Science Project - Water Purity in South Florida 4b

8/9/2019 Science Project - Water Purity in South Florida 4b

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Running head: RELATIVE WATER PURITY IN SOUTH FLORIDA

A Study of the Relative Purity of Various Sources of Water Found in South FloridaAlan Pnakovich

American Heritage

In partial fulfillment of the requirements for Fifth Period Honors Science

Mr. Learn

December 8, 2008


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Abstract

This experiment was about researching various water testing methods to check the quality

of water sources with which we come in contact in South Florida. Our testing methods include

measuring electrical conductivity to determine the relative amount of dissolved solids, as well as

using chemical-based tests to identify the presence of unhealthy contaminants. We hypothesized

that water samples taken from unpurified sources such as the one exposed to urban pollutants,

should show a higher electrical conductance than samples from treated water, such as tap water

or commercial bottled water. In addition, we wanted to see also if testing the same samples

longer would show that suspended solids present in the samples would settle out, as proved by adecrease in electrical conductivity. We would test and use distilled water as a standard of

comparison, the control.

For the conductivity tests, we purchased a data acquisition device which was able to

stream sample data into Excel in real-time. We also needed to make our own measurement

probe. Furthermore in order to test for unhealthy impurities, we purchased a water test kit to test

four samples for eight contaminants. Nothing in our findings indicated that the water sampled is

unhealthy. Even our neighborhood pond only showed some bacteria present. Our hypothesis

was proven mostly correct. We even proved that water sources would show higher conductivity

levels. We surprised a bit with the result of rain water which showed that it had the lowest level

of solids next to distilled water. At the same time it was also the only source tested that showed

a pH in the slightly acidic range. We expected to see more solids and contaminants in pond

water, whose conductivity proved to be decreased after sitting for more than a month. This

testing approach could also be used to test the safety of water in undeveloped countries, if


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someone is hiking and needs to find safe water to drink, or just to see what kind of effect people

are having on their environment.

Statement of Purpose

The purpose of this experiment is to examine the quality of various sources of water with

which we come into contact in South Florida. Then we compared them to purified distilled

water, the control, by determining the relative amount of dissolved solids in the water sources.

We also tested the presence of any harmful contaminants in those waters.


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Background Research

Water quality is largely determined by the amount and type of dissolved solids in water.

It is also affected by the amount of suspended solids, which affects the clarity of water, known as

turbidity. Measuring the electrical conductance of water is one of many tests that exist to

determine water purity (en.wikipedia.org, 2008). Performing this test would indicate that there

are solids present, but not what the solids are. This requires testing water for contaminants,

which is also part of this experiment.

Electrical conductance, which is the inverse of electrical resistance, is a measure of how

easily electrical current can flow. With higher conductance, current can flow more easily.

Conductance is very useful when testing water purity, and can be used to estimate the amount of

total dissolved solids (salts) or ions in water. The more dissolved solids present in the water, the

higher the conductance of the water. This is because the solids dissolve into positively and

negatively charged ions that can conduct an electrical current proportional to their concentration.

Water that has no dissolved solids or ions conducts electricity several orders of magnitude less

readily than regular tap water (Novak, 2003).

Electrical conductivity is controlled by several factors. Geology and rock composition

determine the chemistry of the watershed soil and ultimately a lake. For example, limestone

leads to higher electrical conductivity because of the dissolution of carbonate minerals in the

basin. Another factor is the size of the watershed, or lake basin, relative to the area of the lake. A

bigger watershed to lake surface area means relatively more water draining into the lake because

of a bigger catchment area, and more contact with soil before reaching the lake. Other sources of

ions to lakes include wastewater from sewage treatment plants, wastewater from septic systems


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and drain field disposal systems, urban runoff from roads, and runoff of water draining from

agricultural fields, which typically has extremely high levels of dissolved salts (Lake Access,

Electrical Conductivity, no date).

