2021-04-05_HYDROLOGY - M2001085

• Permit No: M2001085
• IBM Index Class Name: Hydrology
• Doc Date: 4/5/2021
• Doc Name: Substitute Water Supply Plan
• From: DWR
• To: DRMS
• Email Name: JPL
• Media Type: D
• Archive: No

GSL Sand & Gravel Substitute Water Supply Plan  Page 2 of 5
April 5, 2021
February 2012. Beginning in November 2014 the Applicant began backfilling the pond which
reduced the exposed groundwater surface area from 26.7 acres to 16.05 acres. In December 2015
the exposed groundwater surface area was reduced from 16.05 acres to 10.06 acres and again
reduced to 3.06 acres by June 2018. As of September 2019, current exposed groundwater surface
area is 2.10 acres. It is assumed the 2.10 acre pond has existed since September 2019.

Net evaporative depletions were calculated using a gross annual evaporation of 45 inches from the
exposed water surface, with a credit of 10.8 inches for effective precipitation. The net depletion
of groundwater due to evaporation of groundwater exposed at the site has been calculated to be
6.00 acre-feet for the November 1, 2020 through October 31, 2021 period. The mining depletions
from January 2009 through October 31, 2022 are shown in attached Table 2.

The Alluvial Water Accounting System (“AWAS”) model was used with the alluvial aquifer boundary
condition option to lag depletions to the South Platte River. The following parameters were used
in the model:

Evaporative and operational losses were considered back to January 1, 2009. Total consumptive
use is 8.76 acre-feet per year for November 2020 through October 2021. Lagged evaporative and
operational depletions are 7.41 acre-feet for November 2020 through October 2021, as shown on
the attached Table 4. Dewatering depletions and accretions were also considered back to January
1, 2009.

Replacements

The replacement source for this plan period is fully consumable water leased from the City of
Aurora (“Aurora”). The fully consumable water will be released to the South Platte River at the
outfall of the Metro Wastewater Reclamation District’s Robert W. Hite treatment facility (“Metro
Sewer,” WDID 020070). Metro Sewer is located approximately 10.78 miles upstream of the site. As
such an irrigation season transit loss of 5.39% (0.5% per mile) and a non-irrigation season transit
loss of 2.7% (0.25% per mile) will be assessed on all releases. These transit losses are subject to
change by the Water Commissioner or Division Engineer. A copy of the signed lease agreement
dated April 4, 2019 is attached. The term of the lease is for the period of November 1, 2018
through October 31, 2019 and is renewable for up to five additional one-year extensions provided
by written notification from Aurora. The proposed replacement schedule is provided in attached
Table 6.

Long-term Depletions

The final reclamation plan for DRMS Mining Permit No. M-2001-085 once had been to create a
water storage reservoir through the installation of a slurry wall. The slurry wall was constructed
but did not receive its liner approval from DWR. Based on the Applicant’s statements, the slurry
wall leaked in multiple locations and the pit filled completely with groundwater. This was not in
accordance with their DRMS permit reclamation requirements. Therefore, the Applicant obtained
approval of an amendment to the reclamation mining permit from DRMS to allow for backfilling of
the pit.
Location  X – Dist to
river (feet)
W – Boundary
Dist (feet)
Harmonic
Transmissivity
(gpd/ft)
Specific yield
Gravel Mine (mining and
dewatering depletions)  2,295  3,836  63,000  0.2
Henderson Water Ski Lake
(recharge)  1,808  5,300  61,600  0.2