Impacts of Pavement Condition on Fine Sediment Particle Load in Roadway Stormwater Runoff
Discipline: Ecology Environmental and Earth Sciences
Subcategory: Water
Session: 1
Janyl Madykova - Texas Southern University
Co-Author(s): Hyun-Min Hwang, Texas Southern University, Houston,TX; Russell Wigart, Tahoe Planning and Stormwater Division, El Dorado County, CA; Andrea Buxton, Stormwater Program, Tahoe Resource Conservation District, South Lake Tahoe, CA
Lake Tahoe is one of the largest freshwater lakes in the country, characterized by crystal-clear water. However, the clarity of the lake has experienced a significant decline over the past few decades, primarily attributed to human activities in the Lake Tahoe Basin. In the Tahoe Basin, roadway stormwater runoff is known to carry high fine sediment particle (FSP; < 20 µm) loads that must be mitigated to improve the water column clarity in Lake Tahoe. Previous efforts mostly focused on reduction of FSP loads from traction abrasives. Pavement wear particles, however, have not been recognized as a major source of FSP. This study investigated impacts of asphalt pavement condition on FSP loads in roadway stormwater runoff in South Lake Tahoe. Stormwater samples were collected before (year 1, 2017-2018) and after (year 2, 2018-2019) pavement rehabilitation. Pavement condition was quantified using a pavement condition index (PCI), which was very poor (PCI=29) in year 1 and tremendously improved (PCI=99) in year 2. Stormwater runoff samples were collected using an ISCO automated stormwater sampler and passed through a 20 µm sieve and glass fiber filters to separate FSP. Samples were analyzed for trace elements and organic markers (e.g., hopanes) using inductively coupled plasma-mass spectrometer and gas chromatograph-mass spectrometer, respectively. The contribution of major sources of FSP, including pavement wear, native hillside soil, traction abrasive sand, and vegetation debris, was calculated using a chemical mass balance model. Volume weighted mean FSP concentrations declined 84% from 53.1 mg/L in year 1 to 8.57 mg/L in year 2. Annual FSP loads declined by 87% from 293 kg to 36.7 kg that is equivalent to 756 Lake Clarity Credits per 1 km2 of pavement. Before pavement rehabilitation, pavement wear was the primary source of FSP in stormwater runoff. Pavement materials (asphalt binder and aggregates) accounted for 42.2 ± 9.4% of FSP load in year 1 and declined to 24.8 ± 5.9% in year 2. Volume weighted mean concentration of FSP from pavement wear, native surface soil, and traction abrasives declined from 22.4 mg/L to 2.12 mg/L, 17.5 mg/L to 3.65 mg/L, and 9.23 mg/L to 0.76 mg/L, respectively. This study provides strong evidence that pavement condition improvement can lead to significant reduction in FSP loads in stormwater runoff that can be converted to Lake Clarity Credit. About 75% of residential road pavement surfaces in South Lake Tahoe were in poor/fail conditions. Therefore, the reduction in FSP loads also needs to be included in cost-benefit analyses for pavement asset management in the Lake Tahoe Basin. Traditional assessment of pavement condition has focused on deterioration of pavement in terms of asset management and travel safety.
Funder Acknowledgement(s): This study was supported, in part, by grants from NSF HBCU-UP (HRD 2107146) and CREST RISE (HRD 1829184) awarded to Texas Southern University.
Faculty Advisor: Hyun-Min Hwang, hyun-min.hwang@tsu.edu
Role: Processed stormwater runoff samples to analyze trace elements and organic markers. Interpreted chemical analysis data and stormwater runoff flow data to run a chemical mass balance model. Quantified the contribution of fine sediment particles from major sources.