Micro Siemens, abbreviated S, is used frequently in this report and is the unit of

measure for electrical conductivity (Novak, 2003). In this experiment, the sensor consists of two

metal electrodes that are 2.5 cm apart and protrude into the water. A constant voltage (V) is

applied across the electrodes. An electrical current (I) flows through the water due to this voltage

and is proportional to the concentration of dissolved ions in the water. The more ions present, the

more conductive the water, resulting in a higher electrical current which is measured

electronically. Distilled water has very few dissolved ions and so there is almost no current flow

across the electrode gap, meaning low electrical conductivity.

Total Dissolved Solids (TDS) is an expression for the combined content of all inorganic

and organic substances contained in a liquid which are present in a molecular, ionized or micro-

granular suspended form (Novak, 2003). The principal application of TDS is in the study of

water quality for streams, rivers and lakes. TDS is not generally considered as a primary

pollutant associated with health effects, it is used more as an indication of aesthetic

characteristics of drinking water and as an aggregate indicator of presence of a broad array of

chemical contaminants.

Suspended Solids and Turbidity relate to how clear water is. The greater the amount of

total suspended solids (TSS) in the water, the murkier it appears and the higher the measured

turbidity. The major source of turbidity in the open water zone of most lakes is typically

phytoplankton, but closer to shore, particulates may also be clays and silts from shoreline

erosion, resuspended bottom and organic detritus from stream and/or wastewater discharges.


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What may be harmful, however, are the by-products including chloroform that chlorine produces

when mixed with organic matter.

Hypothesis

If water samples are taken from various sources includes the one exposed to urban

pollutants, and tested, then they would be expected to show a higher electrical conductance than

samples taken from purified water, such as residential tap water, distilled, or commercial bottled

water. In addition, if suspended solids are present in the samples, then the solids would be

expected to settle out over time, and be confirmed in test results by lower conductivity.

Experiment

Materials

Procedure

1) Purchase measurement device, install software, and create the measurement probe.

a) Buy the data acquisition device off the internet. With a computer USB port, the hardware

needed is the Data Acquisition Starter Kit DI-148U by DATAQ Instruments.

b) A CD comes with the hardware containing software to display measurements graphically

in real-time and to pull the data into Excel. Install the software.


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c) To build the probe use a plastic rod, hot glue, and two insulated 14-gauge solid copper

wires one-half meter long.

d) Cut the copper wires and use a hot glue gun to glue the wire to the plastic rod.

e) Ensure the ends are not covered in glue, and should be about 2.5 cm apart.

f) Connect the other stripped end of the signal leads to the acquisition device. Connect one

wire to ground and the other to channel one.

(www.sciencebuddies.org, 2008)

2) Test software and measurement probe

a)

The probe should measure 1.40 volts when held in open air. b) The probe should measure 0.0 volts when the wires are touching each other.

c) Test measurement in clear tap water and in a liquid containing dissolved solids. A liquid

like coffee should produce a lower voltage than tap water.

3) Collect water samples and do conductivity tests

a) Collect water samples from the ocean, a pond in a residential area, a faucet, rain water,

distilled purified water, etc.

b) Put the water samples into cups and label the cups so that the samples can be identified

later on.

c) Wait until the samples are at room temperature, which is around 24 degrees Celsius.

d) Test water samples by placing the probe into the water. Record data into Excel and wait

until the water conductance stabilizes.

e) After completing each test, rinse and dry the probe.

f) Keep water samples undisturbed so you can measure the effect of solids settling out of

the liquid over time.


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4) Use water test kits to determine the impurities contained in some of the samples

a) Find and purchase two or three water test kits.

b) Test for impurities such as bacteria, pesticides, nitrate, nitrites, iron, hardness, chlorine,

copper, alkalinity, pH, and lead.

5) Analyze data

a) The program will automatically save the information into Excel. There are two ways to

display the information, numerically in Excel and in a real time graph.

b) After the water samples conductance stabilizes record the number of volts in a table with

the formula to calculate conductance.c) Using the DI-148U, the formulas are (www.sciencebuddies.org, 2008):

- Resistance, R, ( ) = 225,000 x V / (1.40 V )

- Conductance, G, ( ) = 4.44 x (1.40 V ) / V

(V = voltage in volts, = ohms, and conductance = mhos).

