Date of Award

Spring 2016

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Engineering

Committee Chair

Raja Nagisetty

First Advisor

William Drury

Second Advisor

Kyle Flynn

Third Advisor

Khalid Miah

Abstract

Silver Bow Creek (SBC, Blacktail Creek to Warm Springs Creek) is a small urbanized stream in western Montana (MT) identified as impaired for nitrate, total nitrogen and total phosphorus on the 2014 303(d) list. Enrichment of SBC occurs primarily from a single municipal point source that results in excessive primary production, macrophyte growth, large diel waterquality swings, and nightly hypoxic conditions that likely impair aquatic life uses. The objective of this study is to apply QUAL2K (a surface water-quality model) to a 5.6 km long reach of SBC to predict in-stream dissolved oxygen (DO) concentrations under different nutrient loading scenarios. Using the developed model, existing and future nutrient loads from the wastewater treatment plant will be evaluated to determine the effect on longitudinal DO. Data collection in support of model development on SBC has included (a) continuous DO, conductivity, temperature and pH measurement using YSI Exo Sondes and sampling of (b) nutrients, suspended solids, and alkalinity at four locations. Nearby climatic forcing data were obtained from Bert Mooney Airport, Butte, MT. Preliminary model runs have produced poor results, however, due in part to a large macrophyte biomass present in SBC. Photosynthesis during the day drives DO well above saturation and contributes to hypoxic conditions at night through respiration. Currently QUAL2K does not support macrophytes, so approximations were made using closely spaced point sources with diurnal variation to accommodate the macrophyte DO source/sink. Using these approximations a theoretical total maximum daily load for nutrients was estimated so that dissolved oxygen concentrations are above 4 mg/L. A 70% reduction in nutrient concentrations is required to meet the 4 mg/L dissolved oxygen minimum.

Comments

A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Environmental Engineering

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