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Comparing the Data with the Provisions of the Noise Control Ordinance |
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Prepared by:
Tom Cowan
Tom Stauch
Mike Merino
Denver Environmental Health Department
Environmental Protection Division
605 Bannock St
Denver, CO 80204
Tel: (303) 436-7305
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The Environmental Protection Division of Denver Department of Public Health conducted a community noise survey in the late Spring through the Fall of 1995. The objectives of the survey were to: 1) determine typical noise levels that exist in the types of premises for which Denver's Noise Control Ordinance sets maximum noise limits; 2) use the survey data to evaluate the adequacy of the noise ordinance to abate complaints and prevent further deterioration of the noise environment; 3) establish baseline noise levels at selected locations that could be resurveyed at regular intervals to monitor changes, and 4) develop a Denver noise map.
One hundred seventy eight (178) short-term and 17 long-term sites were used to provide the data necessary to fulfill the survey objectives. The short-term sites were monitored for 20 minutes during the daytime and 10 minutes at night. The long-term sites were monitored for a minimum of 48 hours.
Data supporting L10 and L50 noise descriptors (noise levels exceeded 10% and 50% of the time respectively) was used to evaluate Denver's noise ordinance provisions relating to abatement of complaints and prevention of a deteriorating noise environment.
It was found that average L10 noise levels at short-term residential sites were approximately the same as ordinance standards although some locations were as much as 15 dB(A) below to more than 22 dB(A) above standards. The L50 residential short-term data averaged less than ordinance standards. The wide range of levels found for both the L10 and L50 suggest that a single daytime/nighttime standard may not be appropriate for all residential locations.
The long-term data for residential sites (zoned residential) show both L10 and L50 levels substantially less than ordinance standards. This would indicate the levels of Chapter 36 may be too liberal (high), would not adequately abate complaints, and could allow for deterioration of the noise environment in these residential areas.
Conversely, the long-term data for the residential premises with business zoning show that ordinance levels for this category of residential properties may be too restrictive (low), unrealistic and possibly not readily enforceable.
Similar comparisons of average noise levels in commercial areas showed the L10 levels exceeded ordinance standards while L50 levels were less than ordinance standards. The data indicate that if the maximum allowable noise standard for commercial areas was based on L10 levels, then current standards may be too restrictive and unrealistic. Should the standard be based on L50 levels then the data indicate that current commercial as well as industrial premise noise standards may be too liberal and may not adequately abate complaints nor prevent deterioration of the noise environment.
Since the primary purpose of noise control legislation is to: 1) abate complaints; and 2) prevent areas from becoming any louder, it would follow that a noise standard based on the L50 levels found at the various categories of properties would be appropriate.
A baseline noise level has been established at each short and long-term site so subsequent monitoring may be conducted to describe changes in Denver's noise environment. Additionally, Denver noise maps based on L10,L50, and L90 short term data have been produced.
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In April 1995, Environmental Protection Division.(EPD), Denver Department of Public Health (DDPH) completed a report titled Community Noise Control, City and County of Denver, Proposal for a Baseline Noise Survey and Program/Ordinance Evaluation. The document proposed that a community noise survey (CNS) be conducted in the late Spring through the Fall of 1995. The information and data obtained from the noise survey would aid in examining the adequacy of Denver's Community Noise Program in resolving noise complaints and preventing degradation of Denver's noise environment.
The objectives of the survey were defined and prioritized. They are as follows:
1. Determine the noise levels that currently exist in representative land use categories (premise types) for which Chapter 36 establishes maximum noise levels.
2. Using the data, evaluate the adequacy of noise ordinance requirements to abate complaints and to control, reduce, or prevent further deterioration of Denver's noise environment. Propose ordinance revisions as necessary based on that evaluation.
3. Establish baseline noise levels at selected locations that can be resurveyed at regular intervals to monitor changes in the noise environment.
4. Develop a Denver noise map, preferably using noise contours.
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Two types of noise monitoring sites were selected to fulfill the survey objectives, short-term sites and long term sites. Short term sites were anticipated to show typical daytime and nighttime noise levels at specific locations by short duration grab sampling. The daytime samples were collected by twenty minutes of continuous monitoring and the night time samples were collected by ten minutes of continuous monitoring. The short term sites consisted of 180 addresses systematically selected by computer from the City Tax Assessors data base and comprised 100 residential (R zoned), 30 commercial (B zoned), 30 industrial (I zoned), 10 planned urban development (PUD zoned), and 10 Platte River Valley (PRV zoned) sites. These 180 sites were plotted on the Denver map using EPD's Geographical Information System software, Mapinfo, (Figure 1). The sites on this map were then expanded with a 0.5 mile circle radius to display total coverage of the City. (Figure 2). The final site maps completed at the end of the survey, (Figure 3) include the deletion and addition of monitoring sites as necessitated for reasons to be discussed in "Evaluation of the Data" and "Development of a Noise Map" sections of this report. The total short term sites monitored numbered 178.
Long term (LT) sites were necessary to conduct detailed hour-by-hour noise monitoring at specific locations and were scheduled for a minimum two consecutive 24 hour periods at each location. The hour-by-hour data were used to calculate average levels for daytime and nighttime periods, 24 hour Leqs(average noise level), Ldns(average day night noise level), as well as providing a noise profile at each location including the most quiet and noisy hours, and the effects of rush hour traffic noise. The LT sites were limited to residential use premises, recognizing the fact that more than 98% of the community noise complaints received by EPD are from premises used for residential purposes. Long term sites were not randomly selected and are therefore not necessarily reflective of typical noise environments in residential areas. The LT sites were zoned for residential use, and were specifically selected using the following criteria:
1. Locations with a long history of noise complaints.
2. Locations in lower downtown(LoDo) Denver where new and controversial noise issues are arising from increasing mixed residential and commercial development.
3. Locations where citizens have expressed a particular interest in their neighborhood noise levels and requested to be part of the survey.
