Hydroquestions

Note: some of the questions below have overlap. That is, content of the answer to one question may also appear in the answer to another. This is common in all the sets of study questions.

2. When rain falls on the land, what are the basic factors that govern how much water will move along the surface as “overland flow”?

Water that does not soak into the ground, but runs to a stream, will continue in the hydrologic cycle to eventually become vapor and fall again as rain/snow etc. But water that soaks into the ground will permanently leave the hydrologic cycle.

5. What do the terms “saturated” and “unsaturated” have to do with defining “vadose zone” and “zone of groundwater”?

6. What is the term for lateral movement of water in the vadose zone, and what kind of condition could cause water to move laterally in the vadose zone?

9. What is evapotranspiration and what is its significance in the hydrologic cycle?

12. Groundwater will flow in the direction of __________________________________.

11. Explain why a river that is normally a gaining stream can become temporarily a losing stream during a flood condition.

12. During very high river stage conditions, such as after much heavy rainfall, “bank storage” can be created. What is “bank storage” and what happens to it after overland flow stops raising the level of a river?

18. How could you use a topographic map to determine the approximate boundaries of a “groundwater basin”.

19. State the basic relationship between surface topography and the configuration of the water table’s “topography”.

20. At a certain point along Hogwaller Creek the water level between rain falls in the spring is about 4.5 ft deep in the early spring (lots of water flowing through there). In the early fall it is less than 2 ft deep between rain falls and there is less water flowing in the stream. Regarding the local ground water situation, what can you say about the gradient of the water table in that vicinity at these two times of the year?

2. If you needed to estimate the total volume of water in a particular aquifer, what information would you need to obtain to make that estimate?

It should be pretty obvious that you need to know the aerial extent of the aquifer (that is, the extent of the aquifer in a horizontal sense) and the average thickness, and the porosity of the material that makes up the aquifer.

3. What is s porosity quantitatively? This is one simple “formula” you should know.

4. Of the following sediment characteristics, explain in what way they affect porosity of the sediment.

 packing [should contrast open vs close packing--which has better porosity?]

 sorting [should contrast good sorting vs poor sorting--which has better porosity?]

5. How does sediment burial (i.e., deep burial vs. shallow burial) tend to affect sediment “packing”?

6. Of the following types of sand, which commonly has a lower porosity and why? [“Why?” has to do with which has better and which has poorer sorting]

I meant to point out that of the common ways that sand is deposited, beach processes and wind-blown dune processes tend to produce very well sorted sands. River sands are not as well sorted. Thus river sands would generally not have as high a porosity as a beach sand.

7. How about shales (rocks formed from clays)--do shales have generally high or generally low porosity as compared to sandstone? (Note that the most abundant bedrock type in the AR River Valley area and in the Ouachitas is shale. It generally is bedrock in the areas of lower elevation throughout these regions. Useful general knowledge.)

8. What kind of porosity is the main porosity of plutonic igneous and metamorphic rocks? Do these rock types in general have high porosity or low porosity?

9. In what kind of situation can limestone and dolomite have high porosities? What part of the state of Arkansas has these kinds of rocks?

10. What is the difference between the "porosity" of a sediment and its "specific yield"? Also, is porosity normally > specific yield or < specific yield?

11. Know how grain size will effect specific yield. If two sediments have the same porosity but one is finer grained than the other, which will have the higher specific yield, the finer or the coarser--or no difference? (This was something I stated, but may not be as obvious in the tables—that is finer sediment will typically have lower specific yield.)

[There are very few “formulas” I will require you to learn. This, however, is one of the ones you should know.]

2. Of the various parameters in Darcy’s Law, which one reflects the water-transmitting properties of the medium (for example, sand) through which water flows?

3. Know how grain size, in general, affects hydraulic conductivity (K). (Do coarser sediments, like coarse sands and gravels, have higher K or lower K than finer sediments, like fine sands and silts?) [Note a brief glance at the handout on range of K for earth materials will tell you this. This is a very useful piece of knowledge to have in your head.]

4. Memorize the "typical" value of hydraulic conductivity (K) for "typical" fine sand (fine sand in the geologists sense, on the low end of fine sand in the engineer’s [ASTM] terminology). Know it in terms of m/d, ft/d, cm/s, and gpd/ft².

I did not give you this in class, but I will give it here. This would be an approximate value for a fairly typical fine sand. You would expect coarser sands to have higher K and very fine sands and silts to have lower): K =

5. Compared to other physical parameters, does the hydraulic conductivity of natural earth materials tend to have a narrow range of values or a wide range of values?

6. Know how sorting, in general, affects hydraulic conductivity (K). (Do well sorted sediments tend to have higher or lower K-values than poorly sorted sediments

7. Would you expect a sand with well rounded grains to have better, poorer, or about the same hydraulic conductivity compared to a sand with angular grains?

8. If doing hydrogeologic work in a coastal region, what factor or factors will possibly affect the hydraulic conductivity parameter you use in calculations involved in groundwater flow? (that is, factors besides the nature of the sediment or rock through which the water flows)

9. For quantitative purposes, what is the best way to determine the hydraulic conductivity of an aquifer? Why is this method better?

10. Regarding that best method to get an accurate determination of K, what is the disadvantage of this method?

[I forgot to mention this. The problem with doing the pumping aquifer test is that it is rather expensive. There must be a well with a pump installed and a monitoring well also. Then someone needs to pay a hydrogeologist (hopefully) lots of bucks to be out there to perform the test and evaluate it.]

11. Which is generally a better means of obtaining hydraulic conductivity of an actual aquifer, a slug test or a pumping aquifer test? Explain why. [Remember that some questions I will put have overlap or get at same thing from a different wording.]

Study Questions from 6th Lecture (Wednesday, 9/6/06)

1. Which is more accurate, determination of K using the Shepherd method or using a permeameter? [If I did not say so in class, the permeameter should be more accurate, because it measures permeability directly from a sample of sediment, water being pushed through the sediment in the lab set up. The Shepherd and Hazen methods estimate K from empirical formulas based on grain size distribution. However, the permeameter measurement is more time consuming than running a sieve analysis required for the Shepherd or Hazen methods. None of these methods are as good as testing in the undisturbed aquifer itself with the pumping aquifer test or the slug test.]

2. In order to apply the Hazen or the Shepherd method of determining hydraulic conductivity, what must you obtain and do before you can apply the equations developed by these researchers?

3. For aquifers that are composites of layers of differing hydraulic conductivities, which is normally higher?--___________

a) the average horizontal hydraulic conductivity

b) the average vertical hydraulic conductivity

c) neither, the average is usually the same

[Look at the sample problem we did in class. The mathematics reflects real behavior in nature.]

4. What would be the significance of a flat water table (horizontal) in a certain area?

5. How can you tell if groundwater is flowing or not in a particular area?

6. What is the general relationship between the surface topography and the "topography" of the water table?

7. Describe the general movement of groundwater in the vicinity of a "gaining" (perennial) stream.[In this answer, you should include both the matter of water moving laterally toward the stream from the valley slope area and also the movement of groundwater longitudinally in the downstream direction].

8. Where with respect to land surface topography do we look for discharge areas for groundwater?

9. What is the difference between an aquifer and an aquitard?

11. What is the difference between a "water-table aquifer" and a "confined aquifer"?

Study Questions from 7th Lecture (Friday 9/8/06)

1. What is a perched water table?

4. What kind of situation with regard to the potentiometric surface will cause a well that is screened in a confined aquifer to be a “flowing well”?

[relate the flowing well to the potentiometric surface—that is, that the potentiometric surface is above the land surface at that point]

5. What is the relationship between the water table the potentiometric surface in an unconfined aquifer?

6. In constructing a potentiometric surface map of a water-table aquifer in a particular area...

a) how would you use existing wells to obtain data for the map of the water table?

8. What is the minimum number of wells necessary to estimate the flow direction and hydraulic gradient of an aquifer in any given location?

[This directly relates to what I described as the ADEQ minimum requirement when contamination investigations are being done and to the homework problem we discussed.]

10. You should also know the formula for transmissivity (T=Kb) and what each parameter is.

11. When considering the transmissivity of aquifers, how does the thickness factor differ in the unconfined aquifer as compared to the confined aquifer?

1. In class we discussed transmissivity of an aquifer in terms of (1) isotropic vs anisotropic and (2) terms of homogeneous vs heterogeneous. Which of these two issues has to do with conditions at a single place, and which has to do with conditions over a range of places?

2. In considering an aquifer's transmissivity, it is important whether the aquifer is homogeneous or heterogeneous. What two main factors must be constant throughout the aquifer in order to consider the aquifer homogeneous with respect to transmissivity? [Consider the formula for T.]

3. Illustrate two different situations in which sedimentation factors can cause an aquifer in unconsolidated sediments to be heterogeneous in its K value (and hence in transmissivity).

