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Hydrogeology of Long Island Pine Barrens Ponds
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Fig.
1 - Location of the study site
Welcome to Stony Brook. Our hydrogeology class has been studying ground water and a system of interconnected ponds within the watershed of the Peconic River in the eastern Pine Barrens (N40*53'30", W72*48'30") which are important to Long Island's (see fig.1) water supply. The Pine Barrens also house a wide variety of rare plants and animals which have adapted to periodic forest fires, and are known as a fire climax ecosystem. Our goal is to study the water chemistry of an area within the Pine Barrens. We also wanted to find out the influences of acid rain and other possible forms of pollution.
Fig. 2
- Calverton Ponds aerial photo
Nine wells were drilled in May to draw water from Long Island's Upper Glacial Aquifer and we drilled an additional one in July. Samples were also taken from the ponds in that area (Fox Pond and Sandy Pond). Samples were taken on a weekly basis for four weeks in July. Then the samples were analyzed by performing several tests and measurements. Bailers were used to sample the water. Before performing the tests, filtering had to be accomplished. Some of the tests we performed were measuring temperature, pH, conductivity, spectrophotometric iron analysis, dissolved oxygen, and ion chromatographic analysis of nitrates and sulfates. In the following sections all these tests are explained in detail. Diagrams, graphs, and figures are shown. Enjoy!!!
This educational research project was sponsored and conducted by the Center for High Pressure Research, the Office of Technology and Society, and the Long Island Groundwater Research Institute. Funding was provided by the National Science Foundation.
Collecting samples from wells and ponds can be fun and educational. The biggest part of collecting samples is making the well. The first step in making a well is to find a clearing that would be close to the groundwater, but in a place where people will be unlikely to disturb it. Then you must move all the fallen leaves and decaying matter to the side. Now you can use the auger, otherwise known as the drill, and turn it into the ground until the bit is full. Then you can take it out and empty it out to the side, banging it upside down if necessary.
Repeat the drilling until the top handlebar part touches the ground. Then you can unscrew it and add the extension. Repeat until you reach water at the bottom of the hole, and drill a little more so more water can go into the well. When the drilling of the hole is complete, you can start with the pipe. You take the pipe, cap the bottom end, and using a hacksaw, cut five slits on that end, so that water can seep into the well without most of the large dirt particles going into the well. After the five slits are cut, roll over the pipe and make five more slits. Now you can lower the pipe into the hole. To test it out, drop a small pebble down the hole, and if it splashes there is water in the bottom. Last, but not least, label it and cap it. Later you can come back to the well and sample the water.
In order to sample the groundwater, first you must find the well, then you can uncap it, using a wrench if necessary. Slowly let the bailer down into the well, letting it sit for a while so water has time to go into the bailer. After it has been in for a few seconds, pull it out gently and carefully empty it out into a large beaker. When two large beakers are full, you can cap the well and do tests on the water.
In retrospect, making wells and collecting samples can be hard work, but it also can be fun.
Fig. 3 -
Auger
Fig 4 -
Bailer
Fig. 5
- Throwing a bailer to collect pond water
Fig.
6 - Using a bailer to sample a well
Filtering is the process by which undissolved impurities are removed from the water. Filtering must be done in order to obtain an accurate pH, dissolved oxygen, temperature, and accurate analysis of ions such as Fe 2+ and NO3 3-.
The first step in filtering is to make sure that all the materials are present (Fig. 7). One piece of equipment is filter paper. There are two types of filter paper. The first type has large pores. This is to filter out the larger particles in the water (prefiltering). The second type of filter paper has small pores, and this is to filter out the smaller particles. Some of the other equipment are the syringe, beakers and the parts of the filter. Next you place your filter paper on the part attached to the black rubber ring. Then attach the part of the filter with the orange rubber ring to the part with the black ring. Then, make sure the parts are interlocked securely. This is a very important step because, if not done properly, the syringe will leak.
Now, put on the cover of the filter and twist it tightly. Next, fill the 60 ml syringe with water. Attach the filter to the top of the syringe. Firmly, yet patiently, push water out of the syringe through the filter into the clean beaker (Fig. 8). Repeat as necessary until the water is fully cleansed and transparent. Sometimes the water will contain smaller particles than the filter paper can remove. In this case, the water cannot be fully cleansed.
