Map of Westchester

Enviornmental Monitoring

Tappan Zee Constructors, LLC (TZC) has installed perimeter environmental monitoring stations near both the Rockland and Westchester County shorelines as part of the New NY Bridge Project’s Environmental Performance Commitments (EPC). These commitments are intended to monitor, minimize and/or mitigate potential adverse effects related to construction noise, vibration and air quality associated with the Project.

Noise Monitoring
Construction noise is being monitored very closely during construction. Highly sophisticated monitoring devices have been installed at locations near the project site to make sure the construction activities are done without exceeding allowable sound levels. The monitoring devices record the level of the sound and automatically report back to the engineers and display the results online. This is the first time a construction project has allowed the public to see the ongoing noise levels on a first of its kind website,

Tappan Zee Constructors, LLC has created a robust program to mitigate noises at the source through the use of specific equipment and techniques and have designated times for different types of work.
  • Pile driving traditionally is the noisiest element in bridge construction and it has the most restrictions. TZC has a plan in place to use vibratory pile driving* and drilled shafts** where possible to minimize the amount of impact pile driving. They will also use sound mitigating shrouds and other techniques to reduce the sound levels produced.
  • Temporary and Movable Noise Barriers
  • Minimization of backup alarms by forward flow of traffic and alternate noise safety devices.
  • Restricted Construction Times: Construction activities will be restricted late night (10pm to 6am), Saturday morning until midday and Sunday all day. During that time, no equipment will be used that emits noise above 70 dBA max measured at an offset distance of 50 feet if the work is on land and at the nearest point of the shoreline if the work is in the water.
While data is specifically linked to construction areas, noise is constantly evaluated outside of construction activities as well to serve as an education component for the public. Traffic, trains, traffic, garbage pickup and even wildlife can contribute to noise levels. Trends will develop after monitors have been running for a few weeks and will help the project team identify existing noise levels. As required by the contract, TZC will respond and correct construction activities that exceed allowable levels. The public can also report noise concerns through the website or call in on the hotline 1-855-TZBRIDGE.

Monitoring, internal reporting, and management of noise levels by TZC have been configured to ensure that any exceedance of the maximum permitted noise levels shall be identified within 30 minutes of the occurrence and the activity causing the exceedance is mitigated within one hour of the first occurrence such that the exceedance is not repeated.


Construction activities will be restricted late night (10pm to 6am), Saturday morning until midday and Sunday all day. During that time, no equipment will be used that emits noise above 70 dBA max measured at an offset distance of 50 feet if the work is on land and at the nearest point of the shoreline if the work is in the water.

Additional Information Noise Levels
Noise is unwanted sound and is perceived differently by each person. Intensity is the sound pressure level, measured in units of decibels (dB). The human ear does not perceive all sound frequencies equally well, as a consequence, measured sound levels are adjusted or weighted to more closely correspond to noise perceived by human hearing. The adjusted noise metric (unit) that most closely duplicates human perception of noise is known as the A-weighted decibel (dBA). Generally, changes in noise levels of 3 dBA or less are barely perceived by most people, whereas a 5 dBA change is readily noticeable and a 10 dBA change is perceived as a doubling (or halving) of noise levels. Highway traffic 50 feet away from a receptor typically produces sound levels of approximately 70 dBA. The figure below provides some additional examples of noise from various sources.

Because very few noises are constant, methods have been developed to describe varying noise levels over extended periods of time. A commonly used method is to describe the fluctuating noise heard over a specific time period as if it has been a steady, unchanging sound. For this condition, a descriptor called the equivalent sound level,Leq, is computed. An Leq is the constant sound level that conveys the same sound energy as the actual fluctuating sound in a given situation and time period (e.g. a one hour time period denoted by Leq(1)). There are many other noise descriptors, including the maximum noise level (Lmax), used to
indicate the maximum noise level during the monitoring period.

*Vibratory Pile Driving is a method of pile driving that uses a specialized vibratory hammer that vibrates the pile causing it to sink into the soil. This technique works well under specific conditions like the conditions present in the Hudson River. Once the pile has reach specific point it will need to be impact driven to finish the process. This method reduces the amount of impact pile driving which is most associated with the environmental annoyances.

**Drilled Shafts are used on and close to shore where TZC will drill holes into the soil and rock then place reinforcing steel and concrete in the shaft to form the foundation piling.

As of September 27, 2013, the hourly Leq noise levels calculations havebeen improved to be more consistent with industry standardcalculations for similar noise level data.  Hourly noise levelsprior to September 27, 2013 will also been updated to be consistent with thecurrent industry standard calculations.

Vibration Monitoring
Vibration monitoring stations continuously record peak particle velocity (PPV) and waveform data on a real-time basis.

PPV is generally measured in inches per second (in/sec.) and represents the movement of the ground from construction or other activity. PPV is used to measure potential effects to structures or human reaction as the result of ground borne vibration. As PPV increases there is greater potential to effect structures or be noticeable to humans. Common construction activities which create ground-borne vibration include pile driving, drilling, jackhammering, pavement breaking, and earthmoving.

The station monitors will collect data continuously, 24-hours a day/7 days a week, during Project construction.

Three stations are located near the Project Site in Westchester County and three stations will be located near the Project Site in Rockland County. Monitor locations will be placed near sensitive receptors as feasible.