[This question is not about the actual sedimentation process that causes the variation in K, but about the way in which the K values are unevenly distributed—we sketched a couple of examples on the board].

4. Two different geologic formations are described as sands. One was deposited as a beach deposit by a receding coast line. The other was deposited by a river system (fluvial). Which is likely to be more heterogeneous with regard to transmissivity?

[Note: I meant to mention in class that beach sands tend to be the same laterally over greater areas than river system sands. That is, river sands tend to be rather heterogeneous in a lateral sense as compared to beach sands.]

5. Describe a factor, other than original sedimentary factors, that can make a hard rock aquifer be heterogeneous?

6. Besides homogeneous vs heterogeneous, an aquifer may also be "isotropic" or "anisotropic" with regard to transmissivity. What does isotropic/anisotropic mean with regard to an aquifer's hydraulic properties?

7. In fractured rock aquifers, what is the most common factor that can introduce anisotropy to the aquifer’s transmissivity? [describe briefly]

8. Which normally have higher storage coefficients, confined aquifers or unconfined? [See the handout on Storativity.]

9. If equal amounts of water are withdrawn from a confined aquifer and a water-table aquifer, which will experience greater lowering of head?

10. What two factors are involved in releasing water from storage in a confined aquifer that is being pumped? That is, where is the water coming from, since the whole confined aquifer remains saturated while it is being pumped? [Note: see the handout and/or book.]

11. In an unconfined aquifer, the storage coefficient is for all practical purposes_______.

12. Does the kinetic energy due to the momentum of moving groundwater contribute significantly to its total energy? If so, why? If not, why not?

13. What is meant by the term “elevation head”? [A simple definition: Elevation head is an expression of the potential energy of a parcel of water due to its elevation, from the force of gravity.]

6. If I schematically sketch a set of nested piezometers showing water levels in them, be able to tell me what the nested piezometers indicate about groundwater flow. [Note: If you understood the example discussed in class you will realize the implication here will be as to whether there is an upward component of flow (head in deeper piezometers is higher than shallower piezometers) or a downward component (head in deeper piezometers is lower) or no vertical flow (all piezometers have same total head).]

7. Why must piezometer measurements of hydraulic head in saline aquifers be adjusted by a correction factor? Also, what part of the total head must be adjusted? [In case you did not get it, we pointed out that the pressure head must be adjusted because the density of saline water is greater than “fresh” water.]

8. If a well is in an aquifer and has the lowermost 20 ft of the well “screened” (i.e. have slots for allowing water to enter the well pipe), and if we want to use the well to measure hydraulic head, how does the well differ from a piezometer in the head it measures?

9. Why must the equation for flow velocity of water in an aquifer (called average linear velocity) include the sediment’s porosity as a parameter?

1. Considering the actual velocity of water moving in typical groundwater aquifers (such as fine to coarse sands) with common hydraulic gradients, what kind of rates are typical? ______

[The example problem on “average linear velocity” points to the answer for this.]

2. What kind of flow does Darcy's Law assume?______ (a) turbulent flow, (b) laminar flow

3. Why is it likely that the assumed condition for Darcy’s Law (mentioned in question 2) actually occurs in nature?

[The answer to this question is that given the very slow movement of water demonstrated by the problem on average linear velocity, it is quite reasonable to assume that flow is laminar through the porous medium, rather than turbulent.]

4. What happens close to a pumping well that may cause the flow of water in the aquifer to not faithfully follow Darcy’s Law?

[In class I pointed out that very close to a pumping well the gradient can become very steep as water flows into the well. Your answer to this question should convey the understanding that a steep gradient will mean a faster flow velocity (take a look back at the equation and see the effect of gradient on velocity). Faster velocity can lead to turbulent flow, annulling the direct applicability of Darcy’s Law.]

5. In layered subsurface situations (such as sediments or sedimentary rocks) with alternating permeable (aquifers) and semi-permeable (aquitards) zones, what is the term used for the change in direction of flow where flow lines encounter the boundary between layers of different hydraulic conductivity?

6. Describe the typical movement of groundwater in aquifers and in aquitards in layered sedimentary sequences. (Describe the movement in terms of the relationship between flow lines and aquifer/aquitard boundaries).

[Here I am not looking for the mathematical expression, but the general, typical flow directions in aquifers and aquitards as related to aquifer/aquitard boundaries.]

_____The principle flow equations that fully model flow through porous media (such as groundwater) are algebraic expressions.

_____The principle flow equations that fully model flow through porous media (such as groundwater) are differential equations (calculus).

_____Most practicing hydrologists dealing with ground water work extensively with differential calculus to solve problems involving groundwater flow.

_____ Most practicing hydrologists dealing with ground water work mainly with algebraic expressions that have been derived from applying differential calculus to situations with limiting assumptions.

_____Flow nets are a method that applies principles of a graphical solution to a complex differential equation (the “LaPlace Equation”)

_____Flow nets are outdated applications that were developed by engineers that are so oversimplified that they bear little resemblance to real hydraulic flow conditions.

_____Computer software that solves hydrologic equations is the only method that is recognized today as having any value in solving hydrogeologic problems involving groundwater.

_____Computer software that solves hydrologic equations is valuable in that the software models can be used to solve for groundwater flow in complex situations that would be difficult to solve for because of the complexity of the calculations that would be required.

1. Under steady-state conditions, in which kind of groundwater system (confined aquifer or unconfined aquifer) does the potentiometric surface tend to be more planar (ie. constant slope over an area)? And in which does the potentiometric surface tend to have curvature (ie. changing slope over an area)?

2. Considering a water-table aquifer, how does the hydraulic gradient close to a discharge point normally compare to the hydraulic gradient of the same aquifer at a distance farther from the discharge point? (In another approach to the question, in which of the two areas does the slope of the water table tend to be steeper?)

3. _______In which kind of aquifer, confined or unconfined, can Darcy’s law can be applied to calculate the amount of flow through the aquifer if certain requirements are met?

4. In the kind of aquifer that Darcy’s law can be applied to, which of the conditions below meet the requirements for applying Darcy’s law for calculating the amount of water flowing through?

10. If we know the answers to the previous question, it is then useful to know what are the most common rock types in various parts of the state in which we live, so that we can have an idea what kind of materials we might expect in the vadose zone at any particular location. Be prepared to answer the following questions about Arkansas.

[In looking at my notes while preparing these study questions, I noticed that I forgot to cover this. You will see it mentioned on a figure in the handout (the one showing the kinds of residence times one can expect for water in shallow vs deep flow systems). Connate water, according to its original definition is water that was in the sediment at the time the sediment was deposited and is “trapped” along with the sediment. Some have shifted the meaning and said we should use “fossil water” for the definition above and use “connate water” for water that has been in the subsurface for substantial amounts of geologic time (no quantity placed on the amount of time—I would guess at least some thousands of years). However, according to the actual meaning of the word “connate” outside of geologic context, the original definition should be retained.]

11. Under what circumstance would a series of sediment layers that are defined as several geologic units ("formations") be lumped together as a single hydrologic unit?

12. Under what circumstance would a single package of sediment that is defined as one geologic unit ("formation") be divided into two or more hydrologic units?

13. Name a confined aquifer in southern Arkansas that is a single geologic unit, but has been split into two hydrologic units by hydrogeologists. (The same formation is also an important aquifer in parts of Louisiana and Mississippi).

[We discussed in class—an important unit to remember in Arkansas—the Sparta Sand.]

14. When there is a regional flow system involving multiple layers, including some layers of lower hydraulic conductivity, and involving a single regional discharge area (for example a river), which statement below is correct?_____

a) Water from the uppermost permeable layer in the system above any semi-confining layers will normally contribute the most water to the discharge zone.

b) Water from deeper, semi-confined layers will normally contribute the most water to the discharge zone.

c) Water from each layer in the system will contribute approximately the same amount to the regional discharge zone.

Study questions from the 15th lecture (Friday, 9/29/06)

1. If a natural steady-state condition is achieved in a groundwater flow system, how will the natural recharge compare to the natural discharge in terms of total quantity?

2. Pumping water from a well in a water-table aquifer will produce a "cone of depression". In such unconfined aquifers, what is "depressed" in the cone of depression? [In case it is not clear, it is the water table that is depressed.]

3. Pumping water from a well in a confined aquifer will produce a cone of depression. In confined aquifers, what is "depressed" to form the cone of depression?

[In the case of a confined aquifer, it is the potentiometric surface that is depressed. (Of course, in essence in the water table aquifer, the water table is the potentiometric surface, so in both cases technically it is the potentiometric surface that is depressed. But in the confined aquifer the potentiometric surface is an imaginary surface, whereas in the water table aquifer it is a physical surface, the top of the saturated zone.)]

