1 - Introduction 2 - Vision Statement 3 - Land Use 4 - Circulation 5 - Conservation 6 - Noise 7 - Safety 8 - Recreation 9 - Historical 10 - Community Design 11 - Glossary - Maps CHAPTER SIX NOISE ELEMENT Introduction The Noise Element is a mandatory General Plan element. The Noise Element identifies and appraises noise problems and forms a basis for land use distribution. The State Office of Planning and Research Noise Element Guidelines require that major noise sources be identified and quantified by preparing generalized noise contours for current and projected conditions. Significant noise sources include traffic on major roadways and highways, railroad operations, airports, and representative industrial activities and fixed noise sources. Noise is often defined simply as unwanted sound, and thus is a subjective reaction to characteristics of a physical phenomenon. Researchers for many years have grappled with the problem of translating objective measurements of sound into directly correlated measures of public reaction to noise. The descriptors of community noise in current use are the results of these efforts, and represent simplified, practical measurement tools to gauge community response. Definitions A-Weighted Sound Level (dB): The sound pressure level obtained by using the A-weighting filter of a sound level meter, expressed in decibels (dB). All sound levels referred to in this policy document are in A-weighted decibels. A-weighting de-emphasizes the very low and very high frequencies of sound in a manner similar to the human ear. Most community noise standards utilize A-weighting, as it provides a high degree of correlation with human annoyance and health effects. Community Noise Equivalent Level (CNEL): The equivalent energy (or energy average) sound level during a 24-hour day, obtained after addition of approximately five decibels to sound levels in the evening from 7:00 p.m. to 10:00 p.m. and ten decibels to sound levels in the night before 7:00 a.m. and after 10:00 p.m. The CNEL is generally computed for annual average conditions. Day/Night Average Sound Level (Ldn): The equivalent energy (or energy average) sound level during a 24-hour day, obtained after addition of ten decibels to sound levels in the night after 10:00 p.m. and before 7:00 a.m. The Ldn is generally computed for annual average conditions. Equivalent Sound Level (Leq): The sound level containing the same total energy as a time varying signal over a given sample period. Thus, the Leq is a single value that expresses the time-averaged total energy of a fluctuating sound level. The Leq is typically computed over 1, 8 and 24-hour sample periods. Fixed Noise Source: Any fixed or mobile source not preempted from local control by federal or state regulations. Fixed noise sources which are typically of concern include, but are not limited to, the following:

HVAC Systems Cooling Towers/Evaporative Condensers Pump Stations Lift Stations Emergency Generators Boilers Steam Valves Steam Turbines Generators Fans Air Compressors Heavy Equipment Conveyor Systems Transformers Pile Drivers Grinders Drill Rigs Gas or Diesel Motors Welders Cutting Equipment Outdoor Speakers Blowers The types of uses which may typically operate the noise sources described above include, but are not limited to: industrial facilities, lumber mills, trucking operations, tire shops, auto maintenance shops, metal fabricating shops, shopping centers, drive-up restaurant windows, car washes, loading docks, batch plants, bottling and canning plants, recycling centers, electric generating stations, race tracks, landfills, sand and gravel operations, and athletic fields. Noise due to operation of powered equipment for real property maintenance or temporary construction activities is not subject to the Noise Element standards. Noise-Sensitive Land Uses: Residential development, except temporary dwellings. Schools: preschool to secondary, college and university, and specialized education and training. Hospitals, nursing and personal care. Churches. Hotels, motels, and bed and breakfast lodging. Outdoor Activity Areas: Common outdoor activity areas of multi-family dwellings, back yards of single-family dwellings, and designated outdoor recreation/activity areas for transient lodging, hospitals, nursing and personal care facilities. Transportation Noise Source: Traffic on public roadways, railroad line operations and aircraft in flight. Control of noise from these sources is preempted by federal and state regulations. Roadways