PPV recordings will be updated on a daily basis.

Air Quality Monitoring
Air quality monitoring stations, including three with meteorological monitoring equipment, will continuously record particulate matter (PM) concentrations and meteorological data on a real-time basis.

PM is generally measured in two size categories: particles with an aerodynamic diameter of less than or equal to 2.5 micrometers (PM2.5), and particles with an aerodynamic diameter of less than or equal to 10 micrometers (PM10, which includes PM2.5). PM2.5 has the ability to reach the lower regions of the respiratory tract, delivering with it other compounds that adsorb to the surfaces of the particles, and is also extremely persistent in the atmosphere. See the FEIS for more information on representative air quality information.

Monitor locations will be placed near sensitive receptors as feasible. The station monitors will collect data continuously, 24-hours a day/7 days a week, during Project construction. The TSI Model DRX Particulate Monitors are a light-scattering laser photometer-type instrument (also referred to as nephelometers) that detect particulates/aerosols by measuring the total amount of light they scatter and provide real-time aerosol/particulate mass readings in micrograms/ cubic meter (µg/m3). Photometer-type meters are commonly used to measure particulate concentrations as part of Community Air Monitoring Programs (CAMPs) to document particulate concentrations during construction-type activities because they provide real-time data that can be assessed quickly and subsequently corrective measures can be implemented quickly as well.

The particulate monitors will be configured to obtain the particulate data averaged over 15-minute intervals. Data from the instruments downwind from the Project activities can be compared with the data collected from the background station as well as the stations that are upwind from Project activities to determine if fugitive particulate emissions are being generated from Project activities. PM2.5 recordings will be updated on a daily basis.

The TSI DRX Monitors are factory-calibrated to Arizona Road Dust/ISO 12103 A1 Test Dust. As of 12:00 a.m. Saturday February 15, 2014, the PM2.5 concentrations provided on this website includes a calibration factor of 0.38, provided by TSI for urban setting applications, to more closely approximate fugitive concentration measurements of the smaller combustion-related particles (e.g. diesel exhausts) that are generally in the PM2.5 range.

Additional information about the DRX Aerosol Monitors used on this project. +

Tappan Zee Constructors, LLC (TZC) will be monitoring particulate matter (PM) concentrations in areas adjacent to the New NY Bridge project construction site.

Engineers will use the DRX Aerosol Monitor manufactured by TSI Incorporated to measure on-site PM concentrations. The data collected from the device is used to evaluate work practices and dust control measures to ensure minimal impact to the surrounding community.

The DRX is a portable, rugged light-scattering laser photometer that detects particles by measuring the total amount of light scattered as the unit pulls air in through the optical chamber. It provides real-time particle mass concentrations in micrograms per cubic meter (µg/m3).  Photometer-type meters like the DRX are commonly used at construction and environmental remediation sites to measure on-site PM concentrations. 

The useful data collected from the DRX is limited to upwind and downwind comparisons. The wind comparisons provide a net impact of the construction activity regardless of the background level at any given time. Rapid increases in PM concentrations can also indicate effects from other nearby local sources of dust or engine exhaust that are not construction-related.

The monitoring stations are located at ground level (approximately 5 to 6 feet above the ground) in the area of the project site, which includes near-field sources such as lawn mowing or leaf blowing activities, motor vehicle traffic, a rail line, and local building heating systems.  All of these sources will at times have an impact on monitor data. 

The PM values recorded by the devices should not be used to compare to the National Ambient Air Quality Standard (NAAQS). Sampling stations that monitor for the NAAQS, such as the sites operated by the New York State Department of Environmental Conservation (NYSDEC), are positioned away from such local sources so they are able to measure regional air pollution concentrations. 

The bridge construction area is impacted by humidity due to local weather and the proximity to the Hudson River and there are significant non-construction related particulate or aerosol sources in the area.  These conditions impact the operation of the DRX and therefore the data collected is expected to be higher than those monitored by the NYSDEC at ambient monitoring stations in Rockland and Westchester counties.

The NAAQS for PM10 is based on a 24-hour average concentration (up to one exceedance per year allowed). The PM2.5 NAAQS are based on an annual average and the annual 98th percentile of the 24-hr average concentration (i.e., 8th highest value in a calendar year), averaged over 3 years. Annual and 24-hour collection periods are unsuitable for monitoring the impact of construction activities, which requires real-time feedback.

When monitoring construction sites for PM concentrations, a shorter sample collection interval is beneficial because it provides quick feedback regarding fugitive dust or unusually high engine emissions that may be generated from project activity.

Photometers are not approved by the United States Environmental Protection Agency as either a Federal Reference Method (FRM) or a Federal Equivalent Method (FEM) for monitoring pollutant concentrations in the context of the NAAQS. However, published reports have shown a positive correlation under controlled conditions when PM2.5 and PM10 data collected with a photometer is compared with data collected using other monitoring system, such as Tapered Element Oscillating Microbalance (TEOM) monitor or a Beta Attenuation Monitor (BAM) which are often used in fixed stations to measure ambient particulate concentrations.  Some models of TEOM and the BAM samplers are FEMs; however, these are generally designed for a permanent installation and require AC power and a temperature-controlled room or enclosure.

Andrew M. Cuomo

New York State
Thruway Authority

Federal Highway

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