Assessment of the Potential for Karst 

in the Rustler Formation at the WIPP Site 

John C. Lorenz 

Sandia National Laboratories 

Pre-publication Draft 

November 10, 2005 
2

TABLE OF CONTENTS

ABSTRACT................................................................................................................................... 5 

1.0 INTRODUCTION................................................................................................................... 7 

2.0 APPROACH.......................................................................................................................... 10 

3.0 GEOLOGIC EVIDENCE CITED FOR KARST AT WIPP ............................................ 12 

3.1 Introduction....................................................................................................................... 12 

3.2 Geologic Evidence for Karst at the Surface ................................................................... 17 

3.2.1 Nash Draw ................................................................................................................. 17 

3.2.2 Topographic Depressions East of Nash Draw........................................................ 20 

3.2.3 Disappearing Streams (“Dolines”) .......................................................................... 21 

3.2.3.1 The Phillips thesis.................................................................................................... 21 

3.2.3.2 Chains of Depressions............................................................................................. 24 

3.2.3.3 “Barrows’ Bathtub” ................................................................................................ 26 

3.2.3.4 WIPP-33................................................................................................................... 27 

3.3 Geologic Evidence for Karst in the Subsurface At and Near WIPP............................ 31 

3.3.1 Cores Containing “Insoluble Residue” and Disrupted Strata (Solution Breccia)

............................................................................................................................................... 31 

3.3.1.1 Background.............................................................................................................. 31 

3.3.1.2 The Ferrall and Gibbons Report.............................................................................. 34 

3.3.1.3 Modern Sedimentological Studies............................................................................ 37 

3.3.2 Stratigraphic Thinning of the Rustler Formation and “Missing” Halite ............ 40 

3.3.2.1 Cross Section Evidence............................................................................................ 40 

3.3.2.2 Volume Constraints.................................................................................................. 46 

3.3.2.3 The Tamarisk Polyhalite Marker Bed and the Concept of Depositional Facies..... 47 

3.3.2.4 Evidence from the Shafts.......................................................................................... 48 

3.3.3 Voids, Gypsum, and Problems Encountered in Drilling at WIPP-33.................. 52 

3.3.3.1 Bit Drops, Limited Core Recovery, and Lost Circulation ....................................... 52 

3.3.3.2 Normal Stratigraphic Section .................................................................................. 53 

3.3.3.3 Discussion and Interpretations................................................................................ 53 

3.4 Summary: Assessment of the Potential for Karst at WIPP Based on Geologic 

Evidence................................................................................................................................... 54 

4.0 POSSIBILITY OF KARST-TYPE, MULTI-ORDERED CONDUITS, AND CONDUIT 

FLOW .......................................................................................................................................... 56 

4.1 Introduction....................................................................................................................... 56 

4.2 Nash Draw as the Largest of a System of Ever-Smaller Karst Features..................... 57 

4.3 Assessing Possible Conduit Flow with Pumping Tests.................................................. 59 

4.3.1 The Value of Hydraulic Testing, and Distinguishing Karst Flow from Fracture 

Flow ...................................................................................................................................... 59 

4.3.2 Fracture Flow............................................................................................................ 59 

4.3.3 Pumping Tests........................................................................................................... 60 

4.3.4 Lack of Culebra-Magenta Interconnections .......................................................... 62 

4.3.5 Potentiometric Heads................................................................................................ 63 

4.4 Conduit Flow, Bypassed “Fossil” Water, and Diffusion ............................................... 66 

4.4.1 Old and Young Water in the Same Unit................................................................. 66 

4.4.2 No Evidence for Conduit Flow; Consideration of Diffusion................................. 67 
3

4.4.3 Conclusion ................................................................................................................. 67 

5.0 PROBABILITY AND ISSUES OF LIMITED WELLBORE SAMPLING.................... 69 

5.1 Introduction....................................................................................................................... 69 

5.2 Probability of Intersecting Fractures with a Drillhole .................................................. 69 

5.3 Probability of Intersecting Karst with a Drillhole......................................................... 70 

5.4 Data from the WIPP Shafts ............................................................................................. 71 

5.5 Volume of Caves................................................................................................................ 71 

5.6 Drilling in the Centers of Depressions ............................................................................ 72 

6.0 NEGATIVE GRAVITY ANOMALIES AND RELATED GEOPHYSICAL 

MEASUREMENTS .................................................................................................................... 74 

6.1 Introduction....................................................................................................................... 74 

6.2 The WIPP-14 Gravity Anomaly ...................................................................................... 76 

6.3 The WIPP-33 Gravity Anomaly ...................................................................................... 77 

6.4 The WIPP-13 and H-3 Gravity Anomalies..................................................................... 78 

6.5 Assessment of the Gravity Anomaly Data ...................................................................... 79 

7.0 ABSENCE OF SURFACE RUNOFF.................................................................................. 80 

8.0 RECHARGE AND DISCHARGE ISSUES........................................................................ 82 

8.1 Introduction....................................................................................................................... 82 

8.2 Correlations Between Malaga Bend and WIPP Site Precipitation .............................. 83 

8.3 Recharge ............................................................................................................................ 84 

8.3.1 Localized Recharge................................................................................................... 84 

8.3.2 Irrigation and Industry Effluent ............................................................................. 84 

8.3.3 Infiltration of Precipitation...................................................................................... 85 

8.4 In Situ Flow........................................................................................................................ 86 

8.4.1 Directions of Flow from Potentiometric Heads...................................................... 87 

8.4.2 Isotopes, Residence Time, and Flow Rates............................................................. 87 

8.4.3 Water Chemistry Domains and Flow Directions................................................... 88 

8.5 Discharge ........................................................................................................................... 94 

8.5.1 Malaga Bend Springs................................................................................................ 94 

8.5.2 Other Discharge Points............................................................................................. 96 

8.5.3 Gypsite “Spring” Deposits ....................................................................................... 96 

8.6 Assessment of Recharge and Discharge Data................................................................. 98 

9.0 SIGNIFICANCE OF LOCALLY EQUIVALENT CULEBRA AND MAGENTA 

HEADS....................................................................................................................................... 100 

9.1 Introduction..................................................................................................................... 100 

9.2 The Data........................................................................................................................... 100 

9.3 Misuses and Mis-citation of Data .................................................................................. 101 

9.4 Assessment of Equivalent Heads in the Two Rustler Members................................. 102 

10.0 SPATIAL VARIABILITY IN THE CHEMISTRY OF CULEBRA FORMATION 

WATERS ................................................................................................................................... 103 

10.1 Introduction................................................................................................................... 103 

10.2 The Data......................................................................................................................... 103 

10.3 Scale of Variability........................................................................................................ 103 

10.4 Possible Causes for Water Chemistry Variability ..................................................... 104 

10.5 Assessment of the Significance of TDS Variability in the Culebra .......................... 105 

11.0 POTENTIAL FOR KARST AT WIPP-13 ..................................................................... 106 
4

11.1 Introduction................................................................................................................... 106 

11.2 Drawdowns.................................................................................................................... 106 

11.3 Breccia and Mixing in the Core................................................................................... 107 

11.4 Summary........................................................................................................................ 108 

12.0 POTENTIAL FOR KARST AT WIPP-14 ..................................................................... 109 

12.1 Introduction................................................................................................................... 109 

12.2 The Data......................................................................................................................... 109 

12.2.1 Patterns.................................................................................................................. 109 

12.2.2 Normal Lithology.................................................................................................. 110 

12.2.3 Gypsum.................................................................................................................. 110 

12.2.4 Mass Deficiency..................................................................................................... 111 

12.3 Misuse of Data............................................................................................................... 112 

12.3.1 “Mud” .................................................................................................................... 112 

12.3.2 “No Core” .............................................................................................................. 113 

12.3.3 Fractures................................................................................................................ 113 

12.4 Assessment of Karst at WIPP-14................................................................................. 113 

13.0 POTENTIAL FOR KARST AT H-3............................................................................... 115 

14.0 SUMMARY ....................................................................................................................... 116 

REFERENCES.......................................................................................................................... 120 
5

Assessment of the Potential for Karst in the Rustler Formation at 

the WIPP Site 

John C. Lorenz 

ABSTRACT 

This report is an independent assessment of the potential for karst dissolution in 

evaporitic strata of the Rustler Formation at the WIPP site. Review of the available data 

suggests that the Rustler strata thicken and thin across the area in depositional patterns related to 

lateral variations in sedimentary accommodation space and normal facies changes. Most of the 

evidence that has been offered for the presence of karst in the subsurface has been used out of 

context, and the different pieces are not mutually supporting. 

Outside of Nash Draw, definitive evidence for the development of karst in the Rustler 

Formation near the WIPP site is limited to the horizon of the Magenta Member in drillhole 

WIPP-33. Most of the other evidence cited by the proponents of karst is more easily interpreted 

as primary sedimentary structures and the localized dissolution of evaporitic strata adjacent to 

the Magenta and Culebra water-bearing units. Some of the cited evidence is invalid, an inherited 

baggage from studies made prior to the widespread knowledge of modern evaporite depositional 

environments and prior to the existence of definitive exposures of the Rustler Formation in the 

WIPP shafts. Some of the evidence is spurious, has been taken out of context, or is mis-quoted. 

Lateral lithologic variations from halite to mudstone within the Rustler Formation under 

the WIPP site have been taken as evidence for the dissolution of halite such as that seen in Nash 

Draw, but are more rationally explained as sedimentary facies changes. Extrapolation of the 

known karst features in Nash Draw eastward to the WIPP site, where conditions are and have 

been significantly different for half a million years, is unwarranted. The volumes of insoluble 

material that would remain after dissolution of halite would be significantly less than the 
6

observed bed thicknesses, thus dissolution is an unlikely explanation for the lateral variations 

from halite to mudstone and siltstone. 

Several surficial depressions at WIPP, suggested to be sinkholes, do not have enough 

catchment area to form a sinkhole, and holes drilled to investigate the subsurface strata do not 

support a sinkhole interpretation. Surface drainage across the WIPP site is poorly developed 

because it has been disrupted by migrating sand dunes and because precipitation is not focused 

by defined catchment areas in this region of low precipitation and low-dip bedding, not because 

it has been captured by sinkholes. There are no known points of discharge from the Rustler 

Formation at WIPP that would indicate the presence of a subsurface karst drainage system. 

The existing drillholes across the WIPP site, though small in diameter, are sufficient to 

assess the probability of karst development along the horizontal fractures that are common in the 

Rustler Formation, and the area of investigation has been augmented significantly by the 

mapping of four large-diameter shafts excavated into the WIPP repository. The general absence 

of dissolution, karsting, and related conduits is corroborated by the pumping tests which have 

interrogated large volumes of the Rustler Formation between drillholes. Diffusion calculations 

suggest that separate isotopic signatures for the water found in the fractures and the water found 

in the pores of the matrix rock between fractures are unlikely, thus the isotopic evidence for 

ancient Rustler formation waters is valid. Geophysical techniques show a number of anomalies, 

but the anomalies do not overlap to portray consistent and mutually supporting patterns that can 

be definitively related to karst void space at any given location. The coincidence of the Culebra 

and Magenta potentiometric heads between Nash Draw and the WIPP site is the inevitable 

intersection of two non-parallel surfaces rather than an indication of karst-related hydraulic 

communication between the two units. 

 The proponents of karst in the Rustler Formation at the WIPP site tend to mix data, to 

take data out of context, and to offer theory as fact. They do not analyze the data or synthesize it 

into a rigorous, mutually supporting framework. They assume that the existence of an anomaly 

rather than the specific characteristics of that anomaly proves the existence of intra-stratal karst 

in the Rustler Formation. In most cases, the interpretations of karst offered are non-unique 

interpretations of data for which more plausible interpretations exist. 
7

1.0 INTRODUCTION 

 This report has been assembled in response to a request from the U.S. Environmental 

Protection Agency (EPA) to address concerns about the possible existence of a karsted layer or 

layers within the Rustler Formation, expressed most comprehensively by Hill (1999) in an 

unpublished “Letter Report” to Sandia National Laboratories. Hill published a slightly revised 

and shorter version of this paper in 2003. 

The Rustler Formation overlies the nuclear waste repository strata (which is within the 

Salado Formation) at the WIPP site in southeastern New Mexico. A karst development in the 

Rustler Formation at this site could conceivably alter flow pathways for leakage away from the 

WIPP site should the repository be breached and contaminants migrate as far upward as the 

Rustler Formation. The primary purpose of this report is to assess the evidence for karst 

development in the Rustler Formation at the WIPP site. The topics discussed here were specified 

by EPA and include those issues raised by the Hill report and by other proponents of karst at the 

WIPP site. 

 The data available for this assessment consist of the geological reports of the area, going 

back to potash resource characterization studies from the 1930’s. Geologic studies include those 

specific to the nuclear “Gnome” experiment that was done in the early 1960’s as part of the 

Plowshares program, as well as the more recent and more numerous WIPP-related studies. 

Where possible, the original core and outcrop descriptions and associated geologic project 

reports have been obtained. The original geophysical and hydrological studies that were 

undertaken to address the question of whether or not karst has been developed in the Rustler 

Formation at the WIPP site have also been assessed for their potential to clarify the geologic 

interpretations. 

Several subtle but important problems with the geologic interpretations that have been 

made at WIPP are discussed here. First, many of the early geologists working in the WIPP area 

(e.g., Vine, Jones, Gard) were educated and made their descriptions of the strata prior to the 

proliferation of studies and resulting knowledge of modern sedimentary depositional

environments that started in the late 1960’s and 1970’s. These geologists did not have the 

background or training to properly interpret the signatures of many of the evaporitic depositional 
8

and diagenetic environments represented by the sedimentary textures in cores and outcrops that 

they studied. 

For example, Gard (1968) invoked a cumbersome, hypothetical system of localized, 

temporary uplifts during deposition of the Salado Formation in order to explain the evidence he 

found for subaerial exposure such as desiccation cracks and truncated bedding found in the halite 

deposits in the Gnome shafts. This was because the prevailing theory at the time was that all 

bedded halites were deposited in marine environments. Studies that have both developed and 

used more recent sedimentology concepts, such as those by Smoot and Lowenstein (1991), 

Harville and Fritz (1986), and Powers and Holt (2000), have shown that, in fact, the thick 

Ochoan evaporites were deposited in irregularly exposed and flooded salt pans marginal to 

marine environments. These studies explain Gard’s evidence for subaerial exposure much more 

neatly and logically, and are consistent with modern sedimentary principles. 

Second, most of the early WIPP geology reports used the prevailing geological 

conventions which blurred the distinctions between lithologies, facies, and depositional/ 

diagenetic environments, i.e., between basic data and interpretations. Under these conventions, it 

was acceptable to label a unit either descriptively by its lithology, by a lithologic shorthand that 

also implied an origin but that wasn’t proven, or by an imprecise combination of the two. 

Some of these early, unsupported interpretations have become entrenched in the 

literature, where they have caused confusion because later authors have assumed that they are 

proven concepts. Some of these interpretations have even been extrapolated to superficially 

similar lithologic units where there is even less basis for the implied interpretation of origin. 

Finally, until drilling of the large-diameter shafts at the WIPP site, most of the important, 

diagnostic sedimentary structures in the Rustler Formation were obscured. Samples were either 

too small (e.g., four-inch diameter and smaller core) or too weathered (outcrop) to display or 

preserve such structures. This left the early geologists dependent on the less definitive, grossscale geologic relationships as the basis for many of their sedimentological interpretations. 

Although the gross-scale relationships are important, the range of possible interpretations that 

can be made based on these relationships can now be culled and the interpretations significantly 

refined using the exposures of previously unknown structures, textures, and sedimentary 

assemblages available in the WIPP shaft excavations. These features are especially useful in 
9

making comparisons to the data available from recent studies of analogous modern evaporite 

depositional environments. 
10

2.0 APPROACH 

An objective assessment of the evidence for karst in the Rustler Formation has been 

attempted, along with an assessment of whether or not the undisputed evidence for karst at Nash 

Draw implies that karst is widely developed in the Rustler Formation elsewhere, specifically in 

the subsurface under the WIPP site. 

Different approaches taken by various scientists are also compared in the discussions 

presented here, assessing the approaches in light of accepted practice. The presentation of 

unsupported statements, and the substitution of theory for evidence, are unacceptable scientific 

methods that would not stand up to rigorous peer review. Much of the evidence offered for the 

existence of karst in the Rustler Formation at the WIPP site is speculative, or at best, speculative 

analogy, and what evidence exists for karst is commonly contradictory and subject to other, more 

plausible interpretations. An attempt is made here to assess the reliability and origin of the data 

that have been used to make various interpretations, and to assess whether those interpretations 

are proven, probable, plausible, merely possible, or even untenable. In this report, indirect 

evidence is not given equal weight with direct evidence, and possible geological models are not 

equated with proven or plausible models. 

 In assessing the issues raised by Hill’s (1999) report, an attempt has been made to find 

the original data and descriptions that underpinned the early interpretations, and to determine 

whether or not they are now assumed to be factual merely because they are entrenched due to 

constant repetition, and whether there was originally a valid basis for making these 

interpretations. An example is the repeated designation of some of the Rustler lithologies that 

are dominated by siliciclastics as “dissolution residue,” discussed below. The interpretations 

have also been assessed as to whether or not they are defendable in light of subsequent 

advancements in geologic knowledge and the acquisition of new data, or whether they are just 

convenient, inherited labels. It appears that many of the interpretations have been 

overextensions of what the data will actually support. 

Specific issues raised by the Hill (1999) “Letter report” to Sandia National Laboratories 

that are addressed below include whether or not there is direct, subsurface evidence for karst at 

the WIPP site, the significance of specific topographic depressions in the land surface, the 
11

importance of small-scale gravity anomalies, the interpretation of data (cores, mud logs, cuttings, 

etc.) found in the well reports, and the validity of interpretations of some deposits found in cores 

as insoluble “residue” derived from recently dissolved halite beds.
12

3.0 GEOLOGIC EVIDENCE CITED FOR KARST AT WIPP 

3.1 Introduction 

The Late Permian and younger strata at the WIPP site in southeastern New Mexico 

(Figure 1), including the Rustler Formation, are relatively flat-lying, having structural dips of 

only a few degrees, generally towards the east. Many of the formations and lithologic units 

within the formations are homogeneous and laterally extensive for miles or even tens of miles. 

The inclined strata have been truncated by erosion, with successively older units exposed at the 

surface westward (Figure 2). Various units of the Rustler Formation have been exposed at Nash 

Draw, west of the WIPP site, and the exposure has led to dissolution of the evaporitic strata and 

deeper local erosion. East of Nash Draw and across the WIPP site, erosion has beveled but has 

not removed the clastic strata of the Permian Dewey Lake and Triassic Santa Rosa Formations, 

which overlie the Rustler Formation. 

Figure 1. Location map for the WIPP site, southeastern New Mexico (from Siegel et al., 1991). 
13

Figure 2. Schematic southwest-northeast cross section across the WIPP site (from Chaturvedi 

and Rehfeldt, 1984). 

Although lateral continuity and homogeneity of bedding are common attributes of the 

local Permian strata, they are not universal, nor are they universal in geologic strata world-wide. 

The lateral variability within the evaporitic to muddy Forty-niner, Tamarisk, and Los Medaños 

Members of the Rustler Formation (Figure 3) contrasts with the lateral homogeneity of the 

intervening, dolomitic Culebra and Magenta Members of the formation. Some of the lateral 

variability in the evaporites in the vicinity of Nash Draw, where the formation has been exposed 

to weathering and erosion at the surface, can be related to relatively recent dissolution. In the 

subsurface, however, most of this variability is the result of lateral variations in depositional 

facies. Historically, the subtle distinction between primary lateral variability created by facies 

changes and the secondary variability imposed on the strata by local dissolution has been blurred 

or ignored by various authors, and some clarification of that distinction is attempted here. 

The term “karst” includes a wide range of features developed during the dissolution of 

rocks, usually of the more soluble carbonate and evaporitic lithologies, by various types of 

naturally occurring, mildly acidic fluids, most commonly rainwater. Karst includes features that 

range from minimal karst development, as in the local enhancement of the widths of existing 

fractures (Figure 4), to enlargement of these conduits and development of cavernous pathways in 
14

the strata, to near-complete removal of the soluble strata with only scattered remnants left to 

prove that the strata once existed. 

Figure 3. Stratigraphic nomenclature and schematic lithology of the members of the Rustler 

Formation. 

Fonn al Stratigraphy 

After Lang (1935), 

Vine (1963), and 

Powers and Holt (1999) 

Forty-niner 

Member 

Magenta Dolomite 

Member 

Tamarisk 

Member 

c ulebra Dolomite 

Member 

Los Medaiios 

Member 

lntonn al Stratigraphy 

of 

Holt and Powers (1988) 

Anhydrite 5 (A5) 

Mudstone-Halite 4 (M4/H4) 

Anhydrite 4 (A4) 

Magenta Dolomite 

Anhydrite 3 (A3) 

Mudstone-Halite 3 (M3/H3) 

Anhydrite 2 (A2) 

Anhydrite 1 (A1) 

Mudstone-Halite 1 (M1/H1) 

Bioturbated Clastic 

Interval 
15

Figure 4. Solution-enhanced fractures in the Madera Limestone: the beginning of karst. (Road 

cut on route NM 217 east of Albuquerque.) 

Most of the discussion of karst at the WIPP site revolves around the presence or absence 

of features suggested to be indicative of an intermediate stage of karst development. However, 

evidence for karst at this site is ambiguous, which has allowed different authors, and sometimes 

even the same authors in different papers, to present different concepts of what the hypothetical 

karst might look like at WIPP site. 

Hill (1999, page 3-5; 2003, page 201) lists the following as “characteristics” of 

intrastratal karst: 
16

1. it can form within the vadose zone, at or near the water table, or in the phreatic 

zone 

2. it usually does not have surface expression, i.e., it is concealed karst 

3. it can form at depth 

4. it is difficult to detect 

5. it is widespread in evaporite rocks 

These are not “characteristics” in a strict sense of the term, the list is not used rigorously, 

and the characteristics are not definitive. The fact that a feature can form in any position relative 

to the water table, points one and three, does not help to define it. “Widespread,” point five, is a 

subjective term and is not equivalent to “universal” as implied by the tenor of the report. 

Obscuration, points two and four, is a key point for Hill, leading to convoluted arguments that 

the lack of specific evidence supporting the presence of karst at WIPP does not negate the 

possibility that it is present, and therefore seeming to allow an unrestricted lateral extrapolation 

of the definitive evidence for karst features in Nash Draw across several miles and into the 

subsurface at the WIPP site. 

Numerous karst-related terms are defined by Hill (1999, pages 3-6) in a mixture of 

descriptive, genetic, and synonymous terms. Hill defines “karst” geomorphically as a landscape 

characterized by closed depressions, disrupted surface drainage, and underground caves and 

drainage systems. The first two of the features are not uniquely indicative of karst: although 

closed depressions and disrupted surface drainage may be the result of a process that produces 

cavernous karst in underlying strata, they can also result from other processes such as the 

irregular coverage of a land surface by glacial till or windblown sand dunes, or tectonically by 

structural reversal of low-angle bedding dips. 

