HYDROGEOLOGY OF PIPELINE CANYON, NEAR GALLUP, NEW MEXICOIntroduction and ScopeA rock-walled canyon has been carved into the outcrop belt of a seriesof Cretaceous sandstones northeast of Gallup, New Mexico . Fracturepatterns associated with three structural features have a localinfluence on the occurrence and movement of ground water . The presence ofsurficial deposits on the floor of Pipeline Canyon, the physiographicexpression and general attitude of the rocks, and the degree of fracturingin the sandstones are factors which control the amount of water rechargedto the various aquifers in this area .Hydrologic and geologic investigations were made of the sedimentaryunits in Pipeline Canyon to determine the hydraulic properties of theaquifers . The objective was to study the dynamics of flow systemsrecharge area where the rocks have been fractured by structural activity .

LocationThe study area is in the - canyon and mesa

miles (24 .1 km) northeast

Plateau . As a result of geologic, physiographic, and hydrologiccharacteristics of the surrounding area, Pipeline Canyon is includedSan Juan Basin . The axis of Pipeline Canyon(9 .6 km) in a northeast to southwest direction and

country of the Colorado

in the

in thetrends nearly 6 milesis approximately 15of the city of Gallup, New Mexico .

The927459III 1111 II

southern half of the canyon is in sections in T. 16 N. , R. 16 W . and

T. 17 N ., R. 16 W ., McKinley County, New

on the Navajo Indian Reservation which also

County (see Figure 1) .

Climate

2

Mexico, and the northern half is

occupies part of McKinley

rPipeline Canyon and the surrounding mesas and ridges are characterized

b y semi-arid climatic conditions . Daytime temperatures generally reach

a high between 80° and 90° F . (26 .6° and 32 .2°C) in the summer and are

between 40° and 50° F . (4 .4° and 10°C) in the winter . The mean annual

temperature is approximately 48 .5° F . (9 .2°C), according to the United

States Weather Bureau at Gallup, New Mexico .

The annual precipitation generally occurs during two seasons in the

area of investigation . Summer rainfall is mostly between July and August,

and winter precipitation occurs between December and February (Hiatt,

1953) . Convectional thunderstorms provide most of the summer precipitation,

whereas -winter precipitation results from frontal activity and is generally

distributed evenly . The mean annual precipitation at Gallup is 10 .65

inches (0 .27 m) (U.S . Weather Bureau, 1938-60) . Limited data from a

mechanical weather station installed at the United Nuclear milling facility

in Pipeline Canyon show that annual precipitation may be greater by as much

as 4 inches (0 .1 m) .

3

Figure 1 . Map showing location of Pipeline Canyon and major structural

features in the area .

)0,01 71 6

Physical Setting

The landforms in the area surrounding Pipeline Canyon are a result of

erosional processes acting upon alternating weak and resistant sedimentary

units . Resistant beds have formed ledges, cliffs, mesas, and rock benches

that are separated by slopes and valleys carved in weak shaly beds (Cooley

and others, 1969) . The Point Lookout Sandstone, the Upper Dalton

Sandstone, the Lower Dalton Sandstone, sandstone lenses in the Dilco Coal

Member, the Upper Gallup Sandstone, and the Lower Gallup Sandstone are the

cliff or ridge formers in Pipeline Canyon . The slopes and canyon floor are

primarily carved in the Gibson Coal Member, the Upper Mulatto Tongue of the

Mancos Shale, the Lower Mulatto Tongue of the Mancos Shale, coal and shale

lenses of the Dilco Coal Member, the Upper D-Cross Tongue of the Mancos

Shale, and the Lower D-Cross Tongue of the Mancos Shale . The lower part of

Pipeline Canyon is flanked by Ram Mesa to the east, and Mesa de Los -_Lobos

bounds the canyon to the north . Elevations are between 6,840 and 7,100 f t

on the canyon floor to over 7,400 ft on the surrounding mesas .

Sedimentary Rocks

The sedimentary rocks exposed in the study area are part of the

Upper Cretaceous Mesa Verde Group deposited near the margin of

widespread epeirogenic sea under conditions of constantly changing

shorelines (Beaumont, 1971) . Based on lithology and sedimentary features,

the sedimentary sequence in the area can be characterized' by three major

environmental

facies :

offshore marine deposits ;

coastal barrier

sandstones ; and nonmarine deposits (Gibbons, 1980) .

A summary of the

lithology and depositional environment of the sedimentary units in Pipeline

4

5

the north. This regional dip is modified in

Canyon appears in Table 1 . Numerous other sedimentary units occur at depth

below the canyon floor, but are not discussed in this paper .

Structure

Pipeline Canyon is on the northwestern flank of the Zuni Uplift .

