Metal concentrations during operation of a Permeable Reactive Barrier containing zero-valent iron.

During the 2012/13 field season, media in the fifth cage was replaced with a new trial media sequence (Statham draft publication). Refilling occurred on the 16th of January. In this process mixed media sequences were homogenised by a cement mixer in 40 L batches and then placed in the PRB cage.

Samples for metal concentration analysis collected six times over each of the 2012/13 and 2013/14 summer seasons. Samples were drawn from the lowest unfrozen depth of each multiport in cage 5. To minimise collection interference the procedure started at the most downstream multiport and continued upgradient.

From each port two 30 mL samples were drawn, the first was filtered to 0.45 microns, the second was used to measure pH, Eh and EC readings. All samples were acidified (pH less than 2 using nitric acid) and frozen for storage and transport to Australia. Element concentrations and analysed by inductively couple plasma-optical emission spectroscopy (ICP-OES) using a Varian 720-ES spectrometer at the Australian Antarctic Division.

The emission intensity of standards and sample solutions was measured following 1:1 in-line mixing with a solution of 0.75% (w/v) CsCl matrix modifier in 10% (v/v) HNO3 containing 5 mg L-1 yttrium as an internal standard. It was deemed unnecessary to use a matrix modifier for the 2014 analysis.