Fig. 7
- Parts of a filter
Fig. 8
- Using a filter
The pH scale is used to determine the basic and acidic balance in a solution. This test is mostly used in science in the testing of water. pH stands for parts of hydrogen. The formula for pH is:
pH= -log[H+].
A liquid is called acidic when it has a high concentration of hydrogen ions. While alkaline substances still contain hydrogen, they do not release it like an acid. The pH scale ranges from 1 to 14. In the scale, the closer to 1, the more acidic the liquid is. 14 is the highest an alkaline substance can get on the scale. A 7 is neutral on the scale.
To find the pH of a liquid, we use a pH meter (see fig. 9). The meter varies with the temperature of the substance. Therefore, it must be standardized before you measure the pH. First you take the temperature of the substance. You use a knob to set it on the pH meter. Next, you take the electrode of the meter and stick it in a solution that has a neutral pH. Adjust the meter so it reads 7. Once again, you rinse the electrode with deionized water. You repeat these steps but with a solution of 4 or 10. Then you adjust the slope of the meter.
Rinse the electrode again. You are ready to test your solution. When you test your solution you must wait until the meter comes to a complete stop. You take the electrode and, for the last time, you rinse it. Now turn off the meter and put it away properly. Remember that once you turn off the meter, you have to restandardize it when you turn it back on.
Fig. 9 -
pH meter
Dissolved oxygen is the oxygen within the water which all living aquatic organisms need to survive. To do the dissolved oxygen test there are a few simple steps to follow.
To do this test, you must first take a sample from the water area. Second, filter the sample. This is very time consuming, so be patient. While doing this, make sure you protect the oxygen test kits from the sun. Third, insert the ampule into the plastic sleeve. Then, insert it in the water. Make sure the tip of the ampule is totally submerged in the water. If it is not in the water, the vacuum will not be correctly filled with sample water, and air will go in the container, and the test will actually be a test of the air. Then press the ampule down into the sleeve with your thumb to break the tip and let the water in.
Next, remove the ampule and shake it. Let it sit for approximately one minute so the chemical reaction can go to completion. Next, compare it to the color chart (Fig. 10). Hold it to the light for a more accurate reading. Before the test the liquid in the ampule was a greenish yellow, but now it should change to a shade of blue. The darker the shade of blue, the more dissolved oxygen there is in the water. It is measured in milligrams per liter. This test is designed to see what organisms can survive in the area of water we studied. At 25 ºC the maximum dissolved oxygen concentration is 8.26mg/l.
Fig. 10
- Measuring dissolved oxygen
Conductivity is defined as how easy electricity can go through a solution. The purpose of using the conductivity meter (Fig. 11) is to find the salt content of a solution, which is also called the total dissolved solid (TDS). In order to do so, you must measure the conductivity of four standard solutions with known salt content. In this way the relationship between conductivity and salt content is known. The relationship that we found was: Conductivity=salt content * 1.8 (Fig. 12). However, this is only valid if you use the right units, which are microsiemens and milligrams per liter.
To use the conductivity meter you must follow some basic steps very carefully. First you must take off the cap on the bottom of the conductivity meter. After doing so, you must clean the bottom of the conductivity meter with deionized water and wipe it dry with Kim wipes. Then you put the bottom of the device (the part you cleaned) in the solution and let it sit. A number should appear on the conductivity meter. If the number is changing, (for instance between a 7 and 8) the average is taken (in this case 7.5). After reading your number, you must multiply it by 10. These are the units, called microsiemens or mS. By dividing the microsiemens by 1.8, one gets the salt content in mg/l. Finally, clean the bottom with deionized water and wipe it dry with Kim wipes, and of course put the cap back on.
There are different sources for the deviations in the data. One possible reason can be that you did not clean the bottom of the device with deioinized water and wipe it dry with Kim wipes. This can cause a deviation because the deioinized water would mix with the solution. Then, the conductivity would be lower. Another deviation can be not multiplying the result by 10. You may have also forgotten to measure filtered water. If you do not filter the water, you can get things in the solution that can interfere with the conductivity. If proper rules are not followed, it can make a large difference in your final results.