4. Pumping water from a well in a water-table aquifer will produce a cone of depression. The size of the area affected by the cone of depression will grow as the well is pumped. In what way does aerial recharge factor into limiting the size of the cone of depression? In other terms, how does aerial recharge affect the size of the cone of depression?

5. Describe the difference between a situation in which a well reduces the amount of ground water flowing from the ground into a gaining stream, verses the situation in which a well actually withdraws water from a stream?

[If you study the handout, concentrating on the area between the well and the river, one of the hypothetical cases shows the cone of depression’s outer limit has lowered the water table from its original elevation but the gradient is still toward the river; however, a lower gradient (gentler slope) now occurs, so the rate of flow into the river will be less. This is essentially diverting some of the water that would otherwise have entered the river, diverting it to the well. But when the cone of depression grows to such an extent that the drawdown in it makes the water table between the well and the river to be lower than the river, then there will be direct flow from the river to the well.]

6. What happens to a surface stream (a gaining stream) if a cone of depression from a pumping well in an unconfined aquifer grows until it intersects the stream?

[This is almost the same question above. You can simply say that discharge from the ground water system to the stream will first be reduced and eventually the well may even draw water from the stream to the well.]

7. Is it possible to dry out a water-table aquifer, that is, to deplete it of its ability to supply water? What could produce such a situation?

[Note that this situation could come about if the discharge from the wells in the aquifer was consistently greater than the recharge coming into the system for a period of time. Water would be continually drawn from storage in the aquifer until it is depleted.]

8.Where in Arkansas is there a threat of the hypothetical situation of Q#7 occurring? (Give the area and the name used for this aquifer, and what is causing it.)

[I told you eastern Arkansas (rice country) and irrigation for rice being the cause. I may not have told you that the aquifer is called the “alluvial aquifer”, which is formed from river sediments of the Arkansas River, White River, and Mississippi River.]

9. Pumping water from a well in a confined aquifer will produce a cone of depression. If the potentiometric surface has not fallen below the top of the aquifer, are void spaces in the aquifer being drained to supply water to the well? If the voids are not being drained, where is the water coming from?

[This concept was discussed in an earlier lecture and again in this one, but it is not easy to pick up at first. Basically the water is coming from reduction in overall porosity because of “collapse of the aquifer skeleton”, that is, grains in the aquifer packing tighter together due to overlying load. Note that, water pressure in the voids formerly held the grains to a more open packing condition, but as head is reduced near the well because of pumpage, the grains get “scrunched” closer together. So, the answer is no, the void spaces are not being drained, the sediment is still saturated, but water is coming from collapse of the aquifer skeleton reducing porosity. (To a smaller degree, it is also coming from expansion of the water itself.)]

10. In confined aquifers, the size of the area affected by the cone of depression will grow as the well is pumped. Discuss how proximity to a recharge area for the aquifer can limit the size of the cone of depression (what makes it stop growing?). [See comment below #12.]

11. In confined aquifers, the size of the area affected by the cone of depression will grow as the well is pumped. Discuss how a thick leaky confining layer above the aquifer can limit the size of the cone of depression.

12. In confined aquifers, the size of the area affected by the cone of depression will grow as the well is pumped. Discuss how a thin leaky confining layer above the aquifer can limit the size of the cone of depression.

[Questions 10-12 deal with three situations we discussed that could contribute water to a confined aquifer that is having water removed from storage by a well’s discharge. You should be able to comment how the cone of depression may grow until it reaches a recharge area for the aquifer, so that the recharge could contribute water that would balance the well’s discharge. Or if there is a leaky confining layer above, water coming from storage in the confining layer can contribute to balancing the well discharge. Or if a leaky confining layer is rather thin, leakage from the storage in confining layer may be insufficient to balance well discharge; thus water may come from an aquifer above the leaky confining layer and flow through the confining layer, again the cone growing until sufficient water coming thru the confining layer balances the withdrawal in the well.]

13. In class we discussed another figure on the handout that showed a situation that can cause saline water from a deep aquifer to come up into a shallow, useful aquifer and thereby contaminate it. The situation involves pumping water from the useful aquifer. Explain in terms of hydraulic head what could cause this. [Your answer should correctly use the term “head” or “hydraulic head”. Point out that the situation prior to pumping had head in the overlying, “good” aquifer being higher than head in the underlying aquifer, so that any interaction between them involved seepage downward through any confining layer. Pumping then lowers head in the overlying aquifer, so that flow is induced from the lower to the higher aquifer.]

14. Where in Arkansas is there a situation where the problem mentioned in Q#13 is a real-life problem? What is the name of the aquifer that has this problem?

13.What will happen to the behavior of a confined aquifer if the cone of depression of the potentiometric surface falls below the level of the top of the aquifer?

Study questions from the 16th lecture (Monday, 10/2/06)

1. Fill in profile view of this figure to illustrate two different geologic situations that could lead to a row of springs along a topographic slope, such as illustrated. Label the sketch sufficiently to explain why the springs are there. Don’t just give a spring type name (and you don’t have to name the spring type name here either).

(If the image does not show here, try clicking on the red X. It might come.)

2. What is potentially wrong with this statement: "The natural pond on that property has no streams flowing into it or out of it. Therefore the only exchange of new water that pond has must be rain water that falls on it and water that evaporates from it."

[Consider our discussion of lakes and the figure we looked at.]

4. What is possibly wrong with this statement?: “We have put surface runoff barriers around that hazardous chemical spill site. Therefore we have eliminated any threat to that wetlands area that is nearby.” (Explain what exactly the remaining potential threat is. Don’t just jot down a couple of phrases.)

5. Concerning aquifers in an alluvial (river) valley hydrologic system, the drilling of a well may encounter aquifer and aquitard material. What part(s) of the alluvial system formed the aquifer deposits?__________ (choose from a, b, c)

and what kind(s) of sediment comprise the aquifer material? __________ (choose from d, e, f)

6. In an alluvial (river) valley hydrologic system, the drilling of a well may encounter aquifer and aquitard material. What part(s) of the alluvial system formed the aquitard deposits? _______ and what kind of sediment comprises the aquitard material?_____

7. In the alluvial (river) valley systems, the aquifers mentioned in Q 5 tend to be _________

c) irregular in aerial extent (i.e. some of them extensive, some of them limited)?

2. Why are alluvial sediments in some areas of Arkansas so thick? Explain briefly how this came about.

3. What part of Arkansas’s "alluvial aquifer" has, on the average, the coarsest sediment?_____

4. Considering the "basin and range" terrane of the southwestern US, in very general terms what are the subsurface materials of the two main components of this terrane, the basins and the ranges, like? (i.e. with regard to whether the subsurface materials are commonly solid, hard rock, or generally unconsolidated sediments).

5. In the alluvial basins of the US southwest, what part of an individual basin tends to have the best aquifer material? ______ And give a brief explanation why.

6. In the alluvial basins of the US southwest, what is the usual general direction of groundwater flow?_______

7. Rancher Frank drills a well in an area of the alluvial basins of the US southwest. He gets a pretty good amount of water at 250 ft depth, but the water quality is not too great because of a high degree of dissolved solids. His friend advises him to have the driller keep going because he might get better water if he drills deeper. Tell him here what you know about water quality with depth in these areas so he can make an “educated decision” about whether to spend more money up front with deeper drilling with the prospect of getting better water deeper down.

8. In the alluvial basin terrane of the southwestern US, is the hydrologic system of each individual basin isolated from the hydrology of other basins? Explain.

9. In the alluvial basin terrane of the southwestern US what kind of streams are the most typical, gaining or losing streams? [Although we did not discuss this, most streams are loosing streams because the area has semi-arid climate. In the higher reaches of the alluvial fans adjacent to the mountain ranges the streams can be gaining for at least part of a year, but almost universally they don’t have to go far before they become loosing streams. In rare instances, like shown in a handout we did not discuss, this situation can be reversed for limited stretches of a stream.]

10. In the glaciated central region of the US (ie. previously glaciated), surficial geologic maps will show the distribution of "glacial till". What is glacial till like, and is it generally of low or of high permeability (does it usually constitute an aquifer or an aquitard)?

11. Some geologists have noted that the hydraulic conductivity of glacial tills is commonly (lower, higher--Choose one) in actual field conditions than when samples are measured by a permeameter in the lab. Explain your answer.

[I forgot to mention in class that in a short course I attended there was an engineer who had worked on a project in which there were glacial deposits. They had taken samples of a glacial till and had permeability run on them using a permeameter in a lab. They designed their project using hydraulic conductivity determined in the lab—very low of course—but then when the well system was put in, it behaved as if the till were much more permeable (though not a bona-fide aquifer, still much leakier than they expected). The instructor was an expert who happened to be from Minnesota. He explained that often in tills a shrinkage fracture system (joints) can develop making the wider scale hydraulic conductivity to be much higher than an individual sample would indicate. That is, there often can be some “secondary porosity” associated with glacial tills.]

