Appendix
Evaluation of Cumulative Hydrologic Impacts on the N-Aquifer^*

1.0 INTRODUCTION

This report was prepared by LFR Levine·Fricke (LFR) at the request of the Natural Resources Defense Council (NRDC) and presents an evaluation of information from United States Geological Survey (USGS) progress reports on "Ground-Water, Surface-Water, and Water-Chemistry Data" for the Black Mesa area, Northern Arizona. Information from the progress reports has been compared with the criteria established in the April 1989 Cumulative Hydrologic Impact Assessment (CHIA) of the Peabody Coal Company (Peabody) Black Mesa/Kayenta Mine prepared by the U.S. Department of the Interior Office of Surface Mining Reclamation and Enforcement (OSMRE). The purpose of this evaluation is to review monitoring data contained in the progress reports, and determine whether material damage can be identified based upon the CHIA criteria. The focus of the review is on groundwater conditions within the N-aquifer, impacts of groundwater extractions on the aquifer, and the associated CHIA criteria. This evaluation is based on review and analysis of the documents listed in Appendix A and background information regarding the geology and groundwater resources of the Black Mesa area of Arizona.

On March 8, 1991, as part of a legal settlement, OSMRE agreed to review Black Mesa N-aquifer monitoring data against the CHIA criteria and thereafter report their findings to the Navajo Nation, Hopi Tribe, and Peabody in annual reports. OSMRE's review is dependent upon receipt of the monitoring data by OSMRE from Peabody.

For our evaluation, LFR compared Black Mesa area monitoring data against material damage criteria established in the 1989 CHIA. Additionally, LFR reviewed other pertinent documents including a January 1988 draft version CHIA (Draft CHIA), OSMRE material damage reviews, and various OSMRE/USGS correspondence regarding the Black Mesa monitoring program and data review. LFR has concluded that material damage has occurred based upon the April 1989 final version CHIA (Final CHIA) Criterion 1. It is difficult to assess material damage to the N-aquifer based upon the other three Final CHIA criteria, due to the dependence of the criteria on conceptual groundwater computer modeling and lack of use of available monitoring data. LFR determined that if the data contained in the Progress Reports were evaluated against the Draft CHIA criteria it could be concluded that material damage has likely occurred. In addition, if the Draft CHIA criteria were used, additional material damage would likely become evident if present trends continue. In fact, OSMRE states that it "could not determine whether or not material damage to the hydrologic balance of the N-aquifer has occurred" for multiple CHIA criteria during years that the USGS did not perform a computer simulation. The USGS has, to date, performed computer simulations of the N-aquifer system twice: once for its 1989-90 report and once for its 1992-93 report.

Deficiencies and inconsistencies of reported monitoring data and a general lack of monitoring information make a complete evaluation of hydrogeologic conditions in the Black Mesa area difficult. Additionally, the 1989 CHIA criteria minimize the importance of actual monitoring data collected as they are primarily based upon predicted groundwater conditions established using groundwater models. These inadequacies suggest that the applicable agencies are probably not able to provide adequate ongoing oversight of N-aquifer conditions as they pertain to mine-related withdrawals.

2.0 OBJECTIVE

The objectives of this report are to determine whether material damage can be identified, based upon black mesa CHIA criteria, and to evaluate conclusions contained in the OSMRE material damage reviews. To accomplish the objectives, LFR compared monitoring data contained in the USGS progress reports and other pertinent documents with the criteria as explained in the CHIA and performed a review of the OSMRE material damage reviews. In light of data inadequacies, additional resource material was also reviewed to establish historic conditions and evaluate current trends. The scope of this evaluation is limited to impacts of pumping on the N-aquifer groundwater resource and does not address other pertinent criteria such as groundwater and/or surface water quality.

3.0 HYDROGEOLOGY OF THE BLACK MESA AREA

The Black Mesa region of northeastern Arizona is located in the Plateau Uplands Hydrogeologic Province and is characterized by high isolated mesas and steep-walled canyons. The Black Mesa, with an area of approximately 5,400 square miles, is underlain by thick sequences of relatively flat-lying, well-lithified sedimentary rocks. The mesa land surface rises steeply on the east side to more than 3,000 feet above the surrounding lowland, while it slopes gradually toward the lowland to the west.

A thin veneer of recent unconsolidated sediments covers the surface of the mesa with floodplain alluvial deposits generally occurring in narrow bands along major drainage channels. The underlying sedimentary rock sequence, Permian to Late Tertiary in age, is highly variable and consists of up to 10,000 feet of interbedded sandstone, mudstone, siltstone, limestone, coal, and gypsum deposits (Lopes and Hoffman 1996).

Several water-bearing zones (aquifers) underlie the Black Mesa area. The primary aquifer in the Black Mesa area is the Jurassic-age N-aquifer, which includes the highly productive Navajo Sandstone and the underlying Wingate Sandstone (Cooley et al. 1969). The N-aquifer is more than 1,200 feet thick in the northwestern portion of the mesa and thins toward the southeast corner of the mesa. The N-aquifer is unconfined around the margins of the mesa where it is exposed and overlying sediments have been removed by erosion. Beneath approximately 3,500 square miles of Black Mesa, however, the N-aquifer is fully saturated and confined by sediments of the overlying D-aquifer and Carmel Formation (Lopes and Hoffman 1996). Recharge to the N-aquifer occurs primarily in the area near Shonto, north and northwest of the mesa, where the N-aquifer is exposed at the surface (Lopes and Hoffman 1996).

The D-aquifer generally consists of isolated thin sandstone layers of the Morrison Formation and the Cow Springs Member of the Entrada Sandstone, separated by thick sequences of lower permeability mudstone and siltstone (Cooley et al. 1969). The thickness of the D-aquifer varies from less than 100 feet in the area northwest of the mesa to 1,300 feet in the central portions of the mesa (Lopes and Hoffman 1996). Groundwater occurs under both unconfined and confined conditions within the D-aquifer. Hydraulic heads in the D-aquifer are as much as 600 feet higher than those of the underlying N-aquifer, resulting in a significant potential downward gradient toward the N-aquifer. Recharge to the D-aquifer primarily occurs along the eastern slope of the mesa where the unit is exposed at higher elevations (Lopes and Hoffman 1996).

