Septic in New Market, MD

Last updated: Mar 21, 2026

In New Market, MD, your yard often backs up to rolling hills, historic streets, and quiet cul-de-sac neighborhoods rather than a single, city-wide sewer line. That blend of charm and rural feel means many homes rely on septic systems, tucked behind homes and in side yards where they're easy to overlook but essential to daily life.

Is septic common in New Market? Should I expect septic if I own or buy a home? Yes. Most single-family homes here are on private septic systems rather than connected to a municipal sewer, especially in older neighborhoods or properties with larger lots. If you own or are buying in New Market, you should plan for a septic system unless the property sits in an area with public sewer service. When buying, ask for a septic disclosure and arrange a professional septic inspection to understand tank age, soil conditions, and the health of the drainage field. A clear picture upfront can save surprises later and help guide any needed maintenance or upgrades.

Why homes typically use septic systems in New Market comes down to the land and the way development spread here. Many lots are rural or semi-rural, with space and soil that lend themselves to on-site treatment. Extending centralized sewer lines to every hillside or farmable field can be costly and impractical, so septic systems became the practical, cost-effective solution for single-family homes. Properly designed and located septic systems protect wells, streams, and groundwater, which is especially important in watershed areas around our town.

High-level explanation of why septic exists here: a typical system places a concrete or fiberglass septic tank underground, where solids settle and fats and oils rise to the top. Bacteria in the tank begin breaking down the waste, and clarified liquid exits to a drain field or bed where it percolates through the soil. The soil then acts as a natural filter, removing many pollutants before water re-enters the groundwater. Regular maintenance—most homes pump every 3–5 years, and many get annual inspections—keeps the system healthy and reduces the risk of backups or effluent surfacing in the yard.

Think of Septic.fyi as your friendly neighbor who's also a local septic pro: practical, trustworthy, and here to help you keep your New Market home running smoothly. You'll find hands-on guidance, maintenance tips, and common issues tailored to our area's soils and climate as you explore.

Where Septic Systems Are Common in New Market

Map of septic coverage in New Market, MD

Rural and semi‑rural lots dominate

  • Most homes in New Market sit on larger lots, often 1–5 acres, with water supplied by wells and wastewater managed on site.
  • Because centralized sewer lines don't extend to every street or subdivision, septic systems remain the standard wastewater solution for many properties.
  • On older homes and in outlying neighborhoods, you'll typically see conventional or modified septic designs rather than city sewer connections.

Sewer service landscape in New Market

  • The town center and some newer developments may have access to public sewer as infrastructure expands.
  • Outlying rural parcels and established suburbs farther from public lines generally rely on on‑site systems for wastewater management.
  • To confirm whether sewer is available or whether a septic system must be used on a specific property, check with local authorities and your property records.

Soil and system types you'll encounter

  • Soil type drives septic design. New Market properties sit on a mix of soils, including loams, sandy loams, and pockets of clay or shallow bedrock in which drainage can vary.
  • Common septic system types you'll see:
    • Conventional septic systems (tank and drain field) for typical soils and adequate drainability.
    • Mound systems where the native soil drains poorly or the water table is high.
    • Advanced treatment units or aerobic treatment units on properties with higher effluent quality needs or restrictive soils.
  • A licensed installer or the county health department can help determine the right design for your lot.

Maintenance and long‑term care in New Market

  • Regular pumping is essential. Most properties benefit from every 3–5 years, depending on usage and tank size.
  • Protect the drain field: avoid parking or heavy equipment over it, plant trees only at safe distances, and keep roots away from lines.
  • Be water‑smart: spread out laundry, fix leaks, and use only septic-safe products to minimize solids and additives entering the tank.
  • Watch for signs of trouble: gurgling plumbing, damp areas in the drain field, or toilets backing up—address promptly with a licensed septic professional.

Quick checks and planning steps

  1. Confirm sewer availability for your property by contacting the Frederick County Health Department or local planning office.
  2. If septic is needed, have a qualified septic designer assess soil conditions and determine the appropriate system type (conventional, mound, or ATU).
  3. Schedule regular maintenance and establish a pumping interval based on tank size and household use.

Official resources

Septic vs Sewer: What Homeowners in New Market Should Know

Quick context for New Market homeowners

  • In New Market, some homes connect to a municipal sewer system, while others rely on on-site septic systems. Availability depends on your street, local infrastructure, and any expansion plans in the area.
  • Knowing which option serves your property affects long-term costs, maintenance, and environmental impact.

