Air Dispersion Modeling for the National Forest Service Oil Gas Leasing Evaluation

摘要

Three of the western National Forests (Forest) underwent the NEPA process for assessing futureoil and gas (O&G) exploration and production impacts. The standard arrays of environmentalconcerns were evaluated and cumulative impacts assessed in the Environmental ImpactStatement (EIS) process, including air resources. Air resources impacts were especiallychallenging because the Proposed Action and Alternatives (PA&As) were based on potential butundefined leasing scenarios. Any PA&A would have to be evaluated anywhere within the Forestboundary and with emissions ranging from a dry exploratory well to a full production oil or gaswell or combination of O&G wells. In addition, supporting equipment, length of access roads,fuel type, topography, and climatic conditions could all vary greatly depending on how, whereand how many wells were drilled.Our task was to effectively provide an assessment of the potential impact of both exploratory andproduction oil & gas wells on the air resources of the Forests. Determining worstcaseandtypical plantbasedemissions and how they were emitted was challenging. Fulfilling theconcerns of numerous nongovernmentalorganizations, regulatory agencies, parties of interest,as well as the Forest Service proved its own divided challenge.Our analytical dispersion modeling approach was multifaceted using ISCST3 for short termimpacts while employing CALPUFFlitefor long range assessments. Maximum and minimumelevation changes were determined and proportioned for each modeling evaluation; radii ofimpacts were segmented; and generic emissions were calculated for regional expectations.1,2,3The results of our efforts were tabulated in a normalized ‘lookup’table. This lookupor“screening table” allowed the Forest Service to determine if a particular parcel should beconsidered, be evaluated, or be excluded entirely from O&G exploration and/or development. Inaddition, performing this evaluation for all three Forest Service’s Districts allowed forassessment consistency in the region.