As the number of sites in the active remediation and post-remediation stages increases, new approaches are needed to address the monitoring requirements for process control, performance assessment, and compliance purposes. The use of contaminant flux and contaminant mass discharge as metrics to assess risks at contaminated sites and evaluate the performance of site remediation efforts has been gaining increased acceptance within the scientific, regulatory, and user communities. Other SERDP and ESTCP efforts have focused on determining the effectiveness of remedial technologies under different site conditions and optimizing their performance accordingly.