Standard emission minimization measures for construction activities will be implemented, as indicated above.

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1 The nature of the proposed improvements are such that undue construction emissions should not be a concern; overall emissions should be similar to other projects of this type and magnitude. Construction activities will be required to comply with Air Pollution Control Division (APCD) regulations pertaining to fugitive dust. To address the temporary elevated air emissions that may be experienced during construction, standard construction mitigation measures should be incorporated into construction contracts. These could include: Engines and exhaust systems on equipment in good working order Equipment maintained on a regular basis, and equipment subject to inspection by the project manager to ensure maintenance Fugitive dust systematically controlled through diligent implementation of a dust control plan No excessive idling of inactive or unnecessary equipment or vehicles Construction equipment and vehicles use higher-grade fuel to reduce pollutant emissions Stationary equipment located as far from neighbors as possible Construction emissions from the No-Action Alternative will be less than the Proposed Action because new construction is not being proposed for it. However, routine maintenance and upgrade of the existing facilities will be necessary over time and construction emissions from these activities will be similar to those expected from the Proposed Action; the overall quantity would just be expected to be less Mitigation Given that air emissions from implementation of the Proposed Action are not predicted to cause an impact in the future, long-term mitigation measures for air quality are not necessary. Future emissions from on-road mobile sources will be minimized universally through several federal regulations. The Denver area Maintenance Plans for CO, O 3 and PM 10 will serve to avoid and minimize pollutant emissions from I-225 and other project roads. Standard emission minimization measures for construction activities will be implemented, as indicated above. 4.5 TRAFFIC NOISE An analysis of traffic noise was conducted as part of the EA to assess existing and future traffic noise levels at properties near the project corridor. The analysis of existing conditions serves as a baseline for comparing any traffic noise impacts that may occur in the future. Some land uses, such as residences, schools and parks, are viewed by FHWA and CDOT as being more sensitive to traffic noise than other land uses. The project corridor is abutted by predominantly residential land uses (Figure 4-4). This section provides basic noise information, the applicable guiding policy, some existing noise levels within the project corridor and predicted future levels. More detailed information regarding the noise analysis can be found in the Noise Impact Assessment (FHU 2005c). Page 4-39

2 4.5.1 Current Conditions Sound is created when an object vibrates and radiates part of that energy as acoustic pressure or waves through a medium, such as air or water. Sound and noise are measured in units of decibels (db). The db scale is logarithmic, not arithmetic. As an example, two identical noise sources, each producing 60 db, will produce 63 db when operated together. Likewise, a 10-dB increase in sound levels represents 10 times as much sound energy. Some common noise levels are shown in Figure 4-5. Figure 4-5 Typical Noise Levels Sound Decibels Subjective Levels Evaluation Colorado Department of Transportation Jet Engine 140 Noise Abatement Criteria: One-hour L eq 56 dba Category A--Tracts of land in which serenity and quiet Threshold of Pain 130 (exterior) are of extraordinary significance Deafening 66 dba Category B--Residences, motels, public meeting rooms, Rock Band 120 (exterior) schools, churches, libraries, hospitals, picnic areas, playgrounds, active sports areas, and parks. Chain Saw dba Category C--Developed lands, properties or activities (exterior) not included above. Auto Horn dba Category E--Residences, motels, public meeting rooms Very Loud (interior) schools, churches, libraries, hospitals, Lawn Mower 90 and auditoriums. Noisy Factory 80 Vacuum Cleaner 70 Conversation 60 Average Office 50 Moderate Soft music 40 Average residence 30 Faint Whisper 20 Human breathing 10 Very Faint Threshold of hearing 0 Page 4-41

3 The human ear is receptive to a wide range of sound energy levels but is not equally receptive to all sound frequencies. A-weighting of sound frequency ranges is a method used to approximate how the human ear perceives sound, mostly by reducing the contribution from lower frequencies by a specified amount. A-weighted sound levels are reported in dba. Research has shown that most people will not notice a difference in loudness of sound levels of less than 3 dba, which is a 2-fold change in the sound energy. Most people relate a 10-dBA change in sound levels to a doubling of sound loudness. Sound levels diminish with distance from the source because of spreading, atmospheric absorption, interference from other objects and ground effects. "Hard" ground (such as asphalt) and "soft" ground (such as grass) transmit sound differently. Hard ground is more reflective and will produce louder sound levels farther from the source. With traffic noise, a 3-dBA increase in noise could be caused by doubling the traffic volume or cutting the distance from the roadway in half for hard ground. Traffic noise tends to fluctuate constantly over time in accordance with traffic volumes, vehicle types and speeds. This fluctuation makes it difficult to describe the noise impact through a single value, however, the FHWA and CDOT use the one-hour equivalent sound level (L eq ) as their metric for assessing traffic noise impacts. The L eq is the average of the fluctuating noise levels over a time period, or more precisely the continuous noise level that would produce the same sound energy as the fluctuating noise levels. On congested highways like I-225, the loudest traffic noise generally occurs when the largest traffic volume can travel at the highest speed, which may be outside the heaviest traffic periods when traffic becomes overly congested and slows. This loudest period generally describes LOS C for a highway. Noise Criteria Potential impacts from traffic noise were assessed by comparing the predicted traffic noise levels to CDOT s implementation of the FHWA Noise Abatement Criteria (NAC) (Table 4-6). In addition to exceeding the relevant CDOT NAC, a noise impact can occur from a substantial noise increase if the future noise level is expected to increase by 10 dba or more over existing levels. Either of these conditions would lead to evaluation of traffic noise mitigation actions. Existing Traffic Noise Levels Existing traffic noise conditions were evaluated through a combination of noise measurements and computer modeling. Modeling is used because day to day variations in noise levels from changes in traffic or weather conditions can not be captured or quantified by brief noise measurements alone. Modeling estimates noise levels under typical averaged conditions. The measurements are helpful in evaluating noise model parameters. The ultimate purpose of the models is to show whether future traffic noise levels from the proposed project would be high enough to impact neighboring properties and whether noise mitigation should be considered for any such impacts within the study area of the EA. Page 4-42

