Aquatic communities and associated water chemistry in the St. Vrain River near the City of Longmont wastewater-treatment plant

Science Center Objects

The St. Vrain River watershed in northeastern Colorado has experienced rapid urban growth over the last two decades. Population growth has led to increased volumes being treated at wastewater-treatment plants (WWTPs) in the basin. In the last two decades, in-stream restoration efforts and new treatment technologies have been implemented by the City of Longmont, with the goal of improving water quality and the health of aquatic organisms downstream from the WWTP effluent. Historical data on fish and macroinvertebrate communities in the St. Vrain River were collected at varying locations using varying methods, which may limit the ability to assess community changes over time.

In 2005, the U.S. Geological Survey and the City of Longmont, Colo., began a study to document chemical characteristics of St. Vrain Creek that had previously been unavailable either due to high cost of analysis or lack of analytical capability. Stream samples were collected at seven sites on St. Vrain Creek during the spring of 2005 and 2006 for analysis of wastewater compounds. A Lagrangian-sampling design was followed during each sampling event, and time-of-travel studies were conducted just prior to each sampling event to determine appropriate sampling times for the synoptic. In addition, semipermeable membrane devices, passive samplers that concentrate hydrophobic organic chemicals, were installed at six sites during the spring of 2005 and 2006 for approximately 4 weeks. After retrieval, contaminant residues concentrated in the semipermeable membrane devices were recovered and used in a toxicity assay that provided a screen for aryl hydrocarbon receptor type compounds, including polycyclic aromatic hydrocarbons, polychlorinated biphenyls, dioxins, and furans.

In addition, the U.S. Geological Survey summarized information on macroinvertebrate and fish communities known from St. Vrain Creek dating back to the early 1900s in order to assess their utility in evaluating wastewater-treatment plant upgrades and habitat improvement projects.