HYDRO27731

• Permit No: M1980183
• IBM Index Class Name: Hydrology
• Doc Name: HYDROLOGY TEXT PAGE 17 OF 23
• Permit Index Doc Type: Correspondence
• Media Type: D
• Archive: No

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GROUND WATER HYDROLOGY
INTRODUCTION
There are two potential impacts with the mining of
sand and gravel deposits that the proposed MCA 29
pit could have on ground water resources of the area.
These are: Lowering of the ground water table and
pollution of the ground water. It will be shown that
neither the lowering of the ground water table nor
pollution from the mining operations will have any
permanent effect on the ground water resources of
the area.
Ground Water Description
A number of registered wells were found within a
circle of 1/2-mile radius drawn around the center of
both Parcels A and B of the project area, as shown on
the Well Location Map, p.10 . It is possible other
wells not shown on the well location map exist in the
vicinity, but they are unlisted or nonregistered with
the State Engineer's Office. On the basis of 42
registered wells located within the 1/2-mile radii, of
which 32 are shallow alluvial wells, the median
depth to water level was determined to be about 23
feet. Test holes drilled on the MCA 29 site on April 7,
1979 through June 1980, indicate that the water
table ranges from 3 to 26 feet below the ground
surface elevation. The groundwater table elevations
at the project site range from about 4996 feet along
the extreme northwest portion of the proposed pit to
5014 feet, in the extreme southeast area of the
property, as shown on the Ground Water Contour
Map, p.18 . The test hole data confirms the general
southeast to northwest direction of ground water
flow established using data for the wells listed in the
Colorado Ground Water Basic Data Report No. 15
and field measurements of selected wells within the
1/2-mile radius of the site.
POLLUTION OF GROUND WATER
Since mining will be accomplished by the wet pit
method below the average existing ground water
surface in each parcel, no adverse effects on the
existing water quality within or in the vicinity of the
pit(s) will occur due to mining operations. The initial
mining phase above the water table, will not result in
any increase or different ground water
contamination, if any, than would be occurring as a
resulting normal runoff prior to mining. Sediment
from storm runoff will enter the pit but should settle
out within the confines of the pit as described in the
Surface Drainage Section. An NPDES Permit
Application has been made to The Environmental
Protection Agency and the Colorado Department of
Health.
Sanitary facilities will be provided during the mining
operation for the labor force.
GROUND WATER IMPACT
The mining operations are proposed to be operated
"in the wet ". This will not require dewatering of the
areas to be mined. The mining of the sand and gravel
deposit will be accomplished in two phases in each of
the two parcels A and B. The initial mining in Parcel A
above the water table will be accomplished by the
open pit method with "25 -foot setbacks and 3:1
(horizontal to vertical) slopes from the Parcel
boundaries down to the average water table
elevation of 5002 feet. At that point dragline
operations will commence. The remaining gravel
deposit will be mined by the wet pit method to the full
depth. The slopes will continue 3:1 (horizontal to
vertical) to 10 feet below the average existing water
surface of 5002 feet and 2:1 (horizontal to vertical)
from that point to the bedrock surface.
Similarily Parcel B will be mined in two phases. The
open pit method will be utilized down to the average
ground water surface of 5012 feet with 25 -foot
setbacks and 3:1 slopes. At that point wet pit
methods will be utilized with a dragline operation
removing the gravel deposit. The 3:1 (horizontal to
vertical) slopes will continue 10 feet below the
average existing ground water surface with 2:1
(horizontal to vertical) slopes from that point to the
bedrock surface.
The parcels will have different normal water surfaces
to minimize the impact of the mining operations on
the wells in the vicinity of the pits. The normal water
surface in Parcel B will average 5012 feet in
elevation. The normal water surface in Parcel A will
average 5002 feet in elevation.
As stated under the Description of Ground Water
Section all registered wells within a 1 /2 - mile radius of
the pit have been located as shown on the well
location map, p.10. All wells in the vicinity of the
proposed pit are at a relatively safe distance from the
proposed pit and should not be adversely affected by
any localized depression of the water table.
Considering the proposed normal water pool of
Parcel B will be at about 5012 ft. and the water level
in Mrs. Allen's well (the closest well to the mining
operation) is at an elevation of 5005.5 feet (measured
Dec. 10, 1979) the mining operations should not
have any adverse effects on the well.