4 Table 4-6 Noise Abatement Criteria Land Use Category A CDOT NAC (L eq ) 56 dba exterior 66 dba Exterior B sports areas, and parks. C 71 dba Exterior D Undeveloped lands. E 51 dba Interior Description of Land Use Category Tracts of land in which serenity and quiet are of extraordinary significance and serve an important public need and where the preservation of those qualities is to continue to serve its intended purpose. Such areas could include amphitheaters, particular parks, or open spaces which are recognized by appropriate local officials for activities requiring special qualities of serenity and quiet. Residences, motels, hotels, public meeting rooms, schools, churches, libraries, hospitals, picnic areas, playgrounds, active Developed lands, properties or activities not included in categories A and B above. Residences, motels, public meeting rooms, schools, churches, libraries, hospitals, and auditoriums. Ten-minute traffic noise measurements were performed in duplicate at seven locations (Figure 4-6) in the study area to document ambient conditions (FHU 2005c). The locations were representative of residential areas near I-225 and 17 th Place within the project area. There are masonry-block noise barriers along both sides of I-225 throughout the project corridor (Figure 4-6). The west-side wall begins about 1,000 feet north of Colfax Avenue and continues uninterrupted to Sand Creek. The east-side wall begins about 200 feet north of Colfax Avenue and also continues uninterrupted to Sand Creek, and is supplemented by a separate 500-foot section at the I-225 bridge over Colfax Avenue. The barrier height was measured at feet for most of its length, except the bridge section which is about 8-feet high. These barriers reduce traffic noise levels near I-225 in the project corridor. The traffic noise modeling software used for the assessment was the implementation of the FHWA- RD model (STAMINA) contained in SoundPlan Version 6.2 with CDOT vehicle noise emission values added. The existing traffic conditions that were modeled included the current road configurations and traffic volumes. The computer noise models require a considerable amount of input data regarding the geometry of the roadways as well as traffic volumes, vehicle mix, and speeds. A traffic analysis was completed for the project corridor; Chapter 3 Transportation Analysis provides traffic volumes. As a check on computer model parameters, the traffic conditions observed during some noise measurement episodes were used to construct a verification model, which was compared to the measured noise levels. The verification model used the data from one day of noise measurements. The measured and modeled results were in close agreement, indicating that the model was accurately predicting noise levels. Page 4-43

5 Current traffic noise levels during an average PM peak noise hour were modeled at 48 receiver points that represent discrete locations within the project corridor (Figure 4-7). In addition, traffic noise levels were calculated at more than 6,700 regularly-spaced grid nodes covering the project area to create detailed noise contours (Figure 4-7) for a larger area than covered by the discrete receivers. Several Category B locations along the project corridor were either measured or predicted through modeling to equal or exceed the CDOT NAC under existing traffic conditions (Figure 4-7 and Table 4-7). This includes about four residences that front Potomac Street in the northern half of the trailer park/rv park west of I-225. This is due to traffic noise from I-225 as well as Potomac Street. Also impacted are four apartment buildings near Billings Street and Evergreen Avenue. This is due to traffic noise from I-225 as well as Billings Street. It should be noted that a number of other residences are very close to the 66-dBA levels. It should also be noted that noise levels can be affected by relatively small changes in weather. As an example, repeat measurements at one location on the same day but under slightly different weather conditions (wind direction and speed) showed a 3-dBA difference in noise levels and a noticeable change in perception by the observer. The model results reflect still wind conditions. These findings are presented in more detail in the Noise Impact Assessment (FHU 2005c). The existing traffic noise barriers along I-225 were included in the model and reduced traffic noise levels at front row model receivers along I-225 by up to 10 dba. These barriers are performing in accordance with CDOT guidelines and goals. Table 4-7 Noise Impact Summary Number of Noise Impacted Properties (with no additional mitigation) Location Land Type Existing 2025 No- Proposed Action Conditions Action Category B 2100 block Potomac Residential block Billings Residential block Billings Residential block Billings Residential Category C Block East Colfax Commercial Finally, no commercial properties were estimated to reach or exceed the Category C NAC. Page 4-45

