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DEPARTMENT OF LICENSING

Guidelines for the Professional

Practice of On-Site Wastewater

Treatment System Design

www.dol.wa.gov

Summer 2003

PREPARED BY:

On-Site Wastewater Treatment System

Designer Licensing/Inspector Certification Advisory Committee of the

Board of Registration for Professional Engineers and Land Surveyors

Acknowledgments ..................................................................... ii

Introduction ............................................................................. iii

Designer Licensing Law and Related Statute References ............ v

Revised Code of Washington ............................................... v

Washington Administrative Code ........................................ v

Professional Certification of Documents .................................... 1

Legal Definitions ....................................................................... 3

1. The On-site Wastewater Treatment System Designer ...... 3

2. On-Site Wastewater Treatment System Design ............... 3

3. Professional Engineer .................................................... 3

Roles & Responsibilities ............................................................ 4

1. Statement of Purpose - The Design Professional: ............ 4

2. Statement of Purpose - The Local Health

Jurisdiction Regulator: .................................................. 5

Areas of Responsibility for the Design Professional .................... 6

1. Gathering Existing Information ...................................... 7

2. Site Evaluation .............................................................. 8

3. Soil Evaluation ............................................................ 10

4. Preliminary/Conceptual Design Documentation or Site

Evaluation Report ....................................................... 12

5. Design ......................................................................... 13

6. Construction Management ........................................... 15

7. Post Construction Activities ......................................... 17

Guidelines for The Professional Practice of

On-site Wastewater Treatment System Design

Table of Contents

The Department of Licensing has a policy

of providing equal access to its services. If

you need special accomodiation, please call

360-664-1564 or TTY at 360-586-2788.

Acknowledgments

The Board wishes to thank the following volunteers and

Board staff for their contributions to the creation of this

booklet:

Standards of Practice Work Group Members:

Dean Bannister, Able Development Company

Bob Wright, PE, Tryck, Nyman, Hayes, Inc.

Paul Gruver, Soiltech Inc.

Jerry Stonebridge, Stonebridge Construction

Larry Fay, Jefferson County Health & Human Services

Richard Benson, PE, State of Washington, Department

of Health

David Jensen, PE, D.R. Strong Consulting Engineers

Kenneth Mitchell, PE, Irrigation & Hydraulics Unlimited,

Consulting Engineers

Michael Vinatieri, Clark County Health Department

Board Staff:

George Twiss, LS, Executive Director

Joe Vincent Jr., On-Site Program Manager

iii

Introduction

In establishing the statewide program for licensure and

regulation of on-site Designers (chapter 18.210 RCW) the

Washington Legislature was addressing the need to have

uniform standards which all practitioners, regulators and

members of the public could rely upon.

The Department of Health, State Board of Health, Local

Health Districts, Department of Licensing and the Board of

Registration for Professional Engineers and Land Surveyors

(Board) each have a shared responsibility to protect the

public against the design and installation of inadequate or

unsafe on-site wastewater treatments systems. On-site

sewage codes and professional licensing laws exist to meet

a common goal. Where state and local health officials

promulgate and enforce codes intended to protect public

health and environment, the Board has established a

rigorous process that is intended to assure that

practitioners in this profession, whether licensed Designers

or Professional Engineers, can accurately and competently

apply the necessary knowledge to meet those codes. All

design practitioners are obligated to be familiar with and

comply with local ordinances and policies regulating the

design of on-site systems for the jurisdiction in which they

are practicing.

These guidelines are intended to provide design

professionals and health officials with a basic framework of

conduct and practice that illustrates the expected

professionalism and technical skill befitting of those that

hold a license to practice in this profession. They have

been prepared in the spirit of service to the public and to

assist health officials and on-site design professionals to

better understand the requirements of our state laws and

codes. They are not intended to affect or limit the trade or

business of individuals or firms that provide support

services to the on-site wastewater treatment professions.

