Grabación

Water supply systems must be designed to meet maximum day and peak flow demands. In many systems, water treatment production capacity is sized to meet projected maximum daily demands, and storage is used to meet peak hourly flows, including assumed fire flow events. FKAA‘s CUP (#13-00005-W) includes a special dry season Biscayne Aquifer with- drawal limit of 17 mgd on an average day basis from December 1 through April 30. This groundwater withdrawal restriction essentially limits water production at the J. Robert Dean WTP to 17 mgd, although the plant can exceed this amount as long as the plant pumps an equal amount less than 17 mgd on another day during the dry season. FKAA is limited to not pumping more than 2,584 MG during this 5-month period, or an average day produc- tion of 17 mgd. This limiting condition of the CUP goes into effect upon completion and operation of the raw Biscayne Aquifer ASR system per Limiting Condition #31 of the CUP as discussed in Section 3, Water Supply System.

Typically, FKAA’s annual maximum day flow (MDF) occurs in the dry season or during the month of May (1 month after the “dry season”). As such, this limiting condition is a key factor in this Water System Master Plan and impacts the timing of when new treatment capacity is required. For this Master Plan, it is assumed that the plant cannot produce more than 17 mgd during this 5-month period to meet maximum day demands.

The largest historical MDF observed was approximately 22.4 mgd, which occurred on March 25, 2005. The second and third largest pumpage days (from 2000 to 2005) were 22.3 mgd on May 30, 2005, and 22.2 mgd on May 18, 2003. From January 2000 through December 2005, 24 days with pumpage within 5 percent of the historical MDF were re- corded, and 110 days within 90 percent of the historical MDF were recorded. The maximum daily averages for the peak 2-, 3-, and 4-day periods from 2000 through 2005 are 21.8 mgd, 21.1 mgd, and 21.3 mgd, respectively.

The evaluation of when WTP expansions (without storage) are needed to meet projected annual MDFs and what capacity each expansion should be requires a number of assump- tions, as noted below:

• Expansions are constructed to keep the projected annual MDF within approximately 90 to 95 (maximum) percent of the available total treated firm water supply.

• The existing emergency RO plants at Stock Island and Marathon will be retrofitted and upgraded to serve as peak production plants to offset production capacity at Florida City LPRO facility

• Each expansion with LPRO uses 1.5-mgd trains, and each expansion increment will be large enough that another train addition will not be needed for at least 2 years.

• The projected annual MDFs will occur during the dry season (December to April), and the maximum withdrawal from the Biscayne Aquifer will be 17 mgd.

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• Biscayne Aquifer water supply will be lime-softened, although some limited amount may be filtered and blended without softening while still meeting the finished water quality goals.

• Brackish Floridan Aquifer water will be available for LPRO desalting treatment at the J. Robert Dean WTP and possibly, a new RO desalination facility at Ocean Reef, if FKAA decides to construct a facility at that location.

• A limited amount of brackish Floridan aquifer water (approximately 0.68 mgd maximum blended with 17 mgd Biscayne Aquifer or 4 percent of the total combined flow from lime-softened or other treated waters) may be filtered and blended with other product waters while still meeting the finished water quality goals after the LPRO system at Florida City is operational. For this analysis, the existing average blend rate of 0.68 mgd was used when only 17 mgd of treated water can be provided. As LPRO capacity is increased or when additional withdrawals can be taken from the Biscayne aquifer, it is assumed that the amount of Floridan aquifer water that can be blended will increase and the amount will be limited to 4 percent of the combined Biscayne aquifer pumpage plus the treated LPRO flow.

