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. .. i. � . . � . I ��. i � �. �� -: � While zoning ordinances vary significantly across the U.S., most facilities must be placed on property zoned heavy industrial. In addition, the majority of facilities must obtain special land use permits. Such permits con- tain specific requirements with which the facility must comply. These many include operating hours and noise levels to name a few. ��'E � I:�� I�l �.�; z I.: %`:;-�tll�1E�'' 4','us...�� ii; il� I' � f The most common odor detected at a hot mix facility comes from the hydrocarbons driven off the liquid asphalt cement. Overheating the hot mix materials during the drying process is the primary cause. As fuel has become more and more expensive, most owners and operators have become more aware of the cost of overheating materials and have learned to control temperature with greater precision. The fumes, known as "blue smoke", have a characteristic petroleum-type odor. Blue smoke forms as the hydrocarbons condense in the ambient air. Its formation is highly dependent on temperature and the facilify configuration. Minimizing opportunities for the fumes to enter the ambient air and lowering mix/storage temperatures decreases odor levels from the facility. f� i If ' Il:fkk!;-: �,1�4��[c;:t ll-�ak4Erll� ll�!.��I '-� .��: Modern hot mix asphalt facilities fall into two categories: batch and drum mix facilities. As the name implies, batch facilities make individual batches of material. All the ingredients for the batch are fed into a mixer. When mixing is complete, the mixer is emptied, most ohen into a waiting haul truck. Batch facilities usually have smaller hourly production capacities than drum mix facilities. They are suitable for small production runs or frequenf changes in mix type. Drum mix facilities operate on a continuous basis. The mix is stored in storage silos and discharged into haul trucks as needed. They can be either parallel-flow or counterflow, which is an indication of the material flow versus the airFlow within the drum. Material moves in the same direction as the airflow in a parallel-flow drum whereas the material moves against the airflow in a counterflow drum. Modern drum mix facilities almost � exclusively include counterflow drums. This is because they use less fuel and generate lower hydrocarbon emissions than parallel-flow drums.