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 www.bozeman.net 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.
