Septic System Care
Proper septic system maintenance is a critical component of protecting water quality, especially in areas not served by centralized sanitary sewers. An estimated 25 percent of the United States population relies on onsite wastewater systems, with the vast majority being conventional septic tank systems. These systems are designed to treat household wastewater by separating solids and allowing treated liquid effluent to percolate into the soil. When they function correctly, they are an effective method of waste disposal.
However, when septic systems are improperly sited, poorly maintained, or fail, they become a significant source of nonpoint source pollution. Failing systems can release untreated or partially treated wastewater containing harmful pollutants directly into the environment. These pollutants include pathogenic bacteria and viruses, which pose public health risks, and excess nutrients like nitrogen and phosphorus, which can lead to eutrophication in nearby lakes, streams, and coastal waters. Other pollutants of concern include organic matter that depletes dissolved oxygen and household chemicals. Effective pollution prevention programs often include robust septic system management and outreach components.
The failure of a septic system is not always obvious to the property owner. Failures can range from complete hydraulic backups into a home to silent, chronic leakage of undertreated effluent into groundwater. These failures threaten drinking water wells, contaminate recreational waters, and can lead to the closure of shellfish beds. Unlike conspicuous point-source discharges, pollution from failing septic systems is diffuse and can be difficult to trace, making proactive maintenance and management essential for watershed health.
How the pollution pathway works
Understanding the link between septic system maintenance and water quality requires understanding how these systems can fail. A conventional septic system consists of two main parts: the septic tank and the drainfield (or soil absorption field). Wastewater flows from the house into the tank, where heavy solids settle to the bottom as sludge and lighter materials like grease float to the top as scum. Anaerobic bacteria in the tank digest some of the solids. The liquid effluent then flows from the tank into the drainfield, a series of perforated pipes laid in gravel-filled trenches. Here, the soil acts as a natural filter, removing harmful bacteria, viruses, and some nutrients before the water reaches the groundwater.
Pollution occurs when any part of this process breaks down. The most common cause of failure is the clogging of the drainfield. Over time, if the sludge and scum layers in the tank are not pumped out, solids can flow into the drainfield and clog the pipes and surrounding soil. Hydraulic overloading, caused by excessive water use, can also push effluent through the tank too quickly for solids to settle, leading to the same result. When the drainfield is clogged, effluent can no longer percolate into the soil. Instead, it may pond on the surface of the ground, creating a public health hazard and allowing raw sewage to be washed into the storm drain system during rain events.
Alternatively, the effluent may find other pathways, short-circuiting to groundwater without adequate treatment. This is common in systems sited in unsuitable soils (e.g., too sandy or too dense), on steep slopes, or too close to the water table. In these cases, pollutants like nitrogen and bacteria can travel quickly into groundwater, which may supply drinking water wells or discharge into nearby streams and lakes, delivering a concentrated load of contaminants. This is a distinct pollution pathway from sanitary sewer overflows but can release similar pollutants.
Recommended practices
A combination of homeowner diligence and municipal oversight can significantly reduce pollution from septic systems. The following practices address the most common causes of system failure.
Regular Inspection and Pumping
Proactive maintenance is the most effective way to prevent system failure.
- Inspect the system annually. A qualified inspector can check the sludge and scum levels in the tank, look for signs of leaks, and assess the health of the drainfield.
- Pump the septic tank at least once every three years. The exact frequency depends on tank size, household size, and water usage. Pumping removes the accumulated sludge and scum, preventing solids from migrating to and clogging the drainfield.
- Keep detailed records of all maintenance, including pumping dates, inspections, and repairs. Maintain a map showing the location of the tank and drainfield for easy access.
Surveys reveal a significant gap between recommended practices and homeowner actions. A study in the Chesapeake Bay region found that 50% of septic owners had not had their systems inspected within the last three years, and 46% had not had their systems pumped in that same period. Alarmingly, 12% of residents did not know where their septic system was located on their property.
Responsible Household Habits
Daily activities within the home have a direct impact on the septic system’s health and longevity. Promoting these behaviors is a key part of residential stewardship.
