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Groundwater Well Installation Standard Operating Procedure SWE-FSOP-601;Revision 1 Ahtna Southwest Environmental Operations 4.3.5 Installing Filter Pack Based on borehole and well casing dimensions,calculating volumes of filter pack, bentonite pellets/slurry, and grout required. If the project work plans require, determine the filter pack and well screen slot size for the monitoring or extraction well. Place a layer of filter pack (one to two feet, unless otherwise specified in the project-specific work plans) at the bottom of the borehole. • When constructing wells within a cased hole or through hollow stem augers, install the filter pack by pouring and allowing it to free-fall through the center of the drive casing/augers or tremie according to project work plans.Add filter pack slowly while withdrawing the drive casing/augers.Take care to minimize the height of the filter pack inside the auger/drive casing during pouring to avoid potentially "sand locking" the well casing and pulling it up with the auger/drive casing. • Using drive casing or augers, pull the drive casing or augers slowly during filter pack installation in increments no greater than five feet. • For the mud rotary drilling technique, tremie the filter pack into the annular space around the screen. If approved, clean, potable water may be used to assist with the filter pack tremie operation. Monitor filter pack settlement by initially measuring the sand level (before beginning to withdraw the drive casing/augers). Repeatedly take depth soundings using a weighted tape to continually monitor the level of the sand in the auger/drive casing as it is removed. Monitor the top of the well casing to detect any movement due to settlement or from drive casing/auger removal. If the top of the well casing moves upwards at any time during the well installation process, the driller should not be allowed to set drilling equipment (downhole hammers, drill pipe, etc.) on the top of the casing to prevent further movement, which could cause the well casing to bend or break in the borehole. Add filter pack until its height is approximately two feet above the top of the screen (unless otherwise specified in the project work plans), and conduct verification of its placement (by sounding). Then gently surge the filter pack using a surge block or swab to settle the packing material and reduce the possibility of bridging. Resound the height of the filter pack and add more filter pack, placed as necessary. Once filter pack placement is complete, measure and record the depth to the top of the pack in the FLB/notpad or field form SWE-FFRM-401, "Well Construction." 4.3.6 Installing Seals Install a three-foot thick (unless otherwise specified in the project work plans) bentonite seal on top of the filter pack. If pellets or chips are used, add them gradually to avoid bridging. Take repeated depth soundings using a weighted tape to ascertain the top of the bentonite seal. Allow the seal to hydrate for at least 30 minutes before proceeding with the grouting operation. After hydration of the bentonite seal, pump grout through a tremie pipe and fill from the top of the bentonite seal upward. Page 12 of 16