Published
Disturb an acre and the state joins your dirt job.
The county requires a plan, and it must be professionally prepared
Erosion control is the part of a site job that gets treated as good practice rather than as a requirement, right up until somebody asks for the document. Fremont County's code does not leave it discretionary: it requires a plan, and it specifies who has to prepare it.
“A professionally prepared runoff and erosion control plan shall be implemented by the application.”
— Fremont County Development Code, 2011 Edition (Ordinance 2011-04), section 5.09, Runoff and Erosion Control. Consolidated through Ordinance 2026-03. Retrieved 1 September 2026
Two words carry the weight. Professionally prepared rules out a sketch made on the tailgate, and implemented means the plan is a description of what will actually happen rather than a document produced to satisfy a reviewer and then filed.
One acre is where the state joins in — and the county code names the wrong agency
The first thing the county's plan has to address is not a county requirement at all. The county code sets out the trigger, and it also tells you who to apply to. On that second point the code is out of date, and it is worth knowing why before you act on it.
The Development Code is a 2011 text. It says that in Idaho the federal Environmental Protection Agency has issued the general permit for construction site discharges. That stopped being true on 1 July 2021, when the Idaho Department of Environmental Quality took over stormwater permitting from EPA. DEQ now issues the construction general permit under the state's own IPDES programme. The Clean Water Act obligation is unchanged; the agency you deal with is not.
“Discharges from construction activities that disturb one or more acres, including discharges from smaller sites that are part of a common plan of development or sale that disturbs one or more acres, must obtain permit coverage.”
— Idaho Department of Environmental Quality, Stormwater. Retrieved 2 September 2026
- The threshold is one or more acres of disturbance. Note that the county's older text says more than one acre; at exactly one acre those two readings differ, and DEQ's is the one that governs.
- It includes a smaller site that is part of a common plan of development or sale disturbing an acre or more — so a small piece of a bigger scheme counts toward it.
- A site seeking coverage must develop a stormwater pollution prevention plan, so the plan precedes the application rather than following it.
- Applications go through DEQ's IPDES e-permitting system, not to EPA. EPA retains the programme only where the state does not administer it, such as on tribal land.
The common-plan clause is the one that surprises people on a subdivision. Your own disturbance can be well under an acre and still be inside the trigger, because what counts is the larger scheme your work belongs to. An operator clearing half an acre on a plat that will ultimately disturb five is not outside the threshold.
What the pollution prevention plan has to do
The code describes the document's job in three parts, and the third is the one most often neglected.
| Requirement | What it means on site |
|---|---|
| Document the controls | The erosion, sediment and pollution controls the operator intends to use are written down before work rather than improvised. |
| Provide for periodic inspection | The plan itself has to set out how those controls will be checked, so inspection is scheduled rather than occasional. |
| Maintain best management practices | Through the life of the project — not merely at the start and not only when a wet spell is forecast. |
| Update as conditions change | The plan is a living document, and the code says so directly. |
| Keep a copy on site | Physically present at the work, which is the requirement most likely to be missed on a remote job. |
The county then allows a sensible piece of sequencing. This portion of the plan may be made a condition of approval incorporated into the improvement agreement and provided to the County after permit approval but prior to the inception of any site work. The paperwork can follow the permit; it cannot follow the first machine.
The ten things the county's own plan has to show
Beyond the state permit, section 5.09 lists what the plan must identify and demonstrate, in subsections 5.09.020 through 5.09.110. Read together they describe a way of working rather than a set of products to install.
- Identify runoff and erosion hazard areas on the site.
- Identify areas and facilities, both on the site and down slope from it, that are vulnerable to damage from accelerated runoff or erosion.
- Show how retention of existing vegetation will be maximised and land disturbance minimised.
- Show how existing trees that are to be retained will be protected from damage during construction.
- Show how the area disturbed at any one time will be minimised, and how disturbed areas will be stabilised during construction.
- Show how disturbed areas will be promptly and permanently stabilised by re-vegetation or structural techniques, with re-vegetation using locally propagated native plants encouraged.
- Show how runoff velocities will be minimised and drainage ways prepared to handle any acceleration or increase of runoff.
- Show how additional runoff will be retained on site and absorbed, evaporated, or released at a rate not exceeding the pre-application rate.
- Show how sediment resulting from accelerated soil erosion will be retained on site.
