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

ABSTRACT

Three of the western National Forests (Forest) underwent the NEPA process for assessing future oil and gas (O&G) exploration and production impacts.  The standard arrays of environmental concerns were evaluated and cumulative impacts assessed in the Environmental Impact Statement (EIS) process, including air resources.  Air resources impacts were especially challenging because the Proposed Action and Alternatives (PA&As) were based on potential but undefined leasing scenarios.  Any PA&A would have to be evaluated anywhere within the Forest boundary and with emissions ranging from a dry exploratory well to a full production oil or gas well 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, where and how many wells were drilled.

Our task was to effectively provide an assessment of the potential impact of both exploratory and production oil & gas wells on the air resources of the Forests. Determining worst-case and typical plant-based emissions and how they were emitted was challenging. Fulfilling the concerns of numerous non-governmental organizations, 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 term impacts while employing CALPUFF-lite for long range assessments. Maximum and minimum elevation changes were determined and proportioned for each modeling evaluation; radii of impacts were segmented; and generic emissions were calculated for regional expectations.  The results of our efforts were tabulated in a normalized ‘look-up’ table.  This look-up or “screening table” allowed the Forest Service to determine if a particular parcel should be considered, be evaluated, or be excluded entirely from O&G exploration and/or development. In addition, performing this evaluation for all three Forest Service’s Districts allowed for assessment consistency in the region.

Shannon K. Manoulian, Chris Johnson
JBR Environmental Consultants, Inc., 7669 West Riverside Drive, Suite 101, Boise, ID  83714
Erin C. Hallenburg, P.E., QEP
JBR Environmental Consultants, Inc., 8160 South Highland Drive, Sandy, UT  84093