How to tell what you have

  • Check with Frederick County or your utility provider to confirm whether sewer service is available at your address.
  • Review property records or utility bills for "sewer" service vs. "onsite septic." A visible septic tank access lid and a drainfield in the yard indicate an on-site system.
  • If you're unsure, hire a licensed septic professional or contact the county Environmental Health office to verify.

Pros and cons at a glance

  • Septic system (on-site)
    • Pros: independence from city services; potentially lower monthly charges; you control the maintenance timeline.
    • Cons: regular pumping and proper waste disposal are essential; aging components can fail and require repair; environmental risk if poorly maintained.
  • Municipal sewer connection
    • Pros: no septic pumping or tank maintenance; maintenance is handled by the utility; often more straightforward for homes near existing lines.
    • Cons: upfront connection costs; ongoing monthly sewer charges; after connection, responsibility shifts to the utility and local codes.

Maintenance basics for septic systems (homeowner duties)

  • Pump every 3–5 years, or per your system's specific schedule, depending on tank size and usage.
  • Conserve water: install and use low-flow fixtures, fix leaks promptly, and spread high-water-use activities (like laundry) across the week.
  • Do not flush or pour fats, oils, grease, paints, solvents, chemicals, diapers, or wipes (even "flushable" ones) into the system.
  • Keep the drainfield area clear: avoid heavy equipment, protect roots of nearby trees, and don't park on or landscape over the field.

Signs of trouble and what to do

  • Bad odors near the system, wet or lush spots in the yard, or gurgling drains.
  • Slow drains, backups in sinks or toilets, or standing wastewater in the yard.
  • If you notice issues, contact a licensed septic contractor promptly for an evaluation and plan.

Connecting to sewer: what to expect (if sewer is available)

  • Step 1: Confirm sewer availability with the local utility or Frederick County.
  • Step 2: Obtain a professional assessment to determine required conversions and any back-end work.
  • Step 3: Secure necessary permits and select a contractor for the connection work.
  • Step 4: Complete the hook-up; decommission the old septic system as required by local code.

Official resources

  • Maryland Department of the Environment – On-site Sewage Disposal Systems (OSDS) program:
  • United States Environmental Protection Agency – Septic Systems: https://www.epa.gov/septic

Typical Septic System Types in New Market

Conventional gravity septic systems

  • How they work: A septic tank settles solids; clarified liquid flows by gravity to a subsurface drainfield where it is absorbed and treated by the soil.
  • Ideal conditions: Sufficient soil depth, good soil percolation, and a stable water table.
  • What you'll typically see: A buried tank and a network of perforated pipes with trenches in the native soil.
  • Pros: Generally the lowest upfront cost; simple design and maintenance.
  • Cons: Performance depends on soil conditions; a poorly drained or shallow site may require an alternative system.
  • Maintenance you can follow:
    1. Have the tank pumped every 3–5 years (frequency depends on household size and tank size).
    2. Keep heavy equipment off the drainfield; don't plant trees or shrubs with deep roots over it.
    3. Use water-saving fixtures and spread loads (dishwashers, laundry) to reduce input.
    4. Watch for signs of trouble (gurgling drains, damp spots, or slow drains) and call a licensed pro promptly.

Mound systems

  • Why they're used: When soil is shallow, has a high water table, or poor percolation, a sand-filled mound is built above grade to provide a suitable treatment area.
  • How they work: A septic tank feeds effluent into a dosing chamber, which then distributes to elevated sand/soil layers through lines and vents.
  • Pros: Can make septic service possible in challenging soils; long-term performance when properly designed and maintained.
  • Cons: Higher installation cost; requires more space and regular professional servicing.
  • Maintenance you can follow:
    1. Schedule professional inspections and pumping as recommended.
    2. Keep the mound surface free of vehicles and heavy loads.
    3. Avoid landscaping changes that compress or disturb the mound soil.
    4. Make sure any irrigation or rainwater drainage does not pool on or near the mound.

