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Regional Flow in the Rustler Formation
Modeling the paths and rates of transport of radionuclides in groundwater entails
many parameters, known or approximated. If the PA model was grossly correct, if
regional flow based on current hydraulic heads in the Culebra was all that mattered,
the DOE claim that the Rustler is a barrier to contaminant transport might be
justified.
The DOE model directs Culebra flow paths southward to Malaga Bend, a distant discharge area on the Pecos River. Had they incorporated the low hydraulic heads at WIPP-29 (2968 ft.) and Laguna Grande (2950 ft.), modeled paths would have turned west to Nash Draw (Phillips and Snow, 1998, p. A-8). Computed travel times through the Culebra would have been much shorter if model heads had been realistically represented.
Tests have revealed such a great range of transmissivity (hydraulic conductivity times aquifer thickness) near wells completed in the Culebra that the degree of channeling must be the main variable across the site. Transmissivity increases westward by five to six orders of magnitude (Phillips and Snow, 1998, p A-3). Of 42 wells tested, high measurements were reported at WIPP-13, H-6, P-14, H-11, DOE-1 and DOE-2 (Figure 5). The observed irregular increase of transmissivity from east to west reflects a systematic increase in the dissolution of fracture fillings, the coalescence of smaller channels into larger conduits, and the development of cross-connecting fractures and channels to other Rustler strata (Hill, 1999, Neill, et. al., 1998). Since pumping tests in the Culebra produce greatly different responses at adjacent observation wells, the conservative approach to modeling would be to utilize at each location the highest measured transmissivity. Instead, DOE has arbitrarily assumed, at wells within 1.5 miles of the center of the WIPP site, transmissivity values that are one to two orders of magnitude smaller than the highest values revealed by the hydrologic tests (Phillips and Snow, 1998, p. A-3). The consequence is that computed travel times across the first 1.5 miles are exaggerated by similar magnitudes.
Evidence of Karst
The strongest direct evidence of a saturated karst system that will influence flows
from WIPP was the penetration of five caverns below the sinkhole at WIPP-33,
located about 2600 ft. west of the WIPP site (See Figure 5). Those caverns totaled 29.5 ft. in height, occurring in
the Dewey Lake Red Beds, and in the Forty-Niner and Magenta members of the Rustler
(Sandia Labs, 1981, Phillips and Snow, 1998). The WIPP-33 sinkhole is the most
westerly of four in a chain aligned eastwards 2450 ft. to within 1000 ft. of the
WIPP site boundary. It can be surmised that an extensive karst conduit underlies the
chain. A similar chain of nine sinkholes is aligned E-W just north of the WIPP site
boundary. There the WIPP-14 drillhole revealed 74 ft. of residual clay, much gypsum,
but no caves, perhaps because the hole was drilled eccentric to the sinkhole formed
over collapsed caverns. At both sites, trenching and augering done by Phillips (1987)
revealed conical depressions in the near-surface Mescalero caliche, culminating at a
chimney, proving that they are sinkholes, not wind-deflation features. Phillips'
investigation showed that there are several true sinkholes on site, including some
that have been observed (e.g., during September, 1984) to conduct storm waters
rapidly into the underlying formations. Coincident with several surface depressions
on the WIPP site, Barrows (1983 and 1985) discovered anomalous gravity lows,
probably due to gypsification of anhydrite or to karst caverns. Phillips (1987)
showed that the gravity anomalies coincide with solution chimneys through, and
downwarping of, the Mescalero caliche horizon.
From hydrological testing of WIPP-area boreholes, there can be derived many indirect lines of evidence for karst hydrology. The one borehole east of the WIPP site (P-18) indicates water-tightness, presumably because gypsum fracture fillings remain complete. Westward across the WIPP site toward Nash Draw, the increasing transmissivities measured in the Culebra are consistent with dissolution and removal of salt beds, subsidence damage to the gypsum-filled fractures of the Culebra (Neill, et. al., 1998, p. 11), fracturing of the brittle anhydrites above and below the Culebra, and with solution-enlarged fractures and karst conduits that coalesce downstream. Other hydrologic observations are consistent with karst. These include anomalous drawdowns interpreted as high Culebra transmissibility between certain wells but not others (Phillips and Snow, 1997). Lateral channel interconnections are implied by equal Culebra heads at some adjacent wells, and vertical channels are indicated by equal heads in the Culebra and Magenta dolomites at the same wells (Phillips and Snow, 1997). Former anhydrite beds have been converted to gypsum by freshwater recharge (Snyder, 1985). Westward freshening of Rustler waters can best be reconciled with westerly flow and vertical recharge. The youthful ages of some waters sampled from the Rustler can be attributed to rapid, local infiltration (Hill, 1999, pp. 54, 55).