The D- and N-aquifers are separated by a lower-permeability confining unit, or aquitard, consisting of the lower Entrada Sandstone and the Carmel Formation. This confining unit consists of generally less than 300 feet of mudstone and silty sandstone, which restricts the downward flow of poor quality water from the overlying D-aquifer into the underlying N-aquifer; however, recent studies have shown that leakage of poor quality water from the D-aquifer to the underlying N-aquifer may be significant in the southeast portion of the mesa (Lopes and Hoffman 1996).

Groundwater flow in the N-aquifer is generally from the recharge area north of the mesa, from surface elevations greater than 6,300 feet above sea level, toward the south-southeast beneath Black Mesa (Lopes and Hoffman 1996). Because the thickness of the N-aquifer decreases significantly in the southern portion of the mesa, the direction of regional groundwater flow beneath the central portion of the mesa generally diverges toward the northeast and southwest (Lopes and Hoffman 1996). Groundwater from the N-aquifer discharges to Laguna Creek and Moenkopi Wash, as well as to springs along the margins of the mesa where the N-aquifer outcrops. Water withdrawn from the N-aquifer takes many years to be replenished through the recharge area; therefore, long-term impacts on springs may result from groundwater pumping.

Precipitation in the Black Mesa area ranges from 7 inches per year to 18 inches per year near Shonto and in the higher elevations of the mesa (Lopes and Hoffman 1996). Precipitation recharging the shallow unconsolidated sediments and the upper D-aquifer results in shallow flow outward toward the margins of the mesa and the occurrence of springs along surface drainage-ways.

4.0 BASIS OF EVALUATION

Pursuant to the Surface Mining Control and Reclamation Act of 1977, OSMRE performed a CHIA of the Peabody Coal Company's Black Mesa/Kayenta Mine on the Black Mesa Area in Northern Arizona. In January 1988, OSMRE issued a copy of its CHIA for the Black Mesa area. In April 1989, a revised CHIA for the Black Mesa was issued. Differences between the Draft and Final CHIA are discussed in Section 5.2 of this document. The purpose of the Black Mesa CHIA was to determine whether Peabody's proposed extraction of approximately 4,000 acre-feet of water per year from the N-aquifer would cause material damage to the aquifer.

The hydrologic concerns addressed in the CHIA are primarily related to the diminution of the N-aquifer water resource related to potential adverse impacts on water quantity and quality. As part of the CHIA, 1,324 wells and springs were investigated for potential impacts from mining. OSMRE concluded that none of the projected impacts associated with the proposed mine operation exceeded material damage criteria determined in the CHIA process; therefore, it anticipated no material damage to the hydrologic balance within the study area.

To determine long-term effects on the Black Mesa area hydrologic system resulting from industrial and municipal groundwater withdrawals from the N-aquifer, the USGS compiles data collected for the Black Mesa monitoring program into progress reports. To date, sixteen progress reports have been published, beginning in 1978. Most of the reports summarize one year of data.

The progress reports typically contain information on N-aquifer groundwater levels, the volume of groundwater withdrawn from the N-aquifer, surface water flows, spring discharges, and water quality data. Each report contains primarily new data, except for some limited historical data used for comparison. Some of the reports also contain additional information pertinent to the monitoring program, such as flowmeter test results and groundwater modeling simulation summaries. Data are presented in table format with collection points shown on accompanying figures. Explanation of the data and comparison with previously collected data are usually limited to brief narratives and a few graphs.

On March 8, 1991, OSMRE agreed to begin reviewing Black Mesa N-aquifer monitoring data against the CHIA criteria and subsequently report their findings to the Navajo Nation, Hopi Tribe, and Peabody in annual reports. The OSMRE reports contain a brief introduction, geologic summary, and individual evaluation of the N-aquifer material damage CHIA criteria (similar to Section 5.1 of this report). To date, five OSMRE reports have been published, all of which have concluded, "[M]aterial damage to the hydrologic balance of the N-aquifer outside Peabody's permit area, caused by mining, has not occurred."

Considerable OSMRE/USGS correspondence regarding the Black Mesa monitoring program and data review has occurred. The correspondence seems to focus on concerns relating to the criteria accuracy and, in particular, the association of material damage criteria with conceptual computer modeling.

5.0 DISCUSSION

To evaluate the impact of groundwater withdrawals on the N-aquifer, CHIA criteria were established to allow for comparison of future groundwater levels and surface water flows to baseline water levels and flows established in the CHIA. Within the CHIA, pertinent baseline years are listed as January 1, 1980 through December 31, 1984 for surface water quantity evaluations, and 1985 for groundwater level evaluations.

Section 5.1 of this report includes an evaluation of each criterion, Section 5.2 discusses Black Mesa CHIA criteria language and basis, and Section 5.3 discusses some of the difficulties encountered when comparing Black Mesa monitoring data to CHIA criteria.

5.1 EVALUATION OF CHIA CRITERIA

The Black Mesa CHIA criteria are summarized in Section 5.2.2 of the CHIA. LFR limited the evaluation discussed in this report to those criteria specifically pertinent to N-aquifer groundwater resources.

Below is a summary of Black Mesa CHIA criteria along with associated observations from our evaluation.

Criterion 1: Maintain potentiometric head 100 feet above top of N-aquifer at any point to preserve confined state of aquifer. This criterion was established to protect the structural stability of the N-aquifer due to a reduction of potentiometric head and water stored within the aquifer. Confined aquifers are typically dependent upon water pressure contained within the matrix pore space to retain structural integrity; without the additional support of pore space water pressure some aquifers can compact, causing a permanent loss of storage capacity and, in some cases, surface land subsidence. Because the N-aquifer in the Black Mesa area is comprised primarily of cemented sandstone, the likelihood of aquifer compaction occurring is lessened. This likelihood of N-aquifer compaction is recognized on page 5-6 of the CHIA; however, "as an added insurance," the criterion is retained.

LFR was able to locate measuring point elevations for the N-aquifer wells listed in the USGS progress reports and evaluate measured water levels based upon this criterion. Of the 15 wells listed as existing within the confined portion of the N-aquifer in the USGS progress reports, 6 have a potentiometric head within 100 feet of the top of the N-aquifer. Four of these six wells (Rough Rock, 10T-258, 10R-111, and Sweetwater Mesa) are located near the aquifer boundary between confined and unconfined portions of the N-aquifer and behave more like wells existing in the unconfined portion of the aquifer. The progress reports map the Rough Rock well in the unconfined portion of the N-aquifer.

