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Battle Mountain Resources—San Luis SL-SOP-Groundwater Well Decommissioning <br /> STANDARD OPERATING PROCEDURES REVISION: 0 -May 6,2019 <br /> 4.4. Over-Drilling <br /> Over-drilling is the technique used to physically remove an entire monitoring well, <br /> its sand pack and the old grout column and fill. In situations where PVC screens <br /> and risers are expected to sever and removal of all well materials is required, over- <br /> drilling will be required. Over-drilling is called for when a riser can't be pulled and <br /> it penetrates a confining layer. Compared to the other procedures, over-drilling is <br /> the least common method of well decommissioning. <br /> A "temporary casing" may be necessary when extraordinary conditions are present, <br /> such as a high concentration of mobile contaminants in the overburden, depth to <br /> water is shallow, there is poor construction documentation or shoddy construction <br /> practices. The approach involves installing a large diameter steel casing around the <br /> outside of the well followed by drilling/pulling/grouting within this casing. The casing <br /> is withdrawn at the end of pulling, grouting and (perhaps) drilling. If the confining <br /> layer is less than 5 feet thick, the casing should be installed to the top of the confining <br /> layer. Otherwise, it is installed to a depth of 2 feet below the top of the confining <br /> layer. After the outer casing has been set, the well can be removed and grouted <br /> through pulling if possible or removed and grouted by drilling inside the casing. <br /> Over-drilling is used where casing pulling is determined to be unfeasible, or where <br /> installation of a temporary casing is necessary to prevent cross-contamination, <br /> such as when a confining layer is present and contamination in the deeper aquifer <br /> could migrate to the upper aquifer as the well is pulled. The over-drilling method <br /> should: <br /> • Follow the original well bore; <br /> • Create a borehole of the same or greater diameter than the original boring; and <br /> • Remove all of the well construction materials. <br /> In over-drilling the difficulty lies in keeping the augers centered on the old well as the <br /> bit is lowered; it will tend to wander off. As a precaution, the well column should be <br /> filled with grout before over-drilling. Then without allowing the grout to dry, the driller <br /> proceeds with over- drilling the well. Grouting first guarantees that if the drill wanders <br /> off the old well and the effort is less than 100% successful, the remaining well portion <br /> will at least have been grouted. There are many methods for over-drilling. Please <br /> note that the following methods are not suitable for all types of casing, and the advice <br /> of an experienced driller should be sought. <br /> • Conventional augering (i.e., a hollow stem auger fitted with a pilot bit). The <br /> pilot bit will grind the well construction materials, which will be brought to the <br /> well surface by the auger. <br /> • A conventional cable tool rig to advance "temporary" casing having a larger <br /> diameter than the original boring. The cable tool kit is advanced within the <br /> casing to grind the well construction materials and soils, which are periodically <br /> removed with large diameter bailer. This method is not applicable to bedrock <br /> wells. <br /> • An over-reaming tool with a pilot bit nearly the same size as the inside <br /> diameter of the casing and a reaming bit slightly larger than the original <br /> borehole diameter. This method can be used for wells with steel casings. <br /> SL-SOP Well Decommissioning EA, Inc. <br /> Battle Mountain Resources, Inc. Page 8 of 21 Ma!Y 6, 2019 <br />