Shoreline onsite septic systems: The issues
Septic systems are a good way to safely manage wastewater but are not without their problems. Improperly maintained or aging systems can fail, causing major issues for property owners and tenants and potentially contaminating wells and contributing to pollution in nearby water bodies. Many systems were installed decades ago and are reaching the end of their useful lives. Transitioning properties from septic systems to centralized sewer service also introduces new, ongoing costs to households that may already be financially strained. Some rural areas are experiencing population growth and development pressure, which poses challenges around the best options for handling increased demand for utility services while minimizing impacts of greater wastewater loads on local watersheds.
These problems are magnified by flooding and by rising water tables. A flood can prevent systems from draining properly, cause backups into a home or business, and even displace tanks and pipes. Rising water tables in coastal areas or near floodplains can also impair the ability of soils to percolate effluent from septic drainfields. Typically a few feet of vertical separation is needed between drainfields and the water table for proper functionality. Several studies conducted by researchers at the University of Rhode Island “suggest elevated groundwater tables and storm surge have noticeable impacts on soil treatment area performance by reducing the amount of unsaturated soil available to treat wastewater.”
Typical cross section of a shoreline property with an on-site septic system drain field positioned just above the water table; displaying current conditions, and the risk of future failure created by rising sea level and the resulting elevated groundwater.
Citation: Center for Coastal Resources Management, Virginia Institute of Marine Science. (2019) The Problem of Failing Septic Systems. Rivers & Coast, Summer 2019, Vol. 14. Virginia Institute of Marine Science, William & Mary. https://doi.org/10.25773/tkeg-gp63
In a closer view, this illustrates how traditional, in-ground septic systems require unsaturated sediment to function; (below) sea level rise is increasing water table levels leading to septic system failure.
Credit: Molly Mitchell, PhD, Center for Coastal Resources Management at the Virginia Institute of Marine Science
Climate change is contributing to heavier rain events and more frequent flooding, and sea level rise is raising groundwater tables in some low-lying coastal and riverine areas. Sites that were once suitable for in-ground septic systems may no longer be appropriate today or in the coming decades due to these factors, but upgrading individual systems or connecting properties to centralized sewer systems can be costly.
These changing conditions raise questions for communities, local leaders, regulators, wastewater utilities, and planners about the best way to manage wastewater in low-lying rural areas going forward.
Important questions include:
- Where are these issues occurring already?
- Where are they expected to occur in the future?
- How should interventions (policies, funding, technical assistance, etc.) be prioritized?
- How can these problems be mitigated or avoided?
- What are the pros and cons of potential solutions, particularly connecting rural coastal properties to sewer service?
- Are some people or groups disproportionately exposed to these issues? Who will be subjected to these challenges in the future?
- Do people and communities have the financial and technical ability to cope with these challenges? Are they able to access grants, loans, or other assistance programs?
A number of studies have been completed recently or are underway to better understand the extent of these problems and to evaluate and recommend potential solutions. The below projects are focused along the east coast of the U.S., where these issues have become a concern more rapidly in part due to geography (e.g. many small, sparsely developed peninsulas surrounding the Chesapeake Bay), faster rates of sea level rise, and recent damaging coastal storms.
Studies on Sea Level Rise Affecting Septic on the East Coast:
- Virginia – Virginia Wastewater Data Viewer
- Maryland – Septic to Sewer? Justice-focused strategies for addressing coastal septic failures under sea-level rise and increased flooding
- North & South Carolina – Climate Change and Onsite Wastewater Treatment Systems in the Coastal Carolinas
- Rhode Island – Onsite Wastewater Treatment Systems and Climate Change
Going forward, communities and states will need to consider updating regulations for where septic systems can be located, what design specifications they must meet, and what technology is allowed in particular soil conditions. Adjustments could include increasing setbacks from water bodies, updating regulations to account for more recent floodplain maps, groundwater information, or sea level rise projections, and even updating comprehensive growth plans to take these changing conditions into account.
Options for addressing problems with existing septic systems:
- Replace existing septic systems with different technology (e.g. mound or elevated septic systems, or reclamation and reuse systems) that can function with higher water tables or other challenging site conditions
- Flood-proof systems to reduce damage during storms
- Transition properties from septic to centralized sewer
- Connect groups of properties to new decentralized community systems that require less infrastructure than if they were to connect to sewer service
All of these solutions require significant amounts of funding. Many states offer subsidies, often in the form of low-interest loans, to upgrade individual septic systems. A variety of state and federal funding sources are available to communities and tribal nations for larger projects, like extending sewer service; more information on these opportunities can be found on EPA’s Funding for Septic Systems page. One example of a comprehensive program that provides financial and other support to septic users is described in this blog post: Struggling with Septic: North Carolina Towns take a Proactive Approach to Support Property Owners on Decentralized Systems.
Additional Resources
For an overview of this issue and more information on projects in Virginia and Delaware, check out this webinar from March 2023.
For those who depend on a septic system and experience a flood, the U.S. EPA has guidance on how to manage the situation on this website: Septic Systems – What to Do after the Flood.
Another EFCN blog post covers a related topic: Saltwater Intrusion: Should Your Utility Be Concerned?