Sand filtration beds (bed systems)

  • What they are: An additional or alternative treatment method using a sand-filled bed that further treats effluent before it returns to the soil.
  • When used: Often selected when initial soil treatment is limited or enhanced treatment is desired.
  • Pros: Improved effluent quality; adaptable to a range of site conditions.
  • Cons: More complex than a standard drainfield; higher service costs.
  • Maintenance tips:
    1. Regular inspections by a licensed designer/installer.
    2. Protect the bed from compaction and fertilizer runoff.
    3. Monitor for surface dampness or odors and address quickly.

Aerobic Treatment Units (ATUs) and packaged systems

  • What they are: Small, electrically powered systems that aerobically digest waste before sending effluent to a drainfield or polishing filter.
  • Pros: Produce higher-quality effluent; useful where soils are restrictive or space is limited.
  • Cons: Higher operating costs due to electricity and maintenance; more frequent service contracts required.
  • Maintenance you can follow:
    1. Annual servicing by a licensed septic contractor.
    2. Keep alarms and power sources in working order.
    3. Avoid dumping harsh chemicals down drains; use septic-safe cleaners.
    4. Inspect for unusual noises or odors and address promptly.

Drip irrigation and low-pressure dose (LPD) systems

  • How they work: Small doses of treated wastewater are distributed through emitters or small lines to the root zones, reducing stress on the soil.
  • Pros: Efficient water use; can work in compact sites or soils with limited absorption.
  • Cons: Requires precise design and professional installation; ongoing monitoring for emitter blockages.
  • Maintenance tips:
    1. Schedule regular checks of emitters and lines.
    2. Protect components from root intrusion and physical damage.
    3. Keep up with local permit requirements for alterations.

What to expect for New Market homeowners

  • Most homes with stable soils rely on conventional gravity systems.
  • If site conditions aren't ideal, a licensed professional may recommend mound, ATU, or sand filtration options.
  • Regardless of type, proper maintenance, timely pumping, and adherence to local guidelines help protect your system and the surrounding groundwater.

Resources

Common Septic Issues in New Market

High water table and seasonal groundwater

New Market's rainfall patterns and local geology can leave soils saturated during spring thaws and after heavy rains. A high water table reduces the soil's ability to adequately treat effluent and can push liquid waste to the surface or into the drainfield, leading to backups, odors, and soggy patches.

  • What to watch:
    • Wet, swampy areas over the drainfield, especially after rain
    • Gurgling plumbing, toilets slow to flush, or sewage odors in the yard
    • Surging water or pooled liquid near the septic area during wet seasons
  • What you can do:
    1. Schedule a professional pump-out and system inspection to assess field condition
    2. Minimize irrigation and avoid rainwater drainage toward the drainfield during wet periods
    3. Protect the drainfield from compaction by keeping vehicles and heavy equipment away
    4. Consider a redesigned or raised system if chronic saturation is confirmed

Learn more: Maryland Department of the Environment Onsite Wastewater

Shallow soils and bedrock proximity

Frederick County, including New Market, often features shallow soils with limestone bedrock not far below the surface. This reduces vertical drainage and can restrict proper effluent percolation, increasing the risk of surface discharge or drainfield failure.

  • What to watch:
    • Rapid drainage tests indicating poor vertical absorption
    • Drainfield frost-heave or standing water in the system area
    • Frequent back-ups during heavy-use periods
  • What you can do:
    1. Have a licensed onsite wastewater designer evaluate soil depth and bedrock limits
    2. Consider alternative designs such as mound systems or enhanced distribution
    3. Ensure setbacks from wells, foundations, and property lines are met
    4. Use soil amendments only when advised by a pro; avoid DIY fixes

Learn more: EPA Septic Systems overview https://www.epa.gov/septic

Tree roots and landscape encroachment

Root intrusion is a common cause of drainfield damage in residential lots with mature trees or shifting landscaping. In New Market, roots can grow toward pipes or clog infiltration beds, reducing treatment area and causing early system failure.

  • What to watch:
    • Cracked or displaced pipes, back-ups after heavy rain
    • Roots visibly invading the drainfield area
    • Sudden drops in system performance after planting trees or shrubs nearby
  • What you can do:
    1. Keep trees and large shrubs a safe distance from the septic area (often 15–20+ feet depending on species)
    2. Schedule root barrier installation or relocate planting when possible
    3. Have lines inspected or video-scoped if intrusion is suspected
    4. Maintain a healthy plant-free zone over the drainfield

Aging systems and maintenance gaps

Many older homes rely on systems installed decades ago. Drainfields and components wear out, seals fail, and lack of regular pumping accelerates deterioration. New Market's older properties may be particularly susceptible if maintenance hasn't kept pace with usage.

