Pacific Southwest Research Station

Sources of fine sediment particles (< 20 µm) in urban roadway runoff in the Lake Tahoe Basin

Principal Investigators:
Hyun-Min Hwang, Texas Southern University
Russell Wigart, El Dorado County Department of Transportation
Raphael Townsend, Tahoe Environmental Research Center, University of California, Davis
Alan Heyvaert, Desert Research Institute

Proposal [pdf]

Final Report [pdf]

Project Summary

This study investigated the contribution of winter time road management practices such as abrasive sand application and snow plowing to fine sediment particles in roadway runoff that enters directly or indirectly into Lake Tahoe. Reliable information regarding source apportionment of fine sediment particles is required to advance source control best management practice (BMP) to reduce loadings of fine sediment particles and associated phosphorus in winter time roadway runoff to improve Lake Tahoe water column clarity.

This study collected roadway runoff from two sites on Pioneer-Trail, which is a major traffic road in the southern Lake Tahoe Basin between November 2012 and May 2014 to identify major sources of fine sediment particles and calculate their contributions. Sieved (20 µm) runoff samples were measured for turbidity, organic matter content, oil and grease content, elemental composition, phosphorus, and molecular organic markers.

The contribution of major sources, including road side hill soil, abrasive sand, pavement wear, vegetation debris, to fine sediment particles was calculated using a chemical mass balance model. Approximately 50% of fine sediment particles in roadway runoff collected from the two study sites originated from non-traffic related sources such as road side hill soil and vegetation debris. Traffic related sources such as abrasive sand (Washoe sand), pavement wear, and tire wear particles accounted for the other half of the fine sediment particles. Road side surface soil contributed 20 to 70% of fine sediment particles that is the highest among the all measured sources. It is interesting to note that asphalt pavement wear particles accounted for 18 to 53%, which is the second most abundant source of fine sediment particles in collected roadway runoff. These particles were produced when snow plow steel blades and snow chains grind asphalt pavement. The contribution of abrasive sand ranged between 7 and 21%. No significant differences were found between the two sampling sites. Chemical mass balance calculation indicates that the vast majority (up to 85%) of phosphorus in fine sediment particles originated from Washoe sand and road side hill soil.

Road side surface soil, pavement wear particles, abrasion sand, and vegetation debris are the major sources of fine sediment particles in roadway runoff. These four sources, combined together, accounted for more than 90% (by mass) of the total fine sediment particles. Road side surface soil contributed 20 to 70% of fine sediment particles that is the highest among the all measured sources. This finding is contrary to the common belief that abrasive sand is the most predominant source of fine sediment particles in roadway runoff in the Lake Tahoe Basin.