1982-02-18_GENERAL DOCUMENTS - M1981302

Home Browse Search

Staff Recommendation Docket #SU-81-20 November 13, 1981 Page Three Noise Noise, although not specifically listed in the Planning Commission con- cerns and suggestions, is obviously an overriding concern as far as impacts to the residential areas of Tantra Subdivision, Hyview Subdivision and the Coliday Mobile Home Park. The latest acoustics report from Charles M. Salter Associates of San Francisco utilizes current state of the art techniques in establishing the ambient (existing) sound levels at four (4) sites, including the Coliday Mobile Home Park, two (2) sites in Hy-View Subdivision and one (1) site on the Tantra area. Minimum and maximum dBA levels were 40 and 60, respectively. The L level , which represents an average level exceeded 50% of the time, rNged from 45 to 47 dBA, with the L level (exceeded only 10% of the time) ranging from 49-53 dBA. Thus , 1Y is safe to say that average daytime ambient level in the residential areas is 45-50 dBA. There are basically three (3) factors that reduce sound levels, and these are listed from the 1st, which requires no action by the applicant, to the last, which requires .the most action by the applicant: 1) Masking by ambient levels 2) Attenuation by distance (conservatively 6 decibel loss for each doubling of distance) by moving noise sources further away from noise receivers 3) Construction of sound barriers which depending on height, bulk and location can reduce sound levels by 5 to 20 decibels. General Goals of Noise Impact Mitigation The optimum goal of mitigation measures is to assure that whenever pos- sible noise levels from the site do not exceed ambient levels in the residential areas. The secondary goal is to assure that any noise level increases are so minimal that there is very little or no impact. Finally, at points in time and locations where noise increases will have noticeable impact, operations should be scheduled and otherwise tailored so as to minimize the impact as much as possible. There are a number of sources which estimate expected reactions to noise increases or set standards for maximum daytime noise levels in residental areas. These are listed as follows: Source Noise Level Expected Response, etc. CRS 73 25-12-103 55dBA Higher Level Constitutes _ 5OdBA impulse Nuisance EPA 55dBA outdoor Higher Level interferes 45dBA indoor with normal conversation, activities ISO Recommendation ambient +OdBA No observed reaction R-1996 ambient +5dBA Sporadic complaints (as cited by ambient +10dBA Threats of community Salter Associates) action ambient +15dBA Vigorous community action EPA 50-6OdBA Noise becomes noticeable, may be a few complaints 60-7OdBA Widespread complaints , threat of legal action 70-8OdBA Several threats of legal action, appeals for government intervention