HomeMy WebLinkAbout20112203.tiff Varra Companies, Inc.
Office of Special Projects
1431 East 16th Street Greeley,Colorado 80631 Telephone(970)353-8310 Fax(970) 353-4047
Thursday 4 August 2011
Weld County Clerk to the Board
91510`h Street, 3`d Floor
Greeley,Colorado 80632
Subject: Varra Companies, Inc. - Kurtz Resource and Land Development Project- Regular
Impact (112)Technical Revision Application—TRACT C—Permit M1999-006
Materials submitted to the Colorado Division of Reclamation Mining and Safety (CRMS) -Office
of Mined Land Reclamation (OMLR):
• Correspondence of 3 August 2011 and attending maps and attachments.
ATTACHEMENTS:
• Proof of Placement - Weld County Clerk to the Board
• Technical Revision - Map revised.
• C.G.R.S. Hydrogeologic Evaluation Report of October 2007.
Your signature below acknowledges receipt of the above referenced material, as attached. The
material should be added to the above referenced Application, as originally submitted to the Weld
County Clerk to the Board,and made accessible for public review.
Received On jO[,t ti • y , 2011
By: rnt ,(X.tz411! „,
Office of the Weld County Clerk to the Board of County Commissioners
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7-to - t 1 2011-2203
Varra Companies, Inc. KURTZ RESOURCE AND LAND DEVELOPMENT Project I
OMLR Techncial Revision—TRACT C—M1999-006 July 2011
Varra Companies, Inc.
Office of Special Projects
8120 Gage Street Frederick,Colorado 80516 Telephone(970) 353-8310 Fax(970) 353-4047
Wednesday 3 August 2011
To: Michael Cunningham, E.P.S.
Colorado Division of Reclamation Mining and Safety
Office of Mined Land Reclamation
1313 Sherman St., #215
Denver, CO 80203
From: Varra Companies, Inc.
Bradford Janes, Forester ` C° z' Y" (-`7-"
Subject: M-2009-006 Kurtz Resource Recovery & Land Development Project -
Technical Revision - TRACT C - Reply to the Colorado Office of Mined Land
Reclamation (OMLR) Preliminary Adequacy Review correspondence of 25 July
2011.
Dear Michael:
For greater continuity and ease of reference, we have iterated your comments
necessitating a reply according to its respective item, iterated in a graphical
box, with our comments in blue following:
6.4.7 Exhibit G - Water Resources
1. Please confirm if your current discharge permit covers the additional
discharge points associated with the dewatering of Tract C. If the discharge
permit does not cover the additional dewatering points, then you must commit
to obtaining a revised CDPS General Permit authorizing the addition of
outfalls and submitting the revised permit to the Division prior to commencing
dewatering of Tract C.
Varra Companies, Inc. will maintain its existing CDPS General Permit reflecting
the existing discharge point 009, or subsequently with any necessary revisions
reflecting alternative discharge point locations and relocations prior to the use
of those alternative locations. Only one outfall is planned at any given time for
Tract C at any point in time. Discharge Point DPC. will be the designated active
point of discharge at this time. Revised permits or other authorization from
1
CDPS for the alternative locations will be provided to the OMLR prior to the
dewatering of Tract C at those locations, should that be necessary.
2. The Applicant has stated two discharge points may be used to dewater Tract
C. Please clarify the location of the discharge points and revise the Mining
Plan Map as needed. In addition, please describe the dewatering set-up in
detail.
The locations were shown on the existing maps in the orange triangles, and
labeled 009 and DPC, respectively. Point 009 is the existing approved location,
and point DPC is an alternative point. An additional alternative point (DPC-3) is
shown on the revised extraction plan map, included with this submittal.
3. The Applicant has stated groundwater will be discharged into the pond
immediately north of Tract C. Please provide the following information:
a. Describe the source of water in the pond.
b. Describe approximate total volume of the pond.
c. Describe the inflow/outflow structures of the pond.
d. Provide a brief explanation of how the ponds has historically been used to
manage water flows through the area.
e. What permits, if any, does the Army Corps of Engineers require for
discharging water to the wetlands north of Tract C?
f. Will groundwater undergo settling in temporary basins prior to being
discharged into the pond? If so, please describe how the temporary
basins will be constructed and provide their location on the Mining Plan
Map.
a. What we suspect is an old SCS Conservation Farm Pond north of Tract C
receives tailwaters and irrigation tail waters from the Last Chance Ditch.
