HomeMy WebLinkAbout20040099.tiff n
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GROUNDWATER EVALUATION
FOR PROPOSED HEIT
AGGREGATE OPERATION
WELD COUNTY, COLORADO
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I
' Prepared for:
Banks and Gesso, LLC
720 Kipling, Ste. 117
Lakewood, CO 80215
WWE
Wright Water Engineers, Inc.
fel MARCH 2003
021-110.030
2004-0099
�-. TABLE OF CONTENTS
Page
1.0 INTRODUCTION/PURPOSE 1
2.0 STUDY AREA DESCRIPTION 1
3.0 PROPOSED MINE PLAN 3
4.0 STUDY METHODS 3
4.1 Model Setup 3
4.2 Model Results • 4
4.2.1 Baseline Run 5
4.2.2 Run With Proposed Pit 5
5.0 DISCUSSION 5
6.0 RECOMMENDATIONS FOR MITIGATION OF IMPACTS 6
7.0 REFERENCES 7
TABLES
1 Proposed Wells Near Heit Pit End of Report
FIGURES
1 Vicinity Map End of Report
2 Baseline Run Groundwater Elevations End of Report
3 Change in Groundwater Elevations with Proposed Pit End of Report
DRAWINGS
1 Existing Conditions and Proposed Mine Plan End of Report
-- GROUNDWATER EVALUATION FOR PROPOSED HEIT AGGREGATE
OPERATION, WELD COUNTY, COLORADO
1.0 INTRODUCTION/PURPOSE
This report, which was completed by Wright Water Engineers, Inc. and Calibra Consulting, LLC,
presents the results of an evaluation of potential effects on groundwater and nearby water wells
from proposed mining of the Heit Pit in Weld County. Water wells on the Aquatic and Wetland
Company (AWC) nursery immediately to the north are addressed, in particular. This report was
prepared based on our proposal to you dated December 13, 2002.
This evaluation is based on information provided by Banks and Gesso, LLC on the nature of the
proposed project, review of existing information for the project area, observations of the study
area, and our experience with similar projects in the past. A limited amount of field data was
reviewed for this study, and no additional field measurements were specifically taken. The
results of this evaluation may change based on collection of additional site-specific information.
2.0 STUDY AREA DESCRIPTION
The proposed Heit Pit property consists of approximately 110 acres located in the E 1/2 of
Section 13, T. 2 N., R. 67 W. in Weld County. Figure 1 is a vicinity map of the property.
Figure 1 shows the property boundary, proposed limits of mining, and features relevant for this
study in the vicinity of the property. The South Platte River is located to the east of the site, with
the closest point of the river approximately 200 feet from the proposed pit. A residence and
small lake (likely a reclaimed aggregate pit) are present east of the site. Another small lake
associated with another residence exists southwest of the property. The Lupton Meadows Ditch,
which parallels Little Dry Creek, flows immediately west of the site, and the Meadow Island
Ditch is a short distance to the west. Wetlands exist along both of these ditches. The Koenig Pit,
which was reportedly lined with a slurry wall and excavated by Weld County, exists immediately
to the south of the proposed Heit Pit.
021-110.030 Wright Water Engineers, Inc. Page 1
March 2003
Groundwater Evaluation For Proposed Heit Aggregate Operation
Weld County, Colorado
A nursery owned and operated by AWC exists in Section 13 immediately north of the Heit
Property. Two water supply wells are associated with the nursery: Permit No. 55792-F is a
shallow well with a reported yield of 20 gallons per minute (gpm), which is located a distance
north of the proposed pit; Permit No. 50354-F is for a higher yielding well (250 gpm) that is
located immediately north of the proposed mine (Drawing 1). The focus of this investigation is
on the latter well due to its proximity to the pit and higher permitted yield. The owner of the
wells has expressed concerns with possible impacts from mining of the Heit pit. The
characteristics of the two wells are shown in Table 1, and the locations of the wells are indicated
on Drawing 1.