This uplift or dome is a basement controlled, upthrust bounded, tilted

block formed during the orogeny which occurred in Late Cretaceous and Early

Tertiary periods in the Colorado Plateau province (Cooley and others,

1969) . The sedimentary rocks of the Zuni Uplift generally dip 3° to 4° to

the Pipeline Canyon area by

structural zones associated with basement faulting (Gibbons, 1980) .

Locally, the rocks dip 4° to 8° to the northwest (see Figure 2) . The

Pipelinebasement faulting has formed the Fort Wingate lineament, the

Canyon lineament, and the Pinedale monocline .(see Figure 1) .

The Pipeline Canyon and Fort Wingate lineaments are shown on ERTS

imagery and color aerial photographs . The Pipeline Canyon lineament trends

east-north eastward, whereas the Fort Wingate lineament trends north-north-

eastward'. These two lineaments intersect in Pipeline Canyon in Section 2,

T. 16 N., R . 16 W. The Fort Vingate lineament is not expressed beyond

this intersection (Gibbons, 1980) . Evidence_ of displacement associated

with the basement faulting is not found at the land surface in Pipeline

Canyon . A structure contour map of the top of the Upper D-Cross Tongue

Member of the Mancos Shale shows flexures of approximately 10 ft

(3 .05 m) that appear to follow the strike of the basement faults .

Table In

.qy and General Hydrology of Sedimentary Units* I .

peline Canyon

After Gibbons (1980) • After Molenaar (1977)

€>N YN

mao°lLStratigraphicUnit Lithology and Thickness EnvironmentalFacies General Hydrology

>,e'

CoMY a Alluviumoat Light yellow-brown, fine to coarse-grainedsandy clays or clayey sands . Thickness rangesfrom 0-13S ft (0-41 .1 m) .---------- Yields small amounts ofwater to wells throughoutSan Juan Basin .

Point LookoutSandstone"IGrayish-orange to very light-gray, fine tomedium-grained, massive sandstone . Thicknessranges from SO to ISO ft (15 .2-45 .7 m) . •

Regressivecoastalbarriersandstone •

Not water bearing in PipelineCanyon. Yields water towells in southern San JuanBasin .

•••

Crevasse CanyonFormation Predominantly light-gray shale with lenses ofvery light-gray slltstone and fine-grainedsandstone . Lenticular coals are coupon .

Nonmarinedeposits •

Not water bearing inPipeline Canyon .

i on CoalMember

kegThickness ranges from 200 to 280 ft (61-85 .3 m) .

Crevasse CanyonFormation

Predominantly light-gray shale with lenses ofvery light-gray siltstone and fine-grainedsandstone . Often merges with the Gibson Coal

Nonmerinedeposits •

Not water bearing inPipeline Canyon .

Nartlett BarrenHemberKcb

Member through fades changes . Does not containcoal . Thickness ranges from 0 to 90 ft(0-27 .4 m) .

Crevasse CanyonFormation Upper Dalton Sandstone Member (Kcdu) and LowerDalton Sandstone Member (Kcdl) are yellowish-gray fine to coarse-grained sandstones withsiltstone lenses . Separated by 20 to 30 ft

Coastalbarriersandstone •

Not utilized as aquifer inPipeline Canyon . Yieldswater to a few wells in theGallup area .DaltonSandstone

MemberKcd

(6-9 .1 m)

Upper Mulatto Tongue of MancosShale (Kavau) . Total unit approximately 180 ft(51 .8 m) including Upper Mulatto Tongue .

Crevasse CanyonFormation

Brownish to dark-gray sandy shale and thin-bedded, fine- rained sandstone . Approximately40 ft (12 .2 m thick .

•

Offshoremarinedeposits

Usually not water bearing .

love- MulattoTongue oftiancos Shale

KMI

> Crevasse CanyonFormationUpper part of unit consists of light-gray toyellowish-brown, fine to medium-praised

ltonmarinedeposits •

Not utilized as aquifer inPipeline Canyon . Yields

sandstone and siltstone ; light-gray to dark- water to wells for domestic_ gray shale and coal . Middle part of unit is and stock purposes inmassive, often crossbedded . fine-grained sand- southern San Juan Basin .

bilco CoalMemberKcdcstone . Lower part of unit consists of dark-gray, highly carbonaceous shale (near coal) ;light-gmay to grayish-brown shale where incontact with siltstone and thin-bedded sand-stone . Approximately 150 ft (45 .7 m) thick .

GallupSandstone Light-gray . fine to coarse-grained, massivesandstone with crossbeddinq . Discontinuous oil Fluvialchannelsandstone ••

Not utilized as aquifer inPipeline Canyon .

