OSCAR vs Conventional Systems in Snohomish: Which Fixes Failing Septics?

Receiving a notice that your septic system has failed its inspection is stressful. For homeowners in Snohomish County, with its unique soil compositions and strict environmental regulations, this news often brings a wave of questions about cost, complexity, and the best path forward.

But a failed system isn’t a dead end—it’s an opportunity to upgrade to a modern, reliable solution that protects your property value and the local environment. The two primary options you’ll face are a traditional conventional septic system and an advanced engineered system like OSCAR.

This guide provides a deep comparison to help you understand which system is the right choice for your failing septic system, your property, and your peace of mind.

OSCAR System Overview

When a conventional system isn’t an option, the OSCAR system often emerges as the leading solution. It is a highly effective, engineered system specifically designed for challenging properties.

What is an OSCAR system?

OSCAR stands for On-Site Sand Coil Area Recharge. It is a specialized, low-profile septic system that uses a drip dispersal method. Instead of relying on a large gravel-filled trench, an OSCAR system utilizes coiled drip tubing laid over a carefully prepared sand bed. This design allows for the slow, even, and highly treated distribution of effluent into the soil.

It was developed specifically for properties that cannot support a conventional gravity system due to common Snohomish County challenges like:

• Shallow restrictive layers of soil (hardpan or glacial till).
• Limited physical space for a large drain field.
• High seasonal water tables.

The OSCAR system is a fully recognized and approved technology in Snohomish and King counties and is frequently the go-to solution for difficult sites from Monroe to the foothills.

How long does an OSCAR last?

With a professional design from a team like Davis Septic Design, proper installation, and consistent maintenance, an OSCAR system can last 20 to 30 years or more. Its longevity is directly tied to diligent care, including routine inspections and pump-outs, using only septic-safe household products, and avoiding soil compaction over the drain field area.

Cost comparison: OSCAR vs. conventional

There’s no hiding it: OSCAR systems generally have a 15% to 30% higher upfront cost than conventional systems. This is due to the advanced design requirements, the complexity of the installation (which involves pumps, drip lines, and sand beds), and the use of specialized components.

However, the true value emerges over time. For a property with poor soil, a cheaper conventional system is at high risk of premature failure, leading to more costs down the road. An OSCAR system, while a larger initial investment, provides a reliable, long-term solution that equalizes in value by preventing future failures.

Conventional Septic System Basics

The traditional gravity-fed system is the most common type of septic system, and for the right property, it remains an excellent choice.

Traditional gravity systems – pros and cons

Pros:

• Lower Upfront Cost: It is the most affordable system to design and install.
• Simpler Design: With fewer moving parts, maintenance is straightforward.
• Widely Understood: Most septic professionals are familiar with its operation and repair.

Cons:

• Requires Good Soil: It is completely dependent on deep, permeable soil to function correctly.
• Site Limitations: Not suitable for properties with steep slopes, heavy clay soil, or high groundwater.
• Large Footprint: Requires significant space, making it difficult for smaller lots with tight setbacks.

When to repair vs. replace

After a failed inspection, the big question is whether you can repair your existing system or if a full replacement is necessary.

Repair might be an option if:

• The issue is a minor clog in the drain field or a problem with the tank itself.
• The surrounding soil still percolates well and the absorption area is structurally intact.

Replacement is likely required if:

• The drain field is fully saturated and no longer absorbs effluent.
• The septic tank is cracked, leaking, or structurally compromised.
• A Snohomish County health inspector has reviewed the site and mandates a full system redesign to meet current codes.

Pro Tip: If your property’s as-built drawing (CAD) is over 20 years old, the county may require a completely new design to comply with modern standards, even if the failure seems minor.

Soil & Site Compatibility

The single most important factor determining your septic system choice is your soil. A professional soil log is the only way to know for sure what your property can support.

What soil suits an OSCAR system?