Irrigation and return irrigation from the former crop lands within Tract C
flowed directly into the farm pond, where water levels were managed by a
mechanical gate installed in the western end of the pond, releasing waters
into an established draw that is presently vegetated with wetland species.
h. The pond is estimated to be approximately 0.95± acres in size in its
current wetted state with a potential depth of approximately 4.0± feet
mean depth and at approximately 1.45± acres of surface exposed water.
When full the pond would hold approximately 252,E 4Hcu.ft. of water x
7.48gal/c u.ft. water = 1,889.807.() gallons of water when full.
Varra Companies, Inc.-M-2009-006 July 2011 Technical Revision 2
Kurtz Resource Recovery &Land Development Project Correspondence of 3 August 2011
c. Inflow is from an existing field irrigation trench leading into the pond at its
southeast corner near the estimated location of discharge point DPC
located in the northeast corner of Tract C. Outflow is through an existing
irrigation gate located in the western end of the pond, at the location
shown on the revised extraction plan map.
d. Again, this is an old farm pond that historically receives and returns
irrigation waters from the farm land now planned for extraction and
identified as Tract C. Excess waters are released from an established
gate into an established draw where waters could be further directed to
irrigate the lower wet meadow pastureland, that is also occupied by
wetland species of vegetation, and delineated as wetlands with the Army
Corps of Engineers. The waters eventually make their way north to an
existing unnamed brook that runs west to east parallel to and eventually
emptying into into St. Vrain Creek just as the Creek turns north and
crosses Colorado I Iighway 66.
e. The waters have historically been directed into the draw and wetland
meadow to the north of the farm pond. We are unaware of any
restrictions identified by the Army Corps in this regard.
f. The water to be discharged into the farm pond are essentially clear
groundwaters pumped directly into either an established or excavated and
erosion filtered ditch and into the farm pond. No prior settling is
anticipated as necessary at this time.
4. The Applicant has not addressed how dewatering may potentially impact the
adjacent wetlands in this Technical Revision or in the original submittal. It
may be that this information was omitted in the original Reclamation Permit
Application since it was not evident if Tract C would be mined at the time of
the submittal. In order for the Division to determine that the potential
impacts to the hydrologic balance will be minimized, the Applicant must
provide additional information demonstrating what the impacts could be and
how they will be mitigated. This will likely involve gathering existing data or
obtaining new data in order to construct some modeling that will protect the
behavior of the surface and groundwater regimes once mining has reached its
maximum disturbance. In addition, once these projections have been made,
there should be a plan which will quantify the damage threshold that will
initiate remedial actions and what those remedial actions will be.
At the time of our permitting of the removal and correlated wetland creation to
offset removal of the seep ditch in Section 28, C.G.R.S. provided an impact study
for any planned extraction of the Tract C area, labeled Tract B, but
encompassing the same area. The Tract B area was slightly larger as it didn't
Varra Companies,Inc. -M-2009-006 July 2011 Technical Revision 3
Kurtz Resource Recovery&Land Development Project Correspondence of 3 August 2011
•
account for a second oil and gas well, so the existing proposal now labeled Tract
C is slightly smaller than that imagined in the October 2007 study, and
consequently will have even less potential for impacting surrounding lands.
In this instance, wetlands will be recharged during the extraction process by the
waters leaving the existing pond at the established irrigation gate on the west
end. Additionally. much of the delineated wetland is established from surficial
flows from the Last Chance Irrigation waters in the natural tributary entering the
wetmeadow pasture from the southeast. Subsequently, activities are not
anticipated to adversely impact wetland groundwater levels due to the surficial
recharge related to discharge waters from Tract C entering the pasturelands
from the established pond irrigation gate.
As a fall back, three tensiometers will he established within the root zone of the
wetland vegetation west of the influence from the established pond and below
Tract C as shown on the Revised Extraction Plan Map. The tensiometers will be
placed within the upper two feet of the solum as a minimum, or otherwise if
deeper, to the extent of the majority root zone. The tensiometers will indicate
field capacity during the growing season and will be monitored on a weekly
basis.
If field capacity is lost at any two tensiometer locations within four consecutive
weeks during the growing season then supplemental surficial irrigation of the
affected area will be introduced to the location of wetland vegetation, not
otherwise watered by the Last Chance Ditch tributary to the east, until field
capacities are restored and maintained for an equivalent period of four
consecutive weeks as determined by placed tensiometers.
