400 RIVERSIDE RD SEPA 016 - 039 - RIVERSIDE BUSINESS PARK Land Use Decision Documents 2025-04-14

I ADT is 33,000,significantly lower than the ADT at the nearby Interstate 5. The ADT at the Interstate 5 station is 75,598 vehicles per day. Ten percent of the ADT is equal to the traffic volume in vehicles I per hour which is needed along with the posted speed of the route to determine the noise generated by the traffic. Using a traffic volume of 7,560 vehicles per hour, a posted speed of 60 miles per hour, and Table 7-3 from the WSDOT guidance manual, the traffic noise level for the project is 79.8 dBA I (WSDOT,2013). The WSDOT guidance states ambient noise levels in urban areas during the daytime are found to be approximately 60-65 dBA, which is significantly less than the background noise due to traffic;therefore,79.8 dBA was used as the background noise to determine the extents of the action I area. The construction techniques and equipment used by the project are likely to produce sound levels I above the area's ambient levels. To be conservative, three pieces of construction equipment likely to be used by the project have been assumed to be operating at the same time to represent the loudest noise produced by the project. The three chosen pieces of equipment were: a Dump Truck at an I estimated 76 dBA, Backhoe at an estimated 78 dBA, and Concrete Pump Truck at an estimated 81 dBA. The two pieces of equipment producing the least noise (dump truck at 76 dBA and backhoe at 78 dBA) were added together for a difference of 2. Using the rules for decibel additional per table 7- I 5, 2 dBA was added to the highest value between the two (backhoe at 78 dBA) to get a combined noise level of 80 dBA. Continuing with the rules of decibel additional, the difference between the previous noise level of 80 dBA and the loudest remaining piece of equipment (Concrete Pump Truck I at 81 dBA) is 1 dBA; therefore, 3 dBA was added to the loudest between the two (Concrete Dump Truck at 81 dBA) to produce the assumed maximum construction noise level of the project at 84 dBA (WSDOT, 2015). IThe terrestrial sound action area is estimated to have a radius of approximately 81 feet using the typical method described in the WSDOT manual. A standard attenuation rate of 6 dBA per doubling was I applied to the estimated construction noise. No other reduction factors, such as the topography or vegetation of the site were used to attenuate the noise over a shorter distance; however, it is likely under real world conditions the noise will attenuate to background levels much more quickly than Iestimated. Table 3:Terrestrial Noise Attenuation I Terrestrial Attenuation Table Hard Sites Construction Distance from Source Noise Ambient Sound Measured Noise Pressure (Feet) (Miles) (dBA) (dBA) (Micro-Pascals) (atm) I50 0.009469697 84 79.8 316978.6385 3.21154E-08 100 0.018939394 78 79.8 158865.6469 1.60958E-08 200 0.037878788 72 79.8 79621.43411 8.06701E-09 I 400 0.075757576 66 79.8 39905.2463 4.04308E-09 800 0.151515152 60 79.8 20000 2.02634E-09 1600 0.303030303 54 79.8 10023.74467 1.01558E-09 I 3200 0.606060606 48 79.8 5023.772863 5.08994E-10 6400 1.212121212 42 79.8 2517.850824 2.55101E-10 12800 2.424242424 36 79.8 1261.914689 1.27854E-10 I 25600 4.848484848 30 79.8 632.455532 6.40786E-11 I Soundview Consultants LLC December 8,2016 I 1413.0003 Riverside Business Park-FEMA ESA Habitat Assessment Report Page 5