PERCOLATION AND INFILTRATION RATES OF DISSOLVED DEICER SOLUTIONS

Infiltration and percolation rates of deicers through the subsurface from the point of application on impervious surfaces to the point of discharge are simulated by benchtop experiments carried out in transparent 21x12x12 cm tanks filled with either (1) a poorly sorted earth material, or (2) one of three sorted size fractions (fine, medium, or coarse sand). At the start of the experiment, a 3mm deep scarp along the longer wall of the tank is filled with 20mL of tinted deicer brine solution of a specific concentration. The NaCl solutions (0.05-5% NaCl) are selected to correlate with NaCl solutions in equilibrium with ice or snow in the temperature range between 25 and 31 degrees Fahrenheit. The brine solutions are tinted with a blue dye with an absorbance peak at 600 nm (CAS# 3844-45-9). Each experimental sequence is captured with high-resolution time-lapse photography with exposure intervals selected between 20 seconds and 5 minutes depending on the brine concentration. The duration of the experiments varies between 2 and 5 days, resulting in a sequence of 800-2500 frames lasting 30 seconds up to 2 minutes in a video mode. The time compression allows for easy visualization of the infiltration and/or percolation processes. The monitored parameters are the style of brine transport and the dilution mechanism as the experiment proceeds. The principal transport mechanism through the underlying freshwater column follows two different patterns: (1) general advancing front and (2) a set of faster advancing projecting finger-like convective cells. The degree of dilution of the advancing brine solutions is estimated from the corresponding change of the density of blue color as the brines percolate into and through the surrounding colorless fresh water. Selected high-resolution images are mapped and contoured using the same wavelength as the blue dye. The calibration of blue color density with the degree of dilution is done by spectrophotometric measurements of 8 sequential dilutions prepared separately by diluting each subsequent test solution by a factor of 2. Preliminary assessments of the experimental data indicate that the brine percolation rates decrease as the experiment proceeds following an exponential slow down as the solution advances. Selected videos and image analysis will be shown with the poster presentation.