Septic in Arlington, WA

Here in Arlington, Washington, you'll notice a mix of quiet residential streets, green spaces, and the practical reality that many homes rely on a septic system to handle wastewater. The damp climate and soil conditions here make on-site treatment a straightforward, affordable option for everyday living, so it's common to find well-maintained septic systems supporting comfortable, efficient households.

Is septic common in Arlington? Yes. In neighborhoods outside the city core where public sewer lines don't reach every driveway, most homes rely on a septic system. If you own or are buying a home in Arlington, you should expect a septic—unless the property is connected to municipal wastewater. When you're reviewing a listing or closing documents, look for records of pumping, inspections, and the septic design details. Knowing when the tank was pumped last and what the drain field looks like can save headaches down the road.

Why do Arlington homes use septic systems? It comes down to practicality and geography. Arlington has a mix of older homes on larger lots and newer developments a bit farther from centralized sewer lines. In many of these areas, extending sewer service isn't just expensive; it can also be disruptive to established neighborhoods. A properly designed on-site system provides a reliable way to treat wastewater without the need for costly mains, while working with the soil and groundwater conditions found here. Local regulations and inspections are in place to keep systems functioning safely and protect the surrounding environment.

High-level what-it-is and why it works here: a septic system is an on-site treatment solution—typically a buried tank that settles solids and a drain field where liquid is dispersed through the soil. Microbes in the soil, plus the designed flow paths, help break down waste and filter water before it returns to the ground. The result is a compact, private wastewater solution that fits well with Arlington's landscapes and lot sizes when it's properly planned and maintained.

As your neighbor and a local septic contractor, I'm here to help you navigate the basics with practical, down-to-earth guidance—maintenance schedules, what to ask for when you hire someone, and simple steps to keep your Arlington system healthy. You'll find the essentials here to keep things running smoothly, with a friendly, trusted voice nearby.

Where Septic Systems Are Common in Arlington

What areas in Arlington typically use septic systems?

In Arlington, septic systems are most common in the rural and fringe areas outside the City of Arlington's established sewer service area, as well as in older neighborhoods where sewer lines weren't extended historically. These spaces tend to be less dense, with properties that aren't connected to municipal wastewater lines yet.

• Rural and semi-rural corridors outside the city sewer boundary
• Unincorporated Snohomish County neighborhoods surrounding Arlington
• Older subdivisions where sewer expansions did not reach at the time of development
• Properties with larger lots where on-site disposal and treatment can be more practical

Why this is the pattern: extending sewer mains to every property is expensive, and many Arlington-area parcels were built when septic was the standard option. Local soil conditions, groundwater levels, and slope also influence whether a septic system is appropriate and cost-effective. When the municipal system expands or a property is annexed into the city's sewer service area, septic is typically replaced by sewer connections.

How to confirm whether your area uses septic

To plan confidently, start by confirming whether your property is inside the city sewer service area or in a non-sewer zone.

1. Check the City of Arlington sewer service map or contact the city's utilities department to confirm sewer access for your street or subdivision.
2. If you are outside the sewer service area, contact the Snohomish County health/public health district or a licensed septic designer to review site conditions and system options (including soil tests and percolation rates).
3. Review soils and water table expectations for your specific lot. A professional site evaluation will determine whether an on-site septic system can be designed to meet local standards.
4. If you already have a septic system, schedule regular inspections and maintenance to protect your investment and local groundwater.

Why soils, zoning, and lot size matter in Arlington

• Soils and groundwater: Absorption fields need suitable soil with adequate drainage and a safe distance to groundwater and wells. In some Arlington locales, high groundwater or restrictive soils can limit septic effectiveness or require alternative designs (e.g., larger reserve areas, mound systems).
• Lot size and layout: Larger lots are more commonly served by conventional septic systems, while tighter urban plots may be connected to sewer or require compact/separated designs.
• Environmental protections: Proximity to streams, wetlands, or flood-prone zones in Arlington prompts stricter setbacks and design criteria to prevent contamination and protect water quality.
• Service planning: The City and county coordinate on infrastructure expansion. When sewer mains reach new areas, septic systems may be decommissioned in favor of sewer connections, influencing long-term planning for homeowners.

