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Show dispersion coefficients used to calcu l ate the meta l s emissions limits were used to calculate the de mi nimis hydrocarbon l evels . Under Tier III , the applicant coulo-demonstrate by s i te - specif i c dispersion modeling using EPA Guideline model s and the ass umotions discussed above that his hyd r oca rbon em is sions, alt houqh hiqhe r than the de minimis l eve l s , do not resu lt in ambient levels - that pose-Signi f icant risk. Thus, as under Tier II, th e CO l e ve l that occ ur s d ur ing the trial burn would become the perm i tted level . It s ho uld be noted that, under this scheme for es t ablishing CO l imits in the permit, hydrocarbon emissions would be monitored only during the trial burn. We believe that continuous monitoring of hydrocarbon emissions is not practicable -- opera:ion and maintenance costs can be very high. Moreover, we believe that limiting CO levels to those that occur during the trial burn will ensure that hydrocarbon emissions do not exceed those that occur during the trial burn. We plan to request comments on using this three-tiered approach to establish CO limits for boilers and industrial furnaces well in the notice of supplemental information. Given that many of the issues pertaining to the controls for incinerators, boilers and industrial furnaces are virtually identical, we plan to publish the incinerator proposal and the boiler and furnace notice of supplemental information in the Federal Register concurrently. We plan to allow a 60 day comment period for both notices and to copromulgate the rules by late 1988. Permit Writer Guidance Documents To enable incinerator permit writers to control metals and PIC emissions immediately under the omnibus authority of HSWA Section 3005(c)(3), rather than waiting until the amendments are promulgated in late 1988, we are developing guidance documents. The omnibus authority allows the permit writer to establish permit conditions as necessary to protect human health and the environment. Thus, the guidance documents will recommend that the permit writer implement the controls that will be proposed as discussed above. The guidance documents are scheduled to be available to the Regions and States in early 1988. - 4- |