CHAPTER 12
NOISE
12.1 INTRODUCTION
The purpose of this chapter is to quantify the current, or baseline, and
projected noise conditions in the unincorporated county (i.e., areas excluding
the incorporated areas of Yuba City and Live Oak). Specifically this involves:
The noise information in this chapter has been prepared in accordance with Guidelines for the Preparation and Content of the Noise Element of the General Plan issued by the California Department of Health Services and the State of California General Plan Guidelines published by the Office of Planning and Research.
BACKGROUND INFORMATION ON ENVIRONMENTAL ACOUSTICS
Noise Terminology
Sound travels through the air as waves of minute air pressure fluctuations caused by some type of vibration. In general, sound waves travel away from the noise source as an expanding spherical surface. The energy contained in a sound wave is consequently spread over an increasing area as it travels away from the source. This results in a decrease in loudness at greater distances from the noise source.
Sound-level meters measure the pressure fluctuations caused by sound waves. Because of the ability of the human ear to respond to a wide dynamic range of sound pressure fluctuations, loudness is measured in terms of a logarithmic decibel (dB) scale. The scale measures pressure fluctuations in a convenient notation and corresponds to our auditory perception of increasing loudness.
Most sounds consist of a broad range of sound frequencies. Because the
human ear is not equally sensitive to all frequencies, several frequency-weighting
schemes have been used to develop composite decibel scales that approximate
the way the human ear responds to noise levels. The A- weighted decibel
scale (dBA) is the most widely used for this purpose. Typical A-weighted
noise levels for various types of sound sources are summarized in Figure
12.1-1.
Time-varying sound levels are often described in terms of an equivalent
constant decibel level. Equivalent sound levels (Leq) are used to develop
single-value descriptions of average noise exposure over various periods
of time. Such average noise exposure values often include additional weighting
factors for annoyance potential attributable to time of day or other considerations.
The Leq data used for these average noise exposure descriptors are generally
based on A-weighted sound-level measurements.
Average noise exposure over a 24-hour period is often presented as a day-night average sound level (Ldn). Ldn values are calculated from hourly Leq values, with the Leq values for the nighttime period (10 p.m.-7 a.m.) increased by 10 dB to reflect the greater disturbance potential from nighttime noise.
The community noise equivalent level (CNEL) is also used to characterize average noise levels over a 24-hour period, with weighting factors included for evening and nighttime noise levels. Leq values for the evening period (7 p.m.-10 p.m.) are increased by 5 dB, while Leq values for the nighttime period (10 p.m.-7 a.m.) are increased by 10 dB.
Another noise metric often used to describe a given noise environment is the percentile level. This is the sound level that is exceeded during a given percentage of a stated measurement period. An example of this is L10, which is the sound level exceeded 10% of the time. L1, L10, L50, L90, and L99 are the most commonly used exceedance metrics. L1 generally corresponds to the maximum sound level during the measurement period, L99 is the minimum noise level, L50 is the median sound level, and L90 is usually considered to represent the ambient sound level.
Ambient noise is the all-encompassing noise associated with a given environment at a specified time that is usually a composite of sound from many sources at many directions near and far. No particular sound is dominant in ambient noise.
Noise contours are lines drawn on a map around a source indicating constant levels of noise exposure. Leq, Ldn, and CNEL are commonly used noise contour metrics.
FIGURE 12.1-1
A-WEIGHTED SOUND LEVELS AND HUMAN RESPONSE
Equivalencies between Various Noise Descriptors
The value at a site calculated from a set of measurements taken over a given 24-hour period will be slightly lower than the CNEL value calculated over the same time period. Except in situations where unusually high evening noise levels occur, the CNEL value will be within 1.5 dB of the Ldn value for the same set of noise measurements.
The relationship between peak hourly Leq values from traffic and associated Ldn values depends on the distribution of traffic over the entire day. There is no precise way to convert a peak hourly Leq value to an Ldn value. However, in urban areas near heavy traffic, the peak hourly L eq value is typically 2-4 dB lower than the daily Ldn value. In less heavily developed areas, the peak hourly Leq is often equal to the daily Ldn value. In rural areas with little nighttime traffic, the peak hourly Leq value will often be 3-4 dB greater than the daily Ldn value.