Helpful official resources

• Washington State Department of Health – Onsite Wastewater (Septic) Program: guidance on permits, design, and maintenance.
• U.S. Environmental Protection Agency – Septic Systems overview and homeowner advice. https://www.epa.gov/septic
• Snohomish Health District (public health authority for Snohomish County) – general information on onsite wastewater and related services. https://www.snohd.org/
• City of Arlington – Utilities and sewer service information (to verify whether your property is within the sewer service area). https://www.arlingtonwa.gov/

Septic vs Sewer: What Homeowners in Arlington Should Know

How septic systems and sewers differ

• Wastewater path: Sewer systems bring all household wastewater to a centralized treatment plant; septic systems treat and disperse within your property's drainfield.
• Ownership and responsibility: With sewer, the utility owns the network and handles maintenance beyond your cleanout; with a septic, you own and are responsible for the septic tank, drainfield, and monitoring.
• Environmental footprint: Public sewer relies on large-scale treatment plants; a well-functioning septic system can protect groundwater when properly designed, installed, and maintained.
• Cost model: Sewer users pay a monthly or quarterly utility bill; septic owners budget for periodic pumping, inspections, and potential repairs.
• Maintenance duties: Sewer systems require little homeowner involvement beyond preventing clogs near the home; septic systems demand regular pumping, inspections, and careful waste disposal to protect the drainfield.

Arlington-specific factors

• Local soils and groundwater: Arlington sits in Snohomish County with varied soils that influence drainfield performance. Proper site evaluation is essential for long-term function.
• Climate considerations: Wet winters and seasonal rainfall impact the load on your system and the drainfield's drainage capacity.
• Regulations and permitting: Arlington-area installations and replacements must follow state and county septic rules, with permit and inspection steps coordinated through the local health authority and state agencies.

Costs and practical considerations

• Upfront costs: Septic system installation or replacement can be substantial (tank, distribution, and drainfield). Sewer connection costs depend on distance to the public Main and any required trenching.
• Ongoing costs: Annual septic maintenance (pumping every 3–5 years on typical residential sizing) vs monthly sewer charges. Budgets vary by usage, system size, and local rates.
• Environmental safeguards: Proper disposal habits (no oils, solvents, or non-flushables) protect the drainfield and reduce the risk of costly repairs.
• When to expect major work: If a drainfield fails, or if the tank is not emptied on schedule, you may face expensive repairs or a sewer connection if available in your area.

Is your home currently on sewer or septic?

1. Check property records or past utility bills to see if a sewer service account exists.
2. Look for a septic tank cleanout lid or a buried tank access point in the yard.
3. Contact the local utility or Snohomish County/Snohomish Health District to confirm service status for your address.
4. If you're unsure, a licensed septic professional can locate and identify the system type.

What to expect with a septic system

• Pumping and inspection cadence: Schedule a septic pump every 3–5 years (adjust based on tank size and household water use). Have the drainfield and outlet baffles inspected when you pump.
• Everyday care: Use water-saving fixtures, minimize garbage disposal use, and avoid flushing non-degradables ( wipes, feminine products, chemicals) to protect the drainfield.
• Troubleshooting: Slow drains, gurgling, or foul odors may indicate a problem. A professional evaluation can confirm whether pumping, filter replacement, or drainfield repair is needed.

What to expect with sewer service

• Regular bills: A predictable monthly sewer charge from the city or utility, in addition to water usage.
• System integrity: The utility handles major sewer line maintenance, but you should still avoid dumping fats, oils, greases, and flushables that cause clogs at the main.
• Potential improvements: If sewer access is planned for your neighborhood, you may see assessments or hook-up timelines from the utility.

Official resources and where to start

• Washington State Department of Ecology – Onsite Sewage Systems:
• Washington State Department of Health – Onsite Sewage Systems:
• Snohomish Health District – Septic Systems (environmental health):
• Snohomish County – Sewer and wastewater information: https://www.snohomishcountywa.gov/ (search for wastewater or sewer integration for your address)
• Arlington utility inquiries and local regulations: check the City of Arlington or Snohomish County pages for your address to confirm current sewer availability and requirements.

