Hydrogeological study of a sequenced permeable reactive barrier

A hydrogeological study of a sequenced permeable reactive barrier (PRB) was undertaken by environmental engineering student, Daniel Kirby, in fulfilment of the final year engineering thesis unit, ENG460 - Engineering Thesis, at Murdoch University, Perth, WA. The project was conducted in collaboration with Golder Associate. The study was conducted at contaminated site located in Bellevue, WA. In 2001 a large explosion and chemical fire occurred at a liquid waste treatment and recycling facility located at the site, in response to this contamination Golder Associates designed and installed a PRB treatment system in 2010. A permeable reactive barrier is a groundwater treatment design, which makes use of the natural groundwater flow to channel contaminants through an engineered in-situ treatment area. This treatment system was designed to consist of two different and separate barriers filled with two different reactive material. The first contains sawdust used to treat nitrates through the microbial process of denitrification. The second contains Zero Valent Iron (ZVI), a non-toxic granular material used to treat chlorinated solvents in the groundwater. The objective of this project was to study flow paths of the PRB at the contaminated site and identify potential for flow to bypass the PRB treatment system. Achieving this objective involved analysing groundwater level data from pressure transducers and previous historical monitoring rounds. In addition to the water level analysis, two tracer studies were conducted at two different locations at the site. The tracer studies involved using the organic dye fluorescein to further understand the flow paths of the site and to validate suspected flows that may bypass the PRB treatment system. The two tracer studies developed for use in this thesis were designed based on a literature review on relevant topics, and through liaising with academic staff at Murdoch University and the project manager at Golder Associates. The first tracer study aimed to validate contaminated flow that directly bypasses the ZVI barrier. The second tracer study, conducted at the centre of the PRB system, aimed to provide information on the lateral water movement and dispersivities through the PRB treatment system. The results of the groundwater level assessment identified areas that potential flow bypassing the treatment system could be present, the area of concern was identified to be the south-western portion of the PRB treatment system. The tracer study that was conducted within this area failed to validate the bypass, the source of this failure has been attributed to an error in the selection of the injection and monitoring wells. The second tracer study which was conducted at the centre of the PRB treatment system. The data obtained from the second study did not provide the ideal result as no significant tracer concentration was detection in the monitoring wells. A number of reasons for the lack of tracer detection have been discussed, including a lack of connectivity between injection and monitoring wells due to the presence of impermeable clay layers. It has been acknowledged that there is insufficient data collected during the study to accurately conclude on whether contaminated flow is bypassing the PRB treatment system