Septic in Stanfield, NC

Last updated: Mar 21, 2026

Welcome to Stanfield, a place where friendly neighbors, wide yards, and easygoing mornings blend into everyday practicality. If you're house-hunting or settling into a Stanfield home, you'll notice a straightforward truth behind the scenes: many homes here run on septic systems rather than a municipal sewer line. That's not a sign of trouble—it's a normal part of how Stanfield was built and how families keep wastewater management simple and affordable.

Is septic common in Stanfield? Should I expect septic if I own or buy a home? In Stanfield, yes—septic systems are a common, practical reality. Not every street is tied to a city sewer, and lots here were frequently designed with on-site wastewater treatment in mind. If you own or are buying a home here, plan on septic being part of daily life unless you've confirmed a sewer connection. It's a good idea to review the system's history with the seller or a home inspector, including the last pump date and any repairs.

Why homes typically use septic systems in Stanfield

Property layout and lot sizes: Many Stanfield homes sit on larger lots, which naturally suits on-site wastewater systems.
Sewer expansion realities: Extending municipal sewer lines can be costly and slow, so septic remains the practical choice on many streets.
Groundwater and wells: With abundant wells and sensitive groundwater near some neighborhoods, on-site treatment helps protect water supplies when properly designed and maintained.
Local building patterns: In this region, homes have long relied on gravity-flow drainage and well-planned drain fields, making septic a reliable, cost-effective option.

High-level explanation (why septic exists here)

A septic system provides a simple, on-site way to treat household wastewater. Wastewater from the house goes into a septic tank where solids settle and scum forms, while liquids move to a drain field where soil and natural bacteria finish the job. A well-designed system, pumped at the right intervals, protects your home, your yard, and the water you share with neighbors. Typical maintenance includes a periodic inspection and a pump every few years (often every 3–5, depending on tank size and family usage). When cared for, a Stanfield septic system runs reliably for many years.

Here you'll find practical, neighborly guidance you can trust, from a local pro who knows the terrain, soil, and everyday realities of septic care in Stanfield.

Where Septic Systems Are Common in Stanfield

Rural, undeveloped pockets outside municipal sewer

In Stanfield, many homes rely on septic because the town's sewer lines don't reach every street or subdivision. Development often occurred in ways that left outer areas without centralized wastewater service. You'll see septic more in farms, older homesteads, and newer homes built beyond the sewer map.

Large lot sizes are common, often 0.5 to 2 acres, which leaves space for a drain field and reserve area.
Predominantly single-family homes on individual parcels outside town boundaries.
Subdivisions planned before sewer expansions, or in areas where public sewer hasn't been extended yet.

Soil and drainage patterns that favor on-site systems

Septic performance depends on soil, slope, and groundwater. Stanfield's mix of soils means some blocks are ideal for well-designed OSW systems, while others require careful site evaluation.

Soils with moderate percolation rates support efficient leach fields; very tight clays or very sandy patches each pose unique design challenges.
Seasonal high water tables and proximity to streams influence setback distances and system sizing.
Proper drainage around the drain field and avoiding surface runoff help protect the leach field and nearby wells.

Lot size, zoning, and historical development

Zoning and history shape where septic shows up. Outer Stanfield neighborhoods and rural acreages were frequently developed with on-site systems when municipal sewer wasn't available.

Typical lots range from about half an acre to a few acres, giving room for the sewer-free leach field.
Older areas just outside town limits often rely on septic as the standard wastewater solution.
In newer developments lacking public sewer, septic design becomes a key part of site planning.

Where you'll usually find septic in Stanfield

Farmsteads and rural homes that predate widespread sewer expansion.
Outlying residential streets and subdivisions beyond Stanfield's sewer reach.
Properties that pair private wells with on-site wastewater systems, underscoring the need for proper well spacing and protection.