6) Review results and draw conclusions

a) Review the table of final results for the conductance of the samples

b) Determine if the differences between the samples are as expected.

c) The general rule is that the higher the number of volts the lower the conductance, and the

purer the water sample would be.

Data and Observations

Log . (10/05/08): We received the data acquisition and logging device on Thursday

October 2, 2008. The following Sunday we installed the software on our laptop and explored

how it worked. Before making our working probe, we did some simple tests with solutions like

supersaturated salt water, tap water and coffee to ensure that the device was working properly, to


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test some of the device settings such as sample frequency, and to get used to recording results

using the real-time data feed into Excel. Then we built our own testing probe, as described

above, and conducted our first actual tests on tap, rain and ocean water, recording results into

Excel. During these first tests, sample rate was set to a frequency of once per second. We let the

readings to continue for about eight minutes for tap water, seven minutes for ocean water, and

less than two minutes for rain water. The instructions with the device gave no advice on how

long to run the test or at what sample rate, so we thought we had tested for enough time period.

The results came mostly as expected, with tap water measuring 3.4 micro Siemens (S) and

ocean water about 9 S, much higher conductivity due to dissolved salts. We were surprised thatrain water, at about 2.1 S, showed a lower conductivity that tap water, meaning that rain is

purer that tap water as far as dissolved solids.

Log . (10/19/08): After reviewing results from two weeks earlier, we started to concerned

if we did not allowed the sampling to continue for a long enough period, so we switched sample

rate to once every two seconds. We also let the tests to run longer, stopping the sampling when

the reading appeared to stabilize. This time we ran the tests for thirteen minutes for the same

samples of tap and rain water, nineteen minutes for ocean water, and thirty three minutes for a

new sample of water from a residential pond. Once again, the results were the same as we

expected on a comparative basis, with rain measuring the lowest at about 1.9 S, tap water at 2.5

S, residential pond water at 3.8 S, and ocean the highest at 7.5 S. At this point, we were still

not ready to draw any conclusions about solids settling out over the past two weeks because we

believed that our first tests were not running for a long enough period of time.

Log . (11/02/08): Again, after reviewing the prior set of test results we were concerned

that we did not let enough sampling time for the measurements to stabilize. We decided to


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standardize our test using a sample frequency of two seconds and to run the test through 1,000

samples, which took thirty-three minutes. We also added a fifth sample which was a commercial

bottled drinking water. The results were two of our prior sample rose in conductivity, and two

decreased. Rain rose to 2.0 S from 1.9 S, tap water rose to 2.9 S from 2.5 S, while pond

water dropped to 3.5 S from 3.8 S and ocean water dropped to 6.7 S from 7.5 S.

Considering that ocean and pond water contained the most solids, we thought that perhaps the

decrease in conductivity was because of solids settling out over time. Our new sample, bottled

water, measured 3.1 S, slightly higher in conductivity and dissolved solids, than tap water.

Log . (11/16/08): Conductivity tests in this cycle showed that rain water remained at 2 S,while bottled water rose to 3.5 from 3.1 S. After dropping two weeks earlier, pond water rose to

4 S, its highest reading. However, ocean water rose a lot to 10.7 S from 6.7 S, for reasons

that we could not explain. We also added distilled water this cycle. Its result showed at the

lowest of any reading surpassing rain at 0.8 S conductivity. Now we also knew that distilled

water can also be used for the standard of comparison or the control in the group.

Log . (11/23/08): We only performed conductivity tests on three samples this cycle, as we

had a complete set of eight tests to conduct on four samples with a water kit which tests for

contaminants in water. Rain water rose a bit in conductivity to 2.3 S and the sample appeared to

fluctuate during the test as it had not before. Pond water remained at 4.0 S. The results for the

contaminant tests are shown below, with no results that could be considered to indicate

unhealthy water. Pond water did show the presence of bacteria.

