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to control dust. The proposed requirements include demonstrating at least an overall average 75 percent reduction from uncontrolled PM-10 emissions, preparing a dust control plan to be approved by the APCD, performing surface surveys for moisture analysis, and performing visible emission tests or evaluations. The applicant shall maintain proper records of the dust control plan which shall be available for scheduled and unscheduled inspection by the County and the APCD. 4. To minimize emissions from the loaders and other equipment used on site, low- sulfur fuel should be used, and the equipment should have routine maintenance and tuning performed biweekly. 3.6 Noise 3.6.1 Setting i Noise Measurement and Terminology Noise is customarily measured in decibels (dB), units related to the apparent loudness of sound. An A-weighted decibel (dBA) represents sound frequencies that are normally heard by the human ear. On this scale, the normal range of human hearing extends from about 3 dBA to 140 dBA, with speech normally occurring between 60 and 65 dBA. A 10-dBA increase in the level of a continuous noise represents a perceived doubling of loudness, whereas a 3-dBA increase is just noticeable to most people. Because environmental noise levels fluctuate over time, a time-averaged noise level in dBA is often used to characterize the acoustic environment at a given location. The average noise intensity over a given time is the energy equivalent noise level (Leq). The day-night equivalent noise level (Ldn) is a 24-hour Leq which is derived by adding a 10 dBA "penalty" to noise levels measured between 10 p.m.. and 7 a.m. The community noise equivalent level (CNEL) incorporates an additional 5 dBA penalty to sound levels measured between 7 p.m. and 10 p.m. These "penalties" account for the greater sensitivity of people to high noise levels at night. Table 3.6-1 shows the noise levels of different activities and the response criteria of various noise levels. 80