Traffic data representing annual average traffic volumes for existing conditions were obtained from Caltrans for the State highways within the City of Grass Valley, and from the General Plan traffic consultant for local roadways. Day/evening/night traffic distribution for State Routes (SR) 49, 20, and 174 were based upon 24-hour noise measurement data. Truck mix data for the State highways were also based upon Caltrans data. Using these data and Federal Highway Administration (FHWA) methodology, explained later in the Noise Element, traffic noise levels as defined by CNEL were calculated for existing traffic volumes for the State highways and local roadways. Distances from the center lines of each of the roadway segments to the 60 and 65 dB CNEL contours are summarized in Table 6-1. Figure 6-1 is a map showing these contours. Figure 6-2 is a map of future (Year 2020) noise contours, based upon projected traffic volumes and road width specifications (see Circulation Element). In some cases, the actual distances to noise level contours may vary from the distances predicted by the FHWA model. Factors such as roadway curvature, roadway grade, shielding from local topography or structures, elevated roadways, or elevated receivers may affect actual sound propagation. Therefore the distances reported in Table 6-1 are generally considered to be conservative estimates of noise exposure along roadways in the City of Grass Valley. Significant variations in topography occur in the Grass Valley area. In many cases, the existing topography which occurs adjacent to the major roadways affects sound propagation due to roadway traffic. The effects of factors such as topography, roadway curvature, grade, etc. can be determined from site-specific traffic noise measurements. The noise measurement results can be compared to the FHWA model results by entering the observed traffic volumes, speed and distance as inputs to the FHWA model. The differences between the measured and predicted noise levels can be used to adjust the FHWA model and more precisely determine the locations of the traffic noise contours. Table 6-2 has been prepared to serve as a guide when applying the traffic noise exposure contour information presented in this section to areas with varying topography. The table is used by adding the correction factor to the noise level predicted at a given distance. It should be noted that the adjustment factors presented in this table are intended to provide conservative results, and that complex situations should be evaluated by an acoustical consultant where the potential for significant noise impact exists. TABLE 6-1 EXISTING TRAFFIC NOISE CONTOUR DATA Segment Description CNEL At 100 Feet* Distance to Traffic CNEL Contour* 60 dB 65 dB State Route 49 1 2 3 4 5 6 7 8 Begin Freeway to Grass Val. Int. Grass Val. Int. To S.R. 20 S.R. 20 to N. Auburn Street N. Auburn Street to S.R. 174 S.R. 174 to Bennett Street Bennett Street to Idaho Maryland Idaho Maryland to Brunswick Road Brunswick Road to Banner Ridge 69.7 71.1 71.6 72.5 72.5 72.6 71.8 71.7 444 554 593 684 684 697 613 599 206 257 275 318 318 324 284 278 State Route 20 9 10 West Boundary to Mill Street Mill Street to S.R. 49 67.6 68.0 321 340 149 158 State Route 174 11 12 13 14 Brunswick Road to Empire Mine Road Empire Mine Road to Race Street Race Street to Ophir Road Ophir Road to S.R. 49 59.6 56.9 56.7 57.4 94 62 60 69 44 29 28 32 Alta Street 15 16 West Main to Alta Vista Alta Vista to Ridge Road 54.9 54.1 46 40 21 19 South Auburn Street 17 18 19 Mohawk Street to School Alley School Alley to Whiting Street Whiting Street to Mc Knight Way 57.6 57.0 57.2 69 63 65 32 29 30 Banner Lava Cap 20 Entire Length 54.6 44 20 Brighton Street 21 Mc Courtney to Chapel 54.5 43 20 Brunswick Road 22 23 24 49/20 O.C. to Idaho Maryland Idaho Maryland to Loma Rica Drive Loma Rica Drive to Bennett Street 62.8 60.3 60.3 155 104 104 72 48 48 Dorsey Drive 25 26 Ridge Road to E. Main Street E. Main Street to Segworth 53.7 56.1 38 55 18 25 Empire Street 27 28 29 49/20 O.C. to Le Duc Street Le Duc Street to Kate Hayes Street Kate Hayes Street to Grass Valley Limit 55.6 55.0 54.9 51 46 45 24 21 21 Freeman Lane 30 Mc Knight Way to Taylorville Road 57.8 71 33 Hughes Road 31 East Main Street to Ridge Road 57.6 69 32 Idaho Maryland Road 32 Brunswick Road to 49/20 O.C. 54.2 41 19 La Barr Meadows 33 Entire Length 58.7 82 38 Loma Rica Road 34 Entire Length 57.0 63 29 Mc Courtney Road 35 Entire Length 58.0 74 34 West Mc Knight Way 36 Taylorville Road to Freeman 