Septic in Bauxite, AR

Nestled in the rolling hills of Saline County, Bauxite homes often sit on leafy lots where the hum of a septic system is a familiar part of daily life. This is a town where many families value the independence and practicality of an on-site wastewater system that works right on your property.

Is septic common in Bauxite? Should I expect septic if I own or buy a home?

Yes. In Bauxite, many residential properties are not connected to a town sewer, so a septic system is the norm rather than the exception. If you're buying a home here, it's smart to assume there's a septic system and to plan for a full, local-inspection as part of your purchase. Knowing the tank size, age, and the condition of the drain field can save you surprises down the road.

What to check when you're buying a home with septic

• Tank size and age, and the date of the last pump-out
• Location of the septic tank and drain field, plus access for future maintenance
• Any maintenance records or permits on file
• Signs of past problems (standing water, soggy areas, odors, or slow-draining fixtures)
• Whether a licensed pro has conducted a recent inspection

Why homes typically use septic systems in Bauxite

• Rural layout and lot sizes: Many properties aren't near a municipal sewer line, making on-site treatment the practical option.
• Infrastructure costs: Extending sewer mains to every street or property isn't always economical in this region.
• Local zoning and property design: On-site wastewater treatment fits well with how homes are spaced and how land is used around here.

High-level explanation: why a septic exists here

A conventional septic system treats household wastewater underground on your property. Wastewater flows into a septic tank, where solids settle to the bottom and scum rises to the top. Clarified liquid then exits to a drain field or leach field, where soil and microbes further treat it before it percolates away. Proper design, installation, and ongoing maintenance—pump-outs at intervals based on tank size and usage, protecting the system from harsh chemicals, and avoiding roots near the field—keep the system functioning well. In Bauxite, a well-designed system works with local soils and groundwater patterns to protect your home and yard.

Tips to keep your system healthy

• Use water efficiently and spread out high-water activities
• Only flush toilet paper and human waste; avoid wipes, greases, and chemicals
• Schedule regular inspections and pump-outs per local guidance
• Keep the drain field clear of heavy machinery, trees, and deep footing near the area

As your neighbor and a local septic contractor, I'm here to help you understand what's in place, how to care for it, and what to watch for as seasons change in Bauxite.

Where Septic Systems Are Common in Bauxite

Areas in Bauxite where septic is the norm

• Rural and semi-rural homes outside the city sewer service area rely on septic systems as the practical wastewater solution.
• Single-family houses on larger lots, often 0.5 acres or more, where extending a sewer line isn't economical.
• Farms and properties with multiple structures (outbuildings or additional dwellings) where centralized sewer isn't available.
• Older neighborhoods and subdivisions developed before centralized sewer lines were installed.
• Homes on hills, slopes, or uneven terrain where gravity-fed sewer connections are difficult or costly.

Why septic systems fit Bauxite

• Public sewer access is unevenly distributed in and around Bauxite, so most homes rely on on-site wastewater treatment.
• Property sizes in many parts of town lend themselves to properly designed drainfields that meet onsite requirements.
• Septic systems offer a homeowner-managed alternative when municipal service is not feasible, provided installation and maintenance follow local rules.
• In areas with diverse soils, a properly designed septic system allows the drainfield to interact with the soil for natural treatment, which is why soil testing and proper siting matter.

Soils, terrain, and water considerations

• Drainfield placement depends on percolation test results, soil depth, and the ability of the native soil to filter effluent.
• Sloped or hillside sites require careful distribution and setback planning to ensure water does not flow into wells, structures, or zones with drainage issues.
• Shallow groundwater or high water tables can limit drainfield locations and may necessitate alternative designs or closer coordination with the health department.
• Some parts of Saline County have soil types that drain well, while others may be slower to percolate; each property requires site-specific evaluation.

How to tell if a property uses septic

• Look for a concrete or plastic access cover in the yard that marks the septic tank; a second cover may indicate the distribution box or leach field.
• If nearby older properties do not have sewer lines running along the street, septic is a common assumption.
• When purchasing, request the seller's septic paperwork, including tank location, pump history, and field integrity notes.