6 4.5.2 Consequences The noise analysis was conducted to assess whether future noise levels near the project corridor would exceed the relevant CDOT NAC or cause a substantial noise increase. Noise models were constructed and run for I-225 and the other major project streets using predicted future (2025) PM traffic volumes and road layouts. The findings are presented in more detail in the Noise Impact Assessment (FHU 2005c). No-Action Alternative Model results for the No-Action Alternative (Figure 4-8) are very similar to the existing conditions results. Not surprisingly, the traffic noise patterns are similar to existing noise contours pushed out a bit farther from the roads due to increased traffic volumes, so the impacted areas would be slightly larger overall. The impacts are summarized in Table 4-7 and Figure 4-8. The same Category B areas would be affected as under existing conditions with eight additional residences (approximately 22 overall) predicted to be at or above the CDOT Category B NAC. No noisesensitive areas are expected to experience a 10-dBA increase as the largest increase is predicted to be 4 dba. One commercial property is predicted to reach or exceed the Category C NAC. Proposed Action The Proposed Action model was designed with noise barriers comparable in size to the existing noise barriers and at a similar location as the existing barriers given the new construction. In several locations, the existing noise barriers will have to be removed and replaced up to 20-feet farther from the I-225 centerline (Figure 4-9) to accommodate the Proposed Action. The replacement barriers will be as tall as the current barriers or taller (i.e., ramp retaining walls). In addition, 1-meter jersey barriers were assumed along the new elevated roads. Model results for the 2025 Proposed Action (Figure 4-10) differ from the other model results (Table 4-7). A cluster of mobile homes on the 2100 block of N. Potomac Street puts the number of residences predicted to equal or exceed the CDOT NAC at 12. However, all of the residences on N. Billings Street are estimated to be below the CDOT NAC, which is a benefit to 10 residences. This reduction is due to traffic noise being blocked by the new ramps serving the 17 th Place interchange. In total, about half the number of residences are impacted by the Proposed Action, so it is a net benefit relative to the No-Action Alternative. No noise-sensitive areas are expected to experience a 10-dBA increase as the largest increase is predicted to be 5 dba. In the impacted residential area (Figure 4-10), the difference will be 2 dba or less. However, noise will decrease by as much as 7 dba at other locations. No commercial properties are estimated to equal or exceed the Category C NAC. Page 4-47

7 4.5.3 Mitigation The noise analysis was conducted to assess whether future noise levels near the project corridor would cause a noise impact. For all of the situations modeled, some Category B receivers were calculated to be at or above the CDOT NAC (Table 4-7) even with the noise barriers described. This finding means that additional noise mitigation actions should be evaluated. Non-barrier noise mitigation was considered but does not appear to be feasible due to operational constraints and physical space limitations. These factors are detailed in the Noise Impact Assessment (FHU 2005c). Barriers appear to be the only viable mitigation. There are currently fairly new and comprehensive noise barriers along both sides of I-225 in the project area. These barriers were calculated to provide more than 10 dba of traffic noise reduction for several front-row receivers under current conditions and lesser amounts for receivers farther away, so the existing barriers are performing well. The Proposed Action will require portions of the existing noise barriers to be removed. Where the barriers need to be removed, they will be replaced by a either a new section of barrier, a retaining wall, or a combination of retaining wall and barrier that is at least as high as the existing barrier. The locations where noise barriers will be replaced are indicated on Figure 4-9. Along the east and west sides of I-225, the current 12 ft high barrier will be replaced mostly by the retaining wall that supports the ramps and the new bridge abutment. The retaining wall along the ramps will be solid and will act a noise barrier to noise from the I-225 mainline. The retaining wall along the west side ramp will cross under the new 17 th Place bridge and will be approximately 25 feet high at that location (effectively doubling the height of the existing noise barrier). As the retaining wall height decreased to the north of the new bridge, a noise barrier will be installed on top of the retaining wall to maintain an effective noise barrier height of at least 12 feet. The new noise barrier will connect to the existing barriers to remain. The will be no gaps in this retaining wall/noise barrier. The combination of maintaining the existing barriers and adding noise-blocking interchange ramps at 17 th Place will actually increase the number of receivers that will have overall noise reduction benefits of 10 dba or more, even with no other mitigation actions. As presented above, the Proposed Action will have approximately 12 residences along Potomac Street at or above the CDOT NAC. These receivers are calculated to receive a noise reduction of 7-11 dba from the replacement barrier and retaining wall. This result is well within CDOT s mitigation guidelines. For these receivers to receive an additional 5 dba minimum noise reduction (12-16 dba total) would require an 8-foot higher minimum barrier height for a distance of 1,700 feet north of 17 th Place. This additional noise barrier was found to be unreasonable following CDOT s guidelines and is not recommended. These impacted receivers will still receive 7-11 dba traffic noise reduction from the Proposed Action. Typical noise reduction measures would be implemented during construction of the Proposed Action to minimize noise. Page 4-51