Typical Septic System Types in Arlington

Conventional gravity septic systems

• How it works: A two-compartment septic tank captures solids, and clarified effluent flows by gravity to a buried drainfield or leach field. The soil and microbial activity treat the effluent before it re-enters the groundwater.
• Site fit: Best where soils are well-drained, with adequate depth to a seasonal high water table and a properly sized drainfield.
• Pros: Simple design, fewer moving parts, generally lower upfront cost.
• Cons: Not ideal in compacted, shallow, or very clay-rich soils; performance depends on proper soak area and soil percolation.
• Maintenance tips:
  • Have the tank inspected every 1–3 years and pumped as needed (typically every 3–5 years for a family).
  • Keep heavy equipment off the drainfield and protect the area from roots.

Pressure-dosed systems (dosing) and mound systems

• How it works: If soil percolation is uneven or the water table is high, a pump forces effluent into the drainfield in timed doses. A raised mound can be built to place drainfield soil above the native grade where conditions are better.
• Site fit: Useful in Arlington when native soil is shallow, highly permeable, or when the water table is close to the surface.
• Pros: Expands usable lot areas and improves effluent distribution in marginal soils.
• Cons: Higher installation and maintenance costs; more components to monitor (pump, dosing chamber, valves).
• Maintenance tips:
  • Regular alarms and pump checks; ensure the dosing area remains free of blockages.
  • Schedule professional inspections and follow local guidelines for pump cycles.

Aerobic treatment units (ATUs) and advanced systems

• How it works: ATUs introduce oxygen to the treatment chamber, promoting bacteria that more actively break down waste. Treated effluent may be discharged to a drainfield, irrigation system, or a polishing filter.
• Site fit: Chosen for challenging soils, limited space, or higher effluent quality requirements.
• Pros: Higher level of wastewater treatment; can be viable where conventional systems struggle.
• Cons: Higher energy usage, more routine maintenance, and more parts that may require service.
• Maintenance tips:
  • Service regularly (often quarterly) and keep electrical components dry and accessible.
  • Avoid flushing non-dissolvable items; adhere to recommended waste disposal practices.

Sand filters and constructed wetlands

• How it works: These are secondary or polishing steps placed after the primary treatment system. Sand filters trap solids and let microbes finish polishing the effluent; constructed wetlands use vegetation and soil to provide additional treatment.
• Site fit: Used where space is available, soils are not ideal for drainfields, or additional treatment is desired.
• Pros: Extra treatment and resilience in fluctuating conditions.
• Cons: More land area required; can require specialized maintenance.
• Maintenance tips:
  • Keep inlet/outlet areas clear and monitor vegetation health; schedule professional inspections.

Hybrid and alternative systems

• How it works: Combinations of the above systems tailored to site conditions and regulatory requirements.
• Site fit: When a single-system solution cannot meet soil, water, or space constraints.
• Pros: Flexible, can meet strict local performance standards.
• Cons: Often higher up-front costs and ongoing maintenance.
• Maintenance tips:
  • Follow the specific maintenance plan provided by the installing contractor and local health department.

Maintenance and regulations to know for Arlington homeowners

• Get a professional site assessment to determine which type fits your soil, water table, and lot.
• Regular inspections and timely pumping are essential, regardless of system type.
• Protect the drainfield area from compaction, roots, and vehicles; manage surface water and irrigation carefully.
• Always use the official permitting and inspection resources for on-site Sewage Systems.

Official resources:

• Washington State Department of Ecology – On-site Sewage Systems:
• Snohomish Health District – On-site Sewage Systems: https://www.snohd.org/206/On-site-Sewage-Systems

Common Septic Issues in Arlington

Tree roots and landscaping encroachment

• Why it happens here: Arlington yards often have established trees and shrubs planted near the septic system. Aggressive roots can grow into drain fields, causing clogging and reduced absorption.
• Common signs: standing water or soggy spots above the drain field, slowed toilets, gurgling sounds in pipes, patchy lawn growth over the absorption area.
• What to do:
  • Have a licensed septic professional locate and map the system so you can plan barriers or re-landscape away from the field.
  • If trees are too close, consider root barriers or removing problematic trees.
  • Avoid planting new trees near the drain field and limit heavy landscaping over the area.
  • Regularly inspect for root intrusion during pumping visits.

Soil and groundwater realities in Arlington

• Why it matters: Snohomish County soils can include clay layers and compacted zones, with variable percolation. Shallow depth to bedrock or dense subsoil can hamper effluent distribution.
• Common symptoms: slow drainage, frequent backups during high-use periods, damp or swampy spots in the yard even when it isn't rainy.
• What to do:
  • Get a soil evaluation from a licensed OSS designer before expanding the system or installing a mound or bed system.
  • If the existing system is undersized for your lot or soil, a professional may recommend a redesigned leach field or alternative absorption method.
  • Avoid overloading the system with water or heavy inorganic amendments that can further compact soils.

