## 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 Bre ccia) **............................................................................................................................................... 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 COND UIT 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 Fra cture 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 Formati **on at the WIPP Site** 

**John C. Lorenz**

ABSTRACT

**This report is an independent assessment of the potential for karst dissoluti on 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 c hanges. Most of the**  **evidence that has been offered for the presence of karst in the subsurfa ce 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 Rustl**  **er Formation near the WIPP site is limited to the horizon of the Magenta Member in dril**  **lhole WIPP-33. Most of the other evidence cited by the proponents of karst is more eas**  **ily interpreted as primary sedimentary structures and the localized dissolution of evaporit**  **ic strata adjacent to the Magenta and Culebra water-bearing units. Some of the cited evidence is inva**  **lid, an inherited baggage from studies made prior to the widespread knowledge of modern evaporite deposi**  **tional environments and prior to the existence of definitive exposures of the Rustler For**  **mation 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 Form**  **ation under**
**the WIPP site have been taken as evidence for the dissolution of halite such as t hat seen in Nash**  **Draw, but are more rationally explained as sedimentary facies chang es. Extrapolation of the**  **known karst features in Nash Draw eastward to the WIPP site, where conditions ar e and have**  **been significantly different for half a million years, is unwarranted. The vol umes 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 later al 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 subsurfa ce strata do not**  **support a sinkhole interpretation. Surface drainage across the WIPP site is p oorly developed**  **because it has been disrupted by migrating sand dunes and because prec ipitation is not focused**  **by defined catchment areas in this region of low precipitation and low-dip beddi ng, not because**  **it has been captured by sinkholes. There are no known points of discharge from t he 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 suff icient to**  **assess the probability of karst development along the horizontal fra ctures that are common in the**  **Rustler Formation, and the area of investigation has been augmented significa ntly 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 test s which have**  **interrogated large volumes of the Rustler Formation between drillholes. Di ffusion calculations**  **suggest that separate isotopic signatures for the water found in the fractur es and the water found**  **in the pores of the matrix rock between fractures are unlikely, thus the isotop ic evidence for**  **ancient Rustler formation waters is valid. Geophysical techniques show a num ber of anomalies,**  **but the anomalies do not overlap to portray consistent and mutually supporting pat terns that can**  **be definitively related to karst void space at any given location. The coinc idence of the Culebra**  **and Magenta potentiometric heads between Nash Draw and the WIPP site i s the inevitable**  **intersection of two non-parallel surfaces rather than an indication of karst-rel ated hydraulic** 
**communication between the two units. The proponents of karst in the Rustler Formation at the WIPP site tend to mix da**  **ta, to take data out of context, and to offer theory as fact. They do not analyze the data or s**  **ynthesize it into a rigorous, mutually supporting framework. They assume that the existe**  **nce of an anomaly rather than the specific characteristics of that anomaly proves the e**  **xistence 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. Environmenta l**  **Protection Agency (EPA) to address concerns about the possible existence of a karsted layer or**  **layers within the Rustler Formation, expressed most comprehensively by H ill (1999) in an**  **unpublished “Letter Report” to Sandia National Laboratories. Hill p ublished a slightly revised**  **and shorter version of this paper in 2003. The Rustler Formation overlies the nuclear waste repository strata (whi**  **ch is within the Salado Formation) at the WIPP site in southeastern New Mexico. A karst deve**  **lopment in the Rustler Formation at this site could conceivably alter flow pathways for l**  **eakage away from the WIPP site should the repository be breached and contaminants migrate as f**  **ar upward as the Rustler Formation. The primary purpose of this report is to assess the evi**  **dence for karst development in the Rustler Formation at the WIPP site. The topics discussed he**  **re were specified by EPA and include those issues raised by the Hill report and by other prop**  **onents of karst at the**
**WIPP site. The data available for this assessment consist of the geological report**  **s of the area, going back to potash resource characterization studies from the 1930’s. Geologic st**  **udies 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-rel**  **ated studies. Where possible, the original core and outcrop descriptions and associated ge**  **ologic project reports have been obtained. The original geophysical and hydrological s**  **tudies that were undertaken to address the question of whether or not karst has been developed in the Rust**  **ler Formation at the WIPP site have also been assessed for their potential to cl**  **arify the geologic interpretations.**  **Several subtle but important problems with the geologic interpretat ions 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 str ata 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 e vaporitic depositional** **8**

**and diagenetic environments represented by the sedimentary textures in cor es and outcrops that**  **they studied. For example, Gard (1968) invoked a cumbersome, hypothetical system of localize**  **d, temporary uplifts during deposition of the Salado Formation in order to explai**  **n 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 t**  **he time was that all bedded halites were deposited in marine environments. Studies that have both develo**  **ped 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 pa**  **ns marginal to marine environments. These studies explain Gard’s evidence for subaerial exp**  **osure much more neatly and logically, and are consistent with modern sedimentary princip**  **les. Second, most of the early WIPP geology reports used the prevailing geologi**  **cal conventions which blurred the distinctions between lithologies, facies, and deposi**  **tional/ diagenetic environments, i.e., between basic data and interpretations. Under the**  **se 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 combina**  **tion 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 s uperficially**  **similar lithologic units where there is even less basis for the implied int erpretation 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 obscure d. 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 l ess definitive, gross**  **scale geologic relationships as the basis for many of their sedime ntological interpretations.**  **Although the gross-scale relationships are important, the range of possi ble interpretations that**  **can be made based on these relationships can now be culled and the interpre tations significantly**  **refined using the exposures of previously unknown structures, textures, and sediment ary**  **assemblages available in the WIPP shaft excavations. These feature s are especially useful in** **9**

**making comparisons to the data available from recent studies of analogous moder n evaporite**  **depositional environments. 10** 

2.0 APPROACH

**An objective assessment of the evidence for karst in the Rustler Formation ha s been**  **attempted, along with an assessment of whether or not the undisputed evidence for ka rst at Nash**  **Draw implies that karst is widely developed in the Rustler Formation else where, specifically in** 
**the subsurface under the WIPP site. Different approaches taken by various scientists are also compared in t**  **he discussions presented here, assessing the approaches in light of accepted practic**  **e. The presentation of unsupported statements, and the substitution of theory for evidence, are unaccep**  **table scientific methods that would not stand up to rigorous peer review. Much of the evidence offered fo**  **r the existence of karst in the Rustler Formation at the WIPP site is speculat**  **ive, or at best, speculative analogy, and what evidence exists for karst is commonly contradictory and subje**  **ct to other, more plausible interpretations. An attempt is made here to assess the relia**  **bility and origin of the data that have been used to make various interpretations, and to assess whether those inte**  **rpretations are proven, probable, plausible, merely possible, or even untenable.**  **In this report, indirect evidence is not given equal weight with direct evidence, and possible geologic**  **al models are not equated with proven or plausible models.**  **In assessing the issues raised by Hill’s (1999) report, an attempt ha s 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 mak ing these**  **interpretations. An example is the repeated designation of some of the Rustle r 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 subse quent**  **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 Na**  **tional 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 t**  **he 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 deposit s 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 lit hologic units**  **within the formations are homogeneous and laterally extensive for miles or even te ns of miles.**  **The inclined strata have been truncated by erosion, with successively older unit s exposed at the**  **surface westward (Figure 2). Various units of the Rustler Formation have been e xposed 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 Sant a Rosa Formations,** 
**which overlie the Rustler Formation.**

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

**Figure 2. Schematic southwest-northeast cross section across the WIPP si te (from Chaturvedi**  **and Rehfeldt, 1984).**

**Although lateral continuity and homogeneity of bedding are common attributes of t he**  **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, Tama risk, and Los Medaños**  **Members of the Rustler Formation (Figure 3) contrasts with the latera l homogeneity of the**  **intervening, dolomitic Culebra and Magenta Members of the formation. Some of the la teral**  **variability in the evaporites in the vicinity of Nash Draw, where the for mation has been exposed**  **to weathering and erosion at the surface, can be related to relatively re cent dissolution. In the**  **subsurface, however, most of this variability is the result of lateral var iations in depositional**  **facies. Historically, the subtle distinction between primary lat eral variability created by facies**  **changes and the secondary variability imposed on the strata by local dis solution has been blurred**  **or ignored by various authors, and some clarification of that distinction is attempt ed here.**  **The term “karst” includes a wide range of features developed during the dissolut ion of**  **rocks, usually of the more soluble carbonate and evaporitic lithologies, by va rious types of**  **naturally occurring, mildly acidic fluids, most commonly rainwater. Kars t includes features that**  **range from minimal karst development, as in the local enhancement of the widt hs 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**

**pr ove that the strata once existed.** 

**F igure 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 abs ence**  **of features suggested to be indicative of an intermediate stage of karst devel opment. However,**  **evidence for karst at this site is ambiguous, which has allowed different author s, 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 i s not used rigorously,** 
**and the characteristics are not definitive. The fact that a feature can form i n any position relative**  **to the water table, points one and three, does not help to define it. “Widespread,” p oint five, is a**  **subjective term and is not equivalent to “universal” as implied by the tenor of t he 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 unrestric ted 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 mi**  **xture of descriptive, genetic, and synonymous terms. Hill defines “karst” geomor**  **phically as a landscape characterized by closed depressions, disrupted surface drainage, and undergr**  **ound caves and drainage systems. The first two of the features are not uniquely indicative of ka**  **rst: although closed depressions and disrupted surface drainage may be the result of a p**  **rocess that produces cavernous karst in underlying strata, they can also result from other proce**  **sses such as the irregular coverage of a land surface by glacial till or windblown sand dune**  **s, or tectonically by structural reversal of low-angle bedding dips.**  **The 1972 AGI Glossary of Geology, in the definition of karst, specifies an origin a s a**  **dissolution product and includes the resulting surficial geomorphic features such a s disrupted**  **drainage as part of the characteristics of karst. Although the disrupte d surface drainage**  **described by Hill is both real and widespread at the WIPP site, and althou gh it is similar to that**  **created by karst processes, such features can be created by proc esses 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 flowi ng hydrologic**  **system, implying that dissolution is no longer actively removing rock, but whet her above or**  **below the water table is not specified. Hill defines “intrastratal kar st” 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, a s summarized by**  **Hill (1999, 2003), that karst may be developed in the subsurface at and near the WIPP s ite. In**  **extrapolating the widely recognized karst sinkholes, caves, and collapse fe atures 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 cave rns (sinkholes) in the**  **Rustler Formation on the northwest corner of the WIPP site, and 2) that a disappear ing stream (a**  **“doline”), described by Phillips (1987) as entering one of these topographic dep ressions, is**  **where surface drainage is captured by the inferred subsurface karst conduit system.**  **The following discussion examines the surficial evidence for karst at and nea r the WIPP**  **site, and compares the well developed karst features in the Rustler Formati on in Nash Draw with**  **the local and more ambiguous features claimed as evidence for karst in the are as 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 lie s west**  **of the WIPP site (Figure 1, Figure 5a) and is generally agreed to have be en caused by the**  **removal of evaporites from within the partially exposed Rustler Format ion and from the upper**  **parts of the underlying Salado Formation, by weathering, dissolution, and erosion (Bac hman,**  **1981, 1985, 1990; Mercer, 1983). Unchallenged karst features in and immediately around Nash Draw include numerous caves (many containing secondary clay deposits), si**  **nkholes, fractured and brecciated strata, and saline springs.** **18**

**F igure 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.** 1o4 •o o '

+ w C) 0
a:



### r ;71 ;:: • L A GUN A GR

AN

O£ lf>tt 0£ L A SAL

+

R

. Z9 [ R 31 E

>- "' + 0

I 0

**~** 

# l

**~** R :'IZE 103 • 4 5

PLATA I R 33E EXPLANATION

• W-28

+ w WI LLIA M S S I I< K ' TEST HOLE AND NUMBER

1 0 W-27

**~,.** L o • , ._ + 

### t IDENTIFICATION OF TEST HOLES
A

- AEC E

- ERDA H

- Hydrology P

- Potash \1

- \IIPP

+- +

**~W 30**  t- 

## I

**~** WIPP SITE ' STREAMFlOW GAGING STATION



### ~\> **~** W-25•\

W-26



### .,_,-.~ 

# I
•HILl TANK



# ~I

II[MUDA

IIASIH t-

.. +

+ . .IJ\'A L 

### ., ,

,E

• H-7

t t

e:-10



### ~~ 

# J.

• PROJE:..:r.OME SITE 

# t

+

+ H-8 +-

+ 

### t • H-9
+

**~** 

## I

R 30 E R 31 E

.

**01-.......,....--,...2~_.3-~4** Ml LES
0 2 3 4 KILOMETERS 

# i · 20 

# l

..... ....



# .. ; I ;

0 0 u u H·IO •

R. 32 E

. + 

# L

I T

. 20 s

T Zl s

.

T 22 s

T

. 23 s**19**

**F igure 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 

## •

WIPP-2 5 

## • SNL-1 

### •

WIPP- 3 0 

### •

WIPP-11 

### •

H- 6 DOE-2 • WIPP- 3 4



# ·-

WIPP- 33

P-14



## •

D-2 68



### • 

### •**P- ~**  

# .. WIPP-1 3 • W QS P-2 

## • WQSP-1 

### • WIPP-1 9 

## • VVII-'1-'·14

. C& SH Sh a ft A1r Int a k e S h a ft u.E x h a u s t Sh a ft W

as t e Sh a t

_ nt: RDA- 9 • H- 1 5 H- :! H ! 1

•**3** ee W Q SP-4 W QS P- 6 H-1 9 e DOE-1

• H-11 Approximate Wll-'1-' :site Boundary

P-17 H-17



## • •

Meter s P-1 8 

## •

0 1
, 500 3
, 000 4
, 5 00 6
, 00 0**20**

**insoluble Rustler beds that are/were interbedded with the soluble halit e 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 di ssolution of the**  **interlayered evaporitic strata to the point where the dolomites are sep arated in outcrop by as little** 

**as a meter. Analysis of crosscutting and superimposed geological relationships a**  **llowed 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 Rust**  **ler 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 a t a much slower rate, in the Nash**  **Draw area (Bachman, 1981). The evidence offered for present-day dissolution is t he presence of**  **active, salt-saturated springs in several places around the draw. One ref erence (Geohydrology**  **Associates, 1978) has suggested that the existing sinkholes are being active ly enlarged but that**  **no new sinkholes are forming, although no data are offered to support this interpreta tion.**  **Similar, unequivocal dissolution features (sinkholes, caves, disrupted strata, and thinned**  **strata) are present in other areas where the Rustler Formation is expos ed 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 s**  **pecious. There are many areas of unkarsted evaporite deposits worldwide, and geologic conditi**  **ons 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 WIP P site are**  **evidence for the collapse of karst caverns at depth, presumably within t he Rustler Formation. In**  **order for a lowering of the ground surface to be related to collapse of the underl ying strata, those** **21**

**underlying strata must have been removed or displaced, and will commonly have bee n**  **brecciated. Wells drilled in these depressions to sample and test for karst have not encounter**  **ed either displaced strata or breccias (see below). Hill (1999: her Figure 8, pa**  **ge 18 and Figure 17, page 41) draws hypothetical, funnel-shaped dissolution structures (Figure 6) to expla**  **in why the investigation wells could have missed evidence for karst, and then to suggest that ka**  **rst is likely in the subsurface since the wells must have missed the karst. A funnel-shape**  **d geometry is incompatible with the cylindrical or inverted-funnel shape common to most sink-hol**  **e collapse features. Moreover, the funnel shape, widest at the top, is unlikely since this i**  **s the level of the low-solubility sandstones, siltstones, conglomerates, and shales layers tha**  **t 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 top ographic**  **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 b y Hill (1999).**  **This work focused on the Mescalero Caliche, the uppermost layer of lithified str ata at and near**  **the WIPP site. Phillips implied that the impermeability of such a lay er has been an erroneous**  **cornerstone of the hydrological modeling at WIPP, although he did not cite the refer ences. In**  **fact, the three-dimensional basin-scale modeling of the WIPP hydrolog ic system performed by**  **Corbet and Knupp (1996; see also Corbet, 2000), which provides the conceptual underpinning o f**  **all recent WIPP hydrologic studies and models, does not include the Mescalero Calic he 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 soil producing 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., Bachma**  **n and Machette, 1977). Gile, Hawley, and Grossman (1981) document similar pipes from calcrete**  **s in the Las Cruces, NM area.** **22**

