By: Scott Cowden and Susan Dennis, CH2M

Scott Cowden presented the paper, “San Francisco’s Southeast Plant Odor Characterization Study Identifies Odor Culprits,” co-authored by San Francisco Public Utilities Commission’s Nohemy Revilla and Meei-Lih Ahmad, on Tuesday, March 22, at the Water Environment Federation’s (WEF) Odors and Air Pollutants Conference, held in Milwaukee, WI, March 21-24.

Check out the complete list of CH2M presenters.

Located in San Francisco’s Bayview Hunters Point neighborhood, the Southeast Water Pollution Control Plant (SEP) is San Francisco’s largest and oldest wastewater facility. SEP treats nearly 80 percent of the City and County of San Francisco’s wastewater, which is transported to SEP through conveyance/storage facilities, sewers and five major pump stations. The plant is located in the midst of a mixed industrial, commercial and residential area, with many of the plant neighbors directly across the street from the plant fence line. Odor emissions have historically been an issue for SEP.

As part of the city’s multi-billion dollar Sewer System Improvement Program, San Francisco Public Utilities Commission (SFPUC) worked with CH2M on a comprehensive SEP Odor Characterization Study, which was conducted to provide an up-to-date, in-depth evaluation of the SEP odor emissions. All key odor sources at SEP were identified, ranked and quantified with regard to predicted off-site odor impacts. In addition, findings and recommendations were included for mitigation of odor emissions.

Odor goals or limits at and beyond the SEP fence line were established for setting a benchmark target for meeting both regulatory requirements and for the plant to be considered a good neighbor. Workshops conducted with SFPUC stakeholders resulted in an endorsed odor goal of all new construction to be provided with odor control features to meet a 5 dilutions-to-threshold (D/T) and a 99 percent compliance based on a 1-hour average.

An extensive SEP site odor assessment was also conducted to identify all pertinent odor sources at SEP and the potential impact to the surrounding community, determine and quantify odor concentration inputs for dispersion modeling and verify baseline modeling results. The site odor assessment tasks included a winter and summer Subjective Odor Survey, with field olfactometers and odor panelists, and a winter and summer sampling event, with the goal of quantifying current odorous emissions at the plant, determining seasonal odor emission differences, evaluating existing odor control treatment system performance, and evaluating building and covered area air balance and odor containment issues.

CH2M developed an air dispersion model to characterize the SEP odor emissions and fugitive odor risks. The model was calibrated through a series of tasks and validated through actual fence-line monitoring and comparison to historical odor complaint data. The objectives of the dispersion modeling analysis included:

  • Determine area impacted by individual, combined and overall plant odor emissions for both summer and winter
  • Rank individual and combined odor sources for both summer and winter
  • Conduct sensitivity and “what-if” analyses for specific sources to further evaluate and quantify impacts

SFPUC considered two programs for air dispersion modeling: AERMOD, a steady-state model that incorporates air dispersion based on planetary boundary layer turbulence and scaling, and CALPUFF, a model used by the EPA for assessing long-range transport of pollutants and their impacts. Workshops were held to discuss the two model options. The CALPUFF model was selected for odor control modeling purposes, while the AERMOD model was selected for meeting Bay Area Air Quality Management District permitting requirements.

Model results have proven to be representative of actual existing SEP emissions characteristics and have provided an odor “fingerprint” for the SEP. Furthermore, the model provided the following key conclusions:

  • Revealed which odor sources at SEP are the greatest contributors to offsite odor impacts and therefore should be focal points for future odor control improvements
  • Sensitivity analyses revealed which odor sources can result in offsite odor impacts due to operational inefficiencies (e.g. combustion cold-starts) and process variations (e.g. upstream collection system chemical dosing and process upsets)

So far, the model has been an invaluable tool for SFPUC personnel planning future odor control improvements and has helped validate progress toward achieving the SEP odor goal. The air dispersion model will be updated as future SEP changes occur for use as a long-term odor control management and planning tool.

Scott Cowden is a professional engineer at CH2M, located in the firm’s Corvallis, Oregon office. He brings 28 years of experience in the area of odor control applications for municipal wastewater treatment systems to his role. His expertise includes both vapor phase and liquid phase technologies. He also has extensive experience in the area of odor control master-planning, including site sampling, emissions modeling and dispersion modeling. During his career, Scott has designed vapor phase odor control systems from 500 cfm capacity to greater than 1,000,000 cfm capacity. He also has a broad range of expertise in liquid phase and vapor phase technologies.

Susan Dennis is a professional engineer in CH2M’s San Francisco CA office, and is the CH2M Wastewater Regional Service Lead for the Western US. She has more than 29 years of experience in the planning and design of wastewater treatment and biosolids facilities.  As a senior project manager, she has managed several odor control master planning projects which included extensive site sampling programs and dispersion modeling.  Susan is currently involved in managing the design of the SFPUC Biosolids Digester Facilities Project, for which odor control facilities are a key component.