Principal Drummond Carpenter, Florida, United States
Abstract Submission: Orange County has been facing ongoing water quality degradation, with numerous lakes, rivers, and springs failing to meet mandated water quality standards in both urban and rural areas. Over the past 20 years, more than 150 surface water quality impairments have been documented, many of which are caused by excessive nutrients. To address this issue, the County has focused on mitigating nutrient pollution from surface water runoff, but the contribution of groundwater nutrient pollution to these impairments was relatively unknown. This study evaluated nutrient transport from approximately 86,000 onsite sewage treatment and disposal systems (OSTDS) within unincorporated County limits, and how these septic systems contribute to nutrient loading in surface waterbodies via the groundwater pathway. A septic system prioritization framework was developed to identify high-priority regions where pollution reduction measures are likely to yield significant water quality benefits. These measures include septic-to-sewer retrofits, conventional-to-advanced septic system retrofits, and policy and regulatory adjustments to conventional septic permitting. The Florida Department of Environmental Protection’s regulatory process for developing Priority Focus Areas (PFA) for impaired Florida springs was used as a model to create dozens of Priority Vulnerability Areas (PVAs) around key impaired waterbodies in Orange County. These PVAs were identified using a science-driven approach, starting with the development of a countywide surficial aquifer vulnerability model. This model was paired with a countywide groundwater transport model to assess the extent of groundwater seepage from dense septic regions and establish PVA boundaries. A ranking system for all PVAs was derived to implement septic system interventions over the next several decades. Proposed septic permitting rule changes were also developed to establish acceptable setbacks between lakes and new septic systems, based on groundwater quality fate and transport modeling of nitrogen and phosphorus species