The 1972 AGI Glossary of Geology, in the definition of karst, specifies an origin as a 

dissolution product and includes the resulting surficial geomorphic features such as disrupted 

drainage as part of the characteristics of karst. Although the disrupted surface drainage 

described by Hill is both real and widespread at the WIPP site, and although it is similar to that 

created by karst processes, such features can be created by processes other than dissolution so 

they are not unique evidence for dissolution. 
17

Hill defines “paleokarst” as a karst that is no longer in contact with a flowing hydrologic 

system, implying that dissolution is no longer actively removing rock, but whether above or 

below the water table is not specified. Hill defines “intrastratal karst” as a layer that has been 

partially dissolved in the subsurface, beneath undissolved strata that cover and obscure it. These 

are generally accepted terms. 

3.2 Geologic Evidence for Karst at the Surface 

Specific, local, surficial features have suggested to several authors, as summarized by 

Hill (1999, 2003), that karst may be developed in the subsurface at and near the WIPP site. In 

extrapolating the widely recognized karst sinkholes, caves, and collapse features that are present 

at Nash Draw eastward to the WIPP site, Hill (1999) suggests that 1) five or six topographic 

depressions may be the surface expressions of strata collapsed over caverns (sinkholes) in the 

Rustler Formation on the northwest corner of the WIPP site, and 2) that a disappearing stream (a 

“doline”), described by Phillips (1987) as entering one of these topographic depressions, is 

where surface drainage is captured by the inferred subsurface karst conduit system. 

The following discussion examines the surficial evidence for karst at and near the WIPP 

site, and compares the well developed karst features in the Rustler Formation in Nash Draw with 

the local and more ambiguous features claimed as evidence for karst in the areas east of Nash 

Draw, near and at the WIPP site. 

3.2.1 Nash Draw 

Nash Draw is a surface depression, about 20 miles long and 5-12 miles wide. It lies west 

of the WIPP site (Figure 1, Figure 5a) and is generally agreed to have been caused by the 

removal of evaporites from within the partially exposed Rustler Formation and from the upper 

parts of the underlying Salado Formation, by weathering, dissolution, and erosion (Bachman, 

1981, 1985, 1990; Mercer, 1983). Unchallenged karst features in and immediately around Nash 

Draw include numerous caves (many containing secondary clay deposits), sinkholes, fractured 

and brecciated strata, and saline springs. 
18

Figure 5a. Location map of geographic features at the WIPP site (from Mercer (1983), his 

Figure 1a). The outline of the WIPP area has changed since 1983; see Figure 5b. 

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19

Figure 5b. Location map of the WIPP-area drillholes discussed in the text. 

Dissolution is also indicated by significant thinning of the Rustler Formation in this area, 

with related subsidence of the overlying strata as well as displacement and fracturing of the 

-

WIPP-27 

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20

insoluble Rustler beds that are/were interbedded with the soluble halite and anhydrite/gypsum 

units. Locally, the interval between the Magenta Dolomite and the Culebra Dolomite Members, 

normally a few tens of meters thick in the subsurface, has been thinned by dissolution of the 

interlayered evaporitic strata to the point where the dolomites are separated in outcrop by as little 

as a meter. 

Analysis of crosscutting and superimposed geological relationships allowed Bachman 

(1985) to determine that Nash Draw and the related karst features began to form when erosion by 

westward-flowing streams unroofed the soluble evaporitic units of the Rustler Formation 

500,000-600,000 years ago. Most of the dissolution that formed Nash Draw took place during 

this time, but the process is interpreted to still be active, albeit at a much slower rate, in the Nash 

Draw area (Bachman, 1981). The evidence offered for present-day dissolution is the presence of 

active, salt-saturated springs in several places around the draw. One reference (Geohydrology 

Associates, 1978) has suggested that the existing sinkholes are being actively enlarged but that 

no new sinkholes are forming, although no data are offered to support this interpretation. 

Similar, unequivocal dissolution features (sinkholes, caves, disrupted strata, and thinned 

strata) are present in other areas where the Rustler Formation is exposed at the surface, notably 

in the area of Malaga, 10-12 miles southwest of the WIPP site (Reddy, 1961; Mercer, 1983; 

Bachman, 1980). 

However, the evidence for extrapolating this well-developed karst system eastward to the 

WIPP site is not definitive. Arguments to the effect that “there is no reason NOT to expect karst 

development eastward” (Phillips, 1987), just because the soluble strata are there and because 

globally such strata often have karst features superimposed onto them, are specious. There are 

many areas of unkarsted evaporite deposits worldwide, and geologic conditions at the WIPP site 

are not the same as the conditions at Nash Draw. 

3.2.2 Topographic Depressions East of Nash Draw 

Hill (1999, p. 36-37) suggests that several topographic depressions at the WIPP site are 

evidence for the collapse of karst caverns at depth, presumably within the Rustler Formation. In 

order for a lowering of the ground surface to be related to collapse of the underlying strata, those 
21

underlying strata must have been removed or displaced, and will commonly have been 

brecciated. 

Wells drilled in these depressions to sample and test for karst have not encountered either 

displaced strata or breccias (see below). Hill (1999: her Figure 8, page 18 and Figure 17, page 

41) draws hypothetical, funnel-shaped dissolution structures (Figure 6) to explain why the 

investigation wells could have missed evidence for karst, and then to suggest that karst is likely 

in the subsurface since the wells must have missed the karst. A funnel-shaped geometry is 

incompatible with the cylindrical or inverted-funnel shape common to most sink-hole collapse 

features. Moreover, the funnel shape, widest at the top, is unlikely since this is the level of the 

low-solubility sandstones, siltstones, conglomerates, and shales layers that overlie the Rustler 

Formation at the WIPP site. Hill has not described a plausible process by which a funnel 

geometry might form in these strata. 

3.2.3 Disappearing Streams (“Dolines”) 

3.2.3.1 The Phillips thesis 

Perhaps the most extensive presentation of the hypothesis that surface topographic 

depressions at WIPP might indicate collapse over subsurface voids caused by dissolution in the 

Rustler Formation is found in Phillips’ 1987 PhD dissertation, cited extensively by Hill (1999). 

This work focused on the Mescalero Caliche, the uppermost layer of lithified strata at and near 

the WIPP site. Phillips implied that the impermeability of such a layer has been an erroneous 

cornerstone of the hydrological modeling at WIPP, although he did not cite the references. In 

fact, the three-dimensional basin-scale modeling of the WIPP hydrologic system performed by 

Corbet and Knupp (1996; see also Corbet, 2000), which provides the conceptual underpinning of 

all recent WIPP hydrologic studies and models, does not include the Mescalero Caliche at all. 

 Inhomogeneities are common in the Mescaleo caliche and in caliches in general. 

Caliches, also known as pedogenic calcretes (i.e., calcareous hardgrounds formed by soilproducing processes) commonly develop pipe-like features as they age due to rooting of plants 

and other deposition/dissolution processes that form these layers (e.g., Bachman and Machette, 

1977). Gile, Hawley, and Grossman (1981) document similar pipes from calcretes in the Las 

Cruces, NM area. 
22

Figure 6. Conceptual model of sinkhole formation, from Hill (1999), her Figure 8/page 18. The 

model does not account for the presence of insoluble sandstone layers at the top of the system. 

See text for discussion. 

Phillips (1987, page 6) asserts that some of the depressions found in the hummocky upper 

caliche surface at the WIPP site formed due to “collapse or subsidence of caliche into voids left 

by dissolution of underlying soluble rocks”, and by “dissolution and breaching of caliche by 

infiltrating rainwater”. Phillips documented broken, solution-pitted, and displaced layers of 
23

caliche in hand-augered test holes as deep as 21 feet. He did not present direct evidence that 

there are solution caverns in the deeper strata that may have caused the disruption of the caliche 

layer, but rather used the observations from the caliche layers to infer this conclusion indirectly, 

and then supported his conclusions with peripheral evidence from geophysics and groundwater 

studies. 

Phillips has related depressions in the land surface to depressions in a datum surface at 

depth, but the significance of this relationship is not clear, and the hypothesis of origin as 

collapse over solution voids in the Rustler Formation has not been proven. The depth of 

investigation was a few tens of ft (trenching and auguring), the surface depressions are a few feet 

deep, and measured offsets of the datum are a few tens of feet. Moreover, the significance and 

reliability of Phillips’ datum as a structural horizon are ambiguous at best: he used as a datum a 

horizon defined by the first intersection by the auger of either caliche or sandstone. A 

combination datum such as this does not represent either a structural or a time horizon. 

Moreover, caliche deposition commonly follows the contours of the topography on which it 

forms, thus it cannot be determined whether depressions in the land surface caused depressions 

in the datum or whether both were later offset by a lowering of the strata and land surface 

together. 

More importantly, several hundreds of feet of insoluble Santa Rosa and Dewey Lake 

sandstones and siltstones separate Phillips’ supposed caliche sinkholes near the surface from any 

potential Rustler caverns at depth into which the caliche might have been displaced. Connection 

between the depressions and the Rustler Formation across these intervening layers, and voids in 

the underlying Rustler, are entirely speculative. 

Phillips proposed an absence of perched water tables in these formations and used that to 

support the concept of hydraulic conductivity vertically between the surface, across the 

sandstones, and into the Rustler, via his hypothetical sink hole collapse structures. However, 

other publications have noted or suggested that perched water tables do in fact exist in the 

Dewey Lake strata (e.g., Morgan and Sayre, 1942; Holt and Powers, 1990a; Powers, 1997: 

Mercer et al., 1998). Although larger-scale breccia pipes penetrate these clastic units in several 

places (i.e., Powers, 1996), speculations regarding small-scale penetration of these sandstone 

units and karst-type conduit connection across them that might allow meteoric recharge down 

into the underlying Rustler at the WIPP site are unsupported. 
24

The implication from Phillips’ interpretation that holes in the layer of Mescalero caliche 

allow significant recharge of meteoric waters to the underlying formations is an unproven, overinterpretation of the data. Phillips’ text contains numerous similarly speculative and unsupported 

assertions at a smaller scale, and phrases such as “it could be that”, “appear to be”, and “is 

probably due to” are common, whereas definitive statements relating data to a defensible 

interpretation (“this proves that”) are rare. Moreover, the conclusion that the caliche layer is not 

an impermeable layer is irrelevant, as numerous studies (discussed below) have used the 

percolation/infiltration of rainfall through the formations a primary source of recharge of 

groundwater into the Rustler Formation. 

3.2.3.2 Chains of Depressions 

Phillips suggests that an alignment (a “chain”: 1987, pages 74, 82, 122) of three 

depressions near WIPP-33 (Figure 7, Figure 8) might be indicative of the solution that can occur 

along linear fault trends in some geologic settings. The three depressions of the chain extend 

across a distance of 1500 ft, with the center of the middle one off-line by 100 ft. These 

depressions are shallow, the deepest being about eight feet deep and a few hundred feet wide 

(Figure 9). One of the depressions analyzed by Phillips is only two feet deep, and it is not clear 

that this is significant relative to the surrounding topography. 

 Hill (1999, p. 53) suggests that “the presence of the four WIPP-33 sinkholes trending 

eastward suggests that these cave passages may head eastward in the direction of the WIPP site.” 

These depressions have not been proven to be sinkholes, and “cave passages” have not been 

proven to underlie them, thus this is a speculative, over-interpretation of the data. In fact, only 

three of the depressions are aligned (the fourth and deepest, the WIPP-33 depression, is offset 

from the linear trend to form an “L”): this is a mis-statement of the geometry of the depressions, 

and misleading. Phillips’ and Hill’s suggestion that this alignment of depressions could indicate 

a fault-line trend that leads karst conduits eastward is unsupported by data.
25

Figure 7. “Chain of sinkholes” associated with drillhole WIPP-33, and the proposed feeder 

stream, as mapped by Phillips (1987), his Figure 5/page 75. 

Figure 8. Low-angle aerial photograph of the area mapped in Figure 7, looking southwest. 

Drillhole WIPP-33 is located at the junction of the east-west road and the pipeline. Note the 

absence of well-defined drainages entering the area, and compare to Figure 11. Most of Phillips’ 

vanishing arroyo is not apparent. 

Pipeline 

Road 

WIPP-33 depression 

Vanishing arroyo? 
26

3.2.3.3 “Barrows’ Bathtub” 

 Much discussion has revolved around an ambiguous topographic depression in the 

southwest-central part of the WIPP area, informally called “Barrow’s Bathtub” (Phillips, 1987). 

This depression has been suggested to be an example of a doline/karst depression (Phillips, 1987, 

page 163), a wind-formed “blowout” (Bachman, 1985), or the remnants of an artificial 

excavation into the caliche, dug for road metal, (Phillips, 1987, page 163, cited as a personal 

communication from Hawley). 

The depression was probably first brought up for public discussion during the field trip 

described in Chaturvedi and Channell (1985; Appendix C, Notes for the Karst Hydrology Field 

Trip by Larry Barrows, page 3 [the location is given as being in section 30 of T. 22 S., R. 31 E., 

whereas most others have placed it in section 29]). In these Notes, Barrows briefly states that 

this “dimple,” eight ft deep by 100 ft across, would be “an appropriate location to discuss the 

lack of surface runoff, character of the rainfall, and implications of the water balance,” but he 

does not specifically label this depression as evidence for karst dissolution in the subsurface. 

Others, notably Phillips (1987), have used this depression as evidence for a doline and for 

internal drainage into a karst system. Phillips (1987, pages 163-181) augured and trenched this 

depression, noting that the underlying caliche profile is poorly indurated, and that its surface 

mimics the overlying topography. Caliche is not present in the central parts of the depression, 

where the subsurface “structure” is floored by the Gatuña Formation. Phillips interprets this to 

indicate removal of the caliche and thus formation of the depression by dissolution. He suggests 

(page 165) that the “impregnation” of the underlying Gatuña sandstones with carbonate is “direct 

evidence of rainwater infiltration,” though he does not indicate why the same waters that 

dissolved the carbonates of the caliche zone should have precipitated carbonate in the sandstone. 

In fact, carbonate is the most common cementing material in sandstone worldwide, and is not 

indicative of any particular process. A mechanism by which dissolution might have continued 

from the caliche and through the insoluble sandstone is not offered. Barrow’s contour map of 

the sandstone surface with one-foot contour intervals (Phillips, 1987, Figure 45, page 186) shows 

a sandstone surface that is essentially flat and level. 

Phillips (page 171) compared aerial photographs taken in 1958 with those from 1983 and 

suggested that they show an enlargement and increased angularity of the Barrows’ Bathtub 

depression. Although he inferred from this that the depression is a doline, changes in outline and 
27

size are not exclusive evidence for any particular mode of formation: excavation operations 

would produce the same effects. He also offered an absence of surrounding dunes as evidence 

that this was not a wind-formed blowout (which was Bachman’s [1985, page 21] interpretation), 

even though the area is located within a large, stabilized dune field (e.g., Chugg et al., 1971).

3.2.3.4 WIPP-33 

Phillips (1987) and Barrows (1982) have provided the primary discussions cited by Hill 

(1999) in suggesting that one or more of the hollows noted above accommodate disappearing 

streams or “dolines.” Although these and Hill’s reports imply that such features are common at 

the WIPP site, in fact only the one supposedly feeding the WIPP-33 depression has been 

mapped, and this example is ambiguous, being much smaller and less well defined than the 

dolines found in Nash Draw. 

This feature, inferred to be the course of a shallow, short, captured stream, terminates 

within the WIPP-33 surface hollow described above. It has been used as evidence to suggest that 

the land surface at and near WIPP is one of disrupted drainage, where numerous streams have 

been captured by the inferred system of karst-related subsurface conduits. Phillips (1987) 

suggests that the vanishing arroyo terminates in the eight-ft deep WIPP-33 depression, and he 

has mapped it at small scale (Phillips, 1987, Fig. 5). The valley of this arroyo does not show in 

the two-ft topographic contour lines of his Figures 6, 8, and 9, and the map of the arroyo (Figure 

7) shows it entering one depression, then implausibly flowing uphill to cross the shallow divide 

into the next hollow where WIPP-33 is located. 

An explanation is not provided for why the stream should pass through and beyond the 

first depression, which Phillips (1987, page 114) asserts is also “probably an alluvial doline, 

formed by subsidence or collapse of sandstone and caliche into voids in the Rustler”. No other 

dolines have been mapped near WIPP, although several are obvious within Nash Draw a few 

miles to the west, where much larger and more definitive stream systems have been abruptly 

diverted into obvious sinkholes. 
28

Figure 9. The WIPP-33 depression at ground level, looking west. Post (center of photo) marks 

the drillhole location, person to the right of it on the far side of the hollow for scale.

The poorly constrained rate of disappearance of water from these depressions has been 

offered as evidence that they are dolines. Data on rates of soil percolation would indicate 

whether ponded rainwater would be able to soak into the sandy surficial deposits within the 

observed time frames or whether capture by inferred subsurface drainage would be necessary to 

account for the rate of water disappearance from the hollows, but no such data have been offered. 

Rather, Phillips, citing anecdotal evidence, suggests that because the WIPP-33 depression was 

filled with five feet of water for “a matter of days” (Phillips, 1987, p. 86), disappearance of the 

water is evidence that it had to sink into an underground system. A more plausible interpretation 

of the same observation would be that because the sandy hollow held water at all, there is 

probably no drain outlet into a subterranean plumbing system at the bottom of the depression, 

and that the water seeped slowly into the surrounding sandy deposits. 
29

Phillips (p. 125) writes that “Surface drainage is almost undeveloped east of the Pecos 

River...” and suggests that this is because the drainage has been captured by an underground 

system. This would as easily be explained by drainage disruption during migration of numerous 

sand dunes into the area, now partially stabilized (Figure 10), and the related low level of annual 

precipitation which does not contribute enough water to the surface drainage system to clear 

dune sand from the drainages. The evidence for sand dunes is unequivocal (Figure 10) (Chugg 

et al., 1977), whereas the evidence for karst is nebulous. Poor development of drainage on the 

one-degree structural dip of the local bedding would be expected regardless. 

Figure 10. Low-angle aerial photograph of stabilized and active sand dunes in the area 

immediately northwest of the WIPP site. 

In addition, there are no defined catchment areas on the low-relief topography to funnel 

drainage along specific paths, so the minimal rainfall in the area may not require a developed 

drainage system. In contrast, surface drainage that disappears into several obvious sinkholes in 

nearby Nash Daw is well defined up to the point where it is captured and enters the subsurface 

(Figure 11), and the difference between these undisputed systems and the inferred doline systems 

nearer to the WIPP site is striking. 
30

The absence of well-developed drainage patterns in the hummocky topography at WIPP 

is not a good argument for the presence of dolines east of Livingston Ridge. These arguments do 

not account for the stabilized sand dune field that covers the area, limited rainfall, and 

evapotranspiration that more readily explain the poorly developed modern surface drainage. 

Cavernous porosity in the upper Rustler at WIPP-33 is present, as discussed in section 3.3.3, but 

a relationship between surface drainage at WIPP-33 and upper Rustler porosity still needs to be 

established, and the general lack of integrated drainage is not evidence of ubiquitous karst at 

depth as implied. 

Figure 11. Low-angle aerial photograph of diverted drainage, vanishing streams, and the open 

sinkholes that capture them, in the Forty-niner Member of the Rustler Formation exposed in 

Nash Draw, for comparison with Figure 8. 
31

3.3 Geologic Evidence for Karst in the Subsurface At and Near WIPP 

Evidence for Rustler karst development in the subsurface at and near the WIPP site is not 

definitive like that seen in outcrop in Nash Draw. Hill (1999) has cited all of the possible 

circumstantial evidence to build the case for subsurface karst at the WIPP site. However, most 

of this evidence is indirect, few of the data have unique interpretations, and some of the evidence 

is inconsistent with other evidence. Geophysical, geochemical, and hydrological evidence will 

be discussed later, but the geologic evidence offered by Hill for karst development in the Rustler 

Formation, in the subsurface underneath and in the vicinity of the WIPP site, consists of: 

1. Cores from the Rustler Formation that contain layers that have been interpreted as 

solution breccias and as “insoluble residue.” 

2. Basin-scale stratigraphic thinning of the Rustler, and stratigraphic intervals that 

contain halite in some areas but that do not in other areas, the latter extrapolated 

to indicate that the halite has been removed by dissolution. 

3. Meter-scale bit-drops, encountered in the WIPP-33 borehole, that are inferred to 

be into karst-related caves. 

3.3.1 Cores Containing “Insoluble Residue” and Disrupted Strata (Solution Breccia) 

3.3.1.1 Background 

Loaded Terminology: The words in the phrases “insoluble residue” and “solution 

residue”, and the phrases themselves, have been widely used to describe certain units of the 

Rustler Formation, but the connotations and implications of these phrases are not in fact 

universally appropriate or applicable. Siliceous clay, silt, and sand are largely insoluble, 

especially relative to evaporite minerals, but the fact of insolubility alone is not diagnostic of the 

genesis of beds composed of these materials. The word “residue” has an automatic genetic 

implication, but the mere presence of a layer of clay, quartz, or feldspar does not automatically 

imply, and certainly does not prove, that the layer composed of these materials originated as a 

residue from dissolution of a bed of evaporite strata that contained them. Moreover, it is simpler 

to form such beds by primary deposition than through a multi-stage processes involving 
32

deposition and secondary dissolution, and by Occam’s razor the simpler of the two processes 

should be applied in the absence of evidence for the other. 

Dissolution that produced a presumed residue can also be read to mean that the 

dissolution took place either soon after deposition, or at depth within the stratigraphic column 

eons later. Both are valid processes, but the mere description of a rock unit as a residue, even if 

it is a valid interpretation, does not address the timing of dissolution. Evidence such as the 

presence of truncated bottom-growth halite or gypsum crystals, and/or of the up-turned bedding 

that rims desiccation cracks, along a dissolution horizon (i.e., Powers and Holt, 2000) is 

necessary to support interpretations of the timing of dissolution. “Residue” should not be 

applied to units where the origin cannot be definitively determined by means of accepted 

sedimentological or geochemical evidence, and if a unit is in fact a residue, that by itself does not 

automatically imply timing of dissolution or that it is a result of karst-formation processes. Valid 

interpretations of dissolution and of the timing of that dissolution require support from detailed 

sedimentological studies. 

Many of the studies that have tried to understand evaporite deposition, diagenesis, and 

reworking in modern environments in detail have only been undertaken in the last several 

decades (see Powers and Holt, 2000), thus earlier studies of the WIPP-area evaporite deposits, 

and the early geologists who received their education even earlier, commonly misapplied the 

term “residue”. However, “residue”, “dissolution residue” and “insoluble residue” have become 

entrenched in the literature on the Salado and Rustler Formations. They have been applied 

indiscriminately, sometimes in lieu of a primary lithologic description, to many massive-looking 

clay-rich and/or silty beds for which no diagnostic sedimentary structures were obvious and 

therefore no depositional environment was apparent. Until recently, the phrase “insoluble 

residue” was used as a generalized descriptive term at the WIPP site for massive siltstones, but 

the genetic implications of this phrase have been largely unsupported. 

