Environmental assessment and approvals

The cheapest time to prevent environmental harm is before a project is built. Environmental assessment (EA) is the process of predicting the environmental, social, health and economic effects of a proposed project, comparing alternatives, finding ways to avoid or reduce harm, and giving decision makers and the public the information they need to decide whether and how the project should proceed. Since the United States passed the National Environmental Policy Act in 1970, EA has spread to nearly every country. This lesson describes the general EA process, the federal systems in Canada and the United States and how they changed between 2023 and 2026, the other permits a typical water project needs, methods for predicting and judging impacts, and the role of the public and Indigenous peoples.

Willowbend's largest job this term is the environmental review of a new raw water intake on the Big Sioux River and an off-stream reservoir to store spring runoff for the city's treatment plant (lesson 7). The project would flood about 180 ha (450 acres) of farmland and a small wooded draw, build a pumping station and intake screen in the river, and lay 6 km of pipeline. Martin leads the review; Nadia is responsible for the water quality and air quality chapters and the impact matrix.

The general environmental assessment process

Whatever the jurisdiction, assessments follow similar steps. Screening decides whether a project needs an assessment at all and at what level. Scoping identifies the issues that matter, the valued components to study (such as fish, groundwater, air quality, heritage sites or Indigenous rights) and the boundaries in space and time. Baseline studies describe existing conditions, often over at least a full year to capture seasons. Impact prediction estimates how the project will change each component during construction, operation and closure, using the mass balance, kinetics, water quality and dispersion tools from earlier lessons. Mitigation designs measures to avoid, reduce or offset the effects, and residual effects are those that remain after mitigation. The significance of residual effects is then judged against criteria. Alternatives, including different sites, designs and the option of not proceeding, are compared. The process ends with a decision, conditions and a follow-up program that checks whether predictions were right and mitigation works.

Cumulative effects deserve special mention. A single project may have a small effect, but combined with past, present and reasonably foreseeable future projects in the same watershed or airshed, the total can be large. A river may handle one new outfall but not the fifth. Good assessments set study areas large enough to see these combined effects.

Canada's system and state reviews

Canada's federal Impact Assessment Act of 2019 is a useful comparison. It applies to designated projects such as large mines, pipelines and dams, and in 2023 the Supreme Court of Canada found parts of it beyond federal authority. Parliament amended it in June 2024 to focus on adverse effects within federal jurisdiction, such as fish, migratory birds, federal lands and effects on Indigenous peoples, and to make it easier to rely on provincial assessments.

For a US project, however, the governing law is NEPA, which applies whenever a federal agency proposes, funds or permits an action. A water project that needs a Clean Water Act Section 404 permit from the US Army Corps of Engineers, or federal funding, is a federal action subject to NEPA.

Many states have their own environmental review laws, often called little NEPAs, which apply to state and local actions. California's Environmental Quality Act is the best known. Projects that are both federal actions and subject to a state law usually prepare joint documents to avoid duplication.

NEPA in the United States

The National Environmental Policy Act requires federal agencies to consider the environmental effects of their proposed actions before deciding. Agencies use three levels of review. A categorical exclusion applies to classes of actions that the agency has found normally have no significant effects. An environmental assessment (EA) is a shorter analysis that ends either in a finding of no significant impact (FONSI), often with mitigation commitments, or in a decision to prepare an environmental impact statement (EIS). An EIS, for actions that may significantly affect the environment, involves scoping, a draft statement open for public comment, a final statement and a record of decision. NEPA is procedural: it requires agencies to take a hard look at effects and reasonable alternatives and to disclose them, but it does not require them to choose the least harmful option.

NEPA changed substantially between 2023 and 2026. The Fiscal Responsibility Act of June 2023 amended the statute itself, adding page limits (generally 150 pages for an EIS and 75 for an EA, longer for complex projects) and deadlines (generally two years for an EIS and one year for an EA), and naming a lead agency to coordinate reviews. In 2025 the Council on Environmental Quality, which had issued binding NEPA regulations since 1978, removed them with an interim final rule effective April 11, 2025, and made the removal final in January 2026; each agency now follows its own NEPA procedures, many of them revised in mid-2025. In May 2025 the Supreme Court, in Seven County Infrastructure Coalition v. Eagle County, held that courts must give agencies substantial deference on the scope and depth of their NEPA analyses and that agencies need not analyze the effects of separate upstream or downstream projects. Practitioners now check the procedures of the specific lead agency at the start of every project.

