Conference Agenda

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Session Overview
Session 05A: Stormwater
Monday, 13/Sept/2021:
10:30am - 12:00pm

Location: 110AB

East Building

External Resource:
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10:30am - 11:15am

Advanced Stormwater Treatment Innovation for Materials Recovery Facilities

Jennifer Schmitz

Clear Water Services, United States of America;

This presentation will highlight a case study on a waste and recycling facility located on the Lower Duwamish Waterway in Seattle, Washington. The case study will assess the stormwater challenges the Facility dealt with (run-on, runoff, discharge location variation, remaining in compliance with strict permit regulations) and discuss what steps the Facility did ahead of time in order to evaluate and select the appropriate long term stormwater treatment system.

The Lower Duwamish Waterway is known for legacy contamination due to decades of industrial activity and runoff from residential areas. The Waterway is an approximately 5-mile stretch of the Lower Duwamish River which flows into Elliott Bay and ultimately, the Puget Sound. In 2001, the US Environmental Protection Agency (EPA) added the Lower Duwamish Waterway site to the Superfund National Priorities List. Since then, The Department of Ecology (Washington State Permit Regulator) has led efforts to control sources of sediment pollution in the Waterway with cooperation from the City of Seattle, King County, and EPA.

In the Duwamish cleanup effort, total suspended solids (TSS) contamination was mandated by legislature as an effluent numeric limit. Recology CleanScapes, a recycling waste processing facility (Facility) and direct discharger to the Duwamish Waterway was having a difficult time remaining in compliance with TSS permit effluent limits while also struggling with total metals (zinc and copper) and other pollutants. Clear Water Services (Clear Water) was asked to assist in a design-build treatment selection process and develop a tiered approach for the Facility.

Clear Water was able to prove the efficiency of multiple treatment media and chemistries through bench scale testing and treatability. Using the results, Clear Water and Recology were able to select the best-fit treatment option for the Facility that was most practical for site constraints while also remaining cost effective and within their budget. Clear Water also provided the design and oversight of much needed infrastructure improvements in support of the treatment system selection: combining all site drainage to one discharge location, minimizing runoff from loading and unloading areas and run-on from neighboring properties.

11:15am - 12:00pm

Cold Climate Impacts on Green Stormwater Infrastructure

Kari Nichols

Mead & Hunt, United States of America;

Green Stormwater Infrastructure (GSI) is widely used throughout the largely temperate climate of the Pacific Northwest. However, not all areas of the region are as temperate, and as we are seeing more extreme weather events, we need to consider how GSI may react to more sustained exposure to cold, ice and snow, as well as heat and drought.

Studies around the world have been performed on the performance of GSI facilities in cold climates. Winter runoff conditions, including frozen ground, snow cover, and ice/snow melt events have the potential to adversely impact the performance of GSI, compounded by the addition of sand and chemical deicers to runoff pollutants of concern. In short, a colder climate can impact GSI in a variety of ways.

For instance, a cold climate may result in educed infiltration capacity for GSI. Although frost penetration does not necessarily equate to no permeability, ice lenses may still form, restricting infiltration. Additionally, rain and snowmelt events may reduce or eliminate frost depth in filter media present before and after events; however, larger snow melt events on frozen ground can result in increased runoff.

A colder climate can also reduce the effectiveness of treatment from vegetated systems as the biological function tends to “turn off” in the winter when the vegetation goes dormant. Cold climate regions may also have a shorter growing season, so plant establishment may be more challenging. The effectiveness of other treatments may be similarly reduced—for instance, there may be less sediment removal due to reduced settling velocities in colder water. All of these impacts must be considered in the design and selection of infiltrating best management practices.

Designers may need to include some additional considerations when selecting specific GSI solutions, such as potentially providing larger facilities in cold climates for snow storage and meltwater infiltration as long as road salt and deicing chemical usage is limited. However, the use of GSI still yields the most cost-effective benefits to stormwater runoff management, even in cold climates.

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