**Figure 6. Conceptual model of sinkhole formation, from Hill (1999), her Figure 8/page 18. T he**  **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 uppe r**  **caliche surface at the WIPP site formed due to “collapse or subsidence of c aliche into voids left**  **by dissolution of underlying soluble rocks”, and by “dissolution and breaching of cal iche by**  **infiltrating rainwater”. Phillips documented broken, solution-pitted, and displa ced 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 disru ption of the caliche**  **layer, but rather used the observations from the caliche layers to infer t his 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 sur**  **face 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 de pressions are a few feet**  **deep, and measured offsets of the datum are a few tens of feet. Moreover, the sig nificance and**  **reliability of Phillips’ datum as a structural horizon are ambiguous at b est: 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 hori zon.**  **Moreover, caliche deposition commonly follows the contours of the topography on w hich it**  **forms, thus it cannot be determined whether depressions in the land surface cause d depressions**  **in the datum or whether both were later offset by a lowering of the strata a nd land surface**  **together. More importantly, several hundreds of feet of insoluble Santa Rosa and Dewey La**  **ke 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 dis**  **placed. Connection between the depressions and the Rustler Formation across these intervening l**  **ayers, and voids in the underlying Rustler, are entirely speculative.**  **Phillips proposed an absence of perched water tables in these formati ons 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. H owever,**  **other publications have noted or suggested that perched water tables do in fact e xist 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 t**  **hese clastic units in several places (i.e., Powers, 1996), speculations regarding small-scale penetra**  **tion of these sandstone units and karst-type conduit connection across them that might allow meteoric rec**  **harge down into the underlying Rustler at the WIPP site are unsupported.** **24**

**The implication from Phillips’ interpretation that holes in the layer of Mes calero caliche**  **allow significant recharge of meteoric waters to the underlying formations is an unproven, over**  **interpretation of the data. Phillips’ text contains numerous similarly s peculative and unsupported**  **assertions at a smaller scale, and phrases such as “it could be that”, “ap pear 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 tha t 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 sour ce 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 soluti**  **on that can occur along linear fault trends in some geologic settings. The three depressions of t**  **he chain extend across a distance of 1500 ft, with the center of the middle one off-line by 100 ft. The**  **se depressions are shallow, the deepest being about eight feet deep and a fe**  **w 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 dire**  **ction 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 depre**  **ssion, is offset from the linear trend to form an “L”): this is a mis-statement of the geometr**  **y 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 propose d 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 pipe line. Note the**  **absence of well-defined drainages entering the area, and compare to F igure 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 depress**  **ion (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 duri**  **ng the field trip described in Chaturvedi and Channell (1985; Appendix C, Notes for the Karst Hydrology F**  **ield Trip by Larry Barrows, page 3 [the location is given as being in sect**  **ion 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 loca**  **tion to discuss the lack of surface runoff, character of the rainfall, and implications of the wa**  **ter balance,” but he does not specifically label this depression as evidence for karst dissolution i**  **n 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 tren**  **ched this depression, noting that the underlying caliche profile is poorly indurated, a**  **nd that its surface mimics the overlying topography. Caliche is not present in the central p**  **arts of the depression, where the subsurface “structure” is floored by the Gatuña Formation. Phil**  **lips 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 carb**  **onate is “direct evidence of rainwater infiltration,” though he does not indicate why the same wate**  **rs that dissolved the carbonates of the caliche zone should have precipitated carbonat**  **e in the sandstone. In fact, carbonate is the most common cementing material in sandstone worldw**  **ide, and is not indicative of any particular process. A mechanism by which dissolution mi**  **ght 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: exca vation operations**  **would produce the same effects. He also offered an absence of surrounding dunes a s evidence**  **that this was not a wind-formed blowout (which was Bachman’s [1985, page 21] interpret ation),**  **even though the area is located within a large, stabilized dune field (e.g., Chugg et a l., 1971).** 

3.2.3.4 WIPP-33 **Phillips (1987) and Barrows (1982) have provided the primary discussions cited b y 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 feat**  **ures 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 define**  **d than the**
**dolines found in Nash Draw. This feature, inferred to be the course of a shallow, short, captured stream, ter**  **minates**
**within the WIPP-33 surface hollow described above. It has been used as evidenc e to suggest that**  **the land surface at and near WIPP is one of disrupted drainage, where numerous stream s have**  **been captured by the inferred system of karst-related subsurface conduit s. Phillips (1987)**  **suggests that the vanishing arroyo terminates in the eight-ft deep WIPP-33 dep ression, and he**  **has mapped it at small scale (Phillips, 1987, Fig. 5). The valley of this arroyo doe s 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 t he 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 Rustle r”. 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 p hoto) 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 depress ions has been**  **offered as evidence that they are dolines. Data on rates of soil percolat ion would indicate**  **whether ponded rainwater would be able to soak into the sandy surficial deposit s within the**  **observed time frames or whether capture by inferred subsurface draina ge 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 WI PP-33 depression was**  **filled with five feet of water for “a matter of days” (Phillips, 1987, p. 86), di sappearance of the**  **water is evidence that it had to sink into an underground system. A more plausible int erpretation**  **of the same observation would be that because the sandy hollow held water at a ll, there is**  **probably no drain outlet into a subterranean plumbing system at the bott om 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 t he 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 mi gration of numerous**  **sand dunes into the area, now partially stabilized (Figure 10), and the relate d low level of annual**  **precipitation which does not contribute enough water to the surface drainage syst em 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 regardles s.** 

**Figure 10. Low-angle aerial photograph of stabilized and active sand dunes i n 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 r equire a developed**  **drainage system. In contrast, surface drainage that disappears into sever al obvious sinkholes in**  **nearby Nash Daw is well defined up to the point where it is captured and enter s the subsurface**  **(Figure 11), and the difference between these undisputed systems and the inferr ed doline systems**  **nearer to the WIPP site is striking. 30** 

**The absence of well-developed drainage patterns in the hummocky topograp hy 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 rainfal l, and**  **evapotranspiration that more readily explain the poorly developed modern sur face drainage.**  **Cavernous porosity in the upper Rustler at WIPP-33 is present, as discussed in s ection 3.3.3, but**  **a relationship between surface drainage at WIPP-33 and upper Rustler p orosity still needs to be**  **established, and the general lack of integrated drainage is not evidence of ubiquit ous karst at**  **depth as implied.**

**Figure 11. Low-angle aerial photograph of diverted drainage, vanishing strea ms, and the open**  **sinkholes that capture them, in the Forty-niner Member of the Rustler Formation e xposed 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 WIP P 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 WI PP 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 hydrologi cal evidence will**  **be discussed later, but the geologic evidence offered by Hill for karst dev elopment 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 interpret**  **ed as**
**solution breccias and as “insoluble residue.”**
**2. Basin-scale stratigraphic thinning of the Rustler, and stratigraphic int**  **ervals that contain halite in some areas but that do not in other areas, the latter extrapolat**  **ed to indicate that the halite has been removed by dissolution.** 
**3. Meter-scale bit-drops, encountered in the WIPP-33 borehole, that are infer**  **red to**
**be into karst-related caves.**

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

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 cert**  **ain units of the Rustler Formation, but the connotations and implications of these phrases are not i**  **n fact universally appropriate or applicable. Siliceous clay, silt, and sand ar**  **e largely insoluble, especially relative to evaporite minerals, but the fact of insolubilit**  **y alone is not diagnostic of the genesis of beds composed of these materials. The word “residue” has an automat**  **ic genetic implication, but the mere presence of a layer of clay, quartz, or feldspa**  **r does not automatically imply, and certainly does not prove, that the layer composed of these material**  **s 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 process**  **es involving 32** 

**deposition and secondary dissolution, and by Occam’s razor the simpler of the two p rocesses**  **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 stratigra phic 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 t he**  **presence of truncated bottom-growth halite or gypsum crystals, and/or of t he 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” shoul**  **d 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-for**  **mation 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, diagenesi s, and**  **reworking in modern environments in detail have only been undertaken in the last seve ral**  **decades (see Powers and Holt, 2000), thus earlier studies of the WIPP-area evap orite deposits,**  **and the early geologists who received their education even earlier, commonly mi sapplied 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, t o 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 f or massive siltstones, but**  **the genetic implications of this phrase have been largely unsupported. Since most Rustler outcrops are badly weathered and disrupted, and since cor**  **es of fresh Rustler rock offer only small samples of the formation, it was only with the exca**  **vation of the WIPP air intake, exhaust, and waste-handling shafts that fresh, clean exposure**  **s 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 environment**  **s 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 descr ibed.**  **The term “insoluble residue” and its variations seem to have first been appl ied to the**  **thick, massive to chaotic, clayey unit that separates the top of the Salado For mation from the** 
**base of the Rustler Formation in the Nash Draw area. This unit is one of the more si gnificant**  **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 claye y halite.**  **Jones (1973, p. 20) described this unit as being “composed of clay with crudely interlayered seams of broken and shattered g**  **ypsum and fine-grained sandstone.... The gypsum is clearly the hydrated remnant of anh**  **ydrite and polyhalite seams, for it commonly contains ragged and embayed masses of anhydri**  **te and polyhalite, and, also grades laterally into anhydrite and polyhalite. The cl**  **ay, 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” cont**  **ain 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 publi**  **shed descriptions of the characteristics of many clayey and silty layers called “di**  **ssolution residues” are insufficient to prove that they are the insoluble remnants of dissolved evaporitic strata r**  **ather than primary deposits of non-soluble minerals. Interestingly, the application of the term dr**  **ifted over the years to where it was considered to include beds composed entirely of massive siltst**  **one 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 dissolut ion 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. D isruption of strata**  **also occurs in modern evaporitic depositional environments as a synsedimentary product of the**  **normal depositional and diagenetic processes (Figure 12), and genetic interpre tations of cores**  **showing disrupted layers in the Rustler Formation should be integrated, using mut ually**  **supporting lines of sedimentological evidence such as the character, extent, and cont ext of the**  **disrupted units, not merely their presence. 34** 

**Figure 12. Salt ridges at Bristol Dry Lake, California. The salt ridg es 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 r eference**  **most commonly cited in support of insoluble residues as evidence for subsurfa ce dissolution near**  **the WIPP site, is the Ferrall and Gibbons (1980) description of cores from the Rustl er 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 strat igraphic position as**  **anhydrite beds in other holes, that “where these residues/breccias ex ist, corresponding anhydrite**  **rock has been removed.” This ignores the well established geological princ iple of lateral,**  **depositional facies equivalencies and lithologic variation, reverting to a si mplistic concept of**  **layer-cake stratigraphy. However, the point to be made here is that Ferr all and Gibbons were** **35**

**indiscriminate in their application of the term “residue,” and as such their int erpretive**  **descriptions are not a valid basis for underpinning theories of karst at the WIP P 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 ter**  **m not only omits an indication of the lithologic composition (other than by implying that its minera**  **logy 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 i**  **s 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) descript**  **ion 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 evapor**  **itic layer. There are no descriptions of remnants of red, embayed and altered anhydrite or gypsum be**  **ds 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 laterall**  **y into equivalent, undissolved halites. The most common bedding type described by Ferrall and Gibbons i**  **n these units is structureless or massive bedding, which is a common primary sedim**  **entary texture in evaporitic environments. It is not equivalent to the brecciated and disrupted b**  **edding, showing the bedded remnants of out-of-position layers, that can be, but is not always, ca** **used by post depositional dissolution.**  **The few places where Ferrall and Gibbons provided somewhat better descr iptions of**  **these “residue” strata, they described them as massive or “chaotic” si ltstones cemented with**  **halite, with the halite often in crystalline form. The only potential evidence f or 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 i ncorporated into**  **the strata during disruption of bedding on evaporite depositional surfaces dur ing 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 imm**  **ediate subsurface in poorly consolidated silts and muds in evaporitic environments. This di**  **srupts and 36** 

**even destroys bedding and other evidence of the currents that originally deposit ed 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, form ing large,**  **steeply dipping structures at the depositional surface. When these structur es are buried and then**  **cored, the strata can look like it was brecciated by post-depositional diss olution. Thus, disrupted**  **bedding is not by itself unique evidence for dissolution since it can form in syndeposi tional**  **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 pr**  **ove an origin from dissolution. Regardless, none of the descriptions of the halite-cemented, silty unit**  **s in these cores resemble Jones’ benchmark description of the residual claystone found at the to**  **p of the Salado Formation in outcrop. In fact, Ferrall and Gibbons commonly put quotation marks around t**  **he term “solution residue”, suggesting that they were uncomfortable with the ter**  **m. 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 res**  **idues 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 mine**  **rals. However, halite cement and even crystalline halite are present in all the silts**  **tone units that Ferrall and Gibbons (1980, pages 12, 22) labeled as residues. Moreover, clay is the most common ins**  **oluble material incorporated into halite beds, not silt (typical Salado halites c**  **ontain up to three percent insoluble material, 75% of which is clay: Gard, 1968). A true insoluble residue shoul**  **d 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 descr ibed from the cores, although**  **such successions were not recognized by Ferrall and Gibbons. Lithologicall y, 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 se quences were**  **sometimes truncated, but a simple model of deposition in a shallow-water environm ent that**  **became progressively more saline would account for both this succession of l ithologies and the** **37**

**observed characteristics in each facies, and is similar to the depositi onal sequences reconstructed**  **by Lowenstein (1988) for repetitive cycles of successive lithologies in the Salado Formation.**  **Ferrall and Gibbons (1980) describe few specific characteristics of t he 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 c ontrast,**  **primary depositional origin of these units is strongly supported by the recognit ion 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 detai**  **led 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 specifi cally noted but poorly**  **described “leached voids parallel to bedding.” They were therefore for ced into the improbable**  **speculation that any gypsified rock was immediately removed by the sam e waters that had**  **rehydrated the anhydrite. No description of these voids was provided, nor any j ustification 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-depositiona**  **l dissolution of halites is based indirectly on early, inconclusive descriptions of Rustler cores, encumb**  **ered by an inherited, non-specific terminology. The insoluble residue interpretation is not a unique inte**  **rpretation of the available data, and in fact the data can be more readily explained by si**  **mpler 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 sedimentologi st 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 under**  **take a study specifically to address the question of whether or not there is evidence of post-b**  **urial 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 dissoluti on 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 pr**  **ocesses 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 H**  **olt (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 description**  **s of dissolution zones immediately above and below the Magenta and Culebra Dol**  **omite 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 adj**  **acent beds is to be expected whether or not the rest of the Rustler units have been modified by kars**  **t channels. Regardless, the term “insoluble residue” is notably absent from Lowens**  **tein’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 sh afts at the WIPP site**  **(Holt and Powers, 1984, 1986, 1990b), documented definitive, primary sedimentary textures t hat**  **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) tha t was published**  **in an international, peer-reviewed, scientific journal. The authors were ab le to combine the new**  **features with knowledge of the recent detailed studies of modern evaporitic de positional**  **environments to develop a scientifically supported, plausible reconstru ction of Rustler**  **deposition, and relate it to the present-day distribution of the Rustler litholo gies. All of the**  **structures exposed and documented in the WIPP shafts fit conveniently into a model of sha llow,**  **evaporite salt pans and saline mud flats, with vertical repetitions of lit hologies fitting cycles of**  **fresh water incursion and subsequent evaporation, and lateral lithologic varia tions meshing with**  **geologically sound concepts of lateral facies variations.**
**The definitive absence of karst features in the Rustler Formation in the WIP P 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 Rust ler 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 Formati on 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 s**  **haft 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.” r**  **efers to the “ventilation shaft” that was subsequently enlarged and equipped to be the wast**  **e-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 f**  **ound 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 s**  **ite must be related to dissolution since the thinning trend continues westward to where the Rustl**  **er has been markedly and demonstrably thinned by dissolution in Nash Draw. Although dissolution is a**  **n obvious process at Nash Draw, it is not the only process capable of causi**  **ng marked thinning of the Rustler Formation. The questions are: 1) to what degree, if any, has Nash-Dra**  **w-type dissolution caused the thinning and absence of halite in the Rustler Formation at the WI**  **PP site, 2) are there other equally or perhaps more plausible processes to exp**  **lain this and which process does the data support, and 3) if there are several overlapping processes tha**  **t 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 Livi ngston**  **Ridge for at least a half-million years (Bachman 1985). During that time i t 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 W**  **IPP site. These authors suggest that more halite, progressively deeper in the Rustle**  **r 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, where as 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 are as 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 G ard (1982).** 

