In Cooperation with the Bureau of Land Management 

Completion Reports, Core Logs, and Hydrogeologic Data 

from Wells and Piezometers in Prospect Gulch, San Juan 

County, Colorado 

By Raymond H. Johnson and Douglas B. Yager 

Open-File Report 2006-1030 

U.S. Department of the Interior 

U.S. Geological Survey 
U.S. Department of the Interior 

Gale A. Norton, Secretary 

U.S. Geological Survey 

P. Patrick Leahy, Acting Director 

U.S. Geological Survey, Reston, Virginia 2006 

For product and ordering information: 

World Wide Web: http://www.usgs.gov/pubprod 

Telephone: 1-888-ASK-USGS 

For more information on the USGS—the Federal source for science about the Earth, 

its natural and living resources, natural hazards, and the environment: 

World Wide Web: http://www.usgs.gov 

Telephone: 1-888-ASK-USGS 

Suggested citation: 

Johnson, R.H., Yager, D.B., 2006, Completion reports, core logs, and hydrogeologic data from wells and 

piezometers in Prospect Gulch, San Juan County, Colorado: U.S. Geological Survey Open-File Report 2006-

1030. 

Any use of trade, product, or firm names is for descriptive purposes only and does not imply 

endorsement by the U.S. Government. 

Although this report is in the public domain, permission must be secured from the individual 

copyright owners to reproduce any copyrighted material contained within this report. 

ii
Contents 

Abstract................................................................................................................................................................................6

Introduction .........................................................................................................................................................................6

Geologic Setting .................................................................................................................................................................7

Hydrologic Setting..............................................................................................................................................................9

Well and Piezometer Completion Data...........................................................................................................................9

Core Logs and EDXRF Data.............................................................................................................................................10

Slug-Test Data ..................................................................................................................................................................10

Hydraulic Head Data........................................................................................................................................................11

References Cited ..............................................................................................................................................................12

Figures 

1. Location of Prospect Gulch in the upper Animas River watershed................................................................................14 

2. Boart Longyear Delta Base 540 drilling rig operated by Spectrum Exploration at upper elevation hole in Prospect 

Gulch.......................................................................................................................................................................15 

3. Locations of wells and piezometers in and around Prospect Gulch...............................................................................16

4. Locations of wells and piezometers in Prospect Gulch, middle and upper elevations..................................................17

5. Locations of wells and piezometers in and around Prospect Gulch, lower elevations .................................................18

6. Completion diagram of UPG-D ........................................................................................................................................19

7. Completion diagram of MPG-D .......................................................................................................................................20

8. Completion diagram of LPG-D.........................................................................................................................................21

9. Geoprobe model 5410D rig near the mouth of Prospect Gulch (GPPG-10) operated by the U.S. Geological Survey 

under Bureau of Land Management contract .......................................................................................................22

10. Generalized core log for UPG-D ....................................................................................................................................23

11. Generalized core log for MPG-D ...................................................................................................................................25 

12. Generalized core log for LPG-D. ....................................................................................................................................26

Tables 

1. Completion data for wells and piezometers. ..................................................................................................................27 

2. Data for UPG-D well core on fracture density and orientation ......................................................................................29 

3. Data for MPG-D well core on fracture density and orientation. ....................................................................................30 

4. Data for LPG-D well core on fracture density and orientation.......................................................................................31

5. Results from slug tests....................................................................................................................................................32 

iii
Appendix Files 

A. Leica data.xls..................................................................................................................................................... file online 

B. Core logs.zip. ..................................................................................................................................................... file online

C. Core photos.zip.................................................................................................................................................. file online

D. EDXRF.zip........................................................................................................................................................... file online

E. Slug test data.zip............................................................................................................................................... file online

F. Aqtesolv.zip........................................................................................................................................................ file online

G. Water levels.xls. ............................................................................................................................................... file online

iv
Conversion Factors 

Inch/Pound to SI 

Multiply By To obtain 

Length 

inch 2.54 centimeter (cm) 

inch 25.4 millimeter (mm) 

foot (ft) 0.3048 meter (m) 

mile (mi) 1.609 kilometer (km) 

SI to Inch/Pound 

Multiply By To obtain 

Length 

centimeter (cm) 0.3937 inch 

millimeter (mm) 0.03937 inch 

meter (m) 3.281 foot (ft) 

meters per second (m/s) 3.281 feet per second 

kilometer (km) 0.6214 mile (mi) 

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows: 

°F=(1.8×°C)+32 

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows: 

°C=(°F-32)/1.8 

Vertical coordinate information is referenced to the North American Vertical Datum of 1929 (NAVD 29). 