Since most Rustler outcrops are badly weathered and disrupted, and since cores of fresh 

Rustler rock offer only small samples of the formation, it was only with the excavation of the 

WIPP air intake, exhaust, and waste-handling shafts that fresh, clean exposures of the evaporitic 

Rustler facies could be examined and studied in the kind of detail and with the kind of 

understanding that the recent studies of modern, evaporitic, depositional environments have 

made possible (see Powers and Holt, 1990). Therefore, the Rustler literature must be read 
33

carefully to determine whether or not there are data to support the specific interpretations implied 

by the labels with which the different lithologies have commonly been described. 

The term “insoluble residue” and its variations seem to have first been applied to the 

thick, massive to chaotic, clayey unit that separates the top of the Salado Formation from the 

base of the Rustler Formation in the Nash Draw area. This unit is one of the more significant 

water or brine-producing horizons in the area (Mercer, 1983), and is generally accepted to be a 

remnant left-over from the in situ dissolution of tens to a few hundreds of feet of clayey halite. 

Jones (1973, p. 20) described this unit as being 

“composed of clay with crudely interlayered seams of broken and shattered gypsum and 

fine-grained sandstone.... The gypsum is clearly the hydrated remnant of anhydrite and 

polyhalite seams, for it commonly contains ragged and embayed masses of anhydrite and 

polyhalite, and, also grades laterally into anhydrite and polyhalite. The clay, gypsum, 

and sandstone unit....thins eastward by grading into and intertonguing with rock salt and 

the other precursory rocks from which it originated.” 

Few subsequent descriptions of units described as “dissolution residues” contain as much detail 

or data in support of the genetic interpretation implied by the term. Jones’ description is a 

standard to which all supposed residues can be compared, and in fact the published descriptions 

of the characteristics of many clayey and silty layers called “dissolution residues” are insufficient 

to prove that they are the insoluble remnants of dissolved evaporitic strata rather than primary 

deposits of non-soluble minerals. Interestingly, the application of the term drifted over the years 

to where it was considered to include beds composed entirely of massive siltstone as well as the 

originally clayey layers. 

 Finally, disrupted and brecciated bedding has been widely cited at the WIPP site as 

evidence of collapse and brecciation related to post-depositional dissolution of soluble, 

evaporitic strata. While this is a known process, it is not the only process that produces disrupted 

strata, thus dissolution is not a unique interpretation for brecciated strata. Disruption of strata 

also occurs in modern evaporitic depositional environments as a synsedimentary product of the 

normal depositional and diagenetic processes (Figure 12), and genetic interpretations of cores 

showing disrupted layers in the Rustler Formation should be integrated, using mutually 

supporting lines of sedimentological evidence such as the character, extent, and context of the 

disrupted units, not merely their presence. 
34

Figure 12. Salt ridges at Bristol Dry Lake, California. The salt ridges and associated cracking 

and disruption of bedding are formed by synsedimentary expansion and contraction of layers 

during deposition. Photo by John Karachewski. 

3.3.1.2 The Ferrall and Gibbons Report 

An example of the misuse of the term “insoluble residue,” and probably the reference 

most commonly cited in support of insoluble residues as evidence for subsurface dissolution near 

the WIPP site, is the Ferrall and Gibbons (1980) description of cores from the Rustler Formation 

from WIPP-19 and related boreholes. Hill (1999, p. 50-52) has drawn heavily on the Ferrall and 

Gibbons descriptions of some units in this core as insoluble residues. She suggests, simply 

because many of these “residues” occupy approximately the same stratigraphic position as 

anhydrite beds in other holes, that “where these residues/breccias exist, corresponding anhydrite 

rock has been removed.” This ignores the well established geological principle of lateral, 

depositional facies equivalencies and lithologic variation, reverting to a simplistic concept of 

layer-cake stratigraphy. However, the point to be made here is that Ferrall and Gibbons were 
35

indiscriminate in their application of the term “residue,” and as such their interpretive 

descriptions are not a valid basis for underpinning theories of karst at the WIPP site. 

Ferrall and Gibbons (1980, page 3) recognized six rock types in the Rustler cores: 

“anhydrite, gypsum, halite, solution residue, dolomite, and siltstone”. Of these six, only 

“solution residue” is not a purely objective lithologic descriptor. This term not only omits an 

indication of the lithologic composition (other than by implying that its mineralogy is of low 

solubility), but it also implies an interpretation of the genetic origin of the strata, an interpretation 

that is inferred by unstated analogy to other similar lithologies but which is left unsupported 

during the description of the core. Ferrall and Gibbons’ characterization of their solution 

residues in general is a “siltstone/claystone, exhibiting a wide range of cementation”, but 

numerous units in the cores are described only as non-definitive “solution residues”. 

Nothing in the Ferrall and Gibbons (1980) report resembles Jones’ (1973) description of 

a residue or otherwise justifies an interpretation that the so-labeled layers composed of insoluble 

minerals originated as leftover, insoluble material from a thick evaporitic layer. There are no 

descriptions of remnants of red, embayed and altered anhydrite or gypsum beds that could be the 

hydration products of polyhalite and that would support an interpreted origin as a dissolution 

residue. There is no facies analysis that illustrates gradation laterally into equivalent, 

undissolved halites. The most common bedding type described by Ferrall and Gibbons in these 

units is structureless or massive bedding, which is a common primary sedimentary texture in 

evaporitic environments. It is not equivalent to the brecciated and disrupted bedding, showing 

the bedded remnants of out-of-position layers, that can be, but is not always, caused by postdepositional dissolution. 

The few places where Ferrall and Gibbons provided somewhat better descriptions of 

these “residue” strata, they described them as massive or “chaotic” siltstones cemented with 

halite, with the halite often in crystalline form. The only potential evidence for solution offered 

in any of the descriptions of the units labeled as residues is the presence of local, seemingly 

exotic blocks and clasts of gypsum or anhydrite, but such blocks can also be incorporated into 

the strata during disruption of bedding on evaporite depositional surfaces during the normal 

course of deposition in such environments (e.g., Handford, 1982; Lowenstein, 1988; Powers and 

Holt, 2000). For example, gypsum and halite commonly grow displacively in the immediate 

subsurface in poorly consolidated silts and muds in evaporitic environments. This disrupts and 
36

even destroys bedding and other evidence of the currents that originally deposited the silt and 

mud. Teepee structures and desiccation cracks (Figure 12) can also disrupt primary bedding, 

often to depths of several meters, in halite, carbonate, and gypsum deposits, forming large, 

steeply dipping structures at the depositional surface. When these structures are buried and then 

cored, the strata can look like it was brecciated by post-depositional dissolution. Thus, disrupted 

bedding is not by itself unique evidence for dissolution since it can form in syndepositional 

settings. 

Small-diameter cores rarely sample sufficient volumes of the strata to determine the 

origin of disrupted strata, and citing disrupted strata out of context does not prove an origin from 

dissolution. Regardless, none of the descriptions of the halite-cemented, silty units in these cores 

resemble Jones’ benchmark description of the residual claystone found at the top of the Salado 

Formation in outcrop. In fact, Ferrall and Gibbons commonly put quotation marks around the 

term “solution residue”, suggesting that they were uncomfortable with the term. They 

specifically state (1980, page 22) that they applied the term to several units that they do not 

consider to be residues only because the units “have been leached and are residues in other 

boreholes,” although no evidence or discussion was provided to support that inference. 

Halite, especially in crystalline form, should be rare to absent in a true residue since a 

residue forms by the removal of halite, one of the more soluble evaporite minerals. However, 

halite cement and even crystalline halite are present in all the siltstone units that Ferrall and 

Gibbons (1980, pages 12, 22) labeled as residues. Moreover, clay is the most common insoluble 

material incorporated into halite beds, not silt (typical Salado halites contain up to three percent 

insoluble material, 75% of which is clay: Gard, 1968). A true insoluble residue should be 

composed primarily of clay, not silt and halite. 

An alternative interpretation for these silty units can be constructed from their positions 

within simple, repeated vertical sequences or cycles of facies described from the cores, although 

such successions were not recognized by Ferrall and Gibbons. Lithologically, a sequence starts 

with a bedded siltstone or shale, transitions up into the mis-labeled “residue” of halitic siltstone, 

and finally grades upward into an evaporite, either halite or anhydrite. The sequences were 

sometimes truncated, but a simple model of deposition in a shallow-water environment that 

became progressively more saline would account for both this succession of lithologies and the 
37

observed characteristics in each facies, and is similar to the depositional sequences reconstructed 

by Lowenstein (1988) for repetitive cycles of successive lithologies in the Salado Formation. 

Ferrall and Gibbons (1980) describe few specific characteristics of the material 

considered to be dissolution residues, and what they do describe bears little resemblance to 

Jones’ (1973) description of the clay residuum at the top of the Salado Formation. In contrast, 

primary depositional origin of these units is strongly supported by the recognition of primary 

sedimentary structures and of truncated halite crystals and other diagnostic depositional features 

by Powers and Holt (2000), and Holt and Powers (1984, 1986, 1990b) in laterally equivalent 

strata. This recognition was made possible only by large, fresh, and detailed exposures of the 

Rustler strata in the WIPP shafts. 

Ferrall and Gibbons (1980, page 17) specifically noted that there had not been much 

gypsification in the anhydrite matrix rock adjacent to several specifically noted but poorly 

described “leached voids parallel to bedding.” They were therefore forced into the improbable 

speculation that any gypsified rock was immediately removed by the same waters that had 

rehydrated the anhydrite. No description of these voids was provided, nor any justification for 

inferring that they represent leached zones. 

 To summarize, the evidence that many beds in the Rustler Formation at the WIPP site 

consist of residual insoluble material left over from the post-depositional dissolution of halites is 

based indirectly on early, inconclusive descriptions of Rustler cores, encumbered by an inherited, 

non-specific terminology. The insoluble residue interpretation is not a unique interpretation of 

the available data, and in fact the data can be more readily explained by simpler models of 

primary deposition that are more consistent with recent observations from modern evaporite 

depositional environments (Holt and Powers, 1988; Powers and Holt, 2000). 

3.3.1.3 Modern Sedimentological Studies 

Lowenstein: Tim Lowenstein, a widely recognized evaporite sedimentologist familiar 

with modern depositional environments and modern sedimentary interpretation techniques

(many of which he helped develop), was asked by the State of New Mexico to undertake a study 

specifically to address the question of whether or not there is evidence of post-burial alteration of 

the Rustler Formation. Although Lowenstein (1987) recognized and described many primary 

sedimentary features in his study of cores from five of the holes across the WIPP site, he did not 
38

reach a definitive conclusion, noting that “...identification of evaporite dissolution and the 

amounts of dissolution is interpretative...” (page 34), and writing further that the individual 

geological features present in the cores are “not unequivocal” (page 32) in being diagnostic of 

“late-stage alteration.” 

Lowenstein (1987), in using the term “late-stage alteration” for what evidence he did find 

for diagenesis and dissolution, did not specify whether he believed that these processes took 

place shortly after deposition or much later, after burial. Thus, he left open the question of 

whether such dissolution could have been synsedimentary as advocated by Powers and Holt 

(2000), or the result of much more recent, intrastratal karsting processes as implied by Hill 

(1999, 2003). In fact, Lowenstein’s descriptions of truncated halite crystals at syndepositional 

flooding surfaces (1987, page 16) support synsedimentary dissolution. His descriptions of 

dissolution zones immediately above and below the Magenta and Culebra Dolomite Members 

(1987, page 35) suggest that more recent dissolution is also present locally, but the Magenta and 

Culebra are recognized to be water-bearing, and local dissolution in the adjacent beds is to be 

expected whether or not the rest of the Rustler units have been modified by karst channels. 

Regardless, the term “insoluble residue” is notably absent from Lowenstein’s report. 

Powers and Holt: Powers and Holt (2000), building on the new, unparalleled exposures 

of the Rustler Formation revealed by excavation of the large-diameter shafts at the WIPP site 

(Holt and Powers, 1984, 1986, 1990b), documented definitive, primary sedimentary textures that 

have always been obscured or even destroyed by weathering in outcrop. This new data source 

was significant enough to support a scientific paper (Powers and Holt, 2000) that was published 

in an international, peer-reviewed, scientific journal. The authors were able to combine the new 

features with knowledge of the recent detailed studies of modern evaporitic depositional 

environments to develop a scientifically supported, plausible reconstruction of Rustler 

deposition, and relate it to the present-day distribution of the Rustler lithologies. All of the 

structures exposed and documented in the WIPP shafts fit conveniently into a model of shallow, 

evaporite salt pans and saline mud flats, with vertical repetitions of lithologies fitting cycles of 

fresh water incursion and subsequent evaporation, and lateral lithologic variations meshing with 

geologically sound concepts of lateral facies variations. 

The definitive absence of karst features in the Rustler Formation in the WIPP shafts was 

obscured by an early, out of context observation of a large, unfilled fracture in a halitic siltstone 
39

(not in an anhydrite as implied by Hill) of the Los Medaños Member of the Rustler Formation. 

A photograph of this fracture (Figure 13) was offered as evidence for large, open fractures in the 

subsurface, and has been used by various proponents of karst (e.g., Snow, 2002, page 7/his 

Figure 4) to imply that there was karst development in the Rustler Formation in the WIPP shaft 

Figure 13. Fracture in the Los Medaños Member of the Rustler Formation in one of the shafts at 

the WIPP site. The halite that filled the fracture in situ has been dissolved out by the relatively 

fresh water that flowed out of the overlying Culebra Member and flowed down the shaft walls 

during and after excavation, making it appear to have been an open fracture in the subsurface. 

Original figure and caption from Chaturvedi and Channell (1985). The notation “V.S.” refers to 

the “ventilation shaft” that was subsequently enlarged and equipped to be the waste-handling 

shaft. 
40

(page 39, and Plate 1/page 80, Chaturvedi and Channell, 1985). However, at the time of initial 

excavation, the fracture was filled with halite and was not a karst conduit; the halite was leached 

from the fracture during and after excavation of the initial hole. When the shaft was later 

enlarged by conventional mining (without water), fractures in this zone were found to be filled 

with halite in their in situ condition (Holt and Powers, 1984, Figure 9, fracture notes). 

3.3.2 Stratigraphic Thinning of the Rustler Formation and “Missing” Halite 

 Hill (1999), drawing on a theory advocated by Snyder (1985) and Snyder and Gard 

(1982), suggests that thinning of the Rustler Formation in the vicinity of the WIPP site must be 

related to dissolution since the thinning trend continues westward to where the Rustler has been 

markedly and demonstrably thinned by dissolution in Nash Draw. Although dissolution is an 

obvious process at Nash Draw, it is not the only process capable of causing marked thinning of 

the Rustler Formation. The questions are: 1) to what degree, if any, has Nash-Draw-type 

dissolution caused the thinning and absence of halite in the Rustler Formation at the WIPP site, 

2) are there other equally or perhaps more plausible processes to explain this and which process 

does the data support, and 3) if there are several overlapping processes that have caused thinning, 

how much and where between Nash Draw and the WIPP site do they overlap? 

3.3.2.1 Cross Section Evidence 

 The Rustler Formation has been exhumed and exposed to weathering west of Livingston 

Ridge for at least a half-million years (Bachman 1985). During that time it has been reduced in 

thickness by dissolution of the more soluble beds in the formation. Various authors (e.g., Snyder 

and Gard, 1982; Snyder 1985; Chaturvedi and Channell, 1985) have suggested that this process 

of thinning by dissolution continues eastward into the subsurface, encroaching on the WIPP site. 

These authors suggest that more halite, progressively deeper in the Rustler section, has been 

dissolved westward, the closer one gets to Nash Draw (Figure 14, Figure 15). 

 Although dissolution of sulfate beds is the primary factor controlling thinning of the 

Rustler Formation in outcrop near its western, erosionally truncated edge in Nash Draw, the 

Rustler Formation also thickens and thins numerous times in the subsurface across the basin 

where it has not been subjected to dissolution (Holt and Powers, 1988; Mercer, 1983). This 
41

subsurface thinning is due to lateral depositional facies changes and due to local variations in 

subsidence that accommodated the deposition of thicker or thinner evaporite beds (Figure 16, 

Figure 17). A large area such as the Permain basin doesn’t subside uniformly, and slightly 

deeper parts of the basin accommodated deposition of thicker halites, whereas topographic highs 

allowed deposition of only thin halite beds or none at all. Thus the different halite beds in the 

Rustler Formation thicken, thin, and even vanish due to lateral facies changes in areas of the 

basin where the formation has never been exposed to weathering and dissolution. Thinning by 

itself is not primary evidence for dissolution as suggested by Snyder and Gard (1982). 

Figure 14. Cross section showing the westward thinning of halite beds in the Rustler Formation, 

including the polyhalite in the Tamarisk Member, inferred by Snyder to indicate progressive 

westward dissolution of the halites but more plausibly interpreted as lateral facies changes and 

variations in depositional topography. (From Snyder, 1985; his Figure 2). See also the regional 

cross sections in Holt and Powers (1988). 
42

Figure 15. Proposed levels of halite dissolution (from Snyder, 1985) 

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... 

... .. 

' RUSTLER 

DISSOLUTION· FRONT ? 

No halite in Rustler 

No halite above Culebra 

No halite above Ma9enta 

Several halite layers in the Rustler 

0 2 miles 

iiiiiiiiiii~~ 
43

Figure 16. Isopach map of the Mudstone/Halite-3 interval of the Tamarisk Member of the 

Rustler Formation, showing thinning in all directions, including westward across the WIPP site, 

and indicating that thinning is a function of depositional rather than dissolution (from Powers 

and Holt (1990), their Figure 26/page 102). 
44

Figure 17. Isopach map of the total Rustler Formation, showing the depositional hollow east of 

the WIPP site that controlled thickening and thinning throughout Rustler deposition (from 

Powers and Holt, 1990, their Figure 25/page 101). 

The total thickness of the Rustler Formation decreases by nearly 50%, from more than 

500 ft to less than 300 ft, east and southeast of the WIPP site where it has never been close to the 

surface (Holt and Powers, 1988, their Figure 4.15). The cumulative thickness of the several

halite beds in the Tamarisk Member of the Rustler Formation diminishes from over a hundred 

feet thick to zero both east and west of a depocenter thickening located about ten miles southeast 

of the WIPP site (e.g., Holt and Powers, 1988, their Figure 4.5). The same pattern is present in 

the salt deposits of the Los Medaños Member, the Forty-niner Member, and in a small halite 

within the upper anhydrite of the Rustler (Holt and Powers, 1988), suggesting that this 

depocenter was an area of localized, relatively higher subsidence throughout late Permian time. 
45

Therefore thinning of the Rustler Formation, with or without accompanying thinning of

the component halite beds, is not definitive proof, in and of itself, that the beds have been 

thinned due to dissolution of halite, since thinning and the absence of halite also occur where the 

Rustler Formation is deeply buried and protected from weathering, erosion, and dissolution. 

This does not negate thinning due to dissolution in Rustler strata west of WIPP, but rather 

suggests that such thinning does not prove dissolution since thinning can result from several 

different, or even from several combined causes. 

It is also telling that the supposed dissolution front as reconstructed is thinly tapering, 

thinning by several hundred feet over four or five miles. In contrast, the dissolution front is 

abrupt in other basins where salt dissolution fronts have been definitively documented (e.g., Neal 

et al., 1998; Gustavson et al., 1980). Similar or even greater amounts of thinning in these basins 

takes place over half a mile or less, and steep surface ridges occur where the overlying bedding 

has been draped over the dissolution fronts. In the Holbrook basin of Arizona, the subsurface 

margin of the encroaching salt dissolution front is marked at the surface by a topographic scarp 

with up to a hundred feet of relief, by an abrupt change in the dip of bedding, and locally by 

clusters of sinkholes (Neal and Lorenz, 1998). Similar features are present in other basins (i.e., 

Gustavson et al., 1980). Powers et al. (2003) have recently suggested that the Salado saltdissolution front is marked by the bedding roll-over at the Livingston Ridge escarpment on the 

eastern edge of Nash Draw (Figure 18). Nothing equivalent to this surface demarcation of a saltdissolution front is present at the WIPP site. 
46

Figure 18. Fractured sandstones of the Dewey Lake Formation draped over probable edge of the 

salt-dissolution wedge at the northern edge of Nash Draw. View is to the northwest. 

3.3.2.2 Volume Constraints 

Volumetrically, the total thicknesses of beds labeled as insoluble residues in Rustler cores 

can not reasonably have been derived from the available volume of halite and its probable 

percentage of insoluble material (Powers and Holt, 2000), arguing strongly against an origin of 

so many clay and silt beds as dissolution residues. A quick estimation points out the 

implausibility of such a theory. The cumulative thickness of the massive silty beds labeled as 

"residues" by Ferrall and Gibbons (1980) in WIPP-19 is over 50 ft. If the silt and clay content of 

an average halite is as much as three percent (average values in halites in the Salado Formation 

range from 1-3%: Gard, 1968), a 50 ft residue would require the dissolution of a cumulative 

thickness of some 1500 ft of halite. This is unreasonable considering that the total thickness of 

the Rustler Formation, including the non-halite lithologies, is only 300-500 ft. Moreover, the 

thicknesses of the clay beds do not increase where they have supposedly been added to by 

residues from dissolved halite (Powers and Holt, 1995). 

To look at it another way, the Forty-niner mudstone is about 20-25 ft thick at the WIPP 

shafts. At its thickest, the stratigraphically equivalent halite in drillholes to the east and 
47

southeast is about 40-45 ft thick, and nearly pure. Forty feet of nearly pure halite cannot have 

been the source of a 20-ft thick dissolution residue. 

3.3.2.3 The Tamarisk Polyhalite Marker Bed and the Concept of Depositional Facies 

A prominent polyhalite bed is present in the middle of the thicker salt beds in the 

Tamarisk Member east and southeast of the WIPP site. Polyhalite is less soluble than halite and 

remnants would be expected to be included in the residual material remaining after dissolution of 

this halite bed, as it is in recognized Salado residues. For example, Reddy (1961) described 

remnants of polyhalite in residues of the Salado Formation at the top of salt domes south of 

Carlsbad as distinctive, brick-red to orange gypsum alteration products. However, no embayed 

or red, gypsiferous polyhalite remnants have been reported from the units labeled as residual 

material in any of the Rustler cores examined by Ferrall and Gibbons (1980), or in any of the 

units found in the shafts. 

Chaturvedi and Channell (1985, page 26) cite a personal communication from Snyder, 

who apparently correlated the Tamarisk polyhalite bed in drillhole P-18 with a clay unit in 

drillhole P-6, and suggested that the clay is the remnant residue from the polyhalite bed. 

Polyhalite is commonly formed as an alteration product from an anhydrite bed, thus anhydrite 

and polyhalite can be lateral diagenetic facies equivalents, but the model runs into problems in 

that 1) it is relatively difficult to totally dissolve polyhalite, and 2) it is even more difficult to 

leave behind a thick clay residue as remnant from a virtually clay-free lithology. 

