Both the construction and operations phases of the project will result in increased traffic. Although the increased traffic for the construction phase will be for a fixed period only, the intensity of the increased traffic is likely to be higher than for typical operations and include a considerable number of heavy vehicle deliveries. For operations phase, there will be an increase in the frequency of trips and commensurate increased vehicle presence on the roads. The additional traffic will almost certainly have an impact on existing road users and in the section that follows an attempt is made to define the extent and significance of the impact.
Normally six common air pollutants, also known as criteria pollutants are studied as a part of vehicular air dispersion modelling studies. These pollutants are particulate matters (PM10 and PM2.5), ozone, carbon monoxide gas , sulfur oxides, nitrogen oxides, and lead.
- Complying with state and country environmental laws.
- Determining the environmental consequences of our activities.
- Proposing prudent, feasible and cost-effective strategies and alternatives to avoid or minimize adverse impacts of the activities, and
- Ensuring the mitigation selected is appropriate
Selection of Air Dispersion Model and Analysis
A dispersion model can be described as a series of equations describing the relationships between the concentration of a substance within the atmosphere arising at a selected location, the discharge rate and factors affecting the dispersion and dilution in the atmosphere. The model requires information on the emission characteristics and therefore the local meteorology. Modelling can be used for predict future scenarios, short-term episodes, and long-term trends.
Nearby buildings and sophisticated topography can have significant effects upon the dispersion characteristics of a plume. Buildings may cause a plume to return to ground much closer to the stack than otherwise expected, causing significantly higher substance concentrations. Plumes can impact directly on high buildings under certain environmental condition , which can trap emissions during low-level inversions. Based on the scope of the project, an appropriate model to assess the ground level concentration within the project area and at ambient level outside of the project site shall be assessed.
Project shall be divided into construction and operation phase which can result in fugitive dust emissions and engine exhaust emissions from various types of activities. If sensitive receptors such as schools, hospitals, aged care facilities, or child-care facilities are nearby, or if construction emissions are expected to be high, a shorter construction duration should be considered.USEPA recommends CALINE 4 for Carbon monoxide analysis and AERMOD (a preferred model) to conduct PM and other pollutants model, corresponding AP-42, Chapter 13: EPA’s guidance and methodology to analyze paved road dust shall be used.
Maximum operating conditions under maximum emission scenario are computed to conservatively estimate the maximum ground level operation.
Key steps of the assessment would include:
- Emission estimation to quantify emissions. The emission estimates are going to be supported manufacturers data on comparison with the scheduled operation; within the absence of manufacturers data, emission factors obtained from USEPA, AP-42 or emission estimates from similar operating facility are going to be used
- Obtaining a local meteorological file for months of monitoring throughout a single season for the duration of the monitoring
- Model inputs include stack/vent characteristics such as height, stack type, diameter, exhaust temperature, exit velocity, stack orientation, exhaust flow rate, and emission rate
The regional meteorological data set derived from the information obtained at the monitoring site is validated against the Indian Meteorological Data (IMD) repository. The onsite data is then processed with AERMET to generate meteorological input files and on-site data to improve the full understanding of the atmospheric and dispersion conditions applicable to the project region.
Traffic Noise – Vehicular & Railroad
The Noise Assessment is used to examine potentially impacted areas identified in the screening step by examining the location and estimated severity of noise impacts. This study considers noise source and land use information likely to be available in the project development process. Estimates are made from project noise levels and of existing condition to model the situation of a noise impact contour that defines the outer limit of an impression corridor or area. For the noise computations , transit-specific noise and adjustment data (in tabular and graphical form) modelling method are used. We also assist in assessing operational and construction-related noise and vibration risks. Topic areas we assist with are noise barriers, quiet pavement and bridge noise.
- Step 1: Identify Noise-Sensitive Receivers – Identify noise-sensitive receivers and their proximity to the project and major noise sources.
- Step 2: Determine Project Noise Source Reference Levels – Determine the project noise sources and reference levels.
- Step 3: Estimate Project Noise Exposure by Distance – Estimate project noise exposure at distances beyond 50 ft considering propagation characteristics using a simplified procedure.
- Step 4: Combine Noise Exposure from All Sources – Combine all sources associated with the project to predict the total project noise at the receivers.
- Step 5: Measure Existing Noise Exposure – Measure the existing noise or estimate the existing noise exposure using a simplified procedure.
- Step 6: Inventory Impacts
- Option A:Calculate the difference in noise (existing vs. projected noise) at each noise-sensitive receiver or cluster, finding all moderate and severe effects.
- Option B: Take inventory of noise-sensitive receivers that fall within the moderate and severe noise contours.
- Step 7: Determine Your Noise Mitigation Requirement – Evaluate the requirement for mitigation and repeat the General Noise Assessment using the recommended mitigation.
Some common mitigate ion methods:
- Controlling traffic by directing to other side roads or enforcing speed limit
- Pavement design
- Introduction of buffer zones
- Introduction of noise barriers which are solid obstruction (earth berms or vertical walls) built between the highway and the homes along the highway; effective noise barriers can reduce noise levels by 10 to 15 decibels, cutting the loudness of traffic noise in half.
- A 30 m width of dense vegetation can reduce noise by 10 decibels.
- Insulating buildings can greatly reduce highway traffic noise, especially when windows are sealed and cracks and other openings are filled; sometimes noise-absorbing material can be placed in the walls of new buildings during construction.
|Level of Impact
|Project-generated noise is not likely to cause community annoyance. Noise projections in this range are considered acceptable by FTA and mitigation is not required.
|Project-generated noise in this range is considered to cause impact at the threshold of measurable annoyance.
Moderate impacts serve as an alert to project planners for potential adverse impacts and complaints from the community. Mitigation should be considered at this level of impact based on project specifics and details concerning the affected properties.
|Project-generated noise in this range is likely to cause a high level of community annoyance. The project sponsor should first evaluate alternative locations/alignments to determine whether it is feasible to avoid severe impacts altogether. In densely populated urban areas, evaluation of alternative locations may reveal a trade-off of affected groups, particularly for surface rail alignments. Projects that are characterized as point sources rather than line sources often present greater opportunity for selecting alternative sites. This guidance manual and FTA’s environmental impact regulations both encourage project sites which are compatible with surrounding development when possible. If it is not practical to avoid severe impacts by changing the location of the project, mitigation measures must be considered.
Standards and Guidelines
- Transit Noise and Vibration Impact Assessment Manual, Federal Transit Administration (FTA), U.S. Department of Transportation, Report No. 0123, 2018
- International Financial Corporation (IFC) Environmental, Health, And Safety Guidelines-Noise management, April 2007
- ISO 9613 ‘Acoustics – Attenuation of Sound during Propagation Outdoors – Part 2: General Calculation Method’ (ISO, 1996)
- ISO 1996-2 2007 Acoustics — Description, measurement and assessment of environmental noise