Of the 11 wells monitored that are known to be installed in the confined portion of the aquifer, two (Kayenta West and BM3) have a potentiometric head less than 100 feet above the top of the N-aquifer. The groundwater level at Kayenta West has recently (1996 data) been reported over 11 feet below the approximated top of the N-aquifer and was last reported (1998 data) approximately 0.2 feet above the top of the N-aquifer. The groundwater level at BM3 has recently (1996 data) been within approximately 1 foot of the top of the N-aquifer and was last reported (1998 data) approximately 1.6 feet above the top of the N-aquifer.

OSMRE acknowledges this criterion failure at BM3 in its material damage reviews. However, since the static water level in this well was 99 feet above the top of the N-aquifer when it was first installed (1959) OSMRE concludes that "material damage to the hydrologic balance of the N-aquifer, caused by mining, with respect to maintaining the potentiometric head above the top of the N-aquifer, has not occurred." Monitoring data indicate a water level decline in the BM3 well more than 93 feet since the pre-stress (or pre-mining) period.

OSMRE does not include a discussion of the Kayenta West well in its material damage reviews nor do they include any explanation for the exclusion of Kayenta West data from their reviews. Monitoring data collected from the Kayenta West well is included in the USGS progress reports; however, this data is omitted form the OSMRE reviews. The USGS monitoring data indicate a water level decline in the Kayenta West well of more than 69 feet since the pre-stress period.

Notwithstanding OSMRE's exception for the BM3 well, it appears that material damage to the hydrologic balance of the N-aquifer has occurred based upon CHIA Criterion 1.

Criterion 2: A value of leakage from the D-aquifer not to exceed 10 percent from mine related withdrawals. Continued stresses on the N-aquifer will increase vertical gradients and potentially induce vertical leakage of poor quality water from the overlying D-aquifer. This criterion was established to prevent degradation of N-aquifer water quality due to induced leakage of poor quality groundwater from the overlying D-aquifer.

In order to quantify leakage from the D-aquifer to N-aquifer, water level measurements from, and vertical hydraulic conductivities between, both aquifers are needed. However, since D-aquifer water level data is not monitored, one must use other approaches. Other methods of evaluating D-aquifer leakage to the N-aquifer include inorganic water quality monitoring from the D- and N-aquifers and groundwater flow and transport modeling.

To establish and evaluate this criterion for the CHIA, OSMRE used the USGS N-aquifer model. Specifically, the CHIA evaluated the model's simulation of predicted changes in the annual volume of leakage from the D-aquifer to the N-aquifer attributable to mine related withdrawals. The CHIA predicted no significant change in volume of D-aquifer leakage to the N-aquifer for the simulated period.

In its annual material damage reviews, OSMRE uses inorganic water quality monitoring to analyze for induced leakage. This approach is dependent upon historical inorganic water quality data for the area of study. In the Black Mesa area, the N-aquifer generally has lower inorganic constituent content, including major ions and cations such as chloride and sulfate, than the D-aquifer. A measure of the presence of inorganic constituents is the amount of Total Dissolved Solids (TDS) expressed in milligrams per liter. In OSMRE's analysis, where induced leakage from the D-aquifer is occurring, an increase in TDS would be anticipated in the N-aquifer. Yet, where increases in TDS have been observed for N-aquifer wells, some justification has been made to minimize the increasing values. While increasing TDS trends have been observed for multiple monitoring locations, the trends are noted to be "small" or "statistically insignificant." Other analytical results are disregarded due to sample mislabeling, failure to follow sampling protocol, localized failure of well seals, or changes in pumping trends. OSMRE concludes, "[M]aterial damage to the hydrologic balance of the N-aquifer, caused by mining, with respect to leakage from the D-aquifer to the N-aquifer, has not occurred." OSMRE bases its conclusion upon inorganic water quality analysis only; other methods of analysis are not attempted. No attempt is made to correlate the trends of increasing TDS with the material damage criterion.

If D-aquifer leakage were estimated by evaluating the magnitude of N-aquifer water level declines, as proposed in the Draft CHIA, a material damage conclusion due to degradation of N-aquifer water quality would be more likely. The N-aquifer potentiometric head is more than 100 feet below the baseline altitude in two of the monitored wells (Piñon and Keams Canyon). Additionally, data trends for at least four additional wells (BM2, BM3, BM5, and BM6) indicate that groundwater levels may soon be more than 100 feet lower than the baseline altitude in those wells. Ultimately, six or more of the 11 monitored wells may exhibit groundwater level declines more than 100 feet before mining operations cease.

Criterion 3: A discharge [from N-aquifer springs] reduction of 10 percent or more, caused by mine related withdrawals based on results of N-aquifer simulation. This criterion was established to protect the natural springs in the Black Mesa area. Well capture generally results in reduced discharge from the aquifer, induced leakage to the aquifer, or some combination of those two.

OSMRE used the N-aquifer groundwater model to establish and evaluate this criterion for the CHIA. It bases the criterion on present and future N-aquifer simulations. Apparently, when model updates are unavailable this criterion is based upon the most recent model results or no material damage evaluation is attempted. Within the CHIA, only one spring area (Pasture Canyon) appears to have been evaluated. The CHIA predicted "outflow to the springs in Pasture Canyon would not be affected by the duration of pumping at the mine." However, later in the same paragraph (page 6-39), OSMRE states that the simulated outflow numbers for Pasture Canyon "should be used with caution because the model does not adequately represent important details of the local geology in this area." It also states that "reliable estimation of changes in flow of the Pasture Canyon springs would require detailed study and modeling of that local area."

In its annual material damage reviews, OSMRE bases its analysis of this criterion on the latest USGS N-aquifer model or makes no evaluative attempt. Since the Final CHIA was released in 1989, the USGS has performed modeling simulations twice. The most recent modeling results are contained in the 1992-1993 USGS progress report released in 1995. Therefore, all OSMRE material damage analyses are based upon pre-1995 modeling results. OSMRE concludes either that based upon "the most recent N-aquifer computer model simulation, material damage to the hydrologic balance of the N-aquifer, caused by mining, with respect to N-aquifer discharge has not occurred" or that it "could not determine whether or not material damage to the hydrologic balance of the N-aquifer has occurred" due to a lack of modeling results. Either way, analysis of this criterion as proposed in the 1990 CHIA has not occurred since 1994 data were evaluated.

