August 23, 2010
Attachment A
Assessment of Potential Groundwater Flow Away
From the San Juan Mine, Farmington, New Mexico
By Mike Roark, Nathan Myers, Anne Stewart
SUMMARY
Surface mining of the Fruitland Formation’s #8 coal at the San Juan Mine, located about
10 miles northwest of Farmington, New Mexico, began in 1973, but has now moved
underground. Two open mine pits, the Piñon and Juniper pits, are now undergoing reclamation
by filling the pits with coal combustion by-products interlayered with previously removed
overburden. Coal combustion by-products (CCBs), from the nearby San Juan Generating Plant,
are composed of fly ash, bottom ash, and flue-gas desulfurization products. The New Mexico
Mining and Minerals Division of the Energy, Minerals, and Natural Resources Department has
asked the U.S. Geological Survey (USGS) New Mexico Water Science Center (NMWSC) to
evaluate the potential for groundwater from the reclaimed mine pits to flow to wells or streams.
BACKGROUND
The San Juan Mine area is drained by the Westwater and Shumway Arroyos and is about
one mile north of the San Juan River. The San Juan River and the nearby La Plata River (fig. 1)
are important sources of drinking and irrigation water for communities in this area.
Potentiometric-surface maps show that groundwater north of the mine area generally flows to the
south, but in the mine area flows southwest towards the Piñon and Juniper pits. The
southwestward flow may have been induced by mine dewatering.
Principle geologic units at the mine include the Pictured Cliffs Sandstone and the
overlying Fruitland Formation of Cretaceous age. Aquifers in the mine area include the alluvium
of the Westwater and Shumway Arroyos, the coal seams in the Fruitland Formation, and the
underlying Pictured Cliffs Sandstone.
Geologic units in and near the San Juan mine study area consist primarily of rocks of
Cretaceous and Tertiary age that generally dip to the east (fig. 1). About 4 miles west of the San
Juan Mine area, rock units dip steeply east across the Hogback Monocline (fig. 1). Geologic
units present at the mine include the Pictured Cliffs Sandstone and the overlying Fruitland
Formation of Cretaceous age. The upper two-thirds of the Pictured Cliffs Sandstone consists of a
generally-coarsening upward-sequence of light gray, very fine-grained, massive sandstone
whereas the lower one-third of the formation consists of interbedded shale and sandstone. The
total thickness of the Pictured Cliffs Sandstone varies due to depositional irregularities, but
averages 120 feet in the mine area (San Juan Coal Company, 2009). The Fruitland Formation is
composed of interbedded sandstone, shale, and coal. The lithologies of the rock units contained
in the Fruitland Formation include fine- to medium-grained sandstones, siltstones, sandy and
August 23, 2010
silty claystones, carbonaceous claystones, bentonitic claystones, and coal, including the #8 coal.
The #8 coal is 9- to 13-feet thick in the mine area and the bottom of the #8 coal is about 11 to 20
feet above the top of the Pictured Cliffs Sandstone (San Juan Coal Company, 2009). The aquifers
in the mine area include the alluvium of the Westwater and Shumway Arroyos, the coal seams in
the Fruitland Formation, and the underlying Pictured Cliffs Sandstone.
OBJECTIVES AND SCOPE
The objective of this study is to determine potential groundwater flow paths away from
the San Juan Mine that could allow metals that may be leached from CCBs in the reclaimed mine
pits to reach wells or streams.
The hydrologic bounds of the study area will be the San Juan River on the south, Salt
Creek Wash on the west, the New Mexico-Colorado border on the north, and the La Plata River
on the east (fig. 1). Hydrogeologic information available for the mine area, adjacent aquifers, and
nearby streams will be used in this study.
Tasks to meet the objectives of this study include: 1) compile and review existing
literature and data, 2) evaluate, characterize, and compile water-quality data for the purpose of
calibration of the groundwater flow model, and 3) determine potential groundwater flowpaths
from the reclaimed mine pits to wells or streams. A Scientific-Investigations Reports will be
written and published that describe the data collected during the study and the results of this
study. Data collected by the USGS will be stored in the USGS NWIS data base and will be
available through the USGS NWIS web site. The groundwater-flow model will be archived at
the USGS New Mexico Water Science Center office and will be available on request.
RELEVANCE AND BENEFITS
The study will contribute to the USGS mission by increasing understanding of surfacewater and groundwater hydrology in the Farmington area of the San Juan Basin. Increasing the
understanding of the surface-water and groundwater hydrology also will provide information for
the management decisions of State agencies that manage water and mineral-resources in the
Farmington area.