12. In the glaciated central region, some areas have extensive deposits of "glacial outwash" material. What did these sediments come from? What kind of materials are they generally made of? And are they in general good aquifers or are they generally aquitards?

13. _____Regarding glacial deposits in the "glaciated central region" of the US, which of the following three statements is more correct? Also, explain why.

14. Which hydrogeologic region characterizes the hydrogeology in the deeper subsurface beneath the glacial deposits of the Glaciated Central Region?

Study questions from the 18th lecture (Monday 10/9/06)

1. In the Atlantic and Gulf coastal plain terrane, are the subsurface materials generally of consolidated (ie. hard rock) or of unconsolidated (loose sediment) material?

2. What direction is the regional dip of layers in the coastal plain region in south Arkansas? (That is, toward what direction are the layers inclined downward?)

3. In south Arkansas, what part of the sequence of sediments in the Atlantic and Gulf coastal plain is of marine origin, and what part is fluvial in nature?

[Did I make clear to you that the Cretaceous sediments up through the lowest strata in the Tertiary section, the Paleocene Midway Group, are all of marine origin (beach and offshore sands, clays, and some limestone). Strata above that, that is, the Eocene Wilcox Group and upward from that are “terrestrial”, that is, deposited by land-based systems, mainly rivers and lakes. If I asked this question on a test, I would accept “the lower part of the sequence is of marine origin, but the upper part is fluvial.]

4. What is the name of the geologic formation that is the most important confined aquifer in SE Arkansas, east of I-30 (a large portion of the state)?

5. Where do the confined aquifers within the coastal plain region in Arkansas get their recharge? [The best way to answer this is just to say at their up-dip extension, south of the Ouachitas.]

The following is a question based on something I forgot to cover this morning. It has to do with saline water infiltrating the Sparta Sand in the vicinity of El Dorado, AR.

6. _____What is a mechanism likely to be involved in contamination of the confined aquifer mentioned in question 4 with saline groundwater? Also give a brief explanation for this mechanism.

a) Water drawn down into the confined aquifer through overlying aquitards

b) Water drawn up into the confined aquifer through underlying aquitards

c) Drawing water from extensions of the aquifer that extend to the coast.

[In explaining the correct answer, which is b, point out how lowering of head in the aquifer due to pumping can cause water in underlying aquifers which are commonly more saline to have a higher head than the water in the aquifer, causing water to seep up through the aquitard and contaminate the aquifer. (Note that, head in overlying aquifers may also now be higher than in the aquifer in question and water may come in from overlying aquifers also through overlying aquitards, but normally shallower aquifers are not more saline).]

7. Where is the ultimate discharge area for groundwater in the aquifers of the Atlantic and Gulf coastal plain terrane?

9. At the fresh-water/salt-water interface in the subsurface of coastal areas, does the fresh ground-water tend to overlie or underlie the saline ground-water? (Even though the interface is not horizontal, there is a common occurrence of one somewhat over the other.) Also explain why.

10. What is “passive” salt-water encroachment, and why can withdrawals of groundwater in the areas near the coast lead to passive salt-water encroachment?

11. What is “active” salt-water encroachment, and what condition is necessary for this process to take place?

12. In which situation is the fresh/salt water interface in the ground water system more likely to extend farther out to sea, in the case of an unconfined aquifer or in a confined aquifer?

14. What kind of depositional processes deposited the sediment of what is known as the “High Plains Aquifer”? What kind of sediment is it? And is it consolidated or unconsolidated?

15. Is the "High Plains Aquifer" a confined aquifer or an unconfined aquifer for the most part?

16. Briefly describe the hydrologic crisis that is occurring in the high plains area.

Study Questions from Lecture 19, Wednesday October 11, 2006

1. In the "non-glaciated central region" of the US, is the subsurface material mostly lithified (consolidated into rock) or unlithified (unconsolidated sediments)?

2. What is the bedrock structure like in the central part of the non-glaciated central region (ie. the most extensive parts of the region)?

[This has to do with the layers of sedimentary rock being basically flat-lying, but in places gently warped into broad folds and domes and basins.]

3. What is the bedrock structure like in the Ouachitas and Appalachians part of the non-glaciated central region?

4. Beneath the glacial deposits in the central part of the glaciated central region (i.e. In the area of the craton), what is the bedrock structure like?

5. What kinds of sediment (or rock) compose the principal aquifers in the main part of the "central non-glaciated region" of the U.S.? What forms the aquitards?

[Note that this question is worded so as not to give away the answer to #1. It is actually rock.]

6. From where do the confined aquifers in the non-glaciated central region obtain recharge?

[I forgot to mention this, but there are at least two different sources of recharge, of which I only implied one. (1) up-dip extensions of subsurface beds (such as St. Peter SS is confined in IL and crops out in MO, where it is recharged), and (2) also recharge by seepage through semi-confining units (aquitards).]

7. What kind of situation can cause some aquifers in the central part of the non-glaciated central region to get upward flow from deeper aquifers through leaky confining layers? Does this situation normally improve water quality or degrade it?

[Note: Although I did not mention this, but it is essentially the same situation as addressed in the question about the Sparta sand of the previous lecture questions.]

8. What kind of rock (or sediment) composes the best aquifers in the Appalachians part of the "central non-glaciated region"?

9. What kind of rock (or sediment) composes the best aquifers in the Ouachita Mountains part of the "central non-glaciated region"?

10. What kind of rock (or sediment) composes the best aquifers in the Arkansas River Valley area (here the question is not about the sediments of the flood plain of the Arkansas River, but about the whole area, such as Dover, Johnson County, Yell County, etc)?

[I only mentioned this and did not write it down and we were going fast at that time. In the River Valley area the bedrock is exclusively shale, siltstone, and sandstone, and the sandstones are better than the shale for aquifer material because of more fractures, especially thin-bedded sandstones.]

11. In the Ouachitas of Arkansas, in rock units that make the better aquifers, is the porosity mainly primary porosity or secondary porosity?

12. Contrast the nature of most sandstones in the Arkansas River Valley and Ouachitas as compared to most of the sandstones in northern Arkansas in the Ozarks. I want the contrast to be with regard to the hydraulic characteristics of the sandstones.

[I hope you picked up in lecture that the sandstones of the River Valley and Ouachitas are almost all well-cemented, having little or no primary porosity, whereas many of the sandstones in the Ozarks (northern Arkansas) have little cementation, lots of primary porosity. It should be obvious which will have better K and better S (storage coefficient).]

13. An industry that utilizes water in its process wants to locate in Arkansas, and they want to be “self-sufficient” and use groundwater from wells on their property for the supply. Would you expect wells in the Ouachita Mountains to (on the average) yield more water or less water than wells in the Coastal Plain region to the south?

14. In areas of folded rock, like the Arkansas River Valley area, the potentiometric surface and natural groundwater flow generally follow the trends of _______.

a) bedrock structure (i.e. flowing down inclined strata, away from crests of anticlines and towards troughs of synclines

b) land-surface topography (i.e. groundwater flow more-or-less follows the slope of the land surface, not following the layering of strata).

15. Discuss the process of acidification of rain water before it contacts bedrock.

16. Describe the process of solutioning in limestones and why, in general, the process leads to a few channel ways with a lot of flow.

17. In general the greatest part of limestone solutioning occurs ____

18.. Which situation below tends to have a greater depth of active solutioning?______

(a) a limestone with a high fracture density (i.e. many fractures per unit volume), or

(b) a limestone with a low fracture density (i.e. few fractures per unit volume).

1. Which rock type has a greater tendency to form open passageways and thus more free-flow aquifers, limestone or dolomite? [has to do with relative solubility of the two rocks]

2. Two areas are underlain by limestone bedrock. You are concerned as to which might have a greater abundance of free-flow aquifers. You look at water levels in monitoring wells in each area. Area A has a steeper-sloping water table than area B, which has a fairly flat water table. Which of the two areas has more likelihood of having cavernous passageways and free-flowing groundwater?

3. Two areas are underlain by limestone bedrock. You are concerned as to which might have a greater abundance of free flow aquifers. How could you assess which area has more of a free-flow character, and how would you recognize which one has a diffuse-flow condition? [Note: this question is essentially the same as #2, I could ask the question from either direction.]

4. From the standpoint of groundwater pollution, why does “karst hydrology” pose a greater risk than the groundwater hydrology in other types of geologic terrane?

5. In the "Southeast Coastal Plain" area (S. Georgia & Alabama + all of Florida), what kind of material makes up the principal aquifer of the region? (ie.. is it unconsolidated sand, or is it sandstone, or limestone, or shale, or igneous/metamorphic rock, or what....?)