While these guidelines can be used as a resource, it should

be understood that: design submittal criteria, application

submittal requirements, construction drawing requirements

and code compliance review remain under the jurisdiction

of the local health permitting authority.

If any portion of these guidelines is determined to

conflict with or contradicts Washington State law or

rules, or those local ordinances governing on-site waste-

water treatment systems, those publications and source

documents will prevail.

Designer Licensing

Law and Related

Statute References

 Revised Code of Washington

• Chapter 18.210 RCW..... On-Site Wastewater Treatment

Systems Designer Licensing/Inspector Certification

• Chapter 18.43 RCW ...... Engineers and Land Surveyors

• Chapter 43.20 RCW ...... State Board of Health

• Chapter 70.05 RCW ...... Local Boards of Health

• Chapter 43.70 RCW ...... Department of Health

 Washington Administrative Code

• Chapter 246-272 WAC ... On-Site Sewage Systems

• Chapter 196-30 through 33 WAC.......Licensing and

Practice Rules for On-Site Wastewater Treatment

Systems Design Professionals

Professional

Certification

of Documents

On-site wastewater treatment system Designers and

Professional Engineers are responsible for their professional

design services. The public, health officials, and their

clients rely on their professional expertise. As a result,

professional submissions such as plans, specifications,

calculations and designs must conform to the applicable

regulations and show the identity of the professional that

prepared them.

The applicable law and rules governing stamping are RCW

18.210.130 and WAC 196-33-400 & 500.

While these laws detail the requirements of stamp use, a

good general rule is that professional stamping and signing

of designs, plans or documents should occur whenever the

documents are submitted for review or approval. This

would include all documents in which your professional

judgments and decisions are offered. The following are

provided as examples:

• Site/Soil reports

• Final designs, including calculations, drawings and

specifications

• Construction Reports

• As-builts when required of the licensee

Preliminary documents, designated

as such, must be stamped but are

the only documents that do not

need a signature.

To the left is a copy of the approved

design for On-Site Wastewater

Treatment System Designer

Licensing stamp:

Legal

Definitions

1. The On-site Wastewater Treatment System Designer

The Washington statute (RCW 18.210.010 (3)) defines

the professional Designer as:

“Designer,” “licensee,” or “permit holder” means an

individual authorized under this chapter to perform design

services for on-site wastewater treatment systems.”

2. On-Site Wastewater Treatment System Design

The Washington statute (RCW 18.210.010 (8)) defines

the practice of On-site wastewater design as:

“the development of plans, details, specifications,

instructions, or inspections by application of specialized

knowledge in analysis of soils, on-site wastewater treatment

systems, disposal methods, and technologies to create an

integrated system of collection, transport, distribution,

treatment, and disposal of on-site wastewater.”

3. Professional Engineer

The Washington statute (RCW 18.43.020 (2)) defines

Professional Engineer as:

“...a person who, by reason of his or her special knowledge

of the mathematical and physical sciences and the principles

and methods of engineering analysis and design, acquired

by professional education and practical experience, is

qualified to practice engineering...”

Roles &

Responsibilities

1. Statement of Purpose - The Design Professional:

An on-site wastewater treatment system Designer, whether

a licensed Designer under RCW 18.210 or a licensed

Professional Engineer under RCW 18.43, is engaged in

creating an onsite wastewater treatment system design to

ensure that the systems they design:

• are capable of performing to treatment standards

appropriate for the locations where they are used,

• have been developed in consideration for the needs of

the client for reliability and durability,

• conform with applicable regulations and codes as well

as to the standard of care of the industry, and

• are designed ethically, competently and with due

diligence.

A Designer is responsible for correctly characterizing the

site conditions and wastewater. He or she must be able to

intelligently apply professional judgment in order to prepare

a design that addresses the limitations of the property in

consultation with the client and with consideration of the

ability to install the system. The design must also be

consistent with adopted regulatory standards and prepared

in a manner understandable by others. The Designer must

be able to observe the construction of the onsite sewage

system and verify that it is consistent with the approved

design, evaluate the significance of any deviations from the

design, and document in a clear format his or her findings.