Torrivio staining Is corrnn in outcrops . Appears at thetop of the Upner Gallup Sandstone althoughSandstonetember

Kgtlocally this fluvial sandstone is missing .Approximately 30 ft (9 .1 m) thick . ••

GallupSandstoneUpper 40 to 50 ft (12 .2 to 15 .2 m) consists oflight-gray, fine to coarse-grained massivesandstone often crossbedded . Middle partconsists of continuous coal seam 3 to S ft

Coastalbarriersandstone •

Yields water to domesticand stock wells in PipelineCanyon and throughout South-western flank of San Juan(0 .9-1 .5 m) underlain by approximately 1S ft Basin .Upper GallupSandstoneMe

K9u

(4 .5 m) of clay and shale . Lower 70 to 80 ft(21 .3 m) consists of light-gray, fine to medium-grained massive sandstone locally crossbedded .The total unit is approximately 135 ft (41 .4 m)thick .

Mrncostale Dark-gray to brownish-gray shale : discontinuousthin-bedded, fine-grained Sandstones and silt-stones . Selenite crystals are common . Approxl-Offshoremarinedeposit

Usually not water bearing .

l

(;.(rots;

mately 140 ft (42 .6 m) thick .lonque ti,MUr'KmduGallonSamvtstnne Generally buff to light-gray fins-orate" siltysandstone, grain size becoming finer towardsthe base with increasing percentages of clay .

CoastalbarriersandstoneYields vet .r to domestic 1odstock wells In PipelineCanyon and throughoutlower Gallup Approximately 100 ft (30 .5 ∎) thick . southwestern flank of SanSandstone Juan Basin .Numbert.q I

MancosShale Medium-gray to black marine shales with zones ofcalcareous concretions, a few limestone beds,many thin bentonfte beds, and a few offshoreOffshoremarinedeposits

Usually not water bearing .

,

Lower U-Crnss'Tongue W. her_

Kwylsandstone buildups . Approximately 600 ft(192 .8 ∎) thick .

6

Figure 2 . Aerial photograph of Pipeline Canyon showing both the local

and the regional dip of the sedimentary rocks .

If4.

iLl -.., 9-ftI

:

4 . .

.

I

. -jk4. ; I I Y

I - . ..0-s -

L

. 010(

REGIONAL 30 TO 4* NORTHWARD DIPOF SEDIMENTARY ROCKS LOCAL 4° TO 8° NORTHWEST DIPOF SEDIMENTARY ROCKS

The lineaments reflect monoclinal folds and/or second order structural

features associated with monoclinal folding . The monoclinal folds were

formed by the passive bending or draping of the sedimentary units over the

structural relief generated by basement faulting (Gibbons, 1980) . The

intensity of fracturing increases locally in the hinges of the folds .

Fracture density 'associated with the Fort Wingate lineament and the

Pipeline Canyon lineament increases

regional pattern of an average of 1 every 10 ft (3 .05 ) to about 1

fracture per foot . Regional fracture sets generally strike north-northeast

and west-northwest, and the local fracture zones generally strike

north-northeast and northeast parallel to the fold axis (Gibbons, 1980) .

The Pinedale monocline trends to the northwest across Pipeline Canyon

(see Figures 1 and 2) . Total structural relief across the monocline on the

upper surface of the Dalton Sandstone is between 60 and 125 ft (18 .3 and

38 .1 m) (Gibbons, 1980) . The Pinedale monocline has two hinge zones where

the intensity of fracturing increases in the sandstone units .

Surface Water

All streams in Pipeline Canyon and the surrounding area are ephemeral

in their natural condition . Locally, there are some minor springs and

seeps found at the contact between sandstone and shale units near the

canyon walls . The permanence of the springs seems to depend on the

frequency and amount of precipitation . The ephemeral streams drain to

the south from Pipeline Canyon into the

in the sandstone units from the

7

Rio Puerco of the West .

Mine dewatering operations by Kerr-McGee Nuclear Corporation and

United Nuclear Corporation discharge between 8 and 11 cfs (228 .5 and

314 .3 1/s) into pipeline Canyon arroyo . The water is pumped from the

Westwater Canyon Member of the Morrison -Formation which is

approximately 1,250 f t (390 .5 m) below the canyon floor . Thus, the lower

reach of Pipeline Canyon has had perennial flow since 1977 .

A number of the ephemeral drainageways including the principal arroyo

in Pipeline Canyon show long rectilinear channels (see Figure 1) . This

stream pattern suggests structural control by the underlying bedrock . The

trend of the rectilinear segments of stream channels generally coincides

with the direction of the strike of local fracture zones . The stream

pattern is most distinct where the channel crosses the Dalton Sandstone and

the Upper Gallup Sandstone .

Ground Water

The principal water bearing units in Pipeline Canyon are the-:tower

Gallup Sandstone, the Upper Gallup - Sandstone, the Torrivio Sandstone

Member, the Dilco Coal Member, and the alluvial deposits .

yield water 'for domestic and/or stock supply throughout the San Juan Basin .