6. Regarding the aquifer in question 5 (which is called the "Floridan aquifer"), is it a confined aquifer in Florida or is it an unconfined aquifer? Explain your answer.

[NOTE: I don’t think I said specifically in class, at least not write on board, but you should be able to see from Fig. 7.17 and 7.18 that in some areas (Ocala uplift and part of GA/AL) it is unconfined, and in some areas it is confined by the Hawthorne Fm (the “Upper Confining Unit”).]

7. Why does the cavern system in the Floridan aquifer in the area of the Ocala uplift have cavern development well below the water table?

8. Does the Floridan aquifer system have high-yielding wells or does it generally have low well yields? [You should be able to deduce this from what we have covered.]

11. What is the cause of salt-water encroachment problems in the Floridan aquifer system in the Savannah, GA area?

[See Fig 2-22 of the handouts. We did not discuss in class, but you will see on this contour map of the potentiometric surface for the Floridan aquifer a major cone of depression in the Savannah, GA area (near SC border, on Atlantic coast). That is from the city wells pumping lots of water from this aquifer. The lowering of head in that area below sea level has caused concerns regarding salt water encroachment. To be honest, I do not know the status of that issue now, perhaps it has been resolved. But this at least illustrates how coastal areas have the potential problem of salt water encroachment.]

12. What kind of materials constitute the subsurface of the Colorado Plateau, and what is the general structure of these materials?

13. The area of the Colorado Pleateau and Wyoming Basin is semi arid and therefore surface water supplies are limited. People have therefore turned to groundwater as a water source in the region. What is the main problem encountered with the shallow aquifers in the area as a groundwater resource for city or irrigation water supplies?

14. The area of the Colorado Pleateau and Wyoming Basin is semi arid and therefore surface water supplies are limited. People have therefore turned to groundwater as a water source in the region. What is the main problem encountered with the deep aquifers in the area as a groundwater resource for city or irrigation water supplies?

15. What kind of materials constitute the subsurface of the Appalachian Piedmont and Blue Ridge region? Does ground water there primarily resided in primary porosity or secondary (fracture) porosity?

16. In general, would the Appalachian Piedmont region be classified as an area with abundant groundwater reserves for water supply or as an area with relatively small groundwater supplies?

[If you consider the kind of porosity as covered in question 15, you should be able to get this. The vast majority of the igneous and metamorphic rocks do not develop any kind of solutioning along fractures.]

Study questions from the 21st lecture (Monday, 10/16/06)

1. What constitutes the principal aquifers in the Appalachian Piedmont area?

[Note: in class we may not have used the term “aquifer” in the discussion of this region. However, we could say that zones where fractures are concentrated would constitute a “fractured-rock aquifer”. Also the thick regolith constitutes an aquifer in places where the water table is within the regolith.]

2. In the Appalachian Piedmont and Blue Ridge region there are at least two good reasons why the vicinity of valleys is often the better place to drill for water-supply wells. What are two good reasons?

[Note: your answer should explain both the matter of valleys often coinciding with locus of zones of high fracture density and the matter of the “topography” of the water-table(which you would remember from other lectures is higher under hills, and thus all the water off to the sides of the valley that is above the elevation of the valley floor would constitute “storage” for wells in the valley—Or you might take as your second reason the regolith which can be a factor of feeding groundwater toward the valley).]

3. What are topographic "lineaments", and what is their significance in seeking superior locations for water-supply wells in the Appalachian Piedmont?

4. How would you tie together field measurements of “joint” orientations in bedrock outcrops with topographic lineament analysis for predicting the best places for sources of groundwater in the Appalachian Piedmont and Blue Ridge region?

5. What kind of materials constitute the subsurface of the Northeast and Superior Uplands region? What constitutes the principal aquifers in this area?

6. Is the regolith above bedrock in the Northeast and Superior Uplands region a likely candidate for significant groundwater reserves? And why?

7. What kind of materials constitute the subsurface in the western mountain ranges?

8. What kind of materials constitute the subsurface in the Columbia River Plateau area?

9. What kind of materials constitute the subsurface in the Hawaiian Islands?

10. In areas where lava flows dominate the bedrock, what part(s) of lava flows constitute the main water-bearing and transmitting zones for lateral ground water flow, and why?

11. In areas where lava flows dominate the bedrock, what is the chief factor for vertical hydraulic connectivity between roughly horizontal “aquifer” material?

[Note, the word here is not “conductivity”, but “connectivity”.]

12. Does hydraulic conductivity in basalt lava flow "aquifers" commonly tend to get progressively better in older lavas, or does conductivity tend to become less over time, or stay the same? Why?

[Note, the word here is “conductivity”, not “connectivity”.]

This ends the section covered on the third lecture test.

1. Consider a pumping well in a confined aquifer and a well pumping at the same rate in an unconfined aquifer. If both have the same hydraulic conductivity and saturated thickness, in which of the two (the confined or the unconfined aquifer) will the cone of depression generated be larger? Why?

2. I want you to remember the following assumptions that are used in developing mathematical treatments to drawdown from pumping wells:

 For equations dealing with confined aquifers, aquifers are homogeneous and isotropic

3. Why must the gradient (dh/dl) of the potentiometric surface become progressively steeper at distances closer and closer to a well within the cone of depression caused by pumping?

4. What other physical phenomenon has relationships that Theis and colleagues recognized to be analogous to groundwater flow, from which they by adaptation derived the equations of flow for calculating drawdown produced by pumping wells?

5. What kind of aquifer does the Theis equation for drawdown from pumping wells apply to, confined or unconfined, or equally to both?

4. Why, under steady-state conditions and application of the Theim equation, can we calculate transmissivity, but it is not possible to determine aquifer storativity?

[I spoke of this, but perhaps you did not get it. Since water going to the well is no longer coming out of storage in the aquifer, but rather from some kind of recharge, the storage does not enter into the equation; only the transmissivity does.]

5. Besides the fact that we cannot determine storativity of the aquifer from the Theim equation, what other disadvantages are there to the steady state method?

6. Sometimes aquifer parameters are determined from pumping test data under "transient" conditions. By what do we recognize that the conditions are transient?

7. How many observations wells must be installed in the aquifer in order to use the “Theis time-drawdown” method for determining aquifer parameters?

8. Generally speaking, how long does it take to perform an aquifer test when applying the Theis time-drawdown method?

9. What advantage is there in determining aquifer parameters from the Theis non-equilibrium pumping aquifer test method as compared to the application of the Theim equation to an aquifer test pumped until equilibrium conditions are achieved?

[Note: the main advantage we pointed out is that one can obtain the storage coefficient for the aquifer using this method. In most cases it takes less time to do than waiting for steady state conditions to be achieved, and only requires one observation well.]

Other aspects of the class time relate to quantitative matters of the homework problems.

· Besides recognizing from a Jocob plot that the data represent this condition, know which segment of the plot represents the higher transmissivity, and which the lower, and which segment represents the aquifer material closest to the well and which represents material farther out

· Know that it is possible to calculate the transmissivity of each part of the aquifer by measuring the “change in (h_o-h)” for one log cycle of each segment.

· Which segment’s transmissivity will give a better indication of the well’s overall productivity? [If the well is going to be pumping long time periods, the later segment will tell the productivity, the farther out portion of the line.]

b) an aquifer of limited lateral extent that is in contact with essentially impermeable material, and therefore the aquifer gradually is being depleted during pump test.

d) an aquifer that at some distance from the well has a boundary of complete recharge

5. Which situation is likely to give better data for interpreting T and S from transient time-drawdown data?______

a) observation well is fairly close to the pumping well, where drawdown is relatively high

b) observation well is fairly far from the pumping well, where drawdown is relatively low

c) neither a nor b is better for a location, as long as the observation well is screened through the entire thickness of the aquifer

6. How many observation wells need to be used in performing the Jacob distance-drawdown aquifer test?

[I did not mention in class, but three at least to have some certainty. All three plotted should fall on straight line. If they do not, then there is a facies change or something like that. If you use two wells, you can guesstimate, but you never know whether there might be a facies change or a change in thickness of the layer or something else making the aquifer not fit the assumptions adequately.]

7. Which of the three methods discussed so far can most easily be used to determine just how far out a pumping well’s radius of influence goes at a particular chosen amount of pumping time?

[Do you remember me saying that the “r₀” value on the Jacob distance-drawdown method is the extent of the radius of influence at the time the measurement was made?]

1. To determine the hydraulic properties of an unconfined aquifer, Melissa performed a rising head slug test. What is meant by “rising head” slug test?

2. Match the terms for a slug test: Slug in test ___________ Slug out test___________

3.Briefly describe how a slug test is performed. (You may choose to describe either a “slug in” or a “slug out” (falling head or rising head) slug test.) Be sure to describe what causes there to be interaction between the well and the aquifer so that aquifer parameters can be estimated.