As shown on the Ground Water Contour
Map, p.18, the existing water table generally slopes
from southeast to northwest. The proposed water
surfaces for each of the pits (Parcels A and B) will be
maintained at different levels to lessen the impact on
neighboring wells. The "averaging" of the water
surface in Parcel B at 5012 feet will cause the water
table along the extreme east and south perimeters of
that parcel to be lowered about 2 feet. The closest
well is about 150 feet from the south perimeter of the
proposed pit. At that distance the effect of the mining
operations should be less than 1 foot on the water
table in that well. The closest shallowwell to Parcel A
is more than 1,000 feet from the perimeter of the
proposed pit. As a result the "averaging" of the water
table in the pit due to wet pit mining operations at
5002 feet will not have any adverse effect on
neighboring wells.
The ground water flow through the project area will
not be altered after reclamation procedures are
completed. The resultant change in ground water
flow pattern will only have a localized effect near the
perimeter of the pit as explained earlier and will not
affect the regional ground water flow patterns either
during mining or after reclamation of the area with
permanent reservoirs. However, a ground water
table monitoring program will be instituted prior to
gravel extraction to insure the vicinity water users
will no be materially injured. The monitoring of
ground water levels will continue until the mining
and construction begins. At the time the mining and
construction operations begin, an accelerated
localized monitoring program will begin. Sufficient
readings will be made depending upon the operation
being initiated. Should any adverse effect be
detected, corrective action will be determined and
implemented appropriately.
SURFACE DRAINAGE
INTRODUCTION
The mining and subsequent reclamation of the
proposed mining site near 132nd Avenue and Nome
Street will have no adverse effects on local or
regional drainage. No increase in surface runoff
exiting at the site will occur, because the mine and
the resultant permanent reservoirs will provide
sufficient storage to control incoming runoff.
The proposed mineral conservation area is not
located within the present one - percent frequency
flood plain of the South Platte River.
HISTORIC SURFACE DRAINAGE
The Historic Surface Drainage Map,
p.19 describes existing drainage patterns within
MCA 29. Within Parcel A the drainage generally
flows westward from Nome Street toward Brighton
Road. An existing gravel pit, located near the
southeast corner of Parcel A, detains a small portion
of runoff originating within Parcel A, as well as a
portion of runoff which enters the site from the area
to the east of Nome Street. Any discharge from this
gravel pit would exit from the northwest corner of the
pit. Practically all of the runoff originating from Parcel
A exits the site through a 24 -inch, concrete - encased,
corrugated metal culvert pipe beneath Brighton
Road, located 1,100 feet from the southwest corner
of Parcel A. The irrigation ditches within Parcel A,
also shown on the Historic Surface Drainage Map,
P-19 , assist in the carrying of runoff westward
toward the culvert under Brighton Road. The
remaining and smaller portion of runoff originating
from Parcel A exits the site at the intersection of
132nd Avenue and Brighton Road. Runoff from
Parcel A eventually reaches the South Platte River,
located 1,000 feet to the west of MCA 29.
The majority of surface runoff from Parcel B flows
toward the northeast corner of Parcel B, from which it
then flows into a gully in the 14 -acre tract between
Parcels A and B. This portion of runoff from Parcel B
then flows through the southwest corner of Parcel A,
eventually exiting MCA 29 through the above -
referenced 24 -inch culvert pipe beneath Brighton
Road. A smaller portion of runoff from Parcel B,
generally originating within 300 feet of the west
property line of Parcel B and from the northwest
corner of Parcel B, flows into an existing gravel pit,
located in the northwest corner of Parcel B. This
gravel pit has sufficient storage so that none of the
runoff entering the pit from Parcel B leaves MCA 29
by surface flow.
In addition to the surface runoff originating within
Parcels A and B, runoff from a major storm would
enter the site from a total of 290 acres which are
generally located to the east of Parcels A and B, and
to the west of Parcel B. Practically all of the runoff
from these 290 acres would exit MCA 29 through the
24 -inch culvert under Brighton Road.