Arguments that dissolution must have occurred in the Rustler Formation wherever 

claystone and mudstone are found in the same stratigraphic position as halites use antiquated 

depositional concepts which acknowledge only superimposed, laterally extensive geologic 

layers. Such layer-cake models of stratigraphy were superseded early in the development of 

geological sciences by the well-supported models of lateral depositional-facies equivalents. For 

example, rivers, beaches, and lagoons can all be depositing different types of sediment in 

laterally- and time-equivalent environments, resulting in laterally equivalent deposits of gravel, 

sand and mud. The resulting facies assemblage does not consist of a layer of river gravel 

overlying a layer of beach sand overlying a layer of lagoonal muds unless the environments 

migrate laterally over one another with time. In the same way, relatively pure halite can be the 
48

lateral depositional equivalent to mudstone, as found in the Rustler Formation across the WIPP 

site and in modern depositional environments. 

The fundamental geologic principle of laterally-equivalent facies has been ignored by 

proponents of insoluble residues at the WIPP site, leading to statements such as “...wells... 

where halite is completely missing from the Rustler or is found only below the Culebra, 

encounter several layers of clastics (mudstone, siltstone, and breccia in clay matrix) at different 

horizons in the formation. These layers are at the same stratigraphic locations as the halite layers 

of the wells in Region 4 and may have therefore resulted from dissolution of salt.” (Chaturvedi 

and Channell, 1985, page 28). In essence, the finding of different types of rock at the same 

stratigraphic horizon is not a gross anomaly that can only be explained by special geological 

circumstances; rather it is a common and well-understood geologic occurrence. 

In the Rustler Formation, most of the observed distribution of halites, polyhalites, 

anhydrites, mudstones and siltstones resulted from the deposition of laterally equivalent types of 

rock in laterally equivalent environments: saline mud flats, saline evaporation pans, and deeper 

saline ponds (Powers and Holt, 2000; Holt and Powers, 1984; 1986; 1990b). This type of pattern 

is the normal mode of deposition in modern evaporitic environments (e.g., Handford, 1982). 

The more uniformly thick and more widespread Rustler units such as the Magenta and 

Culebra dolomites were the products of deeper waters which produced much more laterally 

extensive depositional environments, but they too have laterally equivalent facies of different 

lithologic composition. Because of the different depositional environments, the Magenta and 

Culebra facies vary on a scale of up to a hundred of miles rather than on the scale of miles to a 

few tens of miles as seen for the associated evaporitic deposits, and cannot be used as analogs to 

interpret the distribution of evaporitic facies. 

In the vicinity of Nash Draw, the dissolution of halite and related evaporites has been 

superimposed onto the primary depositional patterns of lithologic distribution, and the relative 

importance of the two processes can be difficult to separate in the area between Nash Draw and 

the WIPP site. 

3.3.2.4 Evidence from the Shafts 

The absence of halite can be interpreted to mean either that it was never deposited or that 

it was deposited and then removed. The evidence to support an interpretation of dissolution is 
49

definitive at Nash Draw (e.g., caves, Figure 19; breccias; drastically thinned section), but 

becomes ambiguous in the subsurface to the east. The data presented by Powers and Holt (2000) 

and Holt and Powers (1988) strongly support non-deposition where the Rustler Formation thins 

without having been exposed in outcrop, and this interpretation is compatible with known 

depositional thickness and facies variations from modern environments. 

Figure 19. Dissolution cavern in Rustler strata exposed in Nash Draw. The cavern could be 

either a sinkhole or a spring depending on the water level. 

Thinning due to dissolution overlaps with depositional thinning in the area immediately

east of Nash Draw, and the relative effects of each are difficult to determine in the absence of 

good outcrop. However, excavation of the large-diameter air-intake, exhaust, and wastehandling shafts at the center of the WIPP site have provided data that definitively support an 

interpretation of halite non-deposition and syndepositional dissolution in the vicinity of the 
50

WIPP site, negating interpretations of post-depositional removal by dissolution and karst 

processes. 

These shafts were excavated in a position that is ideal for comparing the hypotheses of 

dissolution vs. non-deposition in the vicinity of the WIPP site, since isopachs of the Rustler 

Formation (Holt and Powers, 1988) show that it is dramatically thinner in the area of the shafts 

and there should be good evidence for dissolution if dissolution caused that thinning. At 309 ft 

thick in the shafts, the Rustler Formation is 176 ft (36%) thinner than the measured 485 ft Rustler 

thickness in a well located five miles east (see the isopach maps in Holt and Powers, 1988), part 

of an overall westward thinning trend. Moreover, the shafts are located in the zone where

Snyder (1985) specifically suggested that halite was removed by subsurface dissolution from 

both the middle (Tamarisk) and upper (Forty-niner) Members of the Rustler Formation. 

Although dissolution was invoked by Snyder as the mechanism that caused both thinning of the 

formation and the absence of halite, the evidence he presented for that interpretation is circular in 

that it consisted only of 1) the fact that the Rustler Formation thins westward, 2) that it contains 

little halite in the western locations, and 3) the inference that much of the anhydrite has been 

converted to gypsum. (This inference was supported only by data from hole WIPP-25, which is 

located in Nash Draw where undisputed dissolution and water infiltration has occurred). 

If the interpretation that broad, subsurface dissolution of the Rustler Formation has 

occurred miles east of Nash Draw is valid, then good evidence to support it should have been 

found in the large, fresh exposures of the Rustler created when the shafts were excavated, since 

these exposures were cut in an area of thinning. They were cleaner and more extensive than any 

previous data from either outcrop or cores, and thus showed important sedimentary details that 

have been previously obscured. However, the characteristics of the Rustler Formation found in 

the shafts document a normal, primary depositional sequence, with little or no evidence for 

recent dissolution and alteration. These characteristics (see the lithology logs from Holt and 

Powers, 1984; 1986; 1990b) include the following: 

1. Definitive primary sedimentary structures found in siltstone and clay units that had 

previously been interpreted as dissolution residues 

2. An absence of dissolution-indicator breccias and disrupted bedding in the Tamarisk 

and Forty-niner Members, the two members, according to Snyder’s (1985) model 

where dissolution should have been most prominent 
51

3. The overwhelming dominance of anhydrite in the Tamarisk and Forty-niner 

Members, unconverted to gypsum as would be expected if there had been sufficient 

water to remove significant thicknesses of halite. The only gypsum present is 

immediately adjacent to the Magenta Member, an acknowledged if poorly productive 

water-bearing unit. No conversion of anhydrite to gypsum was reported even in the 

anhydrites immediately adjacent to the more transmissive Culebra. 

4. Normal dolomite lithologies in the Culebra and Magenta Members, devoid of large 

vugs and karst-type caverns. 

5. The total thickness of bedded salt, present only in the lowest, Los Medaños Member 

of the formation, of only five feet, with the thickest individual bed being only three

feet thick. Since these halite beds thicken to the east and southeast, “thinned” halite 

beds in this, an acknowledged undissolved member, support the contention that the 

geometric thinning of the formation as a whole is the result of primary depositional 

processes rather than secondary dissolution and the removal of material. 

6. There is no evidence of the ten-foot thick polyhalite bed that marks the middle of the 

halitic zones in the Tamarisk Member further to the east and southeast. Remnants of 

this unit might be expected in a dissolution residue, similar to the way they mark the 

residue between the Salado and Rustler formations described by Jones (1973). The

absence of such a prominent, thick, marginally soluble unit from the shaft exposures 

strongly supports the interpretation that it and associated halites were never deposited 

in this area. 

7. A sedimentary channel was found in the air intake shaft, eroded into the A-2 

anhydrite and filled with siltstone and conglomerate. This feature indicates primary 

depositional processes. 

As noted above, the halite filling cracks in the lower Rustler Formation in the original 

ventilation shaft (now the Waste Shaft) was dissolved back from the face of the initial, smalldiameter pilot shaft by drilling fluids and by water dripping down the face of the shaft from the 

Culebra. A photo of this feature (Chaturvedi and Channell, 1985, Plate 1) was considered to be 

evidence of post-depositional dissolution or karst (Figure 13). When the shaft was enlarged, 

using conventional mining without water, the same fractures were found to be filled with halite. 
52

This fracture and the erroneous interpretation continue to be mistakenly offered as evidence for 

subsurface dissolution at the WIPP site. 

3.3.3 Voids, Gypsum, and Problems Encountered in Drilling at WIPP-33 

3.3.3.1 Bit Drops, Limited Core Recovery, and Lost Circulation 

Perhaps the best and least ambiguous evidence for some degree of subsurface karst 

development comes from the records of the WIPP-33 drillhole at the northwestern edge of the 

WIPP site. Four, meter-scale bit-drops were encountered while drilling the WIPP-33 hole, and 

these have been cited as evidence for widespread subsurface conduits related to karst in the 

Rustler Formation east of Nash Draw (e.g., Hill, 1999; Phillips, 1987; Barrows, 1982). Although 

even Bachman (1981) wrote incautiously that the Rustler Formation in WIPP-33 was “found to 

be cavernous throughout,” examination of the drilling records for this hole (Sandia National 

Laboratories and the U.S. Geological Survey, 1981), shows that the bit drops occurred only 

while coring the Forty-niner and Magenta Members. The recorded drops were of 9.5 ft, 6 ft, 2 ft, 

and 5 ft. The evidence in the records of this drillhole for an additional, seven-foot “cavity” near 

the bottom of the Dewey Lake section as suggested by Philips (1987, p. 16, 50) consist of

notations of “lost circulation” and rapid drilling rates on the imprecise drilling-time log (the 

geolograph from the drill rig floor). 

Nine cores were cut in the Forty-niner/Magenta interval, with recovery ranging from zero 

to 46 percent and averaging 27 percent. Five cores were also cut through the Culebra Dolomite, 

and although no bit drops were recorded, recovery averaged only 57%. In contrast, the five 

cores cut across the Salado-Rustler contact averaged 87% recovery. The data report for the hole 

(Sandia National Laboratories and the U.S. Geological Survey, 1981) also documents difficult 

drilling, with notations of lost circulation zones, and drilling ahead without mud and cuttings

returns to the surface at numerous depths. The record briefly mentions but does not describe or 

explain “lost dolomite” in the Magenta interval, and anhydrite that has been hydrated to gypsum 

and perhaps dissolved entirely. The lithologic log indicates that most of the sulfate in this hole 

occurs as gypsum rather than anhydrite, suggesting access by water to much of the formation. 
53

3.3.3.2 Normal Stratigraphic Section 

The stratigraphic tops in this hole are found at normal depths, bedding is horizontal as 

expected, and the breccia blocks in the cores (in the A-3/H-3 interval) are small, suggesting that 

disruption is not great and that there has been no large-scale collapse or other disruption of 

bedding. A video camera lowered into the hole to assess the possibility of cavernous porosity 

was unable to see through the drilling fluid to the side of the drillhole. The caliper log that was 

run in the hole after drilling encountered areas where the hole was somewhat larger than the 

diameter of the drill bit, but these zones (or perhaps the actual enlargement, it is difficult to tell 

from the report) were “not extensive.” 

3.3.3.3 Discussion and Interpretations 

In situ void space is a plausible and even probable explanation for the observations from 

drillhole WIPP-33, but it is not unique, and the sizes of the voids are debatable. Poor recovery of 

core is also common where the material is broken by fractures or faults, and drilling operations 

through evaporites can even create local solution cavities if the mud is not properly maintained at 

full saturation while drilling. 

The void horizons in WIPP-33 are located where dissolution associated with the 

acknowledged water-bearing Magenta would be expected, i.e., strata-bound and adjacent to a 

known source of water. The daily drilling reports document intervals of lost circulation and no 

returns elsewhere in the Rustler section, but the exact horizons of lost circulation cannot be 

determined accurately from the daily drilling reports since an interval that leaks drilling fluid into 

the formation may continue to leak or start to leak again after the hole is much deeper, making it 

seem as if the hole has encountered a new zone of lost circulation as it is being drilled when it is 

only the previous zone accepting fluids again. 

The data from this hole provide direct evidence for subsurface void space, but they are 

not quantitative. Although the data from this hole provide the best evidence for subsurface 

voids, it is an isolated data point and the bit-drop evidence comes from only limited stratigraphic 

levels in the hole, related to a water-bearing unit where dissolution would be expected. There are 

no data for similar voids in the nearby holes, voids that might form an interconnected subsurface 

network as would be expected in a developed karst system. 
54

The vuggy porosity encountered in the WIPP-33 hole, while allowing drilling fluids to 

seep out and making drilling difficult, was not so large or well developed that it allowed drilling 

fluid to completely drain away, which would have made drilling with fluids impossible. The lost 

circulation was in fact controlled by the use of standard oil-field lost-circulation material (the 

“LCM” noted in the drilling reports), typical LCM consisting of relatively small bits of things 

like cotton hulls and/or walnut shells that can be pumped down the hole. Material of this size 

would be incapable of preventing lost circulation by bridging voids where the voids are much 

more than centimeters to a few tens of centimeters in scale, and this is not the scale of cavernous 

porosity typical of a karst system. 

Hill (1999, p. 52) suggests that WIPP-33 penetrated “an unusually thick (44 ft)” layer of 

surficial fill material. The significance she attaches to this observation is not clear: if the thick 

fill represents a hollow created by a stratigraphic section downdropped over a solution void, that 

would also create an obvious offset of the subsurface stratigraphy, but the stratigraphy is normal 

in this hole. It is unlikely that the thick alluvial fill resulted from local, near-surface dissolution 

of the insoluble sandstones and siltstones. Hill diagrams a funnel-shaped zone of disruption, a 

shallow depression of unspecified origin and filled with surficial material, with a localized 

conduit leading into deeper karsted strata at the bottom (see Figure 6), but she does not 

adequately explain how the funnel might have formed. In contrast, the known sinkholes in 

nearby Nash Draw consist of obvious cave openings and diverted drainage, but are not 

associated with marked depressions of the bedrock surface or with thicker units of surficial fill 

material. 

3.4 Summary: Assessment of the Potential for Karst at WIPP Based on Geologic Evidence 

Bit drops, caliper logs, video images, and lost circulation zones provide evidence of a 

high degree of porosity within the Magenta and parts of the Forty-niner Members at WIPP-33. 

Nevertheless, geologic data do not support either the presence of cavernous porosity or the 

extrapolation of these characteristics across the WIPP site. The data commonly cited in support 

of subsurface karst development at the WIPP site consist of questionable labels that have 

improperly and incorrectly assigned an origin to certain lithologies in core descriptions, and a 

thinning of the Rustler Formation that can be explained more plausibly by facies changes since 
55

1) the supposed missing material would have had to have been improbably thick, 2) because it 

does not contain the required volume or clayey types of insoluble material common in 

recognized residues, and 3) because the characteristics of these deposits are more plausibly 

explained by vertical sedimentary facies transitions. The hummocky surface topography at the 

WIPP site is real, but it does not imply karst-related pirating of drainage by subsurface conduits. 
56

4.0 POSSIBILITY OF KARST-TYPE, MULTI-ORDERED CONDUITS, AND 

CONDUIT FLOW

4.1 Introduction 

Hill (2003, pages 201-203) has laid out the theoretical arguments that: 

• Since there is a big karst feature (Nash Draw), stream theory suggests that there 

must be a series of successively smaller conduit-type karst features that feed it, 

and that therefore these smaller features must be present but have not yet been 

found at the WIPP site. 

• Since boreholes are such a small sampling of the subsurface strata, the fact that 

karst-type features have not been recognized in wells, cores, and logs does not 

preclude the possibility that they are present and effective. 

• Since most fluid flow in strata containing karst-related conduits will occur 

through wide-open subsurface conduits, it will bypass the relict, relatively 

immobile water in the less permeable but volumetrically more important pore and 

fracture systems. Therefore most water samples taken from wells drilled into a 

karsted system should be from the more pervasive bypassed matrix water system, 

and might have an isotopic signature different from the waters in the conduits so 

that age dates from the water samples will be unrepresentative of the conduit 

system. 

Hill does not present direct evidence to support the application of these arguments to the 

Rustler Formation, merely stating that “The following principles and process of karst might be 

applicable to the WIPP Site” (1999, page 201). Coming to grips with such an approach to 

science is like debating random speculation. 

The stream-theory argument requires that Nash Draw be part of an equilibrated, fractal 

system, and, if valid, would only be of significance if that system extends outward from Nash 

Draw and encroaches eastward as far as the WIPP site. The argument about unrepresentative 

water sampling would be valid only if conduit flow is in fact a reality, and only if insignificant 

interaction between matrix waters and conduit waters occurs. The vague argument (that an 

intrastratal karst system should be present at or near WIPP but is unrecognized due to the low 
57

probability of sampling it) can be addressed by considering the geometry of the targets relative to 

the geometry of the sampling mechanisms (primarily wellbores). It is also addressed definitively 

by data collected during hydraulic pumping tests, which interrogate large volumes of rock. 

Hill (1999, 2003) presents the three arguments as theory but then draws conclusions as if 

these theories were a proven reality at the WIPP site. The three theories are discussed below. 

4.2 Nash Draw as the Largest of a System of Ever-Smaller Karst Features 

An ordered system, where small channels feed increasingly larger but fewer channels in 

stream systems, is a common pattern developed on homogeneous media and under homogeneous 

conditions. The karst system studied by Sares (1984), and cited by proponents of karst as an 

example of what they would expect to see in the subsurface at WIPP, is developed west of the 

Pecos River on widely exposed and relatively homogeneous anhydrites of the Castile Formation. 

This formation has been subjected to relatively uniform conditions of weathering and erosion 

over a wide area and for a long period of time, and a pattern of ordered stream channels has 

developed on it. In contrast, the Nash Draw-Rustler system is not a homogeneous medium, and 

different parts of the system have been developed under vastly different conditions. The Rustler 

Formation is composed of heterogeneous lithologies, including sandstones, claystones, 

dolomites, anhydrites, and halites, each variable resistance to erosion and dissolution. Moreover, 

significant differences exist between the outcrop conditions at Nash Draw, supposedly the largest 

element of the system, and the subsurface conditions to the east where the rest of the system 

supposedly is developed, but where the Rustler Formation is buried and thus protected from 

surficial erosion and weathering processes. 

Bachman’s field relationships (1985, page 24) indicate that much of Nash Draw formed 

as “The Gatuña stream system eroded into the evaporites of the Rustler Formation, and collapse 

sinks began to form near the end of Gatuña time.... As a result of following the strike of the 

Rustler Formation for a time, Gatuña drainage contributed to coalescing these sinks” (Figure 20). 

Present-day Nash Draw is therefore analogous to an oversize valley/underfit stream in previously 

glaciated terrain, wherein the size of the valley is relict from previous conditions and not directly 

related to the drainage system found there today. More importantly, the Pleistocene surface 

drainage over the outcropping Rustler Formation cut directly into that formation and thus played 
58

a significant part in enlarging Nash Draw to its present size: there is nothing comparable in the 

subsurface to the east, and no reason to believe smaller branches of a system exist there. 

Figure 20. Generalized Pleistocene Gatuña stream system, as reconstructed by Bachman (1985). 

Thus the medium and the conditions across the Rustler Formation were not, and are not, 

homogeneous as would be required for the development of ordered, dendritic drainage patterns, 

and theories of ordered sets of stream channel sizes are not applicable. The presence of a large 

Pleistocene stream, developed under conditions of more precipitation than at present, was 

responsible for dissolving out much of Nash Draw as a large, unique, and localized feature. 

Nash Draw should not be modeled as the largest of a system of pervasive and successively 

smaller upstream conduits. 
59

4.3 Assessing Possible Conduit Flow with Pumping Tests 

4.3.1 The Value of Hydraulic Testing, and Distinguishing Karst Flow from Fracture 

Flow 

 If conduit flow exists in the Rustler Formation at the WIPP site, it should be evident in 

the data from the numerous hydrologic pumping tests done in the formation at and near the site. 

Such tests can sample the hydrologic response and flow capacity of a large volume of strata 

between several widely spaced wells at once, thus the data are representative of significant 

volumes of strata. This offsets concerns that sample sizes have been too small to truly assess the 

potential for karst at the WIPP site. 

Flow dominated by fracture systems (which have low storativity and high transmissivity 

and which therefore give relatively rapid inter-well response times, and, commonly, good 

regional interconnection), has a distinctly different response when tested hydraulically compared 

to flow within karst-related conduit systems (which have high storativity, dampening the interwell response, but which should have limited regional interconnectivity). 

4.3.2 Fracture Flow 

The pumping and slug tests carried out in the Culebra at and near the WIPP site have 

shown both single- and double-porosity hydraulic behavior (Beauheim, 1987b; Beauheim and 

Ruskauff, 1998). Double-porosity behavior typically indicates a combination of matrix and 

fracture porosity in the tested medium, with the matrix providing most of the storage capacity 

and the fractures providing most of the transmissivity. Beauheim and Ruskauff (1998) have 

noted that the Culebra behaves as a double-porosity medium in those regions where open natural 

fractures are thought to dominate hydraulic responses, and as a single-porosity medium where 

fractures are thought to be fewer, smaller, and more commonly plugged with gypsum. 

Hydraulic testing of the Culebra has indicated horizontal directional-flow anisotropies of 

up to 1.6:1 measured in pumping tests, and up to 7:1 measured in tracer tests (Haggerty et al., 

1997; Meigs et al., 1997a,b). This type of behavior is typical of flow within preferentially 

oriented fracture systems (e.g., Lorenz et al., 2002). The measured axis of flow anisotropy at the 

WIPP site is not consistent among the various tests, suggesting local variability in the dominant 

subsurface fracture orientations or in the in situ stress conditions. 
60

Testing has also indicated the presence of local hydraulic boundaries within the Culebra 

Member. “No-flow” boundaries are interpreted as representing decreasing transmissivity, while 

“constant-pressure” boundaries are interpreted as representing increasing transmissivity. This 

indicates that the Culebra Member is not homogeneous. None of these tests indicate the 

presence of karst conduits. 

Outside of Nash Draw, the Magenta has not been found to be transmissive enough to 

sustain the minimum one-gallon-per-minute flow rate required to perform a pumping test. As a 

result, only slug tests have been performed in the Magenta, and these tests have uniformly 

indicated low transmissivity and single-porosity (i.e., unfractured and unkarsted) conditions 

(Beauheim, 1987b; Beauheim et al., 1991; Beauheim and Ruskauff, 1998). 

Transmissivities measured in the Rustler Formation vary by five to six orders of 

magnitude. However, even the highest transmissivities measured (Beauheim and Holt, 1990; 

Beauheim, 1987c) do not indicate or support open-conduit flow. 

4.3.3 Pumping Tests 

A pumping test was carried out in well WIPP-13, where the Culebra was pumped in the 

test well for 36 days, and responses to that test were measured in the Culebra in surrounding 

observation wells (Beauheim, 1987c). Measurable responses were observed in all wells within 

two miles of WIPP-13, as well as in several other wells up to four miles distant. The closest 

wells to the northeast (DOE-2) and northwest (H-6) responded in one and eight hours, 

respectively, indicating a relatively high-permeability but low-storage connection. These results 

indicate good interconnectivity within the Culebra, arguing for a pervasive and interconnected, 

but low-volume, natural-fracture system rather than a system of high-volume karst conduits. 

