Usingmultiple tracers (F-, B, δ11B, and optical brighteners) to distinguish between municipal drinking water and wastewater inputs to urban streams

Releases of municipal waters, including drinking water and wastewater, can considerably alter urban stream chemistry. However, the relative contributions of drinking water versus wastewater to streams have not been quantified previously and are therefore the focus of this study. We sampled streams along a land use gradient that includedwatersheds with impervious surface areas (ISA) ranging from 1.6 to 62.6%. Samples were analyzed for F-, total B, delta B-11, and optical brighteners to determinemunicipalwater inputs to streams. Weobserved low F- ( 75 +/- 20 mu g/L), B (29 +/- 6 mu g/L), and optical brightener (3.66 +/- 0.76 RFU) levels in rural streams, but their concentrations increased with urbanization (up to 475 mu g/L, 227 mu g/L, and 22.09 RFU, respectively). The delta B-11 values for drinking waters (16.52 +/- 0.39%) and wastewaters (untreated = 6.06 +/- 0.88 parts per thousand and treated = 6.46 +/- 0.93 parts per thousand) were distinct, but there was poor correlation between delta B-11 and ISA for the streams (R-2 = 1 x 10(-5); p = 0.99), likely due to variable lithology in the study area. We used inverse and three-component mixing models to quantify municipal water inputs to the streams. In densely urbanizedwatersheds, drinking water and wastewater can respectively contribute up to 54% and 16% of the total streamflow. In addition to our spatial sampling, we collected weekly samples at a suburban stream to test the effects of discharge and seasonality on municipal water tracer behavior. We found that tracer levels did not change significantly (p >= 0.28) with discharge or season, suggesting that municipal water inputs are fairly constant. Understanding the relative proportions of differing municipal water types to streams is crucial in guiding infrastructure improvements to conserve drinking water and reduce harmful wastewater releases. The unique chemical signatures of municipal waters aid in the widespread applicability of our multi-tracer method for identifying water sourcing to urban streams. (C) 2019 Elsevier B.V. All rights reserved.