he 99th percentile cap, and is thus the Table 3 "clean" sludge cap.  The AMSA challenges the risk-based caps in Table 3.  It argues that the assumptions about the rate and duration of sludge application underlying the risk-based concentration caps in Table 3 are irrational with respect to heat-dried sludge, which is applied at lower rates for shorter durations.  For whatever reason, the EPA chose not to respond to this particular claim, and the AMSA has been less than totally clear about what parts of the regulations are allegedly infected by the use of these assumptions.  We are, accordingly, somewhat handicapped in evaluating the challenge.  Nonetheless, on the record, we conclude that the EPA has not adequately justified its use of the assumed rate and duration of application to apply the risk-based caps in Table 3 to heat-dried sludge.


35
The EPA's primary risk-based data is in Table 2.  As explained above, supra pp. 396-97, the EPA used the assumed application rate of 10 metric tons/hectare and duration of 100 years to convert the Table 2 cumulative risk-based limits into the risk-based concentration caps used in Tables 1 and 3.16  The AMSA challenges the use of these assumptions in Table 3.  It argues that these assumptions are irrational as applied to heat-dried sludge because it "is inconceivable that heat dried sludge could ever be applied to land at a rate of 1,000 metric tons/ha."   AMSA Brief at 12.  The AMSA points to undisputed evidence in the record that the recommended application for Milorganite--a principal heat-dried sludge product--is no more than 3.5 metric tons/ha per year17;  and that heat-dried sludges "are applied at low annual rates, usually around 2 to 3 metric tons per hectare, but rarely over 5 metric tons per hectare."18


36
Under the Administrative Procedure Act, the assumed application rate and duration must bear some rational relationship to the actual application rates and durations for land application of sludge.  See Edison Elec. Institute v. EPA, 2 F.3d 438, 446 (D.C.Cir.19