If the pressure transient had propagated to a highly conductive karst conduit, drawdown 

responses would have diminished and tapered off with time as the large-volume conduit supplied 

water to the pumping well. Instead, pressures in all wells dropped gradually and evenly over the 

course of the test, indicating both that there is no large reservoir of fluid in the system and that 

the fractures were fluid-filled. 

No response was observed in the Magenta where it was monitored in H-6, indicating no 

vertical communication between the Culebra and the Magenta. 
61

A more recent (2005), 19-day pumping test at WIPP-11 also suggests that there is a wellconnected, fairly high transmissivity region among wells in the north-central and northwestern 

parts of the WIPP site. The apparent storativity of the Culebra is still low, i.e., the Culebra is 

dominated by fracture flow and not conduit flow. Earlier interference testing had shown the 

existence of two areas at the WIPP site characterized by relatively high conductivity (fractures, 

not conduit flow). In the northwestern area of WIPP, H-6, DOE-2, WIPP-13, WIPP-30, 

WQSP-1, and WQSP-2 (see Figure 5b) all appear to be well connected at the level of the Culebra 

Member (Beauheim, 1986, 1987c; Beauheim and Ruskauff, 1998). In the southeastern part of 

the WIPP site, H-3, H-11, H-15, H-19, WQSP-4, DOE-1, and, to a lesser extent, H-17 and P-17 

appear to be well connected based on pumping tests conducted at H-3, H-11, and H-19 

(Beauheim, 1987a, 1989; Beauheim and Ruskauff, 1998). An interconnected natural fracture 

system provides potentially high flow rates locally, but has very little volume so the porosity and 

storage capacity are low, as seen in these tests. The results are not compatible with the 

properties of a high-volume karst-conduit system. 

These test results reflect a pervasive fracture network rather than discrete channels 

because all wells within an inter-connected region respond when any one of them is pumped, and 

because all wells newly drilled within the connected areas also show the connections (e.g., H-19, 

WQSP-1, WQSP-2, and WQSP-4). Rapid responses to even low pumping rates (3-30 gallons 

per minute) indicate good connectivity but low storativity; karst conduits would show high 

storativity signatures. 

Pumping tests at H-3, H-11, H-19, P-14, WQSP-4, and WIPP-13 all showed decreasing 

transmissivity (“no-flow” boundaries) as the pumping-induced pressure transient propagated 

farther and farther from the pumping well, while surrounding observation wells were drawing 

down (Beauheim, 1987a; 1987c; 1989; Beauheim and Ruskauff, 1998). Of all the wells tested 

near the WIPP site, only the H-6 wells (and WIPP-13 at very long times) show transmissivity 

increasing (similar to a constant-pressure boundary effect) as the pressure transient propagates 

(Beauheim and Ruskauff, 1998). 

Large, highly conductive karst channels would also have appeared as constant-pressure 

boundaries in the pumping-test responses, but the channels would have prevented the responses 

that were observed in wells located beyond the hypothetical channels. For example, the H-6 

wells respond strongly to pumping at WIPP-13, and well D-268 responded to pumping of well 
62

P-14 (Beauheim and Ruskauff, 1998) despite Snow’s suggestion (1998) that a large karst 

channel, presumably capable of capturing flow or at least dampening the hydraulic response, 

exists between them. 

4.3.4 Lack of Culebra-Magenta Interconnections 

The parallel water-level behavior of the Magenta and Culebra observed at wells such as 

WIPP-25, WIPP-27, and H-6 (Figure 21) leads to a question of how well interconnected the

Magenta and Culebra might be. For H-6, the lack of interconnection is shown in Figure 21 by 

the clear lack of a Culebra response to the five pumping episodes in the Magenta at H-6c, evident 

in the first four years of data on the plot. Equally important, no drawdown has been measured in 

any wells completed in the Magenta during testing of the Culebra (Figure 22). 

11 14 17 20 23 26

Time Since 1/1/77 (yr)

926

927

928

929

930

931

932

933

934

935

W

ater-Le

v

el Ele

v

ation (m

a

msl)

Magenta (H-6c)

Culebra (H-6b)

file: H-6C&M-1988-2004.grf

Figure 21. H-6 Magenta and Culebra hydrographs, 1988-2004. Magenta and Culebra water 

levels are monitored in wells separated by only 100 ft on the H-6 pad. The figure shows that 

water levels are generally rising in both units, although the Culebra shows more minor 

fluctuations than the Magenta. It also shows no response in the Culebra to pumping in the 

Magenta during the years 1988-1991. 
63

-1000 0 1000 2000 3000 4000

Time Since Pumping Began in Culebra (min)

50

60

70

80

90

100

110

120

Culebra Pressure (psig)

Magenta

Culebra

60

61

62

63

64

65

Magenta Pressure (psig)

file: W25 M&C PT.grf

Figure 22. WIPP-25 Magenta and Culebra pressures during Culebra pumping test conducted in 

2004. 

This indicates that the two members are hydraulically isolated from each other even in 

wells drilled into the acknowledged karsted terrain of Nash Draw (e.g., WIPP-25), where the 

vertical separation of the two units is at a minimum and where the potential for fracturing and 

vertical communication is the greatest. 

4.3.5 Potentiometric Heads 

The measured patterns of the Culebra and Magenta potentiometric surfaces (Figures 23 and 24) 

suggest that the water-bearing units of the Rustler Formation are poorly interconnected 

hydrologically to each other. The potentiometric heads in both the Magenta and Culebra 

generally slope in different directions, strongly suggesting that the two units are hydraulically 

isolated from each other. A karst system would create good hydraulic connections between the 

units, and the potentiometric heads would be in equilibrium, probably parallel, and possibly even 

equivalent. 
64

Figure 23. Potentiometric heads of the Culebra Dolomite Member of the Rustler Formation. 

From Johnson (2005a). 
65

Potentiometric Surface, Adjusted to Equivalent Freshwater Heads, of the Magenta 

Dolomite Member of the Rustler Formation near the WIPP Site, 2004 

0Ft 10000Ft 20000Ft

APPROX WIPP SITE BOUNDARY

Note: Contour elevations are in feet above mean sea level

WIPP-25

WIPP-30

H-6c H-5c

H-4c

H-11b2

H-10a

H-15 H-2b1

H-14

H-3b1

C-2737

H-18 WIPP-18

H-8a

H-9c

Figure 24. Potentiometric heads of the Magenta Member of the Rustler Formation. The H-14 

and H-18 heads were affected (lowered) by equipment problems. From Johnson (2005b). 
66

Strong deflections of the Magenta potentiometric heads in the vicinity of drillhole 

WIPP-33 near the northwest corner of the WIPP site may indicate a local development of highervolume porosities in this member of the Rustler Formation, but it is the only such indication. 

Few Magenta data points exist southwest of the WIPP, and the contours in this area are not well 

constrained. 

4.4 Conduit Flow, Bypassed “Fossil” Water, and Diffusion 

4.4.1 Old and Young Water in the Same Unit 

 In trying to integrate Lambert and Harvey’s (1987) finding (that isotopic analyses 

indicate water samples from the Rustler Formation are 12,000-16,000 years old), with karst 

theory (where waters should be capable of coursing rapidly through large Rustler conduits), Hill 

(1999, p. 54-55; 2003, page 206) has suggested a compound porosity system. She cites 

Chapman’s (1986; 1988) interpretations to support a theory that there could be two separate 

isotopic compositions of water in the subsurface: old, fossil water and younger, recently 

recharged water. The argument is that water with a relatively old isotopic composition fills and 

is trapped in matrix porosity in the blocks between conduits, and that this is the water most 

frequently sampled since the matrix blocks are larger than conduits and they therefore have the 

highest probability of being intersected by a wellbore, explaining the data that indicate old water 

fills the system. Different water with a young but unsampled isotopic signature supposedly fills 

karst conduits between the matrix blocks but is rarely sampled because there are few such 

conduits, and therefore the Rustler water-sample data showing isotopic indications of mostrecent recharge 12,000-16,000 years ago should not negate the possible presence of a rapidly and 

recently recharged subsurface karst system. 

 Chapman’s (1988, p. 46) assertion that “The salinity differences and uranium isotopic 

data suggest that either the Culebra contains discrete, rapid flow paths interspersed with areas of 

slower groundwater movement and/or that young fresh water leaks into the aquifer,” seems to 

have been the inspiration for this theory. However, Chapman also suggests (same page) that 

“Extreme salinity variations...may be due to leakage of concentrated brines in the Rustler from 

underlying evaporite units.” Chapman prefers the first interpretation, but the sample area 
67

includes Nash Draw and the area south of route NM 128 where local points of fresh water influx 

are known. Moreover, although the locations of Chapman’s “rapid flow paths” are unspecified, 

Chapman suggests that they are broad in scale, extending for miles in length, and thus they do 

not mesh well with Hill’s concept of conduits (anything larger than a centimeter). Nor do they 

fit with or support the proposed locations or sizes of Snow’s (1998) four hypothetical conduit 

channels. Chapman’s concepts do not support Hill’s concept of conduit flow and bypassed 

water. 

Chapman (1986) also suggests that the stable isotope data from Rustler water samples are 

similar to “verifiably young” groundwater samples elsewhere in NM. No one has reviewed or 

explained the reasons for the differences between this and Lambert and Harvey’s (1987) findings 

of older, matrix waters, although authors more often cite Lambert’s work. 

4.4.2 No Evidence for Conduit Flow; Consideration of Diffusion 

Hill’s argument for two water systems at depth is negated by the hydraulic tracer and 

pumping tests, which inherently sample large volumes of rock and which did not produce 

evidence for the presence of conduits. In addition, whether a well directly intersects fractures or 

somehow misses them, pumping the well will preferentially pull water from the most permeable 

part of the system (the fractures). Hence, water in fractures is always, not rarely, sampled. As 

the pressure in the fractures decreases due to pumping, water flows from the matrix into the 

fractures. This water comes from the portion of the matrix that is closest to the fractures, and 

therefore closest to chemical/isotopic equilibrium with the water in the fractures. Therefore, the 

isotopic signature of the water would be much more characteristic of the fractures than of any 

hypothetical older water in the matrix. Furthermore, diffusion would have equilibrated water 

chemistries between the fractures and matrix over the many years that fractures (or conduits) 

have existed. 

4.4.3 Conclusion 

Based on pumping and tracer tests, the concept of two subsurface water populations with 

widely divergent isotopic and age characteristics is untenable. Thus the inference derived from 
68

this concept, that the ages calculated from the isotopic signatures of sampled Rustler waters 

support the potential for karst at WIPP, is invalid. 
69

5.0 PROBABILITY AND ISSUES OF LIMITED WELLBORE SAMPLING 

5.1 Introduction 

Hill (1999) suggests that it is still possible that karst features are present and as yet 

unsampled in the Rustler Formation at the WIPP site, even though only one of the numerous 

wells drilled near the site (exclusive of Nash Draw) encountered evidence for karst, because 

wellbores sample such small areas of a formation. She also suggests that wells drilled in the 

center of topographic depressions to test them for an origin due to subsurface karst have missed 

relatively small (dimensions not estimated) karst conduits leading from the surface depression to 

a more extensive subsurface karst system. 

5.2 Probability of Intersecting Fractures with a Drillhole 

Aside from the hydraulic testing described above, a wellbore is, in fact, a small sampling 

of a formation. The 83⁄4-inch diameter wellbores typical of oilfield operations have a crosssection of less than half a square foot. A wellbore, therefore, is an inefficient way to sample and 

characterize widely scattered or vertical, two-dimensional features such as vertical fractures. 

The probability of intersecting vertical fracture planes with a vertical wellbore is low unless the 

fracture spacing is very small, i.e., the probability of intersecting vertical fractures with an eightinch well is only 50% when the average fracture spacing is only 16 inches (Figure 25), and the 

probability of intersecting a fracture decreases exponentially as fracture spacing increases 

(Lorenz, 1992). 
70

Figure 25. The probability of intersecting fractures with a vertical drillhole is low unless the 

fractures are not vertical (from Lorenz, 1992). 

5.3 Probability of Intersecting Karst with a Drillhole 

However, karst conduits such as postulated by Hill are neither vertical nor twodimensional. Although they may initiate by dissolution along two-dimensional fractures, by the 

time they have widened into conduits that are large enough to significantly affect fluid flow 

within a formation they are three-dimensional features (see Figure 4). Hill (1999) defines a 

conduit as anything over one cm in diameter, but does not provide examples or descriptions of 

actual conduits. The addition of the third dimension significantly increases both the ability to 

conduct fluids and the probability of intersection by a drillhole. 

More significantly, the documented fractures in the Rustler Formation have a variety of 

orientations, ranging from vertical to inclined to horizontal. The probability that a well will 

intersect two-dimensional fractures, or the karst-related conduits developed along them, 

increases as a sine function as the fracture dip decreases from vertical. There is a high 

probability of intersecting horizontal fractures with vertical wells. 
71

Since so many of the documented natural fractures in the Culebra and other members of 

the Rustler Formation are inclined to horizontal, and since potential karst dissolution features 

should be initiated and preferentially developed along fractures, vertical wellbores do in fact 

adequately sample the formation for potential karst. The samples are small, but the potential 

targets, if present, would be big. The absence of karst evidence in wells at the WIPP site, with 

the possible exception of WIPP-33, is a valid indication that karst has not been developed in the 

Rustler Formation at this site. 

5.4 Data from the WIPP Shafts 

The absence of karst is strongly corroborated by the significantly larger-scale, direct 

sampling of the Rustler Formation afforded by the air intake, waste, and exhaust shafts, 

excavated in the central part of the WIPP site to support the subsurface facilities and operations. 

These shafts had unfinished diameters of 20.25 ft, 20.0 ft, and 15.0 ft respectively, and all 

geological features in the penetrated formations, including the Rustler Formation, were carefully 

mapped during excavation (e.g., Holt and Powers, 1984, 1986, and 1990b). 

The three shafts have a combined plan-view area of 812 square ft, as much area as would 

have been sampled by nearly two-thousand standard, oilfield, 83⁄4 inch-diameter wells. The 

Rustler Formation penetrated by the three shafts is 309 ft thick, thus over 53,000 square feet of 

Rustler wall rock were exposed in the three shafts for examination and detailed mapping. No 

evidence of karst was found in the well-exposed rock in the three shafts, excavated at three 

separate, although closely spaced, locations. 

5.5 Volume of Caves 

 Hill (1999, page 21) makes the theoretical argument that the void space of caves in many 

karst terrains constitute only 1-2% of the total rock volume, and that therefore the evidence of 

“caves” (bit drops) encountered while drilling only one of 60 (1.7%) wells in the WIPP area 

(WIPP-33) is consistent with the presence of similar, karst-related void space percentages at 

WIPP. While the assignation of a limiting, maximum percentage to what is a spectrum of 
72

phenomena seems to be an unwarranted restriction, the absence of dissolution in Rustler strata in 

the large, clean, high-volume shafts is perhaps the most telling evidence against this hypothesis. 

5.6 Drilling in the Centers of Depressions 

 Hill (1999) argues that holes WIPP-33 and WIPP-14, drilled to investigate the possibility 

that local topographic depressions indicate an underlying karst system, have merely missed the 

subsurface evidence for karst. This is a nebulous argument for which no rebuttal can ever be 

satisfactory to the arguer, since no matter how many holes are drilled, any and all holes that drill 

through an unkarsted sequence of the Rustler Formation can be alleged to have been merely 

drilled in the wrong location. 

However, the holes drilled to assess these depressions and their associated gravity 

anomalies were located near the centers of the surface topographic depressions (see Figure 9), 

and the location of WIPP-14 was based on the surface features and gravity data that had been 

interpreted by Barrows et al. (1983) and reviewed by Barrows (Sandia National Laboratories and 

D’appolonia Consulting Engineers, 1982, Appendix A). 

It is unclear whether Hill suggests that the surface depressions are caused by an actual 

karst collapse as the underlying Rustler strata became brecciated and displaced during 

dissolution beneath the entire area of the surface depression, as seen in the local breccia pipes, or 

whether Hill infers that the depressions result from large-scale dissolution or subsidence of the 

sandstone layers near the surface. Regardless, neither theory is supported by the data. If it is the 

former case, then the collapse that formed the surficial depressions should have resulted in 

relatively large breccia chimneys, or at least measurable downward displacement of the 

stratigraphic layers, either of which would have a large enough signature to be intersected by the 

wells drilled to test these structures. The wells drilled into these surface depressions/gravity 

anomalies have encountered neither displaced strata nor extensive, definitively post-depositional 

breccias. Moreover, near-surface solution is untenable since the Triassic and Permian siliceous 

sandstones, siltstones, and claystones that underlie the thin recent deposits are highly resistant to 

dissolution. 

An alternative interpretation is that shallow stream channels, formed during the

Pleistocene and partially filled with Gatuña deposits, have been choked by migrating sand dunes. 
73

The upper 97 ft of WIPP-14 core is consistent with Gatuña channel fill, and on trend with a 

Gatuña paleovalley mapped by Bachman (1985, his Figure 20). More recently, Powers and 

Richardson (2004a) have shown that thick Gatuña deposits are present in the SNL-3 drillhole 

along this same trend. Wind-driven sculpting of the surface (including the “blowouts” of 

Bachman, 1981) is a widely recognized process in this part of New Mexico that has continued to 

modify the area. 
74

6.0 NEGATIVE GRAVITY ANOMALIES AND RELATED GEOPHYSICAL 

MEASUREMENTS 

6.1 Introduction 

Numerous remote-sensing techniques have been applied to the WIPP site in an effort to 

characterize the subsurface strata. Each technique seems to have produced local anomalous 

signal responses, suggesting that there might be local anomalies in the subsurface, but there is 

little overlap between the resistivity anomalies (Elliott Geophysical, 1976,1977), gravity 

anomalies (Barrows et al., 1983), seismic anomalies (Barrows et al., 1983), topographic 

anomalies (Phillips, 1987), groundwater flow anomalies (Mercer, 1983, Crawley, 1988), 

potentiometric head anomalies (Beauheim and Ruskauff, 1998), groundwater geochemistry 

anomalies (Mercer, 1983), and electromagnetic anomalies (Earth Technology Corporation, 

1987), and these do not coincide with the positions of the large Rustler karst conduits postulated 

by Snow (1998). A plausible case could be built for subsurface anomalies if indications of the 

anomalies from one or more of the different techniques overlapped in location, depth or size, but 

the different techniques have provided scattered and inconsistent indications. 

The failure of the different techniques to suggest the same locations for subsurface 

anomalies highlights the difficulty and latitude in interpreting these techniques. The sensors 

have presumably responded to one or more real, physical features in the earth, but there is rarely 

a unique or even well-supported interpretation of that response. Recognition of this fact led to 

drilling and coring of test holes in order to physically investigate the shallow strata under several 

of the anomalies, and, in turn-about, to claims that these holes did not confirm or deny the 

remote-sensing signatures. 

Most of the discussion has revolved around the WIPP gravity survey (Barrows et al., 

1983). Hill (1999, p. 37-40; 2003, p. 205) cites the Barrows report as showing four “sharp” 

negative gravity anomalies that are “consistent with” solution caverns, although only the WIPP14 and WIPP-33 anomalies were discussed and attributed to subsurface karsting by Barrows 

himself. Barrows’ discussions are convoluted and sometimes contradictory, and his 

interpretations are not definitive. 
75

For example, there are discrepancies in Barrows’ discussions of the comparison of 

density logs between holes and how or whether they indicate karst in the Rustler Formation. 

Barrows et al. (1983) note that the WIPP-34 velocity survey logged through the Dewey Lake 

Formation has slower overall travel times than the WIPP-13 velocity survey (their Figure 3.1-3, 

discussions on page 54), indicating that the strata at WIPP-34 are anomalously less dense than 

normal and inferring that this difference accounts for the deeper local “seismic time structures” 

at this site. 

He then portrays the same WIPP-34 density log as a normal-response log through the 

Dewey Lake-Rustler section, suggesting that by comparison, a lower density log response in the 

WIPP-14 hole indicates that there is missing material. He extrapolates this to an interpretation of 

mass removal by karst processes in the vicinity of WIPP-14. 

Figure 26. Superposition of the WIPP-14 gravity anomaly and topographic contours (From 

Barrows and Fett, 1985; their Figure 4/page 828). Topographic contour (dashed lines) not 

specified by the authors but probably about five feet. Gravity contours 0.1 mGal. 
76

6.2 The WIPP-14 Gravity Anomaly 

The gravity anomaly explored by the WIPP-14 drillhole is an elongate, narrow pattern on 

the order of 5000 ft long along a curved axis, and 1000 ft across (Figure 26). The overlying 

topographic depression is much smaller, about ten ft deep and 700 ft across, and located about 

600 ft northwest of the center of the gravity anomaly. 

Barrows et al. (1983) calculate that the depth to the top of the “causative structure” that is 

responsible for the WIPP-14 gravity anomaly is shallow, not more than 225 ft below the surface. 

This depth puts the inferred deficiency in mass, i,e., karst, within the Dewey Lake Formation, 

reported to lie between the depths of 141-639 ft in this hole (Sandia National Laboratories and 

U.S. Geological Survey, 1981). This does not correlate to the two zones (300-400 ft, and 650-

750 ft) where Barrows’ calculated the presence of mass deficiencies from the density logs, or 

with the concept of karst development being in the Rustler Formation. Barrows does not address 

these discrepancies or the questions of why and how dissolution of insoluble sandstones, 

siltstones, and shales of the Dewey Lake Formation might have occurred in the karst model he 

builds. The question of why karst should have formed in the Dewey Lake Formation rather than 

in the more soluble, underlying Rustler Formation is left unasked and unanswered. 

The core and geophysical logs from WIPP-14 document a normal stratigraphic

succession, although there is an anomalously thick alluvial fill found at the top of this hole. This 

fill most closely resembles the sandstone and conglomerate of the Gatuña Formation, strongly 

suggesting that the fill is the remnant of a local tributary channel that fed the thick Gatuña fluvial 

deposits (see Figure 20) mapped by Bachman (1985) just to the north. This thick interval of 

relatively porous rock explains the local gravity anomaly more easily than karst in the Dewey 

Lake or Rustler Formations. Elongation of the gravity anomaly is consistent with this 

interpretation as a fluvial channel. 

Barrows also noted that seismic data at the WIPP site above the Castile Formation “are 

considered too unreliable to map” (1982, page 16), yet later in the report (page 57) used this 

shallow seismic data in the vicinity of WIPP-14 to infer that “a seismic time syncline [is] 

coincident with the [shallow] negative gravity anomaly. Both the seismic time syncline and the 

negative anomaly are explained by lateral velocity and inferred density variations comparable to 

those observed in uphole velocity surveys”. The use of “unreliable” data is not sound practice. 
77

Although the shallow reflectors do in fact appear to be depressed, suggesting near-surface, 

lower-velocity sediments, this is consistent with and more easily explained by Bachman’s 

Gatuña-filled paleovalley. 