Working with Decibel Values
The nature of dB scales is such that the individual sound level for different noise sources cannot be added directly to give the combined sound level of these sources. Two noise sources producing equal sound levels at a given location will produce a composite sound level that is 3 dB greater than either sound alone. When two noise sources differ by 10 dB, the composite noise level will be only 0.4 dB greater than the louder source alone.
Most people have difficulty distinguishing the louder of two noise sources if they differ by less than 1.5-2.0 dB. Research into the human perception of changes in sound level indicates the following:
When distance is the only factor considered, sound levels from an isolated noise source will typically decrease by about 6 dB for every doubling of distance away from the noise source. When the noise source is essentially a continuous line (e.g., vehicle traffic on a highway), noise levels decrease by about 3 dB for every doubling of distance. In traffic noise studies, a drop-off rate of 4.5 dB per doubling of distance is often used when the intervening ground between the roadway and the receiver is acoustically "soft" (e.g., ground vegetation, scattered trees, clumps of bushes).
Noise levels at different distances can also be affected by a number
of factors other than just the distance from the noise source. Topographic
features and structural barriers that absorb, reflect, or scatter sound
waves can result in increased or decreased noise levels. Atmospheric conditions
(wind speed and direction, humidity levels, and temperatures) can also
affect the degree to which sound is attenuated over distance.
Echoes off topographical features or buildings can sometimes result in
higher sound levels (lower sound attenuation rates) than normally expected.
Temperature inversion and attitudinal changes in wind conditions can at
times refract sound waves to a location at a considerable distance from
the noise source.
GUIDELINES FOR INTERPRETING NOISE LEVELS
Various federal, state, and local agencies have developed guidelines for evaluating land use compatibility under different noise level ranges.
Federal Agency Guidelines
The Federal Noise Control Act of 1972 (Public Law 92-574) established a requirement that all federal agencies must administer their programs to promote an environment free of noise that jeopardizes public health or welfare. The U.S. Environmental Protection Agency (EPA) was given the responsibility for:
* Providing information to the public regarding identifiable effects
of noise on public health or welfare,
* Publishing information on the levels of environmental noise that will
protect the public health and welfare with an adequate margin of safety,
* Coordinating federal research and activities related to noise control,
and
* Establishing federal noise emission standards for selected products distributed
in interstate commerce.
The Federal Noise Control Act also directed that all federal agencies comply
with applicable federal, state, interstate, and local noise control regulations.
Although the EPA was given major public information and federal agency coordination roles, each federal agency retains authority to adopt noise regulations pertaining to agency programs. The EPA can require other federal agencies to justify their noise regulations for compliance with the Noise Control Act requirements. The Occupational Safety and Health Administration retains primary authority for setting workplace noise exposure standards. The Federal Aviation Administration retains primary jurisdiction over aircraft noise standards.
In 1974, in response to the requirements of the federal Noise Control Act, the EPA identified indoor and outdoor noise limits to protect public health and welfare (communication disruption, sleep disturbance, and hearing damage). Outdoor Ldn limits of 55 dB and indoor Ldn limits of 45 dB are identified as desirable to protect against speech interference and sleep disturbance for residential, educational, and healthcare areas. Noise-level criteria to protect against hearing damage in commercial and industrial areas are identified as 24-hour Leq values of 70 dB (both outdoors and indoors).
The Federal Highway Administration (FHWA) has adopted criteria for evaluating noise impacts associated with federally funded highway projects and for determining whether these impacts are sufficient to justify funding noise mitigation actions (47 FR 131:29653-29656, July 8, 1982). The FHWA noise abatement criteria are based on peak hourly Leq noise levels, not Ldn or 24-hour Leq values. The peak 1-hour Leq criteria for residential, educational, and healthcare facilities are 67 dB outdoors and 52 dB indoors. The peak 1-hour Leq criterion for commercial and industrial areas is 72 dB (outdoors).
