Ferreira, Marcia Metals Concentration on Particles in Highway Runoff (Page 1 of 7) Metals Concentration on Particles in Highway Runoff Marcia Ferreira 1 , Sim-Lin Lau 1 , Michael K. Stenstrom 1* 1 Civil and Environmental Engineering Department, UCLA, Los Angeles, CA, 90095 *Corresponding Author: stenstro@seas.ucla.edu KEYWORDS: heavy metals, best management practices; stormwater runoff, runoff treatment units INTRODUCTION The choice of runoff treatment units (also known as “structural best management practices” or “structural BMPs”) is often based on an empirical estimate of their efficiency, as opposed to the theoretical basis of their removal mechanism. Some studies use percent removal of pollutants as a metric for the efficacy of the treatment unit, however this approach has been criticized in the past decade as flawed by several critical studies (e.g., Strecker et al., 2001). Sedimentation and filtration treatment units are selected on their ability to achieve particle removal efficiency, which does not always translate into pollutant removal efficiency. This work aims to highlight the importance of studying the fractionation of six heavy metals commonly present in highway runoff as basis for the selection of runoff treatment unit. METHODOLOGY Figure 1. Monitoring sites in west Los Angeles (from Han et al., 2006) Three monitoring sites in west Los Angeles (Table 1 and Figure 1) were part of a long- term study sponsored by the California Department of Transportation. These sites were chosen because they range between 95% and 100% pavement, which means that sampled particles are solely from the stormwater runoff and not from unpaved highway shoulders (coarse material). In addition, there is no snow in lower elevations in southern California so no particles from salt or sand used to control snow and ice were captured. Finally, the three sites represent very small catchments, and there was barely any delay between the 4294 WEFTEC 2011 Copyright ©2011 Water Environment Federation. All Rights Reserved.