Browsing by Author "Perkins, Rebekah Lynn"

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    Development and Evaluation of Effective Turbidity Monitoring Methods for Construction Projects
    (Minnesota Department of Transportation Research Services & Library, 2014-07) Perkins, Rebekah Lynn; Hansen, Brad; Wilson, Bruce N.; Gulliver, John S.
    Various agencies have discussed the possibility of using turbidity as an effluent standard for construction site. Turbidity monitoring can be difficult for dynamic construction sites. This project investigated turbidity relationships for conditions of Minnesota and developed protocols for the design and installation of cost-effective monitoring systems. Turbidity characteristics of fourteen different soils in Minnesota were investigated using the laboratory protocols. Trends in turbidity with sediment concentrations were well represented by power functions. The exponent of these power functions was relatively constant between soils and the log-intercept, or scaling parameter varied substantially among the different soils. A regression analysis for the scaling parameter was a function of percent silt, interrill erodibility, and maximum abstraction. A power value of 7/5 was chosen to represent all soils. The field studies were also used to develop turbidity monitoring systems that would be adaptable to construction sites and to collect turbidity data on construction site runoff. Construction site turbidities often exceeded 1000 NTUs and sometimes surpassed 3000 NTUs.
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    Turbidity monitoring on construction sites: insight into the factors influencing the turbidity and TSS relationship
    (2013-05) Perkins, Rebekah Lynn
    Stormwater runoff from construction sites can transport eroded sediment to nearby water bodies degrading water quality and impairing biotic communities. The United States Environmental Protection Agency (EPA) is considering a turbidity limit for effluent stormwater on construction and demolition sites and is requesting data to support that limit (EPA, 2011). Laboratory protocols have been developed herein for studying the factors that impact turbidity from construction site soils. Experimental procedures include the use of a rainfall simulator to generate runoff and turbidity values from soils carefully packed in appropriate test boxes. Turbidity characteristics of fourteen different soils in Minnesota were investigated using the laboratory protocols. Trends in turbidity with sediment concentrations were well represented by power functions. The exponent of these power functions was relatively constant between soils and the log-intercept, or scaling parameter varied substantially among the different soils. Multiple soil properties were evaluated for each soil. An extensive regression analysis resulted in a model using percent silt, interrill erodibility, and maximum abstraction that best represented the intercept term. A power value of 7/5 was chosen to represent all soils. A second laboratory experiment was performed to determine how particle settling affects the coefficients of the turbidity -TSS relationship. The scaling parameter increased with sediment deposition and the power value decreased. Field studies on two construction sites in the Twin Cities of metropolitan area of Minnesota were performed for this project. Grab samples and continuously monitored turbidity were collected for each site. The grab samples also exhibited a strong power relationship between turbidity and TSS with similar coefficients as the laboratory samples. The laboratory relationships were also applied to the observed field conditions to demonstrate their usefulness in estimating turbidity, concentration, sediment load, and load reduction.