h^fDT ivlonlana Wetland Assessment Method 



Mm 25, 1999 



below. 



The total actual functional points for a given 8-acre A4 is 6.3. Total functional units for the AA would be calculated by multiplying 

 6.3 points X 8 acres = 50.4 functional units. A proposed highway project would impact 2 acres of the AA. Assuming a relative h- 

 uniform distribution of functional capacity across the AA, the loss in functional units to the AA would be 2 acres x 6.3 points = 12.6 

 functional units. To compensate for lost wetland functions and values, mitigation would need to be designed that would replace the 

 12.6 functional units. If the predicted total actual functional points for a mitigation project was 5. 1, and the goal were to replace 

 12.6 functional units, the applicant would need at least 2.5 acres of mitigation to compensate for the loss (2.5 x 5.1 = 12.6). If 

 limited to a two-acre mitigation site, the applicant could, in theory, design the mitigation project such that the predicted functional 

 points met or exceeded 6.3, resulting in the replacement of at least 1 2.6 functional units (2 x 6.3 = 12.6), or could obtain an 

 additional site such that the sum of the functional units for the two sites met or exceeded the total 12.6 point replacement 

 requirement. 



Functional Units can also be examined on a function by function basis to compare existing pre-project conditions with predicted post- 

 project conditions. This concept is employed by the HGM method (Smith et al. 1995), and is illustrated by the following table, which 

 assumes a two- acre impact to a lO-acre AA for a h\pothetical project. 



There are several possible ways to determine mitigation needs using this approach, including; 



• designing mitigation for individual functions or cumulatrvely for all functions using the greatest predicted loss in fiinctional 

 umls as the replacement target (m this case, designing mitigation such that each function provides a minimum 5.2 

 functional units or designing the mitigation such that, cumulatively, 5.2 - 5.2 = 10.4 functional units are replaced): or 



• designing mitigation for individual functions or cumulatively for all fiinctions using the average predicted loss in fimctional 

 units as the replacement target {in this case, designing mitigation such that each function provides a minimum 5 functional 

 units [(4.8 + 5.2) ^ 2 = 5] or designing the mitigation such that, cumulatively, 5-^5 = 10 functional units are replaced): or 



designing mitigation for individual functions or cumulatively for aD functions using individual predicted changes in 

 functional units as the target {in this case, 4.8 for function A and 5.2 for function B, or cumulatively using 4.8 + 5.2 

 functional units). 



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There may be circumstances that simply preclude the replacement of a given fiinctionA'alue parameter at the same le\el at which it is 

 rated for an affected wetland. For example, if a project impacts a wetland rated "high" for umqueness due to the presence of a bog. it is 

 very unlikely that the uniqueness parameter could be mitigated at the same level at a replacement wetland because of the difBcult\' 

 associated with bog replacement. In \irtualh all cases, appropriate mitigation of lost wetland functions and values will be subject to 

 coordmation/'negotiation with the regulator.' agencies mvolved in the project. 



It is not the purpose of this evaluation form to dictate wetland mitigation policy. What is and is not considered appropriate mitigation 

 will ultimateh' be determined by the regulator.' agencies; primarily the COE and EPA. While this evaluation method does provide a 

 means for quantifying predicted impacts to wetland functions and values, it is important to stress that coordmation with the regulatory 

 agencies as to the application of this evaluation method and discussed mitigation determination strategies to a given project is crucial 

 and needs to be carried out on a project by project basis. 



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