Sarah Ganley, Vice President, Water Resources, Bohannan Huston, Inc.
How do you remove pollutants ranging from shopping carts to fine sediments within an urbanized channel in a narrow right-of-way without sacrificing flood control and safety? The Albuquerque Metropolitan Arroyo Flood Control Authority (AMAFCA) and the City of Albuquerque (COA) answered this question by designing and constructing a stormwater treatment train. The COA and AMAFCA are MS4s that have NPDES permits for stormwater discharges. As part of MS4 permit compliance, AMAFCA and the COA are required to monitor and enhance stormwater quality through constructed BMPs. The Lower Bear Tributary Water Quality Improvements Project included construction of a stormwater treatment train in a fully developed urbanized setting. As the stormwater runoff moves through this arroyo, it passes through a series of BMPs, referred to as Treatment Cars 1-5, each designed to progressively remove pollutants from the stormwater to help protect the water quality of the Rio Grande and the aquifer. Car 1 slows the runoff down to better remove larger gross pollutants, organic material, and miscellaneous debris. Car 2 employs two additional debris fence structures to capture smaller debris that makes it through, over, or around the Car 1 screens. Cars 1 and 2 have constructed improvements allowing the routine maintenance to be focused in this area of the Lower Bear Arroyo while keeping the remainder of the downstream arroyo more naturalistic. Cars 3 and 4 remove pollutants through vegetation and maximize the amount of runoff that infiltrates into the ground and reaches the aquifer. Car 5 provides an opportunity for additional infiltration because the flow line of the constructed channel is lower than the natural arroyo allowing more time for ponding and infiltration, especially in smaller storms, before the stormwater runoff continues its journey downstream towards the Bear Canyon Arroyo aquifer recharge zone and ultimately to the Rio Grande. The treatment train addresses both stormwater quantity as well as the quality. Cars 1 and 5 have instruments installed in the arroyo that continually measure the depth of flow during storm events allowing calculation of runoff entering and leaving the treatment train. Stormwater quality runoff samples will also be collected above and below the treatment facility to provide for the determination of pollutant load reduction through the treatment train in an arid urbanized and fully developed sub watershed. Lessons learned from this treatment train pilot project through performance monitoring will be formulated into a template for other projects in the region.