USING WIND TUNNEL MODELING TO ASSESS FUTURE ODOR IMPACTS FROM A MUNICIPAL SOLID WASTE LANDFILL

Disposal of municipal solid waste at a landfill involves the decomposition of organic material and the subsequent production of odorous compounds. A significant portion of landfill operations consists of activities designed to minimize the release of these odorous substances. The impact of odors on the surrounding communities is influenced by several factors, including the size and extent of the operation, how close the operation is to the community, the climate (including micrometeorology) and the source of odors. There are several potential sources of odor associated with landfill operations, none of which are typical point sources. These include:Direct emissions from specific types of solid waste as they are brought into the landfill,odors in landfill gas produced by anaerobic microbial decomposition of organic matter present in solid waste,odors from the shredded green waste (yard and landscape trimmings) that supplies a portion of the daily cover at many landfills, andodors produced during the installation of landfill gas collection systems, specifically, trenching operations to install horizontal gas collection piping.The fugitive nature of these landfill odors presents a challenge when trying to assess impacts. Furthermore, as the operation of a landfill continues, the disposal site increases in elevation and moves further away from the property boundary. The changing landfill contours and terrain features can impact the micrometeorology of the site and other factors such as odor transport. During the recent application process for a new Conditional Use Permit for a regional landfill, concerns were raised regarding the changing landfill configuration and the potential for the development of new odor complaint patterns in the surrounding community. An investigation was launched to study the impact that changing landfill contours would have on odor transport to the local community. Several approaches exist for assessing if a source would have an impact on the surrounding community, but physical modeling of the landfill in a wind tunnel was found to provide a good representation of the landfill's surrounding terrain as well as the changing contours of current and future terrain conditions. In the fall of 2001 the County Sanitation Districts of Los Angeles County contracted with the firm Cermak Peterka Petersen, Incorporated (CPP) to undertake a wind tunnel study of the Puente Hills Landfill. Four 1:1200 scale models were constructed to represent existing and future landfill contours, for testing under neutral and stable atmospheric conditions. During the conduct of the study, tracer gases were emitted from defined areas and normalized concentrations were measured downwind on a complex receptor grid. Using a technique established by the authors, odor thresholds were developed based upon the location and temporal patterns of odor complaints, and compared to the modeling results. The simulations confirmed that future landfill contours coupled with additional mitigation would result in odors, if any are present, at levels below established odor thresholds.