Bacteria Outfall Monitoring and TMDL Load Reduction Strategies


Using Intensive Outfall Monitoring and Statistical Models to Create Quantitative Implementation Plans that Comply with Bacteria TMDL Requirements

End Client: Multiple clients including City of Los Angeles and Los Angeles County (in coordination with numerous partners including Larry Walker Associated and CDM Smith)

Paradigm has served as technical lead on multiple Load Reduction Strategies (LRS) to help MS4s comply with the LA River Bacteria TMDL.  The TMDL requires MS4s to bring an 840-square mile area into compliance with receiving water and effluent limitations for E.coli. An LRS allows MS4s to pursue an optional “compliance path” for the TMDL.  Each LRS includes outfall monitoring, statistical modeling and development of an implementation plan for attainment of TMDL wasteload allocations. To date, Paradigm has led LRSs for two mainstem LA River segments and eight tributaries. The monitoring component of LRSs include intensive “snapshot” outfall monitoring events that include flow measurements and indicator bacteria analyses.  For one of the LA River segments, the monitoring included microbial source tracking with Bacteroidales and human viruses. To date, over 300 outfalls have been monitored under the LRS programs. Monitoring data provide high resolution boundary conditions for Monte Carlo models. The statistical models have been used by Paradigm to estimate the effect of dry weather BMPs (including low flow diversions) and evaluate the number of BMPs needed to meet TMDL wasteload allocations (see example modeling output below). Paradigm served as the lead author for the LRS reports, coordinating meetings with other cities who are members of the LRS groups, and has led several meetings with Regional Board staff.  Paradigm continues to support LRS development and implementation as the TMDL compliance schedule progresses.