Practical guidelines for Stanfield homeowners

Confirm soil suitability and percolation: a soil evaluation helps determine leach-field size and design requirements. Consider using the NC State Soil Testing Lab for soil and water guidance:
Hire a licensed septic contractor to design, install, or upgrade your system, and ensure compliance with local setback rules protecting wells, streams, and property lines.
Maintain the system proactively:
- Pump out every 3–5 years (or per your installer's recommendation).
- Conserve water to reduce load on the drain field.
- Keep vehicles and heavy equipment off the drain field to avoid compaction.
Plan for inspection and potential upgrades: older systems may need more frequent pumping or component replacements; newer systems with advanced treatment units may have different maintenance needs.
Use official resources for guidance:
- NC Department of Environmental Quality Onsite Wastewater Program:
- EPA Septic Systems: https://www.epa.gov/septic
- NC State Soil Testing Lab: https://soiltestlab.ncsu.edu/

Septic vs Sewer: What Homeowners in Stanfield Should Know

How septic systems work vs municipal sewer

Septic system (on-site): Wastewater from sinks, toilets, and laundry flows into a septic tank, where solids settle and scum forms. Bacteria digest the waste, and effluent travels to a drain field where soil and microorganisms treat it.
Municipal sewer: Wastewater is collected by public sewer lines and transported to a regional treatment plant. The city or county owns and maintains the pipes, pumps, and treatment facilities; you typically pay a monthly sewer bill.
Key difference for Stanfield homes: the on-site system is managed by you, the sewer system is managed by a local utility. Your maintenance responsibilities shift accordingly.

Signs your home uses septic vs connected to sewer

Utility bills: a standing sewer bill indicates municipal sewer service; no sewer bill often means septic unless you're on a private water/sewer agreement.
On-site indicators: a buried tank lid, access risers, or a drain-field area in your yard suggests a septic system.
Street and documentation: property records, permitting documents, or the county health department can confirm your disposal method.
If in doubt, contact your local utility or the Union County/Stanfield health/environmental health office to verify.

Pros and cons at a glance

Septic system
- Pros: independence from city infrastructure, potentially lower monthly costs, can be economical long-term with good maintenance.
- Cons: you're responsible for pumping, inspecting, and repairing; failures can be costly and disrupt landscaping.
Municipal sewer
- Pros: city maintenance of the network, predictable monthly charges, no on-site drain-field concerns.
- Cons: potential rate increases, connection fees if you're not yet tied to sewer, and dependence on a public system's reliability.
Practical takeaway: for Stanfield homeowners, maintenance quality and long-term costs hinge on proper septic care or smart budgeting for sewer charges.

Maintenance essentials you should know

Pump or have a pro pump your septic tank every 3–5 years (size and usage affect frequency).
Use water efficiently; stagger high-volume wastewater (e.g., laundry) to reduce load.
Only toilet paper goes in toilets; avoid flushable wipes, chemicals, solvents, and grease down drains.
Protect the drain field: keep heavy equipment off, plant appropriately, and avoid patio installations or wells over the field.
Regular inspections: schedule professional checkups every few years to catch issues early.
Document everything: keep a map of tank locations, lids, and pump dates; share records with future buyers or contractors.

When to consider connecting to sewer or switching

Confirm availability: check with the local utility serving Stanfield and nearby areas whether sewer mains are available or planned for your street.
Compare costs: obtain a formal estimate for tying into sewer, including any connection fees, street work, or main line extensions, against septic maintenance costs.
Permits and timing: understand local permit requirements, project timelines, and any required system decommissioning for a septic if you switch to sewer.

Local and official resources

EPA Septic Systems:
North Carolina Cooperative Extension – Homeowner guidance on septic systems:
Union County, NC government (for local regulations and services):
For broader guidance and homeowner best practices, refer to official state and federal sources linked above.

Typical Septic System Types in Stanfield

Conventional gravity septic systems

How it works: Waste from the home goes into a septic tank, where solids settle. Liquid then travels by gravity into a network of perforated pipes (the drainfield) buried in the soil.
Best suited for: Homes with adequate soil depth and good drainage.
Pros: Simple design, generally lower upfront cost, easy to maintain.
Cons: Requires sufficient soil depth and drainage; performance can degrade with high groundwater or dense clays.
Practical note: In Stanfield soils, a site evaluation is essential to confirm you have enough absorption capacity. For overview, see EPA's Onsite Septic page:

Mound systems

How it works: Used when the natural soil has limited depth or drainage near the surface. The drainfield is built above grade on a sand fill, with a shallow signaling layer and necessary aggregate.
Best suited for: Areas with high water tables, poor native soil, or shallow bedrock.
Pros: Expands viable sites that won't fit conventional drains.
Cons: Higher installation cost and more long-term maintenance considerations.
Practical note: Mounds are a common NC solution for challenging Stanfield sites; discuss options with a licensed onsite professional. Additional guidance is available through NC Cooperative Extension:

Sand filter and advanced pretreatment systems (ATU, media filters)

How it works: Pre-treatment (often aerobic) reduces solids and pathogens before effluent reaches the drainfield. The treated effluent then enters a drainfield or spray/irrigation system.
Best suited for: Lots with limited drainage, smaller lots, or soils that don't meet conventional criteria.
Pros: Higher treatment level, better protection for soil and groundwater.
Cons: More complex maintenance and higher ongoing costs; requires regular servicing and monitoring.
Practical note: These are common in North Carolina where soil conditions limit traditional systems. EPA resources and NC DEQ guidance provide detailed maintenance expectations: https://www.epa.gov/septic and https://deq.nc.gov/about/divisions/waste-management/onsite-wastewater

Drip irrigation systems

How it works: Treated wastewater is reused through drip emitters in shallow soil zones or landscape beds, with pretreatment to protect plants and soil.
Best suited for: Properties with suitable vegetation plans and careful design to protect groundwater.
Pros: Efficient water use and flexible landscaping options.
Cons: Requires proper system design, filtration, and ongoing maintenance; not universally permitted in all Stanfield parcels.
Practical note: Check local permitting requirements and a qualified installer's recommendations. Official guidance from NC Extension can help with design considerations: https://content.ces.ncsu.edu/onsite-wastewater-management

Holding tanks and other alternatives

How it works: No drainfield is possible or permitted; wastewater is stored until pumped out.
Best suited for: Very restricted sites or when immediate installation of a drainfield isn't feasible.
Pros: Permitted as a temporary or specific-solution option in some cases.
Cons: High maintenance cost and frequent tank pumping; requires strict pumping schedules and permits.
Practical note: Holding tanks are generally a last resort and require clear local approvals. Your county health department can confirm options.

How to identify what you have in Stanfield

Locate the septic permit or schematics from the original installation or recent updates.
Inspect any visible tank lids and control panels; note if a pump or pressure distribution components exist.
Talk with a licensed septic contractor or the Union County health/Environmental Health office about your exact system type and updates needed.
Get a soil and site evaluation to confirm absorption capacity and determine if a mound, ATU, or other type is appropriate for your lot.

Maintenance reminders

Schedule pumping every 3–5 years for conventional systems (more often for households with high wastewater flow or stricter local codes).
Avoid flushing nonbiodegradable items, oils, or chemicals that can disrupt treatment.
Keep the drainfield area protected from heavy vehicles and excessive landscaping irrigation.
For advanced systems (ATU, sand filters, drip), follow the manufacturer's maintenance plan and have alarms/redundancies checked annually.

Resources

EPA: Septic Systems (onsite wastewater) https://www.epa.gov/septic
NC Department of Environmental Quality – On-Site Wastewater https://deq.nc.gov/about/divisions/waste-management/onsite-wastewater
NC Cooperative Extension – Onsite Wastewater Management https://content.ces.ncsu.edu/onsite-wastewater-management

Common Septic Issues in Stanfield

Soil and Drainfield Challenges in Stanfield

Stanfield sits in the Piedmont and often has heavy clay soils with limited percolation and a relatively shallow groundwater table. That combination makes drain fields less forgiving, especially after wet seasons or heavy rain. When the soil stays saturated, effluent can back up or surface, and standing water can linger around the drain field.

Common indicators: damp, muddy patches over the drain field; lush, water-loving plants over the area; slow draining toilets and sinks.
What this means for your system: standard drain fields may need extra space, a mound system, or a redesigned effluent distribution to work with the local soil.
Practical steps:
1. Have a licensed septic pro assess soil conditions and recommend the right system type for Stanfield soils.
2. Keep heavy equipment and vehicles off the drain field to prevent soil compaction.
3. Plant thoughtfully: avoid large trees or shrubs whose roots could reach the pipes; emphasize shallow-rooted ground cover near the field.
4. Direct roof and gutter runoff away from the drain field to reduce saturation.

Water Management: Rainfall and Groundwater Impact

North Carolina's seasonal rains and Stanfield's groundwater levels can push soils toward saturation, especially after storms. When the ground stays wet, effluent may not percolate properly, leading to backups or surface seepage.