This study will meet the USGS Science Issue of “Water Availability and Use”. The
study will improve watershed characterization and flow-system definition and simulation for the
management of aquifers and streams that serve as important local or regional sources of water
supply. The study also will provide a quantitative understanding of the sources of groundwater
flowing to wells and streams.
APPROACH
Task 1. – Compile and review existing literature and data
Existing geologic and hydrologic literature relevant to the San Juan Mine and associated
groundwater and surface-water systems will be compiled and reviewed. Literature will include
published reports, journal articles, and any available consultant reports. Geologic, hydrologic,
and water-quality data will be compiled from USGS, Bureau of Land Management, MMD, New
Mexico Environment Department, and San Juan Coal Company databases. Compilation and
August 23, 2010
review of literature and data will be used to identify data gaps and to guide the acquisition or
collection of additional data during this study.
Task 2 – Water-Quality Data Evaluation
Existing groundwater and surface-water quality data will be evaluated, characterized, and
compiled to use for calibration of the groundwater flow digital model.
Task 3 – Determine potential groundwater flowpaths from the reclaimed mine pits to wells
or streams
This task has multiple components including, field support of University of New Mexico
data-collection efforts, estimates of groundwater flow (levels, direction, gradient, volume) into
and out of the mine area, estimates of groundwater recharge from precipitation and from surfacewater infiltration, estimates of hydraulic properties of water-bearing units, development of a
conceptual hydrogeologic model of the San Juan Mine area, and development of a digital
groundwater-flow model.
Support of Field Data Collection
The field data collection effort will be supported by the USGS with cooperative water
program funds, for the following tasks:
a) In-situ CCB sample collection with the USGS Geoprobe from location(s) in the Piñon
and/or Juniper pits. This task includes mobilization and demobilitation of the Geoprobe, and use
of the Geoprobe , required materials and time of support staff;
b) Purchase and deployment of safety equipment required for the USGS personnel when
working on the San Juan Mine property; and
c) Purchase and deployment of pressure transducers for continuous logging of water-level
data from selected observation-network wells in the vicinity of the San Juan Mine, to support the
task of characterization of groundwater flow (as is described next).
Groundwater Flow
The direction of groundwater flow in the study area will be determined on the basis of
water levels measured in wells completed in aquifers in the study area, including the # 8 coal
seam and the Pictured Cliffs Sandstone. An inventory of all wells that are available and
accessible and that meet the criteria for an observation-well network will be developed during
the initial phase of the study. Physical data for each well (location, use, construction details, and
completion aquifer) will be entered into the USGS National Water Information System (NWIS)
database. Wells included in the observation-well network will be selected to provide the best
representation of water-level conditions over the study area and within selected aquifers.
Aquifers selected will include the #8 coal seam, the Pictured Cliffs Sandstone, and aquifers
where sufficient water-level data are present to characterize groundwater flow. Predevelopment
potentiometric-surface maps will be constructed for each aquifer for which there is sufficient
data available for a date prior to mine dewatering and widespread well pumping, and will be
used in the development of the conceptual model and digital groundwater-flow model.
August 23, 2010
Water levels in observation-network wells will be measured monthly for the first year of
this study. During the second and third years, water levels will be measured quarterly. Waterlevel data will be entered into the USGS NWIS database and will be available to the MMD and
the public through the USGS NWIS website. In addition, four wells will be instrumented with
submersible pressure transducers to record depth to water below land surface. The transducers
will be set to record at hourly intervals. Data from the transducers will be downloaded quarterly
and will be processed and entered into the USGS NWIS database where it will be available to
MMD and the public through the USGS NWIS website.
Potentiometric-surface maps will be constructed for each aquifer for which sufficient
water-level data are available. These maps will provide a snapshot in time of the potentiometric
surface of the aquifer(s) and will indicate the direction and relative magnitude of groundwater
flow. The potentiometric-surface maps will be used to establish groundwater-flow direction and
hydraulic gradients within aquifers in the mine area. The maps also will be used to assess the
effects of mine dewatering and groundwater pumping in the study area.
Recharge
Groundwater recharge may occur by infiltration of precipitation into the subsurface (areal
recharge) or by infiltration of water from surface-water bodies (focused recharge). Areal
recharge may occur where precipitation exceeds runoff plus evapotranspiration. The volume of
recharge that occurs will be estimated by applying the results of studies by Stone (1984 and
1986) at the nearby Navajo Mine (located about 5 miles south of the San Juan Mine). Stone
(1984 and 1986) determined the amount of recharge to the groundwater system at the Navajo
Mine using a chloride mass-balance technique and a combination of chloride, stable isotope, and
tritium techniques.
