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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
7. Scenarios
The conclusions made in the siting analysis,
technology evaluation, sewer separation and
alternatives analysis sections have been used to
develop seven scenarios for the complete abatement of
the CSOs discharging to Harbor Brook. Each scenario
addresses the lower, middle and upper basins and was
developed with the goal of meeting or exceeding the
requirements of the ACJ. These scenarios include
combinations of Regional Treatment Facilities (RTFs),
disinfection, sewer separation, conveyance to Metro,
and Floatables Control Facilities (FCFs). Replacement
of portions of the HBIS is a commons project for each
Scenario.
Table 7.1 shows overview of scenarios with frequency of overflows, average annual discharges, estimated project and present worth costs.
Table 7.2 presents the project costs, estimated annual
O&M costs and present worth costs.
| Table 7.2. Present worth analysis |
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Scenario
|
Total est. project cost
|
Est. annual O&M cost
|
Present worth
|
|
Scenario 1 - Sewer separation
|
$261,930,000
|
$53,000
|
$262,700,000
|
|
Scenario 2 - Convey and treat at Metro
|
111,390,000
|
450,000
|
117,730,000
|
|
Scenario 3 - Convey-treat at Metro, vortex, FCF
|
91,860,000
|
652,000
|
101,050,000
|
|
Scenario 4 - Vortex facilities, separation, FCF
|
62,830,000
|
609,000
|
71,410,000
|
|
Scenario 5 - Vortex facilities and FCF
|
58,460,000
|
607,000
|
67,020,000
|
|
Scenario 5a - Combo of Scenarios 5 and 6
|
55,230,000
|
678,000
|
64,790,000
|
|
Scenario 6 - Vortex facilities, FCFs, PS upgrades
|
53,410,000
|
731,000
|
63,710,000
|
|
Scenario 7 - ORFs, FCF, FCFs, PS upgrades
|
68,780,000
|
372,000
|
74,020,000
|
|
Scenario 8 - Vortex-offline and upstream storage facilites, FCFs, PS upgrades
|
60,760,000
|
552,000
|
68,540,000
|
|
Scenario 9 - ORF, regional storage, FCFs, PS upgrades
|
69,810,000
|
382,000
|
75,190,000
|
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Notes: Based on ENRCCI = 7314 escalated to midpoint of construction worth cost bsed on 25-yr useful life and discount rate of 5.0%
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A more detailed summary of the costs is included in Appendix F.
Click here for Appendix F. Construction cost summary for abatement scenarios.
This scenario represents the separation of all of the
combined sewers in the Harbor Brook drainage basin.
Sewer separation is considered an effective approach
to CSO abatement. However, there are several major
disadvantages to this scenario. If untreated
stormwater is discharged, it may have a negative
impact on the water quality of Harbor Brook and
Onondaga Lake.
Ownership of the separated sewers will be transferred
to the City of Syracuse following the completion of
construction. As a result, the City would be
responsible for maintaining these new sewers and the
treatment of stormwater under future more stringent
regulations.
Since new sewers would be constructed on almost every
street in the sewer service area, the disruption to
the community would be the most extensive of any
scenario considered. The cost of complete sewer
separation is also estimated to be significantly
greater than the cost of any of the other scenarios.
The estimated project cost for this scenario is $262
million and includes the cost of the HBIS replacement
for $2.34 million. This cost, however does not include
treatment of the stormwater that will likely be
enforced in the future under current environmental
regulations.
This scenario includes the conveyance of all Harbor
Brook CSOs to Metro for storage and subsequent
treatment. The major advantage of this alternative is
that a greater portion of CSO would be captured and
receive treatment at Metro. Although this scenario is
considered effective at improving the water quality of
both Harbor Brook and Onondaga Lake, there are two
significant disadvantages to this scenario. First,
there will be considerable disruption of the community
along the HBIS corridor. Second, the project cost of
this scenario is estimated to be higher than the costs
of several other scenarios considered. The estimated
project cost for this scenario is $111 million.
Under this scenario, CSOs 014 through 078 from the
upper basin would be conveyed to the upper basin RTF
along with CSOs 009 through 013 from the middle basin.
This facility would need to accommodate 175 cfs in
order to meet the ACJ requirements, based on bacteria
modeling results.
For the middle basin, CSO 005 through 008 would be
conveyed to Metro along with CSOs 003 and 004 from the
lower basin. CSO 063 will be directed to the Emerson
FCF.
This scenario will meet the water quality requirements
of the ACJ. Its advantages are that it utilizes
available capacity at Metro, has a lower project cost
compared to full conveyance, and minimizes the
addition of new treatment facilities. The estimated
project cost for this scenario is $91.9 million.
Under this scenario, the upper basin CSOs 009 through
078 would be addressed with the upper basin RTF.
Modeling has shown that this facility would need to
accommodate a peak flow of 175 cfs.
The middle basin CSOs 005 through 008 would receive
targeted sewer separation.
This scenario also includes the Emerson FCF for 063.
An RTF would consolidate CSOs 003 and 004. This
facility is termed the Lower Basin RTF.
This scenario offers a reasonable balance of
minimizing community disruption while meeting the
minimum water quality requirements of the ACJ, not
only in Onondaga Lake but also in Harbor Brook. The
estimated project cost is $63.6 million.