Signs to watch: sudden slow drains after rain, soggy spots near the system, gurgling sounds in plumbing.
Preventive actions:
1. Space out water use (dishwashing, laundry, showers) on laundry-heavy days to reduce load on the tank.
2. Redirect downspouts and surface runoff away from the septic system and drain field.
3. Avoid irrigation or lawn watering directly over the drain field area.
4. If your property borders streams or wetlands, consult a pro about the appropriate system design for high-water-table conditions.
Resources: consider reviewing EPA and NC DEQ guidance on site evaluation and design for wet or high-water-table soils.

Backups, Slow Draining, and Odors

Backups and sluggish drains are common red flags in Stanfield, especially if the system is older or undersized for the household.

Typical causes: excess water use, root intrusion, faulty tank baffles, or a failing effluent pump.
Quick checks:
- Do you notice toilets or drains that take longer than normal to clear?
- Are there unusual odors near the septic tank, drain field, or vents?
Next steps:
1. Limit water use and avoid garbage disposals while diagnosing.
2. Have the tank pumped and inspected by a licensed pro to verify baffles are intact and the effluent is flowing correctly.
3. If the drain field is saturated or damaged, a professional assessment might recommend field repair or replacement.

Root Intrusion and Landscaping

Roots are a frequent culprit when Stanfield homeowners plant trees or large shrubs near the septic system.

Issues caused by roots: cracked pipes, clogged distribution lines, reduced field efficiency.
Management tips:
- Keep mature trees and aggressive root zones away from the septic system—ideally 20 feet or more depending on species.
- Choose low-root-distance plants around the area and maintain a healthy buffer of well-established lawn.
- Periodically inspect the area for signs of roots cracking concrete or PVC pipes and seek professional help if you suspect intrusion.

Maintenance and Proactive Care

Regular maintenance remains the best defense against Stanfield-specific challenges.

Pumping and inspections:
- Typical guidance is every 3–5 years for a standard household, more often if you have a garbage disposal or a lot of bathroom waste, and shorter intervals if the system already shows trouble.
- At a minimum, schedule a professional tank inspection every 2–3 years to check baffles, the pump (if applicable), and overall function.
Simple daily practices:
- Use a modest amount of water per flush and spread out laundry days.
- Don't pour chemicals, solvents, or oils down any drain or the septic tank.
- Catch and treat yard runoff near the drain field to preserve drainage capacity.

Resources:

EPA Septic Systems:

Septic Inspection, Permits & Local Oversight

Who Oversees Permitting in Stanfield, NC

In Stanfield (Union County), septic system permits and inspections are handled at the county level under the North Carolina On-Site Wastewater Program (NOWP). Local Environmental Health staff review plans, issue permits, and conduct inspections to ensure installers follow state standards and site-specific requirements.

Permits cover new systems, repairs or replacements, and changes in use (such as adding a living unit or increasing system capacity).
Inspections occur at key milestones during construction and after installation to confirm proper performance and record-keeping.
State guidelines set the technical rules, while the county administers permits and coordinates inspections.

When You Need a Permits

A permit is typically required before any work starts on a septic system.

New installations, including conventional and alternative systems.
Replacements for failed or inadequately performing systems.
Repairs or modifications that change system components, flow, or setbacks.
Changes in property use that affect wastewater disposal (e.g., adding a dwelling or rental unit).
Abandonment or capping of an existing system.

Skipping the permit can lead to fines, stop-work orders, or a rejection of final approval for the project.

How to Apply for a Permit

Follow these steps to keep the process smooth and predictable.

Hire a licensed professional
Work with a NC-licensed septic designer/installer or a licensed design-build team.
They help ensure the plan meets NC NOWP standards and local requirements.
Complete soil and site evaluations
A qualified professional conducts soil investigations (perc tests) and documents site conditions.
Gather topographic maps and any existing well locations or setbacks required by code.
Prepare the design package
Include system design, layout, setback calculations, soil conditions, and proposed maintenance plan.
Ensure the plan complies with state NOWP criteria and local site constraints.
Submit to the local authority
Submit the permit package to Union County Environmental Health (the local office administering NOWP in Stanfield).
Include the design, soil reports, site plan, and applicable fees.
Respond to reviews and obtain approval
The reviewer may request changes or clarifications.
Once approved, you'll receive the official permit to begin work, plus inspection milestones.