4. Locations within some of Denver's quietest neighborhoods.
5. Locations along some of Denver's busiest traffic corridors.
6. Security of the equipment and validity of the noise measurements were of prime concern, hence all of the sites selected were carefully screened to ensure these requirements were satisfied.
A total of 17 sites were selected for long term monitoring.(figure 4)
In addition to the monitoring sites just described, both short term and long term monitoring was conducted, and to some to degree still in progress in two areas scheduled
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for redevelopment. These two areas are Lowry Air Force Base and Stapleton International Airport. (figures 5 and 6). The data from monitoring sites in these areas has not yet been included with the data collected at the other 178 sites and for now is reported on a separate database.
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All of the noise monitoring was accomplished using a Metrosonics db-604 Sound Level Analyzer which employed a one inch B+K condenser microphone. A Quest type CA-12 calibrator with a B+k adapter was used to routinely calibrate the system. At all locations the microphone was adapted with a random incidence corrector and mounted on a tripod which placed the microphone at a height of at least five feet above the ground. The tripod was normally placed at the property line separating the public premise (street or sidewalk) and the monitoring site and at least ten feet from any large reflecting surface (wall, building etc.)
Environmental conditions were noted and evaluated at each site and dictated whether the noise monitoring would be conducted at any particular time and date. No monitoring was conducted if any the following conditions existed:
1. Precipitation sufficient to cause the streets to become wet.
2. Wind speed in excess of ten miles per hour even though a wind screen was always used on the microphone.
3. The presence of any temporary atypical noise source above minimal (L90) levels such as chain saws used in tree trimming operations, or nearby lawn maintenance equipment.
Each of the 178 sites was monitored for twenty minutes during the daytime hours (7:00 AM to 10:00 PM) and for ten minutes during the nighttime hours (10:00 PM to 7:00 AM). These measurements were normally taken within one to three days of each other and all on weekdays. All daytime monitoring was conducted between the hours of 8:48 AM and 3:43 PM with all but 20 sites monitored between 10:00 AM and 3:00 PM. All nighttime monitoring was conducted between 3:57 AM and 6:59 AM with all but two sites monitored between 4:15 AM and 6:45 AM. These time frames were selected in order to avoid measurements during normal rush hour traffic thus maintaining consistency in the measurements by monitoring all sites under similar conditions.
Field forms (figure 7) were used to document each site. Recorded information included the site address, premise type, zoning, date and time of daytime/ nighttime monitoring, wind speed, temperature, ambient noise sources, and a diagram showing the location of the site and the location of the microphone at the site. At each site the following noise levels were recorded: Leq, L10, L50, L90, L99, and Lmax ( discussion on the meaning and significance of these levels is presented in the section titled "COMPARING THE DATA WITH PROVISIONS OF THE NOISE CONTROL ORDINANCE". All noise level data was entered into a Foxpro data base.
The equipment used to conduct the long term monitoring was exactly the same as used for the short term measurements, except that the microphone was protected against wet weather conditions. Additionally, at three locations the random incidence corrected microphone was replaced with the factory standard directional microphone to reduce the effect of unavoidable nearby reflective surfaces.
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Site address: 123 Steele Street
Premise type: Residential
Zoning: R_2
Date(s): 05/15/95 daytime 05/16/95 nighttime
Time (day): 1:20 PM start 1:40 PM end
Time (night): 5:02 AM start 5:12 AM end
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Wind |
<2mph |
Temp low 80's |
precip none |
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3 to 5 mph |
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Noise conditions (barking dogs, const, AC units, etc.)
DAY: local vehicles, distant lawnmower at 100 yds
NIGHT: birds
Diagram of site (mic location, reflective surfaces, etc)
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The tripod mounted microphone was normally positioned in the backyard of these sites. As some of the long term sites were condominiums or lofts in multi-storied buildings, and did not have a backyard or other secure location at ground level, the microphone was positioned on an outside patio, on the roof, or at an open window.
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The Metro sonics db 604 unit was always secured within the residence at the monitoring location.
Environmental conditions at the long term sites obviously could not be continuously evaluated because none of EPD's personnel was on site other than to setup or remove the noise monitoring equipment. This resulted in uninterrupted monitoring even if wet streets, high winds, or temporary loud atypical noise sources existed. However any long term monitoring that occurred when wet streets or high winds existed was minimized by monitoring only when local weather forecasts were favorable. Additionally any data collected during these adverse weather conditions was not used in the calculations included in this report. The presence of any timely atypical loud noise sources was not reported by any of the monitoring location residents. The overall influence of any such short term noise sources on the 24 hour data is believed to be negligible, although the influence on any particular hourly multiple interval could be significant. Only one 24 hour period of long term data was discarded due to rain/wet street conditions and no hourly multiple intervals were deleted.
The sound level analyzer was normally activated or pre-programmed to start monitoring at 7:00 am and terminate at 7:00 am, 48 to 72 hours later. The programming included data collection and storage at one hour multiple intervals and a measuring/display range of approximately 25.9 to 122.3 db.
The data collected and then uploaded to EPD's computer network was extensive. Included in the data were the Lavg, L10, L50, L90, L99, L95, L0, Lmax for each one hour interval as well as for the total monitoring time. The amplitude distribution for the total number of samples was graphically displayed and 24 hour (1 day) periods were described by the Lavg, Lmax, Ldn, and CNEL (community noise equivalent level).
The short and long term data were analyzed separately. Although the short term sites were selected on the basis of zoning from the City Tax assessors records, they were categorized primarily on the basis of premise use. This resulted in a difference between the numbers and categories of sites initially selected and what is reported in the data summaries (figure 8). For example, a visit to a commercially zoned site (designated B, for business) often revealed that it was in reality a condominium and hence was categorized as a residential premise. Similar situations occurred when a visit to an industrially (I) zoned site revealed that an occupied house existed at that address which then was also categorized as residential. Visits to PUD and PRV zoned sites showed some use as only vacant land and the remainder used as residential, commercial or industrial. These sites were categorized accordingly and used in the analyses for their respective premise categories. However, the sites that were vacant land were used only in determining the various levels for the (ALL) premise category in figure 8.
