Under the Clean Water Act, a developer must obtain Section 401 Water Quality Certification ("401 Certification") before it can obtain a Section 404 Nationwide permit from the U.S. Army Corps of Engineers for "dredge and fill" activities if the activities will have environmental impacts on "waters of the United States." The Corps' regulations define "dredged material" as material that is excavated or dredged from waters of the United States. "Fill material" is any material used for the primary purpose of replacing an aquatic area with dry land or changing the bottom of the elevation of a waterbody. A developer will probably need a Section 404 Nationwide permit from the Corps if she, for example, builds a building or parking lot on or near a creek. As a delegated program under the Clean Water Act, the State of Missouri is responsible for issuing 401 Water Quality Certifications.

By issuing a 401 Certification, the State of Missouri verifies that a proposed development project will not violate water quality standards. As part of the 401 Certification, Missouri may require project developers to take specific actions to ensure the protection of the quality of the waters surrounding the development site. These required actions are called conditions. One of the more common conditions required of project developers is compensatory mitigation. Compensatory mitigation means "the restoration (re-establishment or rehabilitation), establishment (creation), enhancement, and/or, in certain circumstances, preservation of aquatic resources for the purposes of offsetting unavoidable adverse impacts which remain after all appropriate and practicable avoidance and minimization has been achieved." 33 CFR § 332.2 (2008).

Before Missouri can require compensatory mitigation for jurisdictional wetlands as a condition in a 401 Certification, the Corps must first determine that the wetland in question constitutes a jurisdictional wetland, or "waters of the United States," under the Clean Water Act. If the wetland constitutes waters of the United States, then the Corps must determine the wetland's jurisdictional classification.

Depending on the classification of the wetland and the degree of proposed environmental impact, the State then must determine how much compensatory wetland mitigation must be required of the project developer. Some examples of jurisdictional classifications and accompanying mitigation ratios are: (1) farmed wetlands with a 1-1.5 mitigation ratio, (2) wooded wetlands with a 2-4 mitigation ratio, and (3) open water with a 1-1 mitigation ratio.

Once the Department assigns a mitigation ratio to the development project, the project developer must submit an application to the Department for 401 Certification that details how the developer will achieve the mitigation ratio in a way that least impacts the environment. The portion of the 401 Certification detailing the mitigation plan is conveniently called the Mitigation Plan. The Mitigation Plan must be submitted and approved before work can begin on the project.

Missouri prefers that developers conduct or arrange for mitigation to occur on-site and in-kind. In other words, developers should arrange for mitigation to occur in the same watershed as their development and the mitigation project should restore the same type of waters that were impacted by the project. For example, if a developer fills in a stream, then Missouri could require the developer to create another stream in the same watershed as the development project.