Description
Summary:(See the metadata file in the downloadable dataset for more information, including graphs and formulas which cannot be reproduced here) The permeable reactive barrier under assessment was originally constructed in the 2005/06 summer for details refer to (Mumford et al., 2013). The reactive gate consists of five modified Australian Antarctic Division cage pallets with external dimensions 1.8 x L 1.1 W x 0.75 H m. During the 2012/13 field season, media in the fifth cage was replaced with a new trial media sequence. 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. To evaluate the retention time and hydraulic conductivity of the new sequence relative to the pre-existing material, non-reactive tracer tests were conducted over both monitoring seasons. From the conductivity distribution of salt measured downstream from a pulse as shown in Figure 1, the mean fluid age at each point of measurement can be calculated. The further away from the source, the longer the retention time and the more dispersed the response. Method Tracer tests were conducted on the 22nd of January 2013 and 16th of January 2014. For both occasions the tracer source was a pulse of sodium chloride with a conductivity of approximately 50 mS cm-1 pumped at a rate of 0.83 L s-1 for five minutes. At the end of the salt pulse the flow of melt water recommenced at the original rate of 0.91 L s-1. At set time intervals 30 mL of water was drawn for EC measurement from multiports at a depth of 700 mm. For the cages in which media was not replaced four multiports were sampled, in the fifth cage an additional two sample points were included. The EC of all samples was determined over a two day period at room temperature using a TPS WP-81 meter and associated probe. This method and sampling location were consistent for both assessments. However, there was a minor modification in 2014 as multiports 6 (frozen) and 11 (no suction, dry or broken tube) were sampled at 600 mm instead of the standard value of 700 mm. The dataset consists of two excel files: 1. 0-year 2013 tracer test results and calculation 2. 1-year 2014 tracer test results and calculation