Item A: Public Hearing onMetro Plan Amendment (Delta Sand and Gravel)

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Delta Sand & Gravel Mining Area Expansion Noise According to Delta Sand & Gravel, the overburden material used to build the berms will not be sold as resource material and it will be placed back over the trench area once the aquaclude has been constructed inside the trench. Therefore, in the analysis, DSA considered the noise generated during the construction of the berm would be exempt from the DEQ noise regulation limits in accordance with OAR 340-035-0035 (5) (g) and (h). To aid in conducting the noise analyses, DSA first determined that portion of the aquaclude trench where excavation noise would exceed the DEQ noise regulation limits at a residence if noise reduction berms were not constructed by Delta Sand & Gravel. Figure 1 shows that portion of the aquaclude trench where the noise needs to be mitigated to ensure compliance with the DEQ noise regulation assuming a CAT 980H front-end loader with a noise suppression package or a CAT 330L excavator is used to excavate material below the overburden for more than 30 minutes per hour. Figure 2 shows that portion of the aquaclude trench where the noise needs to be mitigated to ensure compliance with the DEQ noise regulation assuming the front-end loader or excavator operates less than 30 minutes per hour. To further explain the two figures, Figure 1 identifies that portion of the aquaclude trench located within 475 feet of a residence and Figure 2 identifies that portion of the aquaclude trench located within 250 feet ofa residence. Four hundred seventy five (475) feet is the setback distance from a residence needed to meet the ambient hourly LSD noise level plus 10 dB limit found at residences along Admiral Lane if a CAT 980H front-end loader with a noise suppression package or CAT 330L excavator operates more than 30 minutes per hour without the presence of a noise reduction berm. Two hundred fifty (250) feet is the setback distance required to not exceed the ambient hourly LIO noise level plus 10 dB limit found at residences along Admiral Lane if the equipment operates less than 30 minutes per hour. The setback distances are conservative because, as the trench excavation moves south along the west property line, the ambient noise levels increase. Consequently, the noise limits are higher at residences south of Admiral Lane and the setback distance could decrease. As can be seen by comparing the informatiQQ in Figure 1 and Figure 2, the use of time limits on the excavation work in the trench can actually be used as a noise mitigation measure itself. If the excavation activity in the trench occurs during less than 30 minutes per hour, then the need for further mitigation is significantly reduced due to the fact tpat the noise limits specified in the DEQ noise regulation are time dependant. The less time the noise is present, the louder the noise can be when it is present. As can be seen in Figure 2, even after reducing the amount of time trench excavation work occurs during an hour, there will be the need to provide some noise reduction measure to ensure the excavation noise is in compliance with the DEQ noise limits at all residences. This means that noise control berms will be needed at times during the excavation of the aquaclude trench. Using the CAT 980H front-end loader sound data provided by the manufacturer (72 dBA at 50 feet) and the CAT 330L excavator measured by DSA, it was determined that when excavation work in the aquaclude trench occurs for more than 30 minutes per hour, a nine foot high benn in the vicinity of the work area shown in Figure 1 will be enough to ensure compliance with the DEQ noise regulations. If the excavation work 137045-M2.doc October 27, 2006 Page 2 of3