IDENTIFICATION OF SEWAGE EXFILTRATION IN COASTAL AREAS THROUGH THE MONITORING OF DRUGS AND STIMULANT CONCENTRATIONS IN URBAN STORM DRAINS

Abstract

One of the major barriers for municipalities responsible for mitigation of sewage exfiltration is locating grossly leaking sections of the sewage conveyance system in a time-, labor- and cost-efficient manner. In this study, water samples were collected from the dense network of manholes overlying the storm drain systems in the tourist area of Waikīkī and inland residential areas on the island of O‘ahu, Hawai‘i. The majority of the sewage conveyance infrastructure in this coastal area is submerged and the storm drains are routinely subject to backflow during high tide. Exfiltration of sewage from the aging conveyance system in this coastal area contaminates the surrounding shallow brackish aquifer, which then enters leaking pipe joints and cracks in the storm water conveyance system. Samples collected from the storm drains were analyzed for the presence of carbamazepine, a commonly prescribed anticonvulsant, pain relief and bipolar disorder treatment drug, which behaves as a conservative tracer in the environment (> 50 days half-life, low sorption). Samples were also analyzed for the more labile anthropogenic tracer caffeine (~4 day half-life). The higher stability of carbamazepine enables detection of this compound at greater distances from sewage release sites while caffeine serves as a better tracer for detecting recent, proximal releases of sewage, given its ephemeral nature and relatively high and ubiquitous presence. The concentration levels and spatial distribution of detection of these two anthropogenic biomarkers were successfully used to identify areas of ongoing sewage exfiltration in Waikīkī and surrounding residential communities. The variation in carbamazepine and caffeine concentrations measured in Waikīkī storm drains over a 1 year period generally correlate with daily visitor arrivals to O‘ahu.