Characterization of Street Sweeping Material for Addressing Total Maximum Daily Waste Load Allocations

Abstract

Municipal separate storm sewer system (MS4) permittees are increasingly required to reduce pollutant of concern (POC) loadings from their service areas to achieve waste load allocations (WLAs) assigned as part of total maximum daily load (TMDL) calculations. Required POC reductions and the associated cost to implement best management practices (BMPs) to achieve reductions necessitate allowing for a wide range of BMP options, including source controls. Challenges in detecting measurable impacts in surface waters have made it difficult to quantify POC reductions from source controls. However, direct measure and characterization of swept material can provide an obtainable quantification, as demonstrated with the analysis and assessment of 58 samples of swept material collected from six MS4 permittees in Virginia. Results presented indicate particles <841 μm are readily transported from a swept surface as part of the rainfall-runoff process, and discussion finds these particles can also be associated with total suspended solids (TSS) in the water column of receiving waters. Total phosphorus in collected material is heavily associated with the particle sizes range examined <250 μm, and total nitrogen is associated for each examined particle size range <841 μm. The content of swept material is impacted by the amount of time since the last rainfall, with a decrease in particles <841 μm when sweeping occurs within 2 days since the last rainfall. The type of surface swept impacts the content of swept material to a lesser degree, with larger fractions of smaller particles collected from parking lots and higher concentrations of total nitrogen associated with material collected from streets. An assessment of the results leads to estimates of the mass of POCs removed for TSS, total nitrogen, and total phosphorus, depending on the amount of time since the last rainfall and the type of surface swept.