Sizing, installation, and maintenance basics

1. Get a professional site evaluation and percolation test from a licensed designer to determine drainfield size.
2. Have a licensed septic contractor install or upgrade components to meet Arkansas requirements.
3. Schedule regular pumping every 3–5 years, or per contractor guidance, to prevent solids buildup.
4. Practice water-conscious use: spread out laundry and dishwashing, fix leaks, and use high-efficiency fixtures.
5. Landscape carefully: avoid heavy equipment or deep-rooting trees over the drainfield, and maintain proper surface drainage.

Maintenance and compliance for Bauxite homes

• Keep records of all inspections, pump-outs, and repairs for future reference or sale.
• Be aware of local setback rules and permit requirements; check with the Arkansas Department of Health for official guidance.
• If you notice sewage odors, damp areas, lush grass over one patch, or surface pooling, contact a licensed septic professional promptly.

Official resources:

• Arkansas Department of Health – Onsite Wastewater Systems:
• U.S. Environmental Protection Agency – Septic Systems: https://www.epa.gov/septic

Septic vs Sewer: What Homeowners in Bauxite Should Know

Understanding septic vs sewer

• A sewer system collects wastewater from many homes and carries it to a municipal or regional treatment plant. The city or district typically handles maintenance, and you receive a utility bill.
• A septic system is on your property: a tank and an underground absorption field treat wastewater on-site. You're responsible for pumping, inspections, and any repairs.
• Pros and trade-offs: septic can offer independence and potentially lower ongoing costs if your land and soils are suitable; sewer connection provides predictable bills and removes on-site maintenance but may involve hookup fees and waits for infrastructure upgrades.
• Costs and timelines vary: septic installation is a major upfront investment with ongoing pumping, while sewer connections depend on distance to the main and any required street or utility work.

How to decide if your Bauxite home should use septic or sewer

1. Step 1 — Check sewer availability: contact your city or county offices to confirm whether a municipal sewer line serves your street or subdivision.
2. Step 2 — Compare long-term costs: obtain quotes for a home sewer connection (hookup and any impact or connection fees) and compare to routine septic pumping, maintenance, and eventual replacement costs.
3. Step 3 — Assess site and soil: soil type, depth to groundwater, flood risk, and lot size matter for septic suitability. A professional site evaluation can determine if an absorption field will work on your property.
4. Step 4 — Consider disruption and timing: sewer hookups may require street work and permits; a septic system involves on-site construction and regular maintenance.
5. Step 5 — Check local rules: some areas require certain setbacks, inspections, or design standards. Verify with local authorities before planning.

Maintenance basics to protect your system

• Schedule regular inspections and pumping: most systems benefit from a professional inspection every 1–3 years and pumping every 3–5 years (frequency depends on household size and system design).
• Use water thoughtfully: install high-efficiency fixtures, spread out laundry loads, and fix leaks to reduce strain on the septic tank.
• Protect the drain field: keep heavy equipment off the absorption area, plant only shallow-rooted vegetation, and direct surface runoff away from the field.
• Be careful what you flush or pour down the drain: avoid wipes, diapers, grease, solvents, paints, and chemicals; dispose of hazardous materials through proper channels.

Local considerations for Bauxite, AR

• Soils and climate vary across Arkansas; a site evaluation helps determine septic viability for your lot.
• Groundwater and well safety: maintain required setbacks between the septic system and wells or water sources to protect drinking water.
• Permits and inspections: your local building department or the Arkansas Department of Health may require permits and final inspections for septic systems or sewer hookups.

Resources

• EPA on Septic Systems:

Typical Septic System Types in Bauxite

Conventional gravity septic systems

A conventional gravity system is the workhorse for many Bauxite homes. It uses a sealed septic tank to separate solids from liquids and a drainfield where clarified effluent percolates into the soil.

• What you'll find: a septic tank, a distribution box, and gravity-fed drainfield trenches with perforated pipes.
• Soil and site needs: adequate soil depth above the seasonal high water table and good soil percolation; steep slopes or shallow bedrock can complicate installation.
• Pros: simple design, lower upfront cost, easy routine maintenance (pump the tank on schedule, watch for roots).
• Cons: requires sufficient drainfield space; not ideal for very shallow soils, high water tables, or dense clay unless site conditions are enhanced.

For a general overview of how septic systems work, see EPA's guidance at

Pressure distribution systems

A pressure distribution system uses a pump chamber to evenly distribute effluent to multiple laterals in the drainfield.