Log . (11/28/08): In this final test cycle, rain and bottled water both tested around 2.5 S,

tap water tested 3.5, while pond water came in surprisingly low at 3.2 S, possibly due to solids

settling out. Ocean water returned to 6.8 S, after jumping to 10.7 two weeks earlier. At this


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point, measurements for several of the samples seem to be jumping around in an unexplainable

manner, maybe because of to their stagnant for close to two months.

Charts

For the conductivity testing portion of this experiment, the data collection charts, or tables, were

prepared in Excel with data fed through a data logging device, and they are voluminous. A test

for each sample involved recording voltage every two seconds for over 33 minutes and then

date/time stamping the record and entering into Excel (by the program). Most of the tables/charts

are 1,000 rows long, and there are 25-30 of these data collections charts in Excel; therefore they

are not reprinted in this report. A summary of the first and last ten rows from one of the tablesis shown below in Table 2.


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For the contamination testing part of this experiment, the results were recorded manually, and are

shown below in table 3. Guidelines for maximum levels of contaminants are shown below the

table, and were provided with the water test kit. The only finding worth to mention is that

bacteria was detected in pond water as well as was nitrate/nitrate from fertilizer. A slightly acidic

pH level was found in the rain water, but a typical level is cited at slightly under 6 (Rain,

Wikipedia, 2008), so this rainwater is less acidic than normal.

While reviewing test results, ocean water was surprisingly low in volts at first at about

0.4-0.5, though it kept on steadily increasing and it had no bacteria, a hardness of 425 ppm, no

pesticides , no lead, no nitrates or nitrites a pH of 8.5 and no chlorine. Pond water was high in

volts 0.7-0.8 it had bacteria, no pesticides, no lead, no nitrites, 0.5 nitrates a pH of 8.5, a hardness

of 120 ppm , and no chlorine. Rain water had a very high voltage 0.8-0.9 it had no hardness,


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chlorine, bacteria, pesticides, lead, nitrates, and nitrites, though it had a pH of 6.5 which is

slightly acidic. Tap had no chlorine, bacteria, pesticides, lead, nitrates, and nitrites; it had a

hardness of 85 ppm and a pH of 7.5.

Graphs

Graph 1 below shows results one of the initial tests, conducted before realizing that voltage

measurements required more time to stabilize than we were letting in earlier experiment.

Measured voltage is converted into micro-Siemens, and graphed versus time in minutes and

seconds below. If it allowed running longer, the rain water conductivity would likely have

dropped to about 2 S.

Graph 2 below is similar to the test above, but was run for 33 minutes until voltage stabilized.


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Graph 3 below shows, for all of the sources, how it takes time for conductivity, as measured

through voltage, to stabilize. A representative test cycle for each of the sources is shown.


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Pictures

Photo 1: Residential pond that was the source for one of the samples in this experiment.

Photo 2: Some samples laid out prior to a conductivity test cycle.


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Photo 3: Supplies used for testing water samples for eight contaminants.

Photo 4: Chief scientist preparing to perform a conductivity test on a sample.


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Photo 5: Four samples, pond, ocean, rain, and tap water selected for contaminants tests.

Photo 6: The yellow color of the pond sample on the left indicates that bacteria is present.


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Analysis and Discussion of Data

Calculations

As shown in the data chart above, data is collected through the DATAQ data acquisition

device as voltage. The voltage readings are passed automatically from the device into Excel and

date/time-stamped. We converted the data to conductance, as micro-Siemens, using the formula:

[ Conductance (in micro-Siemens) = 4.44 x (1.40 voltage) / voltage ]

When we discussed this experiment in Science Buddies, they used a constant of 1.39 in

the formula, but our device measured 1.40 volts in a short circuit condition, so we had to modify

our formula accordingly. When testing our device with the control, distilled water, the

conductivity measured about 0.81 S, which was very close to the number referenced by Novak

(2003) which said that good quality distilled water should have a conductance of 1 micro-

Siemen. This makes us confidence that our device was working accurately enough to make

reasonable relative comparisons between our water sources. Because of the stabilization effect

shown in graphs above, we also had to determine the proper steady-state voltage by observing

results graphically.