58.1 75 35 Mill Street 37 38 Main Street to Neal Street Neal Street to Rhode Island Street 56.0 56.3 54 57 25 26 Neal Street 39 East of Church Street 55.9 53 25 Ridge Road 40 41 Ridge Estates Road to Hughes Road Hughes Road to Alta Street 55.7 57.6 52 69 24 32 Sutton Way 42 43 South of Brunswick North of Brunswick 58.2 60.0 76 100 35 47 Taylorville Road 44 45 Freeman lane to Mc Knight Way Mc Knight Way to Mill Street 52.7 57.3 33 67 15 31 Source: Brown-Buntin Associates, 1998. TABLE 6-2 TRAFFIC NOISE ADJUSTMENTS FOR VARIOUS TOPOGRAPHIC CONDITIONS   Distance from Center of Roadway (Feet) Topographic Situation <200 200 - 400 >400 Hillside overlooks roadway with full view of traffic -0- +1 dB +3 dB Roadway Elevated (>15') -5 dB -2 dB -0- Roadway in cut/below embankment -5 dB -5 dB -5 dB Dense vegetation (100 feet or more) -5 dB -5 dB -5 dB Source: Brown Buntin Associates, 1998. Traffic noise contours were not developed for all segments of local roadways in the City of Grass Valley. For arterial traffic, the predicted distance to the 60 dB CNEL contour is determined by the Average Daily Traffic Volume (ADT) and the posted speed limit. CNEL contours derived from Table 6-1 are only indicators of potential noise conflicts, requiring more detailed analysis to determine traffic noise levels at any given location. Aircraft Noise Levels The Nevada County Airpark is located east of Grass Valley. The facility is a base for local personal and recreational flyers. The Airpark also serves as a transportation facility for business/corporate aviation and aerial fire-fighting operations. Based upon the July, 1990 Nevada County Airpark Master Plan prepared by Hodges and Shutt, there were 160 based aircraft with 75,000 operations per year in 1989. Future upgrades of the facility are recommended in the Master Plan, and the 20-year forecast projects an increase in operations to 116,000 per year. Figure 6-3 shows the 1989 (considered existing for purposes of this Noise Element) CNEL contours for the Nevada County Airpark, which are contained in the Airpark Master Plan. Fixed Noise Sources The production of noise is a result of many industrial processes, even when the best available noise control technology is applied. Noise exposures within industrial facilities are controlled by Federal and State employee health and safety regulations (OSHA and Cal-OSHA), but exterior noise levels may exceed locally acceptable standards. Commercial, recreational and public service facility activities can also produce noise which affects adjacent sensitive land uses. These noise sources can be continuous and may contain tonal components which may be annoying to individuals who live in the nearby vicinity. In addition, noise generation from fixed noise sources may vary based upon climatic conditions, time of day and existing ambient noise levels. From a land use planning perspective, fixed-source noise control issues focus upon two goals: to prevent the introduction of new noise-producing uses in noise-sensitive areas, and to prevent encroachment of noise sensitive uses upon existing noise-producing facilities. The first goal can be achieved by applying noise level performance standards to proposed new noise-producing uses. The second goal can be met by requiring that new noise-sensitive uses in near proximity to noise-producing facilities include mitigation measures to ensure compliance with noise performance standards. The types of uses which may typically produce the noise sources described above include, but are not limited to: wood processing facilities, pump stations, industrial facilities, trucking operations, tire shops, auto maintenance shops, metal fabricating shops, shopping centers, drive-up windows, car washes, loading docks, public works projects, batch plants, bottling and canning plants, recycling centers, electric generating stations, race tracks, landfills, sand and gravel operations, and athletic fields. Discussions with the City of Grass Valley planning staff indicate that noise complaints within the City of Grass Valley have generally been confined to four types of noise sources. The noise sources which have generated noise complaints include car washes, quarry operations, delivery trucks and construction activities. Chevron Car Wash The one specific noise source which the City staff identified as eliciting noise complaints included the Chevron Station car wash which is located at East Main Street and Idaho Maryland Mine Road. The car wash operates 24-hours per day, and has been a