PRINCIPLES OF HYDROGEOLOGY
Fall, 2016
LAB 1: LAYING THE FOUNDATION Dr. Sanders
How to Prepare for This Lab:
1) Read the listtitled"What Should You Bring to This Course?
2) To refresh your understanding of sediments, read the section on "Porosity and Classification of Sediments" in your Fetter textbook.
3) Dig out your old textbooks and your favorite websites from ESCI 211: Physical Geology or ESCI 306: Rocks and Minerals, and refresh your rock classification skills.Review the names of the processes involved in the Rock Cycle.
4) While you've got those old textbooks out, refresh your understanding oftopographic map reading.You might also want to look at the many good online resources on topographic map reading.
5) Read the section on "Glaciated Terrane" in the Fetter textbook, pages 285-288. Although it uses many terms which may not yet be familiar to you, see how much you can get out of it.Pay particular attention to descriptions of these deposits: 1) glacial till, 2) glacial-lacustrine sediments, 3) glacial outwash. For now, you can ignore the information onhydraulic conductivity. We will work more with that in a few weeks.
Supplies:
· Your Fetter textbook, a notebook, and a calculator.
· A rock classificationchart or key (fromyour old textbooks, or print one out from the web.The one here is okay, but your textbooksare probably better resources.
· A printed copy oftheblank rock cycle diagram (.docx)linked here.
· A printed copy of theglacial geology base map (.docx)linked here.
· A ruler with inches and centimeter markings. A meter stick or 6-12 inch ruler is fine.
What to Hand In:
You don't have to hand in anything from this lab, at least not right now.But during the lab, you will take some notes that you will need in a week or two.(When the time comes, I'll say, "Remember those notes you took in your very first lab?Here's where you need to use them.") So, take good notes and keep them in a safe place.
To demonstrate that you have the skill level necessary for you to succeed in this course, you will complete an assessment on the material next week. You must score 85% or better in order to earn credit for it, and you can take it twice.If you don't score 85% on the first or second try, come see me, and we will work together to refresh your knowledge and skills and make sure you are ready to go on.
SEDIMENTS
Examine the sediments in the containers marked A, B, C, D, E, and F. Using the information on pages 70-75 of your textbook, and any other resources you care to use, describe each of the sediments in terms of itsgrain size, grain sorting, and if possible, its mineralogic composition.Hold on to your notes/descriptions, as you will need them later on in this course.
Imagine that these sediments are lithified.What rock would each one make?
SILT AND CLAY:One of the most vexing questions for beginning field hydrogeologists, geotechnical engineers, and soil scientists is telling the difference between silt and clay.Some classifications separate them solely on the basis of grain size, but that ignores a major difference between them:their mineralogic composition. Clay is composed of clay minerals, while silt is primarily composed of tiny, tiny grains of quartz.Containers of "pure" silt and "pure" clay are provided here in the labso you can become more familiar with the differences between the sediments.Examine them carefully and note any differences.Take a very small bit of each one in turn, and try wetting it in the palm of your hand. Note the differences between the sediments when wetted.Take notes on what you observe, and keep them handy, as you may need them later in this course.
ROCKS
Using the printed Rock Cycle diagram (see "What to Bring", above), write the names of the three major classes of rocks in the appropriate spaces. Then, label each of the arrows with the names of the processes that alter rock material as it goes through the cycle.
Examine the rocks in the traysin the lab, paying particular attention to texture and composition.Hand lenses and acid bottles are available for your use.(Be careful with the acid!Use it only when you need to: remember, it only works for one very specific test.Use paper towels to wipe off any drops of acid you apply to a rock.)
Separate the rocks into three piles, one pile for each of the three major classes of rocks you wrote in the boxeson your Rock Cycle diagram.
Within each of the three piles you made, further divide the rocksinto two groups based on their texture or mineralogic composition.Apply the correct geologic term to each group.
You should now have six groups of rocks.Assign rock names to at least two of the rocks in each group (12 rock names, total).For each, take notes on what you observed about the rock that led you to decide on that particular name for it.
GLACIAL GEOLOGY OF NORTHEASTERN ILLINOIS
Read the section on "Glaciated Terrane" inthe Fetter textbook, pages 285-288.Although it uses many terms which may not yet be familiar to you, see how much you can get out of it.Pay particular attention to descriptions of these deposits:1) glacial till, 2) glacial-lacustrine sediments, 3) glacial outwash. For now, you can ignore the information onhydraulic conductivity.We will work much more with that in a few weeks.
