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Home My WebLink About010_WellDesignButte | Anaconda | Great Falls | Bozeman | Kalispell · www.waterenvtech.com 1 MEMORANDUM To: Bill Hanson, Think One Architecture From: Pat Thomson, PG, Water & Environmental Technologies, Inc. Date: February 27, 2023 Re: Barnard Construction Office Building Geothermal Cooling Well Design Introduction This memorandum was prepared by Water & Environmental Technologies (WET) to summarize test well installation and pumping test results, and to provide suggested well design and number of production wells as part of design of Barnard Construction’s new office building, Bozeman, Gallatin County, Montana. Test Boring A six-inch diameter test boring was advanced under oversight by WET by Bridger Drilling, of Belgrade, Montana and completed on November 30, 2022. The test boring/well was drilled using a Foremost DR 24 Dual-Rotary drilling rig to a depth of 231 feet. The exploratory well was drilled strictly to recover samples of drill cuttings from several depths, as well as to estimate water production rates at various depths. A draft boring log identifying encounted lithology is presented in Attachment A. Select soil samples from various depths were submitted for sieve analyses for the purposes of production well screen sizing. Based on the geology observed during drilling, WET elected to perforate the lower-most casing to conduct pumping tests to better estimate potential well yield and further assist with design of the slot opening size, length, and depth intervals for the well screen to be installed. Pump Test Methods Bridger Drilling personnel installed a 40 HP submersible well pump in the test well with the pump intake set at a depth of 168 feet bgs. A Solinst pressure transducer was programmed to record water level data throughout the various phases of the test and lowered to a depth of approximately 185 feet bgs inside the well. In addition, a second transducer was placed in a nearby irrigation well to assess zone of influence and connectivity between shallow and deep water bearing zones. The test phases included the following: •Step Test – The step test consisted of pumping the well at multiple flow rates to determine the well’s maximum flow rate to be used during a yield test. The test began with a flow rate of 100 gpm, and the rate was increased at approximately 100-gpm MEMORANDUM · Love’s Travel Stop & Country Store Fire Suppression Well Butte | Anaconda | Great Falls | Bozeman | Kalispell · www.waterenvtech.com 2 intervals. The step test continued to a flow rate of 300 gpm at which point the drawdown within the well became significant enough to stop the test. Water level data were collected throughout each step of this phase. • Constant Rate Test – The well was pumped at a constant rate of 275 gpm for a period of 8 hours to confirm the aquifer would reach a stable drawdown level. The water level in the well was measured throughout the test and during the period of recovery. Pump Test Results The results of the initial step test and recovery phases indicate the well produced water at a maximum flow rate of approximately 275 gpm. However, recovery of the water level following termination of pumping was rapid indicating potential well restriction. The constant rate yield test was conducted at 275 gpm, which resulted in a maximum drawdown of approximately 110 feet. Similar recovery rates to the step-test pumping also indicated potential well loss. However, analysis of the pumping test data did not indicate significant well loss, but did identify reduced efficiency. Well Design The project design criteria provided a peak target flow rate of 700 to 800 gallon per minute to provide the desired cooling capacity for the building. Based on the results of well testing and analysis, and observations made