Hydraulic properties of water-bearing units
Dam and others (1990), Frenzel (1983), Kernodle (1996), Kernodle and others (1990),
Myers and Villanueva (1986), and San Juan Coal Company (2009) report various properties and
characteristics of water-bearing units in the San Juan Mine area that may be of benefit to this
study. Properties of water-bearing units also may be estimated on the basis of the geologic
properties of the water-bearing unit (Freeze and Cherry, 1980).
Conceptual model
A conceptual model of the groundwater and surface-water system in the study area will
be developed to provide a framework for digital model development. The conceptual model will
describe geologic units and their properties, aquifers and their properties, natural groundwaterflow boundaries and divides, groundwater hydraulic stresses (such as recharge, inflow from
adjoining aquifers, and discharge to wells, springs, and surface-water bodies) that may affect the
aquifer system, estimated groundwater flux through the various aquifers, and the interaction of
surface water and groundwater. The conceptual model also will be used to help determine where
additional data are needed to enable the digital model to adequately simulate groundwater levels
and flow.
August 23, 2010
Digital groundwater flow model
At this time we plan to simulate groundwater flow using MODFLOW, the USGS
modular, 3-D finite difference digital groundwater flow model (Harbaugh and McDonald, 1996).
If geologic or hydrologic conditions warrant another model could be selected for use.
Groundwater and surface-water interaction will be simulated using the Streamflow Routing
Package (SFR2). The potential transport pathways of CCB-derived metals in groundwater to
wells or streams will be simulated during scenario analysis using MODPATH. MODPATH
simulates the path the particles of water follow in an aquifer; it does not perform solute-transport
computations. Initially the numerical model will be based on the conceptual model of the
groundwater system within the study area. If sufficient predevelopment water-level data are
available, a steady-state version of the numerical model will be calibrated to predevelopment
water-level conditions and a transient version of the model will be developed and calibrated to
existing groundwater conditions. If sufficient predevelopment water-level data are not available,
the steady-state model will not be developed and the transient model will be calibrated to
existing groundwater conditions.
Data for the numerical groundwater-flow model will be compiled in a GIS format.
Model boundaries will, as much as possible, be designed to coincide with natural hydrologic
features, such as rivers, groundwater divides, or impermeable rock layers. Artificial boundaries
may have to be constructed where no natural hydrologic boundaries occur within the model
domain, and may be simulated with the MODFLOW General Head Boundary Package (GHB) or
other boundary condition package, depending on conditions at the artificial boundary.
Previously constructed digital groundwater-flow models (Frenzel, 1983; Kernodle, 1996)
will be used to provide guidance for construction of the digital model for this study. The models
developed by Frenzel (1983) and Kernodle (1996) however, probably cannot be directly adapted
for this project because of their differing areal coverage and model grid-cell size. The Frenzel
(1983) and Kernodle (1996) models use grid-cell sizes of 6 miles square and about 1.9 miles
square, respectively, meaning that the entire San Juan Mine area would fit into one or two of
these model cells.
The calibrated digital model will be used to simulate groundwater flow in various
aquifers at and near the San Juan Mine and the interaction of groundwater and surface water
along the San Juan River. Potential groundwater flow paths will be simulated by assuming the
cessation of mine dewatering and considering various scenarios of nearby coal-bed methane
production and the saturation of material in the mine pits with groundwater derived from
recharge or from the surrounding aquifers. Potential movement of CCB leachate will be
evaluated using groundwater-flow model and particle-tracking simulations. The calibrated model
will be used to test various hypothetical scenarios such as climate change, long-term effects of
coal-bed methane water extraction down dip from the mine area, the length of time needed to
saturate fill material in the Piñon and Juniper pits with groundwater after cessation of mine
dewatering, or other scenarios as developed in consultation with MMD personnel.
QUALITY-ASSURANCE PLAN
Field-data collection efforts will follow methods outlined in the USGS National Field
Manual (U.S. Geological Survey, variously dated), and the USGS NMWSC surface-water and
groundwater quality-assurance plans. Interpretation and modeling will follow standard methods
August 23, 2010
described in the USGS Techniques of Water Resources Investigation reports and in the
hydrologic literature.
ARCHIVING PLAN
The USGS requires archival of data, correspondence, and other project materials
produced during the execution of projects. Data collected by USGS personnel will be archived
by entering it into the USGS NWIS database. Correspondence and other project materials will be
inventoried and cataloged at the end of the project and will be shipped to the National Records
Center, Denver, Colorado for storage. The groundwater-flow model will be placed in the USGS
NMWSC digital groundwater-model archive and will be available upon request after publication
of the Scientific-Investigations Report.