Discharges for multiple springs located in the Black Mesa area are monitored and the USGS progress reports contain some of these data. LFR searched the progress reports and other USGS water use reports to obtain spring discharge data for analysis. Of the nine springs for which discharge data were available, seven show a decline of 30 percent or more. Flows have apparently increased in two springs (Dennehotso, Hard Rocks); however, original flows at Hard Rocks were only estimated and the magnitude of change in flow from the spring near Dennehotso tends to imply that some unknown change(s) may have occurred (i.e., new monitoring location, nearby construction, etc.). Some of the monitoring data are questionable due to variable monitoring locations and the lack of any attempt by the USGS to correlate them. Not only have most springs experienced a discharge reduction in excess of 30 percent, but the majority of these appear to have decreased by more than 50 percent (Rock Ledge, Moenkopi School, Many Farms, Whiskey, and Pasture Canyon). Hence, regardless of the monitoring data deficiencies, material damage appears obvious based upon actual conditions. It is unclear why the modeling simulations have not been adjusted to better represent the decrease in spring discharges.

Criterion 4: A discharge [from N-aquifer to washes] reduction of 10 percent or more, caused by mining. This criterion was established to prevent a reduction of flow in the Black Mesa Area washes due to reduction of N-aquifer discharge to the washes. When a stream is in communication with an aquifer and the hydraulic head of the aquifer is greater than the relative elevation of the stream, water will discharge from the aquifer into the stream (gaining stream). As head potentials within the aquifer decrease, the discharge to the gaining stream will diminish. If the head potential within the aquifer decreases below the relative elevation of the stream channel, the stream will begin to lose water to the aquifer (losing stream).

Within the CHIA, the N-aquifer model was again used to evaluate the potential for material damage due to reduced baseflow discharge from the N-aquifer to area washes. Predicted baseflow discharges along Moenkopi Wash and Laguna Creek are discussed. By using various pumping scenarios in multiple model simulations, the USGS was able to attribute approximate baseflow discharge reductions to industrial and/or municipal withdrawals. The CHIA concludes that mine related withdrawals would have a minor impact on baseflow discharges in some instances based upon model results, but never to exceed the material damage criterion.

As with Criterion 3, OSMRE bases its analysis of this criterion on the latest USGS N-aquifer model, which was last run in 1994. OSMRE again concludes that based upon "the most recent N-aquifer computer model simulation, material damage to the hydrologic balance of the N-aquifer, caused by mining, with respect to N-aquifer discharge has not occurred" or that it "could not determine whether or not material damage to the hydrologic balance of the N-aquifer has occurred" due to a lack of modeling results.

Historical data does exist for flow in some area washes; however, the data is limited. For the baseline years (1980-1984), data were only collected for the Moenkopi and Laguna Creek washes. Dinnebito Wash had a monitoring station established in June 1993. Prior to establishing the 10 percent reduction criteria, the CHIA noted that the Moenkopi gauge had been rated as having poor accuracy. As such, the margin of error in measurement of more than 15 percent exceeds the criterion range of 10 percent.

The USGS monitoring reports use low-flow data for comparing wash flows. Low-flow data are based upon daily stream discharges for the months of November through February of a water year. Discharge data collected during these months are considered representative of low flow because the effect of stream loss due to evapotranspiration (losses due to evaporation and transpiration, or the transfer of water to the atmosphere by vegetation) and gain from snowmelt and rainfall (which generally occurs during temperate months) is minimized.

Dinnebito Wash has averaged a mean daily discharge (as low-flow) of approximately 0.50 cubic feet per second (ft3/s), based upon 1994-1997 continuous-record data (the Dinnebito Wash gaging station became operational in June 1993). In 1998, the low-flow discharge measurements for Dinnebito Wash ranged from 0.32 ft3/s to 0.44 ft3/s, a reduction of at least 12 percent. The average mean daily discharge (as low-flow) for the baseline years on Moenkopi Wash was reported to be about 3.2 ft3/s. From 1992 through 1998, the average mean daily discharge (as low-flow) on Moenkopi Wash was reported to be about 2.4 ft3/s. Therefore, there has been a discharge reduction of approximately 25 percent in Moenkopi Wash according to the USGS progress reports. The Laguna Creek monitoring station has been moved to a new location since readings were taken for the baseline years, making evaluation of the data difficult.

SUMMARY

Of the four N-aquifer groundwater resource criteria identified in Section 5.2.2 of the Black Mesa CHIA, one (Criterion 1) is written such that material damage can be readily determined. LFR feels that material damage has occurred based upon Final CHIA Criterion 1. The other three criteria are written such that determining material damage is more difficult. Criteria 2, 3, and 4 are written to be applicable only if their failure can be attributed to mine related groundwater withdrawals. Additionally, evaluation of Criterion 3 is based solely on computer groundwater modeling simulations and Criteria 2 and 4 are directly dependent upon the modeling results. Since the modeling simulations are not performed regularly, OSMRE does not annually review the criteria based upon the simulation results, making it impossible for it to ascertain whether material damage has occurred. Concluding material damage is therefore problematic or impossible based upon the Final CHIA criteria. However, in light of available monitoring data, it seems more difficult to concede OSMRE's conclusion that material damage has not occurred.

Overpumping of the aquifer is evidenced by excessive drawdown in some Black Mesa area groundwater monitoring wells and considerably lower area spring discharges. It appears that additional negative impacts on and resulting damage to the aquifer are imminent. LFR does not feel that the Black Mesa CHIA criteria are necessarily protective of the N-aquifer water resources due to their dependence upon conceptual computer modeling results and disregard of actual monitoring data. Damage to the hydrologic balance of the N-aquifer may be compounding over time due to the lack of protection provided based upon the CHIA criteria and the disregard of actual monitoring data.

Four of the 11 wells located within the confined portion of the N-Aquifer (BM3, Kayenta West, Piñon, and Keams Canyon) have experienced excessive groundwater level declines. Data trends for at least three additional wells (BM2, BM5, and BM6) indicate that excessive groundwater level declines are likely to occur.

When present flows are compared with those recorded for baseline years, discharge reductions of 25 percent or more can be seen in the majority of Black Mesa area springs and in the primary area wash. All springs located in the southern portion of Black Mesa, the area toward which N-aquifer groundwater flows, have experienced large percentage (30 to 82 percent) discharge reductions. While these trends suggest that the hydrologic balance of the N-aquifer has been affected, it is difficult to conclusively determine material damage based upon the CHIA criteria due to the language and basis of the criteria, raising serious concerns about the utility of the CHIA. These concerns are discussed further below.

