2005-04-22_REVISION - M2000016

• Permit No: M2000016
• IBM Index Class Name: REVISION
• Doc Date: 4/22/2005
• Doc Name: Adequacy Review no. 2
• From: DMG
• To: Lafarge West Inc
• Type & Sequence: AM1
• Media Type: D
• Archive: No

M-2000-016, Lafarge West, Inc.: Riverbend Operation, AM-01 April 22, 2005
Adequacy Memo #2 Page 3
mitigation measures. This also relates to comments in the Exhibit G -Water Information
section of this memo.
Rule 6.4.7 EXHIBIT G -Water Information
9. The maps provided in the "Groundwater and Surface Water Evaluation" report prepared
by AMEC (AMEC report) are too small of a scale to evaluate the model output. The
applicant must provide a larger depiction of the ground water model, including maps on
the scale of those submitted as Exhibits C and F. Additionally, the Division needs a
model that shows ground and surface water impacts
• for each cell during dewatering,
• for each proposed clay-lined pit during dewatering and once lined,
• for each of the proposed silt storage ponds during dewatering, as they are filled, and
once completely filled.
The model should represent actual planned operations, including maximum potential
disturbance to the hydrologic balance that may occur as a result of these mining
operations; for example if more than one cell will be dewatered at any one time, this
scenario should be modeled and reported. Wells beyond 600 feet that lie within the
modeled area of affected ground water levels must also be located and identified.
The maps and model must define or predict the cone of depression and/or shadow and
mounding effect expected for any areas to be dewatered and dry mined or as a result of
installation of clay liners or silt storage ponds. The cone of depression and assessment
of other effects should define, at a minimum, the horizontal and vertical extent of
expected impacts. If, during the assessment, the applicant determines that a drawdown
or shadow effect, or mounding will occur offsite that may impact a current ground water
user, property owner (e.g., basement flooding, leach field inundation, decreased
subirrigation, affected sewer or water lines), and/or wetlands, the applicant must provide
a map showing the location of all such structures that may be potentially affected and a
table that lists the structure type and the name, address, and phone number of the
structure owner. Please also commit to mitigation measures to be implemented and
trigger points (both increases and decreases in water level, or other evidence of impacts)
that would put mitigation measures into effect.
10. Page 4 of the AMEC report states, "At the end of the mine life, 10 pits will remain opened
and unlined." The permit application indicates 12 pits will remain open and unlined. If
the model did not adequately represent the applied-for mining conditions, analyses and
conclusions based upon this model cannot be validated. The applicant must address
this discrepancy, and, if the applied-for conditions were not modeled, provide a
reconstructed, reanalyzed hydrologic model.
11. Memo Items 9 and 11: From review of the AMEC report, there is no evidence that
effects of the silt storage ponds were included in the hydrologic model. Therefore, the p.
10 conclusions that "the aquifer system quickly returns to normal and there is little long-
term influence by the mining operations" are based upon an incomplete picture.
Additionally, the extent of mounding and shadowing created by the silt storage ponds
and the clay-lined pits was not quantified or mapped. Please resolve these deficiencies
by providing an accurate model that clearly depicts these impacts.
12. Memo Item 10, and AMEC, p. 9: The referred-to AMEC report provides snapshots of
mine dewatering impacts with output from the AMEC model reflecting ground water
surface elevations at the ends of Years 1, 10, 20, 30, and 40, for comparison with the
"baseline model." The Division needs to see the impacts to ground water, and to surface