# Change in Water Quality of the Vistula River During the Emergency Discharge of Untreated Wastewater
## 1 Introduction
### Data Analysis  
For each of the eight stations, a database was created with 52 days of measurements for 16 water quality parameters, which gives a total of 7072 results. The article presents an analysis of the results of daily measurements of water quality parameters during emergency sewage discharge. Before the sewage system failure, water quality monitoring was carried out only at station S3 with a monthly frequency. Basic descriptive statistics were then determined for all the parameters analyzed within each of the stations considered (mean, standard deviation--SD). The next step was to apply multivariate methods. [PERSON]'s minimum variance algorithm was used for clustering, and the Euclidean measure was used as a similarity measure. The results of the classification are presented graphically in the form of a dendrogram. Data were then analyzed using the non-parametric Friedman test with  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Station** & **Name** & **North** & **East** \\ \hline S1 & 5 km before the collector outlet, Brusselska & 52.22041\({}^{\circ}\) & 21.05380\({}^{\circ}\) \\ S2 & 100 m before the collector outlet & 52.30476\({}^{\circ}\) & 20.95062\({}^{\circ}\) \\  & Place of failure, North Bridge in Warsaw & 52.30601\({}^{\circ}\) & 20.95009\({}^{\circ}\) \\ S3 & 300 m after the collector outlet & 52.30853\({}^{\circ}\) & 20.94791\({}^{\circ}\) \\ S4 & 500 m after the collector outlet, on the & 52.30944\({}^{\circ}\) & 20.94553\({}^{\circ}\) \\  & left bank & 52.30149\({}^{\circ}\) & 20.94632\({}^{\circ}\) \\ S5 & 500 m after the collector outlet, in the & 52.31156\({}^{\circ}\) & 20.94700\({}^{\circ}\) \\ S6 & 500 m after the collector outlet, on the & 52.32329\({}^{\circ}\) & 20.92788\({}^{\circ}\) \\  & right bank & 52.37651\({}^{\circ}\) & 20.87541\({}^{\circ}\) \\ S7 & 2500 m downstream of the collector outlet & 52.32329\({}^{\circ}\) & 20.92788\({}^{\circ}\) \\  & 10 km downstream from the collector outlet, & 52.37651\({}^{\circ}\) & 20.87541\({}^{\circ}\) \\ S8 & 500 m after the discharge of sewage treated & 52.37651\({}^{\circ}\) & 20.87541\({}^{\circ}\) \\  & from “Czajka” & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: List of measuring stations on the Vistula River.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Good Ecological Status [37]** & **Drinking Purpose [38; 39; 40; 41]** \\ \hline TN & 4.0 & - \\ N-NO3\({}^{-}\) & 2.2 & 10 \\ N-NO2\({}^{-}\) & 0.03 & 1 \\ N-NH4\({}^{*}\) & 0.84 & 1.5 \\ TP & 0.30 & 0.4 \\ P-PO4\({}^{3*}\) & 0.10 & - \\ SS & 31 & - \\ TDS & 525 & 1000 \\ EC & 850 & 2500 \\ SO4\({}^{2-}\) & 71.5 & 250 \\ Cl\({}^{-}\) & 75.5 & 250 \\ pH & 6.5–8.4 & 6.5–8.5 \\ COD & 30 & 30 \\ DO & \textgreater{}7.5 & - \\ TOC & 13.6 & - \\ WT & 24 & 25 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Threshold values of water quality parameters.  
post hoc pairwise comparisons using the Wilcoxon rank sum test. Homogeneous subsets of stations were determined using the Bonferroni correction, assuming a significance level of 0.05. In addition, relationships between water quality variables were assessed using [PERSON]'s correlation test. Statistical analysis was performed using R software version 4.3.1 [42].