Goal 2020: Eliminating Surface Water Discharge in Northwest Hillsborough County

During periods when reclaimed water flow exceeds irrigation demand, the Hillsborough County Northwest Regional Water Reclamation Facility (NWRWRF) discharges water to a surface water outfall that ultimately flows to Old Tampa Bay. Surface water discharge currently requires high levels of treatment for nutrient removal, 5 mg/L cBOD5, 5 mg/L total suspended solids (TSS), 3 mg/L total nitrogen (TN), 1 mg/L total phosphorus (TP). The Florida Department of Environmental Protection (FDEP) has approved allocations, which limit the TN and TP loads to surface water and reuse systems. Allocations are set for Old Tampa Bay (TN = 486 tons/year, TP = 104 tons/year) and for the other drainage basins of the bay segments including Hillsborough Bay, Middle Tampa Bay, and Lower Tampa Bay (TBNMC, 2010). Four major facilities in the Hillsborough County Northwest Service Area (NWSA) contribute to Old Tampa Bay. These include the River Oaks and Dale Mabry Advanced Wastewater Treatment Facilities (AWWTFs), and the Van Dyke Wastewater Treatment Facility (WWTF) in addition to the NWRWRF. Water quality requirements in the future for continuing the surface discharge are uncertain and even greater levels of treatment may be required. Eliminating the surface discharge at the NWRWRF, and from the Northwest Service Area overall presents an opportunity to reduce treatment requirements, thereby decreasing operating and maintenance costs and potentially increasing treatment capacity within existing process basins, while enhancing resource conservation and still protecting the aquatic environment. Therefore, Hillsborough County is investigating the feasibility of eliminating the surface water discharges in the NWSA.The River Oaks and Dale Mabry AWWTFs are located in densely populated urban areas, and are the source of frequent aesthetic-related nuisance complaints. In addition, the age of these facilities results in high operating and maintenance costs. As such, decommissioning these facilities, directing flow to the NWRWRF and consolidating treatment at that location offers the potential to reduce operating and maintenance costs while benefiting the community and Old Tampa Bay.To manage reclaimed water in excess of the demands for public access reuse (PAR), alternative groundwater recharge concepts were evaluated, including Aquifer Storage and Recovery (ASR). Implementing groundwater recharge and ASR wells has the potential to substantially decrease the nitrogen load to the Bay by eliminating the need for surface water discharge in periods of excess reclaimed water supply. One aquifer recharge system will inject reclaimed water into the Lower Floridan aquifer (LFA) for aquifer recharge and potential future ASR (Class V wells), and the other will utilize excess reclaimed water to develop a saltwater intrusion barrier in the Upper Floridan aquifer (UFA) between Upper Tampa Bay and regional groundwater well fields (Class I wells).