source of noise complaints from residences in close proximity. Primarily during the nighttime period when noise due to roadway traffic along SR 49 is low, the noise levels due to car wash operations become more apparent and noticeable. Noise level measurements were conducted of car wash operations on August 13, 1998. The noise level measurements were conducted from a distance of 50 feet from the entrance to the car wash. Major noise sources associated with the car wash included the automatic wash and dry cycles. The blowers associated with the drying cycle of the car wash are the dominant noise source. Noise levels associated with operation were approximately 78 dB Lmax and 89 dB SEL for each wash and dry cycle. Assuming that a maximum of 8 operations (4 wash only cycles and 4 wash & dry cycles) occur during a busy hour indicates that the distances to the 50 and 55 dB Leq noise level contours are approximately 160 and 90 feet respectively from the entrance/exit of the car wash. North Star Quarry The North Star Quarry is located east of SR 49 on Idaho-Maryland Mine Road. The North Star Quarry is a rock and gravel mining operation. Noise sources associated with the operation include truck traffic to and from the site, excavation of resource material with a CAT D-8 dozer, loading of aggregate material with CAT 966 & 988 wheel loaders, and processing equipment which include a jaw crusher, roll crusher and deck screen. Brown-Buntin Associates, Inc conducted an analysis of noise impacts associated with the operations of the North Star Quarry in June 1992. The analysis indicated that the distance to the 50 and 55 dB hourly Leq noise level contours is approximately 900 feet and 500 feet respectively from the center of the excavation area. The distance to the 60 dB Ldn noise level contour is approximately 160 feet from the center of the excavation area. Review of current operations at the quarry indicate that they have not changed significantly from the operations used in the analysis which was conducted in 1992. Truck Delivery and Loading Dock Noise Loading dock and truck delivery operations generally occur at most commercial and industrial type uses. The types of uses include, but are not limited to, supermarkets, hardware supply stores, large warehouses and warehouse-size retail establishments, and post offices. Studies of noise levels at loading docks indicate that typical busy loading docks with semi truck arrivals and departures, unloading activities, semi truck passbys on the service roads, and step-side type delivery trucks produce an average hourly noise level of 60 dB Leq, and a maximum noise level of approximately 82 dB at a distance of 50 feet from the loading dock. Generally, the maximum noise levels are due to heavy truck passbys on the service road and the sudden discharge of air from the air brakes. Overall hourly average noise levels are due to all activities including arrivals and departures of trucks, revving of engines, and activities on the loading docks. Residential uses located adjacent to loading docks can be exposed to noise levels which may be considered annoying. Loading docks generally experience use between 3 and 4 hours out of a day. When using a 60 dB Ldn noise level standard, the noise from loading docks would not be considered to be a major noise source, with the 60 dB Ldn contour located approximately 20 feet from the loading dock or service road. However, the 50 dB hourly Leq noise level contour is located approximately 150 feet from the loading dock. Construction Noise During the construction phases of any large commercial, industrial or municipal project, noise from construction activities can dominate the noise environment in the immediate area. Activities involved in construction will generate noise levels, as indicated in Table 6-3, ranging from 70 to 90 dB at a distance of 50 feet. Construction activities can be temporary in nature, but can also be long-term. Construction typically occurs during normal working hours, although due to climatic conditions or impending changes in the season, extended working hours from early morning to late in the evening also can occur. Construction noise impacts could be significant, as nighttime operations or use of unusually noisy equipment could result in annoyance or sleep disruption for nearby residences. TABLE 6-3 CONSTRUCTION EQUIPMENT NOISE Type of Equipment Maximum Level, dBA at 50 feet Scrapers Bulldozers Heavy Trucks Backhoe Pneumatic Tools 88 87 88 85 85 Source: Environmental Noise