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Noise Monitoring Analysis
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L10D |
L10N |
L50D |
L50N |
L90D |
L90N |
LeqD |
LeqN |
|
RES1 |
NUMBER |
113 |
113 |
113 |
113 |
113 |
113 |
113 |
113 |
|
|
RANGE |
40-70 |
42-74 |
37-72 |
37-67 |
35-64 |
36-58 |
39-74 |
42-70 |
|
|
MEDIAN |
55.0 |
51.0 |
46.0 |
46.0 |
43.0 |
44 |
53.2 |
50.4 |
|
|
MEAN |
56.1 |
52.0 |
48.0 |
47.1 |
43.8 |
44.9 |
55 |
51.4 |
|
|
STD DEV |
7.6 |
5.8 |
7.0 |
4.9 |
5.7 |
4.5 |
6.4 |
5.4 |
|
|
95% CONF INT |
54.7-57.5 |
50.9-53.1 |
46.7-49.3 |
46.2-48.0 |
42.8-44.9 |
44.1-45.7 |
53.8-56.2 |
50.5-52.5 |
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RES 2 |
NUMBER |
101 |
101 |
101 |
101 |
101 |
101 |
101 |
101 |
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|
RANGE |
40-77 |
42-74 |
37-72 |
37-67 |
35-64 |
36-58 |
40-75 |
42-70 |
|
|
MEDIAN |
54 |
51 |
46 |
46 |
43 |
44 |
53.1 |
50.4 |
|
|
MEAN |
55.7 |
51.9 |
47.5 |
46.9 |
43.4 |
44.7 |
54.8 |
51.3 |
|
|
STD DEV |
7.4 |
5.8 |
6.7 |
4.9 |
5.4 |
4.5 |
6.2 |
5.4 |
|
|
95% CONF INT |
54.2-57.1 |
50.8-53.0 |
46.2-48.8 |
45.9-47.8 |
42.3-44.4 |
43.8-45.6 |
53.5-56.0 |
50.3-52.3 |
|
RES 3 |
NUMBER |
12 |
12 |
12 |
12 |
12 |
12 |
12 |
12 |
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|
RANGE |
45-72 |
44-61 |
39-66 |
41-56 |
36-59 |
38-56 |
45-69 |
42-61 |
|
|
MEDIAN |
59.5 |
52.5 |
50.5 |
48 |
47 |
46.5 |
56.7 |
51.4 |
|
|
MEAN |
59.5 |
52.5 |
51.5 |
48.9 |
47.6 |
46.1 |
57.3 |
52.6 |
|
|
STD DEV |
8.5 |
5 |
8.3 |
4.9 |
7 |
4.6 |
7.9 |
5.8 |
|
|
95% CONF INT |
54.1-64.9 |
49.0-56.0 |
46.3-56.8 |
45.8-52.0 |
43.1-52.0 |
43.2-49.0 |
52.2-62.3 |
48.9-56.2 |
|
COM |
NUMBER |
29 |
29 |
29 |
29 |
29 |
29 |
29 |
29 |
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|
RANGE |
59-74 |
44-70 |
50-68 |
41-65 |
46-66 |
38-64 |
58-72 |
43-68 |
|
|
MEDIAN |
69 |
64 |
62 |
57 |
57 |
51 |
66.8 |
61.8 |
|
|
MEAN |
68.3 |
62.7 |
61.6 |
54.4 |
56.5 |
50.4 |
66.2 |
60.5 |
|
|
STD DEV |
3.7 |
6 |
5 |
5.4 |
5.1 |
5.6 |
3.7 |
5.3 |
|
|
95% CONF INT |
66.9-69.7 |
60.4-65.0 |
59.7-63.5 |
52.3-56.4 |
54.5-58.4 |
48.3-52.5 |
64.8-67.8 |
58.5-62.6 |
|
IND 1 |
NUMBER |
26 |
26 |
26 |
26 |
26 |
26 |
26 |
26 |
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|
RANGE |
49-76 |
48-71 |
44-70 |
46-65 |
42-63 |
45-59 |
49-76 |
48-67 |
|
|
MEDIAN |
62 |
58 |
55.5 |
55 |
52.5 |
52.5 |
62 |
59.4 |
|
|
MEAN |
62.8 |
58.6 |
56 |
53.6 |
52.2 |
51.6 |
61.6 |
57.6 |
|
|
STD DEV |
6.9 |
6.8 |
6.8 |
5.2 |
5.8 |
4.8 |
6.5 |
6 |
|
|
95% CONF INT |
60.0-65.6 |
55.8-61.4 |
53.2-58.7 |
51.5-55.7 |
49.9-54.6 |
49.6-53.5 |
59.0-64.2 |
55.3-60.1 |
|
ALL |
NUMBER |
177 |
177 |
177 |
177 |
177 |
177 |
177 |
177 |
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|
RANGE |
40-77 |
42-74 |
37-72 |
37-67 |
35-66 |
36-64 |
40-76 |
42-70 |
|
|
MEDIAN |
59 |
54 |
50 |
48 |
46 |
46 |
57.9 |
53 |
|
|
MEAN |
59.4 |
55 |
51.7 |
49.5 |
47.4 |
47 |
58.2 |
54 |
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STD DEV |
8.3 |
7.2 |
8.5 |
5.9 |
7.5 |
5.5 |
7.4 |
6.5 |
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|
95% CONF INT |
58.1-60.6 |
53.9-56.0 |
50.4-52.9 |
48.6-50.4 |
46.3-48.6 |
46.2-47.8 |
57.1-59.3 |
53.1-55.0 |
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RES T |
NUMBER |
11 |
11 |
11 |
11 |
11 |
11 |
11 |
11 |
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RANGE |
67-77 |
49-74 |
46-72 |
41-67 |
43-64 |
38-58 |
62-74 |
49-70 |
|
|
MEDIAN |
69 |
61 |
62 |
53 |
57 |
46 |
66.4 |
61 |
|
|
MEAN |
70.9 |
61.7 |
61.4 |
52.9 |
54.2 |
48 |
67.4 |
60.7 |
|
|
STD DEV |
3.5 |
7.1 |
7.5 |
7.6 |
7.2 |
6.2 |
4.1 |
5.6 |
|
|
95% CONF INT |
68.5-73.2 |
57.0-66.5 |
56.4-66.5 |
47.8-58.0 |
49.3-58.9 |
43.8-52.1 |
64.6-70.1 |
57.0-64.5 |
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The data for the short term sites (figure 8) were divided into the following categories:
Res 1= all premises used as residential with no reference to zoning.
