Abstract
Dry-weather flows in urban channels and streams, often termed “urban drool”, represent an important source of urban surface water impairment, particularly in semi-arid environments. Urban drool is a combination of year-round flows in urban channels, natural streams, and storm-sewer systems (runoff from irrigation return flow, car washes, street cleaning, leakage of groundwater or wastewater into streams or storm sewers, etc.). The purpose of this study was to better understand the extent and sources of urban drool pollution in Denver, Colorado by identifying relationships between urban catchment characteristics and pollutants. Water-quality samples were taken throughout Denver at urban drainage points that were representative of a variety of urban characteristics. Samples were analyzed for total suspended solids (TSS), coliforms, Escherichia Coli (E. coli), nutrients (nitrate, phosphorus, and potassium), dissolved and total organic carbon, and dissolved and total recoverable metals. Results from this study were as follows: (1) most contaminants (nitrate, phosphorus, arsenic, iron, manganese, nickel, selenium, and zinc) were concluded to be primarily loaded from shallow groundwater; (2) anthropogenic effects likely exacerbated groundwater pollutant concentrations and contributions to surface water; (3) nitrate, nickel, and manganese may be partially contributed by industrial inputs; (4) medical marijuana cultivation sites were identified as a potential source of nutrient and zinc pollution; (5) E. coli was a ubiquitous contaminant in all urban waterways; (6) erosion of contaminated urban soils, presumably from construction, was found to significantly increase concentrations of TSS, total phosphorus, and total metals. Increasing urbanization and predicted drier climates suggest that dry-weather flows will become more important to manage; the results from this study provide insight on dry-weather water quality management for the City and County of Denver.
Highlights
Research on urban water impairment is abundant, but the degree of degradation and sources of pollution differ depending on the hydrological and water quality dynamics and specific characteristics of the urban area [1,2,3]
While stormwater runoff has a significant impact on urban pollutant loads, dry-weather urban flows in streams, channels, and storm sewers, termed “urban drool”, has been identified as an important source of contamination to urban waterways [4,5,6,7,8,9]
Each site had a variety of drainage types, evidencing different drainage water quality and sources of dry-weather flow
Summary
Research on urban water impairment is abundant, but the degree of degradation and sources of pollution differ depending on the hydrological and water quality dynamics and specific characteristics of the urban area [1,2,3]. While stormwater runoff has a significant impact on urban pollutant loads, dry-weather urban flows in streams, channels, and storm sewers, termed “urban drool”, has been identified as an important source of contamination to urban waterways [4,5,6,7,8,9]. Dry-weather flows, or urban drool, derives primarily from “nuisance” flows (e.g., overirrigation of ornamental landscaping and turf, car washes, street cleaning, irrigation return flows), permitted and illicit point sources of discharge (e.g., discharges from industrial, construction, and dewatering operations), domestic wastewater and drinking water infras-. The most predominant sources of nonpoint dry-weather flow in semi-arid climates include irrigation return flow and shallow groundwater contributions. Groundwater contributions come from a variety of sources, including, but not limited to, construction dewatering, weep holes (breaks in storm sewers where groundwater seeps), natural seeps, and instream contributions [33]
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