Pollution, Patrick R. Cunniff, 1977. It is difficult to determine the location of a noise contour associated with construction activities due to the variations in types of equipment, number of pieces of equipment and the hours of operation. Therefore, the noise levels shown in Table 6-3 only indicate the maximum noise levels. Community Noise Survey A Community Noise Survey was conducted to document noise exposure in areas of the City containing noise sensitive land uses. For that purpose, noise sensitive land uses in the City of Grass Valley Planning Area were considered to include residential areas, parks and schools. Noise monitoring sites were selected to be representative of typical residential conditions in the City. Short-term noise monitoring was conducted at three sites on August 12, 1998. Each site was monitored three different times during the day and night so that valid estimates of CNEL could be prepared. Three continuous hourly noise monitoring sites were established in the City of Grass Valley as part of the General Plan Update to record day-night statistical noise level trends. The noise level measurements were conducted between August 13 and August 17, 1998. The data collected included the Leq, the maximum level during the measurement period (Lmax) and other statistical descriptors. Noise monitoring sites, measured noise levels, and the measured and estimated CNEL values at each site are summarized in Table 6-1. Community noise monitoring systems were calibrated with acoustical calibrators in the field prior to use. The systems comply with all pertinent requirements of the American National Standards Institute (ANSI) for Type I sound level meters. The Community Noise Survey results indicate that typical noise levels in noise sensitive areas of the City of Grass Valley Planning Area are in the range of 46.9 dB to 68.9 dB CNEL. Traffic on State and local roadways, industrial activities, aircraft overflights and neighborhood activities are the controlling factors for background noise levels in the majority of the Planning Area. In general, most areas of the City of Grass Valley which contain noise sensitive uses are moderately quiet to noisy, and are representative of an urban environment. Some residential areas have outdoor activity areas directly exposed to major noise sources such as State Route 49 and existing industrial areas. Noise exposure at some of those residences may be considered in excess of generally acceptable noise exposure criteria. The Leq values in Table 6-4 represent the average measured noise levels during the sample periods. The Leq values were the basis of the estimated CNEL values. The Lmax values show the maximum noise levels observed during the samples. The L50 and L90 values represent the noise levels exceeded 50 percent and 90 percent of the time during the sample period. TABLE 6-4 SUMMARY OF MEASURED NOISE LEVELS AND ESTIMATED DAY-NIGHT AVERAGE LEVELS (Ldn) IN AREAS CONTAINING NOISE SENSITIVE LAND USES Site Location Time Period Sound Level dB Leq L50 L90 Lmax Estimated CNEL 1 Memorial Park at Oak Street 8/12/98 11:00 a.m. 7:25 p.m. 10:20 p.m. 51.2 50.0 48.4 50 49 45 46 47 43 60.2 57.5 56.4 55.6 2 Condon Park 8/12/98 11:30 a.m. 8:10 p.m. 11:15 p.m. 48.5 47.5 43.5 47 47 41 44 44 40 54.9 56.0 49.5 51.5 3 Sierra College at Robert Ross Way 8/12/98 12:30 p.m. 8:45 p.m. 11:50 p.m. 42.8 42.3 39.4 43 41 38 41 40 36 51.2 50.1 44.7 46.9 4* Corner of Broadview & Hill 8/13-14/98 Ld Le Ln 8/15/98 Ld Le Ln 44.6 43.0 40.9 48.2 46.1 43.4 67.9 62.9 57.1 69.8 65.7 60.0 48.3 51.2 5* 312 Marshall 8/13-14/98 Ld Le Ln 8/15/98 Ld Le Ln 66.8 64.4 60.6 66.5 64.7 60.1 76.7 72.6 71.9 85.7 78.3 73.7 68.9 68.6 6* 888 Freeman 8/13-14/98 Ld Le Ln 8/15/98 Ld Le Ln 45.2 45.1 44.6 45.5 45.8 45.1 63.3 69.0 53.5 65.8 57.1 59.9 51.4 54.9 * = Continuous Monitoring Site Ld = Measured noise level during daytime hours (7:00 a.m. ­ 7:00 p.m.) Le = Measured noise level during the evening hours (7:00 p.m. ­ 10:00 p.m.) Ln = Measured noise level during nighttime hours (10:00 p.m. ­ 7:00 a.m.)Source: Brown-Buntin Associates, 1998 Noise Goal and Objectives 1-NG Protect Grass Valley's relatively quiet environment from unnecessary, annoying and potentially damaging noise. 1-NO Coordination of transportation and land use planning to assure acceptable noise levels. 2-NO Determination of the existing noise environment and development of realistic noise standards for different land uses. 3-NO Establishment of a pattern of land uses that minimizes exposure of community residents to excessive noise. Noise Policies 1-NP Develop a policy framework to function as a guide to planning for appropriate land uses in relation to hazardous and annoying noise. 