Horizontal coordinate information is referenced to the North American Datum of 1927 (NAD 27). 

v
Completion Reports, Core Logs, and Hydrogeologic 

Data from Wells and Piezometers in Prospect 

Gulch, San Juan County, Colorado 

By Raymond H. Johnson and Douglas Yager1

Abstract 

In the late nineteenth century, San Juan County, Colorado, was the center of a metal 

mining boom in the San Juan Mountains. Although most mining activity ceased by the 

1990s, the effects of historical mining continue to contribute metals to ground water and 

surface water. Previous research by the U.S. Geological Survey identified ground-water 

discharge as a significant pathway for the loading of metals to surface water from both acidmine drainage and acid-rock drainage. In an effort to understand the ground-water flow 

system in the upper Animas River watershed, Prospect Gulch was selected for further study 

because of the amount of previous data provided in and around that particular watershed. In 

support of this ground-water research effort, wells and piezometers were installed to allow for 

coring during installation, subsurface hydrologic testing, and the monitoring of ground-water 

hydraulic heads and geochemistry. This report summarizes the data that were collected 

during and after the installation of these wells and piezometers and includes (1) subsurface 

completion details, (2) locations and elevations, (3) geologic logs and elemental data, (4) slug 

test data for the estimation of subsurface hydraulic conductivities, and (5) hydraulic head data. 

Introduction 

In the late nineteenth century, San Juan County, Colorado, was the center of a metal 

mining boom in the San Juan Mountains. Although most mining activity ceased by the 

1990s, the effects of historical mining continue to contribute metals to ground water and 

surface water. These increased metal concentrations degrade stream-water quality and are 

toxic to fish and other aquatic organisms. As a result, viable fish and aquatic habitat is now 

more limited than what existed before mining (Besser and others, in press). Since the 1990s, 

the local economic base has shifted away from hard-rock mining toward tourism with a focus 

on recreational opportunities. Increased population downstream also has increased the 

demand for clean water. While streams in this area have low pH and elevated metal loads due 

to acid-rock drainage, the influence of acid-mine drainage due to historical mining activities 

has degraded preexisting ground-water and surface-water quality (Church and others, in 

press). Determining the ground-water flow and associated dissolved-metal transport is 

critical to protecting ground-water and surface-water resources, determining the influence of 

acid-mine drainage compared to versus preexisting acid-rock drainage, and providing sensible 

remedial options. 

 

1

 U.S. Geological Survey, Minerals Resources Team, Denver, Colorado 

6
 Much of the San Juan Mountains is influenced by historical mining, and many 

surface-water samples (along with other data) have been collected in the upper Animas River 

watershed (fig. 1) by the U.S. Geological Survey (Church and others, in press; 

http://amli.usgs.gov/reports/). Three goals of this watershed characterization project were to 

(1) characterize the surface-water quality, (2) identify abandoned mines that contribute the 

greatest metal loads to surrounding surface waters, and (3) determine premining water quality. 

The ultimate objective was to provide the necessary scientific information for public land 

managers to select effective remedial approaches that would improve watershed quality. 

Ground-water discharge has been identified as a significant pathway for the loading of metals 

to surface water from both acid-mine drainage and from acid-rock drainage (Church and 

others, in press; Mast and others, in press; Kimball and others, 2002; Kimball and others, in 

press). Understanding the ground-water flow and dissolved metal transport is essential in 

determining whether sampled metal loads to streams are related to acid-mine drainage or acidrock drainage, and thus, whether or not an identified source of metal loading should be 

remediated. 

In an effort to understand the ground-water flow system in the upper Animas River 

watershed, Prospect Gulch (fig. 1) was selected for further study because of the amount of 

data provided in and around that particular watershed (Church and others, in press), including 

stream tracer studies (Kimball and others, 2002; Wirt and others, 1999, 2001) and detailed 

maps of hydrothermal alteration (Bove and others, in press). In addition, many of the inactive 

mines within Prospect Gulch are on land managed by the Bureau of Land Management 

(BLM). An understanding of the ground-water flow system is critical in assisting them with 

their remedial efforts. In support of this ground-water research effort, wells and piezometers 

were installed to allow for coring during installation, subsurface hydrologic testing, and the 

monitoring of ground-water hydraulic heads and geochemistry. This report summarizes the 

data that were collected during and after the installation of these wells and piezometers and 

includes (1) subsurface completion details, (2) locations and elevations, (3) geologic logs and 

elemental data, (4) slug test data for the estimation of subsurface hydraulic conductivities, and 

(5) hydraulic head data. 

Geologic Setting 

The predominant rock types in the Prospect Gulch study area consist of intermediateto felsic-composition igneous rocks. These rocks formed following formation of the 28.2-Ma 

San Juan caldera, coincident with and (or) postdating formation of the 27.8-Ma Silverton 

caldera (Yager and Bove, 2002). Intermediate-composition lava flows and minor 

volcaniclastic sedimentary rocks that were deposited on the flanks of central vent volcanoes 

predominate this igneous sequence and are part of the Silverton Volcanics described by 

Lipman and others (1973). Silverton Volcanics lavas and volcaniclastic sediments shed from 

the adjacent volcanoes infilled the San Juan caldera volcanic depression to nearly a kilometer 

in thickness over an approximately 14-km-diameter area. Primary igneous minerals of the 

Silverton Volcanics intermediate-composition porphyritic lavas include, in relative order of 

abundance, plagioclase, quartz, hornblende, pyroxene, ± biotite, and opaque oxide minerals. 

A regional propylitic alteration event affected much of the study area following 

caldera formation and was contemporaneous with Silverton Volcanics deposition (Burbank, 

1960). The propylitic alteration formed as the large thickness of lavas that infilled the San 

Juan caldera cooled and degassed, altering the primary igneous mineral assemblage to a 

secondary assemblage containing chlorite, ± epidote, ± calcite, ± pyrite, fine-grained 

7
muscovite, and iron oxide minerals. This propylitic assemblage was shown to have some 

acid-neutralizing capacity where it was not more intensely altered by later hydrothermal 

alteration events (Yager and others, 2005). 

