Shallow alluvial aquifers have been overlooked as thermal resources for low-carbon cooling in the UK. Most existing groundwater cooling systems in central London, for instance, use the deeply confined Chalk aquifer. Potential over-exploitation of the Chalk aquifer as a heat sink was one of the primary reasons why the River Terrace Gravels aquifer was investigated at the Tate Modern. Other considerations included a higher likelihood of achieving the required groundwater yields and the ability of the shallow River Terrace Gravels aquifer to dissipate heat more effectively than the deeper, confined Chalk. Where net heat rejection is large, the extent to which waste heat can escape the system is critical to the long-term sustainability of the scheme. Factors influencing heat loss include the thickness of cap rock and the ratio of surface area to thermal volume. Cost of scheme development in the River Terrace Gravels was also an important consideration and projected long-term energy savings as a result of sourcing water from a shallower aquifer, with lower pumping lifts, were considerable. Although circumstances where the River Terrace Gravels may be utilized for heating and cooling are limited owing to the restricted area underlain by these deposits, the variable saturation and potential vulnerability of basements to leakage if affected by raised groundwater levels in the vicinity of recharge wells, they may be a viable alternative to the Chalk for some locations. Continued monitoring of the operation of the Tate Modern scheme will provide further evidence of the viability of schemes using the Thames Gravels.

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