Most of the subject property (and the area proposed for mining) consists of a flat, fallow
agricultural field. An area of native vegetation exists on a terrace on the west portion of the
property where the Lupton Meadows Ditch is located. This terrace is two to three feet lower in
elevation than the agricultural field immediately to the east. Based on field observations,
wetlands exist in portions of this lower terrace.
According to the Soil Survey Weld County, Southern Part (SCS 1980), the agricultural field
consists of Altvan loam and Dacono clay loam. Altvan loam is described as a deep, well drained
soil on terraces of old alluvium. Dacono clay loam is described as a deep, well drained soil
formed from mixed alluvium. The soil on the western portion of the property where the
irrigation ditches are located is Aquolls and Aquents, which are deep, poorly drained soils
formed in alluvium with a high water table. This mapping unit may support wetlands.
The Geologic Map of the Platteville Quadrangle, Weld County, Colorado (Soister 1965) shows
the site as being underlain by the alluvium of the South Platte River. The property is included in
the area addressed in the study Hydrogeologic Characteristics of the Valley-Fill Aquifer in the
Brighton Reach of the South Platte River Valley, Colorado (Hun, et al 1972) which shows the
saturated thickness of the alluvium to be around 30 feet. This report identifies the direction of
alluvial groundwater flow to be to the north/northeast in the study area.
021-110.030 Wright Water Engineers, Inc. Page 2
March 2003
Groundwater Evaluation For Proposed Heit Aggregate Operation
Weld County, Colorado
3.0 PROPOSED MINE PLAN
It is proposed to mine the approximately 80 acres of the property that is the agricultural field.
The limit of proposed mining is shown on Figure 1. Prior to mining, a slurry wall will be
constructed to bedrock around the mine area. The slurry wall will limit inflow into the pit during
mining, but some pumping will be needed to keep the excavation dry. It is assumed that the
water pumped from the pit will be discharged off the site. The lined vessel will be used for water
storage at the cessation of mining.
In addition, several acres in the northwest corner of the property may be mined. If this is done,
no slurry wall or lining will occur at the excavation.
4.0 STUDY METHODS
A two-dimensional, steady state, finite-difference model of the study area was developed using
the U.S. Geological Survey's (USGS) MODFLOW-2000 program to represent the groundwater
flow through the shallow unconfined alluvial aquifer in the vicinity of the proposed gravel pit.
The goal of the modeling was to determine the potential impacts to the groundwater flow system
from construction of the slurry walls surrounding the pit. There is little information available
regarding the existing groundwater flow system, and the resulting model should be considered to
be at a conceptual level only. Further information is needed to develop a more refined model of
the system, as discussed below.
4.1 Model Setup
The horizontal extent of the model was determined by the definition of boundary conditions
using the data available from the USGS (Hun, et al 1972). This report shows the extent and
thickness of the alluvial material and the elevation of the water table in 1969. While it is
recognized that the water table of the alluvium varies in response to climatic conditions, the data
in Hun, et al (1972) was considered appropriate for this level of study.
r�
021-110.030 Wright Water Engineers, Inc. Page 3
March 2003
Groundwater Evaluation For Proposed Heit Aggregate Operation
Weld County, Colorado
The model grid is bounded by the extent of the alluvium to the west, the 4,860-foot water table
contour to the south, the centerline of the South Platte River to the east, and the 4,840-foot water
table contour to the north. A uniform cell size of 50 feet in both horizontal directions results in a
grid with 280 rows, 259 columns, and approximately 24,000 active cells.
The bottom of the aquifer was set to the bottom of the alluvial material (See Figure 1). A
number of points along the contours defined by Hun, et al (1972) were used as a data set, which
was then interpolated to the MODFLOW grid.
The north, east, and south boundaries of the model are represented as specified-head boundaries.
