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generate acidic or toxic water. Additionally, analysis of ground water from two piezometers and <br />a seep on site will show the current ground water quality. <br />Sample Results and Analysis <br />Three water samples were gathered on February 2, 2012 from both piezometers on site as well as <br />a seep on site. These locations were selected for sampling based on their location and their <br />usefulness in demonstrating what impacts the backfill chemistry has on the local ground water. <br />Ground water in the area flows, in general, from northeast to southwest. This is inline with the <br />major water feature in the area, the Yampa River (flows east to west). The sample results were <br />then compared to the state water quality standard for ground water that is used for agriculture. <br />Table 1 shows this comparison. <br />The ground water from the wells is within the state standards on almost all of the values. The <br />only exceptions are boron at the North Well, manganese at both wells and the Seep, and <br />selenium at the Seep. The boron and manganese exceedances at the wells must be from a natural <br />source, since the SPLP tests of the backfill do not show manganese or boron values nearly as <br />high. This data can be seen in Table 2. The higher selenium value measured at the Seep is most <br />likely due to the Seep being at the toe of backfilled slope, and thus closer to the Lewis Shale that <br />underlies alluvial deposits in this area. This shale, like many Colorado shales, can contribute <br />selenium to ground water that interacts with it. <br />The SPLP tests show that the backfill material produces slightly basic water just outside of the <br />pH limits for agricultural and domestic ground water. However, the concern with coal waste is <br />that it will produce sulfuric acid due to the oxidation of pyrite in the coal or shale partings. The <br />sulfur content of these samples shows the opposite: very small amounts of mostly sulfate or <br />organic sulfur that would oxidize to produce sulfuric acid. Also, the pH indicates that there is <br />more alkali material present in the backfill (most likely CaCO3 from rock dust) than acidic <br />material. Additionally, the Acid -Base Potential (also known as Acid -Base Accounting) shows a <br />positive value of 45 tons CaCO3/kton of backfill, showing the alkali forming potential of the <br />backfill. <br />If the pH of the piezometers, the seep, and WP -61 are analyzed together, the potential impact of <br />the backfill on the ground water can be observed. Water with a pH just above neutral (7.9 -8) <br />travels (general ground water trend of north east to south west) through backfill (WP -61 pH of <br />8.9) and comes out with a pH of 8 (Seep). This shows that the alkali contribution of the backfill <br />is not sufficient to affect the pH of local ground water very much, if at all. <br />Based on the chemistry of the local ground water shown in the piezometers versus the SPLP <br />results it can be seen that the backfill material placed at the Deakins Pit is not having a negative <br />affect on the local ground water. Additionally, since the Acid -Base Potential showed alkali <br />potential in the SPLPs, the backfill at Deakins is not contributing acid water to the area, which is <br />the biggest concern with coal waste embankments. <br />