  • What to watch:
    • Loud flushes or toilets that drain slowly
    • Standing water in the drainfield or surface odors
    • Frequent repairs or replacement parts
  • What you can do:
    1. Schedule routine pumping every 3–5 years (or per professional guidance)
    2. Use water-saving fixtures and spread out high-water-use activities
    3. Maintain records of maintenance, inspections, and pump-outs
    4. Have a valve and filter inspection during every service

Learn more: Maryland Onsite Wastewater guidance https://mde.maryland.gov/programs/Land/Pages/OnsiteWastewater.aspx

Stormwater infiltration and surface drainage

Heavy rainfall and improper drainage around the home can overwhelm a septic system. In New Market, stormwater that drains toward the drainfield adds unnecessary load, shortening its life and increasing the chance of failures.

  • What to watch:
    • Surface pooling near the drainfield after storms
    • Overflow or backups following major rain events
    • Soggy yards around the system area despite normal rainfall
  • What you can do:
    1. Redirect rooflines, driveways, and sump pump discharge away from the septic area
    2. Install proper grading to shed water away from the drainfield
    3. Create a clean, protected zone around the system free of fertilizer and chemicals
    4. Keep drainage paths clear of debris and ensure proper downspout extensions

Well proximity and groundwater protection

If your property uses a well for drinking water, ensure compliance with local setback requirements to minimize contamination risk from septic effluent. Inadequate separation or compromised systems can threaten groundwater quality.

  • What to watch:
    • Unusual well water taste, odor, or sediment after heavy rains
    • Unexplained changes in well yield or pressure
    • Signs of soil seepage or odors near the wellhead
  • What you can do:
    1. Verify setback distances and follow local health department guidance
    2. Test well water regularly and especially after septic work or storms
    3. Schedule a professional septic inspection if the well shows any concerns

Learn more: EPA Septic Systems overview https://www.epa.gov/septic

Septic Inspection, Permits & Local Oversight

State and local roles in New Market

In Maryland, on-site septic systems are regulated through a combination of state and county oversight. The Maryland Department of the Environment (MDE) sets statewide design and material standards, while the Frederick County Health Department administers permits, plan reviews, inspections, and enforcement for septic installations, repairs, and replacements. For official guidance from the state, see MDE: https://mde.maryland.gov.'>https://mde.maryland.gov. For county-level steps and contacts, visit Frederick County Health Department: https://health.frederickcountymd.gov/ and navigate to Environmental Health / On-site Wastewater Programs.

When you need a permit

  • Any installation, substantial alteration, or replacement of an on-site septic system typically requires an OSDS (on-site sewage disposal system) permit from Frederick County Health Department.
  • Building permits may be required in tandem with septic work depending on the project scope. Always confirm with the local building and health departments before starting.
  • Real estate transactions often trigger a septic condition review or inspection to verify the system's status.

How to apply: step-by-step

  1. Identify the right authority
    • Frederick County Health Department – Environmental Health / On-site Wastewater Program.
  2. Gather basic information
    • Property address, parcel/tax ID, proposed or existing system details, site constraints, and any existing soil/percolation data.
  3. Prepare plan and supporting documents
    • Site drawing showing tank location and drainfield, proposed system design, and any needed soil evaluation results.
  4. Submit the permit package
    • Through the county's portal or in person at the Health Department, along with required fees.
  5. Plan review
    • County reviewers assess compliance with MD and local standards; additional state involvement may occur for certain systems.
  6. Soil evaluation or percolation test (if required)
    • A licensed professional may need to perform and document soil testing for suitability.
  7. Permit approval and scheduling
    • Once approved, you'll receive the permit and schedule inspections with the county.

Inspections: what to expect

  • Pre-construction soil evaluation (if not completed already)
  • Rough-in/installation inspections
    • Tank placement, piping, and backfill; trenching and ground preparation adherence to design
  • Drainfield installation inspection
    • Verification of trench layout, backfill type, and clearance from wells or structures
  • Final inspection and as-built review
    • Confirmation the system matches the approved plan and passes functional testing; submission of as-built drawings

Scheduling inspections and contacts in New Market

  • Contact Frederick County Health Department's Environmental Health division to schedule inspections and confirm permit status.
  • Have your permit number handy, along with project address and a copy of the approved plan.
  • If you're unsure who to contact, start at the Frederick County Government or Health Department homepage and use the "On-site Wastewater" or "Environmental Health" resource links.

