Onsite Compliance Options - Is Storm Water Infiltration Right for Your Facility?
The amendments to the Industrial General Storm Water Permit (IGP) adopted on November 6, 2018 will take effect on July 1, 2020. This presentation will describe storm water infiltration as an Onsite Alternative Compliance Option as provided in Attachment I of the of the IGP Amendments. The opening part of the presentation will review how to determine site suitability for storm water infiltration. This involves evaluating local soil and groundwater conditions, percolation testing to determine infiltration rates, and onsite soil sampling and analysis to identify existing soil contamination, if any, that could be mobilized by infiltration. Design requirements will be discussed including hydrologic calculations (will not present any real world calculations) to determine the storm water flow or volume generated by the 85th Percentile Storm Event based on historical local information, and sizing of the infiltration gallery based on the infiltration rate and the design event flow rate or volume. Ancillary BMPs, including storm water treatment, storm water clarifiers and source controls will be discussed.
Regulatory requirements range from the technically complicated to the mundane, including the fact that hydrologic analysis and calculations and BMP operational parameters must be certified by a California licensed civil engineer, 24-hour drawdown time or design factor of safety, monthly sampling and analysis to demonstrate protection of ground water quality, reporting requirements, and SWPPP Update.
A small portion of the presentation will focus on regulatory benefits of implementing and maintaining an infiltration BMP, including exemption from discharge to Ocean Water Requirements (IGP Section VIII), training qualification, requirement to obtain a QISP (IGP Section IX), implementation of Advanced BMPs (IGP Section X.A.7 & X.H.2), Design Storm Standards for Treatment Control BMPs (IGP Section X.H.6); and Exceedance Response Actions (IGP Section XII).