Mass Loading of First Flush Pollutants with Treatment Strategy Simulations

Abstract

“First flush” is a term for the initial period of stormwater discharge from a storm event. Conventional thinking is that the first flush exhibits high pollutant concentrations. The existence of a first flush in highway runoff has been documented through a comprehensive 4-year runoff monitoring from three highway sites in Los Angeles, California. As part of this study, a numeric definition of the mass first flush ratio is developed; it characterizes the normalized mass of pollutants in the first portion of the normalized runoff volume. Mass first flush ratios have been developed for more than 30 conventional water quality parameters, heavy metals, nutrients, and organic pollutants. This study explores the improved performance that some best management practices (BMPs) exhibit when they can take advantage of the high concentrations of pollutants at the beginning of a storm event. A range of hypothetical events corresponding to the observed mass first flush ratios were simulated. These simulations demonstrate that improved mass removal rates are possible when BMPs can be managed to treat a greater volume of the early runoff. For example, it was shown that for pollutants such as total suspended solids, chemical oxygen demand, total organic carbon/compounds, and oil and grease, infiltration basins that can capture the first 20% of the storm volume and bypass the remaining volume can be twice as effective as a practice that treats 20% of the storm volume throughout the entire period of runoff. Similarly, when a seasonal first flush exists, treating the first few storms of the season entirely is more effective than treating a constant volume throughout the season.

Build-Up/Wash-Off Monitoring and Assessment for Sustainable Management of First Flush in an Urban Area

“…From Figure 13, we evaluated the mass first flush ratio (MFF) [32] which is defined as the ratio between the pollutant mass with respect to runoff volume [33], used to characterize and quantify the magnitude of first flush.…”

Removal, by Vegetated Biofilter, of Medium and Low Concentrations of Pollutants from Simulated Highway Runoff

“…Corresponding author: G. F. Mitchell, mitchelg@ohio.edu. metals (15)(16)(17)(18)(19)(20)(21)(22)(23)(24), except iron (Fe), were near the detection limits for the inductively coupled plasma-optical emission spectrometer, the artificial runoff was formulated to ensure low concentration at five times the typical analytical detection limit, medium concentration at five times the low level, and high concentration at five times the medium level, to ensure removals were measurable. A medium-concentration event used medium-concentration influent followed by low-concentration influent and a low-concentration event used low-concentration influent followed by tap water.…”

Innovative and Reliable Assessment of Polluted Stormwater Runoff for Effective Stormwater Management

“…Despite several sometimes unclear and subjective detection methods, academics, political decision makers and watershed managers unanimously acknowledge the potential usefulness of the FF concept for sustainable, efficient and cost-effective implementation of both conventional structural stormwater control practices and green infrastructure technologies, e.g., [11][12][13][14][15][16][17].…”