any future economic analyses, with the intent of making suggestions for improvements.

Incrementally Impaired Waters and Watersheds

FINDING: The HUC10 delineation used to assess the acreage of various land uses that contribute to the potential impairment is too coarse.

RECOMMENDATION: EPA should use the more refined HUC12 delineation to generate a more precise estimate of the acres to consider for the BMPs in the various land uses.

FINDING: It is not valid to assume that the percent of unassessed waters that would be incrementally affected is zero. A more defensible approach would take into consideration the characteristics of the various WBIDs to predict the likelihood that they would fail to meet the narrative criteria or the numeric nutrient criteria.

Sector Analyses

Table 2-8 summarizes the Committee’s assessment of EPA’s economic analysis by sector. The color coding of Table 2-8 entries reflects the Committee consensus of the accuracy of the EPA evaluation. Green indicates a satisfactory job in addressing the issue, yellow indicates only moderate agreement, and pink indicates unsatisfactory assessment.

The table is based on the cost method used in the EPA analysis, in which the total sector cost was calculated as the product of the number of affected units (or area) and the unit cost. The second column refers to how well EPA determined the number of affected units, including judgments on assumptions used for the number of point discharges that will require treatment upgrades and land areas that will need to have new BMP technologies implemented. The third column deals with the accuracy of unit costs assessments.

The fourth column considers whether the numeric nutrient criteria could be met by existing technologies at the “end-of-pipe” or “edge-of-field” for each sector. The EPA analysis assumes that in every case assimilative capacity exists somewhere in the watershed or waterbody, or that administrative relief is available, such that the each sector does not have to meet the numeric nutrient criteria at the end-of-pipe or edge-of-field. Yet the EPA has not employed watershed modeling to determine if implementing all assumed technologies would allow the numeric nutrient criteria to, in fact, be met. From the regulatory standpoint, if a waterbody violates the numeric nutrient criteria, its assimilative capacity is considered to already be exceeded. Thus, the numeric nutrient criteria were used in this column

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