The Designer must have a good understanding of the

standards and workings of the system being designed and

have the ability to trouble shoot malfunctioning systems.

2. Statement of Purpose - The Local Health

Jurisdiction Regulator:

The role of the health jurisdiction, with respect to the

practice of on-site sewage system design is to apply and

enforce standards that provide basic public health

protection. Standards may be proscriptive or performance

based, but must be sufficient to assure that surface and

ground water will not become contaminated at the density

that on-site sewage systems will be used.

It is the regulator’s responsibility to ensure that adopted

standards are being followed in practice. This may involve

the review of site conditions and plan review to ensure that

the system technology or treatment standards selected in

the design are appropriate for the limitations presented on

the site. It also involves fact finding and reporting to

appropriate authorities when practitioners are not

performing to industry or regulatory standards. The

decision to issue a permit is an affirmation that the design

conforms to or meets the intent of adopted regulatory

standards.

Areas of

Responsibility

for the Design

Professional

Following is an outline of design considerations and general

areas of responsibility for licensed professionals designing

on-site wastewater treatment systems. It is formatted to

follow a step-by-step process a design professional might use

for a typical on-site design project. However, it is recognized

that in practice the design professional may approach

different projects from a different order than presented in

this document. The subjects listed represent general areas

and are not all-inclusive. Local requirements and processes

will not necessarily be consistent with this information, and

may require more from the design professional than is

indicated here. Successfully obtaining a permit for design is

not the sole measure of determining whether the licensed

professional has met their obligation, rather the true

measure is whether due consideration was given to

influences affecting the design and success of the project.

While not all projects will require the same depth of work,

the design professional should be able to justify any and all

decisions or omissions when called upon to do so.

1. Gathering Existing Information

The practice of design includes due consideration of

relevant information about the site and proposed project.

Thorough research is the essential “first step” that an on-

site design professional must incorporate in their service

delivery. Analyzing what information is needed, where to

obtain that information and what impact the information

has on the intended project is a process that a successful

design is based upon. Whether it comes from the client, a

neighbor, public agency, contractor or other design

professional, a Designer holds final responsibility to ensure

that the research and the reliability of the data satisfies the

standard of care.

The following are typical tasks a design professional will

consider when gathering existing information:

Information from Client

• Obtain history of past submittals or proposals for new

systems

• Obtain history of system components for existing

systems (e.g., problems, inspections, type and location)

• Obtain legal lot information (e.g., address, tax

information)

• Obtain relevant property historical data

• Obtain a description of user’s habits and characteristics

• Obtain user’s current and future plans for

improvements or site development

• Obtain information on potable water sources

• Obtain dwelling specifics (e.g., dimensions, room types)

Information Gathered from Other Sources

• Verify plats, surveys, and legal descriptions from county

records

• Identify potential problems regarding zoning, land use,

or other critical areas (e.g., wetlands, flood zone, steep

terrain)

• Identify setback requirements

• Gather soil and geohydrologic information on the

subject area

• Determine well locations

• Investigate relevant characteristics of adjacent sites

• Determine applicable regulations

• Verify availability of public sewers or sewage systems

2. Site Evaluation

The practice of design includes the inspection and analysis

of the physical characteristics and limitations of the subject

site and the surrounding areas to determine the suitability

for design. The site evaluation may be general in nature,

leading to generalized conclusions about future

development, or specific to a design project.

The overall site evaluation takes place at the site usually

after other recorded information has been gathered.

For design purposes the process starts with a physical

review of the site, identifying the property lines and corners

and taking visual note of the lay of the land, i.e., slopes,

cuts or banks, surface water, drainage (on and off the

property), vegetation (type and location), open spaces,

potential building sites, existing improvements, and soil

absorption areas.

Following consultation with the client, a subsurface soil

investigation is conducted and soil logs are prepared in the

areas identified as potential soil absorption drainfields. If

the soils in these areas are not feasible for an on-site

wastewater treatment system (see 3. Soil Evaluation),

additional sites must be investigated and established.

