This update is intended to provide further information to the public about health and safety aspects of the construction of the Permeable Reactive Barrier beneath Central Avenue in Needham, and to provide information that may be useful once construction starts.

Construction Schedule

Barring any unforeseen circumstances, the construction of the Permeable Reactive Barrier will begin during the week of May 14, 2001. Starting May 14, Central Avenue will be blocked off between West Street and Glover Road to allow for the delivery of equipment and supplies for the construction project, and to allow utility re-location to commence. During the week of May 7, workers will be installing silt fencing to protect the wetlands prior to the start of construction.

Personal Protection

The Occupational Safety and Health Administration (OSHA) has created regulations for personal protection during the cleanup of sites contaminated with hazardous materials. These regulations are designed to protect workers who may be exposed to hazardous materials during cleanups. Only OSHA-trained personnel are allowed within the work zone during construction activities. The degree of personal protection required by OSHA regulations is determined by the degree of hazard to the site workers. Personal protection is broken into four levels (A, B, C, and D), with Level A being the most protective, and Level D the least.

Due to the known concentrations of TCE in soil and groundwater beneath Central Avenue, Geo-Con workers and other on-site personnel will be following Level D personal protection requirements. This means that anyone on-site must wear basic safety gear (steel-toed boots, hard hats, safety glasses, orange safety vests). This basic level of protection may be upgraded to include Tyvek coveralls and gloves if the on-site Health and Safety Officer determines that there is a likelihood of workers contacting chemicals dermally.

Geo-Con personnel will also be able to upgrade their protection to Level C if necessary. This decision will be based on the air monitoring that will be conducted during this project. Level C personnel protection involves the same safety clothing as Level D, but also includes an air-purifying respirator. If workers need to upgrade their protective equipment to Level C, the Needham Board of Health and the Town Administrator will be notified. However, please note that although workers will be prepared to use respirators, it is highly unlikely that levels of TCE in air will require the use of respirators to protect workers.

Air Monitoring

The March 30, 2001 update for this project mentioned that air monitoring will be part of the required health and safety activities undertaken by the construction contractor, Geo-Con. Monitoring the air for the presence of volatile organic compounds (VOCs) such as trichloroethylene (TCE) is needed to ensure the protection of site workers (those closest to the contamination) and area residents, even though the levels of TCE are expected to be very low. Air monitoring procedures for this project, summarized below, were outlined in Geo-Con's Health and Safety Plan and reflect DEP's subsequent comments on the Health and Safety Plan. In addition, DEP received input on the draft Health and Safety Plan from the Needham Board of Health and the Board?s technical expert.

There will be three types of air monitoring for VOCs. The first type of air monitoring is the use of a hand-held instrument called a photoionization detector, or PID. The PID is the most commonly used field instrument used to detect total VOCs because of its portability. PIDs are "real-time" monitoring instruments that are able to detect if VOCs are in the air at levels above 1 part per million (ppm), approximately. It will indicate whether high concentrations of VOCs like TCE are released to the ambient air, so that worker protection and control measures can be taken right away. The PID monitoring will take place in close proximity to the trench for the Permeable Reactive Barrier, so that worst-case air emissions will be monitored.

PIDs, however, do not identify which specific volatile organic compound is being measured. To accomplish this, and to achieve levels of detection lower than 1 ppm, a portable gas chromatograph (GC) will be used at the site. The portable GC will be able to analyze air samples collected daily from the perimeter of the work area to determine concentrations of individual VOCs. Air "grab" samples will be collected a minimum of twice per day, during times of maximum potential volatilization, and analyzed by DEP staff on-site. DEP has established "action levels" for TCE concentrations during the construction of the Permeable Reactive Barrier. If concentrations of TCE exceed 100 parts per billion (ppb), it will trigger the need for more frequent air monitoring and possible use of control measures. If TCE concentrations exceed the risk-based action level that has been determined (330 parts per billion), control measures must be taken -- or the project stopped -- until air quality returns to acceptable levels (i.e., below 330 ppb).

The third category of air monitoring is the most sensitive method and measures VOC concentrations over a prescribed period of time. DEP's contractors will collect time-weighted average samples over an 8 - 10 hour period, and these samples will be analyzed at an off-site laboratory. Time-weighted average samples will be collected at the perimeter of the work zone prior to the start of construction (as a reference sample), during the initial stages of the construction, and during the time when construction occurs in the most concentrated area of groundwater contamination.

There will also be dust monitoring during the construction of the Permeable Reactive Barrier. All of the air monitoring data will be available to the Needham Board of Health and its consultants to review, as well as to any other interested party.

In addition, DEP stated in the March 30, 2001 update for this project that we were trying to have "retro-fits" added to on-site construction equipment in order to reduce air emissions from diesel engines. As of this date, Geo-Con has successfully arranged for a catalytic oxidation unit to be retro-fitted onto the excavator that will be used on-site. Other retro-fitted and/or low-emission equipment will also be used on the other equipment if it is available during the period when needed.

Permeable Reactive Barrier Contacts

DEP staff will be on-site each day during the Permeable Reactive Wall construction. Peter Richards and Patrick Hurley will be overseeing the Permeable Reactive Barrier installation and are the DEP staff who have had the most involvement with developing the specifications for this project. The cell phone number to contact the on-site DEP staff during the day is:

617-947-2245

DEP staff will be on-site for the majority of each day of construction, should you have a question or concern during the times of construction. In addition, Patrick Hurley will be carrying a beeper for the duration of the project, and he can be contacted during non-working hours. The number for citizens to call if there are any problems between 5:00 PM and 9:00 AM is:

617-562-6748

Finally, the on-site security guard will also have instructions for contacting DEP staff should the need arise during off hours.