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'-- 30 Attachment 3 Environmental Sound Page 15 must consider existing accepted sounds variations in noise expectafions within the overall geographic area covered, The limits must not be too restrictive for more densely populated aeeas that normally expect more noise. This means that sounds that last for long periods could meet the requirements of the ordinance and still create a problem, especially in parks of the community that expect quieter levels. Ordinance limits are usually related to the use of the property the sound is entering. Sometimes limits are inappropriately based solely on the use ofthe source property, More commonly, some allowance is made for sound entering residential areas from established industrial areas. One common method is to arithmetically average the limits for the two uses. Many communities have adopted local ordinances for controlling noise, The U. 5.. EPA published a model ordinance in 1975, An included survey identified 118 communites with local limits. The most popular limns for noise entering residential areas in daytime were 55 and 60 dBA with the average being 56.75 dBA, The most popular limits for night in residential areas were 50, 45, and 55 dBA in that order, averaging 51.75 dBA. The survey did not distinguish among maximum levels, L10, average levels or other measures. Some ordinances based on the Chicago model are still in effect, including measurement requirements that cannot be met by any instrument made after 1963. Some communities have adopted ordinances limiting specific sources to specified sound levels. At least l8 municipalities and counties in North Carolina now have zoning or general ordinances specifying limits on sound from any source crossing boundazies. These are summarized in the table onthe next page. L10 based on 100 measurements is the most populaz method of measuring and setting limits in North Carolina. The most popular limits are 60 dBA in the daytime and 55 dBA at night" Most using the L10 method also specify a higher maximum level never to be exceeded. The wider availability ofinstnunents to measutetime-average levelhas led to increasinguse ofthis measure in new ordinances, Notice that some communities impose lower levels on sound that contains music or speech or has tonal or repetitive impulsive chazacteristics. Some college towns start the nightperiod later than most communities, and allow higher levels on weekend evenings. These ordinances were originally adopted to allow fraternity parties but with some control. These communities use maximum level limits for ease of enforcement against parties. However, the high lunits allowed during "party hours" aze high for steady sound, and the lower limits are other times are very restrictive for brief sounds. The ChapelHill ordinance revised'm 2001 is the most restrictive known in the state, While not a zoning ordinance, it contains an exemption for sources existing at the time of its adoption, requiring them to meet only the previous ordinance, Wake County has both zoning and general ordinances. The Wake zoning ordinance sets maximum level limits based on duration of sound, It does not make clear how this applies to a sound that varies in leveh