Environmental Health
Surface Water (Lakes, Rivers & Streams)
Henderson WPA Septic System O&M Program
  Henderson Watershed Protection Area  

Septic System O&M Program — Basics

  Who is included in the program?  l  What is required in the New Program?  l 

When will I receive my renewal certificate?  l  Who does the maintenance & inspections?  l

Why is the program divided into "low-risk" and "high-risk" systems?  l

How is risk level determined?  l  What are the fees for this program?  l

Who is exempt from fees?  l  Request a review

Who is Included in the Program?

A property is included in the program if any portion of its on-site sewage system is located within the Henderson or Nisqually Reach Watershed Protection Area (HWPA & NWPA) boundary — including a building with plumbing and any sewage collection, transport, treatment, and disposal components. For additional help, see HWPA boundary map and NWPA boundary map [PDF] (also included are instructions on how to determine if you are within the HWPA).

What is Required in the Program?

Operational Certificates

All septic systems within the HWPA and NWPA are required to have renewable operational certificates. The operational certificates must be kept current and renewed on prescribed schedules. Most certificates will have a 3-year renewal cycle. However, some more complex systems will have a 1-year renewal.

The operational certificate requires routine maintenance and inspections; requirements depend on the site conditions and the type of system. Any problems found during maintenance and inspection must be corrected before the certificate will be renewed. Reports must be sent to the County Health Department at the time of certificate renewal.

If you receive a notice that your Operational Certificate is coming due and you have had your septic system inspected within the previous 6 months, please attach a copy of your inspection report with your renewal form and return to us.

Dye Test Evaluations for "High-Risk" Systems

For systems designated as “High Risk”, a dye test evaluation is required as a condition of the operational certificate renewal.

A dye test is used to help determine if a septic system is failing. While it does not find all possible problems, it is especially useful in disclosing seepage failures. It involves flushing a non-toxic tracer dye down a toilet and placing charcoal packets downhill of the septic system to collect any dye that may be leaking (with the sewage) from the system.

Dye test evaluations must be done every other renewal cycle or every 6 years. These evaluations may be performed by County health department staff or approved professionals.

When Will I Receive My Renewal Certificate?

There are nearly 6,400 septic systems in the HWPA program which will be phased in over a three-year period. Generally, homeowners will receive renewal certificates, based on parcel number. For example, parcel numbers beginning with "0" will be in the first group and those beginning with "7", "8", or "9" will receive their renewal certificates in the third year.

Who Does the Maintenance and Inspections?

County-certified pumpers [PDF], system installers [PDF], and monitoring specialists [PDF], as well as state-licensed designers [PDF] can do routine maintenance and inspections. For a complete list, see Certified Septic System Contractors.

Owners of standard gravity systems, pressure distribution systems, mounds, and Glendon® systems may conduct their own inspections, if they become certified to do self-inspections by attending County-sponsored training. If you are in the Henderson O&M program and would like to become certified to inspect your septic system, see Septic System Inspection Certification.

Why is the Program Divided into "High-Risk" and "Low-Risk" Systems?

The degree of risk a system poses to water quality and public health is determined by a combination of factors that include: proximity to surface waters or drainages, and soil type. These factors influence the likelihood that a system will contaminate surface water if it fails.

All systems are assigned a risk level of either “low” or “high” based on the risk the system poses to water quality and public health.

How is Risk Level Determined?

The determination is made using the following “Risk Level Points” table. Total points to determine a high-risk system is 16 or more, a low-risk system has less than 16 points.

Risk Level Points:

Nonrestrictive Soils — typically sands and sandy loams 0
Restrictive Soils* — typically soils with high silts and clays 10
Proximity to Surface Water — if any part of the sewage system or plumbing is within 100 feet of a stream 6
Any property within 200 feet of Henderson marine shoreline 10
Any property, with a septic system, NOT in proximity to a stream or marine water as defined above 0

Range of points for risk level determination:

  • Low Risk <16
  • High Risk ≥16

*Restrictive class soils is assigned, if any part of the sewage system or plumbing is fully or partially located in restrictive soils.

What are the Fees for this Program?

As of January 1, 2012, annual fees for the program are:

  • Low-risk Systems - $35 per year
  • High-risk Systems - $96 per year
  • Community Systems - $177 per year (Each parcel with an individual septic tank which is connected to the community system will also be charged either the low-risk or high-risk system fee, as applicable.)

Fees began in 2007 and appear on your property tax statement. Due to limited space on the Property Tax Statement, fees are included with the Stormwater Utility charge.

NOTE: For each subsequent year of the program, charges will be automatically adjusted each January 1 by the percentage increase in the June Consumer Price Index for the previous year. The maximum increase will be 3.5%.

Who is Exempt from Paying the Annual Program Fee?

Senior/Disabled Exemption

Any parcel owned by a person who is currently granted an exemption under RCW 84.36.381 through 84.36.385.

Properties Exempted by RCW 90.72.070

  • Confined animal feeding operations subject to the national pollutant discharge elimination system (NPDES) and implementing regulations.
  • Facilities permitted and assessed fees for wastewater discharge under the NPDES.
  • Lands classified as forest land under Chapter 84.33 RCW.
  • Lands classified as timber land under Chapter 84.34 RCW.

Request a Review

Applications for review must be submitted to Environmental Health on a Request for Correction of Rates & Charges form [PDF]. Information, such as maps or photographs, to support the adjustment requested should be included. Applications for review must be received by April 30th of each year for any corrections to be applied to the next tax year.

If a property owner believes the requirements (see list below) of the Henderson Watershed Protection Area have been applied to their property in error, they may request a review. The following requirements will be considered in the Request for Review—no other review or appeal will be allowed:

  • the property is served by a septic system
  • the property drains toward Henderson Inlet
  • the location of any portion of your plumbing and/or septic system is within the HWPA
  • the septic system is a high-risk or low-risk system
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This page last updated: 04/01/22