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What is the Technical Guidance Manual, and why does your septic permit depend on it?
The book every septic permit is written against
Idaho’s septic rules — IDAPA 58.01.03 — say what must be true. They do not, on their own, tell a designer how to get there. That job belongs to a second document, and nearly every page on this site leans on it: the Technical Guidance Manual for Individual and Subsurface Sewage Disposal Systems, published by the Idaho Department of Environmental Quality’s Surface & Wastewater Division — 360 pages, current as of December 2025. DEQ’s committee page describes its scope in one sentence: guidance on “the design, construction, alteration, repair, operation, and maintenance of standard individual and subsurface sewage systems, their components, and alternatives.”
The manual announces how it should be handled on every page of itself:
“Controlled Document--Users are responsible for ensuring they work to the latest approved revision. Printed or electronically transmitted copies are uncontrolled.”
— DEQ Technical Guidance Manual, December 2025, running footer. Retrieved 5 October 2026
“Uncontrolled” is document-control language, not a warning about content: a printed copy is only a snapshot, and the version on DEQ’s site is the one that counts:
“This manual is updated periodically. For the most current version, see https://www.deq.idaho.gov/water-quality/wastewater/septic-and-septage/.”
— DEQ Technical Guidance Manual, December 2025. Retrieved 5 October 2026
Six people maintain it, quarterly
The manual has a custodian, and it is not a desk — it is a committee:
“The Technical Guidance Committee (TGC) is responsible for maintaining the Technical Guidance Manual, reviewing best management practices for individual and subsurface sewage disposal, and providing recommendations on variances and commercially manufactured wastewater treatment components and systems.”
— Idaho Department of Environmental Quality, Septic Technical Guidance Committee page. Retrieved 5 October 2026
“The TGC comprises six members: one DEQ representative (chair), three health district representatives, one State of Idaho-licensed professional engineer, and one licensed installer.”
— Idaho Department of Environmental Quality, Septic Technical Guidance Committee page. Retrieved 5 October 2026
The composition is the interesting part: three of the six seats sit in the health districts — the same offices that issue and inspect permits — and one seat belongs to a working installer. The people affected by the manual are in the room where it changes. Meetings run quarterly unless a special issue warrants a special meeting, and the same committee fields recommendations on variances — the variance routes themselves are covered separately on this site.
Rule and manual: which one commands
The hierarchy matters in an argument. IDAPA 58.01.03 is the rule — minimums with the force of law behind them. The TGM is the guidance — how designers, installers and health districts meet those minimums, section by section, table by table. The rule itself points to the manual at the load-bearing moments: drainfield sizing runs on table values or values specified in the TGM, and alternative-system designs live almost entirely in the manual’s chapters. A permit that follows the manual is almost always a permit that satisfies the rule; a permit argued against the manual has some explaining to do.
What is inside the 360 pages
- Chapter 1 — the program. Permitting and application content, installer duties, product approvals — and section 1.7’s four categories of old systems: existing, approved, abandoned, undocumented.
- Chapter 2 — the ground. Soils, effective soil depth, groundwater, and the separation distances to wells and water — the normal-versus-seasonal groundwater distinction lives here.
- Chapter 3 — the standard system. Wastewater flows, drainfield design, the building sewer’s Plumbing Bureau boundary (section 3.2.2), and the excavation and backfill media approval process (section 3.2.8).
- Chapter 4 — the alternatives. Sand mounds and pressure distribution, capping fill, steep-slope systems, seepage pits, pit privies, incinerators — and grey water systems (section 4.13).
- Chapter 5 — the approved products. Approved septic tanks, pipe materials for specified uses, extended treatment units, proprietary products, and the nitrogen-reduction approvals.
If a question about a septic system starts with “but where does it say” — the answer is usually a chapter number in this book.
The manual moves — and it says when
DEQ logs every change on the committee page. The current year alone:
| Date | What changed |
|---|---|
| December 2025 | Section 2.2.4 surface water separation distances; section 4.25 seepage pits; section 5.12 nitrogen reduction approvals; Appendix C uncommon wastewater flows; Appendix E pumpers guidance manual |
| August 2025 | Appendix C uncommon wastewater flows; section 4.17.5 pit privy abandonment; section 2.2.4.1 surface water separation reductions; section 5.2 septic tank approvals |
| May 2025 | Section 3.3.2 empirical flows; section 4.8.4 ETPS construction; Appendix C uncommon wastewater flows |
| February 2025 | Section 4.26 steep slope system; section 4.15 individual wastewater incinerator |
Four revisions in one year — surface-water distances and tank approvals rewritten in August, seepage pits and nitrogen approvals in December. That is the practical meaning of “controlled document”: a contractor’s three-year-old printed copy can be silently wrong about the very numbers a permit turns on.