Figure 3 is a borehole geophysical log from a well in Section 36,

T. 17 N., R. 16 W . that includes the self-potential (SP) curve, gamma-ray

log, resistivity, and the neutron porosity measurements of some of these

water-bearing units . At the southern entrance to the canyon, the rocks

are above the canyon floor and not water bearing . However, the presence of

alluvial deposits in the canyon, the attitude of the exposed rock units,

and the degree of fracturing in the sandstones allow for significant

ground-water recharge to the aquifers .

8

All these units

Qal

Alluvium

Kcdc

Dilco Coal. Member

Kgt

Torrivio Sandstone Member

Kgu

Upper Gallup Sandstone Member

Kndu

Upper D-Cross Tongue of Mancos Shale

Figure 3 . Borehole geophysical log from Section 36, T .17N . •,

R

.16 .W .

showing some of the water bearing units in Pipeline Canyon .

9

Oal

Kcdc

Kgt

Kgu

Kmdu

FEET BELOW_, _-LAND SURFACE,___ ._-

_

-~ T -

~~ N

1dN

E4w~. d0N

CGF M?IC

yr--33

'O

60'r . "- -~M - FLR N-N --%-- rS .- P . iv 49

lq5R6 LTAN:E GHr3 .

The alluvial deposits on the canyon floor are recharged by direct

precipitation, ephemeral streamflow, and perennial streamflow from local

mine dewatering . Ground-water flow in surficial deposits is from northeast

to southwest along the axis of the canyon . The gradient of the alluvial

flow system generally is similar to the slope of the canyon floor .

The stratigraphic sequence from the Mancos Shale through the Daltonr

Sandstone dip below the land surface in Pipeline Canyon . Rainfall or

surface flow enters the aquifers where they are exposed at the surface

through fractures and along bedding planes . The attitude of the fractures

and bedding planes facilitates the entry of water into the sandstones by

gravity flow . Rocks which are below surficial deposits are recharged by

leakage from the saturated alluvium. Relatively little water

infiltrates the unfractured parts of the sandstone aquifers in the

outcrop areas because of their low permeability and the generally- high

rate of evaporation (Cooley and others-, 1969) . The less permeable shale

units reject most of the available ground-water recharge .

The local fracture system associated with the structural features

in Pipeline Canyon has enhanced the ability of the sedimentary rocks to

capture available ground-water recharge . In much of the canyon,

the alluvial system is entrenched into the intensely fractured zones

associated with the local structural features . Thus, the fracture system

is in direct contact with the available recharge in the saturated alluvium .

Joints in the recharge zones of the Upper and Lower Gallup Sandstones

have been widened by solution. Dissolution of sandstones and

10

OO

limestones in outcrop areas throughout the Colorado Plateau was reported byCooley and others (1969) . This physical-chemical modification of the rocksallows for more efficient capture of available ground-water recharge .

The Lower Gallup Sandstone is recharged at the southern end of Pipe-line Canyon where this unit dips below the land surface . The sequence ofrecharge zones 'along the axis of the canyon is illustrated in Figure 4 .Ground-water recharge zones overlap in areas where saturated alluvial

r -deposits are in contact with several aquifers . In Section 2, T. 16 N., CVR . 16 W ., this phenomenon occurs as a result of deep fluvial incision and ~`

Canyon arroyo . The shape of the resulting cone of depression is similar tothe generalized flow net presented by Ferris and others (1962) for adischarging well near a recharge boundary .

Water-table conditions prevail in areas where aquifeis are rechargedin Pipeline Canyon . However, infiltration from perennial streamflow hascreated ground-water mounds in the local alluvial deposits along the mainarroyos . Artesian conditions may exist in sandstone units which are

1 1

It-subsequent surficial deposition (see Figure 5) .

0

Aquifer tests in Zone 3 of the Upper Gallup Sandstone show a hydraulicconnection between the alluvial sediments and the sandstones .Time-drawdown analyses indicate that the cone of depression intercepts arecharge boundary . Analyses with the approximation developed by Cooper andJacob (1946) and the law of times defined by Ingersoll and others (1948)show that the distance to the recharge source from the pumped well isapproximately equal to the distance to the stream channel of Pipeline

12

Figure 4'. Structural section from NE to SW through Pipeline Canyon .

Areas where sandstones are directly beneath the alluvial

deposits are ground water recharge zones . Vertical exaggeration

is 7 .5 times .

SW

PINEDALE

AJT MSL

OUTLINE OF PIPELINE CANYON SHOWINGLOCATION OF CIIO$$ SECTION

hORIZONTAL SCALEO 1500 FEETO500 METERS

Gal

Kcg

MONOCLINE

KcduKmmuKcdl :Kmml ..Kcdc. ..

