Developing a Water Quality Model (page 2)

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Author: Josie, Grade 8


I think that there will be a correlation in the data I collect for Gravel Run and Centreville Landing. The air and water temperatures should move together, when one goes up so does the other (positive correlation). This is probably because the sites are relatively close together and have the same kind of climate. The pH might have close to a correlation of one, because in looking at past data, I can conclude it is almost always around seven. The amount, not changing for either site. The dissolved oxygen levels should also move together because the DO depends on the temperature of the water. If the temperature goes up, the DO should go down, on both sites. The nitrates should also have positive correlation. Since we measure turbidity at Gravel Run, which is how dirty the water is and clarity at Centreville Landing, how clean the water is, there should be negative correlation, when one goes up the other should go down.


1 of each test kit - Dissolved Oxygen

  • Nitrates
  • pH
  • Turbidity Thermometer

Secchi Disk Computer spreadsheet program


  • Monitor the water quality of two sites along the Chester River for a year.
  • Enter the data (temperature, nitrates, dissolved oxygen, pH, and clarity/turbidity) in a spreadsheet.
  • Using the spreadsheet formula to correlate each set of data for each category.
  • Determine the effect of Gravel Run on Centreville Landing

Nitrates Test

  1. Fill a test tube (0124) to the 5-ml line with sample water.
  2. Add one Nitrate #1 Tablet (2799).
  3. Cap and mix until tablet disintegrates.
  4. Add one Nitrate #2 CTA Tablet (NN-3703).
  5. Cap and mix until tablet disintegrates.
  6. Wait 5 minutes.
  7. Insert test tube into Octa-Slide Viewer.
  8. Match sample color to a color standard. Record as ppm Nitrate-Nitrogen.
  9. To convert reading to ppm Nitrate, multiply results by 4.4.

Secchi Disk

  1. Lower Secchi Disk into water until it just disappears.
  2. Read depth in meters from calibrated line.
  3. Raise Secchi Disk until it just appears. Read depth from calibrated line.
  4. Add readings from Steps 1 and 2. Divide by 2.
  5. Record as Secchi Disk Transparency.


  1. Fill one Turbidity Column (0835) to the 50-ml line with the sample water.
  2. If the black dot on the bottom of the tube is not visible when looking down through the column of liquid, pour out a sufficient amount of the test sample so that the tube is filled to the 25-ml line.
  3. Fill the second Turbidity Column (0835) with an amount of turbidity-free water that is equal to the amount of sample being measured. Distilled water is preferred; however, clear tap water may be used. This is the "clear water" tube.
  4. Place the two tubes side by side and note the difference in clarity.
  5. If the black dot is equally clear in both tubes, the turbidity is zero.
  6. If the black dot in the sample tube is less clear, proceed to Step 4.
  7. Shake the Standard Turbidity Reagent (7520) vigorously.
  8. Add 0.5 ml to the "clear water" tube. Use the sitting rod (1114) to stir contents of both tubes to equally distribute turbid particles.
  9. Check for amount of turbidity by looking down through the solution at the black dot. If the turbidity of the sample water is greater than that of the "clear water", continue to add Standard Turbidity Reagent in 0.5 ml increments to the "clear water" tube, mixing after each addition until the turbidity equals that of the sample.
  10. Record total amount of Turbidity Reagent added. Each 0.5-ml addition to the 50-ml size sample is equal to 5 Jackson Turbidity Units (JTU's). If a 25-ml sample size is used, each 0.5-ml addition of the Standard Turbidity Reagent is equal to 10 Jackson Turbidity Units (JTU's).


  1. At each sampling a wide range and narrow range test should be done. If the reading is within the narrow range, this reading will be used. A wide range test will also be done to a) Serve as a check for the narrow range reading and b) To provide a more accurate reading if the narrow range is exceeded (Note: if the narrow range is exceeded, the color will match one of the two extreme readings, and only the wide range reading will indicate whether the reading is out of range or is exactly one of the extreme readings.
  2. Make sure to rinse the sample test tube 3 times with the water to be tested.
  3. Cap the tube to mix water and the indicator; do not use your finger.
  4. Sometimes due to degradation of the indicator, a color will be obtained that is more or less intense than the octet comparator colors. Redoing with slightly more or less drops can change the intensity for a better "match" without changing the hue.

Dissolved Oxygen

  1. Thoroughly rinse the Water Sampling Bottle (0688-DO) with sample water 3 times (or use a sampling device that does this) then fill the bottle. The sample is then collected from one foot below the surface (where permitted by depth).
  2. Tap the sides of the submerged bottle to dislodge any air bubbles clinging to the inside.
  3. Once a satisfactory sample has been collected, proceed immediately with next steps, to "fix" the sample.
  4. Be careful not to introduce air into the sample while adding the reagents. Simply drop the reagents into sample, holding the reagent bottles vertically.
  5. Add 8 drops of Manganous Sulfate Solution (4167) and 8 drops of Alkaline Potassium Iodide Azide (7166).
  6. Cap and mix by inverting several times. A precipitate will form. Allow the precipitate to settle below the shoulder of the bottle before proceeding.
  7. Add 8 drops of Sulfuric Acid, 1:1 (6141WT).
  8. Cap and gently shake until the reagent and the precipitate have dissolved. A clear yellow to brown-orange color will develop, depending on the oxygen content of the sample.
  9. Fill the titration tube (0299) to the 20-ml line with the "fixed" sample and cap.
  10. Fill the Direct Reading Titrator (0377) with Sodium Thiosulfate, 0.025N(4169).
  11. Insert the Titrator into the center hole of the titration tube cap. While gently swirling the tube, slowly press the plunger to titrate until the yellow-brown color is reduced to a very faint yellow. NOTE: If the color of the "fixed" sample is already a very faint yellow, skip to Step 13.
  12. Remove the Titrator and cap. Be careful not to disturb the Titrator plunger, as the titration begun in Step 12 will be continued in Step 14. Add 8 drops of Starch Indicator Solution (4170WT). Sample should turn blue.
  13. Replace the cap and Titrator. Continue titration until the blue color just disappears. Read the test result where the plunger tip meets the scale.
  14. Record as ppm dissolved oxygen.
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