5. How many pumps will be used to dewater Tract C? Please provide the
location of the pump(s) on the Mining Plan Map.
Only one pump will he utilized. The pump will be established along the northern
boundary of Tract C, and the waters will make their way through either
established, improved, or created ditchworks along the northern boundary of the
Tract until it exits at point I)PC, shown as an orange triangle near the northeast
corner of the Tract and immediately south of the established farm pond. The
actual location of the pump will he updated in the required Annual Report.
6.4.12 Exhibit L - Reclamation Costs
Varga Companies, Inc. - M-2009-006 July 2011 Technical Revision 4
Kurtz Resource Recovery& Land Development Project Correspondence of 3 August 2011
6. The determination of the financial warranty for this site is based on using a
specific pump, pumping rates and electrical costs. Please specify the type of
pump(s) which will be used to dewater Tract C.
The planned pump is a diesel operated 6 inch Goodwin pump with an output of
approximately 500± to 800± gallons/minute.
7. The Applicant has stated the cost to reclaim Tract C has been offset by
reclamation in Tract A. The Division has confirmed that costs associated
with grading Tract C have been offset by grading in Tract A. However,
dewatering, topsoil replacement and seeding costs will need to be added to
the current financial warranty amount of S286,979. Once all of the adequacy
issues have been addressed, the Division will recalculate the financial
warranty amount.
Understood.
ATTACHEMENTS:
• Proof of Placement — Weld County Clerk to the Board
• Technical Revision — Map revised.
• C.G.R.S. Hydrogeologic Evaluation Report of October 2007.
Varra Companies, Inc. -M-2009-006 July 2011 Technical Revision 5
Kurtz Resource Recovery& Land Development Project Correspondence of 3 August 2011
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VARRA COMPANIES, INC. DATE: 2 July 2011
8120 GAGE STREET
FREDERICK, COLORADO 80534 REVISION: 3 August 2011
TELEPHONE: (303) 886-6657 1 OF 2
PAGE: Irle:414k:11.11
Introduction
The following report presents the results of a hydrogeologic evaluation and opinions of the
author (Joby Adams) regarding the existing gravel quarry operations operated by Varra
Companies in Platteville, Colorado in association with CORMS Permit # M1999-006.
Specifically the evaluation was performed to assess possible impacts to wetlands
downgradient of Tract B—a 13.75 acre parcel. Site conditions are depicted on Plate 1.
Background Information
Information provided by current mining operation data and water resource evaluation
reports document local and regional hydrogeology. Soil conditions generally consist of two
to five feet of top soil underlain by sand and gravel deposits, which in turn are underlain by
shale. Over the entire area the average saturated thickness of the sand and gravel
deposits (prior to mining) is estimated at 20 feet. The natural hydraulic gradient as
documented by past water resource investigation reports is on the order of 0.002 feet per
feet, with the depth to water varying between 6 and 15 feet below ground surface. The
natural groundwater flow direction is to the north — northeast. Seasonal water table
fluctuations of between one and three feet are common for this area; however, fluctuations
of greater than ten feet have been documented during drought conditions (Schneider,
1983).
The water table in the vicinity of Tract B will be drawn down to bedrock over an estimated
13 acres. The mine is dewatered by allowing groundwater to flow from the side walls of the
excavation into ditches excavated into the shale bedrock at the toe of the excavation walls.
The ditches are sloped so water drains to the north toward St. Vrain Creek. The water is
then pumped from the excavation into a settling pond located just to the east of an area
identified as wetlands. The water then outfalls to Last Chance Ditch, which flows to the
north.
Project Assumptions
The following are assumptions made in estimating affects of mine dewatering operations.
> The aquifer within the model boundary is homogeneous and isotropic.
Dewatering Evaluation Report
Vann Gravel Operation
Kurtz Pit
Platteville,Colorado
Page 2
> The saturated thickness of the aquifer prior to mine operations is 20 feet (water
table located ten feet below ground surface).
> The average hydraulic conductivity of the sand and gravel deposits is 170 feet per
day.
> Other than dewatering associated with mine operations no other aquifer stresses
such as drought and surrounding well use are accounted for.
> All groundwater solutions are steady state.
> The Pierre Shale which underlies the coarse alluvial deposits is an impermeable
barrier and the average depth from ground surface to the shale is 30 feet.
Overview of Drawdown Estimates
The hydraulic conductivity of the coarse gravel deposits is on the order of 170 feet per day
(Schneider, 1983) which is consistent with published values and pump test evaluations
conducted by the author in similar geologic settings. The average porosity of the local
sand and gravel deposits is estimated at 0.25.
