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Conceptual Design The reservoir was sized to be as large as possible after all other setbacks, roadways, seepage ditches and berms were in place. The ROW dedication and DOH offsets would indicate that an approximate surface area of 48 acres is allowable. The 12 foot high berm would be constructed to account for any severe weather events/wave action or hurricane force winds. The assumed water depth is to be 10 feet given the berm side slopes of 3 Horizontal: 1 Vertical. At full capacity, approximately 232 million gallons of water could be stored. As part of the exercise, the treated water from the Osprey Marsh site is to be used to fill the reservoir. The county blends up to 1 million gallons a day (MGD) of demineralized concentrate from the South County WTP and mixes it with up to 10 MGD of canal water from the 271h Avenue pump station. The 271h Avenue pump station has two (2) 10 MGD pumps that operate individually to send the canal water through a 24" diameter pipe. The treated water from the Osprey site currently discharges by gravity to the lateral J-1 canal. If that water were to be used for the reservoir, a new 11 MGD pump station would need to be installed to convey water from the Osprey Site to the reservoir. A separate pump station would need to be installed on the southeast corner of the reservoir to send water from the reservoir back to the new Surface Water Treatment Plant. Such a pumping array will need to be calibrated and carefully operated to ensure successful conveyance of water during normal and emergency operations. If a power outage were to occur, a very large portable or standby generator would be needed at each and every pumping location to ensure continuity of operation. Water quality from the Osprey Marsh site was evaluated to determine the type and kind of surface water treatment necessary to remove dissolved solids and other non -desirable contaminants to meet state and federal drinking water standards. As such, there is a higher than typical chloride concentration in the Osprey Marsh treated water that would need to be removed for potable water consumption. A very sophisticated treatment train consisting of conventional surface water treatment processes (i.e., flocculation and clarification with plate settlers) to reduce suspended solids concentrations and color, followed by microfiltration (MF)/ultrafiltration (UF) to further reduce suspended solids and bacteria and then low-pressure reverse osmosis (LPRO) to reduce the total dissolved solids concentration (salinity) and microbiologicals to within the drinking water standards would be required. This combination of treatment: processes provides a high level of treatment. One potential concern is the formation of algal toxins from the algal turf scrubber system discharge. Algal toxins in surface water supplies have been reported in several locations in the US. The combination of MF/UF/RO has been reported in literature to remove many of these toxins As shown in Figure 2-1, there is approximately 10 aces of useable space just north of the South County RO plant for a new, separate treatment process as just described. Close proximity to the existing piping infrastructure is ideal, allowing for combination of the finished water from either plant to be sent out to the distribution system. Residual by products from the surface WTP need to be considered for treatment and disposal. One option is to construct a 3,000 foot deep injection well. Another option would be to expand the Osprey Marsh operation, which would require extensive pump modifications, additional water transmission piping and larger maintenance need, for such an operation. In addition, solids dewatering may be necessary as part of the surface water treatment process and this requires 1:\Utilities\UTILITY - Engineering\WATER\Alternative Water Supply\Portofino Preserve aka Blackstone 83 acre site\Due Diligence Report for BCC 02_16_2016\Agenda - Due Diligence Report and OPC for 83 acre site for BCC meeting 02_16_2016 v2 cmc.docx Page 10 of 14 108