Res 2= all premises used as residential and zoned Residential(R)
Res 3= all premises used as residential and not zoned R
Res T= residential sites where heavy motor vehicle traffic was the predominant noise source. An example of such a site is 1700 Colorado Blvd.
Com= all commercial use premises zoned B, PRV, or PUD (Business, Platte River Valley, or Planned Urban Development)
Ind= all industrial use sites zoned Industrial(I)
All= all sites
The data collected was used to calculate the range, average and median noise levels for daytime and night time L10, L50, L90, and Leq.
Residential noise levels
There were 113 Res 1 sites which included residential sites with R, B, PUD, and I zoning. It was important to make this category because Denver's noise ordinance addresses individual properties by use and not by zoning. The categories Res 2 (101 sites) and res 3 (12 sites) are intended to show differences between all residential use (regardless of zoning), pure residential zoned R, and all residential not zoned R.(figure 9)
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Commercial and industrial noise levels
There were 29 commercial (Com) sites and 26 Industrial (Ind) sites.
The data for the long term sites (figure 10) were divided into the following categories:
RES R = residential premises zoned R
RES B = residential premises zoned B or zoned R-3 and surrounded by commercial premises.
RES R sites were all single family houses located in a variety of neighborhoods. RES B sites were all multifamily, multistory dwelling units located in downtown Denver, except for one site that was located near the Cherry Creek Shopping district.
The data show the daytime and night time L10, L50, and L90 levels for the different categories of premises for which Chapter 36 sets maximum noise levels. At any particular monitoring site, short term or long term, the sound level fluctuated over the monitoring time period. There are several descriptors commonly used to quantify and give some meaning to fluctuating noise levels. For the purposes of defining the common noise descriptors of L10, L50, L90, L99, Lmax, and Leq, assume that figure 11 is a graphical representation of the fluctuating noise levels measured at a short term, nighttime residential site for a total of ten minutes duration. The horizontal line drawn near the top of this graph intersects the loudest portions of the fluctuating noise that occurred for one minute of the monitoring time (ten percent of the time). This line
LONG TERM SITES
all noise levels in dBA
|
Premise |
D # |
N # |
L10D |
L10N |
L50D |
L50N |
L90D |
L90N |
|
RES R RNG |
385 |
225 |
39-70 |
34-63 |
35-59 |
31-53 |
31-56 |
30-51 |
|
AVG |
385 |
225 |
49.53 |
43.68 |
43.88 |
40.17 |
41.12 |
37.87 |
|
MED |
385 |
225 |
49 |
44 |
44 |
40 |
41 |
38 |
|
RES B RNG |
228 |
134 |
53-73 |
48-68 |
50-70 |
47-65 |
48-69 |
45-63 |
|
AVG |
228 |
134 |
62.52 |
58.21 |
59.46 |
55.44 |
57.72 |
53.59 |
|
MED |
228 |
134 |
63 |
58 |
60 |
55 |
59 |
53 |
RES R = residential premises zoned R
RES B = residential premises zoned B or zoned R-3 and surrounded by commercial premises.
AVG= mathematical average of numbers, not energy levels
# = the number of hourly samples
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coincides with 58 dB(A) and represents the noise level exceeded ten percent of the time at this monitoring site for this time period (L10). The L10 commonly represents the loudest portions of transient noises (nearby passing motor vehicles, aircraft, etc.) The horizontal line in the middle of the graph identifies the noise level which was exceeded fifty percent of the time (L50) or five minutes (50%) of the monitoring time. The L50 noise of 52 dB(A) approximates the median noise level at this site (half of the time it was 52 dB(A) or louder and half the time it was less than 52 dB(A). The L90, which is 46 dB(A) is the level exceeded 90 percent of the time and is often referred to as the residual (background) noise levels. The L99, not drawn on this graph, indicates the minimum noise levels. The Leq (equivalent) is an energy-average quantity. It is defined as the single sound pressure level that contains the same sound energy as the fluctuating sound during the measurement period. The Leq is the descriptor of choice by the Federal Highway Administration for traffic sources in environmental noise assessments and at most community noise monitoring sites it is normally within 3 dB(A) of the L10. The Lmax, which is 68 dB(A), is the loudest noise measured at this site during this time period.
The amplitude (minimum to maximum decibel levels) and frequency (number of fluctuations in the monitoring period) varied from site to site. Observations made during the noise survey establish the fact that motor vehicles are generally responsible for the fluctuations.
The following discussion evaluates the adequacy of the ordinance to: 1) abate complaints and 2) prevent further deterioration of the noise environment.
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A community noise survey similar to the Denver survey was conducted in Vancouver, British Columbia in the early 1970's. (1) The report stated that the primary purpose of a community noise survey is to establish certain criteria for use in future community noise legislation. It further stated that the usefulness of any such legislation which is not based on data obtained from a survey of this kind is highly questionable since it would be extremely difficult to specify maximum allowable noise levels which are either too high or too low. If these levels were too low, then unrealistic restrictions may be imposed upon various sections of the community. Additionally, the legislation may not readily enforceable. On the other hand, if the specified levels were too high, then the noise environment would probably deteriorate and become louder.