Prospect Gulch is located on the margin of the historic Red Mountain mining district, 

where ore deposits of silver, copper, lead, and zinc sulfides were discovered in 1881 

(Burbank, 1947) and is located near the northwest structural margins of the San Juan and 

Silverton calderas. This area is the locus for several small-volume plugs and dikes of dacite 

to rhyolite composition that intruded along the structural margins of the calderas, long after 

caldera activity ceased. Isotopic ages of intrusions near Prospect Gulch indicate that they also 

formed several million years after eruption of the intermediate-composition Silverton 

Volcanics lavas during the Miocene Epoch, which are thought to have provided the heat 

source for the hydrothermal system that was responsible for mineralization and associated 

alteration in and adjacent to the Red Mountain mining district (Lipman and others, 1976; 

Bove and others, 2001). 

Several alteration types formed contemporaneously with or shortly after felsic 

intrusive activity at ~21 Ma, overprinting the regional propylitic assemblage and locally 

eliminating any acid-neutralizing capacity while introducing acid-generating minerals, 

especially pyrite. These assemblages are particularly evident in the vicinity of Red Mountain 

#3 (fig. 1) whose slopes drain into Prospect Gulch. The summit and slopes of Red Mountain 

#3 are stained with secondary mineral coatings that are caused mainly by the oxidation and 

weathering of pyrite. The mineral coatings impart spectacular hues of red, yellow, and 

brown, which led to the naming of the Red Mountains. 

The geology of the area and types of alteration vary substantially from north to south 

across the Prospect Gulch subbasin (Bove and others, in press). The majority of intensely 

altered terrain is exposed along the northern part of the subbasin on south-facing slopes along 

and beneath the ridge that separates Dry Gulch from Prospect Gulch (see fig. 3). Acid sulfate 

mineralization is exposed near Red Mountain #3 and is characterized by a high sulfidization 

mineral assemblage that includes quartz, alunite, pyrophyllite (QAP assemblage), and pyrite. 

Pervasive silicification accompanied the acid sulfate alteration where it forms highly resistant 

ridges such as those exposed on Red Mountain #3. Poorly indurated and more easily 

weathered argillic (ARG assemblage) alteration occurs on the margins of the quartz-alunitepyrophyllite assemblage (QAP assemblage); dickite (a waxy clay mineral in outcrop) is 

commonly associated with this assemblage. Areas of pervasive quartz-sericite-pyrite (QSP 

assemblage) alteration, locally containing 10 – 20 volume percent pyrite where not oxidized, 

is the largest alteration type exposed in Prospect Gulch. The QSP assemblage commonly 

crops out topographically below or adjacent to the QAP and ARG assemblages. Similar to 

the ARG assemblage, the QSP assemblage is more readily weathered than the QAP 

assemblage. Surficial deposits including debris cones and talus that have formed below Red 

Mountain #3 incorporate clasts of the upslope QAP, ARG, and QSP assemblages. 

In the southern part and lower one-third of Prospect Gulch, regional propylitic 

alteration dominates, although it is locally overprinted by narrow, more intensely altered 

zones of QAP and QSP assemblages that are exposed in northeast-trending gulleys in the 

upper part of the subbasin that drain toward the north into Prospect Gulch. Locally, surficial 

deposits involving mainly propylitically altered clasts, whose source is located along the ridge 

that separates Georgia Gulch from Prospect Gulch (see fig. 3), are volumetrically important. 

A general structural fabric is evident in and around Prospect Gulch based on 

interpretation of mapped veins (D.J. Bove, unpub. data, 2005; Bove and others, in press). 

Northwest-, north-, and northeast-trending veins are evident along with another prominent set 

8
of east-trending veins. These veins may have formed along existing faults or formed 

contemporaneously with mineralization along structural zones of weakness. Definitive 

evidence at the surface of faulting related to vein emplacement, however, is sparse. Eastwest-trending veins are not as common as their north-trending counterparts, but they do occur. 

Major structures, if present, are obscured largely by the intense alteration that has affected 

much of the northern subbasin. Additional detailed mapping is needed to determine offset of 

marker horizons along faults (if any are preserved) such as interbedded volcaniclastic units 

within the Silverton Volcanics. 

Hydrologic Setting 

The stream in Prospect Gulch is approximately 2.4 km in length with an elevation 

change of 800 m. Average annual precipitation is about 114 cm with 94 cm occurring as 

snowfall (Wirt an others, 2001). As a result, most recharge into the ground-water system 

occurs in late May and early June during the spring snowmelt. Late June through September 

is dominated by summer thunderstorms, producing rainfall that provides additional groundwater recharge (Wirt and others, 1999). Snow generally covers the ground surface in most of 

Prospect Gulch from October through early May, preventing any significant recharge to the 

ground water-system. 

