Table 1.

Summary statistics of vertical separations for individual aquifers and shales. OD relative to Ordnance Datum; SD standard deviation

Aquifer or shale	Area (km2)	Min. depth (m OD)	Max. depth (m OD)	Mean depth (m OD)	SD of depth data (m)
Chalk Group	33,165	251	−953	−181	183
Kimmeridge Clay Formation	23,670	257	−1,229	−351	320
Triassic sandstone	44,930	370	−3,400	−667	605
Bowland Shale Formation	24,120	628	−6,697	−1,539	1,097