In deciding what maximum daytime and nighttime noise levels are to be allowed for the types of premises regulated by Chapter 36, several factors such as economic impact vs. community benefit, enforcement problems, and the desires of the community must be considered. However, since the survey showed that motor vehicle traffic is the major noise source in Denver, (as it probably is in most communities), community noise levels may best be controlled by reducing both traffic noise at its source (such as requiring manufacturers to make quieter vehicles) and making acoustical considerations in the design and positioning of busy streets and highways (such as making noise barriers part of the design and positioning busy streets and highways far from residential areas). Unfortunately, this responsibility normally lies with Federal and State agencies and Denver's role in these areas may be limited. Denver's ordinance currently controls motor vehicle noise by limiting noise from individual motor vehicles. The ordinance limits are 80 dB(A) for vehicles weighing less than 10,000 lb. and 88 dB(A) for vehicles weighing more than 10,000 lb.. There are no ordinance limits for the total noise emitted by motor vehicle traffic on any particular street or highway however.
Denver can, however, limit noise from a variety of individual sources, both stationary and mobile, and it has been suggested (Vancouver noise survey report) that it is both economically practical and beneficial to the community to adopt legislation that regulates non-motor vehicle sources exceeding the L10 in a community. It was also suggested that the ultimate goal should be to regulate non-motor vehicle noise sources exceeding the L50 within 5-10 years of the initial legislation. A comparison of the L10 and L50 levels found in the Denver Noise Survey to Denver's current noise limits is discussed below:
L10 DATA
The short term data show that the mean and median L10 levels (both L10D (Day) and L10N (Night) for all the Res 1 sites (residential premises regardless of zoning) approximate 55 dB(A) for daytime and 50 dB(A) for nighttime. These levels coincide with the current ordinance standards. However, considering the range of L10s for different locations we see that some locations are as much as 15 dB(A) below the current daytime standard to more than 22 dB(A) above it. Daytime/nighttime standards of 55/50 are probably not appropriate for all residential locations.
---------------
1. Price, A.J. community Noise Survey of Greater Vancouver" JASA 52,2 (part 1) 1972
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The L10 levels for the Res 2 category sites (zoned Residential(R)) are similar to the RES 1 site data. The L10 levels in the Res 3 category sites (residential not zoned R) are understandably higher (louder) than those of Res 1 and Res 2 sites because they were mostly located in commercial areas having more motor vehicle activity.
The long term data show mean and median L10 levels for the Residential (R) zoned properties are in the 49/44 day/night range and substantially less (quieter) than current ordinance standards. This would indicate that the levels of Chapter 36 may be too liberal (high), would not adequately abate complaints, and could allow for deterioration of the noise environment in these residential areas.
Conversely, the long term data for the Res B (Business zoned properties allowing residential use), show that 63/58 dB(A) are typical day/night L10 levels. Here it would appear that current ordinance levels for residential properties are too restrictive (low), unrealistic and not readily enforceable.
Similar comparisons made with data showing L10 levels in commercial and industrial areas indicate that current ordinance levels may not be appropriate for these categories. For example, average L10 levels in commercial areas (68/63 D/N) were louder than ordinance standards and actually louder than average L10 levels in industrial areas (63/59 D/N). Normally, higher noise levels would be expected in industrial areas where maximum allowable noise levels by ordinance are also higher (80/75 D/N). At virtually all commercial and industrial sites the dominant noise source was motor vehicles; the louder L10 levels at commercial sites can be attributed to normally greater motor vehicle activity in these areas. The data indicate that if the maximum allowable noise standard was based on L10 then commercial standards may be too restrictive and unrealistic. Industrial premise noise standards, on the other hand, may be too liberal and not adequately abate complaints nor prevent deterioration of the noise environment.
L50 DATA
The short term data show that the mean L50 levels (both L50D (Day) and L50N (Night)) for all the Res 1 sites (residential premises regardless of zoning) were 48 dB(A) for daytime and 47 dB(A) for nighttime. The median L50 was 46 dB(A) for both day and night. These levels are below the current ordinance standards. Considering the range of L50s for different locations, some locations are as much as 18 dB(A) below the current daytime standard to as much as 22 dB(A) above it which indicates that one Daytime/nighttime standard may not be appropriate for all residential locations.
The L50 levels for the Res 2 category sites (zoned Residential(R)) are similar to the RES 1 site data. The L50 levels in the Res 3 category sites (residential not zoned R) were understandably higher (louder) than those of Res 1 and Res 2 sites, mainly due to commercial locations and associated motor vehicle activity.
The long term data show mean and median L50 levels for the residential (R) zoned properties are in the 44/40 day/night range and substantially less (quieter) than current ordinance standards. This would indicate that the levels of Chapter 36 may be too liberal, would not adequately abate complaints, and could allow for deterioration of the noise environment in these residential areas.
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Conversely, the long term data for the Res B (Business zoned properties allowing residential use), show that 60/55 dB(A) are typical day/night L50 levels. Here it would appear that current ordinance levels for residential properties are too restrictive, unrealistic and not readily enforceable.
Similar comparisons made with data showing L50 levels in commercial and industrial areas indicate that current ordinance levels may not be appropriate for these categories. For example, average L50 levels in commercial areas (62/54 D/N) were louder than ordinance standards and actually louder than average L50 levels in industrial areas (56/54 D/N). Normally, higher noise levels would be expected in industrial areas where maximum allowable noise levels by ordinance are also higher (80/75 D/N). At virtually all commercial and industrial sites the dominant noise source was motor vehicles and the louder L50 levels at commercial sites can be attributed to normally greater motor vehicle activity in these areas. The data indicate that if the maximum allowable noise standard was based on L50 then commercial as well as industrial standards may be too liberal and would not adequately abate complaints nor prevent deterioration of the noise environment.
The above discussion points out some ways that the Community Noise Survey data can be utilized to examine the appropriateness and feasibility of establishing maximum allowable noise levels for various premises.