Well and Piezometer Completion Data 

In August and September of 2004, three wells and one piezometer were drilled by 

Spectrum Exploration using a Boart Longyear Delta Base 540 drilling rig (fig. 2). The 

locations and elevations of these wells and piezometer are in table 1 and figures 3 – 5. Initial 

well drilling was started using a rotary core bit with a casing advancer to get through 

unconsolidated material and highly fractured, weathered bedrock. All drilling depths are 

reported in feet since these were the units provided by the contractor. In well UPG-D the 22-

ft length of casing was left in the ground, whereas the surface casing was removed from wells 

MPG-D and LPG-D upon completion. Split spoon samples were collected when using the 

rotary core bit. Competent bedrock was drilled using a diamond-encrusted drill bit, and core 

was collected using a wireline system. The resulting drill hole was 3.875 inches in diameter. 

Downhole drilling equipment was cooled using direct water circulation, where the water was 

drawn from Prospect Gulch near each drilling location. Multilevel sample points were 

installed within each borehole (UPG-D, MPG-D, and LPG-D) as shown in figures 6 – 8, 

respectively. Well UPG-D remained an open borehole from the date of drilling completion 

(August 20, 2004) until it was completed with multilevel sampling points on July 11, 2005. 

As indicated in table 1, screened intervals were completed using 0.010-inch, preslotted, 

manufactured PVC pipe, or hand-slotted PVC pipe, or a BARCAD device. The BARCAD 

device is produced by BESST, Inc., and provides a means for sampling deep well locations by 

using compressed gas. The BARCAD device has a check valve that closes under pressure to 

allow water sampling but remains open under normal conditions to allow for ambient 

hydraulic-head measurements. 

During the same time period, 15 piezometers were installed at the base of Prospect 

Gulch by the USGS New Mexico Water Science Center under contract with the BLM. These 

installations were completed using a Geoprobe model 5410D hydraulically powered direct 

push drilling rig (fig. 9). This system drove a 2.125-inch drill stem into the subsurface until 

refusal, which was assumed to be cemented alluvial material or bedrock. A well point or 

9
piezometer was completed within this drill stem with 10/20 mesh sand filled to 2 ft below 

ground surface. The remaining 2 ft was filled with bentonite pellets. In addition, five 

piezometers were installed with the same Geoprobe rig and the same completion procedure by 

the BLM in the area of the Lark Mine (fig. 4, LGP series). The locations of all of these 

“Geoprobe holes” are shown in figures 3 – 5. Installation details and locations are in table 1. 

Latitude, longitude, and elevation for all points listed in table 1 were measured using a Leica 

GPS1200 system with accuracies generally on the order of ± 0.02 m. The original location 

and elevation data file is included as Appendix A. 

Core Logs and EDXRF Data 

Core logs are shown in the following figures: UPG-D in figure 10, MPG-D in figure 

11, and LPG-D in figure 12. The original core log files are in Appendix B and photos of all 

of the cores are in Appendix C. Data on fracture density and orientation for all of the well 

cores are in tables 2 – 4. No coring was completed in any of the piezometer holes. 

Energy dispersive x-ray fluorescence (EDXRF) analyses were acquired on several 

depth intervals of each core while in the field (Appendix D). These data were acquired by 

using a portable EDXRF NitonTM instrument. EDXRF analysis is a nondestructive technique 

that is useful for simultaneous acquisition of a suite of elements over a broad spectral energyexcitation range. The NitonTM instrument uses both Cd109 and Am241 radioisotope x-ray 

sources; each source is used to excite a suite of elements that have lower x-ray excitation 

energy (lower atomic number) than the respective radioisotope used as an excitation source. 

Data acquired are semiquantitative, especially in the field, where the rock matrix analyzed is 

heterogeneous and the silicon-lithium x-ray detector in the NitonTM instrument is at air 

temperature rather than cooled by liquid nitrogen, as is common in laboratory applications. 

Higher analytical accuracy and precision is possible with EDXRF units when homogeneous 

matrices such as rock powders are available for analyses. Nonetheless, the NitonTM field 

EDXRF instrument is useful for providing a semiquantitative assessment of selected elements 

and is useful as a geochemical element screening tool. 

Elements that typically are determined with a high precision and accuracy using the 

Cd109 source include rubidium, strontium, zirconium, and zinc. Analyses for iron, lead, 

arsenic, molybdenum, and manganese also are reported in Appendix C. Samples with low to 

intermediate iron abundances are the most accurate. Spectral overlaps must be evaluated 

when using uncorrected arsenic and lead concentration data, and robust spectral 

deconvolution algorithms are needed when lead and arsenic are both present in a sample. 

Molybdenum concentrations by EDXRF, especially at low concentrations as are typical in 

Prospect Gulch core samples, are at best considered semiquantitative. Using the Am241

 source, 

barium is the only element in high enough concentration to determine results with reasonable 

precision and accuracy. 

