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Home My WebLink About1989-05-09 Mills Report v 8 �' S � D � GROUND WATER FLOW TO AND THE POTENTIAL OF CONTAMINATION AT THE CITY OF BOZEMAN LYMAN CREEK SPICING WATER SOURCE, GAL'LATIN COUNTY, MONTANA A P; oposal Submitted to: Phillip J . Forbes , P . E . City Engineer by: John Mills Consulting Hydrogeologist Bozeman, Montana May 9 , 1989 JOHN ' -LLS Consulting Hydrogeologist 3205 W. Babcock Bozeman, Montana 59715 (406)587-7930 PURPOSE Lyman Creek spring, located along the southwest flank of the Bridger Range, is a primary water source for the City of Bozeman, Montana . The type and extent of the aquifer discharging at Lyman Creek spring is presently unknown. In addition, the rates of ground water circulation and the degree of natural filtration of contaminants in the aquifer are not presently known. The proposed investigation would identify the aquifer and delineate the recharge area of Lyman Creek spring . It would also and identify potential contamination problems by examining the ground water flow rakes and Laths through the aquifer and determining the filtration and adsorption capacity of the aquifer . JUSTIFICATION Lyman Creek spring discharges from an aquifer comprised of the Madison Group, a series of limestones and dolomites which crop out north and east of the Lyman Creek drainage and along the crest of the Bridger Range . Ground water flow through the Madison Group is very commonly karstic - meaning that ground water flows rapidly through solution enlarged fractures and dissolution cavities in the limestones . These fractures and cavities range from a few millimeters to several meters in diameter . Caves are present in outcrops of the Madison Group in the Lyman Creek drainage within 25 m- ' es from the spring. This is a strong indicat.i , ,n hat 'm-ii C. eek springy,; a scharges from a karst aquifer. 2 KarLtic aquifers in mountainous settings commonly have ground water flow velocities similar to that of surface streams (Mills , 1939) . In addition, the natural filtration of ground water which occurs in clastic aquifers is very limited in karst aquifers . As a result, introduced contaminants are transported rapidly to springs intact and without significant dilution. Therefore, karst aquifers are particularly sensitive to contamination from Giardia and other fecal coliforms as well as the organic contaminants which are typically adsorbed on clays in clastic aquifers . Ground water flow paths in karstic aquifers commonly are independent of surface drainages . Consequently, contaminants introduced in one surface drainage under one jurisdiction can rapidly be discharged at a karst spring in a entirely different surface drainage under different land use policies . It seems likely that Lyman Creek spring discharges from a karst aquifer in the Bridger Range . Considering the ground water flow characteristics of karst aquifers , it would be prudent to delineate and protect the recharge area of the spring from potential ground water contamination. METHODOLOGY FOR THE PROPOSED STUDY The proposed study would have three parts including : ( 1 ) water chemistry sampling and spring discharge gauging at Lyman Creek, (2 ) geologic and hydrogeologic mapping, and ( 3 ) data reduction, interpretation, and report preparation. 3 Water chemistry sampling and spring discharge gauging at the outlet- of Lyman Creek spring would begin immediately in order to record conditions that represent the early snow melt period . This sampling and gauging would continue periodically through the 2 to 3 month period of the study . Water analyses would include major ions (Na, Ca , Mg, K, Cl, SO4 , HCO3 , NO3 ) plus any other constituents requested by the City of uozeman. Records of repeated sampling and gauging are critical in examining ground water circulation in mountain ground water systems (Mills , 1989) . The timing of peak discharge and water cheiiiistry changes at Lyman Creek spring would reveal the velocity at which water reaches the spring from the recharge areas . This in turn would reveal the type of ground water flow through tree aquifer. A rapid rise in spring discharge from snow melt is indicative of very permeable karstic ground water systems . In contrast, constant or slowly changing spring discharge rates are characteristic of ground water flow through fine grained aquifers with relatively small ground water velocities . Concurrent with the sampling and gauging phase would be the compilation of geologic maps of the area and preparation of detailed hydrogeologic maps from aerial photography and field reconnaissance . This would help delineate the recharge area of the aquifer that discharges at Lyman Creek spring . Protection of the recharge area from contamination ensures protection of water quality at the spring . Field work may also include dye tracings through the 4 aquifer. Environmentally safe fluorescein dyes would be used . Dye Lracings wot,ld reveal ground water flow paths from various parts of the recharge area to Lyman Creek spring. They would also provide accurate ground water flow rates through the aquifer . The use of dye tracings provides the most accurate identification of ground water flow paths and rates possible . However, dye tracings are not necessary to determine whether the aquifer is actually k:arstic . Therefore , the failure to obtain a permit for dye tracings or negative results from the dye tracings would not hurt the results of the study . PRODUCTS OF THE PROPOSED INVESTIGATION The products of this investigation will include the following : Maps : Accurate and detailed geologic and hydrogeologic maps of the Lyman Cr:eFk ground w-Ler system. These would identify : the extent of the aquifer discharging at Lyman Creek spring, the ground water flow directions through the aquifer, and the parts of the recharge area which are most 1.ikely to contribute contaminants to Lyman Creek spring . Regog.t Prepara.iry Results and interpretations of the investigation will b ,u!,ipj Led, into a report . The report will 5 present : - the results of the water chemistry sampling and spring discharge gauging at Lyman Creek spring, - the results of any dye tracings conducted, - rates or ground water flow to Lyman Creek spring, - directions of ground water flow in the Lyman Creek ground water system, - the filtration and adsorption capacity of the aquifer, - 'the locations of those areas within the Lyman Creek ground water system from which contaminates would most rapidly reach Lyman Creek spring, - an iri(,�xpreLation of the ground water contamination potential in the Lyman Creek ground water system, and an explanation of the hydrodynamics of the Lyman Creek ground water system and its relation to other ground water systems in the Bridger Range . APPROXIMATE, COSTS Fees 30 days @ $200/day $6000 Maps and equipment $ 100 Drafting $ 100 Water Analyses 6 @ $75/sample $ 450 Travc-�1 and expanse* $ 100 Aerial Photography 20 @ $4/ea . $ 80 Total costs* * $6830 * - could be borrowed from Forest Service. ** - cost could be adjusted depending of the scope of the project of interest to the City of Bozeman. 6 SCHEDULE If this project were accepted, sampling and gauging of Lyman Creek spring should start immediately and continue over the next 2 or 3 months . During this time geologic and hydrogeologic mapping would be completed. Data interpretation and report preparation would follow with a projected completion date of mid- August . 7 REFERENCES Mill.s , J . M. , 1989 , Foreland structure and karstic 9 ound water circulation in the eastern Gros Ventre Range, Wyoming; M. S . thesis , University of Wyoming, 101 p . 8