- Show how water quality in adjoining or nearby streams and wetlands will be protected, by retention of existing vegetation, installation of vegetative filter strips, and similar means.
Two of those deserve singling out. The down-slope requirement means the plan is not confined to the property boundary — what your water does after it leaves is part of what has to be addressed. And the pre-application rate of release is a genuine engineering constraint: the site may not shed water faster after the work than it did before, which on ground that is being cleared and compacted is something to design for rather than to hope for.
The phrase that governs the whole job
The requirement to minimise the area disturbed at any one time is the one that changes how a job is sequenced. It is not a limit on total disturbance; it is a limit on how much of it is open simultaneously.
In practice that favours phasing — opening ground, working it, stabilising it, then moving on — over stripping an entire site at the start because the machine is already there. On a short Island Park season that is an awkward trade, and it is exactly the tension worth settling before the work starts rather than in the middle of it, alongside the other seasonal limits covered in how late in the year you can dig.
A practical order of operations
- Measure the total disturbance for the whole scheme, not just your share, and compare it against one acre.
- If it reaches an acre, treat the stormwater pollution prevention plan as the first deliverable, because DEQ coverage is applied for after it exists. Apply to Idaho DEQ through its IPDES e-permitting system, not to EPA.
- Get the county plan professionally prepared. The code's word is professionally, and a plan that fails that description has not met the requirement.
- Walk the down-slope ground and write down what is vulnerable there, since the code requires it and it is the part a site-only survey misses.
- Establish the pre-application rate of release before anything is cleared, because it is the benchmark the finished site is measured against and it cannot be reconstructed afterwards.
- Plan the sequence so that the open area stays small, and price the stabilisation of each phase into that phase rather than deferring all of it to the end.
- Keep the plan on site, in paper, and update it when conditions change — both are explicit requirements and both are cheap to satisfy.
On a single cabin lot the one-acre threshold is often not reached and the county plan is the whole of the obligation. On anything that is part of a plat, the state permit arrives sooner than people expect — and it arrives before the first machine, not after, which is the same reason site preparation is worth planning on paper first.
Common questions
Does Fremont County require an erosion control plan?
Yes. Section 5.09 of the Development Code requires that a professionally prepared runoff and erosion control plan shall be implemented by the application. It is a requirement rather than a recommendation, and it specifies professional preparation.
Who issues the construction stormwater permit in Idaho — EPA or the state?
Idaho DEQ. It took stormwater permitting over from EPA on 1 July 2021 and issues the construction general permit under the state IPDES programme. Fremont County's Development Code still names EPA because the code is a 2011 text; EPA now retains the programme only where the state does not administer it, such as on tribal land.
When does a state stormwater permit get involved in a construction site?
Where construction disturbs one or more acres, including a smaller site that is part of a common plan of development or sale disturbing one or more acres, the site must obtain permit coverage from Idaho DEQ, and must develop a stormwater pollution prevention plan to get it.
My part of the job is under an acre — am I clear?
Not necessarily. The threshold includes work that is part of a common plan of development or sale disturbing one or more acres in total. On a subdivision, a small individual disturbance can still fall inside the trigger.
What must a Storm Water Pollution Prevention Plan contain?
It must document the erosion, sediment and pollution controls intended, provide for periodic inspection of those controls, and maintain best management practices through the life of the project. It must be updated as conditions change and a copy kept on site.
Can the erosion plan be submitted after the permit?
That portion may be made a condition of approval incorporated into the improvement agreement and provided to the County after permit approval, but it must be provided prior to the inception of any site work.
Does the plan have to consider land below my site?
Yes. The plan must identify areas and facilities both on the site and down slope from it that are vulnerable to damage from accelerated runoff or erosion, so it is not confined to the property boundary.
How fast can the finished site shed water?
The plan must show how any additional runoff generated will be retained on-site and absorbed, evaporated, or released from the site at a rate not exceeding the pre-application rate of release.
Is there a limit on how much ground I can open at once?
The plan must show how the area disturbed by construction at any one time will be minimised and how disturbed areas will be stabilised during the construction period. It constrains simultaneous disturbance rather than total disturbance.
What does the code say about re-vegetation?
Disturbed areas must be promptly and permanently stabilised by re-vegetation or structural techniques, and the code specifically encourages re-vegetation with locally propagated native plants.