• When it's a fit: soils with variable percolation, shallow groundwater, or limited room for trenches.
• How it works: a pump and control panel send small amounts of effluent under pressure to many outlets, improving field efficiency.
• Pros: more uniform drainage, can reduce trench length, good for marginal soils.
• Cons: requires electricity and regular maintenance; pump and valve components can need service.

Mound systems

Mounds are elevated drainfields built above the native soil when soils are too shallow or water tables are too high for a conventional system.

• Setup: an above-ground sand fill layer, a dosing tank, and a distribution system that sends effluent into the mound.
• Pros: expands installability in challenging soils; protects groundwater by providing a deeper, staged infiltration path.
• Cons: higher initial cost and more maintenance; requires proper design and grading.

Sand filter systems

A sand filter adds a secondary filtration step before effluent reaches a drainfield.

• How it works: effluent from the tank goes through a lined sand bed or chamber, then into an absorption area.
• Pros: improved effluent treatment in soils with limited absorption or high clay content; can reduce loading on the final drainfield.
• Cons: requires space, ongoing maintenance, and occasional media replacement.

Aerobic Treatment Units (ATU)

ATUs provide enhanced biological treatment by introducing oxygen into the wastewater flow before it reaches the drainfield.

• Benefits: higher-quality effluent, potential for smaller drainfields, useful on marginal soils.
• Maintenance: continuous aeration and regular servicing; electricity dependence.
• Considerations: require licensed installers and periodic inspections per local codes.

Chamber drainfield systems

Chamber systems replace traditional gravel with lightweight, interlocking plastic chambers that increase infiltrative area.

• Pros: easier handling and faster installation; flexible design with shallow depths.
• Cons: must be installed in soils that permit infiltration; some older sites may need evaluation for compatibility.

Evapotranspiration (ET) beds

ET beds rely on evaporation and plant transpiration to dispose of effluent. They are climate-dependent and less common in Arkansas.

• Pros: smaller surface footprint in appropriate climates; can be visually integrated with landscaping.
• Cons: performance varies with weather; not always permitted in every jurisdiction.

Drip irrigation and alternative reuse systems

Some properties use drip irrigation or other reuse methods to distribute treated effluent to landscape areas.

• Pros: water-saving option; reduces groundwater load on the drainfield.
• Cons: requires careful design, monitoring, and regulatory approval; specialized materials and maintenance.

Choosing the right system: 4 practical steps

1. Get a site and soil assessment: percolation tests, soil borings, and groundwater observations guide what will fit.
2. Check local codes and permitting: contact the county health office or ADH to understand approvals needed.
3. Consider family needs and lot constraints: number of bedrooms, water usage, landscaping goals, and space for a drainfield.
4. Engage a licensed septic designer/installer: obtain a formal design, cost estimate, and inspection plan; ensure the system is permitted and inspected.

Local considerations in Bauxite

Bauxite typically presents variable soils with clay content and seasonal groundwater fluctuations. Your installer may recommend a mound, ATU, or pressure distribution if conventional gravity is not suitable. Proper design accounts for lot size, setback requirements, trees, and future home use to protect your groundwater and your investment.

• Soil and groundwater variability in the area means site-specific evaluation is essential.
• Regular maintenance, including tank pumping and system inspections, extends life and reduces surprises.

Official resources

• EPA on Septic Systems:

Common Septic Issues in Bauxite

High water table and seasonal saturation

Bauxite communities often contend with shallow groundwater and heavy clay layers, which can keep effluent from draining through the soil after rains. In these conditions, drainfields can stay saturated, leading to surface wet spots, slow drains, and sewage odors in the yard.

• Why it happens here: clay-rich soils and higher seasonal rainfall can raise the water table, reducing the soil's ability to treat effluent.
• How to recognize it: gurgling toilets, consistently damp patches over the drainfield, and backups after wet weather.
• What to do:
  1. Schedule a visit with a licensed septic designer or installer to test soil depth, percolation, and water table.
  2. Consider an alternative system designed for high-water-table sites (for example, mound or pressure-dosed systems) if your lot and permit allow.
  3. Keep roof drains and surface runoff away from the drainfield; redirect downspouts to dry areas far from the system.
  4. Minimize extra loads during wet periods (see "Water use and seasonal stress" below).
• Resources: Arkansas Department of Health on-site wastewater guidance; EPA septic systems overview.

