01/06/2021
An on‐site sepc evaluaon or site evaluaon means the evaluaon of the soil profile, ground water lev‐
els, and landscape features of a specific lot and locaon by an Environmental Health Specialist for the
purpose of determining whether the site will meet the minimum requirements for the installaon of an
on‐site sepc system.
Test holes are excavated areas which are required to be dug for the purpose of evaluang the soil pro‐
file and ground water levels during the evaluaon. Three test holes must be located in, or adjacent to,
the areas designated as the primary and the reserve drainfield. In sandy soils, each test hole should be
approximately 18 inches in diameter and at least 3 feet deep. In other soils, test holes must be 2 feet
wide and 4 feet deep with a ramp cut into the ground for gaining access into the hole. If test holes dug
in non‐sandy soils do not have an adequate ramp, or if the spoils of the holes are too close and present a
safety hazard, the site will not be evaluated.
Due to a wide fluctuaon in ground water levels, the site may be required to be placed on a winter eval‐
uaon to accurately determine the winter water table. A winter evaluaon requires a bi‐weekly evalua‐
on of the site by an Environmental Health Specialist during the months of December, January, and Feb‐
ruary. The results of the winter evaluaon will then be reviewed and the County will nofy you whether
adequate site condions exist for the placement of an on‐site sepc system. An addional fee will be
assessed for this service payable before December 1st in order to be placed on the winter evaluaon
list.
The installaon of an on‐site sepc system requires an in‐depth site and soil evaluaon and the sub‐
mial of a detailed sepc design demonstrang compliance with applicable state and local rules and
regulaons. If you are planning to install an on‐site sepc system, you must secure the services of an On
‐Site Sepc System Designer or Professional Engineer. Both are licensed by the Washington State De‐
partment of Licensing (DOL). The designer or engineer will evaluate your property by looking at the size
and topography of the site, soil condions, proximity to surface water, and other pernent condi‐
ons. You will want to work with your designer or engineer to develop a site plan that has all the neces‐
sary informaon required for an on‐site sepc system and any future development you may be plan‐
ning. This is required to be included in the design and has to be consistent/idencal with the site plan
that was submied with other applicaons.
When the on‐site sepc designs are complete, you will be required to submit two sets of the designs
with your applicaon packet. An Environmental Health Specialist from the Department of Community
Development will review the site along with the applicaon and design to make sure that it is an appro‐
priate design in compliance with the state and local rules and regulaons.
Item Requiring Setback Primary & Replacement
Drainfield (.)
Sepc Tank &
Pump Chamber (.)
Well or Sucon Line 100 50
Water Supply Line Under Pressure 10 10
Surface Water 100 50
Building Foundaon 10 5
Property Line or Easement Line 5 5
Curtain Drain or Culverted Ditch
Upgradient from system component
Downgradient from system component
10
30
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5
Horizontal Setbacks Requirements for System Components