[This question is not about how to apply formulas, but how the test is performed–see the handout. What I mean by “what causes interaction between the well and the aquifer” is the fact that there is a head difference between the well and the aquifer caused by (1) the slug put into the well and making the water level in the well to be above the level outside the well, or(2) the slug pulled from the well causing water in the well to be lower than the water outside the well. The head difference thus formed will cause water to flow out of or into the well, to or from the aquifer. The rate of flow is influenced by the hydraulic properties of the aquifer.]

4. Although some hydrogeologists almost discount slug tests altogether, even those who are proponents for this type of aquifer test would agree that pumping aquifer tests will give a better estimate of aquifer characteristics. Why??

5. Although most hydrogeologists consider "slug tests" for determining aquifer parameters to be less accurate than pumping aquifer tests, there are some important advantages to slug tests. What advantages are there to slug tests? Be sure to tell what situation more-or-less precludes doing a pumping test, making a slug test the definite method of choice in that situation.

6. Which kind of aquifer test generally involves a more widespread part of the aquifer, a pumping test or a slug test?

7. Can slug tests be used on confined aquifers only, or on unconfined only, or on either confined or unconfined?

a) Water level in the well is 20.25 ft below ground surface while water in aquifer next to well is 19.5 ft below ground surface

b) Water level in the well is 20.25 ft below ground surface while water in aquifer next to well is 20.5 ft below ground surface

c) Water level in the well is 20.25 ft below ground surface while water in aquifer next to well is 18.5 ft below ground surface

10. Well A has a specific capacity of 50 gpm/ft, while well B has a specific capacity of 20 gpm/ft. Which well would be better for providing water for a large irrigation project?

11. If there are two wells pumping in an area such that their respective radii of influence both affect the area, how is drawdown calculated for any specific site in that area?

12. An irrigation well supplies a center pivot sprinkler. Normally it is run for a 24 hour period. When it pumps for that time period it draws the water table down in a neighbor’s domestic well a total of 3.5 ft. Normally another neighbor runs his center pivot at a different time than the first farmer does. When he does, his well pulls the domestic well’s water level down by 2 ft. What would the drawdown be in the domestic well if both pumps ran for 24 hours at the same time?

13. When modeling hydrogeologic situations involving a pumping well and either a recharge boundary or an impermeable boundary, an “image well” is used to mathematically analyze the situation. Where in relation to the boundary and the actual pumping well is the hypothetical image well placed?

[Note that the discussion and the figures should tell you that it would be directly across the boundary and at the same distance from the boundary as the pumping well. The essence of this part of the discussion is similar to the idea of the two pumping wells and the composite cone of depression discussed under #11 above. When there is a hydrologic boundary, either a recharge boundary or a no-flow boundary, it will affect the drawdown caused by a pumping well whose radius of influence intersects the boundary. If there is an impermeable boundary, it will cause drawdown in the direction of the impermeable boundary to increase once the radius of influence reaches that boundary, because it cannot reach farther out into the aquifer for water. If an imaginary well is placed at a position of equal distance from the boundary along a line from the pumping well through the boundary and perpendicular to it, the cone of depression for the imaginary well can be calculated and plotted just like discussed under #11 above. Adding the intersections as discussed above will give values that will properly model the drawdown distribution mathematically. If the boundary is a recharge boundary, for example a river that could leak water to the aquifer when the radius of influence reaches the river, the image well will be an injection well and the cone of depression will be an inverted cone. If at some point the drawdown calculated for the pumping well was 8 ft, while for the same point the drawdown was "-2 ft", that is the rise in water level if an injection well were placed at the point of the image well would be 2 ft, then the total drawdown at that point would be 6 ft.]

Study questions from the 1^st lecture on GROUND WATER CHEMISTRY

(Monday, 11/13/06)

1. What property of water makes it have a chemical reactivity with ionic substances?

2. What kind of chemical bonding characterizes most minerals in the rocks of the earth’s crust?

3. What class of minerals is the most common in the common rocks of the earth’s crust?

(a) carbonates (b) silicates (c) sulfates (d) oxides

4. How does the solubility of carbonate minerals compare to that of silicate minerals in general?

5. If your job sent you to a new area for a particular task, you could look at published geologic maps to see what kind of rocks occur as bedrock in the area. The following areas have rocks of different general character. For each, indicate whether the minerals that constitute the bedrock of the area tend to be of relatively high solubility or of relatively low solubility.

a) A terrane of mostly sandstones and shales

b) A terrane with abundant gypsum and halite

c) A terrane of igneous and metamorphic rocks

d) A terrane composed of limestone and dolostone

6. (a) Name four of the most common cations that occur in natural waters. (b) Name three of the most common anions in natural waters. (For each, indicate the common charge [i.e. valence].)

7. Normally, which has more dissolved constituents in it, groundwater or surface water? Why?

8. What is the most commonly employed unit of concentration used to designate how much of a particular substance occurs in water from a particular source?

9. Know that the concentration unit mg/L is a mass/volume unit; that ppm is a mass/mass unit, and that for low concentrations, the number of mg/L ≈ ppm.

[Note that for the vast majority of groundwater situations the concentration of TDS will be low enough that these units are essentially equivalent.]

10. Know that meq/L (milliequivalents per liter) is a concentration that expresses relative amounts of charge contributed by the ionic species present.

11.What does "total dissolved solids" (TDS) mean in the discussion of groundwater chemistry?

12. Will electricity flow better in water with large amounts of ionic species in it, or with low amounts?

13. Is higher "specific conductance" associated with higher TDS or with lower TDS?

14. Is the "specific conductance" of each ionic species the same? That is, for equal concentrations in mg/L for two different ionic species, will there be the same specific conductance?

Study questions for the 2^nd lecture on GROUND WATER CHEMISTRY

(Wednesday, 11/15/06)

1. What rock types constitute the "carbonate" rocks?

2. In describing groundwater chemistry, "alkaline" water corresponds with______

a) low pH

b) high pH

c) low Eh

d) high Eh

3. In describing groundwater chemistry, "acidic" water corresponds with______

a) low pH

b) high pH

c) low Eh

d) high Eh

4. Rainwater is typically ______.

a) neutral

b) slightly alkaline

c) very alkaline

d) slightly acidic

e) very acidic

5. _____What pH below would be more likely typical of groundwater in an area of extensive limestone bedrock?

(a) 3.5 (b) 6 (c) 7 (d) 9 (e) 12

6. _____What pH below would be more likely typical of groundwater in an area of sandstones and shales, with no carbonate rocks around?

(a) 3.5 (b) 6 (c) 8 (d) 10 (e) 12

7. What are the main sources that produce natural acidity in water that reacts with carbonate rocks and dissolves them in widespread carbonate rock terranes?

8. What ionic species are typically abundant in groundwaters of carbonate rock terranes?

9. When you see the term "Eh" in a discussion of groundwater chemistry, what parameter does that refer to?

10. The chemical terms "oxidizing" and "reducing" are general terms related to oxidation potential.

· Which of these two terms is associated with low Eh?

· Which of the two terms better characterizes water chemistry above the water table?

· Which of the two terms better characterizes water chemistry in the saturated zone at and just below the water table?

· Which of the two better characterizes water chemistry in the saturated zone well below the water table?

11. Under typical pH conditions of groundwater, iron is generally more likely to occur as a dissolved species under ________ (oxidizing, reducing) conditions.

12. Name two other elements that tend to go hand-in-hand with Fe in their behavior in oxidation / reduction chemistry of groundwater (i.e. these tend to occur as insoluble compounds under similar conditions as Fe and they tend to be in solution under conditions in which Fe is in solution).

13. Black shales tend to buffer groundwater seeping through them to a _____chemistry.

a) oxidizing, b) reducing

14. What material occurs in coal and in black shales that produces this chemical condition?

15. What mineral(s) commonly occur(s) in coal and black shales as a result of the Eh conditions of these rocks? (The mineral(s) I am referring to come in during “diagenesis”, that is, the post burial changes in the sediment).

16. Explain why Fe-oxides & hydroxides tend to clog up wells and plumbing in many areas that use water wells. (Explain in terms of chemical change in water as it is extracted from the environment below the water table and brought into the well).

[Note that the thrust of this question is on the fact that the undisturbed water well below the water table typically has a somewhat reducing chemistry and Fe is in solution as Fe²⁺. When it is brought up into contact with the atmosphere in the well it brings in a more oxidizing chemistry, causing Fe to precipitate as oxides and oxyhydroxides.]