Kgu. . . . 6300-

7000-

ALTITUDE IN FEET 5800-MSL

~LLOO(

NE

13

Figure 5 . Schematic diagram of ground water recharge zone in sec . 2 .,

T.16N ., R .16W . No scale intended . Darker bands are shale

units .

SW

LcL BOO(

Gallu Sandstone

NE

adjacent and hydraulically connected to the alluvium in these areas . Ingeneral, the dip of the Pinedale monocline causes the flow systems tochange from water-table to artesian conditions in Pipeline Canyon . On theupthrown side of the monocline, water levels in wells tapping theUpper Gallup Sandstone in T .17N., R.16W ., sec . 36 are below or only a fewfeet above the top of the aquifer . A well in the same formation on thedownthrown side of the monocline shows the water level is 175 ft (53 .3 m~above the top of the unit . The distance between wells which show thechange from water-table to artesian conditions is approximately 7,100 ft(2160 m) .

The volume of natural ground water recharge to the aquifers inPipeline Canyon is difficult to estimate because of the lack of historicalmeasurements of ground water elevations and surface flow in the arroyos .However, the perennial streamflow resulting from local mine dewatering hasbeen measured at two locations approximately 1 .2 miles (1 .9 km) apart (see

14

Weir measurements, local aquifer coefficients, and water-level datawere used in a water budget to estimate recharge to aquifers under

Figure 1) . Weir measurements of average daily flows are presented inTable 2 . .

TABLE 2 . Weir measurements of streamflow in Pipeline Canyon

NORTH WEIR SOUTH WEIRDIFFERENCE

IN FLOW1981 1/s cfs 1/s cfs 1/s cfsMarch 167 .1 5 .9 152 .9 5 .4 1 4 .2 0 .5April 175 .6 6 .2 158 .6 5 .6 17 .0 0 .6May 167 .1 5 .9 152 .9 5 .4 14 .2 0 .5June 158 .6 5 .6 144 .4 5 .1 14 .2 0 .5

present conditions . The Upper Gallup Sandstone, the Torrivio Sandstone

Member, and sandstone lenses of the Dilco Coal Member underly the principal

arroyo in the canyon between the two weirs and, therefore, are recharged by

1 5

The estimates of numbers (2)- and (3) above were made with flow-net analyses4

using known aquifer coefficients, aquifer dimensions, and potentiometric

surfaces . It was assumed that the amount of water in storage in the allu-

vium is constant because water levels in wells .in

these sediments have been

nearly steady since November, 1980 . Thus, the alluvial system has reached

a steady-state condition between recharge from the streamflow and

rocksdischarge either by leakage into the underlying sedimentary

or alluvial underflow beyond the area measured b y the two weirs . The

estimate of loss by evapotranspiration was made using recorded net

evaporation figures obtained in Pipeline Canyon . There are few, if any

phreatophytes growing along the arroyos in Pipeline Canyon .

The balance

streamflow

loss in flow

infiltration. The following water budget

between the weirs :

accounts for the

TABLE 3 . Average daily loss inflow between weirs 47,695 ft3/day

1. Estimated loss to evapotranspiration 3,500 ft 3/day

2 . Estimated loss to alluvial underflow 4,000 ft3/day

3 . Estimated recharge to Upper Gallup 32,000 ft3/day

4 .

Sandstone

Estimated recharge to Torrivio Sandstone 8,000 ft3/dayMember and Dilco Coal Member

TOTAL 47,500 ft /day

of the average daily loss between the two weirs was attributed to recharge

to the Torrivio Sandstone Member and sandstone beds in the Dilco Coal

Member .

Ground water Movement and Discharge

Flow in the 'sandstone aquifers in Pipeline Canyon is generally to ther

north, nearly opposite to the direction of ground-water movement in the

overlying alluvium . Recharge mounds from streamflow infiltration control

the flow direction locally (see Figures 6 and 7) . However, the dip of the

sandstones, facies changes, and wedging-out of aquifers control

ground-water movement in the San Juan Basin outside the recharge area

(Cooley and others, 1969 and Stone, 1981) . The aquifers in these

Cretaceous rocks are probably interconnected, although imperfectly, into a

multiple hydraulic system in most of the western San Juan Basin .: The

development of this system of inter-aquifer movement by leakage in

different parts of the basin helps to direct ground-water discharge to the

reaches .of the Chaco and San Juan Rivers in the northwestern part of this

basin (Cooley and others, 1969) .

The nature of ground-water flow in the Upper Gallup Sandstone in

Pipeline Canyon is shown in Figures 6 and 7 . This sandstone is a single

geologic unit but is three distinct hydrologic units . Figure 3 shows

that there is a shale layer, Zone 2, approximately 20 ft (6 m) thick

which separates Zones 1 and 3 . The shale layer acts as an aquiclude and

persists throughout the Pipeline Canyon area . Borehole geophysics from

a well 5 miles (8 km) to the northwest of the canyon show that the Upper

Gallup Sandstone in this area is also separated by the shale .