For Willowbend's reservoir, the lead federal agency would be the Corps of Engineers because of the Section 404 permit needed to place fill in wetlands and the river. Under the Corps' procedures, Martin expects an EA with a FONSI if mitigation for wetland losses is adequate, rather than a full EIS.

Other approvals for a water project

An assessment rarely stands alone. A reservoir and intake typically need several permits, each with its own technical requirements:

Predicting and judging impacts

Impact prediction uses the quantitative methods of the field: water quality models predict downstream concentrations, dispersion models predict air quality, groundwater models predict drawdown, habitat models predict fish populations, and noise models predict sound levels at homes. Where models are weak, as for many ecological effects, assessments rely on studies of similar projects and expert judgment, and say so. Uncertainty is stated openly, and follow-up monitoring is designed to catch predictions that turn out wrong.

Significance is judged with criteria such as magnitude (how big the change is), geographic extent, duration, frequency, reversibility and the sensitivity or ecological and social context of the receiving environment. Many assessments organize the results in an interaction matrix, an approach that goes back to Luna Leopold's 1971 matrix, with project activities as rows and environmental components as columns. Scoring each interaction makes the reasoning transparent and lets reviewers see which assumptions drive the conclusions.

# Residual effects matrix for the intake and reservoir: product of four 1-3 scores
effects = {   # magnitude, extent, duration, reversibility
    "Wooded habitat flooded":       (2, 1, 3, 3),
    "Fish entrainment at intake":   (2, 2, 3, 2),
    "Downstream low-flow reduction":(2, 2, 2, 1),
    "Reservoir mercury in fish":    (2, 1, 3, 2),
    "Construction dust and noise":  (1, 1, 1, 1),
    "Archaeological sites":         (3, 1, 3, 3),
}
for threshold in (24, 18):
    print(f"Threshold {threshold}:")
    for name, s in sorted(effects.items(), key=lambda kv: -kv[1][0]*kv[1][1]*kv[1][2]*kv[1][3]):
        p = s[0] * s[1] * s[2] * s[3]
        print(f"  {name:31s} score {p:2d}  {'POTENTIALLY SIGNIFICANT' if p >= threshold else ''}")

Threshold 24:
  Archaeological sites            score 27  POTENTIALLY SIGNIFICANT
  Fish entrainment at intake      score 24  POTENTIALLY SIGNIFICANT
  Wooded habitat flooded          score 18  
  Reservoir mercury in fish       score 12  
  Downstream low-flow reduction   score  8  
  Construction dust and noise     score  1  
Threshold 18:
  Archaeological sites            score 27  POTENTIALLY SIGNIFICANT
  Fish entrainment at intake      score 24  POTENTIALLY SIGNIFICANT
  Wooded habitat flooded          score 18  POTENTIALLY SIGNIFICANT
  Reservoir mercury in fish       score 12  
  Downstream low-flow reduction   score  8  
  Construction dust and noise     score  1

With the threshold at 24, only archaeological sites and fish entrainment are flagged; at 18, habitat loss is flagged too. The results point Nadia's team to the mitigation that matters most: a careful archaeological survey before flooding, an intake screen sized for slow approach velocities so that small fish can swim away, and habitat offsets. The matrix also reminds the team of reservoir mercury: flooding soil and vegetation releases mercury that bacteria convert to methylmercury, which accumulates in fish for years after a reservoir fills, a well-documented effect of reservoirs in Canada and the northern United States.

Public participation and Indigenous peoples

Assessment is a public process. Agencies publish draft documents, hold meetings and respond to comments, and the best reviews change the project in response. Federal agencies must consult with federally recognized Tribes on a government-to-government basis when actions may affect tribal lands, resources or rights, including under Section 106 of the National Historic Preservation Act for sites of religious and cultural significance. For the intake and reservoir, the Corps of Engineers and the city engage the Tribes with historical ties to the Big Sioux River valley.

Engineers contribute to assessment as authors of technical chapters, as designers of mitigation, and as people who explain technical results clearly to non-specialists. A well-run assessment is not an obstacle to good projects; it is how good projects are found and bad ones are improved or stopped before money and trust are spent.