Under this scenario, the Upper Basin RTF would take
flow from CSO 014 through 078 as well as CSOs 009
through 013 from the middle basin. Modeling results
show that the Upper Basin RTF would need to
accommodate a peak flow rate of 175 cfs to meet ACJ
requirements.
The remaining middle basin CSOs (005-008) would be
consolidated and conveyed to the Lower Basin RTF along
with CSOs 003 and 004. The Lower Basin RTF would need
to accommodate a peak flow rate of 205 cfs. CSO 063
would receive floatables control as an FCF.
This scenario has a relatively low cost, will meet or
exceed the water quality criteria of the ACJ and will
provide treatment of stormwater in the form of CSO,
that will likely be enforced in the future through
current regulations. The estimated project cost for
this scenario is $58.5 million.
Under this scenario, the upper basin CSOs 014 through
078 would be addressed with the upper basin RTF.
Modeling has shown that this facility would need to
accommodate a peak flow of 155 cfs. Middle basin CSOs
009 through 013 would receive floatables control as
FCFs. Table 7.3 shows the average annual treated volume and frequency of
discharge for the FCFs associated with this scenario.
Table 7.3. Average annual treated discharge frequency and volume at the FCFs
Lower Basin |
|
063
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4.5
|
22
|
| Middle Basin |
|
005*
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0.2
|
26
|
|
006*
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Pump station upgrade
|
-
|
|
006A
|
0.4
|
22
|
|
007
|
0.4
|
50
|
|
008*
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Pump station upgrade
|
-
|
|
009
|
<0.1
|
1
|
|
010
|
<0.1
|
11
|
|
011
|
0.2
|
31
|
|
013
|
<0.1
|
25
|
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*Note: Planned CSO closure
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CSOs 005 through 008 would be consolidated and
conveyed to the Lower Basin RTF along with CSOs 003
and 004. The Lower Basin RTF would need to accommodate
a peak flow rate of 205 cfs. CSO 063 would receive
floatables control as an FCF.
The estimated project cost for this scenario is $55.2
million.
The Upper Basin RTF would address the overflow from
CSOs 014 through 078. Modeling results have shown that
the Upper Basin RTF would need to accommodate a peak
flow rate of 155 cfs.
A combination of FCFs and pumping station upgrades for
the middle basin could be considered for CSO areas 005
through 013. Pumping station and regulator
improvements would eliminate CSOs 006 and 008. For
planning purposes, the remaining scenarios will
include this combination.
For the Lower Basin an RTF would address the flow from
CSOs 003 and 004. The Lower Basin RTF would need to
accommodate a peak rate of 190 cfs to meet ACJ
requirements. CSO 063 would be treated by an FCF. Table 7.3 shows the average
annual treated volume and frequency of discharge for the FCFs associated with scenarios
6, 7, 8, and 9
The estimated project cost for this scenario is to
$53.4 million.
This scenario is similar to scenario 7 above; however,
the Upper and Lower basin RTFs would include the use
of ORFs followed by disinfection in place of the HRT
facility. The Lower Basin ORF would be sized for a
storage volume of 3.7 MG. The Upper Basin ORF would be
sized for a storage volume of 3.4 MG. The Middle Basin
and CSO 063 would be as described in Scenario 6.
The estimated project cost for this scenario is to $68.8 million.
This scenario is similar to scenario 7 above; however,
the Upper and Lower basin RTFs would include the use
of offline-upstream storage followed by half-sized
vortex and disinfection facilities. The Lower Basin
facility would include 1.2 MG of offline storage with
an HRT sized for 95 cfs. The Upper Basin ORF would
include 0.9 MG of upstream storage with an HRT sized
for 78 cfs. The Middle Basin and CSO 063 would be as
described in Scenario 7.
The estimated project cost for this scenario is to
$60.8 million.
This scenario is similar to scenario 7 above; however,
the Upper and Lower Basin RTFs would include the use
of an ORF and regional storage, respectively. The
Upper Basin RTF would require an ORF since capacity
would not be available in the HBIS to dewater a
regional storage facility within a 48-hour period. The
Lower Basin facility would include 5.4 MG of storage.
The Upper Basin ORF would include 3.4 MG of storage.
The Middle Basin and CSO 063 would be as described in
Scenario 7.
The estimated project cost for this scenario is to
$69.8 million.
CSO closure has been considered for each of the scenarios described above. For all
scenarios, CSOs 004, 005, 006, 008, 015, and 016 would be permanently closed.
Additionally, CSO closure would be included as part of any sewer separation.
Based on the information presented in this report and
summarized in Table 7.1, the three more cost-effective
scenarios of the ten evaluated are 5, 5a and 6.
The breakout of
construction costs, O&M costs, and present worth are shown in Appendix F.
While Scenario 6 represents the lowest overall cost,
Scenario 5a provides the best balance of low cost,
reduced number of CSO facilities, and fewer average
annual treated discharges.
Therefore, Scenario 5a is recommended as the preferred Scenario.
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7. Scenarios
Susan Miller, Project Deputy Director
Onondaga County Dept of Water Environment Protection