Inspection Milestones You'll Likely Face

Inspections ensure the installation matches the approved plan and functions correctly.

Pre-installation review or soil test verification (as required).
During installation: tank placement, piping, trenching, backfill, and distribution components.
Backfill completion and initial system testing (where applicable).
Final inspection and system acceptance, with any required documentation filed.

If issues are found, corrections must be completed and re-inspected before final approval.

Fees, Timelines & Compliance

Fees vary by project size, system type, and local requirements.
Timelines depend on plan complexity and workload; allow time for soil evaluation, plan review, and scheduled inspections.
Maintain all permits, inspection approvals, and maintenance records for the life of the system.
Always perform maintenance and pumping on a schedule approved by the installer and maintain records; unpermitted work can compromise system performance and compliance.

Resources & Official Contacts

State-wide standards and NOWP program:
Union County Government (where Environmental Health handles onsite wastewater):

These resources help homeowners confirm which agency is handling permits, understand the design criteria, and access contact information for scheduling inspections in Stanfield.

Septic Maintenance for Homes in Stanfield

Stanfield-specific considerations

Stanfield sits in Union County with clay-rich soils and periodic heavy rainfall. Those conditions can saturate the drain field, especially after storms, leading to slower drainage or backups if the system is not well maintained.
Many Stanfield yards host mature trees. Roots can intrude on the septic tank or drain field if trees are planted too close. Plan plantings with distance from the system in mind.
The local groundwater table can rise in wet seasons. This increases the chance of surface pooling or effluent seeps if the drain field is stressed. Regular maintenance helps prevent problems during wet periods.
Home layouts and older houses in Stanfield may have smaller tanks or aging drain fields. If you're unsure of your system's age or capacity, a local septic professional can assess suitability for current usage.

Routine maintenance you can perform

Schedule professional inspections and pumping
Most households with 2–4 residents and a standard 1,000–1,500 gallon tank should plan a professional pumping every 3–5 years, with more frequent pumping if you have a larger family, a smaller tank, or high solids inputs. Have an annual inspection to catch early issues.
Use water wisely
Distribute laundry, dishwashing, and showering throughout the day to reduce peak flows. Fix leaks promptly and consider low-flow fixtures to minimize load on the tank and leach field.
Be mindful of what goes into the system
Use the septic tank for water, toilet waste, and approved products only. Avoid flushing wipes (even "flushable" ones), diapers, feminine products, coffee grounds, grease, solvents, pesticides, or chemicals that can harm beneficial bacteria.
Protect the drain field
Keep vehicles and heavy equipment off the drain field. Do not plant deep-rooted trees or large shrubs nearby. Maintain a minimum buffer of grass or shallow-rooted ground cover; avoid paving or building over the area.
Maintain proper soil and landscape management
If you notice pooling water, unusually green grass, or soil that remains soft above the drain field after rainfall, call a professional. These can be signs the field is overworked or failing.
Keep good records
Track pumping dates, inspections, repairs, and any changes to usage. A simple file or folder helps you plan future service and supports home-sale disclosures.
Plan for aging systems
If your system is 20 years old or older, or if you've had repeated backups or wet spots, budget for a professional evaluation and possible upgrade. Early planning can prevent emergency replacements.

Seasonal readiness for Stanfield

After heavy spring rains or winter thaws, monitor for slow drains, gurgling sounds, or surface damp spots in the yard. These signals may indicate the drain field is stressed by moisture.
In the dry season, continued use in a tight house or with drought can also impact balance. Conserving water remains important year-round.
If you plan to travel or leave the home vacant in winter, consider winterizing recommendations from a licensed septic professional to protect the system in freezing temperatures.

Signs of trouble and quick actions

Backups, gurgling toilets, or sewage odors inside the home.
Clearly wet or spongy areas over the drain field or discharge from the system.
Slow drains that don't improve with typical fixes.
If you notice any of these, stop using large volumes of water and contact a licensed septic professional promptly. Avoid DIY fixes that involve chemicals or additives not approved by a pro.

Local resources and links

EPA Septic Smart: guidance for homeowners and local codes —
North Carolina Department of Health and Human Services, Onsite Wastewater Management —
Union County Environmental Health (local oversight for Stanfield homes) —
For general questions about Stanfield-specific regulations, consult your county health department or licensed local septic contractor.