Where it touches an owner
The manual is not only for engineers. It is the text of the installer’s credential: EIPH’s licensing exam is built on it, and the district’s own exam page notes:
“The exam is an open-book test, and these documents are available on DEQ’s Septic and Septage web page.”
— Eastern Idaho Public Health, septic installer examination FAQ. Retrieved 5 October 2026
The license in your installer’s pocket certifies an ability to find answers in this manual — that is what “qualified” operationally means. The same chapters answer owner questions directly: what the approved tank list accepts, what a gravelless component’s required trench width is, what the intended-use letter for a nonresidential system must show. And when a dispute reaches the health district, both sides arguing in manual section numbers are speaking the district’s language. The inspection and as-built machinery at the end of every permit is the rule’s, not the manual’s — but everything between application and inspection flows through these pages.
Getting a copy
The current manual lives on DEQ’s septic and septage page — the same URL the manual prints in its own front matter. The committee page gives one practical warning:
“Note: This is a large file. If you have difficulty downloading it, try opening it in a different browser or from your hard drive instead of your browser.”
— Idaho Department of Environmental Quality, Septic Technical Guidance Committee page. Retrieved 5 October 2026
Three hundred sixty pages is a download, not a glance — save it rather than streaming it.
Use it the way the professionals do
- Download the current version from DEQ’s septic and septage page — and check the revision date before relying on any printed section.
- Bring section numbers, not vibes, to disagreements — a dispute conducted in manual citations is a dispute the district can settle quickly.
- Before hiring, ask your installer which TGM chapter governs your system type — the exam guaranteed they know.
- When a rule citation and a manual section seem to conflict, the rule commands — and the committee that reconciles them meets quarterly.
- For help matching a section to your parcel’s situation, call (208) 656-1467.
Common questions
What is the Technical Guidance Manual?
DEQ's 360-page companion to Idaho's septic rules, current as of December 2025, providing guidance on the design, construction, alteration, repair, operation, and maintenance of standard individual and subsurface sewage systems, their components, and alternatives.
Is the Technical Guidance Manual law?
No - IDAPA 58.01.03 is the rule and carries the force of law. The manual is the guidance that shows designers, installers and health districts how to meet the rule, and the rule itself points to the manual at load-bearing moments like drainfield sizing.
Who maintains the manual?
The Technical Guidance Committee - six members: one DEQ representative as chair, three health district representatives, one Idaho-licensed professional engineer, and one licensed installer. The same committee reviews recommendations on variances and manufactured components.
How often is the manual updated?
The committee meets quarterly unless a special issue warrants a special meeting, and the manual is updated periodically - four times in 2025 alone: February, May, August, and December.
What changed in the December 2025 revision?
Section 2.2.4 surface water separation distances, section 4.25 seepage pits, section 5.12 nitrogen reduction approvals, and updates to Appendix C uncommon wastewater flows and the pumpers guidance manual in Appendix E.
What are the manual's five chapters?
Chapter 1 covers the program - permitting, installers, and the four categories of old systems. Chapter 2 covers soils, groundwater and separation. Chapter 3 covers standard system design. Chapter 4 covers alternative systems including grey water. Chapter 5 lists approved products.
How does the installer exam relate to the manual?
Directly - the exam questions are derived from the Technical Guidance Manual and the IDAPA 58.01.03 rules, and the exam is an open-book test using those same documents.
Why does the manual call itself a controlled document?
Because it changes: users are responsible for ensuring they work to the latest approved revision, and printed or electronically transmitted copies are uncontrolled snapshots. DEQ logs every update on its committee page.
Where can I read the manual?
On DEQ's septic and septage web page - the address the manual prints in its own front matter. It is a large file; DEQ suggests saving it to your hard drive rather than opening it in a browser.
Why should a homeowner care about the TGM?
Because it is the reference behind the permit: approved tank lists, gravelless component widths, alternative-system designs, and intended-use letters all live in its chapters - and an argument made in manual section numbers is one the health district can settle quickly.