Todd Engineers: LA Sanitation Districts

Hydrogeologic Technical Support
County Sanitation Districts of
Los Angeles County, California

Todd Engineers has provided technical support to the Sanitation Districts at five of their landfills in Los Angeles County.

The County Sanitation Districts of Los Angeles County (Sanitation Districts) are a combination of special districts serving the wastewater and solid waste management needs of 5.3 million people in Los Angeles County. The Sanitation Districts' service area covers approximately 792 square miles and incorporates 78 cities and many unincorporated areas in the county. The Sanitation Districts operate and maintain a number of wastewater handling and treatment facilities and solid waste landfills in Los Angeles County.

Key Issues
Landfill contaminant monitoring and containment Hydrogeologic characterization in complex bedrock settings Handling of wastewater treatment biosolids Public perceptions and concerns

Todd Engineers has provided technical support to the Sanitation Districts since 1993 for a wide range of issues related to their active and inactive landfills and handling of wastewater treatment plant biosolids. Projects have included review of groundwater monitoring plans, characterization of hydrogeologic conditions, peer review of corrective action plans, expert witness support for landfill continuing operation and expansion plans, assessment of landfill impacts on downgradient groundwater quality, field investigation and assessment of landfill containment facilities, examination of the potential for groundwater impacts from biosolids use on agricultural land, and litigation support relative to claims of downgradient damage from a landfill.

Services Provided
Expert testimony at regulatory and public meetings Characterization of complex hydrogeologic bedrock settings Evaluation of monitoring programs Evaluation of impacts of biosolids application Groundwater modeling of remedial capture zones Contaminant fate and transport assessments Litigation support responding to allegations of landfill impacts

The Spadra Landfill is one of the Districts' older, mostly unlined sites where groundwater has been affected with low levels of volatile organic chemicals (VOCs). Prior to closure of the landfill, the Sanitation Districts commissioned a comprehensive hydrogeologic investigation to evaluate the effectiveness of existing groundwater containment systems in place at the site. Todd Engineers and GeoSyntec Consultants teamed on this extensive program of field investigations, analysis, and reporting. The hydrogeologic investigation included drilling of boreholes and installation of monitoring and extraction wells. Soil and groundwater samples were collected and aquifer tests were performed and analyzed to characterize site hydrogeologic conditions. Computer models were constructed to evaluate the groundwater containment systems under various pumping scenarios. The investigation resulted in an improved characterization of the hydrogeology of the site. Based on the computer modeling performed, recommendations were implemented to install additional groundwater extraction wells in two areas of the site.

The large number of wells monitored during pumping tests allowed for the interpretation of distance-drawdown plots to determine aquifer and well parameters.