Date of Award

8-2011

Document Type

Thesis

Degree Name

Master of Engineering (ME)

Legacy Department

Biosystems Engineering

Advisor

Sawyer, Calvin B.

Committee Member

Hayes , John C.

Committee Member

Privette, III , Charles V.

Abstract

Construction activities have been recognized to have significant impacts on the environment. Excess sediment from construction sites is frequently deposited into nearby surface waters, negatively altering the chemical, physical and biological properties of the water body. This environmental concern has led to strict laws concerning erosion and sediment control, such as imposing permit conditions that limit the concentration of suspended solids that can be present in effluent water from construction sites. However, sediment concentration measurements are not routinely used to detect and correct short-term problems or permit violations because laboratory analysis of sediment concentrations is time-consuming and costly. Nevertheless, timely, accurate field estimation of sediment loading could be facilitated through the development of empirical relationships between suspended solids and turbidity.
Previous research indicates that turbidity measurements may be a more practical method of estimating sediment loads by indirectly relating sediment concentration to turbidity. In addition, recognition of turbidity as an indicator of pollution in surface runoff from disturbed areas has resulted in efforts by the U.S Environmental Protection Agency (EPA) to implement turbidity effluent limitation guidelines to control the discharge of pollutants from construction sites. Therefore, given the importance of a proposed turbidity limit, focus of this research is to determine relationships between representative soils and corresponding turbidity as a function of suspended sediment concentration and sediment settling. Turbidity is not only a function of suspended sediment concentration, but also of particle size, shape, and composition; so this research was needed to analyze turbidity responses based on sediment characteristics of representative South Carolina soils.
First, accuracy and precision of commercially available nephelometers needed to be quantified for use in subsequent sediment/ surface water analysis and potential regulatory compliance. Analysis of accuracy and precision for instruments showed that even though meters may be very precise, they could also be inaccurate. However, three of the four meters that performed well provided statistically accurate and precise results. It was also found that formazin calibration standards may be a better standard than AMCO EPA standards for surface water analysis.
Utilizing representative South Carolina soils, both relationships of turbidity to sediment concentration and turbidity to settling time were used to form mathematical correlations. Turbidity versus suspended sediment concentration and turbidity versus settling time correlated well when top soil and subsoils were classified based on their predominant South Carolina region and their measured clay content. Derived trends for suspended sediment concentration to turbidity correlated well with either a linear or log relationship (R2 values ranging from 0.7945 to 0.9846) as opposed to previous research utilizing a power function or the assumption of a one-to-one relationship. For the correlation of turbidity and sediment settling time, trends were well correlated with a power function (R2 values ranging from 0.7674 to 0.9347). This relationship suggests Stoke's Law was followed; where smaller particles remain in suspension longer and contribute more to turbidity compared to soils with less clay content.
Altogether, results of this research provide a step in determining potential site-specific equations relating sediment concentration to turbidity and sediment settling time to turbidity. With this knowledge, results could ultimately aid in the design of future sediment basins of South Carolina and provide information for potential regulatory compliance.

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