These are the steps to measuring conductivity the correctly. There are mistakes that can be made, but they are easily avoided.
Fig.
11 - Conductivity meter
Fig.
12 - Conductivity of standard solutions
In order to do an iron analysis you must make a blank and standards. Before you do this, you must make Phenanthroline (Phen), Hydroxylamine (HA), and Ammonium Acetate (AA) solution. To make the Phen solution, you must add one reagent to 20 drops of concentrated HCl and add H2O to one liter of water. To make the HA solution, you add 25g of Hydroxylamine to 250 ml of H2O. The Hydroxylamine is extremely toxic, so be careful! To make the AA solution, you must add 50g of Ammonium Acetate to 50ml H2O and 150ml of Acetic Acid. In order to mix the different reagents with their solutions, a magnetic stirrer was used. (Fig. 13)
The standard stock solution contains 20mg/l of Fe which equals 20,000mg/l. The dilutions which made the concentration lower were performed so we could find out what the relationship is between the amount of iron and the absorbance in the spectrometer (Fig. 14). We made standards of4000 mg/l, 2000mg/l, 500mg/l, and 250mg/l. These standards are needed to see how much light a given concentration of iron absorbs. If the liquid is clear, no light is normally absorbed. If the liquid has color, some of the light would be absorbed. The spectrometer measures the percent transmittance.
The spectrometer is a device that measures the concentration of iron in a solution (known as the standards, blank, etc.) The spectrometer uses light to measure the amount of iron in a sample. When you put the sample in the slot, the spectrometer uses the light as an energy source. The answer given on the spectrometer is the percent transmittance. The formula for transmittance is T= I/Io * 100%. T equals transmittance, I is the light that goes out, and Io is the light that comes in. The light that goes out is a smaller number than the light that comes in if the solution has a color. If it is clear like the blank we mention before, the I and Io are equal and 100% transmittance is measured. After you find the T%, then you plug it into the formula, A=-log [T%]. Once you find A, Beer's Law is used, in which A=abc where a equals a constant called the molar absorptivity, b equals the path length which is the diameter of the test tube, and c is the unknown concentration and A equals absorbance. When you put the numbers in the formula, you find the concentration. The concentrations are found by plotting absorbance verses the iron added. The method of standard addition was used in order to get more accurate results.
There can be errors in reading the transmittance percent on the spectrometer. In addition, if the label on the test tube is in the path of the light, it can absorb the light. The solution should be the same amount for all tests made. But systematic errors are possible.
Fig.
13 - Magnetic stirrer
Fig.
14 - Spectrometer
The purpose of ion chromatography is to find out the concentration of ions in an aqueous solution. You do this by separating the different kinds of ions from each other. To separate the ions you take a column and fill it with particles. The particles are the stationary phase, which means they are not moving. Then you place liquid in the column. The liquid is in the mobile phase. At the bottom of the column, place a conductivity meter. Now take the substance you want to separate the ions from and pour it into the column (Fig. 15). Some ions will attach to the particles and remain at the stationary phase. Some ions attach to the mobile phase, (liquid) and thus move faster. The smaller ions always come out faster because they prefer to stay in the mobile phase. The ions Cl -, NO3-, and SO4 2- will come out (within about 5 minutes) at different times because of this. This is how the ions become separated.
There are several factors that affect the speed at which the ions come out. One is the way the particles are arranged. If the particles are unordered, the speed of the ions will decrease and they will come out over a longer period of time. If the particles are ordered the particles will come out faster and at relatively the same time (see fig.8). Once the ions come out they are measured by the conductivity meter. Then the conductivity is plotted as a function of time. Standards are used to get the relationship between conductivity and concentration. You make a graph of the standards with conductivity as a function concentration (Figs. 16, 17 and 18). Once you have that graph you can interpolate (read into the graph) of what your ionconcentrations are.
Fig.
15 - Ion chromatograph
Fig.
16 - Chloride standards
Fig.
17 - Nitrate standards
Fig.
