Masking impact of sediment generated E. coli. on evaluation of environmental health

Thomas Shahady^*

• University of Lynchburg, Lynchburg, United States

The Pigg River, located in south central Virginia USA, is studied over a 6-year (2018-2023) period to better understand river function and pinpoint sources of pollution. The Pigg River is an important resource in central Virginia as it drains significant agricultural lands providing a water source for cattle and agricultural production. It also drains the City of Rocky Mount where both a municipal wastewater facility and low head hydroelectric dam are located. The obsolete low head dam is removed in 2017 prompting concerns over excessive sedimentation flowing downstream contaminating Leesville Lake that is part of a larger pump-storage hydroelectric project. In response, the Pigg River is monitored along with multiple sediment disturbance experiments at selected sites below Rocky Mount to validate these concerns. The study found areas of greatest pollution accumulation just below Rocky Mount then continuing through an 18-20 kilometer stretch of the river. Using Escherichia coli (E. coli) as the primary pollution and health concern indicator, along with Microbial Source Tracking (MST) and other molecular techniques, we found that contamination is extremely high during storm events (> 10,000 CFU/100 ml) and often remained above instantaneous contamination standards of 220 CFU/100 ml during baseline flow. Ruminants are identified as the primary stormwater source of contamination while human markers predominated during baseline flow. Most significantly, areas beyond the dam removal site are identified as 'hot spots' generating the highest readings of contamination. Without clear association between E. coli and MST markers at these hot spots, the study concluded growth and release of E. coli from sediments is the significant source of contamination. These sediments, released in 2017 and impounded since 1915, so significantly elevated E. coli that it masked any ability to discern health concerns otherwise associated with these markers. Hence, legacy sediments must be seen as a confounder toward the usefulness of E. coli as an effective environmental health indicator.