Wet winters and seasonal high water table

• Why it happens: Arlington's wet climate can saturate soils in winter and early spring, reducing the drain field's capacity to absorb effluent.
• Common signs: surface pooling near the drain field after rains, slower flushing, occasional odors.
• What to do:
  • Space out heavy water use (laundry, long showers) during saturated periods.
  • Ensure the system has proper drainage around the field (no driveway runoff or irrigation sprinklers dumping onto the field).
  • Schedule inspections after the wet season to check for effluent accumulation or field distress.

Household water use and waste disposal habits

• Why it matters: High flow, disposables, and chemicals can overwhelm a septic system's natural processes.
• Common issues: frequent pumping needs, solids buildup, pump failures, and reduced infiltration.
• What to do:
  • Use low-flow fixtures and spread out high-volume loads (e.g., don't run multiple appliances at once).
  • Route only human waste and toilet paper into the system; keep fats, oils, grease, coffee grounds, paper towels, wipes labeled "flushable" out.
  • Avoid flushing chemicals, solvents, paints, pesticides, or septic tank additives unless advised by a professional.

System age, components, and maintenance gaps

• Why it matters: Older systems wear out; pumps, floats, effluent screens, and distributed piping can fail with time.
• Symptoms: backups, foul odors, damp areas above the drain field, or alarms on pumping equipment.
• What to do:
  • Plan regular professional inspections every year or so, with pumping every 3–5 years (adjust for family size and usage).
  • Replace failing components promptly and have the system re-certified after major repairs.
  • Keep a maintenance log and follow a pumping schedule tailored to your household.

Practical maintenance steps for Arlington homes

• Steps to protect your system:
  1. Schedule professional inspections and pump-outs on a regular cadence.
  2. Keep vehicles and heavy equipment off the drain field to avoid soil compaction.
  3. Use septic-safe cleaners and avoid dumping chemicals down the drain.
  4. Divert surface runoff away from the drain field and ensure proper grading.
  5. Maintain a simple yard set-back plan: don't plant invasive species with deep roots near the field.

Official resources:

• Washington State Department of Ecology – Onsite Sewage Systems (OSS):
• Washington State Department of Health – Septic Systems:

Septic Inspection, Permits & Local Oversight

Who Oversees Septic Systems in Arlington

• In Arlington (Snohomish County), on-site wastewater systems (OSS) are primarily regulated by the Snohomish Health District (SHD) through their On-Site Sewage Systems program. State-level rules and guidelines come from Washington Ecology and the Washington Department of Health (DOH).
• If you're building, repairing, or abandoning an OSS, SHD issues the necessary OSS permits and conducts inspections to ensure the system meets current codes.
• Ecology provides overarching OSS standards and guidance, while DOH offers statewide health-focused information. For most homeowners, SHD is the day-to-day point of contact for OSS permits and inspections:
• Washington State Department of Health – Onsite Sewage Systems:
• Arlington, WA – Permits & Inspections (city site): https://www.arlingtonwa.gov/

Septic Maintenance for Homes in Arlington

Arlington-specific soil and water considerations

Arlington sits in the Puget Sound lowlands, where heavy winter rainfall and seasonal groundwater can affect septic systems. Many Arlington yards have soils with perched water tables or clay layers that slow drainage. Drain fields can become saturated during the wet season, increasing the risk of backups or surface looses. Tree roots near the system and landscape changes can also interfere with drain lines. Understanding these local conditions helps you plan for protective maintenance and, if needed, a site assessment before installing or upgrading a system.