EXISTING IRRIGATION DITCHES
Historically, various crops on both Parcels A and B
have been irrigated by surface water provided by the
Fulton Ditch, whichis shown on the Historic Surface
Drainage Map, p.19 , Parcel A received water from
Fulton Ditch from a lateral ditch which entered Parcel
B at a point approximately 400 feet north - northeast
of the southeast comer of Parcel B. The lateral then
followed the eastern boundary of Parcel B and
crossed the 14- acre.tract lying between Parcels A
and B, eventually diverging into several smaller
ditches within Parcel A.
Fulton Ditch water frrmerly entered Parcel B directly
by means of a headgate located approximately 450
feet northeast of the southwest corner of Parcel B.
From this point a series of field ditches carried
irrigation water to tie majority of Parcel B.
It is noted no land beyond MCA 29 is irrigated by the
irrigation ditches which are located in MCA 29, other
than the 14 -acre tract between Parcels A & B. The
owner of the 14 -acre tract has retained ownership of
ten shares in the Fulton Ditch. The irrigation ditch
which lies along the western side of Nome Street and
carries water northnrard to the 14 -acre tract will be
left intact during and following mining operations so
that the owner may exercise her rights to use her
shares of the Fulton Ditch on the 14 -acre tract.
SURFACE DRAINAGE DURING MINING
OPERATIONS
Surface drainage within MCA 29 will be altered
somewhat during mining operations. Since the
mining of MCA 29will be accomplished "in the wet"
and in phases, there will be a body or bodies of water
during mining operations. The mine itself will serve
as a detention basin, allowing for temporary storage
of surplus runoff to the mine and also allowing for
adequate sedimentation of any waters which may
need to be removed from the mine. Although most of
the surface runoff to the mine is expected to be
removed naturaIlybypercolation to existing sand and
gravel formations adjacent to MCA 29, the need may
arise to pump such surplus runoff from the mine. Any
pumpage from the mine will eventually be
discharged to the local exterior surface drainage
systems via the 24" culvert beneath Brighton Road
and will only be allowed to occur after other local
runoff has subsided so that local runoff conditions
will not be adversely affected.
ULTIMATE PLAN OF SURFACE DRAINAGE
After removal of the sand and gravel deposits from
MCA 29, the property will be graded as shown in the
Final Configuration Plan, p.22 . MCA 29 will be
formed into two separate reservoirs which will have
sufficient capacity to store the runoff from the 100 -
year storm with no resultant discharge to local
surface drainage systems. It is noted that the Final
Configuration Plan makes allowances for
development of approximately 16 acres for
commercial - industrial purposes and approximately 8
acres for residential use.
The permanent reservoir in Parcel A is expected to
have a normal water surface elevation of 5,002 feet.
Beginning at a setback distance of 25 feet from the
property line or from rights -of -way, the, reservoir will
partially have side slopes on one vertical to three
horizonal.The3:1 side slope will continue downward
to elevation 4992, which is a vertical distance of ten
feet below the normal water surface elevation. From
elevation 4992 downward to the bottom of the pit, the
side slopes will be one vertical to two horizontal.
After the period of mining during which various fine
materials will seal the northern perimeter of Parcel B,
the normal reservoir level in the reservoir within
Parcel A is expected to stabilize at Elevation 5,012. A
side slope of 3:1 will extend from the setback line to
Elevation 5002, and from Elevation 5002 to the
bottom of the pit, the slope will be 2:1.
Both the duration and intensity of a storm are
important considerations in analyzing the effects of a
reservoir on local surface drainage. Since the
reservoirs have substantial storage, the duration of
the 100 -year storm was taken to be twenty -four
hours. Rainfall from the twenty -four hour, 100 -year
storm was estimated to be 3.40 inches, based on the
report, Urban Storm Drainage Criteria Manual,
prepared for the Denver Regional Council of
Governments. The corresponding depth of runoff
was estimated to be 0.58 inches, based on estimated
infiltration and detention /depression losses of 0.08
inches per ten minutes and 0.55 inches, respectively.
The relatively high value for detention /depression
losses is based on flat topography and the storage
effects of the U.S. Highway 85 and Union Pacific
Railroad embankments to the east of MCA 29.
