Analysis of flow processes in fractured chalk under pumped and ambient conditions (UK)Analyse des processus d’écoulement dans un aquifère fissuré de la craie en conditions de pompage et en conditions naturelles (Royaume Uni)Análisis de procesos de flujo en creta fracturada bajo condiciones de bombeo y ambientales (Reino Unido)抽水和自然条件下水流在英国裂隙白垩岩中流动过程分析Análise de processos de escoamento em calcários orgânicos porosos (cré) fracturados sob condições ambientais e em bombagem (Reino Unido)

An integrated set of different measurements has been used to study the behavior of groundwater in an observation well in a fractured rock formation, the UK Chalk, under pumped and ambient conditions. Under pumped conditions, the response of the open borehole was relatively straightforward with flow mainly concentrated along four discrete flow horizons. Furthermore, excellent correspondence was observed between the three methods of borehole flow velocity measurement: impeller flowmeter, heat-pulse flowmeter and dilution testing. Under ambient conditions, the system appeared more complicated. Specifically, in the upper half of the borehole, the impeller flowmeter exhibited substantial downward flow and the heat-pulse flowmeter exhibited almost negligible upward flow, whilst dilution testing indicated significant dilution. It was concluded that this was due to cross-flow occurring over the upper 29 m. Analysis of drawdown data, recovery data and a Drost analysis of the ambient cross-flow data yielded aquifer transmissivity estimates of 2,049, 2,928 and > 4,388 m2/day respectively. The discrepancy between the drawdown and recovery estimates was attributed to non-linear head-losses associated with turbulence and inertial effects. The difference between the pumping test and Drost results was explained by the flow during the pumping test bypassing this aforementioned 29 m region of rock.