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1992-10-19_REVISION - M1988112 (5)
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1992-10-19_REVISION - M1988112 (5)
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Last modified
6/20/2021 5:59:48 AM
Creation date
11/21/2007 9:18:46 PM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
M1988112
IBM Index Class Name
Revision
Doc Date
10/19/1992
Doc Name
ADEQUACY RESPONSES TO ADEQUACY COMMENTS TO TR8 PHASE II SUBMITTAL EXISTING GROUND WATER MONITORING
Type & Sequence
TR8
Media Type
D
Archive
No
Tags
DRMS Re-OCR
Description:
Signifies Re-OCR Process Performed
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<br /> <br />and literature values for porous media. However, these values could vary within an expected <br />range from those presented in tl~e TR-08 submittal and, therefore, we have conducted a <br />sensitivity analysis to evaluate what effect varying these pazameters within a range of expected <br />values would have on the evaluation of the adequacy of the monitoring wells, from the <br />standpoint of detecting a hypothetical contaminant plume. <br />For the sensitivity analysis, we have run a hypothetical base case using the values presented in <br />the TR-08 submittal; specifically, a porosity of 25 percent, a longitudinal dispersivity of l00 feet <br />and a transverse dispersivity of 30 feet. Each of these parameters was [lien varied within the <br />range of expected values to evaluate if the existing monitoring well system can effectively <br />monitor local ground water quality changes (assuming that there is a mechanBsm to drive the <br />seepage from the tailings facility to the ground water over 100 feet below). <br />A typical range of porosity in porous material is 20 to 35 percent (see, e.g. "Bnsic Soils <br />Engineering", by B.K. Hough, Table 2.3, pp. 34-35, 1969). Therefore, a sensitivity analysis <br />was conducted using a porosity value of 20 percent, 25 percent (base case) and 35 percent to <br />evaluate how a hypothetical plume shape would be affected by these variations in porosity. <br />Similarly, dispersivity values can vary based on aquifer hydraulic characteristics and the aquifer <br />matrix. Since actual site-specific dispersivity values are not known, a sensitivlty analysis was <br />conducted using the expected range of dispersivity values that are typically found in porous <br />media, as reported in published literature. Hypothetical plmnes were calculated for the <br />following longitudinal and transverse dispersivities: longitudinal dispersivity = 30 feet, <br />transverse dispersivity = ]0 feet; longitudinal dispersivity 100 feet, transverse dispersivity = <br />30 feet (base case); and longitudinal dispersivity = 200 feet, transverse dispersivity = 60 feet. <br />It should be noted that dispersivity values are generally larger in heterogeneous aquifers, and <br />lower in more homogeneous aquifers. Therefore, we believe that the disppersivity values <br />presented in TR-08 may be conservative. <br />For each of these analyses, the following assumptions were made: <br />(1) The hypothetical source of contamination was a single point, which is considered <br />a worst-case analysis relative to being able to detect a hypothetioal plume at the <br />existing monitoring well system. A larger source area would result in a much <br />wider plume than that demonstrated by this sensitivity analysis. <br />(2) An instantaneous source of equal strength for each case was input directly to the <br />aquifer. There was only one variable for each case for comparison purposes, i.e. <br />porosity or dispersivity. <br />-2- <br />
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