2-NP Perform adequate acoustical analyses prior to approval of new development projects or transportation facilities, if warranted. 3-NP Utilize noise contour data to determine land uses affected by transportation-related noise sources. 4-NP Adopt appropriate noise level standards for existing and future residential areas. 5-NP Utilize noise contour data to determine appropriate land use patterns in areas affected by stationary noise sources. 6-NP Locate sensitive land uses (residential neighborhoods, medical facilities, senior care facilities and schools) away from high noise areas. Noise Implementation Actions and Strategies 1-NI Prohibit development of new noise-sensitive land uses where the noise level due to fixed noise sources will exceed the noise level standards of Table 6-5 (as measured immediately within the property line or within a designated outdoor activity area of the new development) unless effective noise mitigation measures have been incorporated into the development design to achieve the standards specified in Table 6-5. 2-NI. Require that noise created by new development of fixed noise sources be mitigated so as not to exceed the noise level standards of Table 6-5 as measured immediately within the property line of lands designated for noise-sensitive land uses. 3-NI Require that noise created by existing fixed noise sources which undergo modifications requiring City approval be mitigated so as not to exceed the noise level standards of Table 6-5 (as measured immediately within the property line of lands designated for noise-sensitive land uses). If the existing noise level due to those sources exceeds the standards, require that the noise level after modifications be mitigated so as to not exceed the existing noise level. 4-NI Require that an acoustical analysis be performed where new development of fixed noise sources, or modification of existing fixed noise sources, is likely to produce noise levels exceeding the performance standards of Table 6-5, and that noise mitigation be included in the project design. 5-NI Prohibit new development of noise-sensitive land uses in areas exposed to existing or projected future levels of noise from transportation noise sources which exceed the levels specified in Table 6-6, unless the project design includes effective mitigation measures to reduce exterior noise and noise levels in interior spaces to the levels specified in Table 6-6. TABLE 6-5 NOISE LEVEL PERFORMANCE STANDARDS FIXED NOISE SOURCES Noise Level Descriptor Daytime (7 a.m. to 10 p.m.) Nighttime (10 p.m. to 7 a.m.) Hourly Leq, dB 55 50 Maximum level, dB 75 65 Each of the noise levels specified above shall be lowered by five dB for simple tone noises, noises consisting primarily of speech or music, or for recurring impulsive noises (e.g., humming sounds, outdoor speaker systems, shooting ranges). These noise level standards do not apply to residential units established in conjunction with industrial or commercial uses (e.g., caretaker dwellings). 6-NI Require mitigation of noise created by new transportation noise sources so as not to exceed the levels specified in Table 6-6 at designated outdoor activity areas and interior spaces of existing noise-sensitive land uses. 7-NI Adopt the following criteria applicable to roadway improvement projects: Where the existing traffic noise level at the designated outdoor activity area of the affected noise-sensitive use is 65 dB Ldn or less, noise created by a roadway improvement project shall be mitigated so as not to exceed the ambient noise level by more than 3 dB Ldn. Where the existing traffic noise level at the designated outdoor activity area of the affected noise-sensitive use exceeds 65 dB Ldn, noise created by a roadway improvement project shall be mitigated so as not to exceed the ambient noise level by more than 1.5 dB Ldn. 8-NI Require an acoustical analysis and appropriate mitigation measures where new transportation noise sources are likely to produce noise levels exceeding the standards of Table 6-6 at existing or planned noise-sensitive uses. 9-NI Require an acoustical analysis and mitigation measures where noise-sensitive land uses are proposed in areas exposed to existing or projected exterior noise levels exceeding the levels specified in Table 6-5 or Table 6-6. TABLE 6-6 MAXIMUM ALLOWABLE NOISE EXPOSURE TRANSPORTATION