is mitigation accomplished in a region comprehensively for a number of various impact projects. It may be established as a single-party site such as for use solely by a state's transportation department for transportation-related aquatic resource impacts or it may be a multi-party site such as an entrepreneurial enterprise open to any clients needing mitigation within a specific geographic area. This mitigation typically involves the consolidation of what would otherwise occur as small, fragmented wetland mitigation projects into one large contiguous site. By nature of its use, consolidated mitigation is always off-site mitigation. By consolidating compensation requirements, this mitigation can more effectively replace lost wetland functions within a watershed, as well as provide economies of scale relative to the planning, implementation, monitoring, and management of mitigation projects. Consolidated mitigation may come in different forms, namely: mitigation centers, mitigation banks, and in-lieu-fee mitigation arrangements.
Mitigation Banks - Mitigation banking has been defined as wetland restoration, creation, enhancement, and in exceptional circumstances, preservation undertaken expressly for the purpose of compensating for unavoidable wetland losses in advance of development actions, when such compensation cannot be achieved at the development site or would not be as environmentally beneficial. Units of restored, created, enhanced, or preserved wetlands are expressed as "credits" which may subsequently be withdrawn to offset "debits" incurred at a project development site. Ideally, mitigation banks are constructed and functioning in advance of development impacts, and are seen as a way of reducing uncertainty in the CWA Section 404 permit program by having established compensatory mitigation credit available to an applicant. For federal aid highway projects, the Transportation Equity Act for the 21st Century (TEA-21) established a preference for the use of mitigation banking over project-specific mitigation. This preference is governed by criteria such as the service area of the approved bank, the availability of credits, and considerations such locally important aquatic resource functions and in-kind versus out-of-kind mitigation.
Mitigation Centers - Mitigation centers are similar to mitigation banks with the exception that restoration, creation, and enhancement activities may occur concurrent with project impacts or development actions rather than in advance of project impacts. Components for the restoration, creation, enhancement, or preservation of wetlands and aquatic resources are expressed as "credits" which may subsequently be purchased or funded by a client to offset aquatic resource impacts incurred at the permitted project development site.
In-Lieu-Fee Mitigation Programs - "In-Lieu-Fee" mitigation occurs in circumstances where a permittee provides funds to an in-lieu-fee sponsor instead of either completing project-specific mitigation or purchasing credits from an approved mitigation bank. The program sponsor periodically funds a consolidated mitigation project from the proceeds of the accumulated in-lieu-fees.