17. What is the role of bacteria in effecting the clogging of wells in areas with Fe in solution.

18. In class we looked at a diagram for the behavior of Fe under variations in Eh-pH conditions. We emphasized what going up in Eh or going down in Eh will do in terms of Fe becoming soluble or precipitating. Consider the diagram and tell me what would happen if relatively acidic water with some Fe in solution were passed through a filter packed with crushed limestone.

Study questions for the 3^rd lecture on GROUND WATER CHEMISTRY

(Friday, 11/17/06)

1. Describe basically what cation exchange is.

2. What common geologic materials tend to have significant "cation exchange capacity"?

3. Describe a way in which having materials with high cation exchange capacity can be beneficial to an aquifer. [It relates to restricting movement of certain kinds of pollutants.]

4. How can clay minerals be carriers of heavy metal pollutants in surface waters?

5. Describe the difference between the way in which clays of the smectite family, such as the most prominent of these, montmorillonite, receive exchangeable cations, as compared to other common clays.

6. Which clay minerals have higher cation exchange capacity? (smectite or other clays)

7. Some geologic formations have sediments that were deposited in inland seas, and these were subsequently buried under other sediments. If such sediments have an amount of montmorillonite, in what way would groundwater seeping through these sediments be affected?

8. Describe briefly how diagenetic conversion of montmorillonite to illite can tend to make aquifer waters become more Na-rich with time.

Questions below are related to a handout on how dissolved ionic species affect water use.

9. What ionic species in water are the main factors in making water to be called "hard water"?

10. What kind of bedrock will produce "hard water" in wells penetrating it?

[Note that in these terranes, some surface streams may be fed by springs (i.e. gaining streams) with water that has long been in contact with the bedrock and is quite saturated in the hard-water generating elements.]

11. What constituents, when present in relatively high concentrations in water, tend to make "scale" problems in boilers using the water?

12. What is a common source of Cl^- in groundwater in inland areas?

[Note: in addition to the source given in the handout, there is another source-- sedimentary evaporite deposits. “Evaporite” deposits sometimes contain extensive beds of “rock salt” (halite, NaCl).]

13. What are three common sources of Na⁺ in groundwater in inland areas?

[Note: One of these is in the note for question 12. Regarding the two sources mentioned in the handout, the second is the matter discussed in the previous lecture regarding smectite clays, like montmorillonite.]

14. What is a common source of sulfate in groundwater?

[Note: the handout mentions gypsum and pyrite. These two minerals are major sources. If you are asked this on a test, I would rather you say regarding gypsum, “From gypsum in sedimentary evaporite deposits”, because that is the kind of situation in which gypsum is most typically present in any significant quantity. Regarding pyrite, you should indicate “from oxidation of pyrite”, because pyrite is FeS₂, which produces SO₄ by oxidation.]

15. What does “TDS” stand for in groundwater chemistry? [= ”Total Dissolved Solids”, bottom of handout.]

16. In terms of TDS, which generally is taken as an indicator of good water quality vs poor quality?______

a) High TDS is an indicator of good water quality
b) Low TDS is an indicator of good water quality
c) Neither low nor high TDS is consistently an indicator of water quality

Study questions for the 4^th lecture on GROUND WATER CHEMISTRY

(Monday, 11/20/06)

1. If I show a triangular (ternary) diagram such as the one depicted in the Power Point presentation, if I have a point plotted to represent the composition of a water sample, then you should be able to tell me what % each of the three constituents contribute to the solution.

2. What is the significance of a number of points representing separate water samples all plotting in a cluster on a ternary diagram or a Piper diagram?

3. On a "Piper" quadralinear diagram for showing the relative concentrations of dissolved species, how could we recognize that a particular water source was the product of mixing of two other known water sources?

[If in the example given you couldn’t see the forest through the trees, the point is that if the compositions of two different water sources are plotted, then samples from different degrees of mixing of the two will plot on a line that connects the two mixed waters.]

4. Why do we often plot graphical representations of chemical analyses instead of simply using tables of data from analysis of water samples?

Study questions for the 5^th lecture on GROUND WATER CHEMISTRY

(Monday, 11/27/06)

1. Considering water quality, which of the two, surface water or groundwater, more commonly has problems with:

 too much total dissolved solids? ______________________________

 too much suspended matter? ________________________________

2. Which of the following would not be considered a contaminant in groundwater?_____

a) diesel fuel

b) a high concentration of Na⁺ and Cl^- from dissolution of halite deposits in the subsurface

c) colloform bacteria

d) none of the above

e) all of the above

3. The Gizmo Aquifer in the subsurface of Volunteer County Tennessee is classified by the EPA as a “Class III” aquifer. Would that water be suitable for putting in a well for your farm home? (I could change this question around and have Class I or II in it.)

4. _____Which EPA class of water will have the most stringent protection regulations?

a) Class I, (b) Class II, (c) Class III

5. Why are agri-chemicals considered "non-point-source" contaminants?

6. Discuss two common contaminants from agri-chemicals.

7. What does the term "leachate" refer to in the topic of groundwater contamination?

8. In considering potential sites to put a municipal solid waste landfill, what kind of natural earth materials that might potentially be in the vadose zone are desirable for choosing the best site?

[The comments in the discussion of natural attenuation should lead you to this answer.]

9. In what way do microbes in the subsurface aid in “natural attenuation” of contaminants in the environment?

10. What is the purpose of a “clay cap” on a landfill? Also comment on other measures taken to address the same phenomenon as the clay cap. (Don’t just list the measures, but also comment on what those measures do.)

[Note that one matter you would mention would be the sloping of the upper surface. You should also say that this is to promote water that falls on the landfill to run off instead of soak in to reduce potential leachate.]

11. Sketch and label a basic “leachate collection system” for a solid waste landfill. Include a brief discussion of how it works to prevent leachate from reaching the groundwater system.

[There was one figure we referenced from the text that would be sufficient for sketching a general situation for leachate collection.]

12. What major industry often must store brines in storage lagoons and then inject them into deep subsurface? (While in storage, these brines are a potential source of groundwater pollution.)

13. Injection of brines or manufactured industrial wastes into the subsurface is practiced legally in some places. What two hydrogeologic factors are the main ones required to be met in order to do this?

14. What is the difference between how a chemical spill will affect the environment as opposed to a leaking storage tank?

15. What is a LUST in groundwater pollution acronym jargon?

15. Explain what the source of acidity is in situations of “acid mine drainage”. [Don’t just say “pyrite”; explain what happens to the pyrite and why it produces acidity.]

16. Before mining came into a particular area there was no significant acidity to the ground or surface waters. After simply extracting some of the rock and soil in the mining process, acidic waters started to “show up”. Why was there no significant acidity before mining, but it became acidic after mining?

17. In some areas there is significant pyrite for producing acidity, yet in the final analysis the waters do not end up with low pH, even without addition of lime for neutralizing. The physical outlay of the mine site may be just like others that are producing acid mine drainage. Why is there no acid mine drainage?

[You should figure out from the handouts and Power Point that this has to do with there being, in addition to the pyrite (a potential acidifier), an abundance of natural neutralizers in the surrounding material (such as calcite or siderite or gypsum.]

18. Why are toxic trace elements (such as Pb, Hg, etc) commonly also a problem associated with acid mine drainage in mines that are for metallic ores?

[This has to do with the comment that associated with metallic ore deposits there are often elevated amounts of elements normally in trace concentration in common rock. The acidity makes the water reactive and can leach these out and contaminate the water.]

Study questions for the 6^th lecture on GROUND WATER CHEMISTRY

(Wednesday, 11/29/06)

1. Concerning contaminants in groundwater (and surface water), standards have been promulgated by the EPA. Concentrations of contaminants are given by EPA to define for each potential contaminant a MCLG (or called RMCL), a MCL, and an SMCL. What are the differences between these three acronyms and which, if any of them, are enforceable?

2. Cite three purposes of water quality monitoring in groundwater studies.

3. Where in a well does a "filter pack" go? Is it normally made of well-sorted sand or of poorly sorted sand? Should it be coarser or finer than the formation in which the well is installed?

[The illustration is sufficient to know where the filter pack goes. In class we mentioned, perhaps too quickly to jot down, that the filter pack is made of well-sorted sand (for permeability). It will be coarser than the aquifer material so that it can allow a larger opening in the well screen. The pore spaces between sand grains, however, must be small enough to keep out the aquifer material.]

4. Where in a well does a “bentonite seal” go? What is its purpose? Which kind of aquifer is it more critical for, confined or unconfined?

5. In what sort of situation should a well screen for a water-table aquifer monitoring well definitely be made long enough to “straddle” the water table (i.e. part of screen is below water table and part is above)?

6. Sections of PVC pipe are normally put together with glue, however one can obtain a more expensive PVC pipe with threads for screwing sections together. Which type would you recommend for a monitoring well installed to monitor for low-level contaminants? Why? [We did not talk about this in class. Think about it.]