6.3 The WIPP-33 Gravity Anomaly 

The gravity anomaly at WIPP-33 is outside the main WIPP area and was not covered by 

the main gravity map (Barrows et al., 1983, their Figures 2.1-3 and 2.1-4). Rather, this anomaly 

was documented in an associated reconnaissance gravity survey consisting of two intersecting 2-

D vertical gravity profiles specifically shot to assess the topographic depression. The gravity 

signature of the anomaly shows closure in all four directions in the two gravity lines (Barrows et 

al., 1983, their Figure 2.3.1-3, page 50), so it is probably roughly circular and perhaps 1500 ft 

across. The overlying topographic depression is about eight feet deep and 200 ft in diameter, 

reasonably well centered on the gravity anomaly. Barrows calculated that the top of the 

“causative structure” for the gravity anomaly, inferred to be void space related to karst, is at a 

depth of 450 ft. 

The text of the basic data report for WIPP-33 (Sandia National Laboratories and United 

States Geological Survey, 1981) notes that this well drilled through an “unusually thick” 

sequence of “surficial Holocene deposits” (44 ft according to the abstract, although this is 

difficult to corroborate in the accompanying Table 3 lithologic log). These deposits are 

described as filling a “small closed basin,” although the interpretation that the surficial basin was 

closed at the time of deposition appears to be speculative, or at least not supported with direct 

sedimentological evidence in the basic data report. 

Much has been made of this gravity anomaly because it coincides with a surface 

depression and because the WIPP-33 drillhole encountered bit drops in the Forty-niner and 

Magenta Members of the Rustler, suggesting subsurface void space at several intervals between 

the depths of 420-470 ft. This is consistent with the Barrows’ gravity calculations of the depth of 

void space, and there are possible overlaps between this gravity anomaly and the resistivity 

anomaly noted in the northwest corner of WIPP, suggestive of water-filled, high-porosity 

features at an unspecified depth (Elliott Geophysical, 1977). This is also the approximate 

domain of interconnected natural fractures in the Culebra Member described by Beauheim and 
78

Ruskauff (1998) on the basis of hydrology tests. However, the core and geophysical logs from 

this hole document depths for the stratigraphic tops that were penetrated that are on trend with 

those of surrounding boreholes, i.e., the stratigraphic tops are not lower than normal, not 

downthrown into a karst-related depression. 

6.4 The WIPP-13 and H-3 Gravity Anomalies 

Hill (1999) suggests that two other gravity anomalies at and near WIPP also indicate the 

locations of subsurface karst. These locations are around the WIPP-13 and H-3 drillholes. Hill 

(1999, p. 48) states that “both WIPP-13 and H-3 are located within negative gravity features 

(sinkholes?).” The Rustler strata cored in both these holes show some disruption, possible 

indications of dissolution but more plausibly interpreted as syndepositional disruption since they 

are overlain by undisrupted strata with primary depositional structures. Although Holt and 

Powers (1988) infer some stratigraphic displacement of the angular sulfate fragments 

encountered in the WIPP-13 core just below the contact with the A-3 sulfate of the Tamarisk, 

they also report two thin anhydrite beds and a polyhalite bed to the east in a stratigraphically 

equivalent halite bed. This angular fragment can as easily represent a stratigraphically in-place 

remnant of one of these thin units, as Holt and Powers (1988) and Powers and Holt (2000) 

describe how the polyhalite, and presumably the upper anhydrites, converge with the base of A-3 

westward from the depositional center of the unit. In addition, the shaft mapping shows a thin 

sulfate bed in this stratigraphic position, with a breccia and conglomerates at the base of A-3 and 

overlain by an erosional surface. Both holes encountered normal stratigraphic successions, and 

the cored breccias are too thin and too deep to have affected the gravity survey. 

The WIPP-13 gravity anomaly is nearly circular, about 2000 ft across. With only -0.15 

mgal of relief, it is relatively shallow. The H-3 gravity anomaly has similar relief according to 

the gravity map (Barrows et al., 1983, their Figure 2.1-4), although Hill reports it as a -0.45 mgal 

depression. It is also circular and shallow, about 3500 ft across. Neither anomaly is a “sharp” 

departure from the regional trends as suggested by Hill. 
79

6.5 Assessment of the Gravity Anomaly Data 

 Hill and Barrows have used questionable correlations between large (thousands of feet 

across) irregular gravity anomalies and small (hundreds of feet in diameter), circular topographic 

features, to reach poorly supported but definitively stated conclusions. They have been selective 

in using the array of available data, presenting only those data that they feel support their concept 

of subsurface karst and ignoring other data. They have not attempted to explain topographic 

depressions that do not have associated gravity anomalies, nor have they integrated the other 

available remote sensing/geophysical data into their models and conclusions. Most of the 

anomalies considered by Hill are broad and shallow, not fitting a rigorous definition of the term 

“anomaly”: only the WIPP-14 and possibly the WIPP-33 anomalies could be considered to be 

“sharp” departures form the regional gravity trends when compared to other anomalies across the 

area. 
80

7.0 ABSENCE OF SURFACE RUNOFF 

Hill (1999, p. 40-42), suggests that: 1) because the WIPP site “is characterized by almost 

no surface runoff” despite 12 inches of annual precipitation, and 2) because the chloride massbalance techniques used by Campbell et al. (1996) suggested that infiltration of water through 

the soils is not the major source of recharge into the Rustler Formation [“...our data do not 

support direct infiltration through the overlying soil as the major source of aquifer recharge...”, 

page 164], that therefore 3) recharge of the subsurface Rustler units must be through surface 

runoff that flows primarily into sinkholes, and 4) that therefore there must be sinkholes and an 

associated subsurface karst system at the WIPP site. 

This is an over-extended extrapolation from the original observation (no surface runoff), 

which of itself does not point exclusively to the presence of sinkholes. In fact, nothing on the 

surface in the vicinity of the WIPP site east of Livingston Ridge is similar in shape or scale to the 

obvious stream piracy by sinkholes seen in Nash Draw and elsewhere in southeastern New 

Mexico (see Figure 11). In comparison, the short “disappearing arroyo” near WIPP-33 (see 

Figure 8) does not actually reach the WIPP-33 enclosed surface expression. Hill (1999, p. 42) 

therefore falls back on an artificial and not wholly analogous example where water seeping from 

the Dewey Lake into the WIPP exhaust shaft “may be due to the focusing of water downward 

from the WIPP site parking lot (K. Larson, personal communication).” Water in fact is perched 

locally within the uppermost Dewey Lake Formation (Powers, 1997; Holt and Powers, 1990a) at 

the WIPP site. Hill’s unproven implication is that the surface depressions at the WIPP-14 and 

WIPP-33 drillhole sites are locations similar to the parking lot in form and effect. The analogy 

fails since the former would be resultant features, whereas the parking lot catchment area is a 

causative feature. 

Even if all 12 inches of rain came at once, potential runoff pathways across the site area 

are dammed by a blanket of stabilized and unstabilized sand dunes. Such sands are also capable 

of soaking up large volumes of rainwater (Geohydrology Associates, 1978), thus the 12 inches of 

rain per year need not have carved out an integrated drainage system on the low-relief 

topography. Discussions of evapotranspiration rates and the rapid infiltration of rainwater into 
81

sandy material that blankets the WIPP site are given below under Recharge and Discharge 

Issues. The surface-water runoff argument is poorly defined, circumstantial evidence. 
82

8.0 RECHARGE AND DISCHARGE ISSUES 

8.1 Introduction 

Questions of recharge of the Rustler water-bearing units in the vicinity of the WIPP site, 

the locations of discharge from them, and the groundwater flow between, are somewhat openended since so few data are available. The location(s) and modes of recharge are largely 

theoretical, and few data concerning recharge and discharge points have been collected since 

Robinson and Lang (1938) first proposed that the waters in the Culebra and Magenta Members 

and/or in the brine aquifer collect in Nash Draw and discharge at the numerous springs at Malaga 

Bend on the Pecos River southwest of the WIPP site. 

Malaga Bend is still widely accepted, de facto, as the probable discharge point for some 

Rustler groundwaters and the brine aquifer. Recharge locations are another story. 

Measurements of the potentiometric heads and of the chemistry of the waters found in the 

Rustler have been significantly improved during recent studies, yet the significance of these data 

is still under debate. The modeling of Corbet (1998) and Corbet and Knupp (1996) suggests that 

many of the observed patterns of groundwater geochemistry can most readily be explained by 

assuming that, over geologic time scales, there is a certain amount of vertical connectivity across 

formation boundaries as well as the widely accepted and more rapid lateral flow within members 

of the Rustler Formation. 

Within these loose constraints, arguments have been made for flow through karst-related 

channels in the Rustler Formation at the WIPP site. Hill (1999; page 44 and Appendix A)

suggests that records of rainfall near the WIPP site from September of 1986 through December 

of 1988 can be correlated with discharge variations at the Malaga Bend springs. Discharge from 

these numerous and obscure springs in the alluvium at and below the riverbed was calculated by 

subtracting flow in the Pecos River measured at gauging stations below the springs from river 

discharge measurements made above them. 

In the following discussions, it is useful to note that the proponents of karst at the WIPP 

site make little or no distinction between the recharge potential and fluid-flow characteristics of 

the Rustler Formation where it crops out in Nash Draw and these characteristics where it is 

buried by insoluble younger strata east of Livingston Ridge. Although the formation is 
83

stratigraphically continuous laterally between these two domains, the data suggest that 

hydrologically the formation comprises two different, although connected, systems. Within 

Nash Draw, the data suggest that caves, sinks, fractured strata, and a thinner formation allow 

good hydrologic communication within the Culebra and Magenta Members of the Rustler 

Formation, rapid fluid flow, and, probably, recent local recharge. Eastward, however, where the 

formation is protected by overlying strata, it is not disrupted and therefore it has lower hydraulic 

conductivity. Nondiscrimination between data from the two domains, which show a difference 

of nearly two orders of magnitude in transmissivity values (Powers et al., 2003), obscures the 

important differences between them. 

8.2 Correlations Between Malaga Bend and WIPP Site Precipitation 

Hill (1999) found a 90- to 94-day lag-time response between precipitation in the area east 

of Carlsbad and discharge pulses at Malaga Bend in five out of eight cases, “suggestive of a 

possible connection” between the WIPP site and Malaga Bend. Hill did not discuss the 

numerous other rainfall spikes in the records that are not associated with river discharge peaks, 

and she did not try to correlate the volume of rainfall with volume of spring discharge. She also 

noted but did not account for the fact that Pierce Canyon, south of the WIPP site and the only

large drainage east of the Pecos for miles around, also empties into the river between the two 

gauging stations. 

Hill (1999) acknowledged that her study was poorly controlled and that it might not be 

statistically meaningful since it did not account for factors such as irrigation, Pecos flood pulses, 

or industry water withdrawals at Nash Draw, and because it made no differentiation between 

precipitation over Nash Draw (where sinkhole catchment of drainage is known) and precipitation 

over the WIPP site where she was trying to prove the connection. She nevertheless justified the 

study with the statement (1999, page 47) that “The purpose of the above exercise is to show that 

actual measurements of recharge/discharge should be made in any serious attempt of studying 

karst at the WIPP site”, and although she did not in fact do this herself, the reader is ultimately 

left with the impression that she considered that the data support the presence of karst in the 

Rustler at the WIPP site. 
84

Ultimately, however, the poorly constrained behavior of groundwater in the area in and 

between the widely recognized dissolution/karst features at Nash Draw and the Malaga Bend 

springs is immaterial to the understanding of groundwater at the WIPP site to the east. Although 

climatically similar, the geology and the surface catchments are dissimilar. 

8.3 Recharge 

The following is a brief summary of groundwater recharge, flow, and discharge in the 

Rustler members at and near the WIPP site. Like the discharge points, recharge mechanisms and 

locations are typically assumed rather than documented. The water budget calculated by 

Geohydrology Associates (1978) suggests that in the WIPP site and Nash Draw areas, water 

inflow from precipitation and industry/oilfield brines exceeds outflow (evapotranspiration plus 

discharge at the Malaga Bend springs) by 3,327 acre-ft per year. This net increase appears to 

correspond in general to the observed increase in potentiometric heads in the Culebra across the 

area, although the exact source of recharge is debatable. 

8.3.1 Localized Recharge 

Specific potential recharge locations, where the Rustler Formation crops out or is near 

enough to the surface to be recharged by precipitation, are rarely specified by authors. The 

Forty-niner, Magenta, Tamarisk, and Culebra Members of the Rustler Formation all crop out in 

various areas in Nash Draw. Several sinkholes that capture overland drainage are obvious from 

the air within this area of closed drainage (e.g., Figure 11), but details of these sinkholes have not 

been published, although Bachman (1981) did map a number of them. Because Nash Draw is a 

closed-drainage depression, rain falling into it evaporates, gets collected in the brine ponds, or is 

funneled underground. Mercer (1983) suggested that the Rustler might also be recharged at Bear 

Grass Draw, about 30 miles northwest of the WIPP site, but did not present data to support this 

inference. Other authors have not offered opinions or evidence for locations where recharge of 

the Rustler Formation is occurring or could plausibly occur. 

8.3.2 Irrigation and Industry Effluent 

Theis et al. (1942, page 68-69) noted that water levels in Culebra water wells in Nash 

Draw south of Laguna Grande de la Sal rose during the summer in conjunction with irrigation, 
85

whereas water levels fell during this season in wells outside the areas of irrigation. They 

attributed this to direct recharge to the Culebra from irrigation operations. This correspondence 

between water levels and irrigation is observed only in the southwestern end of Nash Draw, 

where the Rustler Formation is exposed, the Culebra is near to the surface, and where 

dissolution-related disruption of Rustler bedding allows rapid communication between the 

surface and subsurface units. This model is not applicable to the WIPP site where the Rustler 

Formation is buried beneath insoluble sandstones. 

Brine effluents from potash mill operations have been discharged to the surface for 

decades, and Geohydrology Associates (1978), treating the Culebra, the Rustler/Salado brine 

aquifer, the Santa Rosa Sandstone, and alluvium together as a single aquifer, suggested that as 

much as 40% of the recharge to the groundwaters in Nash Draw comes from the effluent of 

potash mills and oilfield brines, and that this discharge has significantly raised the potentiometric 

levels. However, recent drilling of the SNL-1 drillhole immediately south of a potash tailings 

pile just outside the northeastern arm of Nash Draw, and analysis of the underlying Culebra 

waters, suggests that there is no chemical signature from the tailings in the local groundwater 

(Powers and Richardson, 2004b). 

Geohydrology Associates (1978) noted that the water chemistry from specific springs is 

dissimilar to that of industrial brines, and other studies have suggested that the difference in 

chemistry between the brines in the effluent ponds in Nash Draw and the brines discharging from 

the springs at Malaga Bend indicates little communication between discharge ponds and the local 

aquifers. 

8.3.3 Infiltration of Precipitation 

Geohydrology Associates (1978) suggested that 60% of the water inflow to local aquifers 

in Nash Draw and surrounding areas comes from the 12 inches of precipitation per year, 

infiltrating at about half an inch per year despite rates of potential evapotranspiration which can 

exceed precipitation by an order of magnitude during the summer (Sares, 1984). This infiltration 

rate is consistent with four earlier studies cited by Geohydrology Associates, but it is 

significantly higher than the 0.2-2 mm/yr infiltration rates calculated more recently by Campbell 

et al. (1996) for a much more restricted area on Livingston Ridge. Corbet (1998) and Corbet and 

Knupp (1996) have suggested that some of the lateral variations in geochemical signatures of the 
86

waters in the Culebra can be explained by local, long-term recharge from vertical infiltration. 

Moreover, their models suggest that most precipitation over the WIPP site enters the higherpermeability sandstones of the Dewey Lake and Santa Rosa Formations, and that only a limited 

vertical “leakage” of this water filters down into units of the Rustler Formation. 

Theis et al. (1942) noted a sharp rise in the water levels in wells in the vicinity of Laguna 

Grande de la Sal 14 days after rainfall, suggesting rapid transfer of precipitation into the aquifers 

in that area of Nash Draw. However, influx of water into the more deeply buried Rustler strata 

east of Nash Draw is a different matter. Monitoring of the Dewey Lake water-table aquifer at 

wells H-3d and WQSP-6A at the WIPP site has never shown a water level response to rainfall 

events. The observations of Theis et al. (1942) are probably related to karst flow into sinkholes 

at Nash Draw, whereas the absence of karst at the WIPP site prevents rapid, karst-related waterlevel responses to rainfall in that area. 

8.4 In Situ Flow 

 The directions of flow in the Rustler units at the WIPP site have not been directly 

measured, but rather are inferred from measurements of the potentiometric heads in the different 

units using the assumption that water flows down pressure gradients. Flow directions, and rates, 

can also be inferred from isotopic data and variations in water chemistry. Because these 

parameters are not directly measured, there has been room for argument in how the primary 

parameters that were used to derive flow directions should be interpreted. 

One interpretation is that the water-chemistry data thought to imply directions of flow 

different from those indicated by current potentiometric contours are the result of a reversal of 

flow direction since Pleistocene time due to changes in precipitation and recharge areas. The 

proponents of karst, however, suggest that the data are compatible with rapid present-day flow 

westward away from the WIPP site to nearby discharge areas. More recently, Corbet (1998) has 

suggested that waters with different chemistries may have different recharge areas, and that 

limited amounts of mixing of these waters may be occurring along flow paths. 
87

8.4.1 Directions of Flow from Potentiometric Heads 

Based on water levels measured in wells and corrected for water densities, the overall 

present-day flow is to the south in the Culebra, and westward in the Magenta (Mercer, 1983; 

Johnson, 2005a,b) (Figures 23 and 24). These trends have not changed significantly since the 

heads were measured by Robinson and Lang (1938). Crawley (1988) corroborated the inferred 

Culebra flow directions, and contributed several three-well pressure-difference calculations to 

confirm local flow towards the southeast in the southern part of the WIPP site. 

8.4.2 Isotopes, Residence Time, and Flow Rates 

Chapman (1986) suggested that the stable oxygen isotope composition of Rustler water is 

not different from modern meteoric ground water and that therefore the Rustler is presently being 

recharged through percolation. This would imply that water flows relatively rapidly through the 

Rustler Formation from recharge areas to point(s) of discharge, the rapid flow implying a 

possible subsurface karst system. 

On the other hand, Lambert (1987) and Lambert and Harvey (1987) interpreted the 

isotopic composition of Rustler water samples to indicate that Rustler water was emplaced over 

10,000 years ago, and that therefore waters in the Rustler members have moved slowly if at all 

since recharge during the Pleistocene. 

Campbell et al. (1996) also studied oxygen isotopes, in the local soil profiles rather than 

from the Rustler, and reached a corroborating conclusion that there is the potential for only “a 

small amount of infiltration (.2- to 2 mm/yr) through the desert soil” down to recharge the 

Rustler, and that therefore “water in the Rustler Formation need not have been recharged in the 

past (>10,000 yrs) under different climatic conditions” (page 153). However, they complicated 

their interpretations by stating that, since their data did not support surficial infiltration as a 

mechanism, “If modern recharge is occurring to the Rustler Formation, it must be water which 

has been recharged from surface runoff through karst features or other direct conduits that 

minimize evaporation.” The key word is the “if” that starts the quoted sentence: the Campbell 

study did not prove or disprove whether the Rustler members are actually being recharged at 

present, only that there is minimal potential for recharge. The inference relating to karst is 

speculation, and not based on their data or on subsurface water sampling, and Campbell et al. do 

not require nor state that recharge through karst is occurring at the WIPP site itself. 
88

Siegel et al. (1991) report radiocarbon dates from Culebra waters that indicate ages of at 

least 10,000-16,000 years, supporting Lambert and Harvey’s (1987) isotopic data and inferences 

of slow rates of groundwater movement within the Culebra. Siegel et al. also measured 

hydrogen ratios in gypsum and noted that the ratios are not consistent with the formation of 

gypsum by the hydration of anhydrite by meteoric waters, again supporting a model where 

groundwater does not move quickly through the Rustler Formation. Finally, they compared the 

strontium ratios in gypsum and carbonates in the Rustler, Dewey Lake, and surface rocks, and 

showed that the secondary sulfates and carbonates in the Rustler did not form in a hydrological 

regime connected to the surface. 

These isotopic data and interpretations, except for the interpretations of the same data 

presented by Chapman, support a model of slow groundwater movement through the Rustler 

Formation.

8.4.3 Water Chemistry Domains and Flow Directions 

Several geochemical domains are recognized in the water-bearing members of the Rustler 

Formation. In general, the salinities, densities, and Total Dissolved Solids (TDS) contents 

increase eastward, which suggests to some that the overall flow is in that direction on the 

grounds that waters that have been in an aquifer system longer have had more time to interact 

with the chemistry of the host strata and are therefore more highly mineralized. However, such 

an interpretation runs counter to the measured heads in the Culebra and Magenta (Figures 23 and 

24), which suggest southerly and westerly flow, respectively. 

Different authors have mapped and interpreted the groundwater chemistry domains of the 

Rustler Formation in slightly different ways. Ramey (1985) defined three geochemical zones 

(Figure 27): 

• Zone A from the eastern WIPP site to the east, with NaCl-type water with high 

concentrations of K and Mg; 

• Zone B south of the WIPP site, with CaSO4 water and relatively low TDS; and 

• Zone C over most of the WIPP site and to the north and west, with NaCl-type 

water with low concentrations of K and Mg. 

Chapman (1988) recognized three broadly similar zones, although she differentiated 

Ramey’s Zone A from his Zone C on the basis of Ca concentration (Figure 28). 
89

Figure 27. Geochemistry domains for Rustler formation waters as suggested by Ramey (1985). 

In most of the mapped area the samples were taken from the Culebra interval; in Nash Draw, 

however, the groundwaters are not confined to the Culebra reservoir and some mixing is likely. 
90

Figure 28. Geochemistry domains for Culebra waters as suggested by Chapman (1988) 

(including arrows indicating “idealized groundwater flow paths.”) 

Siegel et al. (1991) split off the western part of Nash Draw in mapping four recognizable 

water-chemistry facies in the Culebra (Figure 29): 

• A: eastern half of WIPP, highly saline, TDS >100,000 mg/L, NaCl type water rich 

in Mg and Ca 

• B: southwest of WIPP and south, relatively fresh water, TDS <10,000mg/L, 

CaSO4 type water 

• C: east half of Nash Draw and east to mid-point of WIPP, NaCl-dominated waters 

of variable compositions, TDS 10,000-80,000 mg/L (increasing eastward). This 

may be a mixing zone between facies A and facies B. 

• D: west half of Nash Draw and westward: contaminated by potash mining effluent
91

Figure 29. Geochemistry domains for Culebra waters as suggested by Siegel et al. (1991). 

N 

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92

In a relatively uniform, confined aquifer, solute concentrations should generally increase 

in the downgradient direction. With such an assumption, the chemistry of the Culebra would 

suggest west to east flow. The present-day potentiometric heads, however, suggest flow in other 

directions. Heads measured in the Magenta suggest a westward potential flow (Figure 24), and 

heads in the Culebra suggest a generally southward potential flow (Figure 23). Moreover, 

eastward flow does not fit with discharge of any of the Rustler water-bearing units at the springs 

at Malaga Bend on the Pecos River to the south. 