Slug-Test Data 

Slug tests were completed in all piezometer and well points during the period of June 

23 – 27, 2005. These tests were completed by inserting a 0.25-inch polypropylene line below 

the water table along with a pressure transducer. The water in the casing above the end of the 

polypropylene line was air-lifted using nitrogen (slug change in water level), and the changing 

water levels were measured with the pressure transducer. The pressure transducer system 

used a Geokon 4500C vibrating-wire pressure transducer paired with a Geokon 8001 single10
channel data logger. All slug-test results were analyzed using Aqtesolv for Windows version 

3.50 Professional by HydroSOLVE, Inc., and followed the procedures for choosing slug test 

analysis methods discussed in Butler (1997). The slug-test data and individual wellcompletion data used for the analyses are in Appendix E. In the analyses, the diameter of the 

air tube and the transducer wire (9 mm of solid “equipment”) were accounted for in 

calculating the inner diameter of the casing. All Aqtesolv files are in Appendix F. All tests 

were analyzed using the Kansas Geological Survey (KGS) model for the analysis of slug tests 

(Hyder and others, 1994; Butler, 1997), and the results are in table 5. Confined conditions 

were used only for the lower elevation well (LPG-D). All slug-test results were also analyzed 

with the solution methods of Hvorslev (1951) and Bouwer and Rice (1976), which provided 

very similar results in all cases. 

 Slug-test results indicate three general areas of similar hydraulic conductivities, which 

are (1) near-surface alluvial/colluvial material, (2) bedrock, and (3) alluvial/colluvial material 

in the middle of Prospect Gulch. The majority of piezometers (all GPPG wells, MPG-D-13 

and LPG-D-25) are completed in the near-surface alluvial/colluvial material and provide a 

range of hydraulic conductivities from 7.9 x 10-7 m/s to 1.2 x 10-5 m/s. These results are 

typical for shallow deposits with a large variation in depositional environment. Of these 

piezometers, GPPG-12 (7.9 x 10-7 m/s) is very shallow and was completed in clayey/silty 

stream overbank deposits in a marshy area. GPPG-8 (1.2 x 10-5 m/s) was completed in an 

abandoned stream-channel deposit. A representative value for these alluvial/colluvial 

materials that overlie bedrock is approximately 5 x 10-6 m/s. The two bedrock monitoring 

points, LPG-86 and LPG-159, had hydraulic conductivities of 4.8 x 10-7 m/s and 7.8 x 10-7

m/s, respectively, for a representative value of approximately 5 x 10-7 m/s. The 

alluvial/colluvial material in the middle of Prospect Gulch (LGP-3 and LGP-5) is classified 

separately, with hydraulic conductivities of 3.4 x 10-7 m/s and 7.9 x 10-8 m/s, respectively, 

because of its lower hydraulic conductivity due to higher silt/clay contents associated with the 

very hydrothermally altered source rock. 

Hydraulic Head Data 

Hydraulic head data from all measured wells and piezometers from installation 

through June, 2006, are in Appendix G. Because of the limited time period of 

measurement and limited number of measurement locations in the interior of Prospect Gulch, 

a discussion of the data is presented below in lieu of graphs and hydraulic-head elevation 

maps. 

Well UPG-D: The upper elevation well (UPG-D) shows the greatest variation in 

hydraulic heads during the time that this was an open borehole. This hole was dry in the 

summer of 2004, except for a brief period after a precipitation event in September 2004. In 

the spring of 2005, the hydraulic head was at 37 ft below ground surface. As a multilevel 

completion, this well shows a very strong downward gradient (hydraulic-head elevation 

change divided by monitoring-point elevation change = 0.87). 

Well MPG-S: The shallow piezometer (MPG-S) near the stream in the middle of 

Prospect Gulch shows relatively stable water levels because it is very close to the stream. 

Well MPG-D: The deep middle elevation well (MPG-D) consistently shows a 

perched water-table system in the colluvial material above the fractured bedrock (MPG-D13). The colluvial material at depth (MPG-D-51) is commonly unsaturated, as is the fractured 

bedrock just below the colluvial material (MPG-D-110). A deeper water table occurs with 

depth at approximately 165 ft (MPG-D-173) with seasonal changes in saturated/unsaturated 

11
conditions. The deeper ground-water system appears to have a delayed response to recharge 

during the year, possibly because it is being recharged by snowmelt at higher elevations. The 

shallow colluvial system responds very quickly to recharge events and is seasonally variable 

(MPG-D-13 and LGP-1 through LGP-5). 

Well LPG-D and piezometers: At the base of Prospect Gulch, many of the 

piezometers are measuring deep ground water that is discharging to Cement Creek. Because 

this is a discharge zone, seasonal variations in hydraulic head are minimal. However, GPPG8, 9, 10, and 11 do appear to measure shallow water from seasonal recharge events because 

these points are all in the alluvial material close to the mouth of Prospect Gulch. In the lower 

elevation well (LPG), there is a strong upward gradient (0.19) representing a confined groundwater discharge zone in the bedrock. 

References Cited 

Besser, J.M., Finger, S.E., and Church, S.E., in press, Impacts of historical mining on aquatic 

ecosystems—An ecological risk assessment, in Church, S.E., von Guerard, Paul, and 

Finger, S.E., eds., Integrated investigations of environmental effects of historical mining 

in the Animas River watershed, San Juan County, Colorado: U.S. Geological Survey 

Professional Paper 1651. 

Bouwer, H., and Rice, R.C., 1976, A slug test method for determining hydraulic conductivity 

of unconfined aquifers with completely or partially penetrating wells: Water Resources 

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Bove, D.J., Hon, K., Budding, K.E., Slack, J.F., Snee, L.W., and Yeoman, R.A., 2001, 

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mineralization in the western San Juan Mountains, Colorado: U.S. Geological Survey 

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River Watershed, San Juan County, Colorado: U.S. Geological Survey Professional 

Paper 1651.