during drilling, WET proposes installation of two extraction wells and two injection wells. Bth the extraction well pair and redundant well pair include an active well and paired redundant well. The redundant wells will provide backup in the event of disruption or failure of the primary well. The proposed well design for the extraction wells is 10-inch diameter to accommodate a pump size required for the maximum design flow. The extraction wells will be drilled to a total depth of 230 feet below ground surface (bgs) based on conditions observed while drilling the pilot test boring. Actual depths and completion details will be determined at the time of installation. Each boring will be completed with 10-inch diameter steel casing to a depth of approximately 205 feet and 25 feet of 8-inch diameter telescoped stainless steel v-wrap wire 0.200 slot screen to 230 feet. Injection wells will be constructed as six-inch wells and extend to approximately 230 feet bgs. The injection well borings will be drilled to 10-inch diameter to a depth of 230 feet. The well will be completed with six-inch diameter steel to a depth of 135 feet and 95 feet of 6- inch stainless steel v-slot screen to a depth of 230 feet. The injection well screen will include 0.100 slot screen from 230 feet up to 205 feet, then 0.040 slot screen from a depth of 205 feet up to 135 feet. Following placement of the screen and casing, the outer larger diameter steel will be extracted while placing gravel-pack around the screened interval and a bentonite-cement grout seal from approximately 130 feet to eight feet below ground surface. MEMORANDUM · Love’s Travel Stop & Country Store Fire Suppression Well Butte | Anaconda | Great Falls | Bozeman | Kalispell · www.waterenvtech.com 3 Well Development Each well will be adequately developed using surge and pumping techniques. The extraction wells will be developed until turbidity measurements are less than 5 nephelometric turbidity units (NTUs). The injection wells will be developed until less than 50 NTUs. MEMORANDUM · Love’s Travel Stop & Country Store Fire Suppression Well Butte | Anaconda | Great Falls | Bozeman | Kalispell · www.waterenvtech.com 4 ATTACHMENT A 240 220 200 180 160 140 120 100 80 60 40 20 0 CLAYEY SANDS, SAND - CLAY MIXTURES WELL - GRADED GRAVELS, GRAVEL - SAND MIXTURES, LITTLE TO NO FINES WITH COBBLES INTERMIXED CLAYEY GRAVELS, GRAVEL - SAND - CLAY MIXTURES WELL - GRADED GRAVELS, GRAVEL - SAND MIXTURES, LITTLE TO NO FINES WITH COBBLES INTERMIXED SILTY - SANDS, SAND - SILT MIXTURES WELL - GRADED SANDS, GRAVELLY SANDS, LITTLE OR NO FINES SILTY - SANDS, SAND - SILT MIXTURES WELL - GRADED GRAVELS, GRAVEL - SAND MIXTURES, LITTLE TO NO FINES WITH COBBLES INTERMIXED CLAYEY GRAVELS, GRAVEL - SAND - CLAY MIXTURES WELL - GRADED GRAVELS, GRAVEL - SAND MIXTURES, LITTLE TO NO FINES WITH COBBLES INTERMIXED CLAYEY GRAVELS, GRAVEL - SAND - CLAY MIXTURES WELL - GRADED GRAVELS, GRAVEL - SAND MIXTURES, LITTLE TO NO FINES WITH COBBLES INTERMIXED CLAYEY GRAVELS, GRAVEL - SAND - CLAY MIXTURES ORGANIC SILTS AND ORGANIC SILTY CLAYS OF LOW PLASTICITY WELL - GRADED GRAVELS, GRAVEL - SAND MIXTURES, LITTLE TO NO FINES WITH COBBLES INTERMIXED ORGANIC SILTS AND ORGANIC SILTY CLAYS OF LOW PLASTICITY CLAYEY GRAVELS, GRAVEL - SAND - CLAY MIXTURES WELL - GRADED GRAVELS, GRAVEL - SAND MIXTURES, LITTLE TO NO FINES WITH COBBLES INTERMIXED ORGANIC SILTS AND ORGANIC SILTY CLAYS OF LOW PLASTICITY 240 220 200 180 160 140 120 100 80 60 40 20 0 Lithology Description amsl (NAVD 88) BORING AND WELL CONSTRUCTION LOG Boring/Well # : TD WELL: (MT SP-N83 IF) (MT SP-N83 IF) Depth(ft) N/A N/A STEEL/6"-2 232 N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A DUAL ROTARY MIKE SHIRLEY 11/28/2022 BRIDGER DRILLING STICK UP 11/30/2022 PILOT HOLE NM NM NM 232 N/A NM THINK1 10075502501 1 Lithology Key GW GC SM SW SC OL