Clay soils and poor percolation

Arkansas soils in and around Bauxite can be slow to absorb water, making standard drainfield trenches insufficient. Saturated soils stay wet longer and effluent may back up or surface.

• Why it happens here: high clay content reduces infiltration and can cluster wet zones in the absorption area.
• How to recognize it: standing water in the leach field after rain, dense soil with little pore space, or frequent backups.
• What to do:
  1. Get a soil test and percolation rate done by a licensed professional.
  2. If percolation is slow, explore options such as a mound system, advanced treatment unit, or redesigned absorption trenches sized for the soil.
  3. Maintain the drainfield by keeping traffic, vehicles, and heavy loads off the area.
  4. Use water-saving fixtures to reduce hydraulic load.
• Resources: ADH On-Site Wastewater Systems pages; EPA septic system basics.

Tree roots and landscape proximity

Nearby trees and shrubs can invade drainfields with roots that clog or crack pipes, leading to backups and costly repairs.

• How it shows up: roots showing in the yard, sudden changes in drain times, or repeated backups.
• What to do:
  1. Plant trees and shrubs away from the drainfield; establish root barriers where needed.
  2. Have a professional inspect for root intrusion and repair damaged pipes.
  3. Monitor the system after heavy rains; roots won't fix themselves—proactive trimming and barriers help long-term.
• Resources: ADH guidelines on protecting septic systems near trees; EPA septic care tips.

Heavy rainfall and surface runoff

Intense rain can overwhelm a system by introducing large volumes of water or by saturating the soil around the drainfield.

• How it shows up: toilets that gurgle after storms, damp zones on the field, or backups during heavy rain.
• What to do:
  1. Redirect rainwater from roofs, driveways, and patios away from the drainfield.
  2. Pause nonessential water use during and after big storms (dishwashers, laundry, long showers).
  3. Ensure proper grading so surface water runs away from the system.
• Resources: EPA rainwater and septic care tips; ADH guidance on site grading.

Aging or poorly installed systems

Older tanks, broken baffles, cracked lids, or improper installation are common failure points that can lead to dysfunction or health hazards.

• How it shows up: persistent odors, standing water above the field, or frequent pumping needs.
• What to do:
  1. Have a licensed professional inspect for cracks, leaks, and baffle integrity.
  2. Plan timely replacement or upgrades if components are failing.
  3. Ensure any future work complies with current Arkansas on-site wastewater standards.
• Resources: ADH on-site system standards; EPA septic system care.

Inadequate maintenance and infrequent pumping

Neglecting routine maintenance accelerates failure. Most homes benefit from regular pumping and inspection.

• Typical guidance: pump every 2–3 years for average usage; more often for high wastewater volumes (e.g., multiple occupants, commercial-like use).
• What to do:
  1. Schedule regular inspections with a licensed pump technician.
  2. Keep a maintenance log and address issues promptly rather than waiting for failures.
  3. Use water-saving devices and avoid putting solids, fats, or chemicals into the system.
• Resources: ADH on-site waste management practices; EPA septic care basics.

Official resources:

• Arkansas Department of Health: On-Site Wastewater Systems (
• EPA: Septic Systems Overview (https://www.epa.gov/septic)

Septic Inspection, Permits & Local Oversight

Permits and Oversight in Arkansas

In Arkansas, most septic system projects are routed through your local county health department, under the policies of the Arkansas Department of Health (ADH). ADEQ also provides guidance for on-site wastewater and environmental compliance that can apply to certain systems or situations. Start with the local health office to confirm who issues the permit and what documents are needed; state resources below can help you understand the rules and expectations.

When You Need a Permit

• New system installation on a vacant or existing property
• Replacement of an failed or failing system
• Major repairs or changes to the design or capacity of a system
• Any trenching, tank replacement, or drainfield modification
• Situations requiring a soil evaluation or site plan update

Steps to Get a Permit (Arkansas)

1. Confirm jurisdiction: contact your local county health department (or city building department if applicable) to confirm who issues the permit for septic projects.
2. Gather required professionals: you may need a licensed septic designer or engineer and a qualified installer; some counties require soil evaluation by a licensed professional.
3. Prepare plans and documents: provide a site plan, system design, soil test results (if required), setbacks from wells and structures, and lot layout.
4. Submit and pay: turn in the permit application package, pay any fees, and respond to any plan questions from reviewers.
5. Receive the permit and schedule inspections: once approved, you'll schedule the installation to align with the inspection steps.

What Inspectors Look For

• Compliance with Arkansas On-Site Wastewater rules and local codes
• Proper setbacks from wells, streams, property lines, and structures
• Accurate soil evaluation data and appropriate drainfield design
• Correct tank placement, baffle orientation, and venting
• Adequate bedding, backfill, and surface restoration after installation

Inspections During Construction

• Pre-approval site evaluation (verification of soil suitability and drainage considerations)
• In-progress inspections (tank placement, trenching, pipe hangers, and backfill)
• Tank and riser inspection (seal, lids, and access)
• Final inspection (system tested, with approved operation criteria met)

After Installation: Records, Maintenance & Compliance

• Keep all permits, plans, and inspection records in a safe place; you may need them for pest control, real estate transactions, or future modifications.
• Follow recommended maintenance schedules (pumping intervals and inspections) as advised by your installer or local health authority.
• If you sell the home, disclose the septic system details and provide available records; some counties require documentation of system condition.
• Expect possible periodic reviews for certain system types or if modifications occur; stay informed with local requirements.

Resources & Contacts

• Arkansas Department of Health – Septic Systems:
• Arkansas Department of Environmental Quality – On-Site Wastewater:
• EPA – Septic Systems general guidance: https://www.epa.gov/septic

Septic Maintenance for Homes in Bauxite

Understanding how Bauxite soils affect your system

Bauxite sits in central Arkansas where soils can be heavy clay with variable depths to groundwater. In many Bauxite lots, seasonal high water tables and shallow bedrock can limit how quickly effluent soaks into the drain field. Heavy rains and rapid changes in moisture can cause short-term pressure on the system, leading to surface damp spots or backups if the field isn't given time to rest. Knowing your site conditions helps you plan smarter maintenance and avoid costly repairs.

Regular pumping and inspections

Regular pumping and professional inspections are the heart of keeping a septic system healthy in Bauxite's climate. Follow these steps:

1. Identify your tank size and type (conventional, compartmented, or aerobic) and locate access lids. If you can't find records, a licensed septic contractor can confirm tank size from the system design.
2. Schedule pumping every 3–5 years for typical family use (more often if you have a larger household or a system with a small drain field). In clay-heavy soils or areas with fluctuating water tables, annual pumping may be advised if usage is high.
3. After pumping, have the system inspected by a licensed pro: check baffles or tees, inspect any effluent filters, verify pump operation (if applicable), and assess drain-field conditions.
4. Keep detailed records of each service (date, tank size, pumped depth, and any repairs). This history helps you plan future maintenance and is useful if municipal or county inspections occur.

Daily habits to protect the system

Small daily choices add up to long-term system health. Use these practices to reduce strain on the drain field:

• Spread out laundry and dishwashing loads; use high-efficiency appliances and fix leaks promptly.
• Conserve water to avoid overloading the tank and field.
• Only flush wastewater and toilet tissue—no wipes, grease, solvents, paints, pesticides, or chemicals.
• Use septic-safe products and avoid pouring fats, oils, and grease down the drain.
• Keep a separate trash can for non-flushable items to reduce solids entering the tank.

Drain field protection in Bauxite

The drain field is your most vulnerable component in clay soils and near groundwater. Protect it with these tips:

• Prevent soil compaction: don't park cars or heavy equipment on the drain field, and minimize foot traffic over the area.
• Plant carefully: keep trees and shrubs with aggressive roots away; opt for shallow-rooted ground covers instead.
• Maintain a setback: keep septic-related equipment, storage, and fertilizer/pesticide applications away from the drain field.
• Ensure surface drainage diverts water away from the drain field and not toward it.

Seasonal considerations for Bauxite

Seasonal moisture changes affect system performance. Plan around these realities:

• After heavy rainfall or flooding, avoid heavy wastewater loads for 24–48 hours to reduce the risk of surface pooling and backflow.
• In winter, insulate the drain field area if possible and monitor for frost heave that could shift pipes or lids.
• In spring, watch for sudden wet conditions that can slow absorption; if you see persistent damp spots, call a pro for a check.