16

Figure 6 ; Potentiometric surface of Zone 3 of the Upper Gallup Sandstone .

Dotted area indicates where sandstone is recharged by downward

leakage through the overlying alluvial deposits .

1 7

lgonzale

001736

1 8

F

Figure' 7 . Potentiometric surface of Zone 1 of the Upper Gallup Sandstone .

Note that the recharge area is south of where Zone 3 is

recharged .

i

1 9

Figure 6 shows that the recharge zone for the upper sandstone body

(Zone 3) is in Sections 35 and 36, T . 17 N., R. 16 W . The recharge zone

for the lower sandstone body (Zone 1) is further to the south (see Figure

7) . There are no aquifer tests to indicate whether there is significant

downward leakage from Zone 3 into Zone 1 in this area . However, long-term

aquifer tests 'in Zone 3 show no detectable downward leakage from the

Torrivio Member of the Gallup Sandstone . This sandstone is separated frm

Zone 3 by a similar shale layer. Once the various aquifers of the Gallup O\K1

Sandstone become fully saturated, inter-aquifer movement by leakage r'r

increases .

00

Hydraulic Properties of the Aquifers

The ranges for aquifer properties which appear in Table 4

were computed from either pumping or bailing tests . Data obtained- from

pumping Zone 3 of the Upper Gallup Sandstone show that the transmissivity

is similar to what was reported by Mercer and Cooper (1970), Mercer

Lappala-(1972), and Mc Lean (1980) . However, in each of these cases, the

thickness of the Gallup Sandstone was greater than that of Zone 3 by over

100 ft (30 .4 m) . The hydraulic conductivity of the upper Gallup sandstone

is therefore higher in Pipeline Canyon than. in

surrounding areas

. The

increased intensity of fracturing in the canyon and the chemical weathering

of the rocks in the recharge zone are thought to be responsible for the

higher values .

The hydraulic conductivity of the alluvium in Pipeline Canyon is

relatively low as a result of large percentages of silt and clay derived

from the weathering of local shale units . There have been no aquifer tests

and

TA RI .F 4 .--IlydrauIIr. properties of aquifers In PlpeIIne Canyon

)001740

Pumping Tests Railing Tests

. ;Ic unit Numher of tcstq TransmIsslvtty(ft /day)

Coefficient Yield(rpm)

Specific Capacity Numhor of tests hydraulic conductivityof storage (Rpm/ft) (ft/day)

A I I h ;v him --- --- --- --- --- 3 0 .25 - 1 .81'pper fillipCanulat .m ; • 10 110-323 0,004 - 0 .05 3-25 0 .2 - 0 .7 --- ---(7nne 1)

2 25-70 --- 2-23 --- --- ---I'ppwr Cal I ; ;pSan ;I • ; t .i

in the Dilco Coal Member or the Torrivio Sandstone Member . The Dilco

primarily yields small amounts of water to domestic and stock wells

throughout the southern San Juan Basin .

The coefficient of storage from tests . in

Zone 3 of the Upper Gallup

Sandstone is between 4 x 10-3 and 5 x 10-2 . The majority of the valuesr

obtained were greater than I x 10-2 indicating water-table conditions . The .

portion of the aquifer tested was on the upthrown side of the Pinedale,

Monocline . Cooley and others (1969) suggested that the fine-grained

aquifers in the San Juan Basin drain slowly and that storage

coefficients calculated from short-term tests would approach those of

artesian aquifers and be too low . The tests from which the coefficient of

storage of Zone 3 was calculated were 72 and 91 hours in length . Thus, the

coefficient of storage for this unit may be-somewhat higher than presented

in Table 4 .

Water Quality

The characterization of ground water in the study area is complex in

that there exist several individual aquifers each with distinctive water

quality . The aquifers are recharged in part unnaturally by perennial

streamflow sustained by uranium mine dewatering operations and by leakage

from uranium mill tailings disposal ponds, as well as naturally by

precipitation and runoff . Thus, the source of the recharge in addition to

the geochemical properties of the rocks is responsible for the chemical

nature of the ground water . Table 5 illustrates how the quality of water

varies both within a geologic unit and also from unit to unit .

20

*Well completed in Upper Gallup Sandstone, Zone 1**Bureau of Indian Affairs Field Number***Recorded information does not distinguish which member of Gallup Sandstone well is completed in .

