Wright, Timothy Edwin James; (2004) Predicting the applicability of aquifer storage recovery (ASR) in the UK Chalk aquifer. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Aquifer Storage Recovery (ASR) is a cyclic form of artificial recharge where water is injected and abstracted from the same borehole. Widely utilised in the USA, there has been significant caution over the development of ASR as a method of artificial recharge in the UK. A primary concern has been double-porosity effects, especially for the Chalk aquifer. The Chalk, characterised as a fractured rock with a double-porosity, forms one of the major aquifers within the UK. It is formed of blocks of a small-grained highly porous (30 - 50%) media, separated by fractures which contribute about 0.1 - 1% of the porosity. Within the chalk matrix blocks, groundwater flow is negligible due to the small pore throats, so fracture flow dominates. The primary difficulty in making ASR effective in a double-porosity aquifer is the diffusion of solutes from low-quality native water within the matrix into the recharge water stored within the fractures. A novel form of double-porosity solute transport model, the DP-Pulse model, has been developed which discretises the flow velocity and fracture space while keeping time and space within the rock matrix as continuous variables. The aquifer is characterised by two parameters, a characteristic diffusion time, tcb, and a porosity ratio and also by the shape of the blocks. The DP-Pulse model was calibrated to data obtained from an ASR test site within the Chalk of southern England. Subsequently, the DP-Pulse model was incorporated into an Operational Research (OR) model allowing determination of the optimal testing and conditioning procedure, given an ideal operational scenario for a proposed ASR system. This OR model was used to examine a number of potential methods for improving testing efficiency. Application of the model allowed a number of conclusions of practical importance for the potential development of ASR in the UK Chalk aquifer.

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