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Harbor Brook CSO Abatement Project Facility Plan (Aug 2005)
by Brown and Caldwell
for Onondaga County Dept of Water Environment Protection
2. Harbor Brook In-Water System
The original HB IWS concept included the construction
of a storage structure at the mouth of Harbor Brook
along with the associated Harbor Brook Floatables
Control Facility (HB FCF), located just upstream. The
HB IWS was to be constructed in two increments, the
demonstration phase and the full size, both of which
would provide temporary containment of wet-weather
discharges for subsequent treatment at Metro. The
design basis for the demonstration facility was to
capture Harbor Brook flows (including CSOs, urban
stormwater, and baseflow) for up to the one-half of
the 1-year frequency, 2-hour duration, design storm
event, defined in 15-minute rainfall intervals, which
equates to a storage volume of 13 million gallons
(MG). Upon successful demonstration, the facility
would be expanded to capture the 1-year design storm,
with a storage volume of 26 MG.
The HB IWS is a form of storage that would consist of
a series of floating pontoons to which heavy gauge PVC
curtains would be attached. The curtains would be
arranged to create separate cells or bays to capture
wet-weather flows. Curtain weights would be used to
keep the curtains fixed to the lake bottom. A
conceptual layout of the HB IWS is provided on Figure
2.1. A more specific layout would be developed to meet
actual site conditions. The floating pontoons, PVC
curtains, curtain weights, and a pump station that
would return captured flow to the treatment plant
following a wet-weather event are shown. Openings
between cells would allow the flow to pass from cell
to cell. The cell openings would be located to
minimize the potential for the short-circuiting of
flow through each cell. These openings would also
allow for fish passage through the HB IWS.
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Figure 2.1. Conceptual layout of the Harbor Brook in-water system
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When an overflow event occurs, the wet-weather flow
would be directed to the HB IWS through the first
cell, displacing the clean water that it normally
holds. Wet-weather flow would proceed through each
consecutive cell either until the wet-weather event is
captured, or until the clean water is completely
displaced and the facility is full of stormwater.
Flow through IWS installations located in Sweden and
in Fresh Creek, NY have shown that the arrangement of
the ports between the cells creates a flow pattern
that approximates plug flow through the facility. Plug
flow is a theoretical flow pattern where material is
discharged from the facility in the same order in
which it enters.
A pumping station, drawing from the first cell would
be used to convey captured flow to Metro, once
treatment capacity is available following a
wet-weather event. Solid material would tend to settle
within the first cell of the HB IWS. Provisions would
need to be made to remove these accumulated solids on
a regular basis and for their subsequent treatment and
disposal. The frequency of solids removal would be
established during the facility demonstration.
The original HB IWS required several unique features
based on specific site constraints and its status as a
demonstration facility. A flow diversion structure
with a tilting-weir gate would be located onshore near
the mouth of Harbor Brook. In the open position, the
gate would allow flow to drain naturally to the Lake.
In the closed position, the gate would divert
wet-weather flow to the HB IWS.
Level sensors located within key CSO outfalls would be
used to determine the start and end of an overflow
event, and control the position of the gate with the
goal of capturing the “first flush” as well as
additional CSOs up to a combined stream and CSO volume
of 13 MG (demonstration phase). The sensors and a
number of rain gages at different points in the Harbor
Brook basin would be connected to a supervisory
control and data acquisition system (SCADA) at Metro.
In a similar manner, a level sensor would be installed
at the US Geological Survey (USGS) Gauging Station on
Harbor Brook, approximately 1000 feet upstream of
Onondaga Lake to measure the volume of flow that
enters the HB IWS.
On March 16, 1999 the County and its consultants
presented the HB IWS concept to EPA officials at the
Region 2 offices. The principal EPA concern at that
time, related to Onondaga Lake’s designation as a
Federal Superfund Site, pursuant to the Comprehensive
Environmental Response, Compensation Liability Act
(CERCLA). Because of the magnitude of the Superfund
issue, as described below, other possible concerns,
such as impacts to floodplain, wetlands, fish and
wildlife, were not investigated further.
The Onondaga Lake Superfund Site includes eight NPL
Subsites. The two areas of immediate concern to the HB
IWS are the Lake Bottom subsite and the Wastebed
B/Harbor Brook subsite.
These subsites include sediments and groundwater that
are contaminated with mercury, benzene, toluene,
ethylbenzene, xylenes (BTEX), chlorinated benzenes,
polynuclear aromatic hydrocarbons (PAHs), PCBs,
polychlorinated dibenzo-p-dioxins or polychlorinated
dibenzofurans, and calcite.
A Remedial Investigation (RI) and Feasibility Study
(FS) was conducted by Honeywell for the Lake Bottom
subsite to document the nature and extent of the
contamination in the Lake, assess the human health and
ecological risks posed by this contamination and to
identify and evaluate remedial alternatives to address
the contaminated sediments. NYSDEC issued a Proposed
Remedial Action Plan (PRAP) for the Onondaga Lake
Bottom subsite in late November 2004. The selected
remedial action will be decided upon in a Record of
Decision (ROD) issued by NYSDEC which is currently
scheduled for March, 2005. After the issuance of a
ROD, the approved remedial action would then be
designed and implemented.
Some of these issues could be avoided if the proposed
HB IWS were to be constructed following remediation;
however, the timing on completion of remediation is
currently unknown. The NYSDEC estimates that it will
take approximately 3 years to design the lake bottom
remedy and 4 years to construct it. This estimate does
not include addressing the remediation of the Wastebed
B/Harbor Brook NPL subsite
All of these unknowns would require further
investigation and add to the complexity and
uncertainty as to when and how, or whether, this site
could realistically be remediated and used for the
site of the IWS. The current extent of the
contamination in the vicinity of the proposed IWS and
the presence of ongoing contaminant releases were not
known to the ACJ parties when the ACJ was written.
As a result of the impediments identified above, the HB IWS is not considered a viable CSO abatement approach for the Harbor Brook Basin.
In consideration of the impediments outlined in
Section 2.2, as well as the requirements of the State
Environmental Quality Review Act (SEQRA), alternatives
for the abatement of Harbor Brook CSOs have been
developed and evaluated. The ACJ states:
If the [HB IWS] project is not deemed technically
acceptable, the County will proceed with the design
and construction of the Delaware and State Fair RTFs
[regional treatment facilities] at a schedule to be
proposed by the County to DEC. [Appendix B, p. 10]
This facility plan, however, goes beyond the wording
in the ACJ and includes a complete review of
alternative technologies and potential sites for CSO
abatement facilities to address the 18 permitted CSOs
that discharge to Harbor Brook. As required under the
ACJ, opportunities for sewer separation have also been
evaluated as a comprehensive and/or partial CSO
abatement approach as well.
An evaluation of technologies and alternative sites
has been completed in order to provide a thorough
analysis of the options available for the abatement of
CSOs discharging to Harbor Brook. The technologies and
site options were evaluated independently based on
certain criteria. Selected technologies were then
assembled into treatment processes at specific sites.
These site-specific abatement alternatives were
further evaluated based on cost, and then assembled
into various scenario combinations designed to achieve
abatement of the Harbor Brook CSOs.
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2. In-water system
Env Info Document
Susan Miller, Project Deputy Director
Onondaga County Dept of Water Environment Protection