GEO 360 - Project One - DUE October 21
Hydrologic Mapping: Development of a Conceptual Model
A hypothetical areal study provides the basis for the following problems in which maps will be prepared to investigate several aspects of the occurrence of ground water and to illustrate problems in the preparation of maps. The region to be mapped has been glaciated, and the land surface is underlain by till everywhere except in two stream valleys where sand and gravel overlie the till. These unconsolidated deposits constitute one unconfined aquifer. They are underlain by limestone in which the strata are horizontal. The limestone contains ground water confined beneath the till. The piezometric surface for the limestone aquifer dips toward the south, although this fact is not well shown by the provided data. The region has a humid climate.
You will be working in groups (note more than three people and no one author projects) on this project. To ensure that each student participates, you will evaluate your peers with the provided guidelines (see the end of the handout). I would encourage students to do the assignment themselves and then compile the information into one group report. Please turn in the peer evaluation form individually and not with the project.
Data have been collected from 25 wells (Table 1). For wells number 1 and 20, well logs (from the drillers) are provided (Table 2). You are provided a topographic map and several base maps upon which you are to prepare the other types of maps. You are also provided information about the wells, such as elevation of the land surface and depth to the water level (Table 1).
Working in your groups, you have to:
A) Draw two stratigraphic columns: One for well 1 and one for well 20. In addition to the geology, incorporate the hydrostratigraphy (hydrogeologic information, i.e. water table or potentiometric surface, color code aquifers and/or aquitards, etc.) (10)
B) Prepare two cross-sections, one along B-B’ (use wells 13, 14, and 17) and one along C-C’ (use 7, 12, 14, and 20) include the geology, hydrostratigraphy, land surface, the water table, the bedrock surface, and the potentiometric surface. Include a legend. (10)
C) Describe the general geology and topography of the area - use the stratigraphic columns, the cross-sections, and the topographic map (Figure 1) as the basis of description. The description focus is on the whole area not just what is seen from the wells. (5)
D) Prepare a contour map of the bedrock surface. Use Figure 2 as your base map, a 20-ft contour interval, and include the 1400-ft contour. Table 4 may be useful in your calculations. (6)
Calculate the slope of the bedrock surface (magnitude and direction). (2)
Approximate the depth at which wells 2 and 5 would intersect the bedrock. (2)
E) Prepare an isopach map (contour map displaying unit thickness) of the till. Use Figure 3 as your base map, a 20-ft contour interval, and include the 60-ft contour. Keep in mind you have more data available than just the table. (6)
Describe the thickness of the tile in the area. What role do the stream valleys have on the thickness? (2)
Approximate the thickness of the till at wells 2 and 5 assuming the wells intersected the bedrock. (2)
F) Prepare a contour map of the water table. Use Figure 4 as your base map, a 20-ft contour interval, and include the 1480-ft contour. (7)
Draw flowlines (assume homogeneous and isotropic) (2)
Calculate the gradient of the water table. If more than one dominant direction is identified, provide multiple gradients. (2)
Include a table showing your calculations and data (Tables 3 and 4 may be useful templates, but please generate your table using a computer). (1)
Describe the relation between the topography of the region and the water table (How does the water compare to the topography). (2)
Draw a cross-section along A-A’ (use 2, 4, and 8) as an aid in your description. (3)
Explain, in hydrologic terms, why the marshy areas occur at locations indicated in Figure 1. (2)
Which wells did you use in construction of the water table AND why did you use the wells you used? (1)
G) Prepare a contour map of the potentiometric surface. Use Figure 5 as your base map, a 10-ft contour interval, and include the 1530-ft contour. (5)
Draw flowlines (assume isotropic homogeneous). (2)
Calculate the gradient of the potentiometric surface. If more than one dominant direction, provide multiple gradients. (2)
Include a table showing your data and the calculations. (Tables 3 and 4 may be useful templates, but please generate your table using a computer). (1)
Describe the shape of the potentiometric surface. (2)
Why do you think the potentiometric surface has this shape? What is the potential control? (2)
Which wells did you use in the construction of the potentiometric surface map and why did you use the wells you did? (1)
H) Prepare a map of the tracts of potential artesian flow (areas where the level of water is above the surface). Use Figure 6 as your base map, a 2-ft contour interval. Your interval will begin at 0 ft, and there will be no negative numbers. (4)
How did you decide where the artesian flow might occur? (1)
I) Based upon all of the information presented and created, describe in THREE DETAILED PARAGRAPHS the hydrogeology of the region. (15)
Additional basemaps are available on-line
Table 1: Record of Wells
WellNumber / Type of
Well / Land Surface
Elevation / Depth / Depth to
Bedrock / Water Level
ft. AMSL / ft. / ft. / ft.
