Interpreting Chemical Results
The streams of Pennsylvania are subject to many sources and types of pollution. According to the Pennsylvania Department of Environmental Protection (DEP), nonpoint source pollution affects over 3,600 stream miles (5,760 km) statewide. Two primary causes of non-point source pollution in Pennsylvania streams are abandoned mine drainage and sedimentation.
Chemical testing measures the concentration of dissolved and suspended substances in the water. These substances may be naturally occurring or introduced pollutants. Chemical testing only reveals a snapshot of what is occurring in the stream at the time that the testing occurs. The DCNR Watershed Education program utilizes LaMotte Brand® water quality testing kits, but other testing kits are also suitable for educational stream monitoring.
What Does Chemical Testing Tell Us?
- Current stream water conditions
- Detects introduced pollutants (fertilizers, abandoned mine drainage, sewage, etc.)
- Determines natural constituents of a stream (oxygen levels, alkalinity, etc.)
- Helps to track seasonal trends
What Are Some Common Sources of Chemical Pollutants in Our Streams?
- Farmland/Residential Lawns – higher turbidity, nitrates, phosphates
- Forest harvest – higher turbidity
- Pasture – increased bacteria, turbidity, nitrates, phosphates, etc.
- Mining – decreased pH (in some cases), reduced alkalinity, increased iron and other metals (abandoned mine drainage– AMD is the largest polluter of PA streams)
- Industrial discharge - increased toxins, pH (higher or lower than neutral depending on the discharge)
- Septic systems failure – increased bacteria, nitrates, phosphates, etc.
- Construction sites – increased turbidity and toxins
- Urban runoff – increased turbidity, nitrates, phosphates
Before beginning any type of chemical water testing, safety must be the first priority. Everyone (including instructors and volunteers) participating in the water testing should wear latex or nitrile gloves and safety glasses. These gloves and glasses should be worn at all times. Once testing is completed, hands must be washed thoroughly with soap and water. Instructors should always have a fully stocked first aid kit and an unexpired eye wash kit. Always provide a seal-able chemical waste bottle.
Make sure to have copies of the official “Safety Data Sheet” (SDS) (formerly Material Safety Data Sheets (MSDS) in your chemical testing trunk. Safety Data Sheet pdf (339 kb)
Before opening any chemicals or obtaining a water sample, students should read all enclosed directions. The best method is to practice testing procedures indoors before going to the stream. At the stream, make sure to have enough instructors and volunteers that are familiar with the test kits.
DCNR’s Watershed Education program strives for quality assurance and quality control. The same chosen stream location should be monitored at least twice per year. Always keep a copy of the Freshwater Acceptance Levels for Chemical Parameters in your chemical testing trunk or on your tablet. Freshwater Acceptance Levels for Chemical Parameters Data Sheet pdf (50 kb)
To increase consistency, make sure that your students do the following:
- Use the same test kits and the same methods each time.
- Hold dropper bottles vertically (upside down) to dispense liquid; one drop at a time.
- Fill and use direct reading titrators according to manufacturer directions. How to use a LaMotte Direct Reading Titrator pdf (81 kb)
- Rinse glassware 3 times with the sample water prior to filling for test.
- Rinse glassware 3 times with distilled water after each test. All post-test rinse water should go into the chemical waste bottle. NOT into the stream!
- Collect water for all chemistry tests during the same time period.
- Conduct the same test at least twice using the same kit but with different students. Conduct a third test if results do not agree.
- Always record your data in the Watershed Education database
LaMotte test kit methods used in Watershed Education can be classified as:
A. Colorimetric - pH, Nitrate, Iron
Colorimetric tests work on Beer’s Law; the higher the concentration of a substance, the darker the color developed in the test, so more light is absorbed by the sample. In other words, when you add the indicator solution to the test sample it will change color, which will tell you the concentration of what you are testing for in the sample. For example, the pH test uses an indicator that changes color with changes in the concentration of hydrogen ions, or the acidity of the solution.
B. Turbidimetric – Turbidity
In this test, no reagent is added to the water sample being tested, instead a turbidity standard is created by adding turbidity reagent to the distilled (or tap) water sample until it matches the turbidity of your sample. If your sample is too turbid to see the black dot at the 25 ml level, you must dilute it and calculate the results accordingly. For example, if you dilute 1 part sample to 1 part distilled water, multiply the results by 2; 1 part sample with 3 parts distilled water, multiply the results by 4.
You will likely use less turbidity reagent if you use the 25 ml sample line, but remember to use the test results scale to calculate JTUs or just double the results if using the 25 ml line.
C. Titrimetric - DO, Hardness, Alkalinity
The test sample is first treated with an indicator, and then a standard titrant is added until a color change indicates a completed reaction. This method is used to determine the concentration of a substance in a sample solution. We recommend the direct reading titrator (DRT) or dropper pipette (drop count) method. In the first, the recordable results are read directly from the scale of the DRT, and in the second, the number of drops used are counted and multiplied by a given number to obtain the recordable results.
To get an accurate picture of a stream's water quality, tests have to be done on a regular basis over a period of years. A stream should be monitored a minimum of twice per year. This gives a broad view of the stream which will weed out seasonal variations from long-term changes. In order to obtain useful data for trend analysis, a group should consider the long-term commitment involved in this type of monitoring.
The results of many chemical tests can indicate that there is an immediate problem. By sampling several sites upstream from the initial test site, the source of the pollution can be found. Depending on the chemical test performed, the source may be point or non-point. Contact your local Department of Environmental Protection (DEP) office once a suspected source is discovered- http://www.depweb.state.pa.us/portal/server.pt/community/report_an_incident/6010
WE Chemical Data sheet pdf (51 kb )
Remember that chemical measurements are only part of the overall water quality picture. Visual surveys, biological surveys, physical parameters, and historical research are just as important in determining stream conditions.