To access gas energy today, we simply have our homes hooked up to the adjacent gas line. That line taps into an energy source that may be located hundreds of miles away. But prior to the 1950s, before natural gas pipelines were built across the countries, cities and towns created their own gas. How? By heating coal and other ingredients in large brick ovens at facilities called manufactured gas plants. As the coal was heated, it produced a gas that was filtered from the ovens and stored in tanks. That fuel was used to light homes, businesses and street lamps.
Coal tar was a by-product of the process, and was often left behind in subsurface structures and soils when the MGPs were closed in favor of more efficient energy production sources. The waste and contamination from MGPs still pose an environmental and public health concern today at the approximately 3,500 MGP sites around the country.
In the last decade, management of liabilities associated with former MGP sites has become an environ-mental challenge. Former MGPs have gained attention from regulators as sources of on- and off-site soil, sediment, surface water and groundwater contamination.
Former MGP sites represent a sizable amount of unused land often in prime redevelopment areas. The U.S. Environmental Protection Agency Brownfields Program, Land Revitalization Initiative, and a wide variety of other programs encourage investigation, remediation and redevelopment of abandoned, unused or under-developed properties.
However, prior to redevelopment, a MGP site must be investigated to determine on-site and potential off-site environmental impacts. The impacts then must be quantified – on a site-by-site basis – in order to deter-mine the best remediation plan. After the site has been remediated to appropriate cleanup levels, redevelopment can move forward.
Coal tar in the ground does not have the thick consistency that you may think of as tar. It is instead an oily liquid with a very strong odor that smells like creosote or mothballs. When coal tar is exposed on the ground surface, it can partially solidify and start to look like ordinary asphalt, but it keeps the same odor as when it is found underground.
The presence of sustained and unfamiliar odors at a site can be perceived by local residents as a potential health risk. Complaints about odors can bring a project to a halt and cause costly delays. In a worst case scenario, real or perceived, community exposure to site emissions wind up in court.
Odors at MGP sites have typically been difficult to quantify. However, the odors can keep a site from being remediated. So what can be done to manage this problem?
MGP site owners must manage their remediation site odor and air emissions – and the risks that come with them – by first determining the level of measurement and control required to meet their project’s objectives. Traditional difficulties in qualifying and quantifying potential nuisance odors can be overcome through proper training of the field staff taking measurements and the use of effective instrumentation. For example, field staff can be trained in methods to describe both the nature and intensity of odors from excavation sites. In addition, instrumentation is available to measure chemicals that can cause odors. When odor intensity or chemical concentrations exceed predetermined levels, odor control measures can be implemented.
Two common methods for dealing with odors include good housekeeping practices and creating an artificial barrier to prevent odors from getting into the air. Examples of good housekeeping include minimizing stockpiling of soil on site and reducing the size of exposed areas in excavations. A common way to handle odors is to apply foam to exposed areas and prevent odor emissions.
In certain circumstances, excavation and other remedial activities can be performed beneath a temporary structure containing an air handling system. Through this system, air is drawn from the outside into the structure, and the odors and other emissions are then captured and treated. This option can significantly increase the cost and prolong the schedule of a development project and is only used in circumstances when other methods may be difficult to implement or are not expected to be effective in mitigating odors.
An example of a successful commercial redevelopment of a former MGP site is the remediation of the Adriaen’s Landing site in Hartford, Conn. The site was developed by the Capital City Economic Development Authority, a quasi-public authority established by the state of Connecticut to stimulate new investment in and around Hartford. The entire development plan includes the Connecticut Convention Center, a Marriott Hotel, the Connecticut Science Center, an enhanced riverfront and a residential, retail and entertainment district. Part of the retail area and convention center was built on top of the former MGP site.
As part of the remediation, an air-monitoring program was used to monitor emissions in real time and to implement effective controls to protect the community. This program included trained personnel who con-ducted odor monitoring to record the nature and intensity of odors. If measurements were greater than a specified level, foaming of exposed areas was used to mitigate odors. Covering inactive excavation areas was also successfully used to mitigate odors as well.
Odors can be a significant issue in dealing with the development of former MGP sites. While they pose a challenge, measurement techniques and control measures are available to minimize the effect on the community. An effective odor measurement and control strategy can address odors as they appear and facilitate the development of former MGP sites.