NOISE SOURCE Land Use Ldn/CNEL, dB, at Outdoor Activity Areas Interior Spaces Ldn/CNEL,dB Leq, dB1 Residential 602 45 -- Transient Lodging 603 45 -- Hospitals, Nursing Homes 602 45 -- Theaters, Auditoriums, Music Halls -- -- 35 Churches, Meeting Halls 602 -- 40 Office Buildings -- -- 45 Schools, Libraries, Museums -- -- 45 Playgrounds, Neighborhood Parks 70 -- -- 1 As determined for a typical worst-case hour during periods of use. 2 Where it is not possible to reduce noise in outdoor activity areas to 60 dB Ldn/CNEL using a practical application of the best-available noise reduction measures, an exterior noise level of up to 65 dB Ldn/CNEL may be allowed provided that available exterior noise level reduction measures have been implemented and interior noise levels are in compliance with this table. 3 In the case of hotel/motel facilities or other transient lodging, there may be no designated outdoor activity areas (e.g., pool areas). In such cases, only the interior noise level criterion will apply. 10-NI Apply the following standards and practices to acoustical analyses: Where the locations of outdoor activity areas are not known or designated, the exterior noise level standards shall be applied immediately inside the property line of the receiving land use. In rural areas with large residential lots, the exterior noise level standard shall be applied at a point 100 feet from the residence. Where it is not practical to mitigate exterior noise levels at patios or balconies of apartment complexes, a common area such as a pool or recreation area may be designated as the outdoor activity area. Where noise mitigation measures are required to achieve the standards of Tables 6-5 and 6-6, the emphasis of such measures shall be placed upon site planning and project design. The use of noise barriers shall be considered a means of achieving the noise standards only after all other practical design-related noise mitigation measures have been integrated into the project. When determining the effectiveness of noise mitigation measures, the noise standards shall be applied on the receptor side of noise barriers or other property line noise mitigation measures. If dwellings are located and constructed in accordance with the Noise Element, it may be assumed that the resulting exterior and interior noise levels will conform to the noise standards imposed by lending agencies such as HUD, FHA and CalVet. Construction of new single-family dwellings or modification of existing dwellings in developed areas may not be subject to City review with respect to satisfaction of the standards of the Noise Element. As a consequence, such dwellings may be constructed or modified in areas where noise levels exceed the standards of the Noise Element. It is not the responsibility of the City to ensure that such dwellings meet the noise standards of the Noise Element, or the HUD/FHA/CalVet noise standards. Noise Methodologies and Modeling Techniques A common statistical tool to measure the ambient noise level is the average, or equivalent, sound level (Ldn), which is the sound level corresponding to a steady-state A-weighted sound level in decibels (dB) containing the same total energy as a time-varying signal over a given time period (usually one hour). The Leq is the foundation of the composite noise descriptors such as Ldn and CNEL, and shows very good correlation with community response to noise. TABLE 6-7 REQUIREMENTS FOR AN ACOUSTICAL ANALYSIS An acoustical analysis prepared pursuant to the Noise Element shall: Be the financial responsibility of the applicant. Be prepared by a qualified person experienced in the fields of environmental noise assessment and architectural acoustics. Include representative noise level measurements with sufficient sampling periods and locations to adequately describe local conditions and the predominant noise sources. Estimate existing and projected cumulative (20 years) noise levels in terms of Ldn or CNEL and the standards of Table 6-5, and compare those levels to the adopted policies and standards of the Noise Element. Recommend appropriate mitigation to achieve compliance with the adopted policies and standards of the Noise Element, giving preference to proper site planning and design over mitigation measures which require the construction of noise barriers or structural modifications to noise-sensitive buildings. Estimate noise exposure after the prescribed mitigation measures have been implemented. Describe a post-project assessment program which could