7. The hollow-stem auger drill rig is often used for installing monitoring wells in water table aquifers. What kind of material is this rig suitable for?______

a) Water-table aquifers in loosely consolidated sediments

b) Confined aquifers in fractured hard rock

c) Water-table aquifers in fractured hard rock

d) In free-flow limestone aquifers

8. What is a “split-spoon” sampler or a “Shelby tube” used for in well drilling?

9. What are the objectives in "well development"? What kind of action between the well and the aquifer must be made to obtain the most effective development?

10. Which does the job of well development better, a surge block, over pumping, or a water-jet device?

11. If doing water sampling for a client with regard to determining water quality and compliance with mandated MCL's it is important to be sure that the analytical lab is accurate and consistent in its analyses. Describe a way to be sure the lab you use is accurate in their analyses.

12. If doing water sampling for a client with regard to determining water quality and compliance with mandated MCL's it is important to be sure that the analytical lab is accurate and consistent in its analyses. Describe a way to be sure the lab you use is consistent in their analyses.

13. When sampling water in a well, why should the well be pumped or bailed prior to sampling if at all possible?

14. What kind of contaminants lend themselves to detection using soil-gas (vadose zone gas) analyzers?

15. What does the acronym VOCs stand for?

Study questions for the 7^th lecture on GROUND WATER CHEMISTRY

(Friday, 12/1/06)

1. Describe a couple of "pathways" to the aquifer from the land surface along which contaminants can move.

2. If a liquid contaminant is released at the surface, describe the difference in the way the liquid will move through coarse sand vs a very fine sand, as it works its way downward.

3. What does the acronym LNAPL stand for? What does DNAPL stand for?

4. In discussing groundwater contaminants we may refer to some contaminants as "floaters". What constitutes a contaminant a "floater"? (There are two factors needed to make a “floater”.)

[Note that the liquid must be less dense than water and also immiscible (or nearly so) in water.]

5. Name at least one floater and describe the way it behaves when it reaches the water table.

6. In the case of a LNAPL, does the dissolved component of the liquid commonly move faster or slower or at the same rate as the undissolved component?

7. What constitutes a contaminant a "sinker"? Describe the way a sinker behaves when it reaches the water table.

8. What constitutes a contaminant a "mixer"; describe the way a mixer behaves when it reaches the water table.

9. If a contaminant has invaded an aquifer underlain by a semi-confining layer (ie. leaky confining layer), what kind of condition could make spreading of the contaminant into an underlying aquifer through the semi-confining layer more likely or a greater problem?

10. Dissolved contaminants can move in an aquifer by both diffusion and advection. What is the difference between these? Which of the two is more important in migration of contaminants?

11. What is the effect of "mechanical dispersion" on (a) the size of a contaminant plume over time, and (b) the concentration of the contaminant in the plume over time.

12. If an aquifer is not isotropic, but rather has a hydraulic conductivity (K) that is greater in the direction perpendicular to the hydraulic gradient than the K in the direction parallel to the hydraulic gradient, how would that condition affect the contaminant plume? You can sketch a comparison between an isotropic aquifer and the one in question here if you like.

13. How will the presence of pumping water wells in an aquifer in the general vicinity of a contamination plume affect the shape of the contaminant plume? Illustrate.

14. An aquifer consists of fine sand with a few, thin, coarse sand layers in it. A pump test is done and the average hydraulic conductivity (K) is determined for the aquifer. Later a contaminant is discovered to have leaked into the aquifer and the average K and hydraulic gradient are used with appropriate equations to determine the rate of movement of the water and thus of the contaminant. Will this calculation accurately predict the extent of contaminant migration? Why or why not?

15. We learned earlier in the course a formula for calculating the "average linear velocity" of groundwater using the porosity, hydraulic conductivity, and the hydraulic gradient. In dealing with contaminant hydrogeology, what can that formula be used for? _____

a) Calculating the time the leading edge of a contaminant plume will reach a certain down-gradient site.

b) Calculating the time that all contaminant will have passed a particular site down gradient from the source of contamination.

c) Calculating the concentration in the contamination plume

d) Calculating how far the center of mass of the contaminant plume will have moved after an amount of time

16. In placing monitoring wells at a site of potential groundwater contamination, what is the minimum number of wells that ought to be installed and what are some important principles that ought to be incorporated in the choices for placement of those wells? (Answer may be accompanied by a sketch map of well placement.)

17. Describe geologic factors that could produce a “trailing effect”, in which groundwater contaminants move slower than would be predicted by equations formulated for homogeneous isotropic aquifers.

18. What kind of contaminants do clays in subsurface materials tend to retard in the spread of groundwater pollutants? Why?

19. What kind of contaminants does organic matter in subsurface materials tend to retard in the spread of groundwater pollutants? Why?

Study questions for the 8^th lecture on GROUND WATER CHEMISTRY

(Monday, 12/4/06)

1. Regarding subsurface contamination with hazardous substances, in order to remediate the site, sometimes "source removal" is necessary. What kinds of things might be removed in this process?

2. If contaminated soil is removed from a site, what must be done with it?

3. What are some measures that might be taken to prevent infiltration of rain water into a subsurface contamination site?

[Reminder—we discussed this in our coverage of landfills earlier.]

4. What is a “slurry trench wall” used for in groundwater remediation efforts?

5. What is a “grout curtain”, and how is one made? How effective is a grout curtain considered to be in comparison to a slurry trench wall for blocking the movement of groundwater? [Note: It would be helpful to include a sketch of a layout in answer, if this question is asked. Also I mentioned that it cannot be determined for certain that all the porosity got plugged by the grout.]

6. What is a “sheet-pile cutoff”, and how is one made? What is the basic problem with a sheet-pile cutoff with regard to its use in contaminant source control?

7. In controlling the movement of a plume of contaminated groundwater, sometimes "pressure ridges" are employed. What is a pressure ridge, and how is a pressure ridge created?

8. Concerning the choice of location of an extraction well for intercepting a contamination plume in a "pump-and-treat" method of groundwater remediation, why is it usually better to locate the well just "downstream" from the plume and not in the plume itself?

9. What is a "well-head protection zone”?

10. Draw a map view of a single extraction well and a hypothetical "capture zone". For your map, draw a north arrow and let us "pretend" than the hydraulic gradient before installing the extraction well is such that the flow direction is toward the SW. On your map, indicate with a labeled arrow this general direction of groundwater flow prior to pumping. Then indicate the configuration of a capture zone using a series of flow lines. Also indicate flow lines just outside the capture zone. Finally show the position of the stagnation point to the system.

[Note that the exact width of the capture zone and the exact position of the stagnation point would depend on hydraulic gradient, K, b, and the well's pumping rate. The purpose here is to be sure that you know the general configuration of such systems. See the figure referenced in the power point presentation (from your text). Don’t just draw half of the capture zone, like it is in the figure in the text. Your sketch should show how the capture zone is for the most part up-gradient of the well, with a kind of parabolic shape, including a small area down-gradient of the well, and the stagnation point being the point of the capture zone boundary farthest down gradient of the well. I say all this to encourage you to look carefully at that diagram.]

11. Place an (a) for Analytical Model or a (b) for Numerical Model with each of the following statements:

______ Breaks down a geographic area into a matrix of cells given known or estimated hydraulic properties and calculates flow between all the cells

______ QUICKFLOW is an example of

______ MODFLOW is an example of

______ Solves algebraic expressions to analyze groundwater flow similar to those we used throughout the semester. However, it can handle many wells, hydraulic boundaries, etc.

12. Which groundwater flow model that we discussed can be used to analyze a complex situation that is heterogeneous and has a number of layers of differing hydraulic properties (that is, a 3-dimensional model)?

13. How does a “permeable treatment bed” work in decontaminating polluted groundwater? Illustrate where it would be placed in relation to a plume of contamination and how groundwater interacts with it.

14. What kind of pollutants can be treated with the following types of permeable treatment beds?

a) limestone

b) activated carbon

15. A similar question to #14 could be asked from this angle: An in situ permeable treatment trench (treatment bed) may be installed to treat groundwater. Name a kind of treatment material that could be put in the trench for the following kinds of contaminants.

16. Basically how does "bioremediation" work? Why is oxygenated water with N and P sometimes injected into contamination plumes that are being treated with "bioremediation" techniques?

17. What general kind of contaminant is typically treatable with bioremediation techniques?

[It should be clear to you that it is various toxic organic chemicals, that is, C-H compounds that are turned into CO₂ + H₂O by digestion action of naturally occurring microbes in the subsurface.]

18. How does “vapor extraction” work, and what kind of pollutants are successfully treated with this method?ADVANCE \d4

Choices for second blank -- (c) elevation (d) pressure (e) total

Curved (changing slope)____________________________

Study Questions, Lecture #14, Wednesday, 9/27/06

The End