• It is assumed that the existing Stock Island and Marathon seawater RO facilities will be upgraded to operate at their 2.0 mgd and 1.0 mgd permitted capacities, respectively. Two trains at Stock Island that are equipped with Toyobo membranes have been shown that each train can produce approximately 0.625 mgd with the new membranes. The remaining two trains at Stock Island and the two trains at Marathon with the “old” DuPont B10 permeators will need to be replaced with new Toyobo membranes, and the permits modified for the increased production to 2.0 and 1.0 mgd, respectively, in 2009 and 2010. FKAA will also need to decide that these seawater RO treatment units will be used to meet peak demands rather than just be limited to emergency supply only. Our analysis assumes that 3 mgd of water can be used from these facilities to meet peak day demands.

• “Firm” WTP production capacities (or capacities with the largest unit process or pump out of service) are used for the analysis.

Exhibit 4-9 presents the projected maximum day demands from 2006 through 2025 (from Section 2, Population and Water Demand Forecast Summary), and the required treatment plant expansions needed to meet these demands.

Assuming that water withdrawals from the Biscayne Aquifer cannot exceed 17 mgd during the dry season when peak demands typically occur, then brackish water LPRO facilities totaling 4.5 mgd are needed as soon as possible (assumed to be operational in 2009). In addition, it will be necessary for FKAA to change the operational policy for the Stock Island and Marathon saltwater RO (SWRO) plants so that they can be operated as peaking plants to meet peak day demands several times during the year rather than just during emer- gencies. Additionally, improvements to the two SWRO facilities will allow the Stock Island and Marathon SWRO plants to produce 2 mgd and 1 mgd, respectively. The third additional water supply source will be a new brackish water LPRO plant at Ocean Reef that will

provide 1.5 mgd of potable water that will be used to reduce the demands at the Florida City Dean WTP.

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WB122005005DFB Exhibit 4-9

Water Treatment Capacities To Meet Maximum Day Demands (All values shown are in mgd)

Average Day Demand Maximum Day Dry Season Demand J. Robert Dean WTP Biscayne Aquifer ASR Floridan Aquifer Bypass Stock Island SWRO Marathon SWRO Florida City Dean WTP LPRO Ocean Reef LPRO WTP Total Dry Season Production Capacity Avg Day Demand vs. Dry Season Capacity Max Day Dry Season Demand vs. Dry Season Capacity 2006 18.58 23.23 17 0 0.7 1.5 0.5 0 0 19.7 1.12 -3.53 2007 18.77 23.46 17 0 0.7 1.5 0.5 0 0 19.7 0.93 -3.76 2008 19.2 24 17 3 0 1.5 0.5 0 0 22 2.8 -2 2009 19.64 24.55 17 3 0 2.5 0.5 0 0 23 3.36 -1.55 2010 20.07 25.09 17 0 0.9 2.5 1.25 4.5 1.5 27.65 7.58 2.56 2011 20.48 25.6 17 0 0.9 2.5 1.25 4.5 1.5 27.65 7.17 2.05 2012 20.88 26.1 17 0 0.9 2.5 1.25 4.5 1.5 27.65 6.77 1.55 2013 21.28 26.6 17 0 0.9 2.5 1.25 6 1.5 29.15 7.87 2.55 2014 21.68 27.1 17 0 0.9 2.5 1.25 6 1.5 29.15 7.47 2.05 2015 22.08 27.6 17 0 0.9 2.5 1.25 6 1.5 29.15 7.07 1.55 2016 22.35 27.94 17 0 0.9 2.5 1.25 6 1.5 29.15 6.8 1.21 2017 22.61 28.26 17 0 0.9 2.5 1.25 6 1.5 29.15 6.54 0.89 2018 22.88 28.6 17 0 0.9 2.5 1.25 6 1.5 29.15 6.27 0.55 2019 23.14 28.93 17 0 0.9 2.5 1.25 6 1.5 29.15 6.01 0.22 2020 23.41 29.26 17 0 0.9 2.5 1.25 6 1.5 29.15 5.74 -0.11 2021 23.5 29.38 17 0 0.9 2.5 1.25 6 1.5 29.15 5.65 -0.23 2022 23.6 29.5 17 0 0.9 2.5 1.25 6 1.5 29.15 5.55 -0.35 2023 23.7 29.63 17 0 0.9 2.5 1.25 6 1.5 29.15 5.45 -0.48 2024 23.78 29.73 17 0 0.9 2.5 1.25 6 1.5 29.15 5.37 -0.58 2025 23.88 29.85 17 0 0.9 2.5 1.25 6 1.5 29.15 5.27 -0.7 Notes:

SWRO=Seawater reverse osmosis desalting BWRO=Brackish water reverse osmosis desalting

Note 1: Biscayne Aquifer flow during dry season limited to 17 mgd; total of lime-softened flows

Note 2: Florida aquifer maximum bypass/blend flow rate ranges from approximately 0.68 to 1.0 mgd depending upon Biscayne and Floridan aquifer raw water qualities and product water quality and quantity from each operating treatment unit. It is assumed that the Floridan aquifer blend is 4 percent of combined Biscayne and LPRO treated water produced.

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WB122005005DFB Exhibit 4-9

Water Treatment Capacities To Meet Maximum Day Demands (All values shown are in mgd)

Average Day Demand Maximum Day Dry Season Demand J. Robert Dean WTP Biscayne Aquifer ASR Floridan Aquifer Bypass Stock Island SWRO Marathon SWRO Florida City Dean WTP LPRO Ocean Reef LPRO WTP Total Dry Season Production Capacity Avg Day Demand vs. Dry Season Capacity Max Day Dry Season Demand vs. Dry Season Capacity Note 3: It is assumed that the Stock Island SWRO system is limited to 1.525 mgd and that the Marathon SWRO system is limited to

0.45 mgd, which is based on operation of the "old" DuPont B10 permeators and existing firm capacity limitations. Improvements to each of these stations will result in the capacity of the Stock Island and Marathon SWRO systems to be increased to 2.5 mgd and 1.25 mgd, respectively, by 2009 and 2010. FKAA will also need to designate these two SWRO facilities as peak demand facilities and not just emergency water supply facilities. Need to purchase spare motor and impeller for HP pump in order to meet redundancy requirements of firm capacity of FDEP.

Note 4: The RO permeate Phase 2 capacity is 6 mgd without any Floridan bypass blend added to permeate. The RO plant is designed to allow for a max of 0.576 mgd Floridan bypass to blend with the permeate prior to the degasifier. This will bring the total max finished water capacity of the RO plant to 6.576 mgd.

Note 5: It is assumed that the Ocean Reef LPRO "brackish" water plant will be sized for 4.5 mgd in capacity; 1.5 mgd of this capacity can be utilized to offset Florida City Dean WTP Production requirements. This facility is planned to be online by 2010.

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With these additional treatment facilities, one additional 1.5-mgd LPRO expansion will be needed in 2013 at the Florida City Dean WTP to meet projected annual MDFs.

FKAA’s projected MDFs could also be met by using treatment plant production and the considerable storage volume FKAA has available because of its unique transmission and distribution system. FKAA currently has 44 MG of storage in the system, including 12 MG of storage at the J. Robert Dean WTP. Even if the existing finished water storage volume is not considered in meeting the projected MDFs, the existing storage capacity at Florida City could possibly lessen the needed RO capacities projected for 2017 and still meet the

projected MDF demands. There is a possibility that consecutive days could occur where demands are at or near the MDF values. The existing storage in the system can be used as needed to meet the needs during these potential high demand periods. If 3 MG of the 44 MG storage capacity could be reserved to help alleviate peak day flow events, it could serve as a buffer to meet MDFs as long as the maximum day demand did not occur more than 2 or 3 consecutive days. It would have to be assumed that if storage was used to meet these peak flow events, mandatory water restrictions and other conservation measures would be in place to minimize the odds for a maximum day flow to occur more than 1 or 2 days before a significant drop off in demand is observed.

If storage capacity can be effectively utilized to meet peak day flows, then the additional 1.5 mgd projected for 2017 could be deferred indefinitely.