Once the site review is completed, initial mapping may

take place.

Relative to the design, initial mapping includes

establishment of horizontal and vertical controls, locating

existing site features and collecting topographic features

and other site conditions that may affect the design and

function of the system. In the context of this document, the

term “mapping” is not intended to include work restricted

to the licensed practice of surveying. It refers to the

collection of data points within defined property boundaries

established by others.

In addition to evaluating site characteristics for new

development, site evaluation may include the process of a

designer determining the nature and probable cause of

malfunction or failure of an existing system. It should be

clear that not all systems that exhibit signs of malfunction

are actually in failure, and as a result, the designer has a

responsibility to use care in determining an action plan.

Whenever possible, diagnosis of the system malfunction

or failure should occur prior to preparing a replacement

system design. When evaluating a malfunctioning system

the designer should, at a minimum, consider soil,

hydraulic, biological and chemical factors. Establishing

the cause of a system malfunction may require the designer

to develop a detailed history of the system. If historical

information is not available, the designer may have no

option but to forego an attempt to determine the cause

of failure and simply develop a design as though for a

new system.

The following are typical tasks a design professional will

consider when conducting a site evaluation:

• Identify existing structures (house and outbuildings)

• Identify components of existing systems

• Verify location of potable water source

• Verify existing property dimensions, property lines, and

corners

• Assess quantity and type of vegetation on property

• Evaluate topography of the site and adjacent properties

• Identify surface waters, ground waters, and assess

drainage (geohydrology)

• Identify location of utilities and easements

• Identify the most appropriate location for drainfields

• Identify potential construction pathways

• Establish and record horizontal and vertical control

3. Soil Evaluation

The practice of design includes the inspection and analysis

of the physical characteristics and limitations of the site

soils to determine the suitability for design.

The practice of design includes gathering preliminary soil

data, field inspection, recording and testing, and sampling

for laboratory analysis of the physical characteristics and

limitations of site soils. The information is used to

determine suitability for an on-site system, and the most

appropriate type of treatment and dispersal system.

Preliminary data gathering includes collection of available

background information on the proposed drainfield site

such as soil survey maps and/or previously prepared

geotechnical reports or soil logs. Direct soil evaluation

includes visual and tactile inspection of soil profiles at the

site and may also include field tests and/or sampling for

laboratory analysis.

An appropriate number of test pits must be examined in

order to prepare a detailed description of the soil profile

(usually at least three to five pits for residential systems) in

representative locations in both the proposed primary and

reserve drainfield areas. Characteristics to be determined

include soil texture, structure, and level of consistency,

color and color patterns, root penetration, percent of gravel

and moisture content.

The evaluator must also be able to identify any restrictive

layers (clay, bedrock, hardpan, and redoximorphic features

that may indicate seasonal saturated conditions and affect

drainage or aeration). The evaluator may also conduct field

tests or collect samples for laboratory analysis as

appropriate such as sieve analyses, hydrometer tests, bulk

density test, etc. The evaluator should use commonly

accepted nomenclature to document findings and justify

decision-making for design purposes and for future use by

the regulator and installer.

The above information is analyzed to verify site feasibility,

to determine a suitable loading rate for drainfield sizing and

to select the most appropriate and long-term cost effective

system that matches owner needs to site conditions and

limitations.

The following are typical tasks a design professional will

consider when evaluating site soils:

• Determine the location and number of test holes needed

• Excavate test holes

• Visually inspect the soil

• Complete logs of soil sampling

• Determine soil classifications and types

• Determine depth of suitable unsaturated soil

• Determine and locate restrictive or impervious layers

• Determine location and nature if fill material is present

• Determine depth of seasonal water table

• Compare soil test results to previously gathered soil and

geohydrologic information

4. Preliminary/Conceptual Design Documentation or

Site Evaluation Report

The practice of design includes the compilation,

documentation and interpretation of all the information

gathered.