An OSCAR system is the engineered solution for properties where conventional systems are not viable. It is ideal for sites with:

• Shallow or restrictive soils (less than 12 inches of usable soil depth).
• Dense layers of glacial till or hardpan close to the surface.
• Sloped lots where gravity flow is impractical.
• Environmentally sensitive areas requiring uniform, highly treated dispersal.

How soil type affects septic choice

The results of your soil log will point you directly to the right system type.

• Clay Soil: Has slow percolation rates. It almost always requires an engineered system like a mound, an Aerobic Treatment Unit (ATU), or an OSCAR.
• Sandy Loam: Considered perfect for a conventional gravity system.
• Gravelly Soils: Can percolate too quickly, risking groundwater contamination. These sites often need an engineered system to ensure proper treatment before dispersal.

In Snohomish County, discovering inadequate soil conditions during an inspection is a common trigger for a mandated upgrade to an engineered system.

Real-World Repair Scenarios

Understanding when a replacement becomes necessary can be clarified with real-world examples.

When repairing isn’t feasible—case examples

A simple repair is often off the table for properties with significant issues, such as:

• Drain fields that are completely saturated and consistently fail percolation tests.
• Pipes that have been crushed or broken by encroaching tree roots.
• Evidence of illegal or unpermitted modifications made by previous owners.

Case Example: A homeowner on a 0.4-acre lot in Snohomish failed their routine inspection. Their conventional gravity system was too close to a property line, and the soil was a dense glacial till. Repair was impossible. Davis Septic Design was brought in to design an OSCAR system that could fit within the tight setbacks and function properly in the challenging soil.

Who qualifies for an OSCAR upgrade?

To upgrade to an OSCAR system, you must meet certain criteria:

• A recent soil log and site evaluation must be completed by a licensed designer.
• Your existing system must be officially designated as failing or inadequate.
• Your property likely has constraints like a small lot size or a high water table.
• The design must be approved by the Snohomish Health District.

Davis Septic Design provides comprehensive feasibility studies to evaluate your property and determine if an OSCAR system is the best and most compliant solution for you.

How long does installation take?

A typical project timeline for a replacement system is:

• Soil Log & Design: 1–2 weeks
• Permit Approval: 2–4 weeks (can vary based on the health department’s workload)
• Installation: Approximately 1 week

Complex sites with steep slopes or difficult access may take longer. We recommend starting the soil testing process in the spring or summer to ensure faster processing and better weather for installation.

Maintenance and Longevity

The long-term health of your system depends on understanding its unique maintenance needs.

Routine upkeep differences

OSCAR System:

• Requires periodic maintenance of the pump station and controls.
• May need occasional flushing of the drip lines to ensure they are clear.
• Regular monitoring of the sand media integrity is part of the inspection.

Conventional System:

• Simpler upkeep, primarily involving tank pumping and occasional line checks.
• No pumps or complex moving parts to service.

For Both Systems: Plan to pump your septic tank every 3-5 years and never overload the system with grease, “flushable” wipes, or harsh chemicals.

When to call for service

Be proactive and call for a professional consultation if you notice any warning signs:

• Pooling water or foul odors near the tank or drain field.
• Alarms sounding from the control panel (specific to OSCAR and other engineered systems).
• Sewage backups in your home’s drains.

The team at Davis Septic Design offers consultations to help you diagnose issues early, potentially saving you from a more costly emergency repair.

Final Advice

Making the right decision requires a clear assessment of your situation.

Decision checklist for homeowners

Ask yourself these questions to determine the best path forward:

• ✅ Do I have limited space or challenging soil conditions?
• ✅ Has my system officially failed an inspection?
• ✅ Is my priority a long-lasting system that meets all current codes?
• ✅ Is my property near wetlands or other environmentally sensitive areas?
• ✅ Am I prepared to invest in a reliable, engineered solution for long-term peace of mind?

If you answered “yes” to several of these, an OSCAR system is likely the right choice for your property.