1 / Drilled / 1516 / 102 / 95 / -4.1a
2 / Dug / 1524 / 12 / -5.4
3 / Drilled / 1518 / 129 / 123 / +3.9b
4 / Drilled / 1503 / 117 / 111 / +16.7
5 / Dug / 1494 / 11 / -5.9
6 / Dug / 1492 / 9 / -4.1
7 / Dug / 1504 / 8 / -3.8
8 / Drilled / 1503 / 119 / 100 / +11.8
9 / Dug / 1506 / 12 / -4.9
10 / Dug / 1578 / 21 / -14.7
11 / Drilled / 1543 / 140 / 115 / -17.3
12 / Dug / 1527 / 6 / -1.6
13 / Drilled / 1514 / 132 / 118 / +7.0
14 / Drilled / 1543 / 133 / 125 / -12.5
15 / Dug / 1537 / 14 / -8.1
16 / Drilled / 1538 / 124 / 116 / -10.9
17 / Drilled / 1511 / 71 / 63 / -.03
18 / Dug / 1504 / 13 / -5.2
19 / Dug / 1486 / 9 / -4.9
20 / Drilled / 1481 / 79 / 64 / +5.2
21 / Dug / 1485 / 8 / -3.6
22 / Dug / 1505 / 9 / -4.0
23 / Dug / 1535 / 16 / -8.8
24 / Drilled / 1502 / 74 / 68 / -1.2
25 / Dug / 1525 / 14 / -7.6
a Minus indicates feet below land surface
b Plus indicates feet above land surface
Table 2: Logs of Wells
(ft.) / (ft.)
Well 1
Sand, fine to coarse, with thin beds of pebble gravel and layers of hard silt / 21 / 21Till, hard; cuttings consist of gravel, sand, silt and clay; sandy layer with water at 37-38 ft. / 74 / 95
Limestone, gray medium-hard, fractured / 7 / 102
Well 20
Soil, sandy / 1 / 1Gravel, sandy and sand / 8 / 9
Sand, fine and silt / 9 / 18
Hardpan (till), hard, quicksand at 28-33 ft. / 46 / 64
Limerock, gray, easy-drilling; water at 72 and 78 ft. / 15 / 79
Table 3: Tabulation Sheet for Water-table data
Well Number / Land Surface Elevation / Depth to Water / Water Elevationft. AMSL / ft. below surface / ft. AMSL
2
5
6
7
9
10
12
15
18
19
21
22
23
Table 4: Tabulation Sheet for Water-table data
WellNumber / Land Surface
Elevation / Depth to Bedrock / Thickness of Till / Bedrock Surface Elevation / Depth to Water / Water Elevation
ft. AMSL / ft. / ft. / ft. AMSL / ft. above surface / ft. AMSL
1
3
4
8
11
13
14
16
17
20
24
Figure 1: Topographic Map of the ground water study region with cross-sections AA’, BB’, and CC’ identified. Contour lines show land-surface topography, contour interval, 20 ft. Shaded area is underlain by sand and gravel, and unshaded area by till. Open circles represent dug wells and solid circles drilled wells, numbers refer to well records in Tables 1 and 2.
Figure 2: Basemap for use to generate a bedrock surface map.
Figure 3: Basemap for use to generate a thickness of till map.
Figure 4: Basemap for use to generate a water-table map.
Figure 5: Basemap for use to a piezometric-surface map.
Figure 6: Basemap for use to identify tracts of potential artesian flow.
Peer Group Evaluation
Name: ______
Group: ______
Project: ______
A. Please provide numerical scores for each of the members of the group, including yourself. When evaluating the members of the group, consider the following: 1) Did the person attend all of the class meetings and outside class meetings; 2) Did the person ask relevant questions and make valuable contributions to discussions that promoted understanding; 3) Did the person contribute significant ideas to the group product; 4) Did the person conduct the responsibilities of their role for this project; 5) Did the person demonstrate knowledge of the course material necessary for this project; 6) Did the person demonstrate good work ethic by doing their fair share of the work in a timely manner; and 7) Did the person demonstrate respect for other members of the group? Assign a score from 1 to 5 for each of the seven categories, with a 5 being the highest score. The overall score is the sum of the seven categories and should be a number between 7 and 35. Remember, your scores should be based on behavior and contributions, not personalities or relationships.
Name (Role) / Attend. / Discuss / Idea / Role / Knowl. / WorkEthic / Respect / Overall
1. ______
2. ______
3. ______
4. ______
B. Please provide additional comments about each member of the group. In particular, it is important to explain very high and very low scores.
1.
2.
3.
C. Acknowledgement of individual(s) who assisted this group in completing the project:
D. My signature below indicates that I have devoted considerable thought and effort to the evaluation of my peers and that this evaluation has been completed to the best of my knowledge and ability.
Signed:______Date:______