Comparisons of Water pH in Sources both Polluted and Non-Polluted by Waste Runoff in Southeastern Wisconsin
The purpose of this experiment was to test the hypothesis that there is a lower pH in water sources known to be impaired by pollutants compared to waters that are unimpaired in Waukesha and Milwaukee counties of Southeastern Wisconsin. By using information and a map (Figure 1& 2) from the Milwaukee Metropolitan Sewage District we were able to determine where impaired sites were located. We measured pH from ten water bodies that were considered clean, and ten from water bodies that were considered impaired according to MMSD. The MMSD considers waters that are affected by pollution such as waste runoff to be impaired (MMSD, 2012). We calculated the mean pH of both the clean waters (7.54) and the impaired waters (8.06). Our hypothesis was not supported (p= 0.02), but rather favored the opposite: that the impaired water bodies had a higher pH than the unimpaired water bodies.
Keywords: water pH, pollution, Southeastern Wisconsin
According to the EPA, the 1986 Quality Criteria for Water recommends a pH range of 6.5 to 9.0 to support freshwater organisms (EPA, 2012). However, human impact may introduce properties into water that could compromise the current pH. Polluted surface runoff may arise from chemicals such as pesticides, herbicides, and vehicular pollutants, animal wastes, fertilizers, and street litter (Duda, Lenat, and Penrose, 1982). Industrial applications contribute pollution as well, such as gaseous sulfur dioxide, which is produced by sewage treatment plants. The gas is oxidized in the atmosphere when rain occurs, producing an acidic rain (Devai and DeLaune, 1999). If levels of emissions from plants and factories are high enough, acidic rain could impact the surrounding water bodies by making the water more acidic.
This experiment was designed to test the hypothesis that there is a lower pH in water sources known to be polluted such as chemical wastes from human and industrial activity compared to waters that are unimpaired in the Milwaukee and Waukesha counties of Southeastern Wisconsin.
On 2 October 2012 at 0800 CDT, we drove to five impaired and eight clean water sources, which were determined based on the Milwaukee Metropolitan Sewage District reports on impaired and clean water body areas in Southeastern Wisconsin (Figure 1 & 2) from March 2012 (MMSD, 2012). Polluted water sources are considered by the MMSD to be impaired. Due to time constraints we collected 13 total sites on 2 October and seven sites on 4 October, two of which were clean sources and five that were polluted sources (Table 1).
To determine the pH of all the water bodies we used a PASCO Xplorer GLX PASport 2002© pH meter. We kept the pH and temperature probes in the water for two minutes and recorded the pH value that was displayed on the meter screen after the two minute period. We then placed the pH probe back in the buffer solution bottle and turned the meter off to conserve energy. The spot tested within our chosen location was selected based on the ease of water access only, not other factors such as clarity, pollution, or flow. A basic compass was used to specify the location of the area tested. We performed a T-test (tail 1, type 2) using Microsoft Excel 2010©.
Figure 1. Milwaukee Metropolitan Sewage district map of impaired water bodies of Southeast Wisconsin.
Figure 2. Milwaukee Metropolitan Sewage District map legend related to Fig.1.
Table 1. Impaired and clean water areas with their testing locations relative to indicated points, pH, and description of site
The mean of the pH levels in clean water (7.54) and polluted (8.06) water sites as well as the standard deviation of clean (+/-0.508) and polluted (+/-0.562) water sites were calculated (Figure 3). The determined p-value (p= 0.02) does reveal statistical significance.
Figure 3. Comparison of average pH in the clean and polluted water sources (p=0.02). Error bars represent standard deviation (+/-0.508) (+/-0.562) for clean and impaired waters, respectively.
Despite statistical significance, our hypothesis was not supported. The pH was higher or more basic on average in impaired waters than clean waters. Although impaired waters measured a higher pH, no readings exceeded EPA criteria as listed in the introduction. We associated impaired water sources with pollution in the form of gaseous emissions, such as sulfur dioxide, which can enter water bodies in precipitation and run off from streets (Devai and DeLaune, 1999). One reason that the pH may have been higher in the impaired areas could be due to increased photosynthesis by algae. In photosynthesis, algae remove carbon dioxide from the water. This process decreases the concentration of carbonic acid making the water more alkaline (NOAA, 2012).
There are several factors involved that may have affected the results, including the precision of the pH meter and the two minute time duration that was passed before we recorded the pH. Perhaps longer water exposure of the probe was necessary to acquire a more accurate reading because the pH reading did not reach a stable value after two minutes. Changes in weather (i.e. temperature changes, sunlight exposure) between the two days of data gathering may have altered water properties and resulted in inconsistent pH. Also, weather changes and human activity may have further impacted or improved the site quality since the MMSD data was provided in March 2012, so that areas that were once considered clean by the MMSD may have become impaired, and vice versa. Determining the specific pollutant of impaired sites could not be done due to lack of time and resources, but if we were to conduct a follow – up experiment, we would collect the water samples from each source again and test levels of nutrients such as phosphorus, nitrogen and carbon in addition to heavy metals such as lead and copper within the same day. We could then attempt to make correlations between these concentrations, pollution, and pH.
Devai I., DeLaune R. (1999). Emission of reduced malodorous sulfur gases from wastewater treatment plants. Water Environment Research. 71(2) 203-208.
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