Cambridege Environmental

58 Charles Street
Cambridge, MA 02141
Phone: 617-225-0810

411 Aviation Way
Frederick, MD 21701
Phone: 301-695-0251

Hot-mix Asphalt Plants and Cement Kilns

Cambridge Environmental assesses potential impacts to the environment and public health from atmospheric emissions from hot-mix asphalt facilities, cement kilns, and other facilities.

We have performed numerous evaluations of the local impacts of both criteria pollutants and hazardous air pollutants emitted from hot-mix asphalt plants. The U.S. EPA has determined that hot-mix asphalt plants are minor sources of air pollution, and the permitting processes required by most state regulatory agencies for these facilities is often straightforward. However, because hot-mix asphalt needs to be manufactured relatively close to where it is applied, it is produced at thousands of small facilities, often near residential centers and roadways, rather than at a few large facilities at distant locations. Thus, construction and operation of hot-mix plants often requires the approval of local agencies such as zoning boards, planning boards, and boards of health. As objective experts in the field, we have helped local boards and developers alike by holistically assessing potential risks, and in responding to local, site-specific concerns.

Cement kilns are well suited to the destruction of organic hazardous wastes because of the kilns' high temperatures, long residence times, and high levels of high-surface-area inert materials. Such kilns are also subject to extensive regulatory requirements with regard to the detailed measurement and modeling of airborne emissions. We conduct complex multi-pathway assessments of exposures and risks to health from these emissions, and thus determine whether impacts are or are not acceptably small.

Our services in these areas are primarily conducted by Drs. Stephen Zemba and Michael Ames who perform emissions estimates and calculations, atmospheric dispersion and deposition modeling, and multi-pathway environmental fate and transport modeling. Both individuals studied engineering at the Massachusetts Institute of Technology. Dr. Laura Green, a board certified toxicologist, has extensive experience in evaluating the potential health effects of emissions related to hot-mix asphalt, and has testified at many public meetings on this and related topics.

Sample Projects

Detailed local air quality modeling of emissions from a hot-mix asphalt plant

For almost four decades, a hot-mix asphalt plant operated at a location that had once been home only to industrial facilities. Over time, residential developments and schools were built in the area, and not all of the newcomers were pleased to find themselves near the asphalt facility. When the plant needed to obtain a new special use permit from the city, the plant's neighbors and the city required that the facility demonstrate that its operation would not lead to exceedences of any federal or state air quality standards. Among the city's unusual conditions for this evaluation was the requirement that near-field PM2.5 impacts from both mobile emissions and ground-level fugitive dust sources be included in the modeling. Because neither federal nor state guidance for assessing these emissions had been established at the time of the assessment, Cambridge Environmental needed to develop and apply an assortment of methods to comply with the city's requests. Our work was reviewed and approved by the city's air quality consultants and a consultant hired by the local condominium association. Our emissions and dispersion modeling estimates were also benchmarked against source-oriented PM10 monitoring data collected by the city. We presented our findings at many (sometimes contentious) public meetings regarding the impacts of the hot-mix plant, and answered numerous concerns from both elected officials and the general public.

Health risk assessment of a proposed hot-mix asphalt facility in a high-income suburb

A developer proposed building a hot-mix asphalt facility in a high-income suburb. Although the proposed site-plan included a significant buffer-area, and the plant was to be located in a quarry - which quarry had been operating for more than a century - ambiguous by-laws and the objections of some local residents led to an extensive inquiry. Our role was to estimate possible health-risks from the cumulative impacts of the facility per se, the trucks associated with the facility, and "grandfathered" facilities such as the quarry and a concrete-batching plant. Impacts to nearest neighbors and a local elementary school were of particular interest, especially since the asthma incidence at the school appeared to be significantly higher than expected, based on comparable data from schools across the state. The interested parties included the state Department of Health, the state Department of Environmental Protection, the local Board of Health, the local Planning Board, the Planning Board's own consultants, and technical experts hired by opponents to the project. Accordingly, we undertook many detailed and issue-specific analyses, which analyses were both extensively documented and thoroughly scrutinized, and presented our findings at numerous public hearings.

Food chain-based risk assessment of emissions from a cement kiln using hazardous waste as a supplemental fuel

Because a Portland cement manufacturing facility in Indiana uses hazardous waste as an alternative fuel, its emissions were subject to Federal Maximum Achievable Control Technology (MACT) restrictions, and it was required by the regional branch of the U.S. EPA to perform a multi-pathway (i.e., food-chain) risk assessment of their airborne emissions. Cambridge Environmental conducted this assessment using both measured and MACT-based pollutant emission rates, and both EPA default modeling parameters and a variety of facility and site-specific data. Our risk assessment showed that, even if the facility emitted pollutants at the maximum allowable rates, the best estimates of resulting, or "residual" risks to the health of local residents, farmers, and subsistence fishers would be within regulatory guidelines. Cambridge Environmental also demonstrated that the highly conservative default assumptions recommended by the EPA for use in modeling the emissions, transport, and fate of pollutants that are frequently found to be the major contributors to risk-estimates (in particular, mercury, dioxin, and hexavalent chromium) greatly overestimate the off-site concentrations of these compounds, and hence their potential to harm the environment or public health.