2.2 Convert or upgrade underperforming or failing septic systems in priority areas

Chapter 2. Septic Systems
Science Solutions
Activities to Reduce Nutrient Inputs

Key Message: Underperforming or failing septic systems can impact water quality of priority waterbodies. Replacing these systems with central sewer service can protect and improve water quality. Where septic-to-sewer conversion is not feasible or is cost-prohibitive, replacing or upgrading systems with advanced technologies can also deliver water quality benefits.

Importance

Many septic systems in Sarasota County are underperforming or failing due to aging designs, degraded components, or poor maintenance. Sea level rise and increased rainfall intensify these issues by increasing soil saturation and raising water tables. Reducing nitrogen pollution from these systems in priority areas is an effective way to protect and enhance water quality.

Overview

The first edition of the Community Playbook for Healthy Waterways recommended improving knowledge about septic system locations and status, and prioritizing upgrades or conversions. Since then, Sarasota County completed the Septic System Replacement Implementation Plan (Sarasota County 2023, 2024), updating the septic system inventory. The Plan reviewed, analyzed, and updated the County’s septic system inventory, indicating there are approximately 44,989 septic tanks in the County, of which 22,204 (49%) are within the County Public Utilities service area.

Septic Systems to Central Sewer Service

The Phillippi Creek Septic System Replacement Program (PCSSRP) has eliminated 9,932 septic systems, redirecting wastewater to the Bee Ridge Wastewater Treatment Facility (WWTF) (Sarasota County 2023). The Program aims to eliminate approximately 14,000 systems through a multi-year implementation plan. An additional 15,000 septic systems have been identified in South County, though no replacement plan is in place yet.

The Septic System Replacement Implementation Plan developed a prioritization methodology based on potential water quality improvements, affordability, funding potential, and infrastructure impacts. Highest priority areas identified include South County, Central County, and Bee Ridge West. Two implementation alternatives were developed:

  • Option One (Figure 2.2.1): Focuses on high- and medium-density areas, costs $1.07–1.31 billion, and includes 14,902 existing systems and 17,870 future connections. Estimated nitrogen reduction is 211,036 pounds/year.
  • Option Two (Figure 2.2.2): Focuses on larger, lower-density areas, costs $1.26–1.53 billion, and includes 14,676 existing systems and 17,800 future connections. Estimated nitrogen reduction is also 211,036 pounds/year.
infographic of septic implementation option 1 with costs, construction schedule, and water quality criteria

Figure 2.2.1. Option One from the Sarasota County Septic System Replacement Implementation Plan for converting septic systems to central sanitary sewer service. SOURCE: Sarasota County 2024

infographic of septic implementation option 2 with costs, construction schedule, and water quality criteria

Figure 2.2.2. Option Two from the Sarasota County Septic System Replacement Implementation Plan for converting septic systems to central sanitary sewer service. SOURCE: Sarasota County 2024

Sarasota County Commissioners postponed implementing a replacement program until the Advanced Wastewater Treatment (AWT) conversions at Bee Ridge WRF (2025) and Venice Gardens WRF (2026) are complete, with Central County’s conversion still in design. This delay ensures wastewater facilities have adequate capacity for additional loads and results in reduced nitrogen levels in reclaimed water from upgraded facilities.

Enhanced Nutrient Reduction Technologies

Conventional septic systems reduce nitrogen inputs by approximately 30%–40% (Toor et al., 2011b) between the tank and drainfield where organic nitrogen is converted to ammonia then nitrate. Additional denitrification can occur naturally if the leachate flows through anaerobic, carbon-rich soils. Enhanced nutrient reduction septic systems (ENR-OSTDS) replicate these environments within the system.

Florida’s 2023 legislation (HB 1379) requires ENR-OSTDS in areas managed under Basin Management Action Plans (BMAPs), Pollution Reduction Plans (PRPs), and Reasonable Assurance Plans (RAPs). As of July 1, 2023, new septic systems on lots one acre or less in impaired watersheds must use ENR-OSTDS. By July 2, 2030, existing systems must connect to sewer if available, or upgrade to systems reducing nitrogen by at least 65%.

FDEP-approved ENR-OSTDS technologies include:

  • In-ground nitrogen-reducing biofilters (INRBs)
  • NSF 245-certified aerobic treatment units
  • Performance-Based Treatment Systems approved by the state

According to FDEP’s BMAP and Alternative Restoration Plans OSTDS Requirements map, these rules apply in two Sarasota County areas: South Venice (Alligator Creek WBID 2030 TMDL Plan) and south of University Parkway between North Honore Ave and Lorraine Road (Tampa Bay Estuary RAP).

Approach

Septic to Sewer Conversion

Replacing failing systems with central sewer service should remain a priority. Although the Septic System Replacement Implementation Plan is postponed, grant applications to support phased implementation could begin now. Separate proposals could target each WRF service area, starting with Bee Ridge in 2025 and Venice Gardens in 2026. The Plan includes a helpful overview of potential funding sources, timelines, and matching requirements. The Plan provides a useful overview of funding opportunities, important dates for the application process, and matching requirements. The County should continue implementing conversions through the PCSSRP.

Enhanced Nutrient Removal Septic Technologies

In areas not prioritized for sewer connection, advanced septic technologies should be used to retrofit or replace failing systems. These systems are ideal for site-specific deployment, particularly in areas lacking natural denitrification conditions.

For the two identified areas in Sarasota County, new systems on one-acre lots or smaller must meet ENR-OSTDS standards. By 2030, existing systems in these areas must upgrade or connect to sewer. In other areas, upgrades remain voluntary.

Public outreach is key. Educational materials should help property owners recognize failing systems, understand the benefits and options for advanced systems, and compare installation and maintenance costs. Sarasota County might explore incentives to help offset the additional cost of ENR-OSTDS.

Resources

Status

Sarasota County Septic System Replacement Implementation Plan postponed; No activity on prioritizing and incentivizing advanced technology replacement or retrofits for underperforming or failing septic systems

Performance Measure

  • Funding secured for Sarasota County Septic System Replacement Implementation Plan, either in whole or part
  • Targeted outreach and education about Nutrient Reduction Onsite Sewage Treatment Systems

Experts or Leads

Sarasota County Public Utilities

Cost Estimate

$1.07–1.53 billion for Option One of the Sarasota County Septic System Replacement Implementation Plan in whole
$50,000 for education and outreach.

Related Activities

Chapter 1.2, Chapter 2.1, Chapter 2.3, Chapter 2.4, Chapter 2.5

 

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Other Septic System Activities

2.1 Quantify annual nutrient loads from septic systems

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