**Figure 14. Cross section showing the westward thinning of halite beds in the Rustle r Formation,**  **including the polyhalite in the Tamarisk Member, inferred by Snyder to indi cate progressive**  **westward dissolution of the halites but more plausibly interpreted as lat eral facies changes and**  **variations in depositional topography. (From Snyder, 1985; his Figure 2). See als o the regional**  **cross sections in Holt and Powers (1988). 42** 

**F igure 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 M ember of the**  **Rustler Formation, showing thinning in all directions, including westward across t he WIPP site,**  **and indicating that thinning is a function of depositional rather than dissolution (from P owers**  **and Holt (1990), their Figure 26/page 102). 44** 

**Figure 17. Isopach map of the total Rustler Formation, showing the depositional hol low east of**  **the WIPP site that controlled thickening and thinning throughout Rustler deposition (f rom**  **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 bee n 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 ove r a hundred**  **feet thick to zero both east and west of a depocenter thickening located about te n miles southeast**  **of the WIPP site (e.g., Holt and Powers, 1988, their Figure 4.5). The same pattern is p resent in**  **the salt deposits of the Los Medaños Member, the Forty-niner Member, and in a s mall halite**  **within the upper anhydrite of the Rustler (Holt and Powers, 1988), suggesting that thi s**  **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 whe**  **re the Rustler Formation is deeply buried and protected from weathering, eros**  **ion, and dissolution. This does not negate thinning due to dissolution in Rustler strata west of WIPP, but rathe**  **r suggests that such thinning does not prove dissolution since thinning can result from seve**  **ral 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 dissolut ion front is**  **abrupt in other basins where salt dissolution fronts have been definitively d ocumented (e.g., Neal**  **et al., 1998; Gustavson et al., 1980). Similar or even greater amounts of thinning in these basi ns**  **takes place over half a mile or less, and steep surface ridges occur wher e the overlying bedding**  **has been draped over the dissolution fronts. In the Holbrook basin of Arizona, the subs urface**  **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 lo cally by**  **clusters of sinkholes (Neal and Lorenz, 1998). Similar features are present in ot her basins (i.e.,**  **Gustavson et al., 1980). Powers et al. (2003) have recently suggested that the Salado sa lt**  **dissolution front is marked by the bedding roll-over at the Livingston Ridge es carpment on the**  **eastern edge of Nash Draw (Figure 18). Nothing equivalent to this surface de marcation of a salt**  **dissolution front is present at the WIPP site. 46** 

**Figure 18. Fractured sandstones of the Dewey Lake Formation draped over prob able 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 resi dues 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 silt y beds labeled as**  **"residues" by Ferrall and Gibbons (1980) in WIPP-19 is over 50 ft. If the silt and c lay 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 thic**  **kness 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 a**  **dded 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 drillhol**  **es to the east and 47** 

**southeast is about 40-45 ft thick, and nearly pure. Forty feet of nearly pure halit e 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 be ds 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 a fter 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 dom es south of**  **Carlsbad as distinctive, brick-red to orange gypsum alteration produc ts. 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 (198 0), 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 wit h a clay unit in**  **drillhole P-6, and suggested that the clay is the remnant residue from the polyhalit e bed.**  **Polyhalite is commonly formed as an alteration product from an anhydrite b ed, thus anhydrite**  **and polyhalite can be lateral diagenetic facies equivalents, but the m odel runs into problems in**  **that 1) it is relatively difficult to totally dissolve polyhalite, and 2) it i s even more difficult to**  **leave behind a thick clay residue as remnant from a virtually clay-fre e 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 exte**  **nsive geologic layers. Such layer-cake models of stratigraphy were superseded ear**  **ly in the development of geological sciences by the well-supported models of lateral deposi**  **tional-facies equivalents. For example, rivers, beaches, and lagoons can all be depositing different ty**  **pes of sediment in laterally- and time-equivalent environments, resulting in laterally equiva**  **lent 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, relativel**  **y 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 a**  **s “...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 cl**  **ay matrix) at different horizons in the formation. These layers are at the same stratigraphic locat**  **ions 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 sam**  **e stratigraphic horizon is not a gross anomaly that can only be explained by sp**  **ecial geological circumstances; rather it is a common and well-understood geologic occurrence.**  **In the Rustler Formation, most of the observed distribution of halites, polyhal ites,**  **anhydrites, mudstones and siltstones resulted from the deposition of laterally equivalent types of**  **rock in laterally equivalent environments: saline mud flats, saline evaporation p ans, 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 fa**  **cies of different lithologic composition. Because of the different depositional environments, the Ma**  **genta and Culebra facies vary on a scale of up to a hundred of miles rather than on the sca**  **le of miles to a few tens of miles as seen for the associated evaporitic deposits, and cannot b**  **e 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 distri bution, 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 dissol ution is** **49**

**definitive at Nash Draw (e.g., caves, Figure 19; breccias; drasticall y thinned section), but**  **becomes ambiguous in the subsurface to the east. The data presented by Powe rs and Holt (2000)**  **and Holt and Powers (1988) strongly support non-deposition where the Rustler Formation thi ns**  **without having been exposed in outcrop, and this interpretation is compatible wit h known**  **depositional thickness and facies variations from modern environments.**

**Figure 19. Dissolution cavern in Rustler strata exposed in Nash Draw. The cav ern 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 dete**  **rmine in the absence of good outcrop. However, excavation of the large-diameter air-intake, exhaust**  **, and waste handling shafts at the center of the WIPP site have provided data that definitive**  **ly support an interpretation of halite non-deposition and syndepositional dissolution in the vicini**  **ty of the 50** 

**WIPP site, negating interpretations of post-depositional removal by dissol ution and karst** 

**processes. These shafts were excavated in a position that is ideal for comparing t**  **he hypotheses of dissolution vs. non-deposition in the vicinity of the WIPP site, since isopachs of the Rus**  **tler 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 a nd 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 subs**  **urface 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 t**  **he formation and the absence of halite, the evidence he presented for that interpre**  **tation is circular in that it consisted only of 1) the fact that the Rustler Formation thins westward, 2) t**  **hat it contains little halite in the western locations, and 3) the inference that much of the anhy**  **drite 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 occur**  **red). If the interpretation that broad, subsurface dissolution of the Rustler Forma**  **tion 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 ex**  **tensive than any previous data from either outcrop or cores, and thus showed important sedimentary de**  **tails that have been previously obscured. However, the characteristics of the Rustle**  **r Formation found in the shafts document a normal, primary depositional sequence, with little or no evi**  **dence 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 Ta**  **marisk 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 suffici ent**  **water to remove significant thicknesses of halite. The only gypsum present is**  **immediately adjacent to the Magenta Member, an acknowledged if poorly pr oductive**  **water-bearing unit. No conversion of anhydrite to gypsum was reported eve n 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 Memb**  **er 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” halit e**  **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 depos**  **itional 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 mar k 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 expos**  **ures strongly supports the interpretation that it and associated halites were ne**  **ver 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 ori**  **ginal ventilation shaft (now the Waste Shaft) was dissolved back from the face of the**  **initial, small diameter pilot shaft by drilling fluids and by water dripping down the fac**  **e 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 fil**  **led with halite. 52** 

**This fracture and the erroneous interpretation continue to be mistakenly offe red 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 subsurfac e karst**  **development comes from the records of the WIPP-33 drillhole at the northwestern ed ge of the**  **WIPP site. Four, meter-scale bit-drops were encountered while drilli ng the WIPP-33 hole, and**  **these have been cited as evidence for widespread subsurface conduits rel ated 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 “f ound 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 occurr ed 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 “cavi ty” 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 dril**  **ling-time log (the geolograph from the drill rig floor).**  **Nine cores were cut in the Forty-niner/Magenta interval, with recovery ra nging from zero**  **to 46 percent and averaging 27 percent. Five cores were also cut through the Cul ebra 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 dat a report for the hole**  **(Sandia National Laboratories and the U.S. Geological Survey, 1981) also document s 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 h**  **ydrated to gypsum and perhaps dissolved entirely. The lithologic log indicates that most of the s**  **ulfate 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 horizont al as**  **expected, and the breccia blocks in the cores (in the A-3/H-3 interval) are s mall, suggesting that**  **disruption is not great and that there has been no large-scale collapse or ot her disruption of**  **bedding. A video camera lowered into the hole to assess the possibility of ca vernous porosity**  **was unable to see through the drilling fluid to the side of the drillhole. The caliper lo g that was**  **run in the hole after drilling encountered areas where the hole was somewhat la rger than the**  **diameter of the drill bit, but these zones (or perhaps the actual enlarg ement, 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 observati ons from**  **drillhole WIPP-33, but it is not unique, and the sizes of the voids are debatable. Poor rec overy of**  **core is also common where the material is broken by fractures or faults, and dr illing operations**  **through evaporites can even create local solution cavities if the mud is not proper ly 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 ad**  **jacent to a known source of water. The daily drilling reports document intervals of lost cir**  **culation and no returns elsewhere in the Rustler section, but the exact horizons of lost circ**  **ulation 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 deep**  **er, making it**
**seem as if the hole has encountered a new zone of lost circulation as it is bei ng 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 sub**  **surface voids, it is an isolated data point and the bit-drop evidence comes from only limite**  **d stratigraphic levels in the hole, related to a water-bearing unit where dissolution would be ex**  **pected. There are no data for similar voids in the nearby holes, voids that might form an interconnected su**  **bsurface 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 imposs ible. The lost**  **circulation was in fact controlled by the use of standard oil-field lost-circ ulation material (the**  **“LCM” noted in the drilling reports), typical LCM consisting of relativel y small bits of things**  **like cotton hulls and/or walnut shells that can be pumped down the hole. Material of thi s 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 s cale 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 obser**  **vation is not clear: if the thick fill represents a hollow created by a stratigraphic section downdropped ove**  **r a solution void, that would also create an obvious offset of the subsurface stratigraphy, but the s**  **tratigraphy is normal in this hole. It is unlikely that the thick alluvial fill resulted from local, nea**  **r-surface dissolution of the insoluble sandstones and siltstones. Hill diagrams a funnel-shaped zone of disr**  **uption, a shallow depression of unspecified origin and filled with surficial materia**  **l, with a localized conduit leading into deeper karsted strata at the bottom (see Figure 6), but s**  **he does not adequately explain how the funnel might have formed. In contrast, the known sinkholes i**  **n nearby Nash Draw consist of obvious cave openings and diverted drainage, but a**  **re not associated with marked depressions of the bedrock surface or with thicker uni**  **ts of surficial fill**
**material.**

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

**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 Mem bers at WIPP-33.**  **Nevertheless, geologic data do not support either the presence of caver nous 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 lab els that have**  **improperly and incorrectly assigned an origin to certain lithologies in c ore descriptions, and a**  **thinning of the Rustler Formation that can be explained more plausibly by f acies changes since** **55**

**1) the supposed missing material would have had to have been improbably thic k, 2) because it**  **does not contain the required volume or clayey types of insoluble material comm on in**  **recognized residues, and 3) because the characteristics of these deposi ts are more plausibly**  **explained by vertical sedimentary facies transitions. The hummocky su rface topography at the**  **WIPP site is real, but it does not imply karst-related pirating of dra inage 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 suggest s that there**  **must be a series of successively smaller conduit-type karst featur es that feed it,**  **and that therefore these smaller features must be present but have not ye t 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, relat**  **ively immobile water in the less permeable but volumetrically more impor**  **tant pore and fracture systems. Therefore most water samples taken from wells drill**  **ed 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 s**  **o that age dates from the water samples will be unrepresentative of the c**  **onduit system.**  **Hill does not present direct evidence to support the application of these arguments to the**  **Rustler Formation, merely stating that “The following principles a nd process of karst might be**  **applicable to the WIPP Site” (1999, page 201). Coming to grips with such an approach t o**  **science is like debating random speculation. The stream-theory argument requires that Nash Draw be part of an equil**  **ibrated, fractal system, and, if valid, would only be of significance if that system extends outwa**  **rd from Nash Draw and encroaches eastward as far as the WIPP site. The argument about unre**  **presentative water sampling would be valid only if conduit flow is in fact a reality, and onl**  **y if insignificant interaction between matrix waters and conduit waters occurs. The vague arg**  **ument (that an intrastratal karst system should be present at or near WIPP but is unre**  **cognized due to the low 57** 

**probability of sampling it) can be addressed by considering the geom etry 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 l arge 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 theorie s 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 few er channels in**  **stream systems, is a common pattern developed on homogeneous media and under homoge neous**  **conditions. The karst system studied by Sares (1984), and cited by proponents of ka rst as an**  **example of what they would expect to see in the subsurface at WIPP, is develo ped west of the**  **Pecos River on widely exposed and relatively homogeneous anhydrites of the Casti le Formation.**  **This formation has been subjected to relatively uniform conditions of weatheri ng 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 c onditions. The Rustler**  **Formation is composed of heterogeneous lithologies, including sandstones, claystone s,**  **dolomites, anhydrites, and halites, each variable resistance to erosion and dis solution. Moreover,**  **significant differences exist between the outcrop conditions at Nash D raw, 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 Form**  **ation, and collapse sinks began to form near the end of Gatuña time.... As a result of following the str**  **ike of the Rustler Formation for a time, Gatuña drainage contributed to coalescing the**  **se sinks” (Figure 20). Present-day Nash Draw is therefore analogous to an oversize valley/underfi**  **t 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 Pleistoc**  **ene surface drainage over the outcropping Rustler Formation cut directly into that formati**  **on and thus played 58** 

**a significant part in enlarging Nash Draw to its present size: the re is nothing comparable in the**  **subsurface to the east, and no reason to believe smaller branches of a sy stem exist there.** 

