This study aims to asses the occurrence and location of Combined Sewage Overflows (CSO) in Washington D.C. CSOs pose a major health risk to aquatic recreationalists, as bacteria present in raw sewage are destructive to the digestive system, and in rare cases are fatal. The EPA, has found Washington D.C. guilty of CSOs, but proper testing of Potomac River water and identification of CSO discharge locations have not occurred. A series of Cochran-Mantel-Haenszel (CMH), Wilcoxon, and Correlation tests are run on E. coli abundance and precipitation data to evaluate whether CSOs are making the Potomac River more polluted along Washington D.C. than before it. Results show significantly more E. coli in the river within the city, but the role of CSOs in that is less certain. Positive relationships between E. coli abundance and precipitation are found before and within the city limits, but p-values remain > 0.05, except for site 21. Additionally, residual values for CMH Test Series A indicate CSO occurrence, but are not backed up by significant p-values. CMH Test Series B and C residual values indicate CSO occurrence at the Tidal Basin and Shipping Canal, but are also not backed up by significant p-values. Although not all results are significant, the sign of tests results at all monitoring sites examined are consistent to what one would expect if CSOs were actually present. This clearly indicates some mechanism polluting the Potomac River along Washington D.C., which is more likely combined sewage overflows. This analysis serves as a foundation for water sampling assessments in the Potomac River, that will hopefully lead to additional studies.


Crawford, Alex


Earth Sciences


Applied Statistics | Environmental Health and Protection | Environmental Indicators and Impact Assessment | Environmental Monitoring | Hydrology | Pathogenic Microbiology

Publication Date


Degree Granted

Bachelor of Arts

Document Type

Senior Independent Study Thesis



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