The concept of controlled pumping was first developed by the United Alkali Company in their Saltfield at Preesall near Fleetwood, Lancashire. With the formation of I.C.I the techniques used at Preesall were used to develop a controlled brinefield at Holford near Northwich in the 1930’s. Cavities are developed within the deeper dry rockhead environment, their shape being controlled by precise placement of injection points within the developing void with continual monitoring using sonar equipment. The production methods and geometry of the void are designed to preserve the integrity of the overlying ground. Water is introduced under pressure to raise the brine to the surface, dissolving salt from the cavity walls until maximum size and shape are attained. Each cavity takes several years to reach a maximum size and form, and in the past it was then capped off and left full of saturated brine, however, current practice often involves use of the caverns for gas storage. The spacing and size of the cavities is related to the salt bed thickness and the cavities are designed to remain permanently stable. The Lower Keuper Saliferous Beds at Holford are some 240 metres thick and the cavities are at least 120 metres from the surface. Each cavity reaches a height and diameter of several hundred metres and the initial boreholes are developed on a grid pattern some 120 metres apart.
Controlled pumping is currently operated by Inovyn Enterprises at the Holford Brinefield, to the south-east of Northwich, and by British Salt Ltd (now part of Tata Chemicals Europe Ltd) at Warmingham, south of Middlewich.