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I .. I I I I I I I .. I I I I I I -. I I Noise Analysis Noise is defined as any unwanted sound. Sound travels in a wave motion and produces a sound pressure level. This sound pressure level is commonly measured in decibels. Decibels (dB) represent the logarithmie increase in sound energy relative to a reference energy level. A sound increase of 3 dB is barely perceptible to the human ear, a 5 dB inerease is clearly notieeable, and a 10 dB increase is heard as twice as loud. For example, if the sound energy is doubled (e.g., the amount of traffic doubles), there is a 3 dB increase in noise, which is just barely noticeable to most people. On the other hand, if traffie increases to where there is 10 times the sound energy level over a referenee level, then there is a lO dB inerease and it is heard as twice as loud. To approximate the way that an average person hears sound, an adjustment, or weighting, of the high- and low- pitched sounds is made. The adjusted sound levels are stated in units of "A-weighted decibels" (dBA). In Minnesota, traffic noise impacts are evaluated by measuring and/or modeling the traffic noise levels that are exceeded 10 pereent and 50 percent of the time during the hours of the day and/or night that has the heaviest traffic. These numbers are identified as the LIO and L50 levels. For example, an LIO value of 65 decibels means that the noise level was at or greater than 65 decibels during 10 percent of the measurement period (i.e., more than 6 minutes per hour). Regulatory Framework The MPCA is the governmental regulatory agency responsible for implementing regulations controlling traffic noise in Minnesota. Minnesota State noise standards have been established specifically for daytime and nighttime periods. For residential land uses (identified as Noise Area Classifieation 1 or NAC- I), the Minnesota State standards for LIO are 65 decibels for daytime and 55 decibels for nighttime; the standards for L50 are 60 decibels for daytime and 50 decibels for nighttime. For parkland with no overnight uses (such as Cummings Park), NAC-l daytime standards apply to both daytime and nighttime noisc levels. Minnesota Statute 116.07, Subd. 2a. states that municipal and county roads, except in the cities of Minneapolis and St. Paul, are exempt from state noise standards. All the roads near the proposed project site are county or city roads (with the exception ofI-694) and are therefore exempt from standards. State standards are included in this study for reference only and are depicted in Table 22. TABLE 22 MINNESOTA STATE NOISE STANDARDS MPCA State Noise Standards Land Use Code Day (7 a.m. - 10 p.m.) dBA Night (10 p.m. - 7 a.m.) dBA Residential NAC-1 Llo of 65 Lso of 60 LIO of 55 LsD of 50 . ~ Commercial NAC-2 LIO of 70 Lso of 65 Llo of70 LsD of 65 -"-. Industrial NAC-3 LIO of 80 Lso of 75 LID of 80 L500f75 Guidant Campus Master Plan Final AUAR and Mitigation Plan - 49- January 2003