5.2 DISCUSSION OF BLACK MESA CHIA CRITERIA

As noted above, three of the four material damage criteria in the Black Mesa CHIA are difficult to evaluate due to the vague language and the basis used for the Final CHIA criteria. For our evaluation, LFR reviewed both the Final CHIA and the Draft CHIA. Some improvements were incorporated into the text of the Final CHIA from comments generated by the Draft CHIA, such as the removal of reference to "the time of bond release" from the criteria and a discussion pertaining to the likelihood of aquifer compaction in a consolidated sandstone aquifer. However, it appears that the Draft CHIA was probably more protective of N-aquifer resources in the Black Mesa area than the Final CHIA. LFR concerns are discussed below.

A primary problem with the Final CHIA is that most material damage criteria are dependent upon computer groundwater modeling simulations. The third criterion is based directly upon modeling results. The second and fourth criteria use modeling to evaluate the percentage effect due to mine-related withdrawals, and are thus indirectly dependent upon modeling results. While groundwater modeling can be a useful predictive tool for future use planning and protection of groundwater resources, it should never be used to supplant actual monitoring data.

The accuracy and resolution of geological and hydrogeological data used to construct the model limit modeling results. Often, computer models are created based upon generalized data available for the area of study. The Black Mesa area groundwater flow model was not constructed specifically for the purpose of monitoring and identifying material damage to the N-aquifer or its associated springs and washes. OSMRE recognized the limitations of computer modeling, yet retained the material damage criteria dependency upon modeling results. Section 6.2.2.4 of the CHIA states that "simulated water levels had about one chance in three of being more than 40 feet different from actual water levels before 1965, when little water-level change occurred. As water levels have changed more rapidly since 1970, the simulated levels may have become less accurate." In addition, the CHIA states: "The calibrated data are not unique; equally close agreement to the observed heads could have been reached using different recharge values balanced by different aquifer characteristics." OSMRE concludes CHIA section 6.2.2.4 by stating: "The predictive accuracy of any model is related to the accuracy of the estimates of aquifer parameters used and predictions of future pumpage. During the 1965-1984 calibration period, maximum annual withdrawals were about 50 percent of annual recharge. If future withdrawals were much greater, unanticipated responses in the aquifer may occur that would require additional refinement of the model." Inaccurate estimates of aquifer recharge would create erroneously high water level predictions from modeling. LFR believes that estimates for N-aquifer recharge incorporated into the model were erroneously high. Essentially, these high recharge estimates create the illusion that stresses placed on the aquifer will have less of an impact.

Others, including the USGS, noted concerns regarding the utilization of the N-aquifer model for material damage predictions and analysis. In January 1996 the USGS Hydrologic and Research Department Chief sent a letter to OSMRE (USGS, 1996) stating the need to update the groundwater model used for evaluation in the CHIA. Concerns pointed out in the 1996 letter included the probability that "recharge rates for the past 10,000 years could be less than half of previous estimates" and that C14 and tritium data indicate that "the overlying D-aquifer could be leaking into the N-aquifer." The letter also points out that "observed system responses appear to be diverging for a few locations." In another letter from the USGS (USGS 1998), it is stated that "the model is indicative of long-term effects until such effects can be substantiated over time or by site-specific investigations." Following the latest (1994) model run, results for which are summarized in the 1992-1993 USGS progress report, the USGS states that "an apparent disparity between simulated and actual water-level changes in the continuous-record observation wells and in the Chilchinbito PM3 well suggest the need for analysis of model calibration and sensitivity."

In September 1989, the United States Environmental Protection Agency (U.S. EPA) provided OSMRE with comments regarding the Draft Environmental Impact Statement associated with the 1989 CHIA. In its cover letter, U.S. EPA states that it believes mine-related withdrawals of N-aquifer water resources "may result in significant adverse environmental impacts to water resources . . . that should be avoided" and that "the lack of sufficient information on water resource conditions severely impedes evaluation of impacts, alternatives, and appropriate mitigation measures." Later, in its detailed comments, U.S. EPA states, "[W]hile EPA accepts the approach taken in modeling hydrologic baseline conditions and impacts, the conclusiveness of this effort is undermined by lack of data. This limitation, compounded by use of material damage criteria based on thresholds much less sensitive than required under NEPA, lead us to reject the evaluation of hydrologic impacts." They then go on to discuss the importance of developing a good monitoring program to obtain actual data.

Three of the four criteria apply only if the effects are caused by mining (or overpumping related to mining); however, it is difficult to quantify effects on the aquifer that are attributable to specific mining operations. It should be noted that mine-related pumping accounts for the majority of the water withdrawn from the N-aquifer. For example, in 1998, 57 percent (4,030 acre-feet) of the total water withdrawn from the aquifer (7,060 acre-feet in 1998) was for mine usage. Of the total volume withdrawn from the N-aquifer, 5,470 acre-feet were withdrawn from the confined portion. Mine-related withdrawals accounted for 74 percent (4,030 acre-feet) of the 1998 volume withdrawn from the confined portion of the N-aquifer. Mine-related withdrawals have historically accounted for an even larger percentage of the total withdrawals; however, municipal demands are growing while mining demands have remained relatively constant since the early 1970s.

Finally, the Draft CHIA contained five material damage criteria, of which four seemed somewhat protective of the N-aquifer water resources (with a high level of evaluative effort). While three of the five Draft CHIA criteria were applicable only if failure could be attributed to mine-related withdrawals, concluding material damage based upon Draft CHIA criteria was not dependent upon modeling. For the Final CHIA, OSMRE completely removed one of the Draft criteria and adjusted the language for two of the other criteria. Final CHIA Criterion 1 remained unchanged from the Draft. The criteria changes are discussed below.

Draft CHIA Criterion 1 reads: "Maintain potentiometric head 100 feet above top of N-aquifer at any point to preserve confined state of aquifer." This criterion remains unchanged in the Final CHIA. OSMRE retained this criterion as "added insurance" due to the low likelihood of aquifer compaction.

Draft CHIA Criterion 2 reads: "At bond release, potentiometric head in N-aquifer is within 100 feet of baseline altitude." This criterion was established to prevent degradation of N-aquifer water quality due to an increased migration rate of water from the overlying D-aquifer. The wording of the Final Criterion 2 is: "A value of leakage from the D-aquifer not to exceed 10 percent from mine-related withdrawals." Evaluation is more readily conducted based upon the Draft CHIA criterion.

The N-aquifer potentiometric head is more than 100 feet below the baseline altitude in two of the monitored wells (Piñon and Keams Canyon). Additionally, data trends for at least four additional wells (BM2, BM3, BM5, and BM6) indicate that groundwater levels may soon be more than 100 feet lower than the baseline altitude in those wells. Ultimately, six or more of the 11 monitored wells may exhibit groundwater level declines of more than 100 feet. Therefore, based upon the Draft CHIA criterion, material damage appears to have occurred and additional damage appears imminent.

