Dr. Keller seeks to understand the processes through which contaminants may accumulate or transform in soil, air or water, as well as in the biota, with an emphasis on developing better management strategies for dealing with pollutants in the environment. Current research topics involve the treatment of soils which have been contaminated with hazardous wastes, as well as larger scale pollution management at the watershed scale. In addition to analyzing the scientific issues involved, Dr. Keller is interested in the development of management strategies to suit the characteristics of each site, minimizing risk at least cost. Dr. Keller has had several years of experience developing management strategies in the private sector, which he brings to his Bren School courses and projects.

Dr. Keller is known for his involvement in the phasing out of the gasoline additive MTBE as part of a UC-wide project; his research found MTBE to seriously affect water resources while providing only modest air quality benefits relative to other alternatives.

Dr. Keller also was the facilitator for the award-winning Nitrogen TMDL process for the Santa Clara River. Previous TMDLs in the region had been very contentious, but through a combination of science-supported decision-making and a willingness to try out many ideas proposed by the stakeholders, the Santa Clara River TMDL Steering Committee was able to reach a consensus, which was fully supported by the RWQCB. The steering committee received the 2000 H. David Nahai Water Quality Award for their work.

He has also worked with several Regional Water Quality Control Boards on TMDL processes, including nutrients in the Napa River, PCBs in San Francisco Bay, organophosphate pesticides in the Newport Bay watershed, and an assessment of TMDL priorities in the South Coast area of Santa Barbara County. These experiences have not only served to train many graduate students at the Bren School, but have also resulted in important advances in the modeling and management of watershed-scale water quality. Dr. Keller teaches a course on Sustainable Watershed Management, which is open to professionals through the UCSB Extension Program. He has been recognized with the Bren School Teaching Award.

Dr. Keller is also well-known for his expertise in the fate and transport of pollutants, including organic liquids (NAPLs) as well as organic pesticides associated with clay particles; he has over 50 peer-reviewed publications in top journals. His research team also works on technologies to solve important water-quality problems, and recently was covered in the New York Times for a major improvement in the technology to skim oil spills in marine environments, which can significantly reduce the risk of the oil spill reaching coastal resources.