 Various ideas have been offered to explain this dilemma. Chapman suggests that the 

southern area of low TDS and Ca-SO4 waters corresponds to an area where salt is not present 

(“complete removal”). Local non-deposition of halite would explain the water chemistry equally 

well, but the basic idea, that formation waters are less saline where there is less interbedded 

formation halite, is plausible. Chapman also suggested that the “major hydrochemical facies 

change from Na-Cl to Ca-SO4” is due to influx of a large quantity of low-TDS water”, and 

suggests recharge through local, unspecified, gypsum caves. 

Beauheim and Holt (1990, page 150) suggest that the water chemistry changes across the 

region are related to concurrent east to west changes in the Rustler lithology, as anhydrite 

changes to gypsum and ultimately gets dissolved westward at Nash Draw. The observation of 

greater mineralization of Rustler Formation waters eastward has been used to support an 

interpretation that flow through the formation, no matter in what direction, is slower in the 

eastern region, i.e., that long residence time has allowed greater rock-water interaction and 

resulted in greater mineralization of the water (e.g., Mercer, 1983). This inference of variable 

flow rates is indirectly supported by the regional differences in the potential for flow, as 

measured by generally lower transmissivities in eastern wells than in western wells. Mercer 

(1983) also inferred slower groundwater movement under the WIPP site, the boundary between 

fast and slow movement being at approximately the western edge of the site. 

 The discrepancy in flow directions inferred from the different data has also been 

suggested to be caused by a Pleistocene flow reversal: Ramey (1985) and Siegel et al. (1991) 

note that modern (potential) flow directions within the Culebra are not consistent with modern 

salinity distributions and that TDS decreases in the implied direction of flow, which is not typical 

of a steady-state system. They explain this by suggesting that the TDS distribution is a fossil one 

that has been overprinted by modern flow (head) vectors (Figure 30). Siegel et al. (1991) report 
93

eastward-increasing uranium isotope ratios suggestive of “recharge from a near-surface 

Pleistocene infiltration zone flowing from WNW”, and suggest that these data imply a change in 

flow direction in the Culebra during the last 12,000-30,000 years. 

Figure 30. Suggested flow reversal in the Culebra from Pleistocene time (broad arrow outlines) 

to the present (smaller black arrows) (From Siegel et al., 1991, their Figure 1-34/page 1-96). 

N 

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- ·- Facies Border 

o, o , • Well Location 

dho • • olho. '''"" Nash Draw 
94

 Corbet (1998) suggests that the different chemistry domains observed in the Culebra, as 

well as the apparent discrepancy between flow directions inferred from these domains and the 

flow directions inferred from the potentiometric heads, do not have to be explained by lateral, 

strata-bound migration of water through the formation. He suggests that the geochemistry 

domains can best be explained by considering that all members of the Rustler Formation are part 

of a single integrated groundwater system that is connected through vertical “leakage.” More 

leakage occurs in areas where halite is absent from the Rustler, such as south and west of the 

WIPP site, than were halite is abundant in the Rustler, such as east of the WIPP site. Thus the 

chemistry domains are related to different amounts of vertical leakage through varying 

geochemical/host-rock environments rather than to lateral flow and varying residence times of 

the waters in the formation. This interpretation is consistent with the observed heads. 

 Regardless, the high salinities and mineralization in the Culebra at the WIPP site are not 

compatible with the rapid groundwater flow rates typical of karst conduits as suggested by Hill 

(1999). Hill also suggests that the variable chemistry of the Culebra waters described here 

suggests karst development, and this is addressed below. 

8.5 Discharge 

8.5.1 Malaga Bend Springs 

There are conflicting interpretations of the few data available that indicate where the 

Rustler members discharge. One’s perception of whether or not defining specific discharge 

locations is a problem depends on whether or not one believes the Rustler members are presently 

being recharged to a significant degree and if so, whether this recharge occurs at WIPP: if the 

Rustler is accepting water and passing it rapidly through a high-volume, high-conductivity karst 

type of groundwater system, then it needs discharge points where significant amounts of water 

can be eliminated from the system as fast as it is recharged. As pointed out by Lambert (1983), 

dissolution of a geologic system of evaporites cannot take place if no outlets for the dissolution 

brines exist. On the other hand, few discharge points for minor amounts of water would be

consistent with a Rustler water system that is largely relict and relatively immobile under the 

WIPP site. To consider the system from the other end, if the identified discharge points are 
95

related only to groundwater flow in the karsted terrain at Nash Draw, then they are largely 

irrelevant to hydrology at the WIPP site. 

To date, outlets for the Rustler members have not been definitively identified. As early 

as 1938, Robinson and Lang suggested that the Rustler waters from the Nash Draw area 

discharge in springs at Malaga Bend on the Pecos River (Figure 31), citing an increase in the 

chloride of the river water at this location as evidence. Morgan (1942) estimated that 350 tons of 

salt a day and 200 gallons per minute were being discharged via these springs. However, Theis 

et al. (1942) suggested that the salt water discharge at Malaga Bend comes from the brine aquifer 

at the Salado/Rustler contact, and that very little of the salt contribution to Malaga Bend is from 

the Culebra (the Magenta Member had not yet been recognized as a different layer within the 

Rustler Formation). 

Regardless of which layer the water in the springs comes from, Geohydrology Associates 

(1978), who lumped the Culebra, Magenta, brine aquifer, and alluvium as a single aquifer for 

their calculations, calculated that aquifer outflow at Malaga Bend Springs is only about one 

percent of the total of rainwater precipitated in the potential catchment area. The remaining 99% 

is lost to evapotranspiration. 
96

Figure 31. Map of the Malaga Bend Springs (from Chaturvedi and Channell, 1985, their Figure 

16/page 44). 

8.5.2 Other Discharge Points 

Lakes are commonly discharge points for groundwater, and Robinson and Lang (1938) 

noted that potentiometric head measurements suggest that Rustler ground waters flow towards 

Laguna Grande de la Sal, making it a possible discharge point. However, they also noted that the 

chemistry of the lake water is different from that of the local groundwater, and that it is 

improbable that the lake brine re-enters the Rustler Formation from the bottom of the lake. 

Mercer (1983) suggested that Rustler discharge from the Nash Draw catchment might 

include Surprise Spring at the edge of, or sometimes submerged below, Laguna Grande de la Sal. 

Geohydrology Associates (1978) believed that two-thirds of the topographic hollows, including 

local lakes in their study area (centered on Nash Draw) are likely to be sites of groundwater 

discharge to the surface, as well as, or perhaps instead of, being sinkholes. Hill (2003) cites 

Snow (2002) as indicating that there may be a point-source karst-type discharge into Laguna 

Pequena, and Sares (1984) for other karst-type point source discharge locations further south in 

the Pecos River valley. 

These discharge points are plausibly, even probably, sourced in the Rustler Formation, 

but no definitive data have been collected to indicate what parts of the Rustler are contributing to 

them. Karst and high hydraulic conductivities in the Nash Draw area contrast with the low 

hydraulic conductivity Rustler Formation characteristics measured at the WIPP site, and the 

simplest interpretation is that the discharged waters at Malaga Springs are derived primarily from 

Nash Draw. Although Hill (1999) suggests that Surprise Springs at the edge of Laguna Grande 

de la Sal within Nash Draw is a possible discharge point for the Nash Draw watershed including 

the WIPP site, the connection to WIPP is speculation. 

8.5.3 Gypsite “Spring” Deposits 

Bachman (1985) suggested that local beds of gypsite (re-sedimented gypsum sand) near 

WIPP-25 in the eastern part of Nash Draw are evidence that springs drained the upper Rustler 

Formation from below the WIPP site, discharging at the base of the nearby Livingston Ridge 
97

escarpment. Hill (1999, p. 53) took this piece of data and extended it to infer that gypsite springs 

indicate karst. 

Whether or not gypsite springs indicate karst, on closer examination, the gypsite deposits 

reveal few definitive features that are diagnostic of their origin. Although they are associated 

with snail fossils (suggestive of damp conditions), and vertebrate bones (of unknown 

significance), they do not display the travertine-type bedding commonly formed around springs 

that produce highly mineralized water. Gypsite sand is currently forming in Nash Draw where 

the primary gypsum/anhydrite beds are exposed to weathering and erosion (Figure 32), but the 

local active springs are not forming and depositing gypsite. 

Some of the gypsite deposits in the area display eolian crossbedding (Figure 33), 

suggesting that gypsite originated as weathered sands, reworked by winds and deposited as 

dunes. The gypsite deposits near WIPP-25 probably do not record the locations of spring 

discharge points for the Rustler, and as such are poor evidence for karst. 

 
98

Figure 32. Gypsite derived from decomposing gypsum beds under present-day weathering 

conditions, Laguna Quatro area. 

Figure 33. Large-scale, steep-angle crossbedding, typical of eolian sand dunes, in gypsite 

deposits in a road cut along route NM 128. 

8.6 Assessment of Recharge and Discharge Data 

 The relatively small volumes of water and brine that are being discharged from the few 

known and potential Rustler discharge sites are consistent with the volumes of water that would 

be remnant from local precipitation after evapotranspiration. This supports the hypothesis that 

water gets from the surface into and through the Rustler, and to the discharge points, but does not 

specify a recharge mechanism. Recharge mechanisms might include localized sink holes or 

more widespread percolation. However, what little definitive data exist suggest that recharge, 

flow, and discharge within the Rustler Formation are relatively rapid within the confines of Nash 

Draw, but that the same aquifer horizons are entirely different systems with different 
99

characteristics to the east, under the WIPP site. There, a higher degree of mineralization of the 

formation waters, lower measured hydraulic conductivities, and isotopic studies support a system 

of slow groundwater flow. The potentiometric head data suggest that flow in the Rustler 

members is slow, but that it would flow to the south (Culebra) and west (Magenta). The data 

suggest that if a karst conduit system exists in the Rustler Formation, it is confined to the Nash 

Draw area. 
100

9.0 SIGNIFICANCE OF LOCALLY EQUIVALENT CULEBRA AND MAGENTA 

HEADS 

9.1 Introduction 

 The measured potentiometric heads of the Culebra and Magenta vary regionally, sloping 

irregularly but generally southward (Culebra, Figure 23) or westward (Magenta, Figure 24). 

Over most of the area, they are at different levels, showing that the members are individually 

confined and hydraulically unconnected to each other. The difference between the Culebra and 

Magenta heads diminishes from as much as 155 ft at the center of the WIPP site to a few feet in 

the WIPP-25 and WIPP-27 holes in Nash Draw. 

Locally, in the vicinity of WIPP-25 in Nash Draw and west of the WIPP site, the 

measured heads of the waters in the two members are nearly equal. Hill (1999), apparently 

drawing on Snow’s (1998) paper, suggests that the hydraulic heads are also equal in the vicinity 

of H-6 and WIPP-13, inferring that this indicates hydraulic communication between the two 

units (“...that the integrity of the Magenta and Culebra as distinct water-bearing zones has been 

breached...” : Hill, 1999, page 56). Hill then suggests that this implies the development of karst 

passageways at depth. 

Chaturvedi and Channell (1985) have also suggested that there is vertical, karst-related, 

cross-stratigraphic hydraulic connection between the Magenta and Culebra west of the WIPP 

site, based on a gradual, westward merging of the potentiometric heads from the two units. 

9.2 The Data 

The uncertainty ranges on Magenta and Culebra heads do in fact overlap at H-6 and 

WIPP-25. However, this by itself does not prove that hydraulic connectivity exists between the 

two members. Implying that it does is an example of using isolated data points out of context. 

The plane of the Magenta potentiometric head slopes down to the west (Figure 24) and therefore 

must cross the southward-sloping Culebra regional trend (Figure 23) somewhere. The crossover 

line is not a physical intersection; it is a line on a map where the two potentiometric surfaces 

would intersect. It trends north-south and occurs several miles west of the WIPP site, with a 
101

local bend to the east caused by an embayment in the regional Magenta potentiometric surface 

near the northwest corner of the WIPP site (Figure 24). The crossover line follows the trend of 

Livingston Ridge northwest of the WIPP site and includes WIPP-25, extends from there almost 

as far east as H-6, then bends northwestward under Nash Draw. 

At WIPP-25, drilled in an area of recognized karst and collapse, where both hydraulic 

heads and water chemistries from the Culebra and Magenta are similar (Lambert and Robinson, 

1984) and where hydraulic connectivity between the members might in fact be expected, the 

absence of any response in the Magenta while the Culebra was pumped recently (Figure 21) 

shows that the degree of actual hydraulic connection is at best low. 

At H-6, Mercer (1983, page 61) notes significant differences in sodium chloride 

concentrations between the Magenta and Culebra in the adjacent test wells H-6a and H-6b: 

Culebra water samples contain 16 times as much dissolved sodium as do samples from the 

Magenta (18,000 vs. 1,100 mg/L), and over 23 times as much chloride (28,000 vs. 1,200 mg/L) 

(Mercer, 1983; Randall et al., 1988). In addition, pumping tests provide definitive evidence for 

the absence of a connection between the two members at H-6 (see Figures 21 and 22). During 

the WIPP-13 multipad pumping test of the Culebra, approximately 18 ft of drawdown was 

observed in H-6a and H-6b, both completed in the Culebra at that time, but no response was 

observed in H-6c, completed in the Magenta (Beauheim, 1987c). Lack of connection between 

Culebra and Magenta has also been repeatedly demonstrated during the WQSP water quality 

pumping of both the Culebra and Magenta on the H-6 hydropad. 

Thus, the lack of responses in other Rustler members when specific members are pumped 

at WIPP-25 and H-6 shows that the members are not well connected and that karst conduits are 

not present. 

9.3 Misuses and Mis-citation of Data 

Some of the arguments for karst based on hydraulic equivalence of heads in various wells 

have been muddled by careless use of the data. For example, Snow (1998, 2002), repeated by 

Hill (1999), cites data from wells H-6, WIPP-13, WIPP-33, and WIPP-25 as evidence of vertical 

hydraulic connections between the Magenta and Culebra across the Tamarisk anhydrite. 

However, such data were never obtained from two of these wells: the water levels in the 
102

Magenta have never been monitored at WIPP-13, and water levels have never been monitored in 

either the Culebra or Magenta at WIPP-33. Thus, there is no factual basis whatsoever for 

Snow’s assertions regarding WIPP-13 and WIPP-33; the data from the other two wells have been 

addressed above. 

Some of Snow’s conceptual modeling is physically impossible and/or internally 

inconsistent. For example, if the hypothetical karst channels are located above the present water 

table as postulated, their effects will not be apparent, and their existence cannot be proven by 

pumping tests (which can only measure the flow in water-saturated zones) as asserted by Snow. 

The assertion that the hypothetical karst channels are presently dry also requires that they must 

be located above the present water table, which is in the siliciclastic Dewey Lake beds. This is 

inconsistent with the location of the strata that would be prone to karst dissolution, and with the 

assertions that karsting is located in the Rustler Formation which is below the water table. 

9.4 Assessment of Equivalent Heads in the Two Rustler Members 

 The intersection of the potentiometric heads of the two Rustler members is a localized 

phenomenon, the inevitable intersection of two non-parallel surfaces, that has no regional 

significance. Water chemistry and the lack of interference during pumping tests both support 

hydraulic isolation of the Culebra from the Magenta, and argue strongly against the development 

of a subsurface karst system within the Rustler Formation at the WIPP site. 
103

10.0 SPATIAL VARIABILITY IN THE CHEMISTRY OF CULEBRA FORMATION 

WATERS 

10.1 Introduction 

Hill (1999, p. 64) suggests that spatial and/or temporal changes in water chemistry and 

salinity are characteristic of groundwater in karst systems, due to local influxes of fresh water at 

sink holes that would mix erratically at depth with long-term residence matrix water already in 

the system. She then cites examples of spatial variability in the chemistry of the Culebra 

formation waters and argues that they indicate the development of a subsurface karst system at 

and near the WIPP site. Hill does not correlate the observed geochemical variations with 

specific possible point recharge locations, but rather uses only the generalized existence of 

variable groundwater geochemistry in the Rustler Formation at the WIPP site as evidence for 

karst. She does not analyze the characteristics of that variation in order to support the karst 

theory. 

10.2 The Data 

The variability in water chemistry of the Culebra can be defined in different ways, and 

the rate at which it changes laterally is an important characteristic for this discussion. Different 

divisions of the subsurface water chemistry in the Culebra have been previously illustrated in 

Figures 27 through 29. The three schemes of mapping variations in the water chemistry in the 

Culebra are basically compatible. The lines drawn on the maps by the authors to divide the 

geochemical domains are somewhat arbitrary since the chemical composition of the waters 

changes gradually, explaining variations in the mapped boundaries. 

10.3 Scale of Variability 

None of the water-chemistry data support the existence of localized pockets of chemical 

variability associated with large influxes of fresh water through karst sinkholes. The water 

chemistry varies gradually and on a broad scale (kilometers). No evidence is seen of significant 
104

water quality changes between wells tens or a few hundred meters apart, nor are anomalous 

“pockets” of relatively fresh water found that are surrounded by wells containing more saline 

water. 

Hill cites Chapman (1988) as mapping regions of low salinity and facies changes from 

Na-Cl to Ca-SO4 over the region of the H-1, H-2, and H-3 drillholes, but this is a gradual, not an 

abrupt change. Chapman draws a dotted line at about this location delineating two of the water 

facies domains (Figure 28); Ramey (1985) draws the boundary between his similar zone A and 

zone B geochemical water facies a mile or more to the east (Figure 27). The positions of the 

lines on the map are subjective delineations of broad geochemical domains; they are not 

indicators of abrupt changes in water chemistry. 

In any case, the fact that water-chemistry varies does not necessarily prove the presence 

of karst at depth. Rather, the characteristics of that variation should be analyzed and compared 

to measured chemistry variations in known karst systems or to expected variation given modeled 

rates of fluid flux and the potential reactivity between water and the host rock. 

10.4 Possible Causes for Water Chemistry Variability 

Chapman (1988) observed linear correlations between TDS and chloride content and 

between chloride and sodium in Culebra waters, and took these relationships to indicate that the 

increase in salinity eastward in the Culebra is due to dissolution of halite. She also observed that 

a parallel increase in potassium and magnesium is “probably due to the dissolution of evaporite 

minerals co-existing with the halite.” From these, she inferred that the “major hydrochemical 

facies change from Na-Cl to Ca-SO4” is due to the influx of a large quantity of low-TDS water, 

suggesting recharge through gypsum caves. 

While the basic observations may be valid, they do not exclusively imply that therefore 

halite has been dissolved from the western parts of the study area, or that one can therefore 

assume that this implies the development of karst. Siegel et al. (1991) also suggested that “A 

likely explanation for the less saline waters south of the WIPP site is that at the time of influx of 

the present generation of Culebra ground water from the WNW, Rustler halite was absent 

adjacent to the Culebra in that area, and did not provide a source of NaCl.” 
105

In the absence of sedimentological data, the data showing a change from sodium-chloride 

to calcium-sulfate waters may be explained in several ways. Two of them are: 1) the removal of 

halite in the calcium-sulfate area, or 2) non-deposition of halite. The mere absence of halite does 

not dictate a choice between these two options. However, making the choice has important 

implications: if the halite was there and has been removed, karst features could have been 

developed in the overlying strata during the dissolution phase. If the halite was never there, as 

argued above in this report, then the strata were not subjected to halite dissolution and karst is 

unlikely to have developed. Calcium-sulfate waters could have developed where salt was never 

present and where low-mobility waters took on the general character of the host rock during long 

residence times. 

10.5 Assessment of the Significance of TDS Variability in the Culebra 

Hill (1999, page 64) suggests that salinity variations are characteristic of karst, and uses 

the bald, broad fact of salinity variations across the region of the WIPP site, not the specific 

characteristics of that variation, as evidence for the probable subsurface development of 

intrastratal karst. Hill uses generalized concepts and theory to suggest that specific 

interpretations have been proven, an inversion of the more widely accepted scientific process and 

logic which use specific data to prove or to construct broader-scale interpretations. 

The Culebra water chemistry data from drillholes at and surrounding the WIPP site have 

not been used rigorously to support an interpretation of karsted Rustler Formation in this area. 

There is variability in the geochemistry of Rustler formation waters, but the scale of that 

variability is not compatible with the scale or type of variability that would be expected in 

adjacent holes that sampled both fresh, karst-introduced meteoric waters and saline, longresidence waters. Hill’s one example of local extreme variability turns out to be suspect, 

possibly contaminated data. The variability of formation waters found within the confines of 

Nash Draw is of a different, more highly variable scale, but both hydrologically and 

geologically, this is a significantly different area. 
106

11.0 POTENTIAL FOR KARST AT WIPP-13 

11.1 Introduction 

 The cores from several holes (WIPP-13, WIPP-14, and H-3) have been cited by Hill 

(1999, 2003) as showing evidence for karsted strata, and well tests at these sites have been 

suggested to be anomalous, the anomalies taken to be support for possible karst. These examples 

are examined below. 

The WIPP-13 drillhole was sited to investigate the possibility that a resistivity anomaly 

reported by Elliott Geophysical (1977) was caused by a geological feature similar to the breccia 

pipes known elsewhere in the basin (Sandia National Laboratories and the U.S. Geological 

Survey, 1979). A subsequent gravity survey (Barrows et al., 1983) indicated that the resistivity 

anomaly is located within the area of a broader gravity anomaly, further piquing interest in this 

site. However, the drillhole penetrated a normal stratigraphic section with only localized, 

apparent brecciation of a thin sulfate bed within the Tamarisk mudstone unit. 

Nevertheless, Hill (1999) suggests that the disrupted bedding in cores from this hole, and 

the pumping tests at this site that produced anomalous (to her) responses, indicate karst. Hill 

cites the mere presence of well-test variations, without investigating or analyzing their 

characteristics, to support an interpretation of karst in the Rustler Formation at this site, and she 

does not describe stratigraphic relationships or sedimentological characteristics from the core 

that would allow distinctions to be made between post-depositional, solution-related disruption 

and syndepositional disruption of bedding. 

11.2 Drawdowns 

 As noted above, Hill (1999, p. 59-61) suggests that there were significant variations 

during a pumping test at WIPP-13. Beauheim (1987c) did report a no-flow boundary, indicating 

a decrease in Culebra transmissivity somewhere “fairly close to WIPP-13,” but a no-flow 

boundary indicates a barrier to flow, not an open, karst-type pathway. Such boundaries can be 

caused by sealed faults and sedimentary limits to a reservoir, or by other types of lateral 

decreases in permeability. 
107

Beauheim also reported several ambiguous responses to the WIPP-13 pumping test in 

observation well ERDA-9, a mile and a half to the southeast. These included: 1) drawdown was 

several hundred hours “late” in ERDA-9, suggesting that no high-flow pathway connects the two 

wells and not suggestive of a rapid-response karst network, although 2) recovery from the 

drawdown was rapid, possibly indicating rapid recharge from a separate, high-flow source, and 

3) “drawdown in the middle of the recovery period (1700 hrs) appeared to be a response to a

separate event.” The Culebra fluids in the nearby exhaust shaft behaved similarly to those in 

ERDA-9, “as if a withdrawal of fluid from the Culebra at some location temporarily caused 

drawdown at the exhaust shaft”. 

