Developer’s Expert Differs with DOT on Projections of Future Noise Levels

posted in: April 2010 | 0

Noise – current, future, acceptable or compatible – has taken center stage in the debate over the proposed O`oma Beachside Villages just a short distance south of the Keahole airport on the Kona Coast of the Big Island.

As a rule, the level most people would describe as ‘very quiet’ is around 30 decibels (dB), while 100 dB is deafening. The decibel scale is itself logarithmic, which means that something measured at 70 dB has 10 times the acoustic energy of 60 dB and 100 times the energy of 50 dB.

Since 1980, the Federal Aviation Administration has had a set of land use compatibility guidelines for noise exposures. Residential uses were deemed to be compatible with noise exposures up to 65 DNL (the average sound over a 24-hour period). Residential uses above that were allowed only when building codes required insulation and other noise-mitigation measures sufficient to reduce the indoor noise levels to 40 dB. The only residential uses allowed in areas where the DNL exceeded 75 would be transient accommodations, and even then, only when noise-level reduction (NLR) measures achieved indoor levels of 40 dB.

Given the fact that construction in Hawai`i typically does not use the levels of insulation seen elsewhere in the United States, the difference between indoor and outdoor noise levels is not nearly so great here. To address that, the state Department of Transportation has adopted its own recommendations for compatible land uses. Residential construction of all types (including transient lodgings with limited outdoor use and high-density apartments with limited outdoor use) are classified as compatible up to the 60 DNL contour line.

Within the 60 to 65 DNL contour, residential uses are generally not compatible. However, in a footnote to the guidelines, the DOT states, “where the community determines that these uses must be allowed, Noise Level Reduction (NLR) measures to achieve interior levels of 45 DNL or less should be incorporated into building codes and be considered in individual approvals.” In Hawai`i, “normal local construction employing natural ventilation can be expected to provide an average NLR of approximately 9 dB. Total closure plus air conditioning may be required to provide additional outdoor-to-indoor NLR, and will not eliminate outdoor noise problems.”

An Imperfect Metric

The DNL is a measurement of average noise, and, like other averages, it does not describe very well the extremes that may occur over the course of a day. The average is arrived at by measuring the noises, in decibels, that occur at a given site over the course of a day, with noises that occur between 10 p.m. and 7 a.m. given extra weight (10 dBs are added to the measured levels), to reflect the additional level of the population’s general sensitivity to noise during the night.

Other ways to measure noise exist, and, although they do not factor into what may or may not be regarded as compatible land uses for planning purposes, they do give a number to the level of pain and annoyance that people living near airports or other noise-generating activities experience.

The Sound Exposure Level (SEL) factors in duration of exposure as well as the decibel level. Tables that the developer’s noise expert, Yoichi Ebisu, prepared show noise from overflights of a range of individual aircraft measured at selected sites near the southern boundary of the O`oma property. At Location A, which lies roughly midway between the 55 and 60 DNL contour lines, as shown on a DOT map reflecting 2001 noise levels, the SEL measured during the take-off of a Boeing 737 averaged 92.1 dB. (Over the six days of measurements made by Ebisu in March of 2007, there were 81 take-offs of 737s recorded at Location A.)

Then there is the maximum sound level (or Lmax). This is merely a measure of the peak noise a given aircraft generates when passing over a site. To look at the same set of data for Location A, the maximum sound level for the Boeing 737 take-offs ranged from a low of 75.3 dB to a high of 89.0, with an average Lmax of 81.

At Location B of Ebisu’s study, an area that lies well inside the 55 DNL contour, the sound exposure levels for 64 Boeing 737 take-offs were only slightly less than they were for Location A: 88.7 as opposed to 92.1 dB. The Lmax was 79.8 dB on average.


If one looks at Ebisu’s maps, none of the uses proposed for the O`oma project is incompatible with state guidelines on noise. Even in 2013, when, under the developer’s timetable, construction will have begun, the projections drawn by Ebisu for noise contours indicate that noise-sensitive uses still fall outside the 60 DNL contour. To be sure, the distance between the 60 DNL contour line and the closest lot lines for large-lot houses and multi-family units in the so-called Makai Village is close – on the order of 100 feet or less. It’s a line drive, but doesn’t cross into foul territory.

The story is different if one superimposes the state Department of Transportation’s official Noise Exposure Maps – accepted by the FAA on January 12 – onto the plans for O`oma Beachside Village. By 2013, the DOT maps show the 60 DNL contour will reach as much as 800 feet mauka of where Ebisu had placed it. The entire Makai Village will be in a zone where residential uses are incompatible under state standards. A substantial fraction of the large-lot portion of the development also will fall into the area where the noise level exceeds 60 DNL. In addition, roughly 80 percent of the area to be developed that is included in the Land Use Commission redistricting petition would be subject to the noise disclosure notice requirement; under Ebisu’s maps, less than half would be.

Ebisu’s study was begun before the state Department of Transportation had published draft maps showing both five-year (2013) and long-range forecasts for noise. By the time his study was completed, however, the draft maps were available, and, reading the final noise study and EIS for the O`oma project, it had become clear to Ebisu that a discrepancy existed.

“During the course of this acoustical impact study … the Hawai`i State Department of Transportation, Airports Division produced two pairs of … noise contours for [Keahole] airport for years 2007/2008 and 2012/2013,” Ebisu wrote in his report. “These draft contours [now final] were compared to this acoustical impact study’s noise contours, and were critiqued via correspondences to the HDOTA. Attempts were made to obtain copies of the noise modeling computer input files used for the HDOTA’s draft noise contours, but these attempts were unsuccessful…”

Ebisu alleged that the DOT’s “original modeling assumptions … were considered to be questionable or arbitrary.” He included in his study a list of reasons for the different analyses, including possible incorrect assumptions about day and night winds and corresponding runway uses; “apparent lack of authoritative input from the military when forecasting future military operations” at the airport; failure to take into account the new seaward runway planned for C-17 touch-and-go operations; continuing use of B-737(200) aircraft (Ebisu’s forecasts had assumed these would be phased out and quieter aircraft substituted); and finally “inclusion of questionable noise monitoring data, which if deleted, would contradict the study conclusion that the south side of the airport is noisier than the north side of the airport.”


Patricia Tummons


Volume 20, Number 10 — April 2010


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