U.S. Army Corps of Engineers Issues New Procedures for Determining Compensatory Mitigation Ratios

On February 20, 2012, the U.S. Army Corps of Engineers, South Pacific Division, announced new procedures for determining compensatory mitigation requirements for processing permits under section 404 of the Clean Water Act, section 10 of the Rivers and Harbors Act, and section 103 of the Marine Protection, Research and Sanctuaries Act. 


Compensatory mitigation involves actions that must be taken to offset adverse impacts to wetlands, streams and other aquatic resources authorized by Clean Water Act section 404 permits and other Department of the Army permits. It is the restoration, establishment, enhancement and/or, in certain circumstances, preservation of aquatic resources for the purpose of offsetting unavoidable, adverse impacts that remain after all appropriate and practicable avoidance and minimization of adverse effect has been achieved. The purpose of compensatory mitigation is to develop long-term self-sustaining wetlands and other waters that offset project impacts. As such, compensatory mitigation is a critical tool in helping the federal government to meet the longstanding national goal of “no net loss” of wetland acreage and function.  

Historically, the Corps has determined the required acreage ratio for mitigation (compensatory mitigation ratio) after receiving recommendations from the applicant and the appropriate resource agencies. The Corps would consider the functions and values of the wetlands that might be eliminated or degraded, the functions and values of the proposed mitigation site, and the likelihood of success of the proposed mitigation. Based on all of that information, the Corps would establish the mitigation ratio. 

Until now, the South Pacific Division Regulatory Program has not had procedures or other guidance for determining the mitigation ratios. There were only some general guidelines that required that the rationale used by the Corps to determine the ratio to be documented in the administrative record for the permit action. 

To address this need, a multi-district team was assembled to develop regional procedures for determining and documenting mitigation ratios. 

The New Mitigation Ratio Procedures

The main component of the new procedures is a mitigation ratio checklist that project managers are required to fill out using an applicant’s compensatory mitigation proposal. Project managers then use the checklist to evaluate the applicant’s proposed mitigation for each impact site or type. 

The checklist requires the consideration of several factors, including:

(1)   Qualitative impact-mitigation comparison – This factor is considered if a Corps-approved functional/condition assessment has been obtained.  The quantitative assessment of functional loss at the impact site versus expected functional gain at the mitigation site may warrant a lower or higher ratio. 

(2)   Quantitative impact-mitigation comparison – If a Corps-approved functional/condition assessment has not been obtained, the project manager must use a Before-After-Mitigation-Impact (BAMI) spreadsheet to determine the appropriate mitigation ratio adjustment. Project managers must consider either qualitative or quantitative factors, but not both as they are mutually exclusive. 

(3)   Mitigation site location – The ratio will be increased for mitigation located outside the impacted watershed.

(4)   Net loss of aquatic resource area – The ratio will be increased for mitigation measures that result in rehabilitation, enhancement, or preservation, as opposed to establishment.

(5)   Type conversion – Out-of-kind mitigation generally warrants a higher ratio. 

(6)   Uncertainty – Project managers must consider the inherent uncertainty of mitigation when determining a ratio.  Greater levels of uncertainty will result in a higher ratio. 

(7)   Temporal Loss – Under this factor, project managers consider the amount of time between when the authorized impacts occur and when constructed mitigation is expected to replace lost functions.  A longer delay will warrant a higher ratio. 

A copy of the checklist must be included in the administrative record. 

The procedures apply to the Regulatory Program within the South Pacific Division of the U.S. Army Corps of Engineers which includes Sacramento, San Francisco and Los Angeles, and are applicable for all permit applications that the Corps receives after April 20, 2011, that require compensatory mitigation. 

Conclusion and Implications

The new procedures address a long-standing need in the permitting process and incorporate the most current scientific understanding of mitigation concepts. The Corps intends that they will benefit both the regulated community and the environment by eliminating uncertainty and creating more consistency between different project managers, offices and districts. Because the procedures have a lot of flexibility, however, and the Corps must still make judgment calls throughout the process, it is unclear whether the Corps’ goals will be achieved. The amount of discretion permitted by the procedures could result in continuing inconsistency and uncertainty.