The affects of dewatering on groundwater flow within the study area were evaluated by
use of a two-dimensional analytical groundwater flow model (TWODAN). TWODAN is a 32
bit Windows program for the modeling of two-dimensional groundwater flow. The program
is accepted by the scientific community for evaluating two dimensional groundwater flow
problems and was evaluated in Groundwater, v. 36, No. 3, May-June 1998. Visual
MODFLOW, a three dimensional numerical model, was also used for comparison
purposes and generated very similar results to the analytical model.
A uniform flow field was defined in the model with an unconfined aquifer. The model was
set at approximately 281 acres (3,500 x 3,500 feet). The hydraulic conductivity of the
aquifer at the Varra site was estimated at 170 feet per day. The aquifer thickness was
modeled as 30 feet with a saturated thickness of 20 feet. The static groundwater flow
Dewatering Evaluation Report
Varra Gravel Operation
Kurz Pit
Platteville,Colorado
Page 3
direction of due north was assigned to the model. A bedrock elevation was assigned a
relative elevation of 10 feet.
Eight line sinks were used to simulate dewatering operations. The line sinks were
superimposed over the perimeter of the area identified as Tract B and assigned a head of
15 feet, or five feet above the bedrock surface for a total drawdown of 15 feet over the
entire mine area. Four line sinks were used to simulate the settling pond (identified as 0.95
acre pond). The Cogburn Tributary is a perennial stream and was not accounted for in the
model. Possible inflows from Last Chance Ditch were not accounted for and the model
should provide a conservative prediction of affects on local hydrology. The settling pond
line sinks were assigned a head of 40 feet or ten feet above the water table. Steady state
simulations were then ran and the results are depicted in Attachment A.
The head distribution map generated by the model shows that the gravel quarry is a
groundwater sink for the majority of the model area south of the St. Vrain Creek, which is a
groundwater divide. The model results indicate that the water table will be depressed by
eight to ten feet below the wetlands located some 400 feet directly west of the settling
pond.
The model was then modified to simulate an unlined drainage ditch north of Tract B from
the western edge of the wetlands (just east of Cogburn tributary) to the settling pond. The
ditch was simulated by adding an additional line sink with an assigned head of 38 feet
(eight feet above the water table). The model predicts the settling pond in combination with
a drainage ditch completely abates any drawdown beneath the wetlands. The head
distribution map of the second model run is also presented in Attachment A, along with
MODFLOW model runs.
Dewatering Evaluation Report
Van-a Gravel Operation
Kurtz Pit
Platteville,Colorado
Page 4
Conclusions
The results of analytical and numerical solutions predict that the water table in the vicinity
of Tract B at the Varra Kurtz Pit operation will be lowered by eight to ten feet below
wetlands identified north of the pit— assuming that the entire 13.75 acre pit is dewatered.
Solutions also indicate that dewatering north of the pit can be abated by providing a water
source between the pit and identified wetlands. This can be accomplished by constructing
an unlined conveyance ditch between the pit and wetlands. Providing a water source
along the majority of the north pit face may increase pumping rates in excess of 50%.
Infiltration from the settling pond will adequately protect the wetlands if only one-half of the
pit(or less) is dewatered at any given time.
Remarks
The discussion and recommendations in this report represent our professional opinions.
Our conclusions, opinions and recommendations are based on information available at
this time, and we do not guarantee that undiscovered conditions will not become evident in
the future. CGRS' report was prepared in accordance with currently accepted engineering
practices at this time and location, and no other warranties, representations or
certifications are implied or intended.
This report was prepared by CGRS, INC.
Date ( —va-e-f- 7, 0607—
Joby L. Adams, P.G.
Principal/Hydrogeologist
REFERENCES
Colton, R.B., and Fitch, H.R., 1974, Map showing potential sources of gravel and crushed-rock
aggregate in the Boulder-Fort Collins-Greeley area, Front Range Urban Corridor, Colorado:
U.S. Geol. Survey Misc. Geol. Inv. Map I-855-D.
Schneider, P. A., 1983, Shallow groundwater in the Boulder—Fort Collins—Greeley area,
Colorado, 1975-77: U.S. Geological Survey Water Resources Investigation Report
83-4058.
ATTACHMENT A
MODEL RESULTS
Varra Kurtz Pit Simulation
Settling Pond Only
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