The 100 -year volume of inflow to the Parcel A
reservoir was estimated to be 29.1 acre -feet,
consisting of 11.5 acre -feet of runoff from a total of
238 acres draining into the reservoir, and 17.6 acre -
feet of direct rainfall falling on the reservoir's surface
area of 62 acres. Assuming that no outflow would
occur under the 100 -year storm, the reservoir level
would rise to Elevation 5002.5 Since the invert of the
existing 24" culvert beneath Brighton Road lies at
approximately Elevation 5004 feet, no surface
discharge from the reservoir in Parcel A is expected
to occur during the 100 -year storm. Following any
storm, including the 100 -year storm, runoff to the
reservoir will be temporarily detained and then will
percolate through existing sand and gravel formation
to the South Platte River.
A further analysis of the Parcel A reservoir was made
which assumed that 100% of the 100 -year rainfall
would be effective in producing runoff. Under this
assumption, a total inflow to the reservoir of 85 acre -
feet would occur. With no outflow from the reservoir,
the reservoir level would rise to Elevation 5003.4
feet. Therefore, no surface discharge from the
reservoir in Parcel A is indicated under this extreme
condition, since the invert elevation of the existing
24" culvert is 5004 feet.
With respect to the reservoir in Parcel B, the
estimated volume of inflow underthe 100 -year storm
is 15.0 acre -feet. This volume consists of 4.2 acre -
feet of runoff from the 86 acres which drain into the
reservoir, and 10.8 acre -feet of direct rainfall on the
reservoir's surface area of 38 acres. As there will be
no surface drainage outlet for this reservoir, the
reservoir level is expected to increase to Elevation
5012.4 during the 100 -year storm. If 100% of the
100 -year rainfall were to result in runoff, a total
inflow of 35.1 acre -feet would occur, causing the
reservoir level to increase to Elevation 5012.9 feet.
Under either circumstance the reservoir in Parcel B
will have sufficient detention storage so that no
surface discharge will occur. Temporarily detained
runoff will percolate tothe South Platte Riverthrough
existing sand and gravel formations.
Since there will be no surface discharge from either
reservoir under conditions at least as severe as the
100 -year storm, the plan for final reclamation of the
project will not aggravate local flooding. The plan for
final reclamation will actually result in a lesser
degree of local flooding by retaining all of the runoff
which enters the reservoir, including that which
would have passed through the property under pre -
mining conditions. This storm waterwill not be lostto
the South Platte River basin but will percolate to the
river through the sands and gravels existing between
the mine and the river itself.
FLOOD HAZARD INFORMATION
The South Platte River flood plain immediately west
of MCA 29 has been defined in a report„ entitled
"Flood Hazard Area Delineation, South Platte River,
Adams County," prepared for the Urban Drainage
and Flood Control District and the Colorado Water
Conservation Board, dated September 1977.
According to this report, the one - percent frequency
flood plain of the South Platte River lies completely to
the west of Brighton Road in the vicinity of MCA 29.
The only location where the one - per -cent flood could
encroach upon MCA 29 is at the existing 24 -inch
culvert beneath Brighton Road, approximately 1,100
feet northeast of the southwest corner of Parcel A.
Based on the above - referenced report, the one -
percent frequency flood elevation of the South Platte
River at the 24" culvert is 5003.7. According to a 2-
foot contour interval topographic map prepared for
Brannan Sand and Gravel Company, the minimum
surface elevation of Parcel A near the 24 -inch culvert
is no lower than 5004. Therefore, no flood hazard
from the South Platte River exists.
WATER RIGHTS
The irrigation ditches which currently provide water
for agricultural purposes within MCA 29 enter Parcel
A from its southeast corner along Nome Street and
enter Parcel B directly from a headgateon the Fulton
Ditch (refer to Historic Surface Drainage
Map), P. 19.No laterals within the proposed mining
area extend beyond the mining area to serve other
lands, except for the 14 -acre tract between Parcels A
and B. The ditch which supplies water to the 14 -acre
tract will be kept intact during and following the
mining operations so that the 14 -acre tract may
continue to be irrigated. Therefore, the mining of
MCA 29 does not adversely affect local water rights,
and no ditches need to be relocated or restored after
final reclamation.
THE BSUNI1'bPF SAND & GRAVEL CQ.'
H1**1310L0C;1 TEXT
Pem,it Number yy71009 -4.
Class: OPermit
_Section
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! Class: O Revision
Type /Seq : _
Clan: O RepprtA ydro OGeneral
Doc Type: -0 y_LLIZ Q ' 1 -__
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Applcati n ( I only) ABid nroemnt O Inspection
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