Demonstrating Compliance with Level 2 ERA Process Using a Combination of Volume and Flow-Based Treatment Control BMPs
As a facility moves from Level 1 Exceedance Response Action (ERA) to Level 2 ERA, they will be challenged to develop new best management practices (BMPs) and likely a combination of BMPs to address those facility stormwater discharges that contain pollutants exceeding the Numeric Action Levels (NALs). The Industrial General Permit (IGP) includes specific design standards for Treatment Control BMPs, both for volume-based BMPs and for flow-based BMPs. We have found that many industrial facilities either do not have the required space to satisfy the IGP volume-based treatment control BMP design standards or that simple retention strategies will not provide adequate pollutant removal to satisfy NALs. Similarly, many sites have very large drainage areas (such as landfills) and satisfying the IGP design standards for flow-based treatment systems result in large flow rates that prove to be impractical or infeasible to manage. This presentation will address innovative methods of conducting site hydrology evaluations, combining volume- and flow-based treatment technologies, and arguments for compliance with the Level 2 ERA process.
Using an example site for illustration, I will show how existing retention basins are often inadequate to satisfy the IGP design standards due to inadequate basin drawdown. There appears to be some confusion amongst the regulated community that simply designing a retention basin to meet the IGP design standards will satisfy the permit requirements; however, the implicit assumption is that the basin will drawdown in 24 – 48 hours to allow for the basin capacity to be renewed for the next storm or back-to-back storms. Further, using the same example, I will show how applying the IGP design standard to establish a flow-based treatment system often results in an extremely large and impractical treatment system. I will present the results of a continuous simulation model that was used as a predictive planning tool to assess the impact of various retention basin volumes and treatment system flow rates on both the number of untreated water discharge days and the total volume of water bypassed untreated by the overall system. We will use this tool for sizing basins and sizing active treatment systems, and predicting the volume of water treated. These are the data needed to develop the arguments for compliance in the Level 2 ERA Action Plan.
The balance of the presentation will focus on arguments that can be made to demonstrate IGP compliance in the Level 2 Action Plan. These arguments may be presented individually or in combination. The Level 2 ERA compliance arguments are.
Equivalent Water Volume Treated: One would calculate the annual average volume of water that would be treated (and bypassed untreated) by applying one of the IGP flow-based design standards using historical rainfall. Then, compare this average annual volume of treated and bypassed water to the predicted performance of the proposed hybrid retention/treatment system. A site example is provided.
Equivalent Mass Removal: One would calculate the annual average volume of water treated (and bypassed untreated) as above. Then, using that annual average volume of water, one would calculate the pollutant mass that would be discharged when discharging at the NALs (i.e., kilograms of TSS or iron). One would calculate the predicted annual average mass of pollutants discharged from the site when operating the proposed hybrid retention/treatment system. One would need to be able to assess the pollutant reduction by treatment as well as apply an average pollutant concentration for the water bypassed untreated.
Technical and Economic Feasibility: Assess treatment flow rates by graphically comparing percent water treated (versus bypassed) with flow rates and identifying the “knee of the curve” or point where large increases in flow rate (cost) result in small increases in percent water treated (benefit).
Patrick Galvin is a professional civil engineer and California Industrial General Permit Trainer of Record. He has an MS in Civil Engineering from Loyola Marymount University, Los Angeles. Mr. Galvin has more than 30 years of consulting experience and works extensively on industrial stormwater sites in California and Oregon. He specializes on complex site evaluations and innovative practical BMP design and implementation.