18 - Sulfate standards
The class performed simulations with a sandbox model (see fig.19), which showed the different zones of aquifers, ground water, the effects of pollutants, and the effects of pumping out water. One could see the cone of depression that formed around a well during pumping. Some of the zones the sandbox simulated were the zone of aeration and the zone of saturation. With this simulation of the zones, we were able to see the effects of pollutants on our ground water. One effect we saw was that it polluted some drinking water. After polluting the ground water we had to figure out how to take out the pollutants from the ground water. We got the answer by pumping water out from the water table. By pumping the water, we removed some pollution and we lowered the water table. But when we lowered the water table, a nearby body of water (in this case a river) lost water until it was completely dry. We continued polluting the ground water and pumping the pollution out so everyone in the classroom had the opportunity to pollute the water and clean it out (Fig. 20).
Fig.
19 - Sandbox aquifer model
Fig.
20 - Using the sandbox model
A computer simulation with systems like lakes and ponds was used to show the influence of different volumes of water in a system on the concentration of a pollutant and its residence time. Also, the change in flow rate and its impact on the pollutant concentration was studied. Two assumptions are made. The first is that the system is in a steady state and the second is that there is complete immediate mixing of the pollutant entering the system.
Qs = Flow Rate (m3/s) V = Volume (m3 ) K = Decay Constant Cm= Concentration (mg/l) Co= Initial concentration of pollutant
The two main conclusions are:
the higher the flow rate the higher the pollutant concentration but the shorter the residence time.
the larger the volume the lower the pollutant concentration and the longer the residence time.
The results of all data collected and performed analysis are shown in tables 1 through 4. We studied a system of ponds on Long Island. The ponds consist of the larger Sandy Pond and the smaller Fox and Block Ponds. We have also observed the groundwater in the area through a system of wells. In our analysis, the temperature was an important factor. The temperature was needed to standardize the pH meter. This is because the pH varies with the temperature. Dissolved oxygen also varies with the temperature. The higher the temperature, the lower the O2 contents, and vice versa. The pH was measured by a special meter. The pH range measured was from 4.03 to 6.7. The pH for unpolluted rain is 5.65. People have shown that rain over Long Island is acid (pH=4.4). The reason why the collected groundwater is still acid is because the soil has a low buffer capacity which means it can not neutralize acids. The soil consists mainly of quartz (SiO2) and has no limestone, which would be a good buffer. Therefore, the acid remains in the water.
Dissolved oxygen in the pond system is important to organisms which live in it. Organisms need at least 6mg/L to survive. The dissolved oxygen ranged from 5-10 mg/l in our studies. We therefore conclude that there is (at least during the time of sampling) enough dissolved oxygen for microorganisms to survive. The conductivity was measured because it can be related to the salt content. The salt content (total dissolved solids) of the ponds ranged from 20 to 70 mg/L. Highly mineralized drinking water contains up to 500 mg/L. The water that we studied can be called poorly mineralized. This explains the type of vegetation that lives in the ponds and the Pine Barrens.
We also observed the chloride, nitrate, and sulfate concentrations through a test called ion chromatography. We discovered that the levels were all below maximum consumption limits. For chloride we found a maximum of 1.2 mg/L in our wells and ponds. The permissible concentration is 300 mg/L. Even though it is low, it shows that we are close to the ocean since the origin of chloride is seasalt. Nitrate has an origin from forest burning, fossil fuels, auto emission, and fertilizers. The consumption rate of nitrates is 50 mg/L. We had a high of 6 mg/L. The interpretation of the nitrate concentration is not easy because it shows seasonal variations. When plants grow they take up nitrate, and when they die they release it again. Therefore the nitrate levels should be low in July which is in agreement with what we found. Sulfate comes from seasalt, forest burning, and fossil fuel burning. The concentration is low, but even so we conclude that one can see even in the remote parts of the Pine Barrens the sign of pollution. Sulfur dioxides dissolve in rain and form sulfuric acid. When the acid dissociates, sulfate is formed in the water. During the analysis we studied the concentration of iron through a spectrometer. All samples but one well had typical levels of iron for Long Island waters. Well #1 had significantly higher Fe contents. A possible source for iron could be pyrite (FeS2).
A game of charades - The
answer is "salt content".
A box
turtle that inhabits the Calverton Ponds area
The
students
Instructors Julie Castano,
Joakim Bebie and Glenn Richard