WRIR 01-4210: Hydraulic-Property Estimates for Use With a Transient Ground-Water Flow Model of the Death Valley Regional Ground-Water Flow System, Nevada and California
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The hydraulic-property estimates from aquifer-test results are statistically summarized for each of the HGU's in the hydrogeologic framework of the DVRFS. Horizontal hydraulic conductivity values are presented for all tests; specific yield and storativity values are presented for each HGU, if available. A summary of the hydraulic conductivity estimates of HGUs and subunits for HGUs are presented in table 2. A compilation of hydraulic-property estimates is provided in appendix A.
Most basin-fill sediments are included in the younger alluvial aquifer (YAA) and the older alluvial Aquifer (OAA; fig. 3). The YAA and OAA consist of Holocene to Pliocene sand, gravelly sand, sandy gravel, and gravel, with cobbles, boulders, silty to clayey intervals, and thin interbeds of clay and silt, that were deposited mostly in alluvial fans, floodplains, and stream channels. Eolian silt and sand, landslide deposits, debris flows, talus, colluvium, basalt flows, and tuff layers are present locally (that is, are discontinuous and not considered regional, areal-extensive units). Sediments generally are uncemented at and near the water table, but become more indurated with increasing depth. This combined HGU tends to be an aquifer where present, but finer grained sediments and intercalated volcanics locally can impede ground-water movement.
Forty-three analyses of hydraulic properties were compiled for the combined YAA and OAA, 25 from single-well aquifer tests and 18 from multiple-well aquifer tests. Tested intervals of the boreholes ranged from 6 to 161 m. Aquifer-test pumping rates ranged from 0.5 to 84 L/s with a minimum pumping time of 91 minutes. Aquifer-test analyses for pumping wells were omitted from the statistical summary, when an observation well was available to avoid biasing.
The horizontal hydraulic-conductivity values ranged from 0.001 to 130 m/d with geometric and arithmetic means of 2 m/d and 11 m/d, respectively. The 95-percent confidence interval about the geometric mean for these values ranged from 0.6 to 4 m/d.
Specific-yield estimates from late-time data (water levels measured near the end of the aquifer test), estimated in 14 analyses using Neuman (1975). These estimates ranged from 0.0004 to 0.2 with an arithmetic mean of 0.03 with the low value excluded (the low minimum value of 0.0004 suggests that the Neuman (1975) method was not applicable because of possible aquifer heterogeneity or dual-porosity conditions).
The alluvial confining unit (ACU) consists of Holocene to Pliocene playa, lake, marsh, and spring-deposited clay, marl, limestone, silt, sand, gravel; evaporite deposits, and thin tuff layers. The ACU tends to be a regional confining unit, but limestone and sand layers can be productive local aquifers, although the limestone component is probably limited in areal extent. The ACU is restricted to the topographically lowest areas of structural basins in the Death Valley region (fig. 3). Sediments that comprise the ACU may interfinger with those of the YAA and OAA, can be absent with depth, or may be present elsewhere beneath deposits of sand and gravel. The YAA and OAA and the ACU are shown as a single unit in figure 3.
Fifteen analyses of hydraulic properties were compiled for the ACU, 7 from single-well aquifer tests and 8 from multiple-well aquifer tests from 12 wells in the Amargosa Desert and Cave Valley. Test-interval thicknesses ranged from 0.3 to 235 m. Aquifer-test pumping rates ranged from 14 to 114 L/s with a minimum pumping time of 160 minutes. To avoid biasing, aquifer-test analyses for pumping wells were omitted from the statistical summary when an observation well was available.
Horizontal hydraulic-conductivity values ranged from 0.003 to 34 m/d with geometric and arithmetic means of 3 m/d and 11 m/d, respectively. The 95-percent confidence interval about the geometric mean for these values ranged from 0.6 to 10 m/d. The high value of 34 m/d was for a well in the Amargosa Desert and may reflect the hydraulic properties of spring-carbonate deposits, rather than clayey playa deposits.