be used to evaluate the effectiveness of the proposed mitigation measures. Two composite noise descriptors are in common use today: Ldn and CNEL. The Ldn (Day-Night Average Level) is based upon the average hourly Leq over a 24-hour day, with a +10 decibel weighting applied to nighttime (10:00 p.m. to 7:00 a.m.) Leq values. The nighttime penalty is based upon the assumption that people react to nighttime noise exposures as though they were subjectively twice as loud as daytime exposures. The CNEL (Community Noise Equivalent Level), like Ldn, is based upon the weighted average hourly Leq over a 24-hour day, except that an additional +4.77 decibel penalty is applied to evening (7:00 p.m. to 10:00 p.m.) hourly Leq values. The Ldn descriptor is a simplification of the CNEL concept, but the two will usually agree, for a given situation, within 1 dB. Like the Leq, these descriptors are also averages and tend to disguise short-term variations in the noise environment. Because they presume increased evening or nighttime sensitivity, these descriptors are best applied as criteria for land uses where nighttime noise exposures are critical to the acceptability of the noise environment, such as residential developments. Noise modeling techniques use source-specific data including average levels of activity, hours of operation, seasonal fluctuations, and average levels of noise from source operations. Modeling methods have been developed for a number of environmental noise sources including roadways, railroad line operations and industrial plants. Such methods produce reliable results as long as data inputs and assumptions are valid. The Federal Highway Administration (FHWA) Highway Traffic Noise Prediction Model (FHWA-RD-77-108) was used to develop CNEL contours for all highways and major roadways in the City of Grass Valley Planning Area. The FHWA Model is the analytical method presently favored for traffic noise prediction by most state and local agencies, including Caltrans. The current version of the model is based upon the CALVENO noise emission factors for automobiles, medium trucks, and heavy trucks, with consideration given to vehicle volume, speed, roadway configuration, distance to the receiver and the acoustical characteristics of the site. The FHWA Model predicts hourly Leq values for free-flowing traffic conditions, and is generally considered to be accurate within 1.5 dB. To predict CNEL values, it is necessary to determine the hourly distribution of traffic for a typical 24-hour day and to adjust the traffic volume input data to yield an equivalent hourly traffic volume. The modeling methods used in this chapter closely follow recommendations made by the State Office of Noise Control, and were supplemented where appropriate by field-measured noise level data to account for local conditions. The noise exposure contours are based upon annual average conditions. Because local topography, vegetation or intervening structures may significantly affect noise exposure at a particular location, the noise contours should not be considered site-specific. Existing Regulatory Framework The 1982 General Plan Noise Element is based upon recommendations by the California State Office of Noise Control as contained in the Guidelines for the Preparation and Content of Noise Elements of the General Plan. The criteria in the Noise Element are established for determining potential noise conflicts between various land uses and noise sources. The standards are based upon the CNEL/Ldn descriptor. Table 6-8 provides compatibility guidelines for land uses, in relation to noise levels. As described above, the CNEL and Ldn are 24-hour average noise level descriptors, which apply penalties to noise which occurs during the evening and nighttime hours. The CNEL and Ldn descriptors have been found to provide good correlation to the potential for annoyance from transportation-related noise sources. However, they do not provide a good correlation to the potential for annoyance from non-transportation or stationary noise sources such as industrial and commercial operations. This is due to the fact that many times stationary noise sources may operate between 8 and 10 hours per day, or will have noise sources such as loading docks, pressure relief valves or alarms which tend to be short duration noise events. When applying an Ldn or CNEL criterion, the noise levels associated with these types of short term operations are averaged over a 24-hour period, thus underscoring the potential for annoyance.