There are also human based considerations such as tolerance and acceptance, perception, aesthetic values and the community's desire to preserve or improve the noise environment in Denver. These values must be balanced with practicality, feasibility, enforceability and cost considerations.
These as well as additional issues were considered in this Division's analyses of Noise Control Ordinance provisions. The issues are discussed below in an issues-discussion-options format.
Denver's Community Noise Ordinance is as comprehensive and, in many areas, more restrictive than those of many other U.S. cities. Although it has been an effective tool in controlling community noise for more than 20 years, there are some Denver residents who question whether Chapter 36 is comprehensive and restrictive enough. Clearly, there are some Denver residents, as well as some Denver business owners, who believe Chapter 36 is too restrictive and in some aspects unfair. Analysis of the data obtained from the baseline community noise survey could provide some of the information and insight necessary to evaluate the ordinance. This analysis will be useful in any revision of the provisions of Chapter 36.
Below are some issues/topics that should be addressed in any discussion of noise ordinance revisions. If revisions are made, it is important to keep in mind that the ordinance should be kept as straight foreword, simple and workable as possible. This minimizes enforcement time and cost. More complicated ordinances require more expensive and sophisticated noise monitoring equipment, create more room for error, and violations may be more difficult to prove in court.
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I. HOUSEKEEPING ISSUES (Issues which EPD believes are necessary revisions to the noise ordinance and which may not be very controversial.)
1) Should the ordinance be revised to clearly specify permissible levels with reference to both the source and the receiving premises and clearly specify where the noise measurements are taken?
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ISSUE |
DISCUSSION |
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1) Revisions to Table A (Source premise, receiving premise, crossing property lines). 36-6 |
The requirements of Section 36-6 and Table A which describes where noise is emitted, received, and measured, is frequently misinterpreted and questioned by the regulated community as well as the noise complainant. Revising the Table to clearly specify permissible levels with reference to both the source premise and the receiving premise, and clearly specify where the noise measurements are conducted would eliminate misinterpretation. |
2) Should the barking dog noise from commercial kennels be considered a noise source subject to the property line noise limits of Chapter 36?
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2) DOG BARKING NOISE 36-10 |
Noise from individual barking dogs is covered under the Animal Control Ordinance. However, aggregate barking dog noise from commercial dog kennels could be considered a noise source subject to property line noise limits of Chapter 36. |
3) Should the ordinance be revised to contain alternative noise standards for emergency power generators?
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3) EMERGENCY POWER GENERATORS 36-2 and 36-6 |
Emergency power generators which are installed as backup power supplies at hospitals, nursing and retirement homes, office buildings, etc. have been the cause of numerous noise complaints. Although they can be quite loud (greater than 80 dB(A) at 25 feet) they only operate in emergency situations when normal electric service is interrupted and during scheduled routine testing periods. Because of their infrequent use and the great expense normally incurred to attenuate these noise sources, perhaps they should be exempt from property line noise limits during emergency operation. They could also be limited to 88 dB(A) during the routine testing period which could be restricted (Time of day, length of test, frequency of tests). This exemption should only apply to those generators that are used to provide emergency power in emergency situations or as required by the Denver Fire Dept. Generators not used for these purposes should still be required to meet the property line noise limits of Table A. |
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4) Should train noise be regulated by the noise ordinance?
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4) RAILROAD NOISE 36-6(b) |
Chapter 36 does not address noise from trains. With more new residential development along the railroad right of way in LoDo, train noise has become an issue. However, train noise comes under the jurisdiction of Federal Regulation CFR 40-205, which may supersede Chapter 36 and therefore be exempt from local regulation. |
5) Should rules and regulations be written pursuant to the noise ordinance?
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5) RULES AND REGULATIONS |
There are currently no rules and regulations for implementing the provisions of Chapter 36 and there have been questions as to the meaning of some ordinance requirements. There are frequent question about the definition of "any noise" (Sect. 36-6(a)) in relation to Table A. Does it mean any noise, even one second in duration during a 24 hour period, or is some other frequency and/or duration intended? Determining violations of this standard has always been at the judgment of the noise investigator. Rules and regulations may be the logical place for technical specifics such as the number of times or the percentage of time a noise exceeded the limit within a specified time period, time given for compliance relative to the exceedance of limits, and different measurement criteria relative to the nature of the noise (continuous, fluctuating, intermittent, impact, and frequency components). |
II. TECHNICAL (controversial issues where a community consensus can probably be reached)
1) Should background sound level in the Denver Noise Ordinance be defined as the residual sound level (L90)?
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ISSUE |
DISCUSSION |
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1) Background sound level 36-2 and 36-6 |
The noise ordinance does not define background sound level. This term should be added to the definitions. Background levels must always be taken into consideration when establishing a violation of noise standards. Noise ordinance standards could be revised so that violations would be based on exceedance of background sound levels. Background sound may be defined in several ways. The definition from the Illinois Environmental Protection Act defines background sound as the sound level which is exceeded 90 percent (L90) of the time during the period of observation during which the noise source in question is inaudible. EPD has been determining background sound levels for the past 23 years in a manner which may approximate L90. Another common definition of background sound level is the total sound pressure level in the area of interest excluding the noise source of interest (Leq). The difference between these two definitions can be quite significant. For example, in a typical quiet neighborhood the L90 may be 40 dB(A) whereas the Leq may be in the upper 50 dB(A) range. |
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2) Should the noise ordinance address noise within buildings or should it pertain only to "community noise" traveling between separate parcels of land?
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2) Definition of property line 36-2 |
The Chapter 36 definition of property line implies real property and separate parcels. Although the current definition implies and has been interpreted not to include walls, floors or ceilings of any residential unit within an apartment or condominium building, or complex. If that is the intent, then it needs to be clearly stated. Within building or condominium complexes where no clear property lines exist, ventilation noise, loud music or other amplified sound are common complaints. Historically it was never the intent of Denver's community noise ordinance to control noises within apartment buildings and condominiums. It may be more practical in these types of residential settings for noise complaints to be addressed and abated by the landlord and/or homeowners associations through enforcement of lease agreements and covenants specifically designed to control such noises. Complainants would still have the option to request the Denver Police Department to investigate disturbances and complaints of loud music. |
3) Should there be tighter restrictions on construction noise during the weekends (e.g., fewer hours of exemptions than during the weekdays.