Estimates of the horizontal hydraulic conductivity (app. A) for the ACU unit are equal or slightly greater than those of the YAA and OAA units. This result appears to be counter intuitive since confining units are expected to have hydraulic conductivities significantly lower than those of aquifers. However, the wells used for the ACU aquifer tests may be completed in more permeable alluvial deposits rather than playa deposits of lower permeability. Thomas and others (1989) indicate that playa deposits within the Smith Creek Valley in Lander County, Nev., possess vertical hydraulic-conductivity values of about 0.03 m/d, which suggests that the hydraulic conductivity of playa deposits is much less than that estimated for this unit using estimates from within the DVRFS.
Storativity values from seven analyses ranged from 0.00009 to 0.04 with an arithmetic mean of 0.01 (app. A). The specific yield from one analysis was estimated to be 0.01 (app. A). The apparent overlap of storativity and specific-yield values for this HGU may indicate that ground water in the ACU is variably confined, semi-confined, or unconfined.
The lava flow unit (LFU) consists of Holocene to Miocene basaltic and rhyolitic lava flows (typically with interbedded tuffs) interbedded with, and underlying, basin-fill sediments as well as localized cinder cones in topographic basins (fig. 3). Individual lava flows are not laterally extensive. Cinder cones typically are above the water table. Figure 3 includes some rhyolitic to rhyodacitic lava flows assigned to underlying volcanic HGUs and omits older basalt and andesite lava flows that do not have surface exposure.
Only two hydraulic-property analyses were conducted in the LFU at two separate locations. One analysis was from a single-well pumping test and the other from a slug-injection test. Test-interval thicknesses for the boreholes ranged from 61 to 80 m. For the pumping test the well was pumped at a rate of 8.4 L/s for 220 minutes. The horizontal hydraulic-conductivity value from this test was 4 m/d. The horizontal hydraulic-conductivity estimate from the slug test was 0.002 m/d. Because of the small number of hydraulic-property estimates available for this unit, estimates for the lava-flow component of the Tertiary volcanics HGU may be useful for numerical simulation of the LFU (see "Tertiary Volcanic Rocks").
The younger volcanic unit (YVU) and the volcaniclastic and sedimentary rocks unit (VSU) consists of Pliocene to Eocene variably cemented conglomerate, gravelly sandstone, sandstone, siltstone, shale, calcareous shale, limestone, and intercalated tuff layers. The YVU and the VSU consist of erosional and faulted remnants of sedimentary rocks deposited in diverse terrestrial settings within syntectonic basins (fig. 3). Coarser-grained rocks, if not permeated by calcite or other cementing minerals, can be very productive aquifers. Finer-grained rocks typically impede ground-water flow over large areas. With decreasing cementation, lithologies comprising this HGU grade into those in the YAA, the OAA, and the ACU. The YVU and the VSU are considered as separate units in the DVRFS hydrogeologic framework but are combined in this report (table 1).
Fifteen analyses of hydraulic properties were compiled for the YVU and VSU, all of which represent single-well aquifer tests. Test-interval thicknesses ranged from 8 to 70 m. Aquifer-test pumping rates ranged from 0.2 to 41 L/s with a minimum pumping time of 180 minutes.
Horizontal hydraulic-conductivity values for the YVU and the VSU ranged from 0.00004 to 6 m/d with geometric and arithmetic means of 0.06 m/d and 1.5 m/d, respectively. The 95-percent confidence interval about the geometric mean of the horizontal hydraulic-conductivity values ranged from 0.01 to 0.4 m/d. Storativity was estimated from one aquifer test to be 0.006 (app. A).
The Tertiary volcanic rocks unit (TV) consists of Pliocene to Miocene non-welded to densely welded ash-flow tuff, depositional and fault-related tuff breccia, ash-fall tuff, reworked tuff, volcaniclastic rocks, and rhyolite, comendite, and trachyte lava flows. This HGU represents a combination of several proposed hydrogeologic units for the transient DVRFS flow model and includes the Thirsty Canyon/Timber Mountain volcanic aquifer (TMVA), the Paintbrush volcanic aquifer (PVA), the Calico Hills volcanic unit (CHVU), the Wahmonie volcanic unit (WVU), the Belted Range unit (BRU), and the Crater Flat volcanic unit (CFVU). The volcanic rocks that comprise this HGU tend to have both fracture and matrix permeability. Fracturing, which is most intense near faults, can enhance permeability (Faunt, 1997). Alteration of rock-forming minerals to zeolite, clay, carbonate, silica, and other minerals, which is most intense toward eruptive centers, can reduce permeability (Laczniak and others, 1996). Therefore, hydraulic properties within this HGU are extremely variable laterally and with depth. Moreover, certain combinations of lithology and structure can result in very transmissive intervals or as major impediments to ground-water flow over large areas. The Tertiary volcanics unit is widely distributed in the west-central part of the Death Valley region (fig. 3). The distribution of this HGU is controlled largely by the extent of nested calderas from which middle Miocene and younger volcanic rocks of the SWNVF erupted. The Tertiary volcanics intertongue with the YAA, the OAA, the ACU, the YVU, and the VSU.
One-hundred fifty-nine analyses of hydraulic properties were compiled for the Tertiary volcanics, 116 from single-well aquifer tests and 43 from multiple-well aquifer tests. Test-interval thicknesses for boreholes screened in the Tertiary volcanics ranged from 7 m to almost 1,600 m. Aquifer-test pumping rates ranged from 0.1 to 44 L/s with a minimum pumping time of 89 minutes. To avoid biasing, aquifer-test analyses for pumping wells were omitted from the statistical summary when an observation well was available and slug-injection tests conducted over a number of smaller intervals within a larger interval also were omitted.
Horizontal hydraulic-conductivity values ranged from 0.000001 to 180 m/d with geometric and arithmetic means of 0.1 m/d and 4 m/d, respectively. The 95-percent confidence interval about the geometric mean for these values ranged from 0.08 to 0.2 m/d.
The hydraulic-conductivity estimates also were assigned to the corresponding lithostratigraphic formation or group (corresponding to the DVRFS units) and statistically summarized. Tests in wells with open intervals contained in more than one of these proposed HGUs were not used in the statistical summaries. No data were obtained for the WVU. Table 2 presents the geometric mean for the various lithostratigraphically based hydrogeologic units within the Tertiary volcanics.
Four categories of rock were recognized as a basis for evaluating lithology as an influence on hydraulic conductivity: (1) non-welded to densely welded ash-flow tuff (85 analyses); (2) rhyolite, rhyodacite, and trachyte lava flows with or without a tuff component (25 analyses); (3) tuff breccia with or without a tuff component (15 analyses); and (4) bedded tuff with or without an ash-flow tuff component (15 analyses). The presence of tuff intercalated with other rock types was unavoidable because of limitations in available data. However, the presence of tuff interbeds in intervals consisting mostly of lava flows is considered inconsequential hydraulically. Despite some ambiguity in the data (mainly from variability in the rock property descriptions for the test intervals), it appears that ash-flow tuffs, bedded tuffs, and lava flows are about equally permeable and that all of these lithologies are less permeable than tuff breccias (table 2). Ubiquitous zeolitic and argillic alteration of bedded tuff probably controls the hydraulic properties of test intervals containing bedded tuff and ash-flow tuff (Laczniak and others, 1996, p. 26).
To assess the effect of the degree of welding of ash-flow tuff on hydraulic conductivity, the results of 85 analyses of hydraulic conductivity were categorized by rock type (table 2). Three categories were selected: (1) non-welded to partially welded tuff (43 analyses); (2) partially to moderately welded tuff (35 analyses); and (3) moderately to densely welded tuff (7 analyses). Overlapping rock types, such as non-welded to densely welded tuff, were omitted from the analysis. The hydraulic conductivity of ash-flow tuff generally increases as the degree of welding increases (table 2). This welding increases the propensity of the ash-flow tuffs to fracture, which enhances permeability (Laczniak and others, 1996, p. 25).
On the basis of qualitative descriptions in borehole lithologic logs, ash-flow tuff, bedded tuff, and tuff breccia (omitting lava flows) were combined into two rock categories, unaltered tuff (71 analyses) and altered (zeolitized or argillized) tuff (63 analyses). Clay minerals from the alteration tend to reduce permeability (Laczniak and others, 1996, p. 26). Test intervals of partly altered tuff were omitted from the analysis. Results of the analyses of 134 samples suggest that the mean horizontal hydraulic conductivity of unaltered tuff is greater than altered tuff by about an order of magnitude (table 2).
