HIGHWAY FLARES AND RUNOFF: A POTENTIAL SOURCE OF PERCHLORATE TO SURFACE WATER IN RHODE ISLAND

The US Environmental Protection Agency has established a reference dose for perchlorate of 0.7 µg/Kg/day (equivalent to 24.5 ppb), following epidemiological evidence of adverse health effects associated with perchlorate exposure. Perchlorate in common highway safety flares is a potentially significant source of water contamination. For example, as much as 240,000 gallons of water could be contaminated to 4 µg/L (the California Action Level) by a single unburned flare. The potential impact of perchlorate in highway runoff on surface- and ground-water quality in Rhode Island has not been assessed, but is of particular concern in a state where 70% of the population relies on a surface-water reservoir that is traversed by two major state roads. This study provides a baseline assessment of potential perchlorate contamination through a field study of perchlorate concentrations in highway runoff at top nighttime accident locations in Rhode Island. Two locations in Providence, RI that receive runoff from accident-prone segments of I-95 are being sampled approximately weekly and during runoff events whenever possible. Samples are collected from culverts feeding a detention pond system (or directly from the detention pond in the absence of runoff) and from a Vortech runoff BMP structure that retains a moderate volume of runoff at all times. Sampling began in April, 2005 and will continue through November, 2005. Sampling of runoff events provides information on potential perchlorate accumulation on the road surface between precipitation events. Sampling of water retained in the drainage structures provides time-average values for bulk runoff between sampling events. Electrical conductivity values for samples collected to date range from 68 µS/cm to 1920 µS/cm highlighting the variable water quality during the sampling period. Completed perchlorate analyses will be compared to the new USEPA reference dose. Risks to water resources from flare use will be identified to provide the foundation for development of flare-handling procedures as needed that will minimize potential future impact.