Wirt, L., Leib, K.J., Bove, D.J., Mast, M.A., Evans, J.B., and Meeker, G.P., 1999, 

Determination of chemical-constituent loads during base-flow and storm-runoff 

conditions near historical mines in Prospect Gulch, upper Animas River watershed, 

southwestern Colorado: U.S. Geological Survey Open-File Report 99–159, 39 p. 

Wirt, L., Leib, K.J., Bove, D., and Melick, R., 2001, Metal loading assessment of point and 

non-point sources in a small alpine sub-basin characterized by acid drainage—Prospect 

Gulch, upper Animas River watershed, Colorado: U.S. Geological Survey Open-File 

Report 2001–0258, 36 p. 

Yager, D.B., and Bove, D.J., 2002, Generalized geologic map of part of the upper Animas 

River watershed and vicinity, Silverton, Colorado: U.S. Geological Survey Miscellaneous 

Field Studies Map MF–2377, scale 1:48,000. 

Yager, D.B., McCafferty, A.E., Stanton, M.R., Diehl, S.F., Driscoll, R.L., Fey, D.L., and 

Sutley, S.J., 2005, Net acid production, acid neutralizing capacity, and associated 

geophysical, mineralogical, and geochemical characteristics of Animas River watershed 

rocks near Silverton, Colorado: U.S. Geological Survey Open-File Report 2005, 78 p. 

13
Upper Animas River 

watershed boundary 

Red Mtn. #3

North 

Figure 1. Location of Prospect Gulch in the upper Animas River watershed. 

14
Figure 2. Boart Longyear Delta Base 540 drilling rig operated by Spectrum 

Exploration at upper elevation hole in Prospect Gulch. 

15
Figure 5 boundary Prospect Gulch watershed boundary

Figure 4 boundary 

Piezometers 

Wells 

Figure 3. Locations of wells and piezometers in and around Prospect Gulch. 

16
LGP-4

LGP-5

LGP-3

LGP-1

MPG-D 

LGP-2

MPG-S 

UPG-D 

Piezometers 

Wells 

Figure 4. Locations of wells and piezometers in Prospect Gulch, middle and upper 

elevations. 

17
GPPG-15 

GPPG-14 

GPPG-12 

GPPG-16 

GPPG-11 

GPPG-8 

GPPG-7 

GPPG-6 

GPPG-9 

GPPG-17 

GPPG-10 

GPPG-5 

GPPG-1 

LPG-D 

Piezometers 

Wells 

Figure 5. Locations of wells and piezometers in and around Prospect Gulch, lower 

elevations. 

18
Monitoring-well construction (not to scale) 

Total depth = 223 feet 

201 feet 

110 feet 

Screen = 219.5 - 223 feet 

Explanation

0.75-inch 1-inch 

Sch. 80 PVC 

#60 mesh 

pre-packed screen 

Concrete 

1 foot 

#10-20 sand 

#4-8 sand 

90 feet 

75 feet 

65 feet 

0.75-inch or 1-inch 

Sch. 80 PVC 

10 slot screen 

43 feet 

30 feet 

40 feet 

196 feet 

105 feet 

95 feet 

70 feet 

60 feet 

27 feet 

Bentonite pellets 

Figure 6. Completion diagram of UPG-D. 

19
Monitoring-well construction (not to scale) 

Total depth = 173 feet 

148.9 feet 

125 feet 

Screen = 170.5 - 173 ft. 

Screen = 103 – 113 feet 

Screen = 48.5 – 51 feet 

Explanation 

0.75-inch Sch. 80 PVC 

#60 mesh 

pre-packed screen 

Concrete 

1 foot 

#60 mesh sand 

Collapsed formation 

Bentonite pellets 

#8-12 sand 

95 feet 

53.2 feet 

46.8 feet 

Hand slotted 

35.5 feet 

33.3 feet 

22 feet 

7 feet 

13 feet 

Screen = 11 – 13 feet 

Figure 7. Completion diagram of MPG-D. 

20
Monitoring-well construction (not to scale) 

Total depth = 159 feet 

112.3 feet 

97.7 feet 

Screen = 127.15 – 128.82 feet 

Screen = 79 – 81.5 feet 

Screen = 22 – 24.5 feet 

Explanation 

0.75-inch Sch. 80 PVC 

#60 mesh 

pre-packed screen 

Concrete 

1 foot 

#60 mesh sand 

#8-12 sand 71.2 feet 

60.8 feet 

24.5 feet 

Collapsed 

formation 

Bentonite pellets

Figure 8. Completion diagram of LPG-D. 

21
Figure 9. Geoprobe model 5410D rig near the mouth of Prospect Gulch (GPPG10) operated by the U.S. Geological Survey under Bureau of Land Management 

contract. 

