2018-01-16_HYDROLOGY - M1983090

• Permit No: M1983090
• IBM Index Class Name: Hydrology
• Doc Date: 1/16/2018
• Doc Name Note: Approved SWSP
• Doc Name: Approved SWSP
• From: DNR Water Resources
• To: DRMS
• Email Name: ECS
• Media Type: D
• Archive: No

Poudre Pits Combined SWSP January 16, 2018
Plan IDs 3218, 3589 Et 4585 Page 3 of 10
Operational losses at the La Poudre and North La Poudre sites will consist of 2.20 acre-feet
of water for dust control, 12.50 acre-feet of water lost with 425,000 tons of aggregate, and 13.08
acre-feet of water for the production of 105,000 cubic yards of concrete (assumes 40 gallons of
water per cubic yard of concrete). The aggregate is mined below the water table and is washed;
therefore the water retained in the mined product is considered to be 4.0% of the mined material
by weight. Water for dust control and concrete batching purposes will be pumped from the West
Lake in the La Poudre site. Depletions from the La Poudre and North La Poudre Pits will impact the
Cache la Poudre River upstream of the Whitney Irrigation Ditch (WDID 0300930).
The Alluvial Water Accounting System (AWAS), which uses the Glover method, was used to
determine the lagged depletions to the Cache La Poudre River from past (since 1990) and projected
evaporation and operational losses at each site. The following parameters were used in the model
with the alluvial aquifer boundary condition: the distance (X) from the centroid of the exposed
ground water surface to the river; the width (W) of the aquifer on the side of the river where the
pit is located; the transmissivity (T); and the specific yield (S). The Glover parameters used for
each pit site are shown in the table below.
Table C - Glover Parameters (Evaporative/Operational Losses)
Site Name
X (ft)
W (ft)
T (gpd/ft)
S
Firestein/Tigges
1,112
8,000
120,000
0.20
La Poudre
West Lake/
Lee Parcel
512
4,800
50,000
0.20
Middle Lake
399
4,800
50,000
0.20
East Lake
626
4,800
50,000
0.20
North La Poudre
2,500
4,800
50,000
0.20
Dewatering
Dewatering has occurred at each pit over varying intervals from 1996 through 2015. The Lee
Parcel is the only site that is proposed to be actively dewatered during this SWSP period. In the
past, it was assumed that the pits were dewatered at a rate of 500 gpm with all water released
directly to the river. These assumptions have been revised to reflect the historic average
dewatering rate of 100 gpm where the majority (75%) of the water was recharged in the adjacent
pits with only 25% discharged directly to the river. This is based on a reevaluation of historic
operations by the operator's consultant and a December 20, 2012 letter from Mark Johnson,
Compliance Manager with Bestway Concrete and Aggregates as well as submitted pump
specifications and data showing the 100 gpm is a more accurate estimate than the previously
accepted 500 gpm. Mark Johnson described the recharge operation as occurring simultaneously
with dewatering in that the operator would discharge the water into an adjacent, previously mined,
cell. Once the cell being recharged exceeded its hydraulic capacity the water would then be
diverted directly to the river.
Dewatering operations at the Firestein Pit occurred from January 1996 through June 2001.
With the stated recharge that occurred, the lagged depletions to be replaced in 2018 equal 0.60
acre-feet. Dewatering operations at the Tigges Pit occurred from June 2005 through March 2012.
With the stated recharge that occurred, the lagged depletions to be replaced in 2018 equal 3.11
acre-feet. Dewatering operations at the Roberts Pit occurred from July 2001 until June 2006. With
Office of the State Engineer
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