Industrial projects rarely slip because of construction. They slip earlier: the land is bought, the equipment quoted and the start date already promised to the board, and only then does someone ask whether environmental impact authorization is needed. The answer usually arrives late, with an uncomfortable detail attached — nothing can start without SEMARNAT’s resolution, and the file does not exist yet.
Mexico’s Manifestación de Impacto Ambiental (MIA) is the study used to request environmental impact authorization from SEMARNAT for federally regulated works and activities, under articles 28 and 30 of the LGEEPA. On 1 April 2026 an administrative simplification agreement was published in the Federal Official Gazette, in force since 22 April, changing how it is filed. What it did not change is the thing that actually drives the timeline: the quality of the information you hand in.
What changed in April 2026
The agreement did not rewrite the law. It reorganized the procedures and cut paperwork. Three concrete changes:
| Before | Since 22 April 2026 |
|---|---|
Particular MIA split in two: SEMARNAT-04-002-A (no highly hazardous activity) and -04-002-B (with it) |
A single procedure: SEMARNAT-04-002 |
Regional MIA split into SEMARNAT-04-003-A and -04-003-B |
A single procedure: SEMARNAT-04-003 |
| 12 documentary requirements in each modality | 5 requirements |
| Exemptions, non-requirements, waivers and transfers filed through separate routes | One format, SEMARNAT-04-006, resolved in 20 business days (10 electronically, once the system is live) |
The useful reading is not “it is easier now”. It is this: administrative duplication was removed, technical content was not. The MIA is still the central document and still demands the same characterization of the site, the project and its impacts. What disappears is the parallel paperwork, not the study.
Particular or regional: which one applies
This is the first fork in the road, and the one most often taken wrongly, because people decide by project size when it actually depends on the reach of the effects.
- Particular MIA. The ordinary route: one specific work or activity, with impacts confined to its site and immediate surroundings.
- Regional MIA. When the project is part of a set of linked works, affects a shared ecosystem, or sits in an area where its effects accumulate with those of other developments.
The working test: if your project’s impact only makes sense added to your neighbours’, it is regional. And a third route worth remembering — when the project is already contemplated in a partial plan or a standard that assessed its effects, a preventive report may replace a full MIA. Checking that before commissioning the study saves months.
How long it really takes
The LGEEPA gives SEMARNAT 60 business days to resolve, extendable where complexity justifies it. That is the number quoted in meetings, and the reason project calendars are planned badly, because it has two interruptions almost nobody budgets for:
- Additional information. If the file has gaps, the authority asks for them and the clock stops until you answer. A request for baseline data that was never collected in the field is not answered in a week — it is answered when you go back to the site.
- The lead time, which appears in no legal deadline. Sampling, flora and fauna inventories and site characterization all happen before filing. That work is seasonal — some species are undetectable out of season — and it is the most common reason a project runs late.
Put differently: the 60 business days start counting once the file is complete, and getting there is the long part.
What to gather before you start
What a consultant needs on day one, and what is rarely in one place:
- Exact location and area, with coordinates and site plans.
- Technical description of the project: processes, phases, associated works, schedule and service life.
- Land use and compatibility with the applicable ecological zoning and development plans.
- Expected consumption and discharges: water, energy, waste, emissions and effluent.
- Substances to be handled, with quantities, to determine whether a highly hazardous activity is involved.
- Current condition of the site: vegetation, wildlife, hydrology, and whether forest land-use change is involved.
The last point deserves a warning: if the project involves clearing forest vegetation, a separate forest land-use change procedure runs alongside the MIA. Spotting that on day one avoids rebuilding the whole schedule.
Common mistakes
- Starting the study with construction already contracted. The MIA shapes the design; arriving afterwards makes mitigation measures expensive or unworkable.
- Choosing the modality by size. What defines particular or regional is the reach of the impacts, not the square metres.
- Copying a neighbouring project’s baseline. It is the first thing an evaluator spots, and it guarantees a request for additional information.
- Ignoring the seasonality of fieldwork. An inventory taken out of season has to be repeated.
- Filing and forgetting. The authorization arrives with conditions that must be met and evidenced throughout the project’s life.
Frequently asked questions
Which works need an MIA?
Federally regulated works listed in article 28 of the LGEEPA and its regulations: hydraulic works, chemical, oil, steel and cement industry, developments in coastal zones and wetlands, forest land-use change and activities considered highly hazardous, among others. When in doubt, the right move is to check first, not to assume it does not apply.
What is the difference between a particular and a regional MIA?
The particular assesses one specific work or activity with confined impacts. The regional applies when the project is part of a set of works, affects a shared ecosystem, or its effects accumulate with those of other developments in the area.
How long does SEMARNAT take to resolve?
The LGEEPA provides for 60 business days, extendable. The clock stops if the authority requests additional information, and it does not include the lead time for fieldwork and drafting the study.
What did the April 2026 agreement change?
The procedures with and without highly hazardous activity were merged into SEMARNAT-04-002 (particular) and SEMARNAT-04-003 (regional), documentary requirements dropped from twelve to five, and exemptions, non-requirements, waivers and transfers were consolidated into format SEMARNAT-04-006, resolved in 20 business days. In force since 22 April 2026.
Can construction start while the file is pending?
No. Starting a work or activity subject to assessment without the corresponding authorization is an infringement, and it can lead to closure and an obligation to restore the site, on top of the financial penalty.
Where to start
The decision that saves the most time is taken before the study is commissioned: whether the project needs an MIA at all, under which modality, and whether a preventive report would do. That is half an hour of analysis that can reorder a two-year schedule.
At EcoAsesoria we prepare that file from scoping through to answering the authority’s requests; that is our environmental impact assessment service. When the project expands an existing plant, it usually pays to review it alongside the compliance file you already hold — the work behind our environmental audits — and the water data the MIA will ask for, if a monitoring programme is already running. Tell us about your project, where it is and what stage it is at, and we will tell you which route applies.