Using the map "Surficial Geology of the Chicago Region" (we refer to it as "the Willman map", after its author), study the legend and read the descriptions of the various deposits. Note the colors, stippling (pattern), and the tiny letters identifying each deposit. Decide which of the deposits falls in each of the three categories of glacial deposits (there will be a few misfits, so just go for the major deposits you see on the map).
Now, take the printed glacial geology outline map (see "What to Bring", above) and make your own map. On your map, use shading and labeling to show where you would find the three major types of glacial deposits: till, lacustrine sediments, and outwash.Onecouldspend many hours making this map incredibly precise, but don't bother at this point.The main idea is to familiarize yourself with the overall glacial geology of northeastern Illinois, so if someone asks you general questions like, "Where would I have to go to find deposits of till?", "Why is Chicago so flat?", or "I'm building a home in Lake County; what kind of surficial deposits am I likely tofind there?", you will be able to answer with an educated and informed response.
In addition to the three general types of glacial deposits listed above, three other significant geologic materials are visible on this map. Take a few minutes to familiarize yourself with them:
1)Cahokia alluvium(shown in bright yellow on the map): What is its geologic age?(i.e., when was it deposited?)Along what major geographic features can it be found?Give a 3-4 word (not longer!) description of the type of sediments you would find here.
2)Grayslake peat(shown in a dark green color on the map):Write a 3-4 word description of the type of sediments you would find here.Tell in what general area of the map you are most likely to find this deposit. Describe it in terms of counties or major cities.
3)Silurian "Racine formation" dolomite(shown in purple on the map):How old is this material, in terms of years?How doesthat agecompare with the ages of the material represented everywhere else on this map?Tell in what area of the map and in what part of northeastern Illinois you are most likely to find the dolomite at the surface of the earth. A few patches of it appear within the city of Chicago; why are they there?(To answer this question, you’ll have to think hard about elevation, especially what you know about Chicago's elevation.)
TOPOGRAPHIC MAPS
Examine the map provided.Several sticky notes on the map point to specific topographic or geographic features. Please take special care not to move or remove the sticky notes;keep them in placefor everyone to use.Answer thequestions shown on the sticky notes on themap.Remember, you don't have to hand this in. But fair warning: the assessment will have questions of this nature.
If you need to brush up on your topographic map reading skills, here are some online resources you can study:
· A chapter from a manual by the National Wildfire Coordinating Group (NWCG)(Start with "Interpreting Contour Lines" on page 2.12.)
· For fun, try playing with thisvisualization tool.
USING YOUR MATH SKILLS
The problems below are typical questions in hydrogeology that involve some algebra.Depending on where you are in your math curriculum, you may find them challenging, or you may not.If you do, don't worry: The point is to work out the concepts and skills right away, as opposed to letting it go too long.Just ask for help from your instructor, other Earth Science faculty, the Math tutor, or your classmates.
Well Screen
The pipe with slots in it is a well screen. When drillers build water wells in loose sediment, they first drill the hole, and then insert a well screen attached to a long string of "riser pipe".A piece of riser pipe is with the screen; see if you can thread them together.The screen holds the holeopen so the sediment doesn't collapse, but allows the water to pass through into the well.
How big a hole would be needed (in terms of diameter) in order for this screen to be inserted?What volume of water could the screenhold (just the screen, not the riser), if it were filled with water?
Darcy's Law
Darcy's Law is a fundamental law in hydrogeology. It describes how much water can flow from one point to another over a given time.Here is one way to express Darcy's Law:
Q= −KA(h2−h1)/(L2−L1)
Don't worry about what the variables stand for at this point.If you're curious, there's a discussion of Darcy's Law on p. 81-82 of your textbook.For now, let's just use it to brush up on your algebra skills.
Often, we need to use Darcy's Law to find the value of the variable K. (K happens to be the hydraulic conductivity.Again, don't worry about what it means;we'll get to it in a few weeks.)Rearrange the equation to solve for K.That is, put K by itselfon one side of the equal sign.What does the equation look like now?
Hydraulic Conductivity Values
On page 85, you'll see some typical values of hydraulic conductivity in Table 3.7.Look at the values for clay.Are they larger, or smaller than the values for "well-sorted gravel"?Look at the values for "silt, sandy silts, clayey sands, till". Is this range of values larger than, or smaller than the range of values for well-sorted gravel?
How Much Water Can This Sediment Hold?
Examine the clear plastic tube filled with dry sediment. Without removing the ends, describe the sediment briefly. Using the table on page 75 of your textbook, make an estimate of the porosity of this sediment. Then, determine the volume of water that could be poured into the tube to saturate the sediment without overfilling it.