Table 3.
Magnitude of Mean and Median Differences and Standard Deviations and Results of the Paired Sample t-Tests Comparing the Concentrations of Physical–Chemical Pollutants in Samples Collected Directly Upstream and Directly Downstream of Encampments During Dry Weather Conditions
| Site | Pollutant/parameter | Percent change in the concentrationsa |
Sample size (N) | pb | ||
|---|---|---|---|---|---|---|
| Mean (%) | Median (%) | SDc(%) | ||||
| Alvarado Creek | pH | −1.5 | −0.3 | 2.5 | 8 | 0.133 |
| Electrical conductivity | +1.2 | +1.1 | 1.0 | 8 | 0.007 | |
| Total dissolved solids | +1.3 | +1.5 | 1.1 | 8 | 0.004 | |
| Dissolved oxygen | −23 | −16 | 20 | 8 | 0.017 | |
| Dissolved organic carbon | +1.8 | +1.8 | 5.1 | 8 | 0.177 | |
| Total dissolved nitrogen | −9.6 | −5.4 | 12 | 8 | 0.038 | |
| Nitrate | +46 | +7.4 | 75 | 8 | 0.052 | |
| Phosphate | +4.6 | −3.9 | 36 | 8 | 0.464 | |
| Caffeine | +11 | +1.4 | 28 | 4 | 0.203 | |
| Sucralose | +0.1 | +3.4 | 13 | 4 | 0.299 | |
| Forester Channel | pH | +1.1 | +1.8 | 3.6 | 8 | 0.477 |
| Electrical conductivity | −1.4 | 0 | 5.6 | 8 | 0.266 | |
| Total dissolved solids | +20d | −0.3 | 62e | 8 | 0.225 | |
| Dissolved oxygen | +48 | +51 | 34 | 8 | 0.002 | |
| Dissolved organic carbon | +1.5 | +0.7 | 12 | 8 | 0.441 | |
| Total dissolved nitrogen | −9.7 | −8.6 | 7.6 | 8 | 0.002 | |
| Nitrate | +4.7 | +7.3 | 29 | 8 | 0.396 | |
| Phosphate | −3.3 | −5.7 | 21 | 8 | 0.265 | |
| Caffeine | +41 | −10 | 139 | 8 | 0.251 | |
| Sucralose | +41 | +27 | 106 | 7 | 0.350 | |
Positive (+) values indicate that downstream concentrations were higher than upstream concentrations, and negative (−) values indicate that upstream concentrations were higher than downstream concentrations. A value of 0% indicates that upstream and downstream concentrations were equal.
The p-value from a one-tailed, paired sample t-test of the concentrations in samples collected directly upstream and downstream of encampments. The null hypothesis is that upstream and downstream concentrations are equal; the alternative hypothesis is that downstream concentrations are greater (except for pH and dissolved oxygen, where the alternative hypothesis is that the concentrations are not equal, i.e., two-sided test).
SD of the percent (%) difference between the concentrations in samples collected directly downstream and directly upstream of homeless encampments.
The high mean value is due to a single set of samples where the upstream concentration was very low and the downstream concentration was comparable to values measured on other dates. This data point is likely an outlier.
If the outlier set of data points is omitted (see footnote d), this SD would be equal to 5.4%.