’s total
construction cost. The total cost to construct the Silver Springs/River Pollution Reduction
Project was $2,536,248. Grant funding from the SJRWMD accounted for $1,262,000.
Grant funds from FDEP’s Total Maximum Daily Load of Non-Point Sources (TMDL
NPS) reduction program totaled $274,248. Special legislation from the State of Florida
contributed an additional $500,000 to the completion of the project. The total “out of
pocket” cost to the City of Ocala was $500,000.
The Silver Springs/River Pollution Reduction Project exemplifies ideal cooperation
between state and local agencies to provide much needed improvements to a biologically
sensitive watershed. The project not only improves the water quality in the Silver River,
but the reduction in flood potential represents an opportunity for the City of Ocala to
foster sustainable development in the future.