A site evaluation report is an accumulation of all the

information gathered to this point. A preliminary design

document is a simplified conceptual design without detailed

plans and specifications, final calculations, etc., based

upon information from the site evaluation report. The

preliminary design provides the most important information

needed to verify that a proposed on-site design meets owner

requirements, site conditions and regulations.

The purpose of a site evaluation report is twofold:

• To document the cognitive process used to analyze the

data gathered and arrive at the conclusions and

intended recommendations.

• As a tool to assist the Designer in preparing the most

cost effective design that meets regulations and owner

requirements by matching the right system to site and

soil conditions and help assure proper system layout

and configuration (for drainfield sizing and location,

accounting for any existing structures, landscape

features, slope, contours, elevations, setbacks, lateral

water movement (linear loading), etc.).

The purpose of the preliminary design is to provide:

• a brief written report of findings or narrative describing

the design parameters, site and soil characteristics, and

the proposed treatment and disposal concept.

• a dimensional or scaled drawing of the lot showing the

proposed layout/configuration of the treatment and

disposal components in relation to property lines,

easements, any existing or proposed structures, water

system components, other known utilities, vegetation,

surface water, or any other limiting site conditions.

• all major system components including primary and

reserve disposal areas (for new construction) along with

any needed setbacks, separations, etc.

• potential construction pathways for both drainfield

installation and related site improvements, so that the

existing or proposed on-site system area and related

setbacks can be protected from damage during

construction.

This document may also be provided to the regulator as a

preliminary check to assure the design is viable, meets

regulations and can be approved.

The following are typical tasks a design professional will

consider when forming their preliminary/conceptual design

documentation:

• Prepare a site sketch

• Prepare a written report of findings

5. Design

The practice of design includes a deliberate process that

takes the data collected through the Information Gathering,

Site Evaluation, Soil Evaluation and the Preliminary/

Conceptual Design Documentation phases to create the

construction documents that will be used for review,

permitting, construction, record drawings and O&M.

This phase of the design practice consists of analysis of the

site data, calculations, evaluation and selection of

applicable treatment methods, preparation of the design

drawings, specifications, reports and the permitting

process. It is important to note that a complete design is

one in which drawings, narratives, forms, calculations,

catalog cuts, photos and other data, including detailed

equipment and installation specifications are logically

assembled into a cohesive unit that provides individuals

who may have never seen the site with sufficient

information to grant a construction permit and install the

design without the need for assumptions, completion of any

design tasks by the installer or additional input from the

Designer.

If the site has been developed, all structures, utilities and

ingress & egress pathways should be identified. Property

lines and corners and horizontal distances from

improvements to proposed system must be verified. The

source of potable water and distribution lines must be

identified. If there is an existing on-site wastewater

treatment system, all components including the reserve

area should be flagged. The condition of each component

must be recorded and verify that all minimum setbacks can

be met.

The following are typical tasks a design professional will

consider when preparing their design:

Location

• Identify location of system components

• Establish a benchmark

• Establish system component elevations

• Establish horizontal and vertical control

Type of System

•Determine type of treatment and disposal system

• Estimate daily flow requirements

• Determine wastewater strength requirements

• Determine disposal component configuration (e.g.,

drainfield, mound, etc.)

• Determine treatment component configuration (e.g.,

septic tank, sand filter, ATU etc.)

Final Design Preparation and Application Submittal

• Consult with property owner regarding final design

components

• Produce a detailed drawing for the site, including

property lines, structures, easements, topographical

features, vegetation, etc.

• Produce detailed drawing for system components.

• Establish site preparation requirements

• Document decisions made regarding system location

and features

• Determine total dynamic head pressure requirements,

as required

• Prepare specifications for equipment/materials based on

calculations

• Prepare and submit permit application package

6. Construction Management

The practice of design includes pre-construction site status

verification, pre-installation site preparation and

component/material verification, and final inspection.

