Publication No. 10675
Forensic Groundwater Contamination
Student Laboratory Kit
Materials Included In Kit
Bromcresol purple solution, 0.04%, 100 mL
Hydrochloric acid solution, “Well-site Solution,” 0.1 M, 500 mL
Sodium hydroxide solution, “Testing Solution,” 0.2 M, 750 mL
Groundwater Contamination Worksheet
Pipets, Beral-type, graduated, 70
Reaction plates, 15
Well-Site Master Map
Well-site solution containers, 30
The well samples will be “contaminated” with a dilute hydrochloric acid solution (HCl) and should be prepared as follows in Table 2:
The dilutions can be efficiently carried out right in the graduated well site solution containers. Final volume in all containers should be 40 mL. Each site sample container should be appropriately numbered as it is filled. The properly numbered, well-site samples should be placed where students will have free access to them. Each site sample solution container should have a graduated pipet assigned to it—it is important that these pipets be used only for a particular site sample and that they not be mixed up. Each student team should have a copy of the site-map, a reaction plate, a graduated pipet filled with the bromcresol purple indicator solution, a sample container of the 0.2 M sodium hydroxide “test solution” and another graduated pipet for drop-titrating the “test solution.”
The activity is designed with three possible outcomes, each representing a different source of the contaminant. The well-site samples must be prepared in advance after one of the potential outcomes has been chosen. The samples will contain one of four concentrations of the contaminant: 0–10 ppb, safe background wells; 25 ppb, wells at the fringe of the plume; 50 ppb, wells nearer the source; and 200 ppb, the contaminant source. Table 3 details the three outcomes and the well sample filling protocol for each.
Sodium hydroxide and hydrochloric acid solutions are corrosive to skin and eyes. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.
Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. All resulting mixtures may be disposed of according to Flinn Suggested Disposal Method #26b.
Correlation to Next Generation Science Standards (NGSS)†
Science & Engineering PracticesDeveloping and using models
Planning and carrying out investigations
Analyzing and interpreting data
Disciplinary Core IdeasMS-PS1.B: Chemical Reactions
MS-ESS2.C: The Roles of Water in Earth’s Surface Processes
MS-ESS3.C: Human Impacts on Earth Systems
HS-ESS2.C: The Roles of Water in Earth’s Surface Processes
Systems and system models
Stability and change
MS-LS1-6: Construct a scientific explanation based on evidence for the role of photosynthesis in the cycling of matter and flow of energy into and out of organisms.
Answers to Questions
Groundwater: ACS Information Pamphlet; American Chemical Society, Washington D.C.; 1989.
Forensic Groundwater Contamination
Who is contaminating the groundwater? Become a forensic scientist and help determine the culprit!
At the molecular level, water is engaged in an endless cycle; from streams, to lakes, to rivers, to oceans, then to be evaporated, carried aloft and returned to the surface as precipitation. The water cycle is one of the major biogeochemical cycles upon which all living things on our planet depend.
The lower boundary of the saturated zone is usually an impermeable layer of rock or clay preventing further downward percolation of the water. The saturated zone can be likened to an underground, flowing reservoir and is commonly called an aquifer. Where the land surface falls below the level of the water table, the aquifer will be visible as a lake, pond or stream. The flow of water in these underground systems is driven by gravity and will be in the same general direction as that of the surface waters. Rates of flow may range from millimeters to meters per day.
Groundwater provides one-fifth of all the freshwater used in the United States and one-half of the drinking water. In some regions of the country it provides more than one-half of the freshwater used for crop irrigation, industrial processes and livestock. Its importance as a major source of fresh and potable water cannot be overstated.