Documentation checklist

  • Property address and parcel ID
  • Approved septic design or as-built (if replacing or updating)
  • Soil evaluation/percolation test results (if required)
  • Submittal documents: completed permit application, plan drawings, site map
  • Any prior permits, inspections, or correspondence with the county
  • Access or staging plan for site work

Practical tips and pitfalls to avoid

  • Start the permit process early if you're buying or selling a home; unresolved permits can delay closings or financing.
  • Do not begin installation or site work before permit approval; unpermitted work can lead to fines, required removal, or rework.
  • Keep copies of all inspections and as-built revisions; you may need them for future maintenance or resale.

Resources

Septic Maintenance for Homes in New Market

Why maintenance matters in New Market

New Market homes sit in soils and climates that make careful septic care essential. Wet springs, seasonal rainfall, and varying groundwater levels can stress drain fields more than you might expect. Regular maintenance helps prevent backups, odors, and groundwater concerns that could affect nearby streams or wells. Staying on a solid schedule also saves money over time by avoiding costly repairs.

New Market-specific challenges

  • Wet seasons can saturate drain fields, reducing their ability to absorb effluent.
  • Clay-rich soils common in parts of the region slow drainage and benefit from conservative water use.
  • Proximity to watercourses means keeping solids out of the system and monitoring for any signs of surface or groundwater impact.

Routine maintenance checklist

  1. Identify tank size and access
  2. Locate the septic tank lid(s) and confirm the tank size with a professional if you're unsure.
  3. Mark access points so future service visits are quick and accurate.
  4. Schedule regular pumping
  5. Most households with a 1,000–1,500 gallon tank should consider pumping every 3–5 years, depending on wastewater volume, occupants, and system design.
  6. Have a licensed septic contractor evaluate sludge and scum levels to set a precise pumping interval. See official guidelines below for a starting point.
  7. Conduct annual inspections
  8. Have a licensed professional inspect the distribution box, inlet/outlet baffles, and overall condition of the tank and distribution system.
  9. Ask about effluent filter status and whether a cleanout is needed.
  10. Track water use and waste disposal
  11. Use high-efficiency fixtures and fix leaks promptly.
  12. Avoid flushing non-degradables (wet wipes, paper towels, plastics) and limit grease disposal via pipes.
  13. Maintain a service record
  14. Write down pumping dates, inspection results, and any recommended repairs. Keep this with your home records.

Seasonal considerations

  • Spring: after heavy rains, monitor for damp areas around the drain field and unexpected odors. If you notice issues, call a pro before the problem worsens.
  • Summer: hot, dry periods don't usually harm the system, but conserve water to reduce load on the drain field.
  • Winter: keep access lids clear of snow and ice; frozen lids or vents prevent proper venting and access.

Signs your system needs attention

  • Slow drains, gurgling noises, or sewage backups
  • Gaps in the lawn or soggy patches over the drain field
  • Bad odors near the septic tank or drain field
  • Lush, green patches over a drain field compared with the rest of the yard (indicating water pooling)

Protecting the drain field in New Market

  • Limit traffic on the drain field area and avoid parking vehicles or placing heavy equipment there.
  • Plant only shallow-rooted grasses; avoid trees or shrubs with aggressive roots near the system.
  • Divert surface water away from the drain field with proper grading and gutters.

When to call a professional

  • Any signs of backup, foul odor, or standing water near the drain field
  • Visible tank damage, cracking lids, or sump pump discharges near the system
  • After major renovations or a long period of heavy usage (e.g., hosting a large gathering)

Useful resources and official guidance

Cost Expectations for Septic Services in New Market

Septic Tank Pumping and Cleaning

  • What this service includes: removal of liquid and solids from the septic tank, cleaning interior surfaces, inspecting tank baffles and access lids, and checking the pump chamber (if present). A basic pumping often includes a quick check of toilets and drains for signs of trouble.
  • What's unique to New Market: many homes in the area use 1,000–1,250 gallon tanks; soil and seasonal moisture can influence pumping frequency. Contractors here commonly recommend pumping every 2–3 years for typical family usage.
  • Typical cost in New Market: roughly $250–$450 for a standard 1,000–1,250 gallon tank; about $350–$550 for a 1,500 gallon tank.
  • Official resources: Maryland Department of the Environment (On-site Sewage Disposal)

