Environmental documents tend to be highly complex, large and extremely burdensome for an average member of the public. When an Environmental Impact Statement is posted electronically, you will typically see disclaimers like “Due to the size of the Draft EIS files…” or “for additional supporting technical documents, please contact the agency directly.” Agencies have the responsibility to report complete information, descriptions of data collection methodology, technical documentation of results, analysis and disclosure of known potential impacts.
Unfortunately, the average person has no idea what these potential impacts mean to them. One can provide the most technically accurate description of the impact, down the decibel, but the affected party typically has no baseline comparison or any idea what these technical descriptions equate to “in real life.”
Ok, it’s loud…but how loud is it?
For example, pretend you are a property owner with a property that backs up to a proposed light rail project. You have been notified by the agency that your property may be impacted by noise that would result from the proposed light rail project. You read an excerpt Noise and Vibration Chapter of their Environmental Impact Statement to better understand what this means:
Noise is measured in a logarithmic unit called a decibel (dBA). Human perception of noise is measured in decibels on a scale that has been weighted to middle and high frequency sounds that are more discernible to humans. This scale is called an A-weighted scale. By using this scale, the range of normally encountered sound can be expressed by values from 0 to 120 decibels. On a comparative basis, a 3-decibel change in sound level generally represents a barely-noticeable change outside the laboratory, whereas a 10-decibel change in sound level would typically be perceived as a doubling (or halving) in the loudness of a sound.
Noise levels are commonly measured and analyzed in two ways: Leq (sound level equivalent) and Ldn (24-hour day night average). Leq is a steady sound level over a specified period of time, such as one hour. It is often used to determine noise near areas where quiet is essential at all hours, such as a school or a park. The Ldn is commonly used to describe the 24-hour day-night average and assigns a 10-decibel penalty to night-time hours. Ldn is commonly used to analyze noise impacts in areas where people sleep. In most communities, Ldn is generally found to range between 55 dBA and 75 dBA.
OK, if you’ve read this far and feel like you actually understand how noise is measured, then you are wired much differently than the 95% of the population.
Agencies will also present impact findings qualitatively, with words like “severe” or “moderate.” Returning to the previous example, the agency provides the following qualitative definitions for noise impacts (BTW- these definitions are provided by Federal Transit Administration Guidance on Measuring Noise and Vibration) :
• Severe Impact: Project-generated noise in the severe impact range can be expected to cause a significant percentage of people to be highly annoyed by the new noise and represents the most compelling need for mitigation. Noise mitigation will normally be specified for severe impact areas unless there are truly extenuating circumstances that prevent it.
• Moderate Impact: In this range of noise impact, the change in the cumulative noise level is noticeable to most people but may not be sufficient to cause strong, adverse reactions from the community. In this transitional area, other project-specific factors must be considered to determine the magnitude of the impact and the need for mitigation. These factors include the existing noise level, the predicted level of increase over existing noise levels, the types and numbers of noise sensitive land uses affected, the noise sensitivity of the properties, the effectiveness of the mitigation measures, community views and the cost of mitigating noise to more acceptable levels.
So let’s say that you are told that you have a severe noise impact. From the definitions above, you know that a significant percentage of people would be highly annoyed by the new noise. Severe… Significant… What’s the difference? And what does that even mean?!!