Draft CHIA Criterion 3 reads: "A 25 percent reduction of the potentiometric surface at the location of the [community pumping] well, due to mining." This criterion was created to prevent a reduction of pumping well productivity and the associated increase in pumping costs. As water levels drop in community wells, they will need to be pumped harder and longer to maintain a constant production volume. Draft CHIA Criterion 3 was altogether removed from the Final CHIA; however, discussions regarding the importance of protecting well productivity are retained in Sections 5.1.2 and 7.2.2.3. In U.S. EPA's 1989 letter to OSMRE, U.S. EPA stated, "We consider the criterion originally proposed in the Draft CHIA to be more reasonable" than mitigation for damage to cavitating well pumps as discussed in the Final CHIA as justification for removing the criterion.

Presently, a 25 percent reduction of the potentiometric surface has been observed in three wells (BM3, Kayenta West, and Keams Canyon). BM3 and Kayenta West are both located in close proximity to the Kayenta pumping well system; therefore, the observed water level declines should be considered representative, if not conservative, of water level declines in the well system itself. The Keams Canyon water level decline is representative of water level decreases at the Keams Canyon pumping well system. Data for at least one additional well (BM2) indicate that a 25 percent head reduction is imminent; however, BM2 is not located in the immediate vicinity of a community pumping well system.

From modeling, the CHIA concluded that "simulated water-level changes near Kayenta are strongly affected by pumpage for the community." OSMRE later states: "South and southeast of Kayenta simulated water levels are affected both by the mine and the community." The close proximity of mining withdrawals to the Kayenta community well system, coupled with the relative magnitude of volume withdrawn from the N-aquifer, indicate that mine-related withdrawals do have an impact on water levels in the Kayenta area. In 1998, the Kayenta well system recorded withdrawal of 612.7 acre-feet while Peabody reported a withdrawal of 4,032.9 acre-feet.

For water level declines in the Keams Canyon area, the CHIA concluded: "Pumpage from the mine would account for a maximum of approximately 29 and 22 percent, respectively, at Second Mesa and Keams Canyon" based on model simulations. The Keams Canyon area is located southeast of the Peabody mine. The N-aquifer is recharged primarily from the Shonto area to the northwest of Peabody's mine. The Peabody mine withdraws a large portion of the N-aquifer recharge before it can reach the southern portions of the aquifer. The combined withdrawal from community pumping systems in the vicinity of Keams Canyon and Second Mesa for 1998 was reported as 358.7 acre-feet.

Based upon Draft CHIA Criterion 3, material damage appears to have occurred and additional damage appears imminent.

Draft CHIA Criterion 4 reads: "A discharge [from N-aquifer springs] reduction of 10 percent or more after bond release, caused by mining." This criterion was established to protect the natural springs in the Black Mesa area. The Final CHIA Criterion reads: "A discharge [from N-aquifer springs] reduction of 10 percent or more, caused by mine related withdrawals based on results of N-aquifer simulation." The updated wording makes this criterion completely dependent upon modeling and seems to disregard actual monitoring data.

Again, based upon Draft CHIA Criterion 4, material damage appears to have occurred and additional damage appears imminent.

Draft CHIA Criterion 5 reads: "A discharge [from N-aquifer to washes] reduction of 10 percent or more after bond release, caused by mining." The Final CHIA Criterion reads: "A discharge [from N-aquifer to washes] reduction of 10 percent or more, caused by mining." The removal of a criterion date is productive; however, this criterion remains almost impossible to evaluate due to the lack of consistent monitoring data and an indirect dependence upon groundwater modeling.

5.3 DIFFICULTIES OF EVALUATION

LFR believes actual monitoring data to be essential for protection of the N-aquifer groundwater resources. The presentation of Black Mesa monitoring data in the USGS progress reports does not provide for direct evaluation of the potentially affected areas discussed in the CHIA. Much relevant information is missing altogether, and other data are not correlated with existing baseline information. Evaluation by a layperson would be implausible. However, whereas data presentation within the progress reports does not provide for an easy evaluation, evaluation is possible by an expert (although extremely time consuming). Some of the factors complicating data evaluation are discussed below.

Page 3-1 of the Final CHIA states: "[T]he baseline year for purposes of this CHIA is 1985." Other places within the Final CHIA list pertinent baseline years as January 1, 1980 through December 31, 1984 for surface water quantity evaluations and 1985 for groundwater level evaluations. Not only is there contradiction within the CHIA regarding the establishment of the baseline year(s) used for evaluation, but there seems to be a violation of the principal purpose behind the CHIA in establishing a baseline period following approximately 20 years of mining-related impacts. Since PCC commenced mining operations in 1967, it seems that an attempt to establish a baseline period prior to that time would have been prudent. LFR concedes the overall lack of monitoring data from before 1967. However, it seems that resources spent performing groundwater modeling for determination of CHIA criteria failure may have been better utilized constructing a pre-mining baseline period. It does appear that OSMRE is evaluating Criterion 1 based upon pre-mining (1968) groundwater levels. It is unclear why pre-mining data is used for OSMRE's material damage evaluation of Criterion 1 and not elsewhere. It also seems confusing to establish a baseline year within the CHIA and then perform evaluation of some criteria based upon the baseline year and other criteria based upon pre-mining data.

Elevations of the top of the N-aquifer are reported in feet above mean sea level, whereas measured water levels are reported in feet below ground surface. The USGS progress reports do not compare observed water levels with the corresponding N-aquifer top elevations, nor did they provide measuring point elevations in the first 15 reports. Additional sources of information had to be obtained to determine top elevations of the N-aquifer, the thickness of the N-aquifer, and some measuring point elevations for the monitored wells.

The USGS progress reports do not consistently report data from the same monitoring points. For example, of the nine N-aquifer springs discussed in this evaluation, usually only four or five are listed in the progress reports and the four or five springs discussed vary from report to report. Also, the spring flow data and wash flow data are collected from multiple measuring points over time.

The USGS progress reports present data regarding flow in certain washes (mainly the Moenkopi Wash) for applicable reporting periods, along with rough generalizations about the flow data. However, the baseline flows are not included, making it difficult to evaluate the criterion (reports containing previous flow data are referenced).