The U.S. Department of Housing and Urban Development has established guidelines for evaluating noise impacts on residential projects seeking financial support under various grant programs (44 FR 135:40860-40866, January 23, 1979). Sites are generally considered acceptable for residential use if they are exposed to outdoor Ldn values of 65 dB or less. Sites are considered "normally unacceptable" if they are exposed to outdoor Ldn values of 65-75 dB. Sites are considered unacceptable if they are exposed to outdoor Ldn values above 75 dB.
State Agency Guidelines
In 1987, the California Department of Health Services published guidelines for the noise element of local general plans. These guidelines include a noise level/land use compatibility chart that categorizes various outdoor Ldn ranges into up to four compatibility categories (normally acceptable, conditionally acceptable, normally unacceptable, and clearly unacceptable), depending on land use. For many land uses, the chart shows overlapping Ldn ranges for two or more compatibility categories. The noise element guidelines chart identifies the normally acceptable range for low-density residential uses as less than 60 dB, while the conditionally acceptable range is 55-70 dB. The normally acceptable range for high-density residential uses is identified as Ldn values below 65 dB, while the conditionally acceptable range is identified as 60-70 dB. For educational and medical facilities, Ldn values below 70 dB are considered normally acceptable, while Ldn values of 60-70 dB are considered conditionally acceptable. For office and commercial land uses, Ldn values below 70 dB are considered normally acceptable, while Ldn values of 67.5-77.5 are categorized as conditionally acceptable.
These overlapping Ldn ranges are intended to indicate that local conditions (existing noise levels and community attitudes toward dominant noise sources) should be considered in evaluating land use compatibility at specific locations.
The California State Aeronautics Noise Standards state that an outdoor sound level of 65 CNEL is acceptable for residences and schools. Standards are not specified for other potentially noise-sensitive land uses.
The California Department of Housing and Community Development has adopted noise insulation performance standards for new hotels, motels, and dwellings other than detached single-family structures (24 CCR T25-28). These standards require that "interior CNEL with windows closed, attributable to exterior sources, shall not exceed an annual CNEL of 45 dB in any habitable room."
Other Local Guidelines
The City of Sacramento has adopted specific noise land use compatibility criteria for evaluating noise effects from airports. Although these standards do not apply in Sutter County, they are mentioned here as a point of reference. Sacramento considers exterior noise from Sacramento International Airport (Sac International) as high as 60 CNEL to be acceptable for residences and schools. For all other airports, 65 CNEL is considered to be acceptable.
EXISTING NOISE CONDITIONS IN SUTTER COUNTY
Existing noise conditions in Sutter County are described by:
Noise Sources
The dominant sources of noise in Sutter County are related to transportation and include automobile and truck traffic, aircraft, and trains. Stationary sources in the County include natural gas extraction facilities, construction sites, mining activities, farming activities, and commercial and industrial facilities. These various sources are described in the next section.
Roadway Traffic
State Routes (SRs) 20, 70, 99, and 113 are major sources of traffic noise in the County. Some County roads, primarily those that serve as collectors and arterials in the vicinity of Yuba City, are significant sources of traffic noise. County roads that currently have daily traffic volumes in excess of 2,000 vehicles per day are listed in Table 12.1-1.
Noise levels produced by traffic on state highways and county roads with more than 2,000 vehicles per day have been calculated using the FHWA Traffic Noise Prediction Model (FHWA-RD-77-108). The model estimates traffic noise levels based on roadway geometrics; traffic volumes for automobiles, medium trucks (with two axles and six tires), and heavy trucks (with three or more axles); vehicle speeds; and a noise attenuation rate parameter. A computer-based implementation of the model was used that directly calculates Ldn values based on hourly traffic patterns, hourly truck percentages, and hourly speeds adjusted by the degree of congestion.
Truck percentages assumed in the analysis are based on data provided by California Department of Transportation, FHWA, and the County and are summarized in Table 12.1-2. Data on the roadways and traffic volumes were provided by the County. These data and calculated noise levels are summarized in Tables 12.1-1 and 12.1-4. The calculated Ldn values at 100 feet from the roadway centerline along with the distance to the 70-, 65-, 60-, and 55-Ldn contours are given. Figure 12.1-2 depicts 60-Ldn traffic noise contours lines for roadways in the unincorporated area around Yuba City.
TABLE 12.1-1
SUMMARY OF TRAFFIC DATA AND NOISE MODELING
FOR COUNTY ROADS UNDER EXISTING CONDITIONS
Aircraft
Aircraft operations in the vicinity of airports can be a significant source of noise. Sutter County Airport is the only publicly owned and operated airport in the county. There are also a number of small privately owned and operated landing strips and airports. Airports located in the County are identified in Figure 4.13-1. Noise from aircraft traffic at Sacramento International, which is located about a mile south of the southern border of Sutter County, also influences the noise environment in Sutter County.
In 1993, the Airport Land Use Commission updated noise contour maps for both the Sutter County Airport and Sacramento International. The 65-CNEL contour for Sutter County Airport is depicted in Figure 12.1-4. The 60- and 65-CNEL contours for Sacramento International are depicted in Figure 12.1-4.
Activity at small private landing strips is highly variable. In cases where the strip is used primarily for crop dusting, the use will vary with the farming season. Because use of these strips is highly variable, it is not practical to develop CNEL contours. However, data are available on typical sound levels generated by small aircraft as a function of distance. These data are summarized in Table 12.1-3.
TABLE 12.1-2
TRUCK PERCENTAGES USED IN THE
TRAFFIC NOISE MODELING ANALYSIS
Medium Heavy Total
Roadway Location Autos Trucks Trucks Trucks
State Route 20 Rural 91.0 4.9 4.1 9.0
Urban 94.0 2.7 3.3 6.0
State Route 70 92.2 2.2 5.6 7.8
State Highway 99 South SR-113 88.0 3.5 8.5 12.0
SR-113 to Oswald Rd 83.0 4.2 12.8 17.0
Oswald Rd to Encinal Rd 92.3 2.3 5.4 7.7
North to Encinal Rd 86.5 4.7 8.8 13.5
State Route 113 89.9 2.9 7.2 10.1
All county roads 94.0 2 4 6.0
Source: California Department of Transportation 1991, Rudder and Yaniv
1986.
TABLE 12.1-3
TYPICAL SOUND LEVELS GENERATED BY SMALL AIRCRAFT
MAXIMUM A - WEIGHTED SOUND LEVEL (dBA)
Slant Distance Single Engine Single Engine Twin Engine Twin Engine
(feet) Takeoff Landing Takeoff Takeoff
500 74 66 80 72
1,000 71 63 77 69
2,000 67 59 73 65
4,000 63 55 69 61
8,000 58 50 64 56
Sources: Miller 1982, Bishop 1975
TABLE 12.1-4
SUMMARY OF TRAFFIC DATA AND NOISE MODELING
FOR STATE ROUTES UNDER EXISTING CONDITIONS
FIGURE 12.1-2
EXISTING 60 LDN TRAFFIC NOISE CONTOURS
IN THE YUBA CITY URBAN AREA
FIGURE 12.1-3
65 CNEL CONTOUR FROM SUTTER COUNTY AIRPORT
FIGURE 12.1-4
NOISE CONTOURS FROM SACRAMENTO INTERNATIONAL AIRPORT
Trains
Two rail lines are active in Sutter County, one operated by the Southern Pacific Transportation Company (SPTC) and the other by the Union Pacific (UP).
Noise from rail operations has been modeled using methodology developed by Lotz and Kurzweil (Harris 1979) with support from the Office of Technology Development and Deployment of the Urban Mass Transportation Administration (now the Federal Transit Administration). Train noise attenuation has been calculated using 4.5 dB per doubling of distance as recommended by Piercy and Daigle (Harris 1991).