22
Figure 10. Generalized core log for UPG-D. 

23
Figure 10. Generalized core log for UPG-D—Continued. 

24
Figure 11. Generalized core log for MPG-D. 

25
26

Figure 12. Generalized core log for LPG-D. 
Location Latitude 

(decimal 

degrees) 

Longitude 

(decimal 

degrees) 

Elevation 

(m) 

Elevation 

(ft) 

Type Des

UPG-D-40 37.8952827 -107.6848674 3,607.95 11,837.10 well upper elevation UPG-D-70 37.8952827 -107.6848674 3,607.95 11,837.10 well upper elevation 

UPG-D-105 37.8952827 -107.6848674 3,607.95 11,837.10 well upper elevation 

UPD-D-220 37.8952827 -107.6848674 3,607.95 11,837.10 well upper elevation 

MPG-S-12 37.8915823 -107.6838561 3,451.13 11,322.61 piezometer middle elevation MPG-S-20 37.8915823 -107.6838561 3,451.13 11,322.61 piezometer middle elevation 

MPG-D-13 37.8922303 -107.6811235 3,434.02 11,266.48 well middle elevation MPG-D-51 37.8922303 -107.6811235 3,434.02 11,266.48 well middle elevation 

MPG-D-112 37.8922303 -107.6811235 3,434.02 11,266.48 well middle elevation MPG-D-173 37.8922303 -107.6811235 3,434.02 11,266.48 well middle elevation 

LPG-D-25 37.8829656 -107.6677624 3,146.23 10,322.26 well lower elevation wLPG-D-86 37.8829656 -107.6677624 3,146.23 10,322.26 well lower elevation w

LPG-D-159 37.8829656 -107.6677624 3,146.23 10,322.26 well lower elevation w

LGP-1 37.8926563 -107.6814151 3,445.41 11,303.83 piezometer BLM geoprobe hLGP-2 37.8925464 -107.6810315 3,443.55 11,297.74 piezometer BLM geoprobe hLGP-3 37.8929278 -107.6817195 3,458.31 11,346.16 piezometer BLM geoprobe hLGP-4 37.8930636 -107.6809829 3,460.82 11,354.41 piezometer BLM geoprobe hLGP-5 37.8932301 -107.6815236 3,470.82 11,387.20 piezometer BLM geoprobe h

GPPG 1 37.8798037 -107.6698466 3,126.97 10,259.09 piezometer Geoprobe point GPPG 5 37.8809120 -107.6685758 3,131.78 10,274.85 piezometer Geoprobe point GPPG 6 37.8812179 -107.6685674 3,133.10 10,279.22 piezometer Geoprobe point GPPG 7 37.8814565 -107.6682467 3,132.97 10,278.77 piezometer Geoprobe point GPPG 8 37.8819331 -107.6677976 3,134.49 10,283.75 piezometer Geoprobe point GPPG 9 37.8822729 -107.6678322 3,138.47 10,296.81 piezometer Geoprobe point 

GPPG 10 37.8823739 -107.6673522 3,138.06 10,295.46 piezometer Geoprobe point GPPG 11 37.8827383 -107.6673504 3,140.48 10,303.43 piezometer Geoprobe point GPPG 12 37.8832397 -107.6668191 3,139.84 10,301.31 piezometer Geoprobe point GPPG 14 37.8837821 -107.6666331 3,140.83 10,304.55 piezometer Geoprobe point GPPG 15 37.8840748 -107.6664378 3,141.52 10,306.83 piezometer Geoprobe point GPPG 16 37.8844705 -107.6659293 3,142.29 10,309.37 piezometer Geoprobe point GPPG 17 37.8825523 -107.6669662 3,136.49 10,290.31 piezometer Geoprobe point 

[m, meters; ft, feet; “, inch] Table 1. Completion data for wells and piezometers. 

27
28

Location Install 

date 

Sand 

top (ft) 

Screen 

top (ft) 

Screen 

bottom (ft) 

Sand pack bottom (ft) 

Total hole 

depth (ft) 

Screen type 

UPG-D-40 7/11/2005 27 30 40 43 223 hand-slotted pipe UPG-D-70 7/11/2005 60 65 70 75 223 hand-slotted pipe 

UPG-D-105 7/11/2005 90 95 105 110 223 hand-slotted pipe 

UPD-D-220 7/11/2005 196 219.5 223 223 223 BARCAD 

MPG-S-12 9/3/2004 5 7 12 13 20 hand-slotted pipe MPG-S-20 9/3/2004 15 17 20 20 20 hand-slotted pipe 

MPG-D-13 9/2/2004 7 11 13 13 173 hand-slotted pipe MPG-D-51 9/2/2004 33.3 48.5 51 53.2 173 BARCAD 

MPG-D-112 9/2/2004 95 103 113 125 173 hand-slotted pipe MPG-D-173 9/2/2004 148.9 170.5 173 173 173 BARCAD 

LPG-D-25 8/31/2004 1 22 24.5 24.5 159 BARCAD LPG-D-86 8/31/2004 71.2 79 81.5 97.7 159 BARCAD 

LPG-D-159 8/31/2004 112.3 127.15 128.82 159 159 BARCAD 

LGP-1 2003 2 18.24 23.24 23.24 23.24 0.010" preslotted LGP-2 2003 2 32.95 37.95 37.95 37.95 0.010" preslottedLGP-3 2004 2 17.33 22.33 22.33 22.33 0.010" preslottedLGP-4 2003 2 14.62 19.62 19.62 19.62 0.010" preslottedLGP-5 2004 2 28.33 33.3 33.3 33.3 0.010" preslotted

