Clean, fresh drinking water is rapidly becoming a scarce and valuable resource.  There are a long list of common ways in which surface water can become contaminated and unsafe, such as through the addition of organic wastes from livestock or even human settlements, through chemical runoff from agricultural lands, or through industrial effluents entering a water source.  Point sources of pollution, such as pipes discharging contaminated water from a factory into a stream, are relatively easy to identify.  Non-point pollution sources, such as agricultural runoff that may have many pathways by which it enters a surface water supply, are very hard to manage.  It is becoming necessary to test fresh water streams and reservoirs regularly in order to determine their quality and to detect any new contamination from point or non-point sources.


An inexpensive water testing kit can be obtained from an outdoor equipment supplier and can supply a wealth of information on the quality of a key water supply.  We tested 2 streams with different characteristics for a range of common pollutants and water quality factors in order to contrast them.  One stream was Rapid Creek, flowing down out of the Black Hills and through the Rapid City, SD.  Among the test we completed were pH, chlorine, copper, iron, nitrate, phosphate, dissolved oxygen, and ammonia.




Another creek up in the Black Hills was associated with the Minnesota Ridge Gold Mine and emerged from a steep mountain slope near the base of the grade.  




The measure of acidity is referred to as pH, or the partial concentration of hydrogen ions (H+) in solution.  The pH value is an inverse exponential term; as a result lower pH numbers represent higher H+ concentration and each sequential number value of pH represents a 10 fold increase or decrease in acidity.  A pH of 7 is neutral.  The water we measured at Rapid Creek was basic (pH > 7), actually about 8.5 (left below).  The pH in the mine water, however, was just above 6, or about 100 times more acidic than Rapid Creek.  See right photo below.




Iron was not present in Rapid Creek, but was abundant in the mine water, as well as to a lesser extent in an upstream pond nearby.  The pond sample is on the left below, the mine sample on the right.  It is off the color card scale, but may be 40 ppm iron.




Interestingly, the water emerging from the mountain in the mine creek was clear, though the substrate was quite orange from oxidation of the iron in the water.




A few hours later that same water sample had turned orange, indicating oxidation of the iron by oxygen in the jar to iron oxide in suspension.  This material later precipitated out of solution and settled in the bottom of the jar.


Though nitrates were negligible in the mine water, phosphates were present in high concentration in both the nearby pond water (left) and the mine runoff (right).  Phosphate levels in good quality water should be < 1 ppm.  Much of the phosphate contamination found in surface waters is from detergents and agricultural runoff.  The samples at this mine location may represent natural phosphate dissolved from rock in the mountain by the acidic water.




Another important test of fresh water is the Biochemical Oxygen Demand (BOD) and represents the bacteria present in water that can be detected by the amount of oxygen they take from a sample.  A sample of water is capped full with no air present.  It is wrapped in aluminum foil to prevent any light penetration.  It is then left for 5 days and afterward tested for oxygen content.  That measurement is compared with an oxygen test of another sample taken from the same source at the time of collection.  If the oxygen has decreased in the 5 day sample compared with the immediate test, bacteria are present and have been using up the oxygen in the tube.  You must be careful to not leave any air in the tube before it is capped and wrapped so that no oxygen from the air can diffuse into the water.  Why do you suppose the tube needs to be shielded from light?




The water sample above has been held for 5 days and the BOD test just run.  Oxygen concentration is about 2 ppm in this sample.  On the day the sample was collected the oxygen concentration in the water source was 8 ppm.  We have observed that this water supply is contaminated with bacteria.




Since we have to reuse water over and over again, it is necessary to treat the water we dispose of so that it is suitable for the needs others “downstream”.  A wastewater treatment plant takes a city’s sewage, separated from rainwater runoff, and processes it so that it is purified to a suitable quality for reuse.  The Hot Springs, SD, wastewater treatment plant is a good example of proper and careful treatment and purification of sewage outflow.


The waste water from the city of Hot Springs is routed to the plant through a complex network of underground pipes, diagrammed on the board below.  The plant is in the lower left portion of this map and almost all flow is by gravity feed.  The city’s sewer pipes are kept clean by the formidable truck on the right below, which can remove debris by suction or flush it through the pipe with a high pressure water hose.




After a process in which floating rags and other debris are picked off the top of the waste stream and sand and rocks are separated out, the water proceeds to a settling pond, where it stays for about 1 hour.




            Scott Simianer describes the operation of the settling pond to a Field Ecology student.


Water enters the pond through the center discharge and flows toward the outside.  The rotating arm in the top of the picture scrapes floating oil and grease form the water and deposits it in a grease trap.  Organic solids fall out of the water during this process.


The remaining water next goes to a trickle filter (tank in photo below), where non-photosynthetic algae remove pollutants such as nitrate from the water which the algae use as fertilizer to grow and carry out metabolism.  The tank is filled with “media”, shown in the photo on the right, which forms a substrate on which the algae can adhere and grow as a steady supply of water drips past them.




The water then proceeds from the trickle filter to a second stage settling pond where it is purified to a 30 ppm oxygen concentration, meeting regulatory standards.


The sludge collected in the first settling pond goes into the digester building, where microbes “eat” it and break the solid matter down into a non-septic slurry.  The methane produced as a by product of this decomposition process, a similar process to that which occurs in the soil or in your compost pile, is collected and burned (right below) to heat the digester and keep it at the optimum 95° F temperature that the bacteria prefer.




The treated water is piped to a holding pond from which it is drawn to irrigate cropland.  The treated slurry, about 4-6 % solid in the end product, is collected in the large sprayer truck below and sprayed on cropland as fertilizer.  This fertilizer is so rich in nutrients that it is much sought after by local farmers.