PRODUCTS
A Scientific-Investigations Report that describes data collected during the study and the
results of this study will be written and published. Interim progress reports will be provided
quarterly. Data stored in the NWIS database will be available through the USGS NWIS web site
(http://waterdata.usgs.gov/nm/nwis).
REFERENCES
Beach, L.J. and Jentgen, R.W., 1978, Coal test drilling for the San Juan Mine extension, San
Juan County, New Mexico: U.S. Geological Survey Open-File Report 78-960, 87 p.
Brunett, J.O., Barber, N.L., Burns, A.W., Fogelman, R.P., Gillies, D.C., Lidwin, R.A., and Mack,
T.J., 1997, A quality-assurance plan for District ground-water activities of the U.S. Geological
Survey: U.S. Geological Survey Open-File Report 97-11, 19 p.
Dam, W.L., Kernodle, J.M., Thorne, C.R., Levings G.W., and Craigg, S.D., 1990, Hydrogeology
of the Pictured Cliffs Sandstone in the San Juan Structural Basin, New Mexico, Colorado,
Arizona, and Utah: U.S. Geological Survey Hydrologic Investigations Atlas HA-720D, 2
sheets.
Dames & Moore, 1979, Coal resource occurrence maps and coal development potential maps of
the Waterflow quadrangle, San Juan County, New Mexico: U.S. Geological Survey Open-File
Report 79-793, 26 p.
Freeze, R. A. and J. A. Cherry, 1979, Groundwater: Prentice Hall, Inc., 604 p.
Frenzel, P.F., 1983, Simulated changes in ground-water levels related to the proposed
development of federal coal leases, San Juan Basin, New Mexico: U.S. Geological Survey
Open-File Report 83-949, 63 p.
Kernodle, J.M., 1996, Hydrogeology and steady-state simulation of ground-water flow in the San
Juan Basin, New Mexico, Colorado, Arizona, and Utah: U.S. Geological Survey WaterResources Investigations Report 95-4187, 117 p.
Kernodle, J.M., Thorne, C.R., Levings G.W., Craigg, S.D., and Dam, W.L., 1990, Hydrogeology
of the Kirtland Shale and Fruitland Formation in the San Juan Structural Basin, New Mexico,
Colorado, Arizona, and Utah: U.S. Geological Survey Hydrologic Investigations Atlas HA720C, 2 sheets.
August 23, 2010
Myers, R.C., and Villanueva, E.D., 1986, Geohydrology of the aquifers that may be affected by
the surface mining of coal in the Fruitland Formation in the San Juan Basin, northwestern New
Mexico: U.S. Geological Survey Water-Resources Investigations Report 85-4251, 41 p.
Parkhurst, D.L. and Appelo, C.A.J., 1999, User's guide to PHREEQC (version 2)-A computer
program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical
calculations: USGS Water-Resources Investigations Report 99-4259, 312 p.
Pollock, D. W. 1994. User's guide for MODPATH/MODPATH-PLOT, Version 3: A particle
tracking post processing package for MODFLOW, the U.S. Geological Survey finitedifference ground-water flow model. U.S. Geological Survey Open-File Report 94–464. 249
pp.
San Juan Coal Company, 2009, San Juan Mine permit, subpart 803, Geology Description: San
Juan Coal Company, Waterflow, New Mexico, variously paged.
Stone, W.J., 1984, Preliminary estimates of recharge at the Navajo Mine based on chloride in the
unsaturated zone: Socorro, New Mexico Bureau of Mines and Mineral Resources Open-File
Report 213, 60 p.
Stone, W.J., 1986, Phase-II recharge study at the Navajo Mine based on chloride, stable isotopes,
and tritium in the unsaturated zone: Socorro, New Mexico Bureau of Mines and Mineral
Resources Open-File Report 216, 244 p.
Stone, W.J., 1987, Phase-III recharge study at the Navajo Mine – impact of mining on recharge:
Socorro, New Mexico Bureau of Mines and Mineral Resources Open-File Report 282, 45 p.
U.S. Geological Survey, 1989, Safety and environmental health handbook: U.S. Geological
Survey Handbook 445-1-H, variously paged.
U.S. Geological Survey, variously dated, National field manual for the collection of waterquality data: U.S. Geological Survey Techniques of Water-Resources Investigations, book 9.