GPPG 1 9/16/2004 2 3.25 5.75 5.75 5.75 0.010" preslottedGPPG 5 9/16/2004 2 8.5 13.50 13.50 13.50 0.010" preslottedGPPG 6 9/16/2004 2 4.75 7.25 7.25 7.25 0.010" preslottedGPPG 7 9/16/2004 2 10.3 15.30 15.30 15.30 0.010" preslottedGPPG 8 9/16/2004 2 6.6 11.60 11.60 11.60 0.010" preslottedGPPG 9 9/16/2004 2 4.33 6.83 6.83 6.83 0.010" preslotted

GPPG 10 9/16/2004 2 3.8 8.80 8.80 8.80 0.010" preslotted

GPPG 11 9/16/2004 2 3.5 8.50 8.50 8.50 0.010" preslotted

GPPG 12 9/16/2004 2 4.8 9.80 9.80 9.80 0.010" preslotted

GPPG 14 9/16/2004 2 3.24 5.74 5.74 5.74 0.010" preslotted

GPPG 15 9/16/2004 2 10.95 15.95 15.95 15.95 0.010" preslottedGPPG 16 9/16/2004 2 10.4 15.40 15.40 15.40 0.010" preslottedGPPG 17 9/15/2004 2 3.5 6.00 6.00 6.00 0.010" preslotted

Table 1. Completion data for wells and piezometers—Continued. 
[ft, feet; in, inch] 

Table 2. Data for UPD-D well core on fracture density and orientation. 

Zone 

(ft) 

Approximate 

fracture 

spacing (in) 

Major 

Angle 

(degrees)

Minor 

Angle 

(degrees) 

Comments 

22-27 2-3 40 

27-31 4-7 40 

31-32 1-2 30-40 0 

32-35 3-5 30-40 0 

35-37 6-8 40 0-20 

37-44 2-3 60-70 

30-40 

90 

0 

44-47 4-8 30-50 

47-53 1-3 30-40 

60-70 0 

53-64 8-10 40 

70 0 

64-68 1-4 60-70 0 

90 

68-80 4-9 40-50 

60-70 

0-10 

90 

80-83 2-3 70 40-50 

20 

83-95 6-12 30-50 

70 

95-98.5 2-5 

40-50 

70 

90 

98.5-138 7-10 40-50 

70 

138-167 7-20 60-80 

40-50 

167-169 2-3 70 

90 

90 

0 

169-210 10-16 40-50 

70-80 

210-223.83 7 40-50 

70-80 

80-90 

0 

29
[ft, feet; in, inch] 

Table 3. Data for MPD-D well core on fracture density and orientation.

Zone 

(ft) 

Approximate 

Fracture 

Spacing (in) 

Major 

Angle 

(degrees)

Minor 

Angle 

(degrees) 

Comments 

67-73 5-10 40-50 

0-10 

73-75 Very friable 

75-98 8 40-50 0-10 

70 

98-105 5 40-50 70-80 

90 

105-129 10-15 40-50 

129-141 7-10 50 

70 90 

141-155 Some 5 

Many 1 

50 

70-80 

90 

Very friable 

155-167 1-5 40-50 

70-80 

167-173 Some 5 

Many 1 40-50 Very friable 

30
31

Zone 

(ft) 

Approximate 

Fracture 

Spacing (in) 

Major 

Angle 

(degrees)

Minor 

Angle 

(degrees) 

Comments 

78.58-88.58 1 Too fractured to measure angles 

88.58-100 1-2 60-70 

90 

100-102 7-10 65 

0 

102-114 2-4 40-50 60-70 

0 

114-127 1-2 40-50 60-70 

0 

127-140 7-15 35-50 90 

70 

140-148 3 35-45 

90 70 Lots of vertical quartz infilling 

148-159 7-15 35-50 60-80 

[ft, feet; in, inch]

Table 4. Data for LPD-D well core on fracture density and orientation. 
Location Hydraulic conductivity 

(m/s) 

Comments 

GPPG-5 1.9E-06 Unconfined KGS, average of three tests. GPPG-8 1.0E-05 Unconfined KGS, old stream channel. GPPG-12 7.9E-07 Unconfined KGS, average of two tests, shallow point near wGPPG-14 1.2E-05 Unconfined KGS, average of two tests. GPPG-15 7.1E-06 Unconfined KGS. GPPG-16 4.3E-06 Unconfined KGS, second test better match. MPG-D-13 4.8E-06 Unconfined KGS, average of two tests. LPG-D-25 6.4E-06 Confined KGS, average of three tests. LPG-D-86 4.8E-07 Confined KGS, average of three tests, other methods not a

slightly lower values. 

LPG-D-159 7.8E-07 Confined KGS, average of three tests. LGP-3 3.4E-07 Unconfined KGS, appears to have a more permeable well s

formation K. 

LGP-5 7.9E-08 Unconfined KGS, appears to have a more permeable well s

formation K. 

Alluvial/colluvial 5.E-06 good representative number for modeling Fractured bedrock 5.E-07 good representative number for modeling Middle Prospect Gulch 1.E-07 good representative number for modeling 

[m/s, meters per second; KGS, Kansas Geological Survey; K, hydraulic conductivity] Table 5. Results from slug tests. 

32