While the majority of measuring point elevations for water level data have been incorporated into the latest (1998 data) progress report, N-aquifer top elevation and thickness at observation and pumping wells are still missing for evaluative purposes. Low flows and mean daily discharges for the baseline years of major washes could not be readily obtained to facilitate an evaluation of the baseflow discharge from the N-aquifer to the washes.

6.0 CONCLUSIONS

To determine whether Peabody's extraction of approximately 4,000 acre-feet of water per year from the N-aquifer would cause material damage to the aquifer, OSRME prepared a CHIA report dated April 1989 (4,000 acre-feet is typically used for estimation of mine-related groundwater withdrawals). Actual withdrawals have ranged from 3,430 acre-feet to 4,740 acre-feet over the last 16 years of reported data (1982-1998). The average mine-related withdrawal over the same 16 years has been approximately 3,959 acre-feet. In the CHIA, OSMRE established specific criteria used to determine whether material damage would occur. Based upon groundwater modeling performed for the CHIA, OSRME concluded that none of the projected impacts associated with proposed mine operations exceeded the material damage criteria; therefore, it anticipated no material damage to the hydrologic balance within the study area.

Through considerable analysis and additional data review, LFR overcame the difficulties encountered in evaluating the CHIA criteria. LFR evaluated groundwater, surface water, and water quality data from the Black Mesa monitoring program contained in USGS progress reports to determine if material damage to the N-aquifer can be seen or may be imminent.

Flaws in the CHIA criteria and dependence of the criteria on an underlying model hindered LFR's evaluation. These flaws preclude the OSMRE conclusion, namely that material damage to the N-aquifer has not occurred in the past, is not now occurring, and will not occur in the future. Further, LFR feels that three of the four material damage criteria may not necessarily be protective of N-aquifer water resources because they are either directly or indirectly dependent upon modeling results from a model not specifically designed to evaluate those criteria. The underlying model may reasonably predict regional N-aquifer groundwater conditions in the Black Mesa vicinity; however, the modelers concede that the model does not adequately represent geologic detail to enable conclusions at the scale required in the Final CHIA criteria.

Issues with the Final CHIA aside, material damage can be concluded based upon Criterion 1. Additionally, if the Draft CHIA criteria are reviewed and compared with data collected by the USGS, it is likely that material damage, as defined by the Draft CHIA, has occurred. Finally, if monitoring data were given precedence over modeling predictions, it may be determined that the N-aquifer has been affected, suggesting that material damage has occurred. The Black Mesa monitoring data indicate that excessive pumping of the N-aquifer has caused groundwater level declines and spring discharge reductions exceeding guidelines established in the CHIA. Not only are groundwater resource problems from overpumping the aquifer already evident, but data trends indicate that additional material damage is imminent.

Because of CHIA criteria design flaws, it appears that OSMRE may not be able to accurately determine whether most Final CHIA material damage criteria are being met. In fact, in their annual material damage reviews, OSMRE bases its analysis of Criteria 3 and 4 on the latest USGS N-aquifer model or makes no evaluative attempt. Since the Final CHIA was released in 1989, USGS has performed modeling simulations twice. The most recent modeling results are contained in the 1992-1993 USGS progress report released in 1995. Therefore, all OSMRE material damage analyses are based upon pre-1995 modeling results. Analysis of N-aquifer criteria as proposed in the 1990 CHIA has not occurred since 1994 data was evaluated.

REFERENCES

Brown, J.G., and J.H. Eychaner. 1988. Simulation of Five Ground-Water Withdrawal Projections for the Black Mesa Area, Navajo and Hopi Indian Reservations, Arizona. USGS, Water Resources Investigations Report 88-4000.

Eychaner, J.H. 1983. Geohydrology and Effects of Water Use in the Black Mesa Area, Navajo and Hopi Indian Reservations, Arizona. USGS, Water Supply Paper 2201.

GeoTrans, Inc. 1987. A Two-Dimensional, Finite-Difference Flow Model Simulating the Effects of Withdrawals to the N Aquifer, Black Mesa Area, Arizona. Prepared for Peabody Coal Company. December.

Hart, R.J., and J.P. Sottilare. 1988. Progress Report on the Ground-Water, Surface Water, and Quality-of-Water Monitoring Program, Black Mesa Area, Northeastern Arizona -- 1987-1988. USGS Open-File Report 88-467. August.

----. 1989. Progress Report on the Ground-Water, Surface-Water, and Quality-of-Water Monitoring Program, Black Mesa Area, Northeastern Arizona -- 1988-1989. USGS Open-File Report 89-383. August.

Hill, G.W. 1982. Progress Report on Black Mesa Monitoring Program -- 1982. USGS Basic-Data Report. December.

----. 1983. Progress Report on Black Mesa Monitoring Program -- 1983. USGS Basic-Data Report. December.

----. 1985. Progress Report on Black Mesa Monitoring Program -- 1984. USGS Open-File Report 85-483. August.

Hill, G.W.I., and J.P. Sottilare. 1987. Progress Report on the Ground-Water, Surface Water, and Quality-of-Water Monitoring Program, Black Mesa Area, Northeastern Arizona -- 1987. USGS Open-File Report 87-458. August.

Hill, G.W.I., and M.L. Whetten. 1986. Progress Report on Black Mesa Monitoring Program -- 1985-86. USGS Open-File Report 86-414. July.

Hydro Geo Chem. 1988. Review of Cumulative Hydrologic Impact Assessment, Peabody Coal Company Black Mesa/Kayenta Mines. July 12.

LFR Levine·Fricke. 1997. Evaluation of Impacts of Groundwater Pumping from the N Aquifer, Black Mesa Area, Arizona. August.

Littin, G.R. 1992. Results of Ground-Water, Surface-Water and Water-Quality Monitoring, Black Mesa Area, Northeastern Arizona -- 1990-1991. USGS, Water Resources Investigations Report 92-4045. May.

----. 1993. Results of Ground-Water, Surface-Water and Water-Quality Monitoring, Black Mesa Area, Northeastern Arizona -- 1990-199 1. USGS, Water Resources Investigations Report 93-41 1 1. July.

Littin, G.R., B.M. Baum, and M. Truini. 1998. Ground-Water, Surface-Water and Water-Chemistry Data, Black Mesa Area, Northeastern Arizona -- 1997. USGS, Water Resources Investigations Report 98-.

Littin, G.R., and S.A. Monroe. 1995a. Results of Ground-Water, Surface-Water and Water-Quality Monitoring, Black Mesa Area, Northeastern Arizona -- 1992-1993. USGS, Water Resources Investigations Report 95-4156.