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3) WEEKEND CONSTRUCTION NOISE 36-6(b) |
Denver's noise ordinance currently exempts noise from construction equipment from 7:00 am to 10:00 PM seven days a week. This allows uncontrolled noise from construction equipment any time after 7:00 a.m. on Saturdays and Sundays. Limiting the hours of the weekend days when construction noise is exempt would provide for additional and more appropriate hours of quiet time for citizens weekend sleep habits and lifestyles. |
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4) Should the ordinance completely exempt construction noise from maximum daytime noise limits.
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4) EXTREMELY LOUD CONSTRUCTION NOISE |
Any noise emitted from construction equipment is currently exempt from ordinance limits during the daytime hours. should there be some limit(s) for daytime construction equipment noise? For example, unlimited construction equipment noise creates the potential for nearby persons (other than construction employees)to be exposed to noise levels which could be detrimental to their hearing. Revising the ordinance to prohibit noise in excess of OSHA ceiling limits dB(A) in areas accessible to the public, (some high noise level areas may need to be cordoned off) may minimize this potential hearing hazard |
5) Should there be alternative noise standards for snow removal equipment operated during the nighttime hours?
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5) SNOW REMOVAL EQUIPMENT 36-2 and 36-6 |
The noise emitted from snow removal equipment generates only an occasional complaint. However, strictly speaking the noise limits of Chapter 36 may prohibit snow removal activities during the nighttime hours by limiting this equipment to 50 dB(A) at any residential property lines. Snow removal and safety issues may take precedence over the noise ordinance, therefore perhaps some special provisions for noise from snow removal equipment should be written into the ordinance. |
6) Should the prohibition against nighttime trash collection activities next to or across the street or alley from a residential premises be expanded by adding a specific distance limitation from residential premises as well?
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6) NIGHTTIME TRASH COLLECTION 36-7 |
Section 36-7 prohibits nighttime trash collection if it occurs next to or across the street or alley from a residential premise. There can be situations when the proximity of the residential premise to the location of the trash collection may not satisfy these requirements but still be close enough to be disturbed by noise from trash collection activities. By adding a distance limitation, for example 400 feet, additional residential properties would be protected. The straight line distance requirement would be measured from the trash truck to the property line of residential use premise. |
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7) Should the noise from heavy trucks be restricted below daytime levels during the nighttime hours in defined residential areas?
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7) HEAVY VEHICLE NOISE 36-8 |
The language of section 36-8 that limits the noise from motor vehicles weighing more than 10,000 lb. during the nighttime hours is confusing and could be interpreted in several ways. The ordinance says that during the night time hours, heavy trucks are limited to 80 dB(A) on streets or premises not permitting heavy vehicle traffic and 88 dB(A) on streets and highways designated for heavy vehicle traffic (same as daytime limits). The intent of the ordinance is to limit nighttime heavy truck noise in residential neighborhoods, but compliance is difficult to determine because there is no clear definition of what is meant by streets or premises not permitting heavy vehicle traffic. Streets with no posted weight limits or RTD bus routes or premises such as grocery store parking lots, concrete batch plants or other heavy industry could be considered as designated for heavy vehicle traffic. Streets with less than 10,000 lb. weight limits or residential premises could be considered as not designated for heavy vehicle traffic. In practice, there are many areas where it is unclear (to regulated community as well as the Division) whether or not heavy vehicles are permitted. Two things may be needed: 1) a map of the City clearly indicating what streets are affected; and 2) a definition of what "not permitting heavy vehicle traffic" means. In any case, input from the community in making the determination of where heavy vehicle noise should be restricted at night would be useful. |
III. CONTENTIOUS ISSUES (Issues where a community consensus probably cannot be reached.)
1) Should Table A (Maximum Allowable Noise Levels) be revised:
a) Should the maximum allowable levels set forth in Table A be left as is?
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ISSUE |
DISCUSSION |
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1) REVISIONS TO TABLE A, RELATING TO MAXIMUM ALLOWABLE NOISE LEVELS 36-6 |
Evaluation of the data from the 1995 Denver Community Noise survey shows that the maximum allowable property line levels in Table A may need to be revised. Following is a discussion of some issues: Issue a. CURRENT TABLE A 36-6: The levels in the current ordinance have been in effect since 1972, they are easy to understand, widely known by the public and, until the last few years have been relatively easy to enforce. We could leave these levels unchanged. |
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b) Should the maximum allowable noise levels infringing on various specified premises be based on the use of the receiving premises (as currently written) or should maximum levels be set according to the zoning of the receiving premises? Should there be alternative noise standards and categories for residential premises within or adjacent to industrially or commercially zoned areas?
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1) REVISIONS TO TABLE A, RELATING TO MAXIMUM ALLOWABLE NOISE LEVELS 36-6 |
Issue b. Premise use versus premise zoning 36-6: Denver's ordinance sets maximum levels for noise that may infringe upon specific types of premises (residential, commercial, industrial, public) as defined by the use of the premise with no regard to the zoning. For example, the present ordinance requires industrial or commercial facilities to comply with residential noise standards for isolated pockets of residential use (or even single residences) even though the residential premises and all surrounding premises are zoned industrial or commercial. This has created enforcement problems and has been a very contentious issue. Creating new and more appropriate noise standards and categories for residential premises, not zoned residential, within industrially or commercially zoned areas of the City may provide for a more equitable resolution of complaints in these circumstances. Noise infringing between premises within mixed use PUDs should probably be considered at the time of the establishment of the PUD zone. In these cases it may be appropriate to apply the use of the premises as the limiting criteria in determining maximum allowable noise levels. An alternative may be to tie allowable noise levels strictly to zoning as has been done in some cities. |
c) Should the ordinance be revised to establish lower maximum allowable property line noise limits in quiet residential neighborhoods.
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1) REVISIONS TO TABLE A, RELATING TO MAXIMUM ALLOWABLE NOISE LEVELS 36-6 |
Issue c. QUIET RESIDENTIAL AREAS 36-6: The noise limits crossing residential property lines are currently 55 dB(A) for day time hours and 50 dB(A) for night time hours. The data from the 1995 noise survey shows that there are many residential areas where the daytime and nighttime background sound (L90) can often be in the low to mid thirties. The issue of maintaining desirable low noise levels in these areas, by establishing more restrictive residential standards, could be addressed. A noise source operating at the legal nighttime limit of fifty dB(A) in one of these quiet areas will be perceived by the listener as being two to three times louder than the background noise and a significant noise disturbance. Restricting the nighttime limit to 40 dB(A), for example, would minimize some of the nighttime noise disturbances in Denver's quiet residential areas. |
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d) Should the Denver Noise Ordinance specify maximum allowable noise levels as some specified exceedance of the background sound level, as opposed to set noise levels for various premises (residential, commercial, industrial, public) as is the case in the current ordinance?
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1) REVISIONS TO TABLE A, RELATING TO MAXIMUM ALLOWABLE NOISE LEVELS 36-6 |
Issue d. Defining maximum noise levels in terms of EXCEEDANCE of the L90 (background) 36-6: If we define L90 as background, as previously discussed, we could prevent further degradation of the noise environments in variously impacted neighborhoods. The concept would be to create a standard that limits the intrusive noise to a specified dB(A) level above the background(L90). A property line limit of three to five dB(A) above the L90, for instance, would serve to prevent further degradation of the local noise environment from stationary sources. For example, if the nighttime L90 in a quiet neighborhood was 35 dB(A), any particular noise source could be limited to 38 to 40 dB(A), which is lower than the current 50 dB(A) requirement. In noisy areas where the background may already be above the current residential limits, the current noise limits may be inappropriate. Application of the background-based concept would provide for a more reasonable noise limit for these locations and still prevent further degradation of the noise environment. This type of standard could be more difficult and cumbersome to enforce because the L90 would have to be determined at each location in a consistent and established manner. |
2) Should the ordinance provide for permits to exceed maximum allowable noise levels set forth in Table A?
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2) NOISE PERMITS 36-6(b) |
This office receives numerous requests for "noise permits". EPD does not issue noise permits nor was it the intent of Chapter 36 that such permits be issued. A provision currently exists in Chapter 36 which exempts temporary events such as concerts, sporting events, parades, etc. from noise ordinance requirements if they are "permitted" by the City. The problem is the language of Chapter 36 describing the "City permit" exemption, is not clear and needs revision to eliminate the ambiguity. A suggested rewording is: Any activities which are permitted by law and for which an event-specific temporary license or permit has been granted by (list of appropriate agencies) including, but not limited to parades, sporting events, concerts and fireworks displays. Then, the City agency issuing the permit, which is most familiar with the particulars of the event, could reduce adverse noise impacts resulting from such activity/event by imposing decibel or time limits, or other noise control measures as part of the permit. Another option could be to provide for EPD to issue permits, with conditions, allowing exceedance of the limits of the noise ordinance for temporary events or nighttime construction activities. Conditions limiting and restricting these events or activities could be made enforceable parts of any permits. (There are currently appeal and variance provisions in Chapter 24 of the RMC which allow the Board of Health and Hospitals to authorize variances from the terms of any ordinance enforced by the Department of Health and Hospitals, however this is a cumbersome, time consuming process and may not be workable because the Board only meets once a month.) |
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3) Should developers be required to submit environmental noise impact statements for future projects in Denver?
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3) ENVIRONMENTAL NOISE IMPACT STATEMENTS |
It may be desirable to consider the noise impact of new development on existing neighborhoods in order to prevent or limit degradation of the noise environment. With the pending redevelopment of former Stapleton Airport and Lowry Air Force Base as well as residential development in formerly mostly commercial areas in lower downtown, and infill development in residential neighborhoods, many changes in local noise environments can be expected. Developers could be required to submit environmental noise impact statements for development or redevelopment projects. Effected communities and regulatory agencies could review these impact statements and mitigation plans could be developed for stationary as well as mobile noise sources. Mitigation plans could include abatement/reduction of construction noise, street design, routing traffic away from residential areas, selection and placement of noise emitting mechanical equipment, provision of sound reducing construction materials and techniques to existing and/or new residences, and spacing and arrangement of buildings. Stakeholder input would be useful if provisions are to be made in the noise ordinance (or in Planning/Zoning Ordinances) requiring environmental noise impact statements and noise mitigation plans. We have not been able to find such provisions in other cities, so we have little to use as a paradigm. |
4) Should a mostly commercial building be defined as a residential premise if more than 25% of the gross floor area is used for dwelling units?
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4) Definition of Residential premise in mixed use buildings 36-2(24) |
Currently, if the gross floor area of a mixed use building (e.g., commercial building with some residential units)is at least 25% residential, the entire building is considered residential and entitled to the noise limits for residential premises. This "25% requirement" has been the subject of many complaints from owners of noise sources that may be required to provide noise attenuation to residential levels in a commercial or industrial area. A gross floor area requirement of more than 50% (for example) may be more equitable |
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DEVELOPMENT OF A DENVER NOISE MAP
All the data collected at the short term monitoring sites were used to develop a noise map for the City and County of Denver. Of the 180 sites initially selected to monitor noise levels of the entire City, several sites were eliminated because they were either in accessible, could not be located, or were within close proximity to other sites of the same category. Several sites were added to replace the deleted ones and were chosen to fill in the areas of the Denver map (blank spots in figure 2) where no noise monitoring was conducted.
Noise maps based on average day\night L10 levels, average day/night L50 levels, L90 day levels and L90 night levels have been developed.(figures 12, 13, 14, 15)
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