The fact that there are variations indicates anomalies, but of itself does not specify what 

they are. It is the next level of assessment, i.e., the characteristics of those variations that should 

be considered before drawing conclusions. It is unclear what type of pressure response to 

pumping tests Hill and/or Snow would expect from their hypothetical karst channels. The 

response would be entirely different for fluid-filled or air-filled conduits below or above the 

water table respectively and neither Hill nor Snow are consistent in defining the location of the 

proposed conduits relative the water table. The observed responses are not consistent with the 

presence of fluid-filled, large-scale void spaces and conduits, which would have dampening 

effects on the magnitude of pressure responses due to the larger reservoir volumes involved. 

11.3 Breccia and Mixing in the Core 

Hill (1999, page 38) notes the presence of “collapse breccia and mixing of stratigraphic 

units” in core from the WIPP-13 drillhole, arguing that these indicate the presence of karst, if not 

in the wellbore itself, at least in the nearby strata. Hill (1999, p. 47) cites Holt and Powers 

(1988) as the reference for this core description, quoting (page 5-13) “The strata [in the A2 

anhydrite of the Tamarisk Member] are commonly wavy, may be locally contorted, or 

discontinuous, and in some extreme cases, can exhibit dipping strata (up to 80o in WIPP-13).” 

Hill does not indicate the extent of brecciation or the size of the breccia clasts, i.e., how 

extensive, and therefore how significant, this breccia might be, and infers more significance to 

this than warranted. 
108

Holt and Powers (1988, page 8-16) describe this occurrence in WIPP-13, indicating that 

“Collapse, upward stoping, and mixing of clasts derived from various stratigraphic horizons 

occur in core from WIPP-13 where the deformation is not clearly attributable to Salado 

dissolution. The lowest deformed unit is A-2 [anhydrite 2] and... the source of at least part of 

the deformation is within or below A-2...” Hill suggests that this is “exactly” (just above the 

Culebra) where one would expect karst to form, and “exactly” what she would expect it to look 

like. This is correct in the sense that it is also exactly where localized, bed-boundary dissolution 

related merely to the presence of water in the Culebra has been observed; however, it does not 

imply a widespread karst system. This dissolution horizon is localized adjacent to the Culebra 

aquifer where it is not unexpected. It is present in other cores, and dissolution has not developed 

from this into a widespread karst system. The undeformed beds of the overlying strata show that 

“upward stoping” is of limited vertical/stratigraphic extent. 

Holt and Powers (1988, page 8-16) describe a second deformation horizon higher in the 

section in the WIPP-13 core as “extreme deformation” of the Mudstone-3/ Anhydrite-3 contact 

(in the Tamarisk Member, between the Magenta and Culebra Members). Examination of the 

core shows this deformation to be a rearrangement of clasts, and of fracturing and movement of 

blocks at the base of the overlying anhydrite and within Mudstone-3/Halite-3 itself, but with no 

indication for the involvement of other stratigraphic zones. Exposures of this unit in the air 

intake shaft showed definitive evidence (truncated breccias overlain by laminated anhydrite) that 

the disruption of this unit is syndepositional. 

11.4 Summary 

The breccias found in the WIPP-13 could be interpreted in several different ways. The 

lower interval is most easily explained as a limited zone of dissolution adjacent to the waterbearing Culebra, whereas the upper interval is probably of syndepositional origin. Some of the 

well-test data are ambiguous, but they are not suggestive of karst-type flow of the Rustler waters. 

The large-scale exposures of sedimentary and syn-sedimentary features, and the definitive data 

on the stratigraphic succession offered by the shaft exposures show that wide-spread karst-type 

dissolution is not present in the Rustler Formation at the WIPP site. 
109

12.0 POTENTIAL FOR KARST AT WIPP-14 

12.1 Introduction 

The WIPP-14 drillhole was purposefully sited to investigate the possibility that a circular 

surface topographic depression, about 700 ft in diameter, 10 ft deep, and located above the axis 

of a much larger gravity anomaly, is large enough to have collected sufficient water to create a 

major sinkhole. Controversy exists over the nature, or at least of the interpretation, of the rocks 

interrogated by this drillhole. Hill (1999) suggests that the conversion of anhydrite to gypsum in 

certain beds, and a calculated mass deficiency related to that conversion, indicate karst in the 

subsurface even though the hole did not penetrate or recover evidence for karst. Some of the 

data have been misinterpreted or mis-used by the karst proponents. 

12.2 The Data 

12.2.1 Patterns 

Phillips (1987, page 209) suggests that the WIPP-14 depression is one of “A chain of ten 

thickly vegetated topographic depressions...” that he suggests “...are probably related to deepseated dissolution of the halite and gypsum in the Rustler Formation”, and that five shallow, 

ephemeral “watercourses” drain into this zone. The watercourses supposedly related to this 

chain are not mapped by Phillips, and no depressions other than at the WIPP-14 site, no trends of 

vegetation, and no watercourses, were apparent during a low-level aerial reconnaissance over 

this area in March 2005. 

The maps presented by Phillips in support of a correlation between the gravity anomaly 

and irregular patterns of both “calcareous dissolution residues” and “structural depressions in the 

[Mescalero] caliche” surface are self-fulfilling. Phillips’ maps (his Figures 69 and 70, page 207) 

show only the patterns of residues and depressions that are within and near the general outline of 

the gravity contours. Demonstration of an absence of these residues and depressions in areas 

outside of the gravity contours would be plausible evidence for a correlation, but many of his 

patterns overlap the edges of, and extend beyond, the gravity zone, suggesting that the patterns 
110

are not limited to the depressions. No evidence is presented to demonstrate that the residues and 

depressions are exclusive to the area of the anomaly. 

12.2.2 Normal Lithology 

Most of the units above the Rustler were cored in WIPP-14, but only the top and bottom 

of the Rustler Formation itself were cored, as intended (see Appendix B, page 1; Sandia National 

Laboratories and D’Appolonia Consulting Engineers, 1982). The lithology penetrated by the rest 

of the hole was reconstructed from cuttings and the geophysical logs. The core and logs from the 

WIPP-14 drillhole document a normal stratigraphic section at this location, i.e., the stratigraphic 

tops have not been displaced relative to their expected depths projected from nearby control 

points, and bedding is in a normal, flat-lying attitude (Sandia National Laboratories and 

D’Appolonia Consulting Engineers, 1982; Bachman, 1985). The daily drilling reports and the

geologist’s lithologic log record no unusual lost-circulation or fluid-entry zones, and corerecovery percentages were consistently high. The geophysical logs run in the hole also indicate 

normal lithologies, normal depths, and no anomalous hole diameters. 

12.2.3 Gypsum 

 Hill (1999, page 38) suggests that the WIPP-14 borehole “did not intersect karst, but it 

did intersect 9.5 ft of gypsum and 10 ft of gypsiferous anhydrite in the Forty-niner Member 

directly overlying the Magenta dolomite”, and that this is the same interval of the bit drops 

encountered when drilling WIPP-33, “where one should expect to find karst.” The lithologic log 

for this hole (Sandia National Laboratories and D’Appolonia Consulting Engineers, 1982, Table 

3) shows that gypsum and gypsiferous anhydrite were indeed encountered above both the 

Magenta and Culebra, for a few tens of feet before reverting to thick anhydrites. The presence of 

gypsum in these intervals is not unexpected since the Magenta and Culebra are water-bearing, 

and hydrated anhydrite in these positions is normal. Thus the presence of gypsum is not a strong 

argument for the presence of karst in or near this drillhole. Gypsum occurs in varying amounts 

in most of the Rustler sulfate beds across the WIPP site, so the presence of gypsum is not a good 

indicator of karst. 
111

12.2.4 Mass Deficiency 

 Hill (1999, page 38) notes that “Barrows et al. (1983) interpreted the mass deficiency 

(negative gravity anomaly) at WIPP-14 to be due to density variations caused by the hydration of 

anhydrite to gypsum in the Rustler Formation.” Some layers of hydrated gypsum were 

penetrated in this hole, but without concurrent removal of some of the strata, for which there is 

no evidence, hydration would add mass to the system, resulting in increased thickness of the 

beds as well, and which is not observed. 

Barrows et al. (1983, page 57 and their Figure 3.2.1-2) suggested that because the overall 

thickness of the Rustler Formation does not change between drillholes WIPP-34 and WIPP-14 

even though some of the member units thicken and thin, the presumed dissolution of strata in 

WIPP-14 could have been compensated by a volume increase associated with the hydration of 

anhydrite to gypsum. 

This idea was not thoroughly thought through: the mere fact of uniform thickness was 

offered as sufficient evidence, without exploring the ramifications. No calculations were 

presented to show whether the volumes of anhydrite in WIPP-34 are sufficient, when expanded 

by 38% as gypsum forms, to maintain formation thickness in WIPP-14, or that the thicknesses of 

the gypsum beds in the WIPP-14 hole would be equivalent to the anhydrite beds that could have 

been hydrated in WIPP-34. No notice was taken of the fact that whereas the Tamarisk Member 

is indeed thinner in WIPP-14, the underlying Los Medaños Member is thicker in WIPP-14, and 

that therefore the thinning of the Tamarisk could be related merely to diminished sedimentation 

accommodation space during deposition (i.e., a formation can only be as thick as the depth of the 

hole in which it is deposited). 

Barrows et al. (1983) dismissed lateral facies changes as the possible cause for thickening 

and thinning of the evaporite facies of the Rustler Formation because the related and less soluble 

Magenta and Culebra are uniformly thick and “remarkably persistent” across the area, but this is 

specious geological reasoning. The dolomite layers were deposited in marine environments that 

are not sensitive to the subtle topography of the depositional surface the way shallow evaporitic 

salt pans are, and the Culebra and Magenta Members of the Rustler Formation can not be used as 

standards for the original lateral continuity of all facies. 

Barrows et al. (1983 p. 56/Fig. 3.1-3) were also constrained by the gravity survey to 

model a shallow density change at WIPP-14. Nevertheless, they inferred from log data 
112

(comparing the sonic log from WIPP-14 to the “normal” sonic log from WIPP-34) that there 

should be mass deficiencies in WIPP-14 in the middle of the Dewey Lake Formation, at depths 

of 350-450 ft, and in the Forty-niner Member of the Rustler Formation at depths of 650-700 ft. 

The upper interval was continuously cored, the lower partially cored: no evidence of missing 

material was found in either cores or in the subsequently run geophysical logs. 

The apparent mass deficiency calculated by Barrows et al. for the elongate gravity 

anomaly near the WIPP-14 drillhole can be accounted for by what appears to be a thick interval 

of the low-density Gatuña Formation in the core at the top of the WIPP-14 hole. This would be a 

tributary to the deep Gatuña drainage channel mapped by Bachman north of the WIPP site (see 

Figure 21). Similar thick Gatuña deposits have been encountered on trend with the paleo-valley 

during recent drilling at SNL-3 (Powers and Richardson, 2004a). 

12.3 Misuse of Data 

12.3.1 “Mud” 

Five cuttings samples in an interval 81.4 ft thick at the top of the Los Medaños Member 

were recorded in the well records as consisting “mud, dark-reddish-brown (10R 3⁄4)” in the 

WIPP-14 drillhole (Sandia National Laboratories and D’Appolonia Consulting Engineers, 1982, 

Table 3, page 31). Three of the five samples also contained anhydrite, gypsum, or siltstone 

fragments. This record was interpreted as a mud-filled cavern by Phillips (1987), even though 

the geophysical logs for this interval show an entirely normal signature, including the 10-ft-thick, 

A-1 anhydrite bed, and a complete stratigraphic sequence that is identical to that found in 

drillholes nearby. 

 The designation “10R 3⁄4” refers to a specific reddish-brown color on the Munsell 

geologic color chart. It is a common color for the Rustler mudstones and shales (see other 

logged “mudstones” from this hole), and it is easily distinguished from grayish-brown drilling 

mud. It is most likely that the mudlogger did an unacceptable job of logging the cuttings, and 

omitted the “-stone” in recording them. No lost returns were noted during drilling, and the 

drilling parameters, i.e., weight on bit (12,000 lb), pumping pressure (400 psi), and bit rotation 

speed (100 RPM), were all normal while drilling through this “muddy” interval. There is no 

support for the alleged presence of an eight-ft diameter cave in the subsurface at WIPP-14. 
113

12.3.2 “No Core” 

The graphic image of the lithologic log for the WIPP-14 drillhole (Sandia National

Laboratories and D’Appolonia Consulting Engineers, 1982, their Figure 5) labels an uncored 

240-ft interval with the term “No Core”. This notation was suggested to be evidence of 

cavernous zones by Snow (1998) based presumably on an interpretation that “No Core” meant 

that no core was recovered. The interval might have been more clearly labeled as “Not Cored,” 

since, as indicated in the text, no core was cut in this interval. The WIPP-14 hole was not cored 

continuously, and the zones that the proponents of karst have suggested were zones of lost core 

are actually intervals that were drilled by conventional rotary drilling, as planned (Sandia 

National Laboratories and D’Appolonia Consulting Engineers, 1982). The consecutive core 

numbers (#99 above and #100 below the uncored interval) indicate the logistical rather than 

geological nature of this section. 

12.3.3 Fractures 

Some data from the WIPP-14 hole have been presented with invalid interpretations, for 

example: “Carbonate-filled fractures in the Santa Rosa sandstone beneath WIPP-14 are direct 

evidence of rainwater infiltration” (Phillips, 1987, page 25). Carbonate filling in fractures can be 

precipitated from carbonate-rich waters at any depth, and in fact calcite (calcium carbonate) is 

the most common type of fracture-filling material in geologic strata. Both fractures and 

carbonate fill have multiple possible origins (e.g., Lorenz et al., 1991). This is an example of the 

common practice of presenting bald data as tenuous proof of a concept, without an investigation 

or analysis of the precise meaning of the data being presented. 

12.4 Assessment of Karst at WIPP-14 

 There is no evidence for karst development in the Rustler Formation in the WIPP-14 

drillhole. Proponents of karst at this location have misinterpreted annotations in the lithologic 

log and have ignored critical complementary evidence such as the geophysical logs. The 

stratigraphic section penetrated by the drillhole has not been disrupted or displaced by karstrelated dissolution features. The hydration of anhydrite beds to gypsum is not extensive, and the 
114

gypsum beds are found in positions that are consistent with normal hydration adjacent to the 

Culebra and Magenta water-bearing units. The ambiguous data that have been suggested as 

evidence of karst do not come from the same intervals of the hole and thus do not support a 

cross-referenced, integrated concept of karst development in this drillhole. 
115

13.0 POTENTIAL FOR KARST AT H-3 

Hill (1999, page 38), described the H-3 and WIPP-13 drillholes together, claiming that 

the presence of “collapse breccia and mixing of stratigraphic units” in these two drillholes 

indicated karst development in the Rustler Formation. As noted above, the brecciation of strata 

in these holes can be readily attributed to local dissolution adjacent to the Magenta and Culebra, 

and to synsedimentary disruption of the strata. Beauheim and Holt (1990, p. 159; 161) suggest 

that “Features attributable to dissolution of halite and attendant collapse are found within the 

interval M-3/H-3” in this interval correspond to a highly transmissive zone in the Culebra in the 

southern part of the WIPP site. 
116

14.0 SUMMARY 

 Analysis of the primary data suggests that the overwhelming majority of data support an 

interpretation of fractured but unkarsted strata in the Rustler Formation at and near the WIPP 

site. There are a few data anomalies of ambiguous significance, and some evidence for local 

dissolution at the Magenta horizon in the WIPP-33 drillhole, but extrapolation of the known 

karst features in Nash Draw eastward to the WIPP site, where conditions are and have been 

significantly different for half a million years, is unwarranted. 

 Examination of the early geologic studies indicates that although they were valid studies 

by competent geologists, the state of the science at the time was such that the early conclusions 

reached by these studies were incomplete. This planted the seeds for future misinterpretation. 

Interpretations of “insoluble residues” in the cores were based on undeveloped theory, faulty 

analogy, and severely limited exposures. These early interpretations, however, now constitute an 

inheritance that interferes with a valid interpretation of these strata in light of more detailed and 

accurate knowledge of sedimentary environments developed during the last few decades. More 

recent, better exposures of these strata have documented the presence of primary sedimentary 

structures, proving that they are primary deposits that have not been subjected to post-burial 

dissolution. Most of the observed disruption of bedding can be related to syndepositional 

desiccation and cracking, and to limited dissolution along bedding planes during the minor 

flooding events which initiated each cycle of deposition. 

 Topographic depressions near the WIPP site that have been cited as being the probable 

locations of sinkholes are few, and the data that have been cited to interpret these depressions as 

sinkholes have been taken out of context and have other, more scientifically valid and better 

supported interpretations. The characteristics of these few supposed sinkholes are not similar to 

the characteristics of unambiguous sinkholes, which pirate drainage systems in Nash Draw to the 

west. 

 The stratigraphic thinning commonly cited as evidence of dissolution of the Rustler 

Formation at the WIPP site is in fact related to dissolution only in the immediate vicinity of Nash 

Draw. This dissolution-related thinning overlaps with and obscures the depositional thinning 

and thickening that is common to the Rustler Formation across the Delaware Basin, and which 

was caused by the irregular Permian depositional topography. 
117

Rustler halites were deposited in shallow depressions (“pans”) on this depositional 

surface at the same time that muddy deposits were accumulating at the margins of the pans, and 

this lateral facies equivalency, a well documented and founding principle of stratigraphy, caused 

most of the sedimentary patterns that are mistakenly cited as evidence for post-depositional 

dissolution and removal of halite from the thinner parts of the Rustler Formation in the vicinity 

of the WIPP site. The larger extents of the dolomite layers are not evidence for the original 

extents of the halite layers since the dolomites were deposited in much deeper waters that were 

not affected by the low-relief topography of the depositional surface. It would be impossible to 

obtain the observed thicknesses of muddy and silty deposits that have been called “residues” by 

dissolving the limited available volume of muddy and silty halite. Moreover, the silty and 

muddy beds do not contain evidence of other insoluble remnants that are common in the thicker 

halite beds. 

 The concept that Nash Draw is the largest of a series of sequentially smaller karst-related 

conduits that should extend eastward under the WIPP site is fallacious. Nash Draw formed 

under exceptional circumstances, during rapid erosion of the Rustler evaporite deposits exposed 

at the surface by a local, large drainage system during Pleistocene time. There was no equivalent 

to this at the WIPP site, where the Rustler Formation was and is deeply buried, thus the 

homogeneous medium and uniform conditions required for the development of such an ordered 

system were not obtained. 

 The existing drillholes, though small in diameter, are sufficient to assess the probability 

of karst at the WIPP site, since the karst should have developed preferentially along the 

numerous horizontal fractures present in the Rustler Formation and since the probability of 

hitting a horizontal plane with a vertical drillhole is high. The large-diameter shafts excavated 

into the WIPP repository have provided a large subsurface sampling, at a location where 

significant dissolution was hypothesized to have occurred and which should have had a high 

probability of intersecting evidence for that dissolution. In fact, the shafts offer evidence only 

for primary deposition unaffected by later subsurface dissolution, and that evidence is definitive. 

 The general absence of dissolution, karsting, and related conduits is corroborated by the 

pumping tests which have interrogated large volumes of the Rustler Formation between 

drillholes. These tests have not revealed evidence for karst-related, channel or conduit flow. 

Rather, they suggest that the Culebra and Magenta Members have relatively low conductivity, 
118

but with local indications of low-volume/high conductivity flow that is probably influenced by 

natural fractures. Diffusion calculations indicate that it would be virtually impossible to have 

separate isotopic signatures for the water found in the fractures and the water found in the pores 

of the matrix rock between fractures, as suggested to explain the isotopic evidence for ancient 

formation waters by the proponents of karst. 

 The various geophysical techniques run in the vicinity of the WIPP site show a number of 

anomalies, but the anomalies do not overlap to portray consistent and mutually supporting 

patterns that could be definitively related to specific locations for karst-related void space at 

depth. The most prominent anomaly, the WIPP-14 gravity anomaly, is a curved, linear feature 

that may be due to the presence of thick, low-density deposits of a local Gatuña tributary system. 

The poor development of surface drainage over the WIPP site is due to the absence of 

requirements for such a drainage network. The low rate of precipitation, the presence of sandy 

surficial deposits that quickly soak up precipitation, the low dip of the strata that does not funnel 

drainage in any particular direction, and the shifting of dune sands that blocks drainage as it 

develops, combine to prevent an organized drainage system from forming in this area. It is not 

necessary to postulate a complex process of stream capture by an organized system of sinkholes 

and subsurface drainage to explain this pattern. 

Recharge, flow, and discharge of water in the Rustler Formation are largely theoretical. 

Few direct measurements or observations of this flow are available except for the brine discharge 

from springs at Malaga Bend on the Pecos River, and this discharge is probably from the brine 

aquifer at the Salado-Rustler contact, and limited to drainage from Nash Draw. The springs do 

not support the existence of a karst system in the Rustler Formation at the WIPP site. 

The coincidence of the Culebra and Magenta potentiometric heads between Nash Draw 

and the WIPP site is also mistakenly cited as evidence for karst conduits linking the two units. 

Rather, it is the inevitable intersection of two non-parallel surfaces. In addition to the fact that 

the surfaces diverge westward as well as eastward, water chemistry and well-test data support the 

existence of two separate and non-communicating water bodies in the two units. 

 The evidence for karst in drillholes WIPP-13, WIPP-14, H-3, and H-6 is spurious: many

of the breccias in the core are due to synsedimentary disruption of bedding, and the more severe 

breccias are found where they are most likely to be related to localized dissolution, adjacent to 

the Magenta and Culebra water-bearing units. The significance of the few well-test variations is 
119

ambiguous, but the mere fact of variations does not prove the presence of karst as suggested; 

their characteristics must be analyzed. 

 The proponents of karst in the Rustler Formation at the WIPP site tend to mix data, to 

take data out of context, and to offer theory as fact and to continue to offer misconceptions in the 

face of evidence. They do not analyze the data or synthesize it into a mutually supporting 

framework. Hill commonly used the existence of an anomaly rather than the specific 

characteristics of that variation as evidence for the probable subsurface development of intrastratal karst, and has used generalized concepts and theory to suggest that specific interpretations 

have been proven. This is an inversion of the standard and more widely accepted scientific 

process that uses specific data to prove or to construct broader-scale interpretations. 

When the specific data cited by the proponents of karst at the WIPP site are examined, 

they are commonly non-unique in their possible interpretation. More plausible, less complex 

interpretations are usually possible. The data are cited randomly rather than being assembled 

into an interlocking and mutually supporting scientific case for the presence of karst in the 

subsurface Rustler Formation at the WIPP site. 

 The case for karst development in the Rustler Formation has not been advanced or 

proven. Rather, the data suggest that most of the subsurface evaporitic strata of the Rustler 

Formation at the WIPP site have not been subjected to dissolution since the time of deposition. 
120

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