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Predicting Unsteady Pollutant Removal in Green Stormwater Infrastructure with Transit Time Distribution Theory
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  • Emily A Parker,
  • Stanley B Grant,
  • Yiping Cao,
  • Megan Rippy,
  • Kevin McGuire,
  • Patricia Holden,
  • Marina Feraud,
  • Sumant Avasarala,
  • Haizhou Liu,
  • Wei-Cheng Hung,
  • Megyn Rugh,
  • Jennifer A Jay,
  • Jian Peng,
  • Stella Shao,
  • Dong Li
Emily A Parker
Virginia Tech
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Stanley B Grant
Virginia Tech

Corresponding Author:[email protected]

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Yiping Cao
Source Molecular Corporation
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Megan Rippy
Virginia Tech
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Kevin McGuire
Virginia Tech
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Patricia Holden
University of California, Santa Barbara
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Marina Feraud
UC Santa Barbara
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Sumant Avasarala
University of Tennessee
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Haizhou Liu
UC Riverside
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Wei-Cheng Hung
UCLA
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Megyn Rugh
UCLA
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Jennifer A Jay
UCLA
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Jian Peng
Orange County Environmental Resources
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Stella Shao
GSI Environmental Inc.
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Dong Li
UC Santa Barbara
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Abstract

In this paper, we explore the use of unsteady transit time distribution (TTD) theory to model pollutant removal in biofilters, a popular form of nature-based or “green” stormwater infrastructure (GSI). TTD theory elegantly addresses many unresolved challenges associated with predicting pollutant fate and transport in these systems, including unsteadiness in the water balance (time-varying inflows, outflows, and storage), unsteadiness in pollutant loading, time-dependent reactions and scale-up to GSI networks and urban catchments. From a solution to the unsteady age conservation equation under uniform sampling, we derive an explicit expression for solute breakthrough with or without first-order decay. The solution is calibrated and validated with breakthrough data from 17 simulated storm events (+/- bromide as a conservative tracer) at a field-scale biofilter test facility in Southern California. TTD theory closely reproduces bromide breakthrough concentrations, provided that lateral exchange with the surrounding soil is accounted for. At any given time, according to theory, more than half of water in storage is from the most recent storm, while the rest is a mixture of penultimate and earlier storms. Thus, key management endpoints, such as the treatment credit attributable to GSI, are inexorably linked to the age distribution of water stored and released by these systems.
Feb 2021Published in Water Resources Research volume 57 issue 2. 10.1029/2020WR028579