In recent years, the excessive specific conductance (SC) of Appalachian coal mining runoff waters has become a parameter of concern with the EPA due to its negative effect on aquatic life and water quality. In order to comply with the EPA guidance suggesting an effluent SC of 500 µS/cm, the Appalachian Research Initiative for Environmental Science (ARIES) Center at Virginia Tech requested that testing be done to determine the most effective technologies for reduction of SC. Runoff water was collected from two sites in southwestern Virginia and characterized to determine the source of SC in the water. The main contributing ions were determined to be Na⁺, Mg²⁻, Ca²⁺, and SO₄²⁻. Testing was performed to assess the possibility of using the speciation software, MINEQL+, with a set of empirical equations which predict SC using ionic composition for natural waters with a low to medium SC.
The physicochemical treatment methods tested were ion exchange, excess lime-soda softening, and the Cost Effective Sulfate Removal (CESR) process. Both cation (H⁺ exchanger) and anion (Cl⁻ exchanger) exchange media were tested separately in batch reactors, which resulted in a higher effluent SC than initial SC. The softening method investigated, excess lime-soda softening, also resulted in increased SC levels because non-carbonate hardness levels were high and carbonate concentrations were low. The CESR process successfully lowered SC from 1,500-2,500 µS/cm to below the proposed EPA limit of 500 µS/cm. The success of this process was due to its ability to remove more than 85% of the calcium, magnesium, and sulfate from the water, which together accounted for more than 90% of ions in the source water. / Master of Science / In recent years, mining activities have generated large amounts of unweathered rock from blasting. This rock, which is often stored in valleys near the blasting sites, releases salts into water that passes over the rocks when it rains. The salty water flows into nearby streams populated with freshwater fish and other organisms that suffer when their environmental conditions are changed. The Appalachian Research Initiative for Environmental Science (ARIES) Center at Virginia Tech requested that testing be done to determine which engineering techniques would be most effective for reduction of these salts. The amount of salt in the water is measured by specific conductance (SC), which measures how well the water conducts electricity. Testing was also done to determine which types of salts were in the water; the results showed that the largest contributors were sodium, magnesium, calcium, and sulfate ions.
Three engineering techniques were investigated for removal of the contributing ions: ion exchange, softening, and the Cost Effective Sulfate Removal (CESR) process. Two types of ions exchange, one that targeted the positive ions (cation exchange) and one that targeted the negative ions (anion exchange), were tested. Both forms of ions exchange raised the SC to a higher concentration than the original water. Softening had a similar effect because one of the chemicals added during the process released additional sodium ions into the water. Finally, the CESR process was able to successfully reduce the SC below the limit proposed by the EPA as safe for stream life. This was due to the large reduction of three of the four major ions that was achieved during the CESR process.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/85011 |
| Date | 22 March 2017 |
| Creators | Grey, Catherine Vyvian |
| Contributors | Civil and Environmental Engineering, Boardman, Gregory D., Vikesland, Peter J., Parks, Jeffrey L. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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