1982-02-18_GENERAL DOCUMENTS - M1981302

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Staff Recommendation Docket #SU-81-10 November 13, 1981 Page Four Source (cont'd. ) Noise Level Expected Response, etc. +8OdBA Vigorous community action U.S.D.O.T. ambient +2-3dBA Barely detectable Fed. Hwy. Admin. ambient +5dBA Readily Noticeable Nat' l . Hwy. Institute ambient +10dBA Perceived as doubling of loudness ambient +20dBA Dramatic change CHRP Report 117 L50 = 66dBA Normal voice level speech permitted at 1 foot distance L = 60dBA Permitted at 2 feet L50 = 56dBA Permitted at 3 feet L50 = 54dBA Permitted at 4 feet Operations should be conducted so that very few complaints are generated, thus illustrating a minimal effect on residential neighborhoods. From the informa- tion above, it is felt that 5dBA above ambient levels is a reasonable standard which should not be exceeded. At the sites monitored by Salter Associates , the maximum allowable noise levels would translate as follows : Site Max. Noise Level L10 L50 L90 1 - Mobile Home Park 65dBA 58dBA 52dBA 50dBA 2 - South Hy-View 65dBA 56dBA 52dBA 50dBA 3 - North Hy-View 50dBA 52dBA 50dBA 48dBA 4 - Tantra 61dBA 54dBA 50dBA 48dBA Plant Site The Salter Associates report predicted that worst case conditions at the western operations area would result in sound levels of L = 50-55dBA or 5-10 dBA above the ambient level of L = 45dBA. Acco5r2ing to previously cited sources, this could generate sporadq� to widespread complaints. An alternative noted by Salter was to move the plant site to the east side of the Deepe property, thus approximately doubling distances and decreasing noise levels received in residential areas by 6dBA. The applicant has sub- mitted an alternate mining plan which locates the plant site about 3000 feet from Tantra (South Creek) , Hy-View and the mobile home park. It is felt by staff this this relocation, coupled with the appropriate location of stockpiles in the operations area, should reduce maximum levels from the site to at or below the lower range of ambient levels in the residential areas. In order for stockpiles placed around the plant to be effective in lowering noise levels, the stockpiles must be arranged so that they continuously block the line of sight between the highest residences in Hy-View Subdiviaion and the noise-producing portions of the processing plant. As the stockpiles increase in height above the line of sight, noise attenuation increases. Staff would like to work with the applicants during the design and placement of the plant and stockpiles to insure that the stockpiles will continuously obstruct the line of sight to the residences. Mining The open pit mining operations, which include the use of a backhoe, front end load and haul trucks, have the potential for being the most offensive