ANALYSIS OF BACTERIA AND NUTRIENT LEVELS IN SUBSURFACE STORM DRAINS RECEIVING FLOWS FROM GROUNDWATER SEEPAGE AND URBAN RUNOFF IN DRY WEATHER CONDITIONS

This project examines the relationship between bacterial growth and nutrient loading in subsurface storm drains during dry weather conditions. Isotope analysis identified the source of waters feeding into the storm drains. Storm drains perennially fed by groundwater, seeps and/or dewatering infrastructure, may provide incubator conditions for bacteria proliferation by providing nutrients necessary for bacteria proliferation. Grout lined storm drains also convey storm runoff and dry weather flows (car wash runoff, lawn runoff, and other nuisance flows) away from urban areas into storm drains and ultimately coastal watersheds. As runoff enters storm drains, it carries N and P, which serve as electron acceptors and provides necessary energy for bacteria to multiply. Other elements needed to create incubator conditions are carbon rich input and seed bacteria. Vegetation detritus washed into the storm drain during urban watering or from internal algae growth provides a carbon source and enough wildlife exists in and near storm drains to provide the seed bacteria spawning bacteria growth. Nitrate-N, orthophosphate, bacterial quantities, and flow all demonstrated a positive association in our studies. Throughout the day, the levels of bacteria, P, and N decreased. At night the levels of bacteria and nutrients increased. No evidence was found to support that groundwater baseflow creates incubator conditions in storm drains. A positive association was found between bacteria, flow, and nutrients. The urban runoff flow, not incubator conditions, accounts for the increase in nutrients and bacteria found throughout varying times of the day and night. Runoff brings in bacteria from animal waste and may strip biofilms from rain gutters into storm drains, which are substrates for bacteria to grow on. The urban runoff also brings in nutrients from residential and commercial discharges in the area.