Bulk organic matter in highway runoff waters
Résumé
Several tens of mg/L dissolved organic carbon (DOC) are commonly found in road runoff waters, fairly much more than in uncontaminated natural waters (usually less than 5 mg/L DOC). On the other hand individual fuel contaminants (BTEX, PAHs, MTBE...) usually do not exceed few μg/L in contaminated waters and hopefully account for a weak part of the DOC charge of the effluent waters. Bulk distinction between road traffic derived organic matter and natural organic matter may be achieved by means of common organic geochemical methods. Particulate organic matter was characterised by Rock-Eval pyrolysis and dissolved organic matter (DOM) was separated into hydrophobic and hydrophilic fractions with XAD-8 resin. Two types of road traffic particulate organic matter were distinguishable from natural algal or terrigenous matters: one of tyre origin, the other related to engine soot. Tyre derived particles seem abundant in the first flush of storm runoff. Two "types" of traffic derived DOM were also observed. One type found in tollbooth and parking area runoff has a very high proportion of "XAD-8 hydrophilic" compounds, comparable in that way to condensation water at pipe exhausts; although the other type, on the contrary, is more rich in hydrophobic fractions than natural water DOM. Both types appear to evolve toward near natural DOM characteristics upon storage in storm basins.