Structural BMP Implementation and Bypass: How Big Does My Capture and Treat System Need to Be and Do I Still Have to Sample Bypass to Comply With the IGP?
Facilities trying to comply with the new amendments to California’s Industrial General Stormwater Permit are at a near boiling point in the development of structural best management practices (BMPs). With looming Total Maximum Daily Loads (TMDLs), many becoming effective on July 1, 2020, facilities need to ratchet down their effluent concentrations to meet the Numeric Effluent Limits (NELs) or TMDL Numeric Action Levels (TNALs). Add to that, many facilities that are in Exceedance Response Action (ERA) Level 2 Status for those constituents that are not TMDLs still need to further prevent discharge exceedances of Numeric Action Levels (NALs) or run the risk of regulatory actions or third-party citizen lawsuits. Many facilities have had the past five years to assess their compliance performance through monitoring and reporting. Many facilities have progressed from Baseline Status to ERA Level 1 and further on to ERA Level 2. While some facilities have managed to get back to Baseline through a variety of conventional BMPs such as good housekeeping, filter socks, or other administrative controls, many facilities are stuck in ERA Level 2 and basic BMP implementation is not effective. These facilities are likely candidates for structural BMPs. The Permit specifies a design storm of the 85th percentile, 24-hour storm on a flow or volume basis. However, what happens when the design storm is exceeded and do I need to sample the bypass when it occurs?
A key issue for many IGP permittees is what to do when conventional BMPs (e.g., wattles, storm drain inlet filters, street sweeping, and other housekeeping BMPs) are not effective. For addressing difficult analyte NALs or TMDLs, implementing an advanced system or going with the Compliance Option in Attachment I is a likely scenario. However, this raises questions for those facilities in ERA Level 2 and having to go the BMP demonstration process. Does designing BMPs to the 85th percentile storm actually equal compliance? And, if an advanced BMP is designed to the 85th percentile on a flow or volume basis, does one need to sample bypass, and what happens to those results once collected? The IGP and the Stormwater Multiple Application and Report Tracking System (SMARTS) are not clear on when or where to sample and how those results are to be entered. And, how are the results counted in relation to the ERA process?
This presentation covers structural BMP design scenarios, methods to develop bypass sampling procedures, and data assessment for an ERA Level 2 facility, a TMDL facility, and a TMDL facility using Attachment I options, and methods to address potential bypass for IGP compliance.