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(d) not recover conductor casing prior to cementing in the next casing string 3.11. Drilling Surface Hole, Casing and Cementing Surface casing and cement shall; (a) permanently isolate and protect all sources of potable water from other formations which contain non-potable fluids; (b) prevent cross-flow between different fresh water aquifers or any fluid bearing zone; (c) prevent the sloughing of unconsolidated material into the well bore; and (d) be capable of anchoring the well control equipment. 3.11.1. Surface Casing Set on a Shoe in Cable Tool Drilled Wells It is a recommended practice that surface casing should be cemented to surface. The surface casing may be set on a casing shoe if: (a) there are no shows of water, hydrocarbons or brines in the open hole below the conductor casing; (b) the conductor casing is not leaking; (c) flows of hydrocarbon or artesian water are not expected in the next segment of the well; or (d) one set of casing is cemented across all fresh water zones. 3.11.2. Surface Drilling, Casing -Rotary The surface hole shall be drilled sufficiently deep into bedrock to: (a) secure cemented casing to bedrock; (b) be 15 metres into non-porous competent bedrock and 15 metres below the lowest potable water zone if that water is encountered in bedrock; or (c) below all potable water zones yet above non-potable water zones if 15 metres is not available between the potable and non-potable water zones. 3.11.3. Artesian Water If artesian fresh water flow is expected in a well, a string of casing shall be run above the artesian fresh water zone so that the flow of water can be controlled. A second string shall be run and set below the artesian fresh water zone in order to isolate it from underlying porous formations containing non-potable fluids. 3.11.4. Surface Casing Cementing Surface casing shall be cemented before formations containing non-potable fluids are drilled except where the requirements of section 3.11.1 are met for cable tool operations. Where surface casing is cemented it shall be: (a) cemented full length from total depth to surface; (b) using cement volumes based on caliper volume if available or theoretical annular hole volume plus the volume of the shoe joint plus; (i) 50% excess cement if cement volume is based on theoretical calculation, or (ii) 20% excess up to the designed cement top if cement volume is based on a caliper volume; and (c) cemented using the circulation method. 13