SOURCES OF WATER QUALITY DATA1) New Mexico Environmental Improvement Division (1981-1982 data)2) Cooper and John (1968)3) Mercer and Cooper (1970)

Table 5 Water Quality in Pipeline Canyon and Gallup . New tlexico Area(All values except pH in mg/1)

Welt __Location Formation Na +

K+ Ca++ Mg HC0.1 SO4 C1 - N03 -N TDS p11

16 .16 .2 Kgu-1 * 322

5 327 154 351 1837 27 0 .29 2998 6 .16 .16 .2 Kgu-1 * 375

7 158 48 395 989 27 - 1841 7 .16 .16 .2 Kgu-1 * 81

9 92 27 563 199 23 0 .19 810 7 .16 .16.2 Kgu-1 * 363

12 218 120 387 1341 39 - 2357 -17 .16 .36 Kgu-1 * 506

7 180 104 387 1720 28 6 .83 2602 7 .17 .16 .36 Kgu-1 * 342

- 21 15 258 601 - - 941 7 .17 .16 .36 Kgu-1 * 327

2 24 8 234 198 20 0 .13 1066 7 .17 .16 .36 Kgu-1 * 359

6 1-36 75 278 1136 22 1 .21 1927 7 .17 .16 .36 Kgu-1 * 271

3 28 15 255 395 21 0 .49 860 6 .16.16 .2 Kgu-1 * 175

2 69 61 60 813 37 - 112417 .16 .36 Kgu-1 * 474

7 183 86 392 1406 26 2461 -::Z16 -17 .15 .30 Kgu 120

7 396 154 210 1908 14 0 .19 2743 7 .17 .16 .35 Kgl 179

4 204 - 448 391 11 0.6 1623 r7 .16 .16 .18 Qal 106

2 75 15 308 221 18 616 ~ .16 .16 .18 Qal 94

5 192 38 327 582 18 0.1 1151Pipeline Stream 122

1 21 8 223 150 12 1 .0 442Arroyo 014M-1 **

The wells listed below lie outside Pipeline Canyon or its immediate vicinity . 366Kg *** 144 1 1 266 32 14 0.0514N-102 ** Kg 341 32 11 458 259 153 0.25 102014K-300 ** Kg 997 16 3 752 263 860 0_47 258014K-313 ** Kg 72 228 99 271 835 11 0 1390 7 . :14T-501 ** Kg 1690 20 4 742 ,362 1940 0.09 4400 7 .14T-531 ** Kg 181 2 0 182 146 26 0 .05 452 8 .15T-303 ** Kg 504 157 89 297 1520 16 0.14 2450 8 .16T-339 ** Kg 157 48 13 364 188 13 0 .05 61318T-551 ** Kg 103 47 5 231 126 28 045 455 8 .'14 .18.16 Kg 439 11 3 607 202 185 0 .09 1160 8 .15 .18 .8 Kg 429 5 1 291 532 66 0 .05 1250 8 :.

.9 Kg 195 10 2 264 190 26 0 6n3 8 . :

.14 Kg 139 87 33 321 352 16 0.43 807 7 .!

.18 Kg 213 23 22 303 216 96 0 .14 738 7 .1

.24 Kg 52 134 42 296 319 8 - 758 7 .,

.30 Kg 174 1 1 284 92 18 0 .02 454 8 .f

.24 Kg 92 10 5 214 59 5 0 294 8 .(' .17 Ka 241 46 10 284 331 86 0.05 879 7 . '_

16 .5 .19 Kg 720

- 10 2 308 1250 27 0.02 2190 8 . :16 .18 .7 Kg 273

3 11 3 284 306 50 - 860 8 .'16 .18 .17 Kgu 87

8 42 9 254 120 .6 0.18 413 7 .£16 .18.17 Kgl 724

7 14 1 350 1050 158 0.05 2170 8 . :16 .20.9 Kg 247

- 11 3 428 149 30 0.02 680 8.f15 .9.9 Kcdc 1007 88 23 166 2190 40 0 .61 3440 7 .115 .10.6 Kcdc 204 143 67 312 768 14 0.02 136016 .11 .16 Kcdc 222 139 27 260 684 11 0 1220 7 .f16 .13 .11 Kcdc 91 522 231 638 1890 23 0.05 3120 7 .c

Without exception, the dominant anion found in all the waters in the

study area is the sulfate ion . On the other hand cation makeup of the

waters varies, and this fact may be used to distinguish natural waters from

water that has been contaminated by leakage from mill tailings fluids .' An

examination of the wells in Table 5 that are located outside of Pipeline

Canyon in the southwestern part of the San Juan Basin illustrates that the

water in Gallup Sandstone is dominated by the monovalent cation sodium .

Likewise, in Pipeline Canyon, water in wells 120, 129, 130, 132, 138, 141,

142, 145 147, 338, and 409 (see Table 5) is dominated by the sodium ion .

All of these wells are in Zone 1 of the Upper Gallup Sandstone . The water

quality from the wells in the Lower Gallup Sandstone is also dominated by

sodium and sulfate (see Table 5) .

