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2005-01-24_REVISION - M1999120
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2005-01-24_REVISION - M1999120
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Last modified
6/15/2021 2:49:22 PM
Creation date
11/21/2007 2:30:24 PM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
M1999120
IBM Index Class Name
Revision
Doc Date
1/24/2005
Doc Name
Second Adequacy Response Letter
From
L.G. Everist Inc
To
DMG
Type & Sequence
AM1
Media Type
D
Archive
No
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RE: L. G. Everist, Inc., Fort Lupton Sand and Gravel Mine, DMG #M-1999-120; <br />Second Adequacy Response Letter <br />LGE will continue to collect groundwater monitoring data after one year, and until start of <br />construction of slurry walls in the amendment area, to be used as baseline, pre-mining <br />groundwater data. <br />6. LGE continue to measure groundwater... <br />LGE commits to continuing to measure groundwater in the existing monitoring wells throughout <br />the life of the existing mine, and commits to monitoring groundwater throughout the life of the <br />expansion area as well, until reclamation is complete and LGE is released from its bond. <br />If existing monitoring wells are damaged or are no longer useful due to mining activities in the <br />amendment area, new monitor wells will be installed as close to the original location as possible <br />and appropriate. <br />7. Division does not agree with the 5-foot trigger point... <br />As discussed of our January 19 meeting, LGE is concerned That too small a trigger may cause it <br />(the trigger) to be reached by natural changes in the groundwater table, and/or by the activities <br />of others. We had proposed a trigger of 5 feet based on the maximum shadow effect projected <br />by the groundwater modeling, while the DMG stated that the trigger should be 2 feet to protect <br />adjacent vegetation. <br />We also discussed the use of a 3-month running average groundwater elevation versus a <br />seasonal average elevation (i.e. growing/irrigation and non-growing/non-irrigation seasons) to <br />define groundwater levels for the trigger. As requested, an analysis of these two approaches <br />was completed using the data collected to date from the 14 monitoring wells. The wells have <br />been monitored monthly from May 2004 through December 2004. The attached table (see <br />attached table, Fort Lupton Sand and Gravel Mine Monitoring Well Data and Averages) shows <br />the monitoring well data, the seasonal averages, and the 3-month running averages to date. <br />This table was prepared for illustrative purposes and does not necessarily show the specific <br />numbers that would be used in the trigger. The specific numbers used for the trigger will be <br />based on all the data collected after at least one year of monitoring, and the averages will be re- <br />calculated to include this data. <br />The table shows that the non-growing season average (to date) is less than the growing season <br />average. It is anticipated that the non-growing season average will become even less at all <br />wells when more data is collected since shallow groundwater typically reaches its annual low in <br />late winter or early spring. <br />The table also shows that there is more variation in the 3-month running averages. This is <br />because the running averages reflect changes in groundwater levels over a shorter time period. <br />The 3-month running averages show the changes in groundwater throughout the year, and are <br />a more accurate estimate of the groundwater level at any one time. For example, the July <br />running average is a better estimate of the May-July groundwater elevation than the "growing <br />season average' because of the shorter averaging period. A longer averaging period (e.g., for <br />the seasonal averages) increases the range of the measurements, and consequently, the <br />chance that the trigger will be reached by natural variation. <br />For these reasons, LGE proposes to use the 3-month running averages to define both pre- <br />mining and post-mining groundwater levels. Twelve 3-month running averages that represent <br />pre-mining conditions will be determined for each well once 12 months of monitoring data have <br />LM/F L-Resp2 ndAdeq Revd mg KP-012105. doc <br />
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