EVALUATING SOURCES OF SURFACE WATER CONTAMINATION IN A MIXED-USE WATERSHED NEAR WASHINGTON, D.C

Degradation of urban surface water quality has increased the importance of understanding the spatial and temporal distribution of pollutants within these systems. Contaminants may originate from below the surface (e.g. leaking sewers) and be transported by groundwater into wells or surface water bodies. Surface contaminants may accumulate on impervious surfaces and be rapidly transported by overland flow during precipitation events. Combined sewer overflows are another potential source of surface water contamination in urban areas. One example is the Rock Creek watershed in Maryland and the District of Columbia, which has been designated as impaired due to high levels of E. coli bacteria.

Recent studies have investigated the environmental and anthropogenic factors that may impact water quality in the Rock Creek watershed. Monitoring of microbiological, chemical, and physical water quality parameters coupled with spatial and temporal data analysis using Geographic Information Systems software and statistical analysis determined that water quality is not uniform along Rock Creek. Nitrate concentrations were more closely associated with the northern, agricultural areas compared with the more urbanized southern areas that contained a higher density of older, potentially leaking sewers and greater impervious surface coverage. E. coli concentrations were correlated with rainfall and land use in a pattern that suggests a combination of sources. A subsequent study utilized microbial source tracking to determine that pathogenic bacteria in Rock Creek originate from both human and non-human (e.g. pets and wildlife) sources. These data may ultimately assist decision makers in understanding the relationship between water quality of Rock Creek, the factors studied, and the potential health hazards resulting from precipitation events and aging urban infrastructure.