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Gallatin Regional Park Well Yield Project

Stephan G. Custer
Earth Sciences
Montana State University
Bozeman, MT

Background and context are presented in the exercise.
This is a ground-water-resource evaluation exercise.   The students are asked to use the Montana Ground Water Information Center well data base (accessible from the web) to perform the analysis.  The exercise includes data acquisition, analysis, and writing. 

This assignment is used in a junior/senior level college ground-water resources course.

Students need to be able to read well logs and hydrogeologic information on the well logs:  Total Depth, Pumping Water Level, Static Water Level, Yield, Well Screen, Seals, Specific Capacity, BLM well location method.  Some knowledge of the geology of a Basin and Range valley is helpful.  Knowledge of recovery tests in single wells is conceptually helpful but is not required to do the exercise. This exercise can be used as a vehicle to help students learn these skills and concepts.  

This project is assigned about midway into the hydrogeology course after the geology of alluvial valley fill in a basin and range setting has been developed and after the concept of specific capacity and well yield have been assigned.  The project could be followed by a model pump test, but is not currently used that way. 

This is a project which was brought to me by the Gallatin Parks Board in Bozeman, MT.  The project asks the students to write a consulting report based on analysis of well logs, specific capacity, lithologic logs, and geologic maps.

The goal of the project is to give the students an oppotunity to write a consulting report, learn to access a state-wide data base, select appropriate well logs, practice critical thinking, analyze uncertain data, identify important data, analyze hydrogeologic data, recognition of limitations of existing data and  address a hydrogeologic problem commonly asked by the public.

Gallatin Regional Park Well Yield Project

Last modified  by Steve Custer, Montana State University 25 July 2005

The purpose of this exercise is to familiarize you with data commonly available from well drillers and the Montana Bureau of Mines and Geology. Such data is often used to produce consulting reports. This exercise will also give you practice in writing such reports.  This year you will be working on a real project.    I received the following email:

"Friends of Regional Parks is the volunteer organization that is developing the new county park off Baxter Lane one mile west of the new post office.  We are at the point of drilling a well or wells to furnish necessary irrigation water to those parts of the 100 acres that will be needing supplemental water.  We have been advised by the city of Bozeman parks department that a large well ( perhaps 300 gal per min) would be best for our purposes.    The exact location of Gallatin Region Park is: 100 acres bounded on the North by Baxter Lane, on the West by  future Ferguson Lane ( not yet built),  on the South by Oak Street (also not yet built), and on the East by Davis Lane.  The legal description is:  Tract 3A of Certificate of Survey No.  2202A, located in Section 3, Township 2 South, Range 5 East P. M. M., Gallatin county Montana.   Do you have knowledge of the underground geology of that area, and could you advise us as to the probability of success in drilling such a large well in that area?"

If you have forgotten the BLM method for locating wells you can review the method on the Montana Bureau of Mines and Geology web site or use the Montana Natural Resources Information System GIS linked through the well logs.  A nongraphical description of the BLM method of well location is also available from the Bureau.

Maps have been attached here to help you locate the Park. 
        Plat Map for COS2202A which shows the Park in the lower right quadrant of the plat.
        A map that shows the approximate location of the Park obtained from under Maps and GIS and Active GIS.
        A topographic map that shows the location of the park.
        A digital orthophoto quadrangle that shows the park.  

Please develop well log information from the Montana Bureau of Mines and Geology Ground Water Information Center (GWIC).  Remember, you may need to look at wells adjacent to the section of interest. We will work on data acquisition as a class in a computer room to be announced. We will develop the tables in class followed by small group work to facilitate and expedite data collection.  The general procedure is outlined on the web.  One appendix will include selected wells that help the client understand the geologic materials expected in the park.  One table will include depth of well depth to water, pumping rate, pumping level and specific capacity.  Well locations can be developed from a website related to source-water protection. Go to Department of Enivronmental Quality, then Planning Prevention and Assistance, then source water protection, then source water protection, then SWAP Support and Querry.  Now you must choose a subdivision name with a public water supply and then search and set a distance.  Then select a radius and click on the water tab.  Finally explore ground water.  (Frankly it may be easier to simply plot the wells you are interested in by hand).    One table will include available well logs in the vicinity. Be sure your figures and tables have captions, figure and table numbers, and north arrows. Your figures and tables should be referred to in the text by figure number or table number. A text of approximately 1-2 pages should suffice i f you write clearly.

Please answer the following questions:

1.  What is the geology that controlls  ground-water availablity.
        a.  Use available geologic maps such as Custer and Dixon, 2002b and Custer and Dixon, 2002c.
        b.  Use selected lithologic logs from the Ground-Water-Information Center presented in an appendix to describe the geologic materials expected.
2. How deep will the well have to be to find water?
    (Don't forget sanitary seal considerations; 18 feet of bentonite or concrete seal for public water supply)
3.  Use specific capacity to estimate how much water the park  can they expect in gpm? (What is the yield?)
        a.  Based on existing wells, is a 300 gpm well realistic? (Defend your assertion with data).
        b.  If not what well yield is realistic using specific capacity
4.  (Later in the semester you may be asked to assess what the cone of depression for such a well might be and whether that cone will likely influence any surface water in the area.  This is mentioned at this point to help you think about the maps you select now.)

When writing such a report, you should describe the location and general geology of the site (Custer et al., 2002; Custer and Dixon, 2002a; Custer and Dixon, 2002b and Custer and Dixon, 2002c), use the available data to summarize the types of materials that a driller might encounter, answer the questions that the client is interested in, and identify problems or advantages presented by the groundwater system as indicated by available data. Common figures include: location map, geologic map, hydrogeologic data available, data tables, and the text. A good way to write is to prepare all figures and tables, lay them out in front of you in the order they will be discussed, and write about each. This exercise is designed so that you do not have to go into the field, but you should feel free to use the main library and the web.    You should address problems the lack of field visit introduces to your analysis so your client is aware of the issue.


This exercise will be graded using the linked scoring sheet.