Construction management can be divided into three basic

phases. Each phase is meant to offer assurance that what

has been designed and installed will meet the Designer’s

intentions, specific codes/environmental concerns and user

needs.

The first phase has been defined as the “Preparation” phase

and includes functions such as conducting a pre-

construction conference, assessing post design site

character changes that might impact the system

installation and final use, and the act of design modification

based on that assessment.

The second phase is defined as the “Project Execution”

phase. This phase generally involves Designer verification of

system components, area of component placement,

component elevation, quality of materials and system

hydraulic performance. Verification of cover soil depth,

landscaping and finished drainage characteristics are the

final function of this process and can be one of the most

important considerations of this phase.

The third phase of construction management is defined as

the “Final Inspection” phase. During this phase the

Designer makes the final determination of how well the

design and the installation match. The amount and value of

variations in the installation from the approved plan and

how that might influence or modify the overall function and

performance of the system is evaluated. A final report

detailing those changes, if determined to be significant, is

generated by the Designer and passed on to the appropriate

parties.

The following are typical tasks a design professional will

consider when performing construction management:

Preparation

• Conduct on-site pre-construction conference

• Assess changes in conditions (e.g., soil, topography,

vegetation) that may have occurred since design work

was completed

• Modify design components, if appropriate

Project Execution

• Verify designed treatment components and materials

(e.g., tanks, ATU’s, floats, filter, etc.)

• Verify designed disposal site preparation (e.g., location,

orientation, elevations, soil,)

• Verify designed component construction and materials

(e.g., drain rock, squirt height, etc.)

• Functional test of system

• Verify designed component finished conditions (e.g.,

cover, elevations, drainage, landscaping)

Final Inspection

• Determine consistency between design and installation

• Report inconsistencies

7. Post Construction Activities

The practice of design includes the successful transfer of

system responsibilities to the system operator and the

attainment of closure of the permit and occupancy process.

Post construction activities include accurate documentation

of all of the system components and the system location.

The post construction activities phase includes creating as-

built drawings, providing the owner with operations and

maintenance manuals and fulfilling the requirements of the

permit as issued by the local health jurisdiction.

Upon completion of construction of an onsite sewage

system the Designer should prepare a scaled and

dimensioned as-built drawing. This drawing is intended to

record in detail the system as it was actually built including

where appropriate such operational data that may be

necessary to facilitate future O&M.

As part of or attached to the as-built drawing, the Designer

should record that the materials and equipment meet the

specifications that were established in the design. Where

changes were made the Designer should verify that those

changes are consistent with the design intent and are of

similar or equivalent specification. When pumps, electronic

controllers, hydraulic controllers and other devices with

operating parameters that are determined and set by the

Designer, the Designer should record those settings.

In addition, an operational test should be conducted to

assure system is operating within the design parameters.

The Designer should prepare an O&M manual intended to

provide the user/operator and the O&M technician with

information about the system necessary to operate and

maintain it. The O&M technician and user/operator should

be able to follow the line of reasoning used when the system

was designed.

The O&M manual should include design and measured

performance data for equipment installed, timer settings,

draw-down depths, gallons per inch of tank and actual

pump delivery (gpm).

An operation and maintenance manual should explain the

assumptions made to establish the design parameters and

should include at least the following:

• A list of system “Do’s & Don’ts”.

• A list of relevant contacts related to system components

and ongoing operations.

• An emergency number to call.

• A discussion listing the responsibilities of the user/

operator.

The Designer should walk the user/operator through the

entire system and provide the manual.

The following are typical tasks a design professional will

consider when conducting post construction activities:

Documentation

• Develop a detailed as-built drawing

• Document all system components (e.g., equipment type

and model, system settings)

Operations and Maintenance

• Prepare owners operations and maintenance manual

• Provide training on ongoing operations for the owner

• Provide contact information for follow up, if needed

• Perform operational assessment (e.g., troubleshooting)

for an existing system

• Document system operating parameters

• Identify frequency and type of monitoring (e.g., providing

checklists)