Withdrawal of groundwater can occur by either active or passive means. Active withdrawal requires drilling wells to the depth of the water table or saturated zone and pumping the water to the surface. Passive withdrawal simply requires tapping a free-flowing spring—where the pressure of water trapped between impermeable layers of rock or clay is sufficient to force it to the surface. As most groundwater systems are in a state of dynamic equilibrium, with water flow into the system ultimately equivalent to water flow out of the system, any significant withdrawal is going to alter that equilibrium. If withdrawal remains steady at a low enough rate the result will be a new equilibrium at a lower water level. If withdrawal exceeds a certain rate, and continues to increase, the result is a condition known as overdraft. Under overdraft conditions wells will run dry, land may subside as it settles to fill the void left by the water and in coastal areas saltwater may intrude into the aquifer. Any of these conditions can have severe consequences.
Groundwater naturally contains microorganisms (decomposers naturally present in the soil), gases produced by metabolic processes and decomposition, and dissolved organic and inorganic compounds. Groundwater is by no means pure and all of the basic properties used to describe water are due to naturally present constituents. Hardness is a measure of the levels of calcium and magnesium ions; salinity is defined by the quantity of dissolved salts; and color, taste and odor are caused by a wide variety of compounds.
Water quality is an abstract concept that relates the suitability of water to a particular use. Water being considered for a particular use is subjected to a battery of tests to measure concentrations and levels of a number of constituents and properties. To “pass” these tests the results must fall within defined parameters—or else the water may be judged unsuitable. As an example, water that is too salty is unfit to drink and would be considered contaminated. Drinking water with excessive levels of lead, mercury or pesticide residues would also be considered contaminated. These examples illustrate that contaminants can be either natural or caused by man.
Major sources of non-natural groundwater contaminants vary regionally. A few of the most recently cited include waste from over-applied agricultural and domestic fertilizers, pesticides, sewers, landfills, septic systems, industrial wastewater lagoons, leakage from petroleum transport and storage systems, chemical spills, illegal dumping and highway de-icing salts.
A contaminant follows the same route to the aquifer as the water itself. Percolating down through the soil, the contaminant reaches the saturated zone and enters the normal flow-pattern. The contaminant will move downstream, in most cases tending to fan out and form a plume. As such, contaminant concentration is greatest nearest its source, decreasing as it radiates downstream and away. The contaminant may arise either from a discreet, localized, “point” source or from a dispersed non-point source. An example of a point source would be a leaking pipe or compound dumped down a well. An example of a non-point source would be an agricultural chemical spread over many acres.
Once entering the soil numerous possible fates await contaminants. The contaminant may form insoluble precipitates with soil constituents and be rendered harmless. The contaminant may be adsorbed onto various substrates present in the soil and spread no further. Or the contaminant may be biologically or chemically degraded, converted or decomposed. The contaminant may also be either diluted to harmless levels or mechanically filtered out as it passes through the soil. Any one, or none, of these processes may take place to offset the potential harm caused by the contaminant.
Detection and treatment of contaminants can be understandably very difficult. Aquifers may run tens, hundreds, or thousands of feet below the surface making extensive testing and monitoring of the water challenging and extremely costly. There may be no sign or indication of potential sources when and where a contaminant is detected, necessitating painstaking procedures to trace it. If the interval of distance or time between contaminant detection and its source is too great, tracing it may be impossible. Testing must also be conducted carefully to determine the boundaries of the contaminant plume and the affected area. Also, random testing may not analyze for a particular contaminant that might be present.
A rancher from the Cadillac Ranch on the outskirts of Marion Township was planning to expand his herd of beef cattle. To ensure an ample supply of water for his growing herd he had to drill a new well. Although the site he chose was not far from the Eagle River, he had no land rights adjacent to the river and was forced to drill for groundwater. Being a responsible rancher, he thought it might be a good idea to have the water tested by a nearby laboratory.
Indicator solution, approximately 2 mL
Testing solution, approximately 50 mL
Pipets, Beral-type, graduated, 2
Groundwater Contamination Worksheet
Well-site master map
Well-site solution containers, 40
The well-site and testing solutions are corrosive to skin and eyes. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory.
Student Worksheet PDF