Regular maintenance checklist

• Inspect annually for obvious signs of trouble:
  • Pooling water, soggy areas, or unusual wet spots over the drain field
  • Gurgling sounds in plumbing or toilets that drain slowly
  • Unpleasant odors around plumbing or the yard
• Schedule pumping every 3–5 years for a typical family, but adjust based on tank size, household water use, and soil conditions.
• Practice water efficiency to protect the drain field:
  • Spread major water use (like laundry) across the day
  • Fix leaks promptly; consider high-efficiency toilets, faucets, and appliances
• Protect the drain field:
  • Keep heavy equipment and vehicles off the area
  • Plant only shallow-rooted grasses or non-invasive ground cover over the field; avoid digging or planting trees nearby
• Keep clear records:
  • Document pumping dates, tank size, and system layout
  • Save receipts from inspections and repairs

Pumping and maintenance steps

1. Determine your tank size and household wastewater flow. This helps estimate a realistic pumping interval.
2. Hire a licensed septic pumper for a thorough tank cleaning, baffle inspection, and effluent level check.
3. Request an inspection of the outlet and inlet tees, lids, and any filtration or distribution boxes.
4. After pumping, obtain a written service report and schedule the next service date.
5. Review your household water-use habits with the technician; implement recommended changes to prolong tank life.

Signs your Arlington septic may be under stress

• Slow drains and frequent toilet backups
• Soggy or unusually lush patches above the drain field
• Strong sewage odors near fixtures or outdoors
• Water in the distribution box or septic tank access lids that appears abnormal
• Wastewater surfaces after heavy rain or when laundry runs

Landscaping and Arlington-specific tips

• Favor grass over bare soil above the drain field; heavy foot or vehicle traffic can compact soil and impair drainage.
• Keep trees and shrubs away from the leach field to reduce root intrusion.
• In flood-prone seasons, monitor drainage around the system and avoid directing stormwater or roof runoff toward the drain field.

Do's and don'ts for Arlington homes

• Do:
  • Use phosphate-free household cleaners and avoid flushing solvents, pesticides, oils, and paints
  • Spread out large water uses and fix leaks quickly
  • Schedule professional inspections in addition to routine pumping
• Don't:
  • Flush wipes (even "flushable"), grease, or coffee grounds
  • Pour chemicals, solvents, or antifreeze down drains
  • Drive or park on the drain field or disturb the area with heavy equipment

When to call a pro in Arlington

• You notice persistent backups or rising water around the drain field
• There are strong odors, gurgling sounds, or wet spots that don't improve after pumping
• The system hasn't been evaluated in several years, or you're planning a major remodel or addition
• You suspect a drain-field failure or water well contamination risk

Local and official resources

• Washington State Department of Ecology – Onsite Sewage Systems (OSS):

(For county and local guidance specific to Snohomish County and Arlington, check with the Snohomish County Health District and Arlington municipal resources for current OSS programs and permits.)

Cost Expectations for Septic Services in Arlington

Septic Tank Pumping

• What it includes: removing accumulated solids and scum from the tank, cleaning the baffles if accessible, inspecting tank integrity, and measuring sludge depth. Pumping frequency depends on household size and tank size; in Arlington, many homes use 1,000–1,500 gallon tanks.
• Typical cost in Arlington: roughly $350–$600 for a standard 1,000–1,500 gallon tank; larger tanks or multiple tanks can run $500–$900. Extra disposal fees may apply.
• Arlington-specific notes: wetter winters and seasonal access can affect scheduling; soil and groundwater in Snohomish County influence the optimal pumping interval.
• Steps to expect: Step 1 schedule with a licensed pumper, Step 2 provide access and any required entry permits, Step 3 receive a report with sludge depth and recommendations.
• Resources:
  • Washington State Department of Health – Onsite Sewage Systems:
  • Snohomish County – Onsite Sewage Systems:

Septic System Inspection

• What it includes: visual inspection of the tank lid and baffles, assessment of the leach field, odors, and evidence of failures; may include dye testing or a camera inspection of lines if requested; often required for real estate transactions.
• Typical cost in Arlington: basic visual inspections $150–$350; camera or line inspection $200–$500; full system evaluation $400–$700.
• Arlington-specific notes: inspections help determine if a system needs maintenance before selling or refinancing; local soils can affect field performance and apparent drainage.
• Steps to expect: Step 1 choose a qualified inspector, Step 2 arrange access and provide property details, Step 3 receive a written report with recommended next steps.
• Resources:
  • WA DOH – Onsite Sewage Systems:

Drain Field Repair or Replacement (Leach Field)

