Chloride Characterization from Pavement Runoff Using Automated Samplers and Specific Conductivity Sensors at Three Eastern Massachusetts Locations
David W. Ostendorf
The objective of this research is to relate the chloride concentration of highway runoff through specific conductivity measurements and to characterize the role that the pavement surface texture has in the dissolution kinetics of the chloride residing in this layer. The quantity of deicing agents applied throughout the winter season is correlated to the concentration of chloride in highway runoff and linked to the length of time since application. A unit hydrograph was developed from precipitation measurements and the resulting hydraulic parameters were calibrated for use in a specific conductivity flux model. From this model a pollutograph was developed characterizing a specific conductivity flux source term and a first flush value. These two terms are optimized to characterize the dissolution kinetics and predict chloride runoff concentrations. The runoff decay constants optimized for all three sites reduced to very similar averages of 3.02 x 10-4, 4.21 x 10-4, and 3.6 x 10-4 s-1 respectively for Andover, Cohasset and Plymouth from ranges of three orders of magnitude for each site between individual events over the five year period. The depression storage layers were 0.9, 1.3, and 3.0 mm respectively for Andover, Cohasset and Plymouth indicating a connection between pavement age and texture as Andover is the new of all pavements. Along with the similar calibrated hydraulic parameters, the three sites had very similar optimized chloride source parameters of 5.64 x 10-4, 1.30 x 10-4, and 2.16 x 10-4 mg/m2-s for Andover, Cohasset and Plymouth respectively. The 177 storms modeled between all three sites had source terms ranging from 10-3 to 10-8 and averaged to the above optimized values. A clear indication the lumped parameter linear reservoir approach is applicable to storage facilities and active highway routes. This research provides support understanding the role impervious surface texture has in the chloride dissolution kinetics controlling stormwater runoff quality. A common model has been shown to be able to characterize stormwater runoff hydraulics and chloride flux from both salt storage facilities and heavily traveled highway lanes. Seasonal stormwater quality trends as well as event first flush concentrations have been identified and characterized with calibrated watershed parameters. Automated samplers coupled with continuous monitoring equipment have shown per storm or seasonal correlation between pavement texture, meteorological data, distributed deicing agent data, and water quality information at different Eastern Massachusetts locations.