Septic System Inspections (Maintenance and Pre-Sale)

  • What this service includes: exterior and interior component inspection (tank lids, access ports, pump chamber if present), review of maintenance records, and a basic functional check of the system. For home sales, a thorough assessment is common to determine if pumping, repairs, or field work are needed.
  • What's unique to New Market: many transactions here require a formal septic inspection as part of the closing process; inspectors may suggest service or upgrades to meet local regulations.
  • Typical cost in New Market: about $350–$600 for a standard inspection; more comprehensive evaluations can run higher if additional testing is requested.
  • Official resources: Maryland Department of the Environment https://mde.maryland.gov/programs/water/OEP/onsite/Pages/onsite.aspx

Drain Field Evaluation and Repairs

  • What this service includes: soil and drainage assessment, field inspection, potential camera work in pipes, and tests to determine infiltrative performance. Repairs may involve replacing damaged piping, repairing trenches, or addressing clogged drains.
  • What's unique to New Market: hilly terrain and variable soils can affect field performance; some properties may require targeted repairs rather than full replacement.
  • Typical cost in New Market: minor repairs typically $2,000–$6,000; more extensive field repairs can run $5,000–$12,000. Full drain-field replacement often ranges $7,000–$15,000 or more depending on size and access.
  • Official resources: Maryland Department of the Environment https://mde.maryland.gov/programs/water/OEP/onsite/Pages/onsite.aspx

Cesspool Pumping and Abandonment (for older homes)

  • What this service includes: pumping out existing cesspools, cleaning, and sealing or converting to a compliant septic tank system when suitable; often followed by proper abandonment of the old cesspool.
  • What's unique to New Market: several older homes in the area still rely on cesspools, requiring conversion to meet current health and environmental standards.
  • Typical cost in New Market: pumping $300–$600; conversion or abandonment projects commonly $1,500–$4,000.
  • Official resources: EPA septic system page for general guidance https://www.epa.gov/septic

New System Installation or Major Replacement

  • What this service includes: site evaluation and soil testing, system design, permits, installation of a complete septic system (tank, piping, and drain field), and final inspections.
  • What's unique to New Market: site conditions (slope, groundwater, soil type) heavily influence system design and cost; permits and inspections are locally required.
  • Typical cost in New Market: $10,000–$40,000 or more, depending on tank size, field complexity, and access.
  • Official resources: Maryland Department of the Environment https://mde.maryland.gov/programs/water/OEP/onsite/Pages/onsite.aspx

Aerobic Treatment Unit (ATU) Maintenance and Repairs

  • What this service includes: regular maintenance (filter cleaning or replacement, pump checks, airflow tests), and occasional repairs or component replacement.
  • What's unique to New Market: ATUs may be selected in sites with challenging soils or high-effluent treatment needs; annual maintenance is crucial to prevent costly failures.
  • Typical cost in New Market: annual maintenance visits $150–$350; occasional pump or part replacements add $200–$500 as needed.
  • Official resources: EPA on-site septic guidance https://www.epa.gov/septic

Maintenance Contracts and Preventive Care

  • What this service includes: scheduled inspections, pump-out reminders, priority service windows, and often discounted labor when issues arise.
  • What's unique to New Market: many local contractors offer seasonal maintenance packages aligned with spring/fall home maintenance windows.
  • Typical cost in New Market: $120–$300 per year depending on scope and included services.
  • Official resources: Maryland Department of the Environment service guidelines https://mde.maryland.gov/programs/water/OEP/onsite/Pages/onsite.aspx

Septic Tank Risers, Lids, and Access Improvements

  • What this service includes: installation of risers to improve access for future pumping and inspections, strengthening lids, and improving frost resistance.
  • What's unique to New Market: better access reduces wintertime service challenges in hillier ground and helps long-term maintenance.
  • Typical cost in New Market: $500–$1,000 depending on materials and depth.
  • Official resources: EPA on-site septic guidance https://www.epa.gov/septic