Table 3 below provides a summary for all test cycles performed.


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Graph 4 immediately below is a summary of results of all tests. Each of the tests involved

taking and recording in Excel several hundred to 1,000 voltage measurements that were then

converted into micro-Siemens. Res Pond is short for Residential Pond.


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Error Analysis

Graph 3 above shows that an amount of time is needed for voltage readings to stabilize

once the probe is submersed in the water sample. We could not just simply take an average over

the full test period to get reading on a voltage. Instead, we have to make a graph of voltage

versus time for each test, and the stabilized voltage from the graph is used for the test. Therefore

there will be a certain amount of error would be involved. However, this experiment was

concerned with the relative difference in conductivity between water sources, more than the

absolute measure of conductivity, so this effect should not be a problem.

Some of the readings that appeared to fluctuate on the graphs during the test period were

unexplained, and may have been caused by instability in the power being supplied by the my five


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year old computer. Another possible reason for fluctuating readings may be that once current is

flowing through the water across the probe, the water is affected, possibly becoming charged,

and the ion content altered.

Regarding the tests for contaminants, some of these tests need to use multiple colors

strips over a period of time. One could have mismatched the colors on the test strips when

comparing against the color charts provided with the tests. Also, taking the probe out of the

water to quickly before the voltage stabilized could introduce an error. One also could have

bumped the table holding the device and water sample which then caused the water to shake and

affected the readings. Another possible cause of error would have resulted from not properlycleaning the tips of the probe off with light buffing with sand paper before doing the tests or not

having wiped the probe off after using it before doing another test. However, during our testing

we tried to be very diligent in following good experimental procedures.

Conclusion

Nothing in our findings indicated that any of the water that we sampled with is unhealthy.

Even our neighborhood pond only showed some unhealthy contaminates in the form of bacteria,

and slightly elevate level of nitrate/nitrate from fertilizer. The ideas in this experiments

hypothesis were mostly proven correct. We did expect though that the water sources would show

the higher conductivity levels. Reviewing Graph 4 above, one could conclude that the results in

order of lowest to highest conductivity, and dissolved solids, would be: 1) distilled water, 2) rain,

3) tap water, 4) bottled water, 5) residential pond water, and 6) ocean water.

We surprised a bit that rain water had the lowest level of solids next to the control or

standard of comparison, distilled water. Rain water was also the only test source that showed a


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extended, causing the some bouncing around in the readings during the test period. Also one

may want to find out what the actual reading should be used when the reading dips down and

then begins to rise in conductivity, which happened in our experiment.

Finally different variation could be used to explore the reason for the very different

patterns shown now and then from one test cycle to the next or between water sources. We found

some strange patterns that were repeatable appeared that we do not understand.

Work Cited

Conductance as a Water Quality Measurement. (2008) Retrieved September 27, 2008, from

http://www.sciencebuddies.org/science-fair-projects/project_ideas/Elec_p011.shtmlLake Access. (n.d.). Electrical Conductivity: Measuring Salts in Water. Retrieved September 27,

2008 from http://lakeaccess.org/russ/conductivity.htm.

Lake Access. (n.d.). Turbidity in Lakes. Retrieved September 27, 2008 from

http://lakeaccess.org/russ/turbidity.htm.

Novak, J. (2003) What is Conductivity and How is It Measured? A Technical Handbook For

Industry. Retrieved September 28, 2008 from http://www.vipsys.ru/articles/2008-02-

19_01.pdf.

Rain. (2008). Retrieved November 30, 2008 from http://en.wikipedia.org/wiki/Rain.

Silver Lake Research Corp. (n.d.). Watersafe Science Project 4-Pack. Obtained October 2, 2008

from product documentation concerning Contaminants.

Water Quality. (2008). Retrieved September 28, 2008, from

http://en.wikipedia.org/wiki/Water_quality

Documents

Science Project - Water Purity in South Florida 4b