Storativity in 45 analyses of aquifer tests from the Tertiary volcanics ranged from 0.00004 to 0.004 with an arithmetic mean of 0.001 (app. A). Specific yield from 10 analyses for the Tertiary volcanics ranged from 0.001 to 0.2 with an arithmetic mean of 0.03 (app. A).
The older volcanic unit (OVU) consists mostly of Miocene to Oligocene ash-flow tuff, ash-fall tuff, reworked tuff, tuff breccia, volcaniclastic rocks, rhyolite, comendite, rhyodacite, and dacite lava flows, and shale, sandstone, and conglomerate of sedimentary origin. The volcanic rocks that comprise the OVU tend to have both fracture and matrix permeability. Ash-flow tuffs tend to be non-welded, but can be partly to densely welded. Alteration of ash-flow, ash-fall, and reworked tuffs to zeolite, clay, carbonate, silica, and other minerals is common. The OVU tends to be a regional confining unit and has widespread outcrop exposure in the northern part of the Death Valley region (fig. 3). Older tuffs and lava flows of the OVU also underlie the YVU and the VSU where they are present throughout the NTS. These older tuffs and lava flows can pinch out and intertongue with Tertiary sedimentary rocks in areas such as the southern end of Yucca Mountain (R.W. Spengler, U.S. Geological Survey, written commun., 2001) and between the Bullfrog Hills and Grapevine Mountains (Snow and Lux, 1999).
Forty-six analyses of hydraulic properties were compiled for the OVU, all of which were single-well tests. Test-interval thicknesses ranged from 6 to 1,054 m. Aquifer-test pumping rates ranged from 0.2 to 22 L/s with a minimum pumping time of 620 minutes. Available analyses are spatially well distributed from Railroad Valley to Monitor Valley, immediately north of the Death Valley region model area (fig. 1 and fig. 2), but are spatially restricted from Yucca Flat and Pahute Mesa to Yucca Mountain.
Formations comprising the OVU were among the first volcanic rocks penetrated in shafts and boreholes completed at the NTS to conduct underground nuclear tests (Winograd and Thordarson, 1975). Because these rocks produced little water, Winograd and Thordarson (1975) designated them "the tuff aquitard." Where these rocks produced water, production was erratic and attributed to interconnection of fractures in the aquitard with overlying or underlying aquifers (Winograd and Thordarson, 1975, p. 52). Only eight constant-rate pumping and injection tests were available. Aquifer-test results for OVU probably underestimate its transmissive properties because the estimates come from tests which only sample a relatively small amount of the aquifer.
Horizontal hydraulic-conductivity estimates for OVU ranged from 0.000001 to 1 m/d with geometric and arithmetic means of 0.004 m/d and 0.07 m/d, respectively. The 95-percent confidence interval about the geometric mean for these values ranged from 0.001 to 0.01 m/d. No storativity or specific yield estimates were available.
The rocks of the intrusive confining unit (ICU) consist of Jurassic to Oligocene granodiorite, quartz monzonite, granite, and tonalite. The ICU granitic rocks generally are limited in exposure within the DVRFS (fig. 3). Although these intrusive rocks can produce small quantities of water from fractures and weathered zones where present, they generally impede ground-water flow. In most of the DVRFS, Tertiary and Jurassic granitic rocks occur as small stocks, such as the Climax Stock in Yucca Flat and the Gold Meadows Stock on Rainier Mesa (Houser and others, 1961). On both sides of Death Valley, intrusive bodies are larger, more irregular in shape, and more common than elsewhere in the Death Valley region (Grose and Smith, 1989).
Few aquifer tests have been conducted in this unit in or near the DVRFS. Seven analyses were completed using slug tests, swabbing tests, and a constant-rate injection test in wells at the Climax and Belmont Stocks. Test-interval thicknesses ranged from 8 to 416 m. The injection rate for the constant-rate injection was 4 L/s for 97 minutes.
Horizontal hydraulic-conductivity values estimated for the ICU ranged from 0.0006 to 1 m/d with geometric and arithmetic means of 0.01 m/d and 0.3 m/d, respectively. The 95-percent confidence interval about the geometric mean for these values ranged from 0.001 to 0.01 m/d. No storativity estimates were obtained.