**Figure 20. Generalized Pleistocene Gatuña stream system, as reconstructe d 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 pa**  **tterns, 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 feat**  **ure. Nash Draw should not be modeled as the largest of a system of pervasive and success**  **ively 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 Fra cture
Flow **If conduit flow exists in the Rustler Formation at the WIPP site, it should be evi dent in**  **the data from the numerous hydrologic pumping tests done in the formation at and nea r the site.**  **Such tests can sample the hydrologic response and flow capacity of a la rge volume of strata**  **between several widely spaced wells at once, thus the data are represent ative of significant**  **volumes of strata. This offsets concerns that sample sizes have been too smal l to truly assess the**  **potential for karst at the WIPP site. Flow dominated by fracture systems (which have low storativity and high trans**  **missivity and which therefore give relatively rapid inter-well response times, and, c**  **ommonly, good regional interconnection), has a distinctly different response when tested hy**  **draulically compared to flow within karst-related conduit systems (which have high storativity, dampe**  **ning the inter well 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 m atrix and**  **fracture porosity in the tested medium, with the matrix providing most of the st orage capacity**  **and the fractures providing most of the transmissivity. Beauheim and Ruskauff (1998) ha ve**  **noted that the Culebra behaves as a double-porosity medium in those regions wher e open natural**  **fractures are thought to dominate hydraulic responses, and as a single-porosit y medium where**  **fractures are thought to be fewer, smaller, and more commonly plugged wit h gypsum.**  **Hydraulic testing of the Culebra has indicated horizontal directional-fl ow anisotropies of**  **up to 1.6:1 measured in pumping tests, and up to 7:1 measured in tracer tests (Hagge rty et al.,**  **1997; Meigs et al., 1997a,b). This type of behavior is typical of flow within p referentially**  **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 variabi lity in the dominant** 
**subsurface fracture orientations or in the** in situ **stress conditions. 60** 

**Testing has also indicated the presence of local hydraulic boundaries wi thin the Culebra**  **Member. “No-flow” boundaries are interpreted as representing decre asing transmissivity, while**  **“constant-pressure” boundaries are interpreted as representing inc reasing transmissivity. This**  **indicates that the Culebra Member is not homogeneous. None of these tests indicat e 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 pump ing 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 unkarst ed) conditions**  **(Beauheim, 1987b; Beauheim et al., 1991; Beauheim and Ruskauff, 1998). Transmissivities measured in the Rustler Formation vary by five to six orde**  **rs of magnitude. However, even the highest transmissivities measured (Beauheim a**  **nd 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 pump ed 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 dista nt. 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-s**  **torage 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, dr**  **awdown responses would have diminished and tapered off with time as the large-volume condui**  **t supplied water to the pumping well. Instead, pressures in all wells dropped gra**  **dually and evenly over the course of the test, indicating both that there is no large reservoir of fluid in the s**  **ystem 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 i s a well**  **connected, 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 l ow, 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 relative ly 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 l**  **evel 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 littl**  **e volume so the porosity and storage capacity are low, as seen in these tests. The results are not compa**  **tible with the properties of a high-volume karst-conduit system.**  **These test results reflect a pervasive fracture network rather th an discrete channels**  **because all wells within an inter-connected region respond when any one of t hem is pumped, and**  **because all wells newly drilled within the connected areas also show the con nections (e.g., H-19,**  **WQSP-1, WQSP-2, and WQSP-4). Rapid responses to even low pumping rates (3-30 gall ons**  **per minute) indicate good connectivity but low storativity; karst conduits woul d 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 wel ls 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 tra**  **nsmissivity 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-press ure**  **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 ex ample, 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 a t 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 Mage**  **nta 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 935Water-LevelElevation(mamsl) 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 i**  **n 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 120CulebraPressure(psig)

Magenta Culebra

60 61 62 63 64 65MagentaPressure(psig)

file: W25 M&C PT.grf **Figure 22. WIPP-25 Magenta and Culebra pressures during Culebra pumping t est conducted in**  **2004.**
**This indicates that the two members are hydraulically isolated from each ot her 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 int erconnected**  **hydrologically to each other. The potentiometric heads in both the Magenta and C ulebra**  **generally slope in different directions, strongly suggesting that the tw o 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 para llel, 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 Fres hwater Heads, of the Magenta Dolomite Member of the Rustler Formation near the W IPP 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 WIPP-18 H-18

H-8a H-9c

**Figure 24. Potentiometric heads of the Magenta Member of the Rustler Forma tion. 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 dri llhole**  **WIPP-33 near the northwest corner of the WIPP site may indicate a local develo pment of higher**  **volume 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 are a 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 isotop ic analyses**  **indicate water samples from the Rustler Formation are 12,000-16,000 years old), wit h 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 sepa**  **rate isotopic compositions of water in the subsurface: old, fossil water and young**  **er, recently recharged water. The argument is that water with a relatively old isotop**  **ic composition fills and is trapped in matrix porosity in the blocks between conduits, and that this is t**  **he water most frequently sampled since the matrix blocks are larger than conduits and they t**  **herefore have the highest probability of being intersected by a wellbore, explaini**  **ng the data that indicate old water fills the system. Different water with a young but unsampled isotopi**  **c signature supposedly fills karst conduits between the matrix blocks but is rarely sampled beca**  **use there are few such conduits, and therefore the Rustler water-sample data showing isotopic i**  **ndications of most recent 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 i sotopic**  **data suggest that either the Culebra contains discrete, rapid flow paths inte rspersed with areas of**  **slower groundwater movement and/or that young fresh water leaks into the aquife r,” seems to**  **have been the inspiration for this theory. However, Chapman also suggests (sam e page) that**  **“Extreme salinity variations...may be due to leakage of concentrated brine s in the Rustler from**  **underlying evaporite units.” Chapman prefers the first interpretati on, but the sample area** **67**

**includes Nash Draw and the area south of route NM 128 where local points of fresh wat er influx**  **are known. Moreover, although the locations of Chapman’s “rapid flow paths” are unspec ified,**  **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 centime ter). Nor do they**  **fit with or support the proposed locations or sizes of Snow’s (1998) four hypothetic al conduit**  **channels. Chapman’s concepts do not support Hill’s concept of conduit flow and bypa ssed** 

**water. Chapman (1986) also suggests that the stable isotope data from Rustler water**  **samples are similar to “verifiably young” groundwater samples elsewhere in NM. N**  **o one has reviewed or explained the reasons for the differences between this and Lambert and Har**  **vey’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 inte**  **rsects fractures or somehow misses them, pumping the well will preferentially pull wate**  **r from the most permeable part of the system (the fractures). Hence, water in fractures is alw**  **ays, 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 t**  **he fractures. Therefore, the isotopic signature of the water would be much more characteristic of the f**  **ractures than of any hypothetical older water in the matrix. Furthermore, diffusion would have equili**  **brated water chemistries between the fractures and matrix over the many years th**  **at fractures (or conduits)**
**have existed.**

4.4.3 Conclusion

**Based on pumping and tracer tests, the concept of two subsurface water po pulations with**  **widely divergent isotopic and age characteristics is untenable. Thus the inf erence derived from** **68**

**this concept, that the ages calculated from the isotopic signatures of samp led 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 p resent 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 f**  **or karst, because wellbores sample such small areas of a formation. She also suggests that w**  **ells 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 s**  **urface 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 s mall sampling**  **of a formation. The 83⁄4-inch diameter wellbores typical of oilfield operations have a cross**  **section of less than half a square foot. A wellbore, therefore, is an inefficie nt 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 ve rtical wellbore is low unless the**  **fracture spacing is very small, i.e., the probability of intersectin g vertical fractures with an eight**  **inch well is only 50% when the average fracture spacing is only 16 inches (Fig ure 25), and the**  **probability of intersecting a fracture decreases exponentiall y as fracture spacing increases**  **(Lorenz, 1992). 70** 

**Figure 25. The probability of intersecting fractures with a vertica l 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 tw o**  **dimensional. Although they may initiate by dissolution along two-dimensional frac tures, by the**  **time they have widened into conduits that are large enough to significantly affe ct 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 desc riptions of**  **actual conduits. The addition of the third dimension significantly increases both t he ability to**  **conduct fluids and the probability of intersection by a drillhole. More significantly, the documented fractures in the Rustler Formation have a var**  **iety of orientations, ranging from vertical to inclined to horizontal. The probabili**  **ty 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 vertica**  **l. There is a high probability of intersecting horizontal fractures with vertical well**  **s. 71** 

**Since so many of the documented natural fractures in the Culebra and other membe rs of**  **the Rustler Formation are inclined to horizontal, and since potential karst dissol ution features**  **should be initiated and preferentially developed along fractures, vertic al wellbores do in fact**  **adequately sample the formation for potential karst. The samples are sm all, 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 dev eloped in the** 
**Rustler Formation at this site.**

5.4 Data from the WIPP Shafts

**The absence of karst is strongly corroborated by the significantly la rger-scale, direct**  **sampling of the Rustler Formation afforded by the air intake, waste, and exha ust shafts,**  **excavated in the central part of the WIPP site to support the subsurface fa cilities 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 F**  **ormation, 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 wel ls. The**  **Rustler Formation penetrated by the three shafts is 309 ft thick, thus over 53,000 square f eet of**  **Rustler wall rock were exposed in the three shafts for examination and detailed m apping. No**  **evidence of karst was found in the well-exposed rock in the three shafts, excavate d 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 i n many**  **karst terrains constitute only 1-2% of the total rock volume, and that therefore the evide nce of**  **“caves” (bit drops) encountered while drilling only one of 60 (1.7%) wells in the W IPP area**  **(WIPP-33) is consistent with the presence of similar, karst-related void s pace percentages at**  **WIPP. While the assignation of a limiting, maximum percentage to what is a s pectrum of** **72**

**phenomena seems to be an unwarranted restriction, the absence of dissolution in Rustl er strata in**  **the large, clean, high-volume shafts is perhaps the most telling evidence agai nst this hypothesis.** 

5.6 Drilling in the Centers of Depressions

**Hill (1999) argues that holes WIPP-33 and WIPP-14, drilled to investigate the poss ibility**  **that local topographic depressions indicate an underlying karst system, h ave merely missed the**  **subsurface evidence for karst. This is a nebulous argument for which no rebutta l 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 mer ely**  **drilled in the wrong location. However, the holes drilled to assess these depressions and their associated gra**  **vity anomalies were located near the centers of the surface topographic depr**  **essions (see Figure 9), and the location of WIPP-14 was based on the surface features and gravity data tha**  **t had been interpreted by Barrows et al. (1983) and reviewed by Barrows (Sandia Na**  **tional Laboratories and D’appolonia Consulting Engineers, 1982, Appendix A).**  **It is unclear whether Hill suggests that the surface depressions are cause d by an actual**  **karst collapse as the underlying Rustler strata became brecciat ed and displaced during**  **dissolution beneath the entire area of the surface depression, as seen in the loca l breccia pipes, or**  **whether Hill infers that the depressions result from large-scale dissol ution or subsidence of the**  **sandstone layers near the surface. Regardless, neither theory is supported b y the data. If it is the**  **former case, then the collapse that formed the surficial depressions should ha ve resulted in**  **relatively large breccia chimneys, or at least measurable downwar d 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 surfac e depressions/gravity**  **anomalies have encountered neither displaced strata nor extensive, definitively post-depositional**  **breccias. Moreover, near-surface solution is untenable since the Triassic a nd Permian siliceous**  **sandstones, siltstones, and claystones that underlie the thin recent deposits are hi ghly 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 wi th a**  **Gatuña paleovalley mapped by Bachman (1985, his Figure 20). More recently, P owers and**  **Richardson (2004a) have shown that thick Gatuña deposits are present in the SNL-3 drillhol e**  **along this same trend. Wind-driven sculpting of the surface (including the “blowout s” of**  **Bachman, 1981) is a widely recognized process in this part of New Mexic o 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 eff ort to**  **characterize the subsurface strata. Each technique seems to have produced local anomalous**  **signal responses, suggesting that there might be local anomalies in the su bsurface, but there is**  **little overlap between the resistivity anomalies (Elliott Geoph ysical, 1976,1977), gravity**  **anomalies (Barrows et al., 1983), seismic anomalies (Barrows et al., 1983), to pographic**  **anomalies (Phillips, 1987), groundwater flow anomalies (Mercer, 1983, Crawley, 1988), potentiometric head anomalies (Beauheim and Ruskauff, 1998), groundwater geochemis**  **try anomalies (Mercer, 1983), and electromagnetic anomalies (Earth Technology**  **Corporation, 1987), and these do not coincide with the positions of the large Rustler karst conduits post**  **ulated by Snow (1998). A plausible case could be built for subsurface anomalies i**  **f indications of the anomalies from one or more of the different techniques overlapped in location, depth or siz**  **e, but the different techniques have provided scattered and inconsistent indications.**  **The failure of the different techniques to suggest the same locations for subsurf ace**  **anomalies highlights the difficulty and latitude in interpreting these te chniques. The sensors**  **have presumably responded to one or more real, physical features in the e arth, but there is rarely**  **a unique or even well-supported interpretation of that response. Recognition of thi s fact led to**  **drilling and coring of test holes in order to physically investigate the shall ow 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, alth ough only the WIPP**  **14 and WIPP-33 anomalies were discussed and attributed to subsurface karsting b y 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 comp arison 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 L ake**  **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 anomalousl y less dense than**  **normal and inferring that this difference accounts for the deeper local “seis mic 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 densi ty log response in the**  **WIPP-14 hole indicates that there is missing material. He extrapolates t his 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 c ontours (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 contour s 0.1 mGal.** **76**

6.2 The WIPP-14 Gravity Anomaly

**The gravity anomaly explored by the WIPP-14 drillhole is an elongate, narrow p attern 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 loc**  **ated 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 struc ture” 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 L ake Formation,**  **reported to lie between the depths of 141-639 ft in this hole (Sandia National Lab oratories 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 fr**  **om the density logs, or with the concept of karst development being in the Rustler Formation. Barrow**  **s 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 kar**  **st model he builds. The question of why karst should have formed in the Dewey Lake Formation rat**  **her 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 thi**  **s 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 f**  **ed the thick Gatuña fluvial deposits (see Figure 20) mapped by Bachman (1985) just to the north. This thick int**  **erval of relatively porous rock explains the local gravity anomaly more easily tha**  **n karst in the Dewey Lake or Rustler Formations. Elongation of the gravity anomaly is consistent w**  **ith this interpretation as a fluvial channel.** 
**Barrows also noted that seismic data at the WIPP site above the Castile Fo rmation “are**  **considered too unreliable to map” (1982, page 16), yet later in the report (page 57) us ed 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 tim e syncline and the**  **negative anomaly are explained by lateral velocity and inferred densit y 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 explaine d 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 b y**  **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 tw o intersecting 2-**  **D vertical gravity profiles specifically shot to assess the topogr aphic depression. The gravity**  **signature of the anomaly shows closure in all four directions in the two gravity li nes (Barrows et**  **al., 1983, their Figure 2.3.1-3, page 50), so it is probably roughly circular and pe rhaps 1500 ft**  **across. The overlying topographic depression is about eight feet deep and 200 f t 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 r elated to karst, is at a**  **depth of 450 ft. The text of the basic data report for WIPP-33 (Sandia National Laborator**  **ies and United States Geological Survey, 1981) notes that this well drilled through an “unusually thi**  **ck” sequence of “surficial Holocene deposits” (44 ft according to the abstract**  **, although this is difficult to corroborate in the accompanying Table 3 lithologic log). Thes**  **e deposits are described as filling a “small closed basin,” although the interpretati**  **on that the surficial basin was closed at the time of deposition appears to be speculative, or at least not suppor**  **ted with direct sedimentological evidence in the basic data report.**  **Much has been made of this gravity anomaly because it coincides with a surfac e**  **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 sever al 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-p orosity**  **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 l ogs from**  **this hole document depths for the stratigraphic tops that were penetrated tha t are on trend with**  **those of surrounding boreholes, i.e., the stratigraphic tops are not lower than norma l, 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 indicat e the** 
**locations of subsurface karst. These locations are around the WIPP-13 and H-3 dri llholes. Hill**  **(1999, p. 48) states that “both WIPP-13 and H-3 are located within negative gravity fea tures**  **(sinkholes?).” The Rustler strata cored in both these holes show some disruption, possible**  **indications of dissolution but more plausibly interpreted as syndepositiona l disruption since they**  **are overlain by undisrupted strata with primary depositional structure s. 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 T amarisk,**  **they also report two thin anhydrite beds and a polyhalite bed to the eas t in a stratigraphically**  **equivalent halite bed. This angular fragment can as easily represent a s tratigraphically 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, conver**  **ge with the base of A-3 westward from the depositional center of the unit. In addition, the shaft mapping s**  **hows a thin sulfate bed in this stratigraphic position, with a breccia and conglomer**  **ates 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 si**  **milar relief according to the gravity map (Barrows et al., 1983, their Figure 2.1-4), although Hill reports it a**  **s a -0.45 mgal depression. It is also circular and shallow, about 3500 ft across. Neither anomal**  **y 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 (thousa nds of feet**  **across) irregular gravity anomalies and small (hundreds of feet in diamete r), circular topographic**  **features, to reach poorly supported but definitively stated conclusions. Th ey have been selective**  **in using the array of available data, presenting only those data that they f eel support their concept**  **of subsurface karst and ignoring other data. They have not attempted to explain to pographic**  **depressions that do not have associated gravity anomalies, nor have they integrat ed the other**  **available remote sensing/geophysical data into their models and conclusion s. Most of the**  **anomalies considered by Hill are broad and shallow, not fitting a rigorous de finition of the term**  **“anomaly”: only the WIPP-14 and possibly the WIPP-33 anomalies could be considere d 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 characterize d by almost**  **no surface runoff” despite 12 inches of annual precipitation, and 2) because the chlor ide mass**  **balance techniques used by Campbell et al. (1996) suggested that infiltration of w ater through**  **the soils is not the major source of recharge into the Rustler Formation [“...our da ta do not**  **support direct infiltration through the overlying soil as the major source of a quifer 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 surfa**  **ce 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 simi**  **lar in shape or scale to the obvious stream piracy by sinkholes seen in Nash Draw and elsewhere in s**  **outheastern New Mexico (see Figure 11). In comparison, the short “disappearing arroyo” nea**  **r WIPP-33 (see Figure 8) does not actually reach the WIPP-33 enclosed surface expressi**  **on. Hill (1999, p. 42) therefore falls back on an artificial and not wholly analogous example wher**  **e water seeping from the Dewey Lake into the WIPP exhaust shaft “may be due to the focusing of wa**  **ter downward from the WIPP site parking lot (K. Larson, personal communication).” Water i**  **n fact is perched locally within the uppermost Dewey Lake Formation (Powers, 1997; Holt and Power**  **s, 1990a) at the WIPP site. Hill’s unproven implication is that the surface depressions a**  **t the WIPP-14 and WIPP-33 drillhole sites are locations similar to the parking lot in form and ef**  **fect. The analogy fails since the former would be resultant features, whereas the parkin**  **g lot catchment area is a**
**causative feature. Even if all 12 inches of rain came at once, potential runoff pathways across t**  **he 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-re**  **lief topography. Discussions of evapotranspiration rates and the rapid infiltrat**  **ion of rainwater into 81** 

**sandy material that blankets the WIPP site are given below under Rec harge and Discharge**  **Issues. The surface-water runoff argument is poorly defined, circumstant ial 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 somewh at open**  **ended 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 M agenta Members**  **and/or in the brine aquifer collect in Nash Draw and discharge at the numerous sp rings 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 water**  **s found in the Rustler have been significantly improved during recent studies, yet the si**  **gnificance 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 re**  **adily 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 latera**  **l 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 198 6 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 ca lculated 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 character**  **istics 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 dat a suggest that**  **hydrologically the formation comprises two different, although connected, sy stems. Within**  **Nash Draw, the data suggest that caves, sinks, fractured strata, and a thinner for mation allow**  **good hydrologic communication within the Culebra and Magenta Members of the Rustle r**  **Formation, rapid fluid flow, and, probably, recent local recharge. Eastward, how ever, where the**  **formation is protected by overlying strata, it is not disrupted and therefor e it has lower hydraulic**  **conductivity. Nondiscrimination between data from the two domains, which show a diffe rence**  **of nearly two orders of magnitude in transmissivity values (Powers et al., 2 003), 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 a rea 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 di scharge peaks,**  **and she did not try to correlate the volume of rainfall with volume of spring discharge. S he 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 b e**  **statistically meaningful since it did not account for factors such as irri gation, Pecos flood pulses,**  **or industry water withdrawals at Nash Draw, and because it made no differe ntiation between**  **precipitation over Nash Draw (where sinkhole catchment of drainage is known) and p recipitation**  **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 exer cise is to show that**  **actual measurements of recharge/discharge should be made in any serious att empt 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 presenc e of karst in the** 
**Rustler at the WIPP site. 84** 

**Ultimately, however, the poorly constrained behavior of groundwater in the are a 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 t o the east. Although**  **climatically similar, the geology and the surface catchments are diss imilar.** 

8.3 Recharge

**The following is a brief summary of groundwater recharge, flow, and discha rge in the**  **Rustler members at and near the WIPP site. Like the discharge points, rech arge mechanisms and**  **locations are typically assumed rather than documented. The water budget cal culated by**  **Geohydrology Associates (1978) suggests that in the WIPP site and Nash Draw a reas, water**  **inflow from precipitation and industry/oilfield brines exceeds outflow (eva potranspiration plus**  **discharge at the Malaga Bend springs) by 3,327 acre-ft per year. Thi s net increase appears to**  **correspond in general to the observed increase in potentiometric heads in the Cul ebra across the**  **area, although the exact source of recharge is debatable.**

8.3.1 Localized Recharge **Specific potential recharge locations, where the Rustler Formation cro ps out or is near**  **enough to the surface to be recharged by precipitation, are rarely spec ified by authors. The**  **Forty-niner, Magenta, Tamarisk, and Culebra Members of the Rustler Formati on all crop out in**  **various areas in Nash Draw. Several sinkholes that capture overland drainage a re obvious from**  **the air within this area of closed drainage (e.g., Figure 11), but details of the se sinkholes have not**  **been published, although Bachman (1981) did map a number of them. Because Nash Dra w is a**  **closed-drainage depression, rain falling into it evaporates, gets collec ted in the brine ponds, or is**  **funneled underground. Mercer (1983) suggested that the Rustler might also be rechar ged at Bear**  **Grass Draw, about 30 miles northwest of the WIPP site, but did not present data to s upport this**  **inference. Other authors have not offered opinions or evidence for locations where r echarge 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 N ash**  **Draw south of Laguna Grande de la Sal rose during the summer in conjunction with irrig ation,** **85**

**whereas water levels fell during this season in wells outside the areas of ir rigation. They**  **attributed this to direct recharge to the Culebra from irrigation operat ions. This correspondence**  **between water levels and irrigation is observed only in the southwestern en d of Nash Draw,**  **where the Rustler Formation is exposed, the Culebra is near to the surface, a nd 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 whe re the Rustler** 
**Formation is buried beneath insoluble sandstones. Brine effluents from potash mill operations have been discharged to the surf**  **ace for decades, and Geohydrology Associates (1978), treating the Culebra, the Rustle**  **r/Salado brine aquifer, the Santa Rosa Sandstone, and alluvium together as a single aquifer, suggest**  **ed 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 r**  **aised 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 underly**  **ing Culebra waters, suggests that there is no chemical signature from the tailings in t**  **he local groundwater (Powers and Richardson, 2004b).**  **Geohydrology Associates (1978) noted that the water chemistry from specif ic 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 br ines discharging from**  **the springs at Malaga Bend indicates little communication between disc harge ponds and the local**  **aquifers.**

8.3.3 Infiltration of Precipitation **Geohydrology Associates (1978) suggested that 60% of the water inflow to local aquife rs**  **in Nash Draw and surrounding areas comes from the 12 inches of precipitation p er 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 Assoc iates, but it is**  **significantly higher than the 0.2-2 mm/yr infiltration rates calculated mor e recently by Campbell**  **et al. (1996) for a much more restricted area on Livingston Ridge. Corbet (1998) and Corb et and**  **Knupp (1996) have suggested that some of the lateral variations in geochemical sig natures 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 ent ers the higher**  **permeability sandstones of the Dewey Lake and Santa Rosa Formations, and t hat only a limited**  **vertical “leakage” of this water filters down into units of the Rustler Forma tion.**  **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 p recipitation into the aquifers**  **in that area of Nash Draw. However, influx of water into the more deeply burie d 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 r ainfall**  **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 ra pid, karst-related water**  **level 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 direct ly**  **measured, but rather are inferred from measurements of the potentiometri c heads in the different**  **units using the assumption that water flows down pressure gradients. Flow direc tions, 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 direc**  **tions 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 rec**  **harge areas. The proponents of karst, however, suggest that the data are compatible with rapi**  **d present-day flow westward away from the WIPP site to nearby discharge areas. More rec**  **ently, 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 (Me rcer, 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) corroborate**  **d the inferred Culebra flow directions, and contributed several three-well pressure-dif**  **ference 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 wa ter 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 relative ly rapidly through the**  **Rustler Formation from recharge areas to point(s) of discharge, the rapid f low 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 slowl y if at all**  **since recharge during the Pleistocene. Campbell et al. (1996) also studied oxygen isotopes, in the local soil profiles ra**  **ther than from the Rustler, and reached a corroborating conclusion that there is the pote**  **ntial for only “a small amount of infiltration (.2- to 2 mm/yr) through the desert soil” down to rechar**  **ge the Rustler, and that therefore “water in the Rustler Formation need not have been rec**  **harged in the past (>10,000 yrs) under different climatic conditions” (page 153). However, t**  **hey complicated their interpretations by stating that, since their data did not support surfi**  **cial 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 direc**  **t 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 be**  **ing recharged at present, only that there is minimal potential for recharge. The inference r**  **elating to karst is speculation, and not based on their data or on subsurface water sampling, and Campbe**  **ll et al. do not require nor state that recharge through karst is occurring at the WIPP s**  **ite itself. 88** 

**Siegel et al. (1991) report radiocarbon dates from Culebra waters that indi cate ages of at**  **least 10,000-16,000 years, supporting Lambert and Harvey’s (1987) isotopic data and inf erences**  **of slow rates of groundwater movement within the Culebra. Siegel et al. also mea sured**  **hydrogen ratios in gypsum and noted that the ratios are not consistent with the form ation of**  **gypsum by the hydration of anhydrite by meteoric waters, again supporti ng a model where**  **groundwater does not move quickly through the Rustler Formation. Finally, they comp ared the**  **strontium ratios in gypsum and carbonates in the Rustler, Dewey Lake, and surf ace rocks, and**  **showed that the secondary sulfates and carbonates in the Rustler did not form in a hydr ological**  **regime connected to the surface. These isotopic data and interpretations, except for the interpretations of t**  **he same data presented by Chapman, support a model of slow groundwater movement through the Rustle**  **r Formation.** 

8.4.3 Water Chemistry Domains and Flow Directions **Several geochemical domains are recognized in the water-bearing me mbers 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 dir ection on the**  **grounds that waters that have been in an aquifer system longer have had more tim e to interact**  **with the chemistry of the host strata and are therefore more highly mineraliz ed. However, such**  **an interpretation runs counter to the measured heads in the Culebra and Magenta (Figur es 23 and**  **24), which suggest southerly and westerly flow, respectively. Different authors have mapped and interpreted the groundwater chemistry dom**  **ains of the Rustler Formation in slightly different ways. Ramey (1985) defined three geochem**  **ical zones (Figure 27):** 

• **Zone A from the eastern WIPP site to the east, with NaCl-type water w ith high**  **concentrations of K and Mg;**

• **Zone B south of the WIPP site, with CaSO 4**  **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 differentia ted**  **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; i n Nash Draw,**  **however, the groundwaters are not confined to the Culebra reservoir and some mixing i s likely.** **90**

**Figure 28. Geochemistry domains for Culebra waters as suggested by Chapm an (1988)**  **(including arrows indicating “idealized groundwater flow paths.”)**
**Siegel et al. (1991) split off the western part of Nash Draw in mapping f our recognizable**  **water-chemistry facies in the Culebra (Figure 29):**

• **A: eastern half of WIPP, highly saline, TDS >100,000 mg/L, NaCl type water r ich**  **in Mg and Ca**

• **B: southwest of WIPP and south, relatively fresh water, TDS <10,000mg/L,**
**CaSO 4**  **type water**

• **C: east half of Nash Draw and east to mid-point of WIPP, NaCl-dominated wat ers**  **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 eff luent** **91**

**F igure 29. Geochemistry domains for Culebra waters as suggested by Siegel et al. (1991).**  N

W I PP-29 e / / / / / /

South Well 0 WIPP

- 27 

### e/



## ~/

I

**~I** 

### I I I Q 

### I 

# •
WIPP-28

e WIPP-30

DOE-2 e
H -6 WIPP-13 _/ 

# . / t H-5 / / (

- e WIPP-19 '-- WIPP-Site / Boundary

P -14 e H- 1 6

. -, H-2 e e H- 1 e H-15

H -3 · 

### I

H

- 1 4 e . e D OE -1 )

e H-1 1
H -4 e /

.,.-· 

## ----·-·

**---- ~**  W indmill Well Q

· , 

### I • P

- 17

e FR

- 10 //,.. / 

## "

**~/~ "** 

-:::. 

# "

H -7 e -2 

# • H

- 12 

# ' A

**~,-** 

# "

0 Indian Well "-'' " 

# c

- - - - ----- \ ,1\1• ,\

**\~\\** 1/l;, \ \\\ '

"'' •tl(:'- " ,\

**~,,** USGS-8 " I '

**~'** USGS

- 4 00 D Gnome Shaft ' ::- 0 USGS- 1

H -9 e 

### 8 e E ngleWe ll 

## · 

# . .. H- 1 0 e

Two-Mile We l l 0

0 2 3 4 mi

0 2 4 6 km H-8 

# • A
, B, C, D F ac i es F ac i es Bor d e r o 0 • Well Loca t io n

, 1\ l • • t/

1 , Na s h Dra w

TR I -6331 -78

- 4**92**

**In a relatively uniform, confined aquifer, solute concentrations should generally inc rease**  **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, sugg**  **est 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-beari**  **ng 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-SO 4**  **waters corresponds to an area where salt is not present (“complete removal”). Local non-deposition of halite would explain the water c**  **hemistry equally well, but the basic idea, that formation waters are less saline where t**  **here is less interbedded formation halite, is plausible. Chapman also suggested that the “major hydroche**  **mical facies change from Na-Cl to Ca-SO**  **4 ” 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 bee**  **n used to support an interpretation that flow through the formation, no matter in what direction, is slow**  **er in the eastern region, i.e., that long residence time has allowed greater rock-water i**  **nteraction and resulted in greater mineralization of the water (e.g., Mercer, 1983). This infere**  **nce 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 i**  **n western wells. Mercer (1983) also inferred slower groundwater movement under the WIPP site, the boundary be**  **tween fast and slow movement being at approximately the western edge of the si**  **te. The discrepancy in flow directions inferred from the different data has als**  **o been suggested to be caused by a Pleistocene flow reversal: Ramey (1985) and Si**  **egel et al. (1991) note that modern (potential) flow directions within the Culebra are not consistent w**  **ith 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 e**  **t al. (1991) report 93** 

**eastward-increasing uranium isotope ratios suggestive of “recharge from a near-surface**
**P leistocene 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 

# l
D



## .·· .·

**/south~ell'**



### B e WIPP-30

H-9• Engle Well• 

### .. 

### ··
H

- 5

/WIPPSite Boundary



### A

A, B. C, D Facies

====:) Paleoflow Direction

_,. Flow Direction

- ·- Facies Border

o, o , • Well Location

dho • • olho

. ' ''"" Nash Draw**94**

**Corbet (1998) suggests that the different chemistry domains observed in the Cul ebra, as**  **well as the apparent discrepancy between flow directions inferred from t hese domains and the**  **flow directions inferred from the potentiometric heads, do not have to be explaine d by lateral,**  **strata-bound migration of water through the formation. He suggests that the geochem istry**  **domains can best be explained by considering that all members of the Rus tler 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 sout h and west of the**  **WIPP site, than were halite is abundant in the Rustler, such as east of the WIPP s ite. Thus the**  **chemistry domains are related to different amounts of vertical leakage thr ough varying**  **geochemical/host-rock environments rather than to lateral flow and varying re sidence times of**  **the waters in the formation. This interpretation is consistent with the obser ved heads.**  **Regardless, the high salinities and mineralization in the Culebra at the WIP P site are not**  **compatible with the rapid groundwater flow rates typical of karst conduit s 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 indi cate where the**  **Rustler members discharge. One’s perception of whether or not defining sp ecific discharge**  **locations is a problem depends on whether or not one believes the Rustler mem bers are presently**  **being recharged to a significant degree and if so, whether this recharge occ urs at WIPP: if the**  **Rustler is accepting water and passing it rapidly through a high-volume, hi gh-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 pointe d out by Lambert (1983),**  **dissolution of a geologic system of evaporites cannot take place if no outlet s 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 rel**  **atively 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 are**  **a 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 t**  **hat 350 tons of salt a day and 200 gallons per minute were being discharged via these spr**  **ings. 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 M**  **alaga 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 aqui fer 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 catchm ent 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 wa ters flow towards**  **Laguna Grande de la Sal, making it a possible discharge point. However, the y also noted that the**  **chemistry of the lake water is different from that of the local groundwate r, 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 catchme nt might**  **include Surprise Spring at the edge of, or sometimes submerged below, Laguna G rande de la Sal.**  **Geohydrology Associates (1978) believed that two-thirds of the topographic holl ows, including**  **local lakes in their study area (centered on Nash Draw) are likely to b e 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 discha rge into Laguna**  **Pequena, and Sares (1984) for other karst-type point source discharge locations fur ther south in**  **the Pecos River valley. These discharge points are plausibly, even probably, sourced in the Rust**  **ler Formation, but no definitive data have been collected to indicate what parts of the Rustle**  **r are contributing to them. Karst and high hydraulic conductivities in the Nash Draw area contrast wit**  **h the low hydraulic conductivity Rustler Formation characteristics measured at the**  **WIPP site, and the simplest interpretation is that the discharged waters at Malaga Spr**  **ings are derived primarily from Nash Draw. Although Hill (1999) suggests that Surprise Springs at the edge of L**  **aguna Grande de la Sal within Nash Draw is a possible discharge point for the Nash Dra**  **w 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 drai ned the upper Rustler**  **Formation from below the WIPP site, discharging at the base of the near by Livingston Ridge** **97**

**escarpment. Hill (1999, p. 53) took this piece of data and extended it to infer that gy psite springs** 
**indicate karst. Whether or not gypsite springs indicate karst, on closer examination, the gypsit**  **e deposits reveal few definitive features that are diagnostic of their origin. Althoug**  **h 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 f ormed around springs**  **that produce highly mineralized water. Gypsite sand is currently forming i n Nash Draw where**  **the primary gypsum/anhydrite beds are exposed to weathering and er osion (Figure 32), but the**  **local active springs are not forming and depositing gypsite. Some of the gypsite deposits in the area display eolian crossbedding (Fi**  **gure 33), suggesting that gypsite originated as weathered sands, reworked by wi**  **nds and deposited as dunes. The gypsite deposits near WIPP-25 probably do not record the locations of s**  **pring 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 eol ian 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 discha rged 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 sup ports the hypothesis that**  **water gets from the surface into and through the Rustler, and to the discharge point s, but does not**  **specify a recharge mechanism. Recharge mechanisms might include locali zed 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 t he confines of Nash**  **Draw, but that the same aquifer horizons are entirely different systems w ith different** **99**

**characteristics to the east, under the WIPP site. There, a higher degree of m ineralization of the**  **formation waters, lower measured hydraulic conductivities, and isotopic st udies support a system**  **of slow groundwater flow. The potentiometric head data suggest that flow in the Rust ler**  **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 i s 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 regiona lly, 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 membe rs 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 fe w 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), a pparently**  **drawing on Snow’s (1998) paper, suggests that the hydraulic heads are also equal i n the vicinity**  **of H-6 and WIPP-13, inferring that this indicates hydraulic communication bet ween the two**  **units (“...that the integrity of the Magenta and Culebra as distinct water-be aring zones has been**  **breached...” : Hill, 1999, page 56). Hill then suggests that this implies the develo pment of karst**  **passageways at depth. Chaturvedi and Channell (1985) have also suggested that there is vertical, karst-rela**  **ted, cross-stratigraphic hydraulic connection between the Magenta and Culebra**  **west of the WIPP site, based on a gradual, westward merging of the potentiometric heads fr**  **om 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 e**  **xists between the two members. Implying that it does is an example of using isolated data p**  **oints 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) somewhe**  **re. The crossover line is not a physical intersection; it is a line on a map where the two pote**  **ntiometric 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 pote ntiometric surface**  **near the northwest corner of the WIPP site (Figure 24). The crossover line foll ows the trend of**  **Livingston Ridge northwest of the WIPP site and includes WIPP-25, extends from ther e 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 hydra**  **ulic heads and water chemistries from the Culebra and Magenta are similar (L**  **ambert and Robinson, 1984) and where hydraulic connectivity between the members might in fact be ex**  **pected, the absence of any response in the Magenta while the Culebra was pumped rec**  **ently (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 chlori de**  **concentrations between the Magenta and Culebra in the adjacent test well s 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 evidenc**  **e 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 drawdow**  **n was observed in H-6a and H-6b, both completed in the Culebra at that time, but no resp**  **onse was observed in H-6c, completed in the Magenta (Beauheim, 1987c). Lack of connection be**  **tween Culebra and Magenta has also been repeatedly demonstrated during the WQSP wa**  **ter 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 ar e pumped** 
**at WIPP-25 and H-6 shows that the members are not well connected and that karst condui ts 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 wel ls**  **have been muddled by careless use of the data. For example, Snow (1998, 2002), repeate d 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 anhy drite.**  **However, such data were never obtained from two of these wells: the water l evels in the** **102**

**Magenta have never been monitored at WIPP-13, and water levels have never been monit ored in**  **either the Culebra or Magenta at WIPP-33. Thus, there is no factual basis w hatsoever for**  **Snow’s assertions regarding WIPP-13 and WIPP-33; the data from the other two well s have been** 
**addressed above. Some of Snow’s conceptual modeling is physically impossible and/or interna**  **lly inconsistent. For example, if the hypothetical karst channels are located ab**  **ove the present water table as postulated, their effects will not be apparent, and their exist**  **ence 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 al**  **so requires that they must be located above the present water table, which is in the siliciclasti**  **c Dewey Lake beds. This is inconsistent with the location of the strata that would be prone to karst dissoluti**  **on, 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 i s a localized**  **phenomenon, the inevitable intersection of two non-parallel surfaces, that has no re gional**  **significance. Water chemistry and the lack of interference during pumpi ng tests both support**  **hydraulic isolation of the Culebra from the Magenta, and argue strongly agains t the development**  **of a subsurface karst system within the Rustler Formation at the WIPP sit e.** **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 chemist ry and**  **salinity are characteristic of groundwater in karst systems, due to local i nfluxes of fresh water at**  **sink holes that would mix erratically at depth with long-term residence mat rix water already in**  **the system. She then cites examples of spatial variability in the chemi stry of the Culebra**  **formation waters and argues that they indicate the development of a subsurfac e karst system at**  **and near the WIPP site. Hill does not correlate the observed geochemical va riations 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 diffe rent ways, and**  **the rate at which it changes laterally is an important characteristic f or this discussion. Different**  **divisions of the subsurface water chemistry in the Culebra have been previ ously illustrated in**  **Figures 27 through 29. The three schemes of mapping variations in the water chemist ry in the**  **Culebra are basically compatible. The lines drawn on the maps by the a uthors to divide the**  **geochemical domains are somewhat arbitrary since the chemical composit ion 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 kars t sinkholes. The water**  **chemistry varies gradually and on a broad scale (kilometers). No e vidence is seen of significant** **104**

**water quality changes between wells tens or a few hundred meters apar t, nor are anomalous**  **“pockets” of relatively fresh water found that are surrounded by wells cont aining more saline** 

**water. Hill cites Chapman (1988) as mapping regions of low salinity and facies cha**  **nges from**
**Na-Cl to Ca-SO 4**  **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 tw**  **o of the water facies domains (Figure 28); Ramey (1985) draws the boundary between his sim**  **ilar zone A and zone B geochemical water facies a mile or more to the east (Figure 27). The p**  **ositions 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 necessaril y prove the presence**  **of karst at depth. Rather, the characteristics of that variation should be analy zed and compared**  **to measured chemistry variations in known karst systems or to expected vari ation given modeled**  **rates of fluid flux and the potential reactivity between water and the host ro ck.** 

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 indica**  **te 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 di**  **ssolution of evaporite minerals co-existing with the halite.” From these, she inferred that the “m**  **ajor hydrochemical facies change from Na-Cl to Ca-SO**  **4 ” 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 tha**  **t therefore halite has been dissolved from the western parts of the study area, or that on**  **e can therefore assume that this implies the development of karst. Siegel et al. (1991) als**  **o 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 hal**  **ite 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-c hloride**  **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 abs ence of halite does**  **not dictate a choice between these two options. However, making the choice has im portant**  **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 w as never there, as**  **argued above in this report, then the strata were not subjected to halite dissol ution and karst is**  **unlikely to have developed. Calcium-sulfate waters could have developed where s alt 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 characteristi c of karst, and uses**  **the bald, broad fact of salinity variations across the region of the WIPP sit e, not the specific**  **characteristics of that variation, as evidence for the probable subs urface 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 sci entific process and**  **logic which use specific data to prove or to construct broader-scale inter pretations.**  **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 Format ion 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 tha t would be expected in**  **adjacent holes that sampled both fresh, karst-introduced meteoric waters and saline, long**  **residence waters. Hill’s one example of local extreme variability tur ns out to be suspect,**  **possibly contaminated data. The variability of formation waters found withi n the confines of**  **Nash Draw is of a different, more highly variable scale, but both hydrolog ically 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 kars t. These examples** 
**are examined below. The WIPP-13 drillhole was sited to investigate the possibility that a resi**  **stivity anomaly reported by Elliott Geophysical (1977) was caused by a geological fe**  **ature 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 re**  **sistivity anomaly is located within the area of a broader gravity anomaly, further pi**  **quing interest in this site. However, the drillhole penetrated a normal stratigraphic section wi**  **th 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 thi s hole, and**  **the pumping tests at this site that produced anomalous (to her) responses, indica te karst. Hill**  **cites the mere presence of well-test variations, without investigati ng or analyzing their**  **characteristics, to support an interpretation of karst in the Rustler Forma tion at this site, and she**  **does not describe stratigraphic relationships or sedimentological charac teristics from the core**  **that would allow distinctions to be made between post-depositional, solution-r elated disruption**  **and syndepositional disruption of bedding.**

11.2 Drawdowns

**As noted above, Hill (1999, p. 59-61) suggests that there were significant variat ions**  **during a pumping test at WIPP-13. Beauheim (1987c) did report a no-flow boundary, indi cating**  **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 b oundaries can be**  **caused by sealed faults and sedimentary limits to a reservoir, or by other t ypes of lateral**  **decreases in permeability. 107** 

**Beauheim also reported several ambiguous responses to the WIPP-13 pumpi ng test in**  **observation well ERDA-9, a mile and a half to the southeast. These included: 1) drawdo wn was**  **several hundred hours “late” in ERDA-9, suggesting that no high-flow pathway connect s 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, hi gh-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 sim**  **ilarly to those in ERDA-9, “as if a withdrawal of fluid from the Culebra at some location tempor**  **arily 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 pre**  **ssure response to pumping tests Hill and/or Snow would expect from their hypothetical karst channe**  **ls. The response would be entirely different for fluid-filled or air-filled condui**  **ts below or above the water table respectively and neither Hill nor Snow are consistent in defining t**  **he 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 damp**  **ening effects on the magnitude of pressure responses due to the larger reservoir v**  **olumes involved.**

11.3 Breccia and Mixing in the Core

**Hill (1999, page 38) notes the presence of “collapse breccia and mixing of str atigraphic**  **units” in core from the WIPP-13 drillhole, arguing that these indicate the prese nce 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 80 o**  **in WIPP-13).”**
**Hill does not indicate the extent of brecciation or the size of the breccia cl asts, i.e., how**  **extensive, and therefore how significant, this breccia might be, and infer s 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 strati**  **graphic 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 p**  **art 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 exp**  **ect it to look like. This is correct in the sense that it is also exactly where localize**  **d, bed-boundary dissolution related merely to the presence of water in the Culebra has been observ**  **ed; however, it does not imply a widespread karst system. This dissolution horizon is localized adja**  **cent to the Culebra aquifer where it is not unexpected. It is present in other cores, and dissoluti**  **on has not developed from this into a widespread karst system. The undeformed beds of the overlying st**  **rata 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/ Anhydrit**  **e-3 contact (in the Tamarisk Member, between the Magenta and Culebra Members). Exa**  **mination 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 lam**  **inated 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 wa ys. The**  **lower interval is most easily explained as a limited zone of dissolution adjac ent to the water**  **bearing Culebra, whereas the upper interval is probably of syndepos itional 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 possibil ity that a circular**  **surface topographic depression, about 700 ft in diameter, 10 ft deep, and located abov e the axis**  **of a much larger gravity anomaly, is large enough to have collected sufficie nt water to create a**  **major sinkhole. Controversy exists over the nature, or at least of the interpretat ion, of the rocks**  **interrogated by this drillhole. Hill (1999) suggests that the conversion of anhydri te to gypsum in**  **certain beds, and a calculated mass deficiency related to that conversion, in dicate 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 probab**  **ly related to deep seated dissolution of the halite and gypsum in the Rustler Formation”, and that five sha**  **llow, ephemeral “watercourses” drain into this zone. The watercourses supposedly r**  **elated to this chain are not mapped by Phillips, and no depressions other than at the WIPP-14 site, no tr**  **ends of vegetation, and no watercourses, were apparent during a low-level aerial re**  **connaissance over**
**this area in March 2005. The maps presented by Phillips in support of a correlation between the g**  **ravity anomaly and irregular patterns of both “calcareous dissolution residues” and “struc**  **tural depressions in the [Mescalero] caliche” surface are self-fulfilling. Phillips’ ma**  **ps (his Figures 69 and 70, page 207) show only the patterns of residues and depressions that are within and near the genera**  **l outline of the gravity contours. Demonstration of an absence of these residues and depressi**  **ons in areas outside of the gravity contours would be plausible evidence for a correlation, b**  **ut 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 t he 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, pa**  **ge 1; Sandia National Laboratories and D’Appolonia Consulting Engineers, 1982). The lithology penetrat**  **ed by the rest of the hole was reconstructed from cuttings and the geophysical logs. The c**  **ore 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 f**  **rom nearby control points, and bedding is in a normal, flat-lying attitude (Sandia National Lab**  **oratories 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 core**  **recovery percentages were consistently high. The geophysical logs run i n 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, b ut 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 lithologi c 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 b oth the**  **Magenta and Culebra, for a few tens of feet before reverting to thick anhydrit es. The presence of**  **gypsum in these intervals is not unexpected since the Magenta and Culebra ar e water-bearing,**  **and hydrated anhydrite in these positions is normal. Thus the presence of gy psum is not a strong**  **argument for the presence of karst in or near this drillhole. Gypsum occurs in va rying amounts**  **in most of the Rustler sulfate beds across the WIPP site, so the presence o f 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 defic iency**  **(negative gravity anomaly) at WIPP-14 to be due to density variations cause d by the hydration of**  **anhydrite to gypsum in the Rustler Formation.” Some layers of hydrated gyp sum were**  **penetrated in this hole, but without concurrent removal of some of the strata, for which t here is**  **no evidence, hydration would add mass to the system, resulting in increased thickness of t he**  **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 WIP**  **P-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 hy**  **dration 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 calc**  **ulations were presented to show whether the volumes of anhydrite in WIPP-34 are sufficient, whe**  **n expanded by 38% as gypsum forms, to maintain formation thickness in WIPP-14, or that the thic**  **knesses 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 Ta**  **marisk 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 diminis**  **hed 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 possibl e cause for thickening**  **and thinning of the evaporite facies of the Rustler Formation because the re lated and less soluble**  **Magenta and Culebra are uniformly thick and “remarkably persistent” acr oss 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 w ay shallow evaporitic**  **salt pans are, and the Culebra and Magenta Members of the Rustler Formati on 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 s**  **urvey to model a shallow density change at WIPP-14. Nevertheless, they inferred fr**  **om 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 Forma tion, 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 evi**  **dence of missing material was found in either cores or in the subsequently run geophysical lo**  **gs. The apparent mass deficiency calculated by Barrows et al. for the elonga**  **te gravity anomaly near the WIPP-14 drillhole can be accounted for by what appears t**  **o be a thick interval of the low-density Gatuña Formation in the core at the top of the WIPP-14 hole. This w**  **ould be a tributary to the deep Gatuña drainage channel mapped by Bachman north of the WIP**  **P site (see Figure 21). Similar thick Gatuña deposits have been encountered on trend with the p**  **aleo-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 Memb er**  **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 E ngineers, 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 Phill ips (1987), even though**  **the geophysical logs for this interval show an entirely normal signature, inc luding 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-br own 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 p si), 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 subs urface 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) label**  **s an uncored 240-ft interval with the term “No Core”. This notation was suggested to be evidence o**  **f 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 consecuti**  **ve core numbers (#99 above and #100 below the uncored interval) indicate the logistical rathe**  **r 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 benea th WIPP-14 are direct**  **evidence of rainwater infiltration” (Phillips, 1987, page 25). Carbonate filli ng in fractures can be**  **precipitated from carbonate-rich waters at any depth, and in fact cal cite (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). Thi s is an example of the**  **common practice of presenting bald data as tenuous proof of a concept, with out 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 WI PP-14**  **drillhole. Proponents of karst at this location have misinterpreted annotations in t he lithologic**  **log and have ignored critical complementary evidence such as the geophy sical logs. The**  **stratigraphic section penetrated by the drillhole has not been disrupte d or displaced by karst**  **related 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 adja cent to the**  **Culebra and Magenta water-bearing units. The ambiguous data that have been su ggested 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 breccia**  **tion of strata in these holes can be readily attributed to local dissolution adjacent to the Mage**  **nta 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 a re found within the**  **interval M-3/H-3” in this interval correspond to a highly transmissive zone in the C ulebra in the**  **southern part of the WIPP site. 116** 

14.0 SUMMARY

**Analysis of the primary data suggests that the overwhelming majority of d ata 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 ar**  **e 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 t hat the early conclusions**  **reached by these studies were incomplete. This planted the seeds for fut ure misinterpretation.**  **Interpretations of “insoluble residues” in the cores were based on undevelop ed theory, faulty**  **analogy, and severely limited exposures. These early interpretations, how ever, now constitute an**  **inheritance that interferes with a valid interpretation of these strata i n light of more detailed and**  **accurate knowledge of sedimentary environments developed during the last few de cades. 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 su bjected to post-burial**  **dissolution. Most of the observed disruption of bedding can be related to syndeposi tional**  **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 the**  **se depressions as sinkholes have been taken out of context and have other, more scientifically valid and be**  **tter supported interpretations. The characteristics of these few supposed sinkhol**  **es 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 Rustl**  **er 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 deposit**  **ional thinning and thickening that is common to the Rustler Formation across the Delaware Bas**  **in, and which was caused by the irregular Permian depositional topography.** **117**

**Rustler halites were deposited in shallow depressions (“pans”) on this depo sitional**  **surface at the same time that muddy deposits were accumulating at the ma rgins of the pans, and**  **this lateral facies equivalency, a well documented and founding principle of st ratigraphy, 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 t he 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 w aters that were**  **not affected by the low-relief topography of the depositional surface. I t would be impossible to**  **obtain the observed thicknesses of muddy and silty deposits that have been c alled “residues” by**  **dissolving the limited available volume of muddy and silty halite. Moreover, the sil ty and**  **muddy beds do not contain evidence of other insoluble remnants that are common in the thic ker** 
**halite beds. The concept that Nash Draw is the largest of a series of sequentially smal**  **ler 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 d eposits exposed**  **at the surface by a local, large drainage system during Pleistocene t ime. There was no equivalent**  **to this at the WIPP site, where the Rustler Formation was and is deeply burie d, 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 preferentiall y along the**  **numerous horizontal fractures present in the Rustler Formation and since the p robability of**  **hitting a horizontal plane with a vertical drillhole is high. The large-diamet er shafts excavated**  **into the WIPP repository have provided a large subsurface sampling, at a l ocation 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 sha**  **fts 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 corroborat**  **ed 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 probabl y 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 wa ter 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 sup**  **porting patterns that could be definitively related to specific locations for kar**  **st-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 t**  **ributary system. The poor development of surface drainage over the WIPP site is due to the absenc**  **e of requirements for such a drainage network. The low rate of precipitation, th**  **e presence of sandy surficial deposits that quickly soak up precipitation, the low dip of the stra**  **ta that does not funnel drainage in any particular direction, and the shifting of dune sands that blocks dr**  **ainage 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 org**  **anized system of sinkholes and subsurface drainage to explain this pattern.**  **Recharge, flow, and discharge of water in the Rustler Formation are largely t heoretical.** 
**Few direct measurements or observations of this flow are available ex cept for the brine discharge**  **from springs at Malaga Bend on the Pecos River, and this discharge is probabl y from the brine**  **aquifer at the Salado-Rustler contact, and limited to drainage from Nash Dra w. The springs do**  **not support the existence of a karst system in the Rustler Formation at the WIP P site.**  **The coincidence of the Culebra and Magenta potentiometric heads between N ash 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 a ddition 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 t he 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 w ell-test variations is** **119**

**ambiguous, but the mere fact of variations does not prove the presence of ka rst as suggested;**  **their characteristics must be analyzed. The proponents of karst in the Rustler Formation at the WIPP site tend to mix da**  **ta, to take data out of context, and to offer theory as fact and to continue to offer misconcep**  **tions 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 sp**  **ecific characteristics of that variation as evidence for the probable subsur**  **face development of intra stratal karst, and has used generalized concepts and theory to suggest that spe**  **cific interpretations have been proven. This is an inversion of the standard and more widely accepted scient**  **ific process that uses specific data to prove or to construct broader-scale i**  **nterpretations. When the specific data cited by the proponents of karst at the WIPP site a**  **re examined, they are commonly non-unique in their possible interpretation. More plausib**  **le, less complex interpretations are usually possible. The data are cited randomly rath**  **er than being assembled into an interlocking and mutually supporting scientific case for the pres**  **ence 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 strat a of the Rustler**  **Formation at the WIPP site have not been subjected to dissolution since the time of deposition.** **120**

REFERENCES
**AGI (American Geological Institute), 1972, Glossary of Geology, 805 pages p lus appendices.** 
**Bachman, G.O., 1981, Geology of Nash Draw, Eddy County, New Mexico: U.S. Geological Survey Open-File Report 81-31, 8 p.** 
**Bachman, G.O., 1985, Assessment of Near-Surface Dissolution at and Near the Waste Isolation**  **Pilot Plant (WIPP), Southeastern New Mexico: SAND84-7178, 28 p.**
**Bachman, G.O., 1990, Evaporite Karst in the Pecos Drainage, Southeastern New Mexico, i n,**  **Geological and Hydrological Studies of Evaporites in the Northern Delaware Ba sin for the**  **Waste Isolation Pilot Plant (WIPP), New Mexico, Field Trip #14, November 1-4, 1990,**  **Geological Society of America, p. 181-186.**
**Bachman, G.O., and Machette, M.N., 1977, Calcic soils and calcretes in the southwestern U nited**  **States: U.S. Geological Survey Open-file Report 77-794, 163 p.**
**Barrows, L. J., 1982, WIPP Geohydrology – The Implications of Karst: Memo to W.D. Wea rt,**  **21 p.**
**Barrows, L.J., Shaffer, S.-E., Miller, W.B., and Fett, J.D., 1983, Waste Isolation Pilot Plant**  **(WIPP) Site Gravity Survey and Interpretation: SAND82-2922, 113 p.**
**Barrows, L.J., and Fett, J.D., 1985, A high-precision gravity survey in the Delaware Basin of**  **southeastern New Mexico: Geophysics, v. 50, p. 825-833.**
**Beauheim, R.L., 1986, Hydraulic-Test Interpretations for Well DOE-2 at the Waste Isolation**  **Pilot Plant (WIPP) Site, SAND86-1364, Albuquerque, NM, Sandia National Laborator ies.** 
**Beauheim, R.L., 1987a, Analysis of Pumping Tests of the Culebra Dolomite Conducte d at the H**  **3 Hydropad at the Waste Isolation Pilot Plant (WIPP) Site, SAND86-2311, Albuquer que, NM,**  **Sandia National Laboratories.**
**Beauheim, R.L., 1987b, Interpretations of Single-Well Hydraulic Tests Conduc ted At and Near**  **the Waste Isolation Pilot Plant (WIPP) Site, 1983-1987: SAND87-0039, Albuquerque, NM, Sandia National Laboratories.** 
**Beauheim, R.L., 1987c, Interpretation of the WIPP-13 Multipad Pumping Test of the C ulebra**  **Dolomite at the Waste Isolation Pilot Plant (WIPP) Site: SAND87-2456, 171 p.**
**Beauheim, R.L., 1989, Interpretation of H-11b4 Hydraulic Tests and the H-11 Multi pad**  **Pumping Test of the Culebra Dolomite at the Waste Isolation Pilot Plant (WI PP) Site, SAND89-**  **0536, Sandia National Laboratories. 121** 

**Beauheim, R.L., and Holt, R.M., 1990, Hydrology of the WIPP Site, in, Geological and Hydrological Studies of Evaporites in the Northern Delaware Basin for the**  **Waste Isolation Pilot Plant (WIPP), New Mexico, Field Trip #14, November 1-4, 1990, Geological Society**  **of America, p. 131-179.** 
**Beauheim, R.L., and Ruskauff, G.J., 1998, Analysis of Hydraulic Tests of the Culebra and Magenta Dolomites and Dewey Lake Redbeds Conducted at the Waste Isolation Pi**  **lot Plant Site: Sandia Report SAND98-0049, 226 p.** 
**Beauheim, R.L., Dale, T.F., and Pickens, J.F., 1991, Interpretations of Single-Well Hy draulic**  **Tests of the Rustler Formation Conducted in the Vicinity of the Waste Isolation Pi lot Plant Site,**  **1988-1989: SAND89-0869, Albuquerque, NM, Sandia National Laboratories.**
**Campbell, A.R., Phillips, F.M., and Vanlandingham, R.J., 1996, Stable isotope study of soi l**  **water, WIPP site New Mexico: Estimation of recharge to Rustler Aquifer s: Radioactive Waste**  **Management and Environmental Restoration, v. 20, p. 153-165.**
**Chapman, J.B., 1986, Stable Isotopes in Southeastern New Mexico Groundwater: Im plications**  **for Dating Recharge in the WIPP Area: EEG-35, 76 p.**
**Chapman, J.B., 1988, Chemical and Radiochemical Characteristics of Groundwater in t he**  **Culebra Dolomite, Southeastern New Mexico: EEG-39, 63 p.**
**Chaturvedi, L., and Channell, J.K., 1985, The Rustler Formation as a Transport Medium for Contaminated Groundwater: EEG-32, 84 pages plus appendices.** 
**Chaturvedi, L., and Rehfeldt, K., 1984, Groundwater occurrence and the dissolution of salt at t he**  **WIPP radioactive Waste repository site: EOS, Transactions of the Ameri can Geophysical Union,**  **v. 65, p. 457-459.**
**Chugg, J.C., Anderson, G.W., King, D.L., and Jones, L.H., 1971, Soil survey of Eddy area, New Mexico: US Department of Agriculture, Soil Conservation Service (in coopera**  **tion with New Mexico Agricultural Experiment Station).** 
**Corbet, T.F., 1998, Integration of hydrology and geochemistry of the Culebra Member of the**  **Rustle Formation in the vicinity of the Waste Isolation Pilot Plant (USA), in, U se of**  **Hydrogeochemical Information in Testing Groundwater Flow Models: Works hop Proceedings,**  **Nuclear Energy Agency, Borgholm, Sweden, 1-3 September 1997, p. 135-149.**
**Corbet, T.F., 2000, A groundwater-basin approach to conceptualize and simulate pos t**  **Pleistocene subsurface flow in a semi-arid region, southeastern New Mex ico and western Texas,**  **USA: Hydrogeology Journal, v. 8, p. 310-327.**
**Corbet, T.F., and Knupp, P.M., 1996, The Role of Regional Groundwater Flow in the Hydrogeology of the Culebra Member of the Rustler Formation at the Waste**  **Isolation Pilot Plant 122** 

**(WIPP), Southeastern New Mexico: SAND96-2133, Sandia National Laboratories , Albuquerque,**  **NM.**
**Crawley, M.E., 1988, Hydrostatic Pressure and Fluid-Density Distribution of the C ulebra**  **Dolomite Member of the Rustler Formation Near the Waste Isolation Pilot Plant, Southeastern**  **New Mexico: Westinghouse Electric Corporation, DOE/WIPP 99-030.**
**Earth Technology Corporation, 1987, Final Report for Time Domain Electromagneti c (TDEM)**  **Surveys at the WIPP Site: SAND87-7144, 35 p.**
**Elliott Geophysical Company, 1976, An Experimental Detailed Gravity Sur vey of Known or**  **Suspected Breccia Pipes at Weaver Hill, Hills A&B, and Hills C&D, Eddy County, New**  **Mexico: 3 volumes.**
**Elliott Geophysical Company, 1977, Evaluation of the proposed Los Medaños nucl ear waste**  **disposal site by means of electrical resistivity surveys, Eddy and L ea Counties, New Mexico.** 
**Ferrall, C.C., and Gibbons, J.F., 1980, Core Study of Rustler Formation Over the WIPP Site :**  **SAND79-7110, 80 p.**
**Gard, L.M., 1968, Geologic Studies, Project Gnome, Eddy County, New Mexico: U.S. Geological Survey, Professional Paper 589, 33 p.** 
**Geohydrology Associates, Inc., 1978, Ground-Water Study Related to Proposed Expa nsion of**  **Potash Mining Near Carlsbad, New Mexico: 110 p.**
**Gile, L.H., Hawley, J.W., and Grossman, R.B., 1981, Soils and geomorphology in the Basin and Range area of Southern New Mexico – Guidebook to the Desert Project: Memoir**  **39, New Mexico Bureau of Mines & Mineral Resources, 222 p.** 
**Gustavson, T.C., Finley, R.J., and McGillis, K.A., 1980, Regional dissolution of Permian salt i n**  **the Anadarko, Dalhart, and Palo Duro basins of the Texas Panhandle: Texas Bureau of Ec onomic**  **Geology, Report of Investigations No. 106, 40 p.**
**Haggerty, R., Fleming, S.W., Meigs, L.C., and McKenna, S., 1997, Evaluation of single-well injection-withdrawal tracer-test data with a multirate-diffusion mod**  **el,** in **, Meigs, L.C., Beauheim, R.L., and Jones, T.L. (eds.), Interpretations of Tracer Tests Per**  **formed in the Culebra Dolomite at the Waste Isolation Pilot Plant Site: Sandia National La**  **boratories, SAND97-3109, p. 85-102.** 
**Handford, C.R., 1982, Sedimentology and Evaporite Genesis in a Holocene Continental-Sabkha Playa Basin – Bristol Dry Lake, California: Sedimentology, v. 29, p. 239-253.** 
**Harville, D.G., and Fritz, S.J., 1986, Modes of diagenesis responsible for observed s uccession of**  **potash evaporites in the Salado Formation, Delaware Basin, New Mexico: Jour nal of**  **Sedimentary Petrology, v. 56, p. 684-656. 123** 

**Hill, C.A., 1999, Intrastratal Karst at the WIPP Site: Letter report to S andia National**  **Laboratories, contract #BF-4451, 82 pages plus appendix.**
**Hill, C.A., 2003 Intrastratal Karst at the Waste Isolation Pilot Plant Si te, Southeastern New**  **Mexico: Oklahoma Geological Survey Circular 109, p. 197-209.**
**Holt, R.M, and Powers, D.W., 1984, Geotechnical Activities in the Waste Handling Shaft: WTSD-TME-038, US Department of Energy, Carlsbad, NM.** 
**Holt, R.M., and Powers, D.W., 1986, Geotechnical Activities in the Exhaust Shaft: DOE-WIP P**  **86-008, Carlsbad, NM, US Department of Energy, Carlsbad, NM.**
**Holt, R.M., and Powers, D.W., 1988, Facies Variability and Post-Depositional Altera tion Within**  **the Rustler Formation in the Vicinity of the Waste Isolation Pilot Plant, Sout heastern New**  **Mexico: DOE/WIPP 88-004. Carlsbad, NM: Westinghouse Electric Corporation.**
**Holt, R.M., and Powers, D.W., 1990a, The Late Permian Dewey Lake Formation at the Was te**  **Isolation Pilot Plant, in, Geological and Hydrological Studies of Evaporites in the Northern**  **Delaware Basin for the Waste Isolation Pilot Plant (WIPP), New Me xico, Field Trip #14,**  **November 1-4, 1990, Geological Society of America, p. 107-129.**
**Holt, R.M., and Powers, D.W., 1990b, Geologic Mapping of the Air Intake Shaft at the Was te**  **Isolation Pilot Plant: DOE/WIPP 90-051, US Department of Energy, Carslbad, NM**

**. Johnson, P.B., 2005a, Routine Calculations Report in Support of Task 6 of AP-114,**  **Potentiometric Surface, Adjusted to Equivalent Freshwater Heads, of the Cule bra Dolomite**  **Member of the Rustler Formation near the WIPP Site, March-April 2004. ERMS# 541154. Carlsbad, NM: Sandia WIPP Records Center.** 
**Johnson, P.B., 2005b, CRA Response Activity, Tracking Number 03/17/05A, Revision 0, Records Package Number 533999, Title: Magenta Potentiometric Surface Map. E**  **RMS# 539334. Carlsbad, NM: Sandia WIPP Records Center.** 
**Jones, C.L., 1973, Salt Deposits of Los Medaños Area, Eddy and Lea Counties, New Mex ico,**  **with sections on ground water hydrology by M.E. Cooley and on Surficial Geology b y G.O.**  **Bachman: U.S. Geological Survey Open-File Report USGS-4339-7, 67 p.**
**Jones, C.L., 1981, Geologic Data for Borehole ERDA-9, Eddy County, New Mexico: U.S. Geological Survey Open File Report 81-469, 50 p.** 
**Lambert, S.J., 1983, Dissolution of Evaporites in and Around the Delaware Basin, Southeaste rn**  **New Mexico and West Texas: SAND83-0461, 96 p. 124** 

**Lambert, S.J., 1987, Feasibility Study: Applicability of Geochronologic Methods Involving**  **Radiocarbon and Other Nuclides to the Groundwater Hydrology of the Rustler Forma tion,**  **Southeastern New Mexico: SAND86-1054, 72 p.**
**Lambert, S.J., and Harvey, D.M., 1987, Stable-isotope Geochemistry of Groundwate rs in the**  **Delaware Basin of Southeastern New Mexico: Sandia National Laborat ories Report SAND87-**  **0138.**
**Lambert, S.J., and Robinson, K.L., 1984, Field Geochemical Studies of Groundwaters in N ash**  **Draw, Southeastern New Mexico: Sandia National Laboratories report, S AND83-1122.** 
**Lang, W.B., 1935, Upper Permian Formation of Delaware Basin of Texas and New Mex ico:**  **Bulletin of the American Association of Petroleum Geologists, v. 19, p. 262-270.**
**Lorenz, J.C., 1992, Well-bore geometries for optimum fracture characteriz ation and drainage:**  **West Texas Geological Society Bulletin, v. 32, p. 5-8.**
**Lorenz, J.C., Teufel, L.W., and Warpinski, N.R., 1991, Regional Fractures I: A mechani sm for**  **the formation of regional fractures at depth in flat-lying reservoirs: Ame rican Association of**  **Petroleum Geologists Bulletin, V. 75, p. 1714-1737.**
**Lorenz, J.C., Sterling, J.L., Schechter, D.S., Whigham, C.L., and Jensen, J.L., 2002, Natural fractures in the Spraberry Formation, Midland basin, Texas: The effects of**  **mechanical stratigraphy on fracture variability and reservoir behavior: Ameri**  **can Association of Petroleum Geologists Bulletin, v. 86, p. 505-524.** 
**Lowenstein, T.K., 1987, Post Burial Alteration of the Permian Rustler Formation Evap orites,**  **WIPP Site, New Mexico: EEG-36, 54 p.**
**Lowenstein, T.K., 1988, Origin of depositional cycles in a Permian “saline Giant” : The Salado**  **(McNutt zone) evaporites of New Mexico and Texas: Geological Society of America Bulletin, v.**  **100, p. 592-608.**
**Meigs, L.C., Beauheim, R.L., McCord, J.T., Tsang, Y.W., and Haggerty, R., 1997a, Design, modeling, and current interpretations of the H-19 and H-11 tracer tests at the WIP**  **P site** , in **, Field tracer experiments: Role in the prediction of radionuclide migration: OEC**  **D Proceedings, disposal of radioactive waste, synthesis and proceeding of an NEA/EC GEO**  **TRAP workshop hosted by the Gesellschaft für anlagen- und Reaktorsicherheit (GRS), Cologne, G**  **ermany, p. 157- 169.** 
**Meigs, L.C., Beauheim, R.L., and Jones, T.L. (eds.), 1997b, Interpretations of Trac er Tests**  **Performed in the Culebra Dolomite at the Waste Isolation Pilot Plant Site : Sandia National**  **Laboratories, SAND97-3109, 408 p. 125** 

**Mercer, J.W., 1983, Geohydrology of the Proposed Waste Isolation Pilot Plant site , Los**  **Medaños Area, Southeastern New Mexico: U.S. Geological Survey Water-Resour ces**  **Investigations Report 83-4016, 87 p.**
**Mercer, J.W., and Orr, B.R., 1979, Interim Data Report on the Geohydrology of the Propose d**  **Waste Isolation Pilot Plant Site, Southeast New Mexico: U.S. Geological S urvey Water**  **Resources Investigations 79-98, 178 p.**
**Mercer, J.W., Davis, P., Dennehy, K.F., and Goetz, C.L., 1981, Results of Hydrologic Tests and**  **Water-chemistry Analyses, Wells H-4A, H-4B, and H-4C at the Proposed Wa ste Isolation Pilot**  **Plant Site, Southeastern New Mexico: U.S. Geological Survey Water-Resour ces Investigations**  **81-36, 92 p.**
**Mercer, J.W., Cole, D.L., and Holt, R.M., 1998, Basic data report for drillholes on the H-19 hydropad (Waste Isolation Pilot Plant–WIPP): SAND98-0071, Sandia National**  **Laboratories, Albuquerque, NM.** 
**Morgan, A.M., 1942, Solution-Phenomena in the Pecos Basin in New Mexico, Reports and papers, Transactions of the American Geophysical Union, National Resear**  **ch Council, Hydrology, Dallas, 1941, p. 27-35.** 
**Morgan, A.M., and Sayre, A.N., 1942, Geology: The Pecos River Joint Investigation, Report of**  **the Participating Agencies, National Resources Planning Board, p. 28-38.**
**Neal, J.T., Colpitts, R., and Johnson, K.S., 1998, Evaporite karst in the Holbrook Basin, Arizona, in Borcher, ed., the Joseph F. Poland Symposium on Land Subsidence, Sudbury, MA:**  **Association of Engineering Geologists.**
**Neal, J.T., and Lorenz, J.C., 1998, Holbrook Anticline, Arizona: An exposed analog for fract ured**  **reservoirs over salt-dissolution fronts: SPE 49027, presented at the 1998 Society of Petroleum**  **Engineers Annual Technical Conference and Exhibition, New Orleans, Louisia na, 27-30**  **September, p. 337-342.**
**Phillips, R.H., 1987, The prospects for regional groundwater contamination due to kar st**  **landforms in Mescalero caliche at the WIPP site near Carlsbad, New Mex ico: unpublished PhD**  **dissertation, University of Oregon, 316 p.**
**Powers, D.W., 1996, Tracing Early Breccia Pipe Studies, Waste Isolation Pilot Plant,**  **Southeastern New Mexico: SAND94-0991, 53 p.**
**Powers, D.W., 1997, Geology of Piezometer Holes to Investigate Shallow Water Source s Under**  **the Waste Isolation Pilot Plant** , in, **Intera, 1997, Exhaust Shaft Hydraulic Assessment Data Report, DOE/WIPP 97-2219.** 
**Powers, D.W., and Holt, R.M., 1990, Sedimentology of the Rustler Formation near the Waste Isolation Pilot Plant (WIPP) Site, in, Geological and Hydrological Studies of E**  **vaporites in the 126** 

**Northern Delaware Basin for the Waste Isolation Pilot Plant (WIPP), N ew Mexico, Field Trip**  **#14, November 1-4, 1990, Geological Society of America, p. 79-106.**
**Powers, D.W., and Holt, R.M., 1995, Regional Geological Processes Affecting Rustler Hydrogeology: Westinghouse Electric Corporation, 90 pages plus appendi**  **ces.**
**Powers, D.W., and Holt, R.M., 1999, The Los Medaños Member of the Permian Rustler Formation: New Mexico Geology, v. 21, no. 4, p. 97-103.** 
**Powers, D.W., and Holt, R.M., 2000, The salt that wasn’t there: Mudflat facies equivalents to**  **halite of the Permian Rustler Formation, southeastern New Mexico: Journal of Se dimentary**  **Research, V. 70, p. 29-36.**
**Powers, D.W., Holt, R.M., Beauheim, R.L., and McKenna, S.A., 2003, Geological factors related to the transmissivity of the Culebra Dolomite Member, Permian Ru**  **stler Formation, Delaware Basin, Southeastern New Mexico,**  in **, Johnson, K.S., and Neal, J.T. (eds), Evaporite karst and engineering/environmental problems in the United States: Okla**  **homa Geological Survey Circular 109, p. 211-218.** 
**Powers, D.W., and Richardson, R.G., 2004a, Basic Data Report for Drillhole SNL-3 (C-2949) (Waste Isolation Pilot Plant): DOE/WIPP 03-3294, US Department of Energy**  **, Carlsbad, NM.**
**Powers, D.W., and Richardson, R.G., 2004b, Basic Data Report for Drillhole SNL-1 (C-2953) (Waste Isolation Pilot Plant): DOE/WIPP 04-3301, US Department of Energy**  **, Carlsbad, NM.**
**Ramey, D.S., 1985, Chemistry of Rustler Fluids, Environmental Evaluation Group, Albuquerque, New Mexico, EEG-31, 61 p.** 
**Ramey, D.S., 1987, Chemistry of the Rustler fluids,** in **, Chaturvedi, L., (ed.), The Rustler Formation at the WIPP site: Environmental Evaluation Group, Albuquerque, New Mexi**  **co, EEG 34, p. 8-13.** 
**Randall, W.S., Crawley, M.E., and Lyon, M.L., 1988, 1988 Annual Water Quality Data Report for the Waste Isolation Pilot Plant, March, 1988: DOE-WIPP 88-006, Carlsbad, NM:**  **Westinghouse Electric Corporation.**
**Reddy, G.R., 1961, Geology of the Queen Lake Domes near Malaga, Eddy County, New Mexico: M.Sc. thesis, University of New Mexico, 84 p.** 
**Robinson, T.W., and Lang, W.B., 1938, Geology and Ground-Water Conditions of the Pecos River Valley in the Vicinity of Laguna Grande de la Sal, New Mexico, wit**  **h Special Reference to the Salt Content of the River Water: Biennial Report of the State Engineer of**  **New Mexico, p. 79-100.** **127**

**Sandia National Laboratories and United States Geological Survey, 1979, Basic Data Report for**  **Drillhole WIPP 13 (Waste Isolation Pilot Plant – WIPP): Sandia National Laboratories report**  **SAND79-0273, 16 pages plus appendices.**
**Sandia National Laboratories and the United States Geological Survey, 1981, Ba sic Data Report**  **for Drillhole WIPP 33 (Waste Isolation Pilot Plant – WIPP), SAND80-2011, 27 pages plus**  **appendices.**
**Sandia National Laboratories and D’Appolonia Consulting Engineers, 1982, Basic D ata Report**  **for Drillhole WIPP 14 (Waste Isolation Pilot Plant – WIPP): SAND82-1783, 36 pages plus**  **appendices.**
**Sares, S.W., 1984, Hydrologic and Geomorphic Development of a Low Relief Evaporit e Karst**  **Drainage, Southeastern New Mexico: M.Sc. thesis, University of New Mexic o, 123 p.** 
**Siegel, M.D., Lambert, S.J., and Robinson, K.L, eds,, 1991, Hydrogeochemical Studies of the Rustler Formation and Related Rocks in the Waste Isolation Pilot Plant Area, Sout**  **heastern New Mexico: SAND88-0196.** 
**Smoot, J.P., and Lowenstein, T.K., 1991, Depositional environments of non-marine evaporates**

, in, **Melvin, J.L., (ed.), Evaporites, petroleum and mineral resources: Amsterdam , Elsevier,**  **Developments in Sedimentology, v. 50, p. 189-347.**
**Snow, D.T., 1998, Hydrological Conditions at the WIPP Site at Variance with the Assump tions**  **of DOE in its Performance Assessment: Submitted to the NAS Committee on WIPP, 18 p.** 
**Snow, D.T., 2002, Unsafe radwaste disposal at WIPP: Proceedings of solution mining rese arch**  **institute, Banff, Alberta, Canada, April 28-May 1, 22 p.**
**Snyder, R.P., 1985, Dissolution of Halite and Gypsum, and Hydration of Anhydrite to Gypsum ,**  **Rustler Formation, in the Vicinity of the Waste Isolation Pilot Plant, Southea stern New Mexico:**  **U.S. Geological Survey Open File Report USGS-OFR-85-229, 11 p.**
**Snyder, R.P., and Gard, L.M., Jr., 1982, Evaluation of Breccia Pipes in Southeastern New Mexico and their Relation to the Waste Isolation Pilot Plant (WIPP) Site:**  **U.S. Geological Survey Open File Report 82-968, 73 p.** 
**Theis, C.V., Morgan, A.M., Hale, W.E., and Loeltz, O.J., 1942, Ground-Water Hydrology of Areas in the Pecos Valley, New Mexico: The Pecos River Joint Investigati**  **on, Reports of the Participating Agencies, June, 1942, National Resources Planning Board, p. 38-75.** 
**Vine, J.D., 1963, Surface Geology of the Nash Draw Quadrangle, Eddy County, New Mex ico:**  **U.S. Geological Survey Bulletin 1141-B, p. B1-B46.**