Cost Expectations for Septic Services in Stanfield

Septic Tank Pumping and Cleaning

What it includes: removal of accumulated sludge and scum, cleaning of internal baffles and corners, inspection of inlet/outlet tees, and checking the pump chamber if present. Crews typically pump with a truck-mounted unit and dispose of the liquid at an approved facility.
Stanfield-specific notes: older homes or those without current risers can require temporary access improvements, which may add to cost. If you have two tanks (dual-compartment), expect a higher price.
Typical cost in Stanfield: about $200–$400 for a standard single-tank system; $350–$600 for larger tanks, dual compartments, or difficult access. Disposal fees and travel charges may apply.
Steps to prepare (on-site):
1. Locate and uncover the tank lid(s).
2. Move vehicles and keep bystanders clear.
3. Minimize water use the day of service.
4. Have a contact available for scheduling changes.

Routine Maintenance and Inspections

What it includes: visual inspection of components, sludge/scum depth check, effluent filter cleaning (if present), pump and alarm test, and a high-level system functioning review. Often recommended every 1–2 years, depending on usage and system type.
Stanfield-specific notes: if you have a mound or advanced treatment system, inspectors may perform additional field tests or document seasonal performance.
Typical cost in Stanfield: basic inspection $100–$180; a full system evaluation with a more thorough check or dye test $150–$300.
Quick guidance: regular inspections can prevent costly repairs later; many towns require documentation for permit renewals or upgrades.

Diagnostic Inspections and Camera Evaluation

What it includes: locating all components, inspecting lines for root intrusion or obstructions, and camera inspection of pipes to pinpoint blockages or breaks.
Stanfield-specific notes: in clay-heavy Piedmont soils, access can be trickier; crews may use locating tools or slight trenching to reach lines.
Typical cost in Stanfield: $200–$500 depending on access, depth, and whether a dye test or locator service is included.
When to consider: after repeated backups, unusual odors, or unexplained drainage issues.

Drain Field Repair and Replacement

What it includes: on-site diagnostics to confirm drain-field failure, replacement or repair of failed trenches, piping, or lateral lines, and in some cases installation of a new field or mound system with soil testing and permits.
Stanfield-specific notes: local soil types and weather can influence timing and method (e.g., mound systems may be necessary in compacted or high-water-table sites).
Typical cost in Stanfield: repair of a single trench $3,000–$7,000; full drain-field replacement or mound system $8,000–$25,000+ (costs escalate with size, permits, and site conditions).

System Design, Permitting, and New Installation

What it includes: site evaluation, system design, permit submission, initial installation, and final inspections. This covers conventional, mound, or other advanced-treatment options.
Stanfield-specific notes: county health department or local authorities usually require plan review and inspections; permit fees are common and can vary by project scope.
Typical cost in Stanfield: conventional new systems $10,000–$25,000; mound or advanced systems $20,000–$40,000+. Design and permit fees often $500–$2,000 in addition to the installation.

Perc Testing and Soil Evaluation

What it includes: soil evaluation and percolation tests to determine if a site can support a septic system and which type (conventional vs. mound) is appropriate.
Stanfield-specific notes: Piedmont soils can present unique drainage characteristics, which influence design choices and timelines.
Typical cost in Stanfield: $300–$900, depending on site size, depth to groundwater, and test scope.

Pumps, Alarms, Risers, and Other Components

What it includes: replacement or repair of submersible pumps, float switches, alarms, piping, venting, and lid/riser upgrades for easier future maintenance.
Stanfield-specific notes: many homes benefit from adding or upgrading risers and lids to facilitate future access in compact lots.
Typical cost in Stanfield: pump replacement $300–$1,000; alarms/floats $150–$450; riser kits and lids $200–$600.

Emergency, After-Hours, and Seasonal Services

What it includes: urgent pumping, clogged lines, or backups outside normal business hours, typically with a higher rate and possible travel fees.
Stanfield-specific notes: after-hours service is more common during heavy rain seasons when backups spike.
Typical cost in Stanfield: standard rates plus a possible after-hours surcharge and travel fee.

Official Resources

NC Department of Environmental Quality - Onsite Wastewater Program:
U.S. Environmental Protection Agency - Septic Systems: https://www.epa.gov/septic