The sedimentary rocks confining unit (SCU) consists of Permian to Jurassic interbedded conglomerate, gravelly sandstone, sandstone, siltstone, shale, calcareous shale, limestone, and gypsum. Hydraulic properties are extremely variable. The Shinarump Conglomerate and the Kaibab Limestone are regional aquifers. Other sandstone and limestone intervals transmit water locally. Intervals predominantly composed of shale, such as upper members of the Chinle Formation, are regional confining units. The SCU is exposed in the DVRFS in the upper plate of the Keystone Thrust Fault at the southern end of the Spring Mountains (fig. 1) and also is exposed just east of the DVRFS in the lower plate of the Keystone Thrust Fault in Cottonwood Valley (fig. 1 and fig. 3). A deep well drilled to explore for oil and gas (Virgin River USA 1-A) penetrated the Moenkopi Formation and Kaibab Limestone at Mormon Mesa, just east of the DVRFS (McKay and Kepper, 1988).
Sixteen analyses were used to define the hydraulic-property estimates for the SCU. A drill-stem test from the petroleum exploration well at Mormon Mesa adjacent to the DVRFS provided the only data for this HGU. Fifteen analyses of drill-stem tests of Permian sedimentary rocks in the Colorado Plateau region of southwest Utah have been included in this report to provide additional hydraulic property estimates. The Permian sedimentary rocks of the Colorado Plateau are thought to be hydrologically similar to Mesozoic and Permian sedimentary rocks in the DVRFS because they include some of the same stratigraphic formations and have similar lithologies. Test-interval thicknesses ranged from 4 to 35 m. Aquifer-test pumping rates ranged from 0.1 to 215 L/s with a minimum pumping time of 430 minutes.
Horizontal hydraulic-conductivity values ranged from 0.0002 to 0.3 m/d with geometric and arithmetic means of 0.002 m/d and 0.02 m/d, respectively. The 95-percent confidence interval about the geometric mean for these values ranged from 0.0007 to 0.005 m/d. No estimates of storativities were obtained for the SCU.
The upper carbonate aquifer (UCA) and the lower carbonate aquifer (LCA) interfinger with the upper and lower clastic confining units. The UCA and LCA are Cambrian to Permian carbonate rocks consisting of cherty, siliceous, silty, shaly, and fine-grained limestone and cherty, silty, sandy, and fine-grained dolomite with subordinate chert, shale, siltstone, sandstone, and quartzite. Although clastic intervals confine flow, limestones and dolomites contained in these strata are aquifers that are present in the eastern two-thirds of the Great Basin (Harrill and Prudic, 1998). The LCA is separated physically from the UCA by the Eleana Formation and Chainman Shale (upper clastic confining unit). The Paleozoic carbonate rocks of the UCA and LCA are widely distributed in the eastern and southern parts of the DVRFS (fig. 3). These rocks are missing from the northwestern part of the study area because of thick accumulations of volcanic rocks and a facies change in Mississippian rocks from predominantly limestone and dolomite to predominantly argillite and quartzite.
Thirty-eight analyses of hydraulic properties were compiled for the upper and lower carbonate aquifers, 33 from single-well aquifer tests and 5 from multiple-well aquifer tests. Test-interval thicknesses ranged from 8 to 508 m. Aquifer-test pumping rates ranged from 0.9 to 7 L/s with a minimum pumping time of 180 minutes. To avoid biasing, aquifer-test analyses available for pumping wells were omitted from the statistical summaries when data or analyses for an observation well were available.
Horizontal hydraulic-conductivity values ranged from 0.00001 to 820 m/d with geometric and arithmetic means of 0.6 m/d and 90 m/d, respectively. The 95-percent confidence interval about the geometric mean for these values ranged from 0.2 to 2 m/d. Storativity values from 10 analyses of the pumping tests ranged from 0.0008 to 0.006 with an arithmetic mean of 0.003 (app. A).
The analyses were subdivided and statistically summarized to evaluate differences in hydraulic conductivity for rocks with extensive faulting with or without karst development, and rocks without extensive structural disturbance. The geometric mean of the horizontal hydraulic-conductivity values for extensively faulted and karstic limestone and dolomite was 3 m/d, whereas the geometric mean of hydraulic-conductivity values of unfaulted to simply faulted limestone and dolomite was 0.1 m/d. The difference between the geometric means of these two groups suggests that extensive faulting and karst development significantly increase hydraulic conductivity of the UCA and the LCA.