A few feet below the surface is the Mescalero caliche, which has collapsed into Nash Draw. Testing the hypothesis that the caliche layer does not obstruct rainwater recharge in the vicinity of WIPP, Phillips (1987) dug over 1000 auger holes in and around several closed topographic depressions. The caliche bed has subsided to form funnel shapes below some of the depressions, is dissolved to residual materials in many places, and is absent where solution pipes penetrate it. The deformed caliche surface proves local subsidence, and the solution pipes prove that infiltrating water has locally karstified the caliche. Phillips explored another mile-long karst valley without a surface water course that crosses the west boundary of the WIPP site, and a chain of four sinkholes at WIPP-33 indicating that water carves elongate E-W courses through the underlying Dewey Lake and Rustler beds, at least to the depth of the Magenta Dolomite. Observations of storm infiltration at sinkholes prove that karst conditions exist in the subsurface. About ten inches of rain fell in the vicinity (registered at Loving, 18 miles WSW of WIPP) on September 18-19, 1985, causing the WIPP-33 sinkhole to fill like a bathtub to a depth of five feet, then disappear in a few days (Phillips, 1987, p. 86). Water also ponded in the fourth depression east of WIPP-33 and rapidly infiltrated the ground. Such water can not seep away laterally from closed topographic depressions. It must follow karst conduits to the water table, joining an interconnected, perhaps locally obstructed conduit system that leads to outlets. Mature karst aquifers usually discharge at large-capacity springs along rivers or shores defining the base-level for the system, and have a strong influence on the water table everywhere upstream. Storm waters recharge such a karst system in a matter of hours, typically
causing a sudden rise and a corresponding rapid increase of spring discharges, noted
in days. Wells near WIPP have not been instrumented to provide hydrographs of the
karst system, so none substantiate rapid water level rises, but one typical spring-
flow event has been observed. On September 5, 1984, following a major storm,
Phillips (1987, p. 228) witnessed transient flow into Laguna Grande amounting to at
least 100,000
No tracer tests have been done to determine potential karstic flow paths or groundwater travel times. Phillips and Snow (1998, Figure 4) analyzed the transmissivity data and head distribution among the wells, conceiving that there are preferred channel directions from the shaft area southwards and northwestwards, and from the WIPP site westwards along three paths to Nash Draw. One passes through the NW corner of the WIPP site and WIPP-33, one follows the karst valley near the center of the W boundary, and a third lies just south of the S boundary. Upon examination of many drill logs, on and off-site, Phillips (1997b) found breccia or rock fragments, residual clays, open washed-out zones, or lost core intervals strongly suggestive of dissolution at every stratigraphic interval of the Rustler, but not necessarily features that are open today. If residuum has replaced portions of the salt formerly in the Rustler, the dissolution process has been pervasive and perhaps continual, and occasional open conduits are an inescapable corollary, even if they are locally obstructed by residuum. Dye-tracing of groundwater flows in classic karst areas such as Dalmatia, Florida and Kentucky have demonstrated transient velocities exceeding a mile per day, flows that may even now be matched west of WIPP during storms like those of September, 1984 and 1985 (Phillips, 1987). Travel-time estimates through the WIPP karst (Phillips and Snow, 1998, Snow, 1998 and Hill, 1999) have ranged between 5 years and 500 years from the center of the WIPP site to Nash Draw, but even these may not be conservative. In PA, Culebra transmissivities have been extrapolated from known points of measurement to unknown areas. This concept is invalid because transmissivity in discontinuous karstic rocks does not vary continuously, and because the extremes of Rustler transmissivity are unrepresented in the data set.
Conclusions
The preponderance of evidence supports the contention that PA modeling seriously
underestimates releases of radioactivity to the accessible environment. This is
reason enough for invalidating the certification granted by the EPA. Given its
departures from rationality, the reader should be incredulous that the DOE
application was approved. The EPA was well aware that the basis for objections,
then and now, has always been that there are karst conditions in the Rustler.
The TRU waste has to be removed from the generator sites, even if an adequate permanent repository has not been established. TRU waste disposal underground remains premature, leaving monitored retrievable storage as the only option. A safe temporary facility could be situated near the surface of an old, stable landform, above the water table. For instance, at WIPP, it could probably be established on the Santa Rosa formation, but not on the Dewey Lake/Rustler karstland. It is evident that disposal in salt at WIPP is not the answer, where travel times in the overlying aquifer will be orders of magnitude shorter than PA predicted. The EPA has erred in certifying the repository, and recertification (in 2003) should be defeated. Meanwhile, TRU waste disposal at WIPP should stop, and the waste already in place in the first panel should be retrieved before roof collapse makes it prohibitively costly and dangerous to do so. Dr. Snow's research was supported by a grant from the Citizens' Monitoring and Technical Assessment Fund.
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