Signs your system needs attention

Early detection saves money and avoids backups. Look for:

• toilets or sinks slow to drain, gurgling sounds, or sewage odors inside or outside.
• damp or spongy ground over the drain field, or bright, unusually green patches indicating effluent effect.
• toilets or drains backing up after heavy use; repeated pumping without lasting improvement.

If you notice these signs, contact a licensed septic professional promptly. Do not attempt DIY fixes that involve digging up the drain field.

Official guidance and resources

• EPA Septic Systems:
• Extension resources (Arkansas): extension.arkansas.edu (search for septic system care and maintenance for practical guidance)

Cost Expectations for Septic Services in Bauxite

Septic Tank Pumping

• What it includes: removing built-up sludge and scum from the tank, cleaning interior surfaces, inspecting lids and risers, and checking the tanks' inlet/outlet for obvious issues. In Bauxite, access can vary with rural lots and clay soils, which can affect timing and equipment needs.
• Bauxite specifics: older clay soils and tight access may require a smaller or specialized pump truck; seasonal weather can also influence scheduling.
• Typical cost in Bauxite: roughly $275–$600 per pumping.

Septic System Inspections and Maintenance

• What it includes: visual inspection of the tank and leach field, pump status check (if there's a pump chamber), baffle/gasket condition, effluent filter (if installed), and general system performance. More thorough inspections may include camera evaluations of buried pipes.
• Bauxite specifics: properties with older or nonstandard tanks may require closer inspection or retrofits; some homes rely on less accessible tanks that need careful monitoring.
• Typical cost in Bauxite: basic inspection $150–$350; more thorough with camera/pipeline evaluation $350–$700.

Soil Evaluation and Perc/Percolation Tests

• What it includes: soil borings or field tests to determine absorption capacity, drainage, and suitability for a new or expanded system. Essential for new installations and major upgrades.
• Bauxite specifics: Arkansas soils and local permitting rules mean soil evaluations are a common prerequisite for new work.
• Typical cost in Bauxite: $400–$900 for standard tests; $700–$1,500 when a full soil evaluation is needed.

Drain Field Repair and Replacement

• What it includes: locating damaged trenches or failed distribution lines, repairing pipes or components, and replacing or regrading soil in the drain field area.
• Bauxite specifics: heavy rainfall or high clay content can complicate repairs and may increase restoration work.
• Typical cost in Bauxite: $2,000–$8,000 for repairs; $5,000–$15,000+ for full field replacement.

Mound System Installation/Upgrade

• What it includes: site assessment, design, fill material, raised bed or "mound" construction, installation of the drain field, and permit coordination.
• Bauxite specifics: mound systems are more common in Arkansas when soil conditions aren't suitable for conventional trenches.
• Typical cost in Bauxite: $15,000–$35,000+, depending on size, materials, and permitting.

New System Installation (Conventional or Advanced)

• What it includes: site evaluation, system design, permit pulls, trenching or bed setup, tank installation, distribution system, and final hookups.
• Bauxite specifics: local permits and soil considerations can influence design choices and timing.
• Typical cost in Bauxite: $7,500–$20,000 for conventional systems; $20,000–$40,000+ for advanced or alternative systems (e.g., mound or specialty treatment units).

Septic Tank Risers, Lids, and Cleanouts

• What it includes: adding or upgrading access risers and cleanouts for easier future maintenance and safer inspections.
• Bauxite specifics: improves access for routine maintenance in tighter lots and helps with winter inspections in colder months.
• Typical cost in Bauxite: $150–$450 plus installation.

Emergency Septic Service

• What it includes: rapid response to backups, overflows, or system freeze-related issues; may include temporary solutions to reduce odor and risk while permanent work is planned.
• Bauxite specifics: rural locations may incur travel fees or after-hours surcharges.
• Typical cost in Bauxite: $300–$900 for the service call, plus any pumping or repairs needed.

Decommissioning/Abandoning an Old System

• What it includes: safe removal or sealing of an outdated tank, backfilling, and site restoration to meet code requirements.
• Bauxite specifics: property transactions or renovations often trigger decommissioning; proper sealing reduces environmental risk.
• Typical cost in Bauxite: $1,000–$3,000 depending on tank size and site access.

Official resources

• Arkansas Department of Health – On-Site Wastewater Systems:
• U.S. Environmental Protection Agency – Septic Systems: https://www.epa.gov/septic