The north and south boundaries were assigned elevations of 4,840 and 4,860 feet, respectively,
along their entire lengths. The head along the east boundary varied linearly between the 4,840-
and 4,850-foot contours and between the 4,850 and 4,860-foot contours on the west side. The
shape of the water table contours on the west side of the model indicates that there is some
recharge occurring from the western boundary. This boundary was therefore represented in the
numeric model using the General-Head Boundary Package; the head was set 10 feet above the
water table and the conductance was varied until the simulated water table elevations roughly
matched the observed elevations. Also, it was assumed in all runs that 10 percent of the average
annual precipitation of 15 inches recharges the alluvial aquifer.
Lastly, it is assumed that the slurry wall that will be installed prior to removal of the aggregate
will form an impermeable barrier surrounding the pit. Thus, the proposed pit and the existing pit
to the south were represented as no-flow boundary conditions.
4.2 Model Results
Two different conditions were considered in this study. First, a baseline run was performed to
match the water table elevations of Hun, et al (1972). Once the model adequately represented
the conditions of Hun, et al, the water well to the north of the Heit Pit(Permit No. 50354-F) was
included in the model and a base run was conducted. The well was inserted at column 167 of
row 151 and was assigned an extraction rate of 125 gpm, which assumes that the well produces
021-110.030 Wright Water Engineers, Inc. Page 4
March 2003
Groundwater Evaluation For Proposed Heit Aggregate Operation
Weld County, Colorado
250 gpm for 12 hours a day. Next, the proposed pit was included as a no-flow boundary and the
model was run using the results from the base run as a starting point.
4.2.1 Baseline Run
The simulated water table elevations for the base run are shown in Figure 2. The pit to the south
forms a barrier to groundwater flow and the water table elevations are slightly higher to the south
and lower to the north.
•
4.2.2 Run With Proposed Pit
The simulated water table elevations for the condition representing the proposed pit are shown as
the deviations from the baseline run in Figure 3. From this, it can be seen that construction of the
pit reduces water table elevations to the north of the proposed pit by approximately 3.0 feet, and
increases the water table by approximately 2.0 feet on the southwest corner of the pit. At the
location of the AWC well (Permit No. 50354-F), the water table elevation is approximately 2.2
feet lower than the baseline run. This represents slightly less than a 10 percent decrease in
saturated thickness for the well.
5.0 DISCUSSION
The modeling conducted for this evaluation indicates that construction of the proposed pit will
have a minimal impact on water levels at the well owned by AWC immediately north of the
proposed pit. The projected lowering of the water table by 2.2 feet represents less than 10
percent of the estimated saturated thickness of the well and is likely within the range of expected
natural water table fluctuations. The relatively small decrease in water levels is due to the
permeable nature of the alluvium, which is sufficient to maintain water levels and the yield of the
well even with contributions from the aquifer to the south blocked by the proposed slurry wall
around the pit.
•
021-110.030 Wright Water Engineers, Inc. Page 5
March 2003
Groundwater Evaluation For Proposed Heit Aggregate Operation
Weld County, Colorado
The modeling focused on the well immediately north of the proposed pit, which is the well most
likely to be affected by the pit. However, the modeling results (Figure 3) indicate that the
proposed pit should have minimal effect, if any, on other water wells in the area.
The modeling and conclusions in this study are based on a limited amount of site-specific
information. The model could be refined through incorporation of additional data from the site
and surrounding area and calibrated based on observed water levels.
An unlined excavation in the northwest corner, as may occur, was not included in the modeling.
If the applicant decides to excavate this area, the resulting pit would be relatively small
(≤ 7 acres.) This excavation would not be expected to have any significant effect on groundwater
levels in the area due to the relatively flat slope of the water table. Groundwater would be
increased slightly north of the excavation and lowered slightly south of the excavation due to
"lake leveling" effects of the pit.
