2004-11-01_REVISION - M1977208

• Permit No: M1977208
• IBM Index Class Name: Revision
• Doc Date: 11/1/2004
• Doc Name: Cement Klin Dust Disposal in C-Pit
• From: CEMEX Inc
• To: DMG
• Type & Sequence: TR4
• Media Type: D
• Archive: No

hydraulic gradient of 0.005 (15 ft change in head over 3,000 ft). Considering the hydraulic
conductivity value used for the Dakota sandstone, this results of groundwater flow velocities of
approximately 80 and 40 ft/yr. For all the constituents, the base case, as expected, predicts higher
constituent concentrations at the hypothetical receptor well and results in a "worst case" scenario.
Therefore, only the results of the base case are discussed below.
Figure 1 shows the predicted TDS concentration in the hypothetical Dakota sandstone receptor
well. The background TDS concentration in the Dakota sandstone is 465 mg/L. Seepage of C-Pit
water is predicted to increase the TDS concentration in the Dakota sandstone about 60 mg/L,
resulting in a predicted TDS concentration of approximately 525 mg/L. This predicted TDS
concentration is less than the TDS groundwater protection standard (GWPS) of 581 mg/L. The
GWPS is 1.25 times the Dakota sandstone background TDS concentration (465 mg/L).
Figure 2 shows the predicted selenium concentration in the hypothetical Dakota sandstone
receptor well. The background selenium concentration in the Dakota sandstone was assumed to
be 0.0025 mg/L (one-half of the reported result) since the selenium result was reported as less
than 0.005 mg/L. Seepage of C-Pit water is predicted to increase the selenium concentration in
the Dakota sandstone about 0.004 mg/L, resulting in a predicted selenium concentration of
approximately 0.007 mg/L. This predicted selenium concentration is less than the selenium
GWPS of 0.02 mg/L.
Figure 3 shows the predicted sulfate concentration in the hypothetical Dakota sandstone receptor
well. The background sulfate concentration in the Dakota sandstone is 6 mg/L. Seepage of C-Pit
water is predicted to increase the sulfate concentration in the Dakota sandstone about 20 mg/L,
resulting in a predicted sulfate concentration of approximately 26 mg/L. This predicted sulfate
concentration is less than [he sulfate GWPS of 250 mg/L.
Figure 4 shows the predicted thallium concentration in the hypothetical Dakota sandstone
receptor well. The background thallium concentration in the Dakota sandstone was assumed to
be 0.001 mg/L (one-half of the report result) since the thallium result was reported as less than
0.002 mg/L. Seepage of the C-Pit water is predicted to increase the thallium concentration in the
Dakota sandstone about 0.0001 mg/L., resulting in a predicted thallium concentration of
approximately 0.0011 mg/L. This predicted thallium concentration is less than the thallium
GWPS of 0.002 mg/L.
Figure 5 shows the predicted chloride concentration in the hypothetical Dakota sandstone
receptor well. The background chloride concentration in the Dakota sandstone is 7 mg/L.
Seepage of C-Pit water is predicted to increase [he chloride concentration in the Dakota sandstone
about 9 mg/L, resulting in a predicted chloride concentration of approximately 16 mg/L. This
predicted chloride concentration is less than the chloride GWPS of 250 mg/L.
October 29, 2004 5 Revision 0