Southern Pacific Transportation Company. The SPTC track is identified in Figure 4.13-1. The track enters the County just north of Yuba City and runs north parallel to Live Oak Boulevard and then to SR 99. The track passes through Live Oak and exits the county just north of Riviera Road.
An average of 22 trains per day use the tracks, with 20 being freight trains and two being passenger trains. The average train length is 4,500 feet corresponding to about 65 cars. Ten trains pass during daytime and evening hours (7 a.m. to 10 p.m.) and 12 trains pass during nighttime hours (10 p.m. to 7 a.m.). The average speed is 55 miles per hour. Calculated Ldn values for these train operations are as follows:
Distance from Track Calculated Noise Level
100 feet 76 Ldn
115 feet 75 Ldn
250 feet 70 Ldn
540 feet 65 Ldn
1,170 feet 60 Ldn
SPTC also uses the Yuba City Branch, which connects Yuba City and Marysville.
The track is used once a day with a maximum speed of 15 miles per hour.
The calculated Ldn value at 100 feet is less than 50 dB.
Union Pacific. The UP track is identified in Figure 4.13-1. The track enters the County at the southeast corner of the county south of Pleasant Grove. The tracks then go northwest through Trowbridge and exit the County just north of Rio Oso.
An average of 14 freight trains per day use the tracks. The average train length is about 1 mile, which corresponds to about 75 cars. Seven trains pass during daytime and evening hours (7 a.m. to 10 p.m.) and seven trains pass during nighttime hours (10 p.m. to 7 a.m.). The average speed is 60 miles per hour. Calculated Ldn values for these train operations are as follows:
Distance from Track Calculated Noise Level
100 feet 75 Ldn
215 feet 70 Ldn
465 feet 65 Ldn
1,000 feet 60 Ldn
Natural Gas Extraction Facilities
A significant amount of natural gas is produced in Sutter County. Natural gas fields in the County are identified in Figure 9.5-1. Operations associated with the extraction of natural gas can be a significant source of noise. In Sutter County, natural gas wells require, at a minimum, zoning clearances and in certain situations conditional use permits for surface locations, with special considerations made for access routes and possible conflicts with agricultural activities and environmental factors. Special noise control treatments are required if a well is located within 500 feet of a residence.
Drilling operations are normally conducted on a 24-hour-a-day basis with drilling normally being completed within 10-14 days. A reciprocating natural gas compressor is then put in place at the well head to pressurize the gas for transmission. According to Mike Philips of Anacapa Oil, gas compressors used in Sutter County range in size from 23 horsepower (rated) to 400 horsepower. Approximately 70-85% of the compressors in use range in size from 60 to 120 horsepower. Mr. Philips has measured sound levels of about 94 dBA as measured 10-15 feet from a compressor. This is consistent with predicted sound levels for 60- to 120-horsepower units with muffled exhaust.
A dBA of 94 at 15 feet corresponds to 84 dBA at 50 feet. Using this source noise level and assuming nominal attenuation from atmospheric absorption, the distance to the 70-, 60-, and 50-dBA contours are as follows:
Distance from Source Calculated Noise Level
50 feet 84 dBA
240 feet 70 dBA
735 feet 60 dBA
1,920 feet 50 dBA
Construction Sites
Figure 12.1-5 illustrates noise levels produced by various types of construction equipment. Properly maintained equipment will produce noise levels near the middle of the indicated ranges. The types of construction equipment used for a typical construction project will usually generate noise levels of 80-90 dBA at a distance of 50 feet while the equipment is operating (U.S. Environmental Protection Agency 1971). Construction equipment operations can vary from intermittent to fairly continuous, with multiple pieces of equipment operating concurrently. Assuming that a bulldozer (87 dBA), backhoe (90 dBA), grader (90 dBA), and front-end loader (82 dBA) are operating concurrently in the same area, peak construction-period noise could be as high as about 94 dBA at 50 feet from a construction site.