The surface flow from the mine dewatering operations is relatively low

in content of total dissolved solids (TDS) . and the major cations and

anions . Figure 5 shows that sodium is the dominant cation and sulfate is

the dominate anion in the surface water . The mine water flows south from

Pipeline- Canyon Arroyo into the Rio Puerco . Alluvial wells adjacent to the

Rio Puerco show water quality that is very similar to the surface flow (see

Table 5) .

Leakage of fluids from uranium mill tailings disposal ponds in

Pipeline Canyon is another source of recharge to several aquifers . In the

past, the fluids were highly acidic (pH approximately 1 .5), and high in

concentrations of TDS, sulfates, heavy metals, and ammonia (as a precursor

for N03 formation) . Water quality analyses from wells downgradient from

the disposal ponds show elevated concentrations of SO4 , NO3 , Ca++, Mg++,

TDS, and high acidity . Zone 3 of the Upper Gallup Sandstone, the alluvial

2 1

sediments, the Torrivio Sandstone, and the Dilco Coal Member have receivedfluids by leakage from the tailings disposal area . Waters in theseaquifers that are dominated b y calcium and magnesium cations and thesulfate anion and elevated in nitrate concentrations may be considered aspossibly contaminated by uranium mill tailings solutions, because naturalwaters are generally sodium sulfate dominated and very low3 ppm) in nitrate concentrations .

The geochemical reactions between the acidic fluids from tailingsponds, water entering the aquifers from rainfall, runoff, or surface flow,and the sandstone formations in Pipeline Canyon are complex . The authorsare presently completing a detailed study of the water chemistry of thisarea and will present the results in a forthcoming paper . Uranium milltailngs are presently neutralized with lime before being disposed in pondsor borrow pits in Pipeline Canyon .

ConclusionPipeline Canyon is a major ground-water recharge zone for several

aquifers of the San Juan Basin . The physical factors responsible forefficient capture of available recharge are : increased intensity offracturing of the rocks as a result of basement faulting ; steeply dippingrocks associated monoclinal with folding which allow for gravity entry ofwater along fractures and bedding planes ; dissolution of sandstones in therecharge area ; and the thick deposits of alluvium on the canyon floor,which are often entrenched in the fracture zones .

The sandstone aquifers are hydraulically connected to the overlyingsaturated alluvial deposits . Ground-water mounds in the alluvium control

2 2

(less thani

the flow direction in the sandstones locally . Away from the recharge area,

the structural dip of the aquifers appear to control the flow . A large

volume of water is presently available for aquifer recharge in the lower

end of Pipeline Canyon .

2 3

Beaumont, E. C . 1971 . Stratigraphic distribution of coal in the San Juan

Basin . In Shomaker, J . W ., Beaumont, E. C ., and Kottlowski, F . E.

(eds .) New Mexico Bureau of Mines and Mineral Resources Memoir 25 .

Cooley, M . E . , Harshbarger, J . W ., Akers, J . P ., and Hardt, W. F . 1969 .

Regional hydrogeology of the Navajo and Hopi Indian Reservations,

Arizona, New Mexico, and Utah . U.S . Geol . Survey Prof . Paper 521-A .

Cooper. H. S ., Jr ., and Jacob, C . E. 1946 . A generalized graphical method

for evaluating formation constants and summarizing well-field history .

Trans . Am. Geophys . Union. vol . 27, no . 4 .

Ferris, J . G ., Knowles, D . B ., Brown, R. H., and Stallman, R. W . 1962 .

Theory of aquifer tests . U .S . Geol . Survey Water Supply Paper 1536-E .

Gibbons, J . F., II . 1980 . Geology of the Church Rock area, New Mexico .

Unpublished report prepared for United Nuclear Corporation by Science

Applications, Inc . and Bearpaw Geosciences .

Ingersoll, L. R., Zobel, 0 . J ., and Ingersoll, A . d . 1948 . Heat conduction

with engineering and geological applications . McGraw-Hill Book

Company. New York .

Mc Lean, J . S . 1980 . Aquifer tests in the Gallup Sandstone near

Yah-Ta-Hey, New Mexico . U .S . Geol . Survey Water Res . Investigations

80-25 .

Mercer, J . W . and Cooper, J . B . 1970 . Availability of'ground water in

the Gallup-Tohatchi area, McKinley County, New Mexico . U. S . Geol .

Survey Open-File Report .

REFERENCES

2 4

Mercer, J. W . and Lappala, E . G . 1972 . Erwin-1 production well, city of

Gallup, McKinley County, New Mexico . U.S . -Geol . Survey Open-File

Report.

Stone, W. J . 1981 . Hydrogeology of the Gallup Sandstone, San Juan Basin,

northwest New Mexico . Ground Water. v. 19, no . 1 .

U.S . Weather Bureau . 1938-1960 . Climatological data, annual summary .

Gallup, New Mexico . U.S . Dept . of Commerce .

25