Septic Systems and Soil Testing: Land Buyer Checklist

by discovernwrealtygroup-chime-me

If you’re buying land in Washington State, whether for retirement, rural living, or building a dream home, understanding septic systems and soil testing is crucial. Unlike urban lots connected to city sewer systems, many rural and undeveloped parcels in counties like Lewis, Yakima, and Clark require a private septic system. But before installation, you’ll need to make sure your land passes a soil test (also known as a percolation or “perc” test). This guide walks you through everything land buyers should know, before and after making an offer.

Why Septic Systems Matter for Rural Land Buyers

A septic system handles wastewater treatment on properties that aren’t connected to municipal sewer lines. In rural parts of Washington, especially in less densely populated areas like eastern Clark County or unincorporated Lewis County, septic systems are the norm.

Before buying land, it’s critical to confirm the lot can legally and physically support a septic system. Without a passing soil test, you may not be able to build, or the installation could cost significantly more than expected.

Key reasons septic systems are important to consider:

Permitting: A septic permit from the county is often required before construction begins.
Cost: Installation can range from $6,000 to $25,000+ depending on system type and soil conditions.
Maintenance: Proper care is essential to avoid future issues and costly repairs.

For more info, consult the Washington State Department of Health septic guidelines.

What Is a Perc Test, and Why Do You Need One?

A perc test determines how well your soil drains — a key factor in whether a septic system can be approved for your land. In Washington State, this is typically conducted by a licensed soil scientist or onsite septic system designer.

What the perc test checks:

Soil texture and drainage
Seasonal water tables
Depth to restrictive layers (like clay or bedrock)
Slope of the land

In counties like Yakima or Klickitat, rocky or volcanic soil may pose challenges. Conversely, in flatter regions like Thurston County, clay soils could slow drainage. In either case, an approved septic design is often required before obtaining a building permit.

Cost of a perc test: $700–$1,500 depending on location and complexity.

Best Washington Counties for Septic-Friendly Land

If you’re looking for buildable rural property with good soil and fewer restrictions, here are some counties worth exploring:

Lewis County

Known for affordable land and flexible permitting
Many parcels already come with approved septic designs
Good balance between forested and cleared land

Yakima County

Popular with homesteaders and retirees
Drier climate and sandy loam in some areas can be ideal for drainage
Beware of flood zones and water rights requirements

Clark County (North and East)

Close to Portland metro but still offers a rural feel
Higher property values but often better infrastructure
Strict permitting process — soil testing and design plans usually required

Always check county records for existing perc results or approved septic designs before purchasing.

Pros and Cons of Buying Land with or Without Septic Approval

Buying Land WITH Approved Septic:

Saves time and uncertainty
Can start building sooner
May increase land value

Buying Land WITHOUT Septic Approval:

Cheaper upfront price
Risk that land won’t perc
Delays in permitting or system design

Tip: If a property hasn’t been tested, make your offer contingent on a successful soil test during due diligence.

Key Questions to Ask Before You Buy

Before closing on rural land, ask these septic- and soil-related questions:

Has the property passed a recent perc test?
Is there an existing septic design approved by the county?
What are the soil types and drainage conditions?
Are there wetlands or steep slopes nearby?
How close is the nearest well or water source?

You can check local regulations through each county’s environmental health department, such as Clark County Public Health.

Final Thoughts: Planning Ahead for a Smooth Septic Process

Septic systems and soil testing may not be the most glamorous part of land buying — but they’re essential. Knowing what to look for can save you thousands of dollars and months of delays. Washington’s rural land offers endless potential, but doing your homework up front will ensure your property is truly buildable.

Next Step: If you’re considering buying land in Washington State, explore local listings with septic approval or contact a land expert who can guide you through the testing and permitting process.