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-14- <br />dBA occurs when noise monitoring shows that the outdoor sound <br />level exceeded 65 dBA for over six minutes of a one -hour survey. <br />The "L50" standard is defined by the existing rules as "the sound <br />level, expressed in dBA, which is exceeded fifty percent of the <br />time for a one -hour survey." Thus a violation of an L50 standard <br />of 60 dBA occurs when noise monitoring shows that the outdoor <br />sound level exceeded 60 dBA for at least thirty minutes of a <br />one -hour survey. rules by <br />The Agency is proposing to amend the existing <br />eliminating the L10 and L50 descriptors, which are "statistical" <br />dhe LeQ descriptor. This decision <br />escriptors, and using instead t <br />was reached after significant debate and discussion among <br />interested parties who attended the Noise Committee meetings. <br />Statistical descriptors have their advantages and disadvantages <br />as a regulatory tool. While they are simple to measure, they <br />have technical and practical limitations on their iiee. Because <br />they focus only on the question of whether a certain sound level <br />was exceeded for a certain period of time (six minutes for the L10 <br />and thirty minutes for the L50), statistical descriptors do not <br />give a complete picture of the intensity or loudness of sound <br />measured over the entire one -hour sample. For exampler peaks <br />statistical descriptors are not sensitive to noise energy p In <br />if those peaks do not last the appropriate amount of time. <br />addition, the statistical descriptors do not easily lend <br />themselves to predictive computer modeling, which is frequently <br />