The upper clastic confining unit (UCCU) and the lower clastic confining unit (LCCU) consists of Late Proterozoic to Permian argillite, shale, siltstone, quartzite, sandstone, and conglomerate with subordinate chert, limestone, dolomite, and diabase. The UCCU and LCCU are regional confining units although the limestone, dolomite, and clastic rocks contained in them locally transmit water. Clastic rocks comprising the UCCU and the LCCU are widely exposed in mountainous areas bordering Yucca Flat, Pahrump Valley, and Death Valley (fig. 1). Upper Cambrian to Mississippian formations in this HGU intertongue with the LCA. The UCCU and the LCCU are considered as separate units in the DVRFS hydrogeologic framework but are combined in this report.
Twelve single-well analyses of hydraulic properties were compiled for the UCCU and the LCCU. Seventeen results of permeameter tests also were available. These permeameter tests were used to obtain estimates of matrix permeabilities of these confining units. Available analyses were from wells in and near the central and northeastern sections of the DVRFS. Test-interval thicknesses ranged from 15 to 1,285 m.
Horizontal hydraulic-conductivity values for the UCCU and the LCCU ranged from 0.00000003 to 5 m/d with geometric and arithmetic means of 0.00003 m/d and 0.2 m/d, respectively. The 95-percent confidence interval about the geometric mean for these values ranged from 0.000003 to 0.0003 m/d. The maximum hydraulic-conductivity value was obtained from an aquifer test in the Funeral Mountains (fig. 1) where the quartzites of the LCCU in this area possibly are sufficiently fractured to allow water to flow from Amargosa Desert into Death Valley (D'Agnese and others, 1997).
Because of different deformation behaviors, the UCCU and LCCU were subdivided for further statistical analyses. The UCCU is composed primarily of shale and the LCCU is composed primarily of quartzites. Shales tend to deform plastically, sealing fractures, while quartzites tend to be more brittle when deformed (Faunt, 1997).
Nine analyses of aquifer tests were available for the shale lithologies of the UCCU (Chainman Shale and the Eleana Formation). The geometric and arithmetic means of the horizontal hydraulic-conductivity values were 0.01 m/d and 0.07 m/d, respectively, with a range from 0.0003 to 0.4 m/d. The 95-percent confidence interval about the geometric mean for these values ranged from 0.002 m/d to 0.06 m/d.
Nineteen analyses of aquifer tests (field and laboratory) were available for the quartzitic lithologies of the LCCU. The geometric and arithmetic means of the hydraulic-conductivity values were 0.0000006 m/d and 5 m/d, respectively, with a range from 0.00000003 to 5 m/d. The 95-percent confidence interval about the geometric mean for these values ranged from 0.00000007 to 0.000005 m/d. However, using only the three pumping tests available for the quartzitic formations, a higher geometric mean hydraulic conductivity of 0.05 m/d is obtained with a range from 0.0002 to 5 m/d.
The crystalline confining unit (XCU) consists of Middle Proterozoic crystalline metamorphic and igneous rocks and metamorphosed Late Proterozoic sedimentary rocks. These granites and metamorphic rocks crop out mainly along the southwestern margins of the study area, in the Panamint Range and Black Mountains bordering Death Valley, and in the Nopah Range, Kingston Range, and Mesquite Mountains between Death Valley and Pahrump Valley (fig. 1; Grose and Smith, 1989). In most other areas, the crystalline confining unit forms the basement rock, which is generally deeply buried.
Although these rocks can produce small quantities of water through fractures and weathered zones, they are relatively impermeable and considered the base confining unit (Prudic and others, 1995; Bedinger and others, 1989). Bedinger and others report that rocks of this type, subdivided into weathered, shallow depth (less than 300 m), and deep depth (greater than 300 m) are characterized by hydraulic conductivities represented by geometric means of 0.03, 0.0005, and 0.0000003 m/d, respectively. The 85-percent confidence interval for weathered metamorphic rocks is 0.002 to 0.4 m/d; for shallow depth metamorphics is 0.00001 to 0.02 m/d; and for deep metamorphics is 0.00000002 to 0.000006 m/d (Bedinger and others, 1989).
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