- Conserve water: Reduce the hydraulic load on the system by repairing leaky faucets and toilets, installing low-flow fixtures, and spreading out laundry loads over several days. As many as 75% of system failures have been attributed to hydraulic overloading.
- Dispose of waste properly: Do not flush anything other than human waste and toilet paper. Items like cigarette butts, diapers, coffee grounds, and feminine hygiene products can clog the system.
- Avoid harmful chemicals: Do not pour harsh chemicals, paints, oils, pesticides, or organic solvents down the drain. These can kill the beneficial bacteria that break down waste in the tank and can contaminate groundwater. There is little evidence that commercial septic system additives provide any benefit, and they may be harmful.
- Eliminate garbage disposals: Garbage disposals can double the amount of solids entering a septic tank, increasing the need for pumping and raising the risk of drainfield clogs.
Protecting the Drainfield
The drainfield is a critical and sensitive component of the system.
- Divert other sources of water, such as roof drains and sump pumps, away from the drainfield to prevent saturation.
- Never drive or park heavy vehicles or equipment on the drainfield, as this can compact the soil and crush pipes.
- Do not cover the drainfield with impermeable surfaces like asphalt or concrete, which block oxygen needed for the treatment process.
- Plant only grass over the drainfield. The roots of trees and large shrubs can grow into the pipes and cause damage.
Building a Municipal Management Program
An effective municipal program moves beyond passive education and takes an active role in managing septic systems within its jurisdiction. A comprehensive on-site wastewater management program can protect water quality and save homeowners and local governments money in the long run.
Key components of a successful program include:
- Ordinances and Regulations: Local governments can enact ordinances that require septic system inspections at the time of property transfer, mandate regular pump-outs, or set standards for new system installation and siting.
- Maintenance Tracking: A municipality can track system maintenance, similar to the program in Chesterfield County, Virginia. Private pumpers submit records to the county, which maintains a database and sends reminders to homeowners every five years. The county has the authority to contract a pump-out and charge the owner if they do not comply.
- Financial Assistance: The cost of replacing a failing system, which can range from $3,000 to $7,000 or more, is a major barrier for many homeowners. Municipalities can establish revolving loan funds, as seen in the Puget Sound region, to provide low-interest loans for necessary repairs and replacements.
- Public Outreach: Education is vital. Programs can use flyers, workshops, and media outreach to inform residents about proper system care. The City of Olympia, Washington, spends approximately $40,000 annually on flyers, workshops, and system monitoring.
- Field Screening: To target inspection and repair efforts, municipalities can use field screening techniques to identify areas with a high likelihood of failing systems. Methods include using optical brighteners from laundry detergents as tracers in local streams or using color infrared (CIR) aerial photography to identify stressed vegetation patterns over malfunctioning drainfields.
Effectiveness
The effectiveness of septic systems in removing pollutants varies significantly by system type and site conditions. Even a properly operating conventional system can be a major source of nitrogen, releasing an estimated 10 pounds of nitrogen per person per year to groundwater. This is a primary driver of eutrophication in sensitive water bodies.
While the direct water quality improvement from educational outreach is difficult to quantify, data on the performance of different system technologies demonstrates the potential for significant pollutant load reductions. Advanced treatment systems, such as recirculating sand filters or constructed wetlands, can achieve much higher removal rates for nutrients and other pollutants compared to conventional systems. Communities in nutrient-sensitive watersheds may consider requiring these alternative technologies for new construction or system replacements.
| Onsite Wastewater Disposal Practice | TSS (%) | BOD (%) | Total Nitrogen (%) | Total Phosphorus (%) |
|---|---|---|---|---|
| Conventional System | 72 | 45 | 28 | 57 |
| Mound System | NA | NA | 44 | NA |
| Intermittent Sand Filter | 92 | 92 | 55 | 80 |
| Recirculating Sand Filter | 90 | 92 | 64 | 80 |
| Water Separation System | 60 | 42 | 83 | 30 |
| Constructed Wetlands | 80 | 81 | 90 | NA |
| Onsite Wastewater Disposal Practice | Capital Cost ($/House) | Maintenance ($/Year) |
|---|---|---|
| Conventional System | $4,500 | $70 |
| Mound System | $8,300 | $180 |
| Intermittent Sand Filter | $5,400 | $275 |
| Recirculating Sand Filter | $3,900 | $145 |
| Water Separation System | $8,000 | $300 |
| Constructed Wetlands | $710 | $25 |
Frequently Asked Questions
How often should a septic tank be pumped?
