A number of hours of planning were devoted to the actual execution of the sampling and testing of the water. There were, however, some constraints and possible laboratory errors. The team was lacking some equipment such as an incubator, a sterile environment, autoclave, etc. The samples were taken only at points adjacent to the shore and dissolved oxygen must be measured before 10:00 a.m., but we had no means of getting a boat before that time. A better method for such experiments would include making multiple cultures of each sample.
Although the experiment was testing explicitly for E. coli, a number of other tests were made on the water samples: pH, temperature, dissolved oxygen content, nitrate levels, phosphate levels. The air temperature was also recorded at the time that the samples were taken. The experience of conducting a variety of tests was felt to be an important part of this experiment. It was also felt that since two bodies of water were being compared, significant differences might be explained by data from the ancillary tests.
The ambient air temperature varied only slightly. On the two mornings that samples were taken, the lowest temperature was 21° Celsius, and the highest temperature was 23°C. Since the water temperatures were greater than the air temperatures, it is assumed that the air temperature had no effect on the levels of E. coli. The water temperatures varied from 25°C to 27°C. The range of temperature for the growth of E. coli is 8°C to 49.4°C [ Escherichia coli ]. The air and water temperatures were within this range.
On the second day of sample gathering and testing an error in the use of the pH meter was made. The calibrate button was pressed while the meter was in the test sample, and the calibration liquid was not with the testing kits. The measured pH, however, was within the minimum and maximum limits of 4.0 to 8.5 for E. coli growth [ Escherichia coli ].
Dissolved oxygen levels ranged from 5 ppm to 7 ppm. These are common amounts for summer months (during the winter the dissolved oxygen levels are generally higher). At the time the samples were being taken and tested, New Jersey was having a heat wave with temperatures exceeding 35°C. The team's research uncovered that coliform bacteria survive in waters that lack dissolved oxygen [Coliform Bacteria: A Measure of Water Pollution].
Although unable to find references to the effect of nitrates and phosphates on E. coli, tests were made for both. Nitrate levels at one canal site were 10-20 ppm, were 5-10 ppm at a second canal site, and were 5 ppm or less at the other four sites. At all six sampling sites phosphate levels were at zero ppm.
The traditional methods of testing for Escherichia coli require careful laboratory techniques and a lengthy incubation period at precisely controlled temperatures. A new culture medium from Micrology Laboratories allows for less precision in both inoculation and incubation but still gives reliable E. coli counts. We were able to perform our tests using this new Easygel™ medium in two forms. Both Coliscan and EMB test for E. coli , but Coliscan also tests for other coliform bacteria.
The group decided to test with the two different media so that all team members would have experience using both types. The Coliscan, because of its lighter color, was easier to read, but it did require that E. coli be recognized separately from the other coliform bacteria. The difficulty with EMB stemmed from its very dark color. The surface E.coli were easy to read however, it was difficult to distinguish the metallic green color of the E. coli from the medium in which it was embedded. The consensus was that the use of both types of media was a worthwhile experience.
Although differences in the number of colonies were found between the Coliscan and EMB media, the overall amounts of E. coli were within the range of safe recreational use. For bathing beaches and other recreational waters less than 100 E. coli per 100 ml of water is considered to be excellent. From 100 to 2,000 E. coli per 100 ml of water is considered to be satisfactory.
The hypothesis that the level of E. coli will be greater in the Delaware & Raritan Canal than in Carnegie Lake is shown to be false. The original question, whether canoeing on the lake would be safer than on the canal, which led to the hypothesis and experiment is not of concern since the E. coli levels in both the lake and canal are safe for recreational use. The canoers can feel confident that if they were "accidentally-on purpose" thrown overboard, they would not suffer any ill effects from E.coli.