August 23, 2010
WORK PLAN
2011
Q1 Q2 Q3
X
X
X
Task
Project management
Compile and review existing
literature and data
Water-Quality Data
Evaluation
Determine potential
groundwater flow paths
from reclaimed mine pits to
wells or streams
Field support of UNM data
collection
X
Q4
X
State Fiscal Year and Quarter
2012
2013
2014
Q1 Q2 Q3
Q4 Q1 Q2 Q3 Q4 Q1 Q2
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Estimate Groundwater Flow
Estimate Recharge
Estimate hydraulic
properties of water-bearing
units
X
Develop conceptual model
Develop digital groundwater
flow model
Write Scientific
Investigations Report
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
PERSONNEL
Personnel
Hydrologist
(Project Chief)
Hydrologic
Technician
Student
2011
Q1 Q2 Q3
State Fiscal Year and Quarter – weeks of work
2012
2013
Q4 Q1 Q2 Q3 Q4
Q1 Q2 Q3 Q4
2014
Q1 Q2
8
7
10
10
10
10
11
11
12
12
10
10
8
6
1
1
3
1
1
1
2
1
1
1
0
0
0
0
7
7
5
4
4
4
4
4
4
4
4
3
2
1
X
X
August 23, 2010
BUDGET
Budget detail table showing NET COSTS
Task
Project management
Compile and review existing literature
and data
Water-Quality Data Evaluation
Budget
Element
Personnel
Labor
Hydrologist
2011
Safety
Equipment
Labor
Hydrologist
Student
Hydrologist
Student
Geoprobe
Field support of
UNM data
collection
Labor
(operator)
Labor
Travel
Vehicle
Labor
Determine
potential
groundwater
flow paths from
reclaimed mine
pits to wells or
streams
Groundwater flow
Labor
Hydraulic
properties of
water-bearing
units
Labor
Conceptual model
Labor
Digital
groundwater flow
model
Labor
Write and publish Report
Hydrologist
Hydrologic
Technician
Student
Hydrologist
Student
Hydrologist
Student
Hydrologist
Student
Hydrologist
Student
Supplies
Labor
Editorial
review (EPN)
Manuscript
preparation
(EPN)
Printing
(GPO)
5,400
4,800
2,100
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1,160
800
250
19,000
6,300
2,500
5,400
7,000
3,200
0
4,000
2,500
1,900
300
8,400
0
0
0
1,200
2,400
2,200
100
300
400
500
100
10,500
1,500
10,300
0
0
0
0
0
0
0
0
0
0
0
0
1,500
0
0
8,300
800
0
0
0
2,100
800
6,200
800
13,300
1,700
1,000
0
0
0
0
39,300
5,000
1,000
21,600
4,600
0
0
52,800
3,300
0
0
600
0
0
0
2,000
4,000
2,620
0
0
1,000
8,300
6,100
1,000
200
8,400
1,500
3,400
Hydrologic
Technician
Hydrologist
Travel
Vehicle
Supplies
Equipment
Recharge
5,800
2014
750
Travel
Vehicle
Labor
State Fiscal Year
ESTIMATED NET COST
2012
2013
Hydrologist
Student
1,590
13,400
3,100
August 23, 2010
Budget summary table showing net costs, overhead, and gross costs.
Task
State Fiscal Year
2011
2012
2013
2014
6,550
5,400
4,800
2,100
15,600
0
0
0
9,900
0
0
0
Determine
potential
groundwater flow
paths from
reclaimed mine pits
to wells or streams
57,800
66,000
52,300
56,100
Write and publish
Report
5,520
0
28,800
21,500
Total Net Cost
95,370
71,400
85,900
79,700
Project Support
4,820
13,900
16,800
15,600
Facilities
3,590
6,000
7,200
6,700
Common Services
69,820
48,000
57,800
53,700
Total Gross Cost
173,600
139,300
167,700
155,700
Project Total
$636,300
Project management
Compile and review
existing literature and
data
Water-Quality Data
Evaluation
August 23, 2010
FUNDING
Funding for this project will be provided by the New Mexico Energy, Minerals, and
Natural Resources Department and, if possible, by the USGS. If USGS Cooperative Water
Program funds become available the USGS will match a portion of the project costs (no more
than 50 percent in any given year).
Funding Table
Funding by State Fiscal Year
Agency
2011
2012
2013
2014
NM Energy, Minerals, and
Natural Resources Dept.
150,000
139,300
167,700
155,700
U.S. Geological Survey
23,600
0
0
0
Total Funding
173,600
139,300
167,700
155,700
SAFETY
USGS personnel will follow safety procedures specified in the U.S. Geological Survey
(1989) safety manual, and applicable procedures in place at the San Juan Mine operations, at all
times. All USGS personnel will read and become familiar with the Job Hazard Analyses
developed for this project.
August 23, 2010