• What it includes: diagnosing field failure, removing root intrusion or soil compaction, repairing trenches, or replacing the drain field; in Arlington, mound systems may be used when the water table is high or soil conditions limit conventional fields.
• Typical cost in Arlington: field repair $2,000–$8,000; complete drain-field replacement or mound system $20,000–$60,000+ depending on size and site constraints.
• Arlington-specific notes: soil variability and groundwater levels in Snohomish County can shift the feasibility and cost of repairs; proximity to wells or property lines can require additional setbacks and permitting.
• Steps to expect: Step 1 perform a diagnostic test (often with a service camera or soil probe), Step 2 design an alternative field if needed, Step 3 obtain permits and schedule installation.
• Resources:
  • WA DOH – Onsite Sewage Systems: https://www.doh.wa.gov/LicensesPermitsandCertificates/ProfessionsOrTrades/OnsiteSewageSystemOSS
  • Ecology – Onsite Wastewater Systems: https://www.ecology.wa.gov/Water-and-Sewer/Wastewater/Onsite-wastewater-systems

New Septic System Installation (Design & Permitting)

• What it includes: site evaluation, soil testing (perc tests), system design (conventional or mound), permitting, and installation of tank, drain field, and any required components.
• Typical cost in Arlington: conventional system $15,000–$40,000; mound or complex systems $25,000–$60,000+; permit-related fees often add several hundred to a few thousand dollars.
• Arlington-specific notes: setbacks from wells, streams, and property lines are enforced; local permit approvals from Snohomish County can influence timelines and costs.
• Steps to expect: Step 1 obtain a site evaluation, Step 2 complete soil testing, Step 3 submit plans and permits, Step 4 installation and final inspection.
• Resources:
  • Snohomish County – Onsite Sewage Systems (OSS) information: https://www.snohomishcountywa.gov/1986/Onsite-Sewage-Systems
  • WA DOH – Onsite Sewage Systems: https://www.doh.wa.gov/LicensesPermitsandCertificates/ProfessionsOrTrades/OnsiteSewageSystemOSS

Septic Tank Components Repair (Baffles, Pumps, Lids, Risers)

• What it includes: replacing damaged baffles, upgrading or resealing lids, installing or adjusting risers, and repairing or replacing pumps in pumping chambers.
• Typical cost in Arlington: baffle replacement $100–$400; lid/riser replacement $200–$700; pump replacement $800–$2,500 (parts and labor vary by setup).
• Arlington-specific notes: reliable access to the tank is key in older Arlington homes; adding risers can reduce future disturbance and improve accessibility.
• Steps to expect: Step 1 diagnose component failure, Step 2 obtain replacement parts, Step 3 perform repair and test the system.
• Resources:
  • WA DOH – Onsite Sewage Systems: https://www.doh.wa.gov/LicensesPermitsandCertificates/ProfessionsOrTrades/OnsiteSewageSystemOSS

Drain Field Maintenance and Enhancement

• What it includes: routine maintenance to keep field perforations clear, root intrusion management, and upgrades to improve field performance (e.g., soil conditioning or minor repairs to the distribution network).
• Typical cost in Arlington: maintenance $1,000–$3,000 for minor interventions; enhancements or partial improvements $3,000–$15,000 depending on scope.
• Arlington-specific notes: Arlington soil profiles and drainage patterns can influence maintenance needs; in some cases, seasonal wet periods necessitate more frequent care.
• Steps to expect: Step 1 identify symptoms (wet spots, backups), Step 2 assess drainage and roots, Step 3 implement targeted improvements.
• Resources:
  • Ecology – Onsite Wastewater Systems: https://www.ecology.wa.gov/Water-and-Sewer/Wastewater/Onsite-wastewater-systems

Permit and Plan Fees / Consultation

• What it includes: professional consultations, plan reviews, and county or state permit processing for all major projects (new systems, system replacements, or large repairs).
• Typical cost in Arlington: consultation $100–$300; plan review and permit fees $150–$600+ depending on project size and jurisdiction.
• Arlington-specific notes: Snohomish County permits will govern most work; early budgeting for permits helps avoid delays.
• Steps to expect: Step 1 hire a licensed designer or contractor, Step 2 submit plans, Step 3 obtain approvals and schedule work.
• Resources:
  • Snohomish County – OSS Permit information: https://www.snohomishcountywa.gov/1986/Onsite-Sewage-Systems
  • WA DOH – Onsite Sewage Systems: https://www.doh.wa.gov/LicensesPermitsandCertificates/ProfessionsOrTrades/OnsiteSewageSystemOSS