----. 1995b. Results of Ground-Water, Surface-Water and Water-Quality Monitoring, Black Mesa Area, Northeastern Arizona -- 1994. USGS, Water Resources Investigations Report 95-4283.

----. 1996. Ground-Water, Surface-Water and Water-Quality Monitoring, Black Mesa Area, Northeastern Arizona -- 1995. USGS, Open-File Report 96-616.

Lopes, T.J., and J.P. Hoffman. 1996. Geochemical Analyses of Ground-Water Ages, Recharge Rates, and Hydraulic Conductivity of the N Aquifer, Black Mesa Area, Arizona. USGS, Water Resources Investigation Report 96-4190.

Sottilare, J.P. 1992. Results of Ground-Water, Surface-Water, and Water-Quality Monitoring, Black Mesa Area, Northeastern Arizona -- 1989-90; Bills, D.J., and J.G. Brown, with a section on Simulation of Effects of Pumping. USGS Water Resources Investigations Report 92-4008. April.

S.S. Papadopulos & Associates, Inc. 1993. Navajo Aquifer Water Study Final Report. July.

United States Department of the Interior, Bureau of Indian Affairs. 1989. Memorandum to OSM Reclamation and Enforcement Western Field Operations Regarding "Draft Environmental Impact Statement for the Proposed Permit Application, Black Mesa-Kayenta Mine, Navajo and Hopi Reservations, Arizona." September 18.

United States Department of the Interior, Office of Surface Mining Reclamation and Enforcement. 1988. Cumulative Hydrologic Impact Assessment of the Peabody Coal Company Black Mesa/ Kayenta Mine. January.

----. 1989. Cumulative Hydrologic Impact Assessment of the Peabody Coal Company Black Mesa / Kayenta Mine. April.

----. 1990. Final Environmental Impact Statement for Peabody Coal Company's Black Mesa Kayenta Mine. June.

----. 1992. Review and Analysis of Peabody Coal Company's 1990 "Hydrological Data Report" and the U. S. Geological Survey's "Results of Ground-Water, Surface-Water, and Water-Quality Monitoring, Black Mesa Area, Northeastern Arizona -- 1989-1990." December 14.

----. 1993. Memorandum to OSM Deputy Director -- Operations and Technical Services Regarding "OSM's 1991 N-Aquifer Hydrologic Material Damage Assessment Report for the Black Mesa/Kayenta Mine Complex in Arizona". June 9.

----. 1993. Report on its Review and Analysis of Peabody Coal Company's 1991 "Hydrological Data Report" and the U.S. Geological Survey's "Results of Ground-Water, Surface-Water, and Water-Quality Monitoring, Black Mesa Area, Northeastern Arizona -- 1990-1991". June 16.

----. 1994. Memorandum to OSM Deputy Director - Operations and Technical Services Regarding "OSM's 1992 N-Aquifer Hydrologic Material Damage Assessment Report for the Black Mesa/Kayenta Mine Complex in Arizona". March 17.

----. 1994. Report on its Review and Analysis of Peabody Coal Company's 1992 "Hydrological Data Report" and the U.S. Geological Survey's "Results of Ground-Water, Surface-Water, and Water-Quality Monitoring, Black Mesa Area, Northeastern Arizona -- 1991-1992". March 14.

United States Department of the Interior, Office of Surface Mining Western Regional Coordinating Center. 1987. Letter to Jim Eychaner, U. S. Geological Survey Water Resources Division regarding the draft Black Mesa Area groundwater model. March 9.

----. 1993. Memorandum to OSM Acting Director Regarding "Black Mesa Mine -- United States Geological Survey Groundwater Review." November 4.

----. 1998. Report on its Review and Analysis of Peabody Coal Company's 1996 "Hydrological Data Report -- Black Mesa and Kayenta Mines" and the U.S. Geological Survey's "Results of Ground-Water, Surface-Water, and Water-Quality Monitoring, Black Mesa Area, Northeastern Arizona -- 1996, 1995, 1994, and 1992-1993". June 16.

----. 1998. Letter to Greg Littin, Hydrogeologist -- Water Resources Division, U.S. Geological Survey Regarding the "Review of draft memorandum on the Black Mesa Monitoring Program -- A New Focus." June 16.

----. 1998. Memorandum to Thomas J. Casadevall, Acting Director, U. S. Geological Survey Regarding "Navajo-aquifer Model for Permit Decision on the Peabody Western Coal Company's Black Mesa Mine." September 9.

----. 1999. Letter to Nick B. Melcher, Chief -- Arizona District, U. S. Geological Survey Regarding "Request for Assistance to Evaluate Peabody Western Coal Company's Computer Flow Model of Navajo Aquifer and Analysis of Impacts as a Result of Mining-related Withdrawals". December 13.

----. 2000. Report on its Review and Analysis of Peabody Coal Company's 1998 "Annual Hydrological Data Report" and the U. S. Geological Survey's "Ground-Water, Surface-Water, and Water-Chemistry Data, Black Mesa Area, Northeastern Arizona -- 1998". July 5, corrected August 7.

United States Environmental Protection Agency -- Region IX. 1989. Letter to Mr. Peter Rutledge, Chief - Federal Programs Division -- U.S. Office of Surface Mining Reclamation and Enforcement -- Western Field Operations Regarding the Draft Environmental Impact Statement for the Proposed Permit Application, Black Mesa-Kayenta Mine, Navajo and Hopi Reservations, Arizona September 14.

----. 1990. Letter to Mr. Peter Rutledge, Chief - Federal Programs Division -- U.S. Office of Surface Mining Reclamation and Enforcement -- U. S. Department of the Interior Regarding the Final Environmental Impact Statement for the Proposed Permit Application, Black Mesa-Kayenta Mine, Navajo and Hopi Reservations, Arizona. June 26.

United States Department of the Interior, U. S. Geological Survey -- Water Resources Division. 1987 Preliminary Draft Simulation of Five Groundwater Withdrawal Projections for the Black Mesa Area, Navajo and Hopi Indian Reservations, Arizona. USGS Water-Resources Investigations Report 87-_____. February 6.

----. 1987. Letter to Mr. Keith Kirk at Office of Surface Mining Regarding the review of the draft report on the USGS groundwater model of the Black Mesa area. March 27.

----. 1996. Preliminary Proposal for Update and Recalibration of the USGS Model of Ground-water Flow in the N-Aquifer, Black Mesa Area, Arizona. January 26.

----. 1998. Letter to Mