2021-09-09_REVISION - M2004044 ‎(10)‎

• Permit No: M2004044
• IBM Index Class Name: Revision
• Doc Date: 9/9/2021
• Doc Name: Request For Amendment To Permit
• From: Aggregate Industries-WCR, Inc.
• To: DRMS
• Type & Sequence: AM2
• Email Name: JPL
• Email Name: JLE
• Email Name: AWA
• Media Type: D
• Archive: No

Potential Mining Impacts
Tucson South Resource Groundwater Modeling Study on the Hydrogeologic Effects of
Mining, prepared by Tetra Tech RMC dated August 2004 was submitted as a referral
response to DRMS August 3, 2004. The study is on record with the original application
and attached herein for reference. A groundwater monitoring and mitigation plan
was submitted to the Division as part of an adequacy response to Mr. Larry Oehler dated
November 22, 2004 (in pages 17 -19). The plan was reviewed and approved by the
Division as part of the original permit for the site. A copy of the approved Groundwater
Monitoring and Mitigation Plan is described below.
The hydrogeologic conditions have changed since the 2004 report. However, many of
the changed conditions were considered in the 2004 model. The Challenger Pit north of
the West Area has been reclaimed as a lined storage reservoir. The triangle-shaped
parcel north of the East Area has been backfilled with fines. The Greenhouses in the
northeast corner of the West Area and the small property located entirely within the East
Area are now owned by the City of Aurora and will be mined and reclaimed as part of the
water storage reservoir.
The 2004 report presented eight hydrogeologic scenarios that address the various
conditions and associated groundwater impacts of the for the life of Tucson South Mine.
Scenario 6 described on pages 9 and 10, illustrated on Figures 9 and 10, represent the
current conditions with two exceptions:
1. The wells at the Greenhouse property, now owned by Aurora, will be removed during
mining, and
2. A previously permitted area located south of Highway 7 will not be mined (in the
groundwater model this area was assumed to be wet mined. The net results are likely
minimal).
The changes due to the Aurora property and the absence of mining of the South cell do
not have a material impact on the model simulations.
The model indicates that after installation of the slurry wall, groundwater will mound up
to approximately six feet along the western and southern edges of the West Area. Given
the rise in groundwater level west of the slurry wall, the mining operations will not
increase seepage from the Brighton or Brantner ditches. Similarly, the model indicates
that there will be minimal rise in groundwater level south of the East Area. This is due to
the proximity of the South Platte River.
As mentioned above, Todd Creek Farms Metropolitan District#1 (Todd Creek) operates
several water supply wells between the South Platte River and the slurry wall of the East
Mine Area. Todd Creek is aware of the future slurry wall and has an agreement with Al
acknowledging the construction of the slurry wall and potential impacts to well yields.
Groundwater flows from south-southwest to north-northeast, roughly parallel to the
South Platte River. Consequently, there will be very little if any "shadow effect" (decline
in groundwater level) in the Morgan Smith Natural Area. The proximity of the River also
minimizes the impacts of groundwater levels in the Morgan Smith Natural Area.
The modeling (Scenario 6, Figures 9 and 10) indicates there will be a shadow effect
north of the mine in the narrow strip of unmined alluvial aquifer beneath Tucson Street.
Aggregate Industries—Tucson South Amendment—MLRB 112 Permit Application
Exhibit G-6