6.0 RECOMMENDATIONS FOR MITIGATION OF IMPACTS
This study found that the proposed Heit Pit should not have a significant effect on water wells on
the AWC nursery or in the vicinity of the operation, so measures to mitigate impacts from the pit
are not warranted. However, it is recommended that water levels be measured in the wells on the
AWC nursery and any other wells of concern in the area prior to and during construction of the
pit. This is recommended in order to establish pre-mine groundwater levels in the wells
(especially under the current drought condition) and to assess any potential impacts from the
proposed pit.
021-110.030 Wright Water Engineers, Inc. Page 6
March 2003
7.0 REFERENCES -
Hun, R.T. and P.A. Schneider, Jr. 1972. Hydrogeologic Characteristics of the Valley-Fill
Aquifer in the Brighton Reach of the South Platte River Valley, Colorado. Open File
Report. Denver, CO: U.S. Geological Survey.
Soister, P.E. 1965. Geologic Map of the Platteville Quadrangle, Weld County, Colorado.
Geologic Quad 399. Denver, CO: U.S. Geological Survey.
U.S. Department of Agriculture, Soil Conservation Service (SCS). 1980. Soil Survey Weld
County, Southern Part. Washington, DC: Government Printing Office.
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021-110.030 Wright Water Engineers, Inc. Page 7
March 2003
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TABLE 1
Permitted Wells Near Heit Pit
Per Colorado State Engineer's Office Well Permit Records
Permit Permittee Location Well Well Appropriation Use
Number Otr/qtr Sec. Twn. Rng N/S EMI Depth Yield
_ Distance Distance (ft) (gpm) _ (AF) _
557924 John Windel5Lauranne Rink NW/NE 13 _ 2N 67W 300N 2550E 20 2 Commercial,irrigation,piscatorial,recreation and Incidental evaporation
72389 Wiliam and Georgia barges SW/SW 13 2N 67W 12865 990W 100 15 1 Domestic
38366 Jimmie Freeman SW/SW 13 1N 87W 150N 600W 44 20 Domestic —
231762 Quality Living Homes SE/SW 12 2N 67W 100S 1420W 60 16
6222-RF Eugene Wagner SW/NW 13 2N 67W 48
124264-A Ronald Martinez SW/SE 13 2N 87W 50 15
114644 Chides Bueno _SW/SE 13 2N 67W 40 15 1 Household Use-Permit Expired
124265 Ronald Martinez _SW/SE 13 2N 87W 1100S 2850W 27 5 1 Domestic
_
9722 Jesse Koenig SW/SE 13 2N 67W 25 15 Domestic
_
16464-F Jess Koenig SENSE 13 2N 87W 28 800 Irrigation '
9496 Casper Heft NE/SE 13 2N _ 67W 28 45 Domestic
20136 Casper end Ann Pitt _NE/SE 13 2N 67W 46 1950 Irrigation
41068-F Robert Stahl NW/SW 18 2N 66W 2200S 300W 520 35
167564 Ft.Lupton Fire Prot.Dist. NW/SW 18 2N 66W 15 250 1 Emergency Fire Protection-Permit applica6 on
57967-F Weld County NE/NW 19 - 2N 66W 25 Beason Gravel Pit
56261-F Weld County NE/NW 19 2N 66W 25 Beason Gravel Pit
177555 Marvin Hein NW/NW 19 2N _ 66W 440N 230W 512 15
224180 Robert Alrhart _NW/NE 24 2N _ 67W 270N 2580E 28 20
54659 80 16
174064 Richard Hein SW/SW 18 2N 66W 80N 230W 40 15
630-RR R-J.Vincent Estate SW/SW 12 2N 67W 50 130 _
50354-F John Wlndeli/Leunnne Rink SE/NE 13 2N - 67W 1945N 320E 26 250
117433-A Eugene Wagner NE/NW 13 2N 67W 50 _ 30 Domestic and livestock
Banks and Gesso
Summary Wright Water 200ineers,Inc Des,by GDW
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Figure 3 Change in Groundwater Elevations with Proposed Pit
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