As a general rule, a septic tank should be pumped every three to five years. However, the ideal frequency depends on several factors, including the size of the tank, the number of people in the household, and the volume of wastewater generated. For example, a household with a garbage disposal or a large family may need to pump their tank more frequently, perhaps every one to two years. An annual inspection by a certified professional is the best way to determine when pumping is necessary by measuring the sludge and scum layers.
What are the signs of a failing septic system?
Common signs of a failing septic system include wastewater backing up into household drains, toilets flushing slowly, and foul odors around the septic tank or drainfield. Outside, you might notice wet, spongy ground or unusually lush, green grass over the drainfield area, which can indicate that untreated effluent is surfacing. Pooling water or sewage on the ground surface is a clear sign of system failure. Additionally, if nearby drinking water wells test positive for nitrates or coliform bacteria, a failing septic system could be the source of contamination.
How much does it cost to replace a failing septic system?
The cost to replace a failing septic system varies widely based on geographic location, site conditions, soil type, and the type of system required. A conventional system replacement typically ranges from $3,000 to $7,000. However, if the site has poor soils, a high water table, or is located in a nutrient-sensitive area, a more advanced alternative system may be required. These systems, such as mound systems or sand filters, can have capital costs ranging from $5,000 to over $8,000. These figures do not include costs for permits, soil testing, and system design.
Can chemical additives or cleaners fix a septic system?
There is little scientific evidence that chemical additives, often marketed as septic system cleaners or enhancers, provide any significant benefit. In fact, they can be harmful. Some additives contain organic solvents or other harsh chemicals that can kill the beneficial bacteria necessary for breaking down waste in the tank. This disrupts the natural treatment process and can lead to more solids flowing into the drainfield, increasing the risk of clogs. Furthermore, these chemicals can contaminate groundwater. The most effective way to maintain a system is through regular pumping and proper use, not with additives.
How does a garbage disposal impact a septic system?
Using a garbage disposal can significantly increase the burden on a septic system. It can double the amount of solid waste entering the septic tank, causing the sludge layer to build up much faster. This increased solids loading means the tank must be pumped more frequently to prevent solids from escaping into and clogging the drainfield. The food waste also adds to the nutrient and biological oxygen demand (BOD) of the effluent. For these reasons, many experts recommend against using a garbage disposal in homes with septic systems, or at a minimum, sizing the system larger to accommodate the extra load.
What are alternative septic systems and when are they needed?
Alternative septic systems are technologies designed for sites where a conventional system is not suitable or where higher levels of wastewater treatment are required. They are often needed on properties with poor soil permeability, high groundwater tables, shallow bedrock, or small lot sizes. They are also used in environmentally sensitive areas, such as near lakes or coastal waters, to provide enhanced removal of nutrients like nitrogen and phosphorus. Examples include mound systems, intermittent or recirculating sand filters, and constructed wetlands. These systems are generally more complex and expensive to install and maintain than conventional systems but offer superior pollutant removal.
Why is nitrogen from septic systems a major water quality concern?
Nitrogen is a primary pollutant of concern from septic systems because conventional systems are not effective at removing it. The nitrogen-rich effluent enters groundwater and eventually makes its way to surface waters like streams, lakes, and estuaries. In these water bodies, nitrogen acts as a fertilizer, fueling excessive growth of algae in a process called eutrophication. These algal blooms block sunlight from reaching underwater plants, and when the algae die and decompose, the process consumes dissolved oxygen in the water. This can lead to low-oxygen “dead zones” that kill fish and other aquatic life, severely degrading the ecosystem.