Using the Credit/Debit Method for Temporary Impacts

The information on this page helps to clarify how to use the Credit/Debit Method to calculate the debits for temporary impacts. If all the functions at a site are re-established to their previous levels, compensatory mitigation would only be needed for the temporal loss of functions and for the potential risk the re-establishment would fail. (Temporary impacts are discussed in Section 3.2 of the Credit/Debit Method.)

Will temporary impacts (eventually) be restored on site?  If the answer is yes, then use the following process:

  1. Calculate the impacts (debits) using the Credit/Debit Method (C/D Method) and use the temporal loss factor that matches the Cowardin Class being impacted (e.g., PEM, PSS, PFO)
    1. If the long-term temporary impact is between 1-2 years, then the temporal loss factor will be a minimum of 1.5 or a maximum of 3.5 (use the concurrent temporal loss factor for the subject Cowardin Class from the Appendix table in the C/D Method.). Note: For impacts to PEM wetlands that will be restored on site within 1 year, it has been agency policy (Corps and Ecology) that little to no compensation is required, depending on the case specific factors. However, if the wetland contains a native emergent plant community, compensation will likely be required.
    2. If the long-term temporary impact is over 2 years then use the delayed temporal loss factor for the appropriate Cowardin Class (a minimum of 3 and a maximum of 7)
  2. Using the C/D method, calculate the credits proposed to be generated by the on-site restoration activities, inclusive of the risk factor (use the risk factor Appendix table in the C/D Method).  For on-site restoration this factor would typically be 0.67 for PSS and PFO and 0.5 for PEM. Note: The risk factor may need to be adjusted depending on the project and the extent of the temporary impacts. 
    1. It is possible that the proposed re-establishment could increase the functioning of the site if re-establishment involves replacing an invasive-plant dominated community with native plants.
  3. The number of credits the applicant needs to compensate for the temporary long-term impacts from the project is the difference between number 1 and 2 above.

If the long-term temporary impacts will NOT be restored on-site, then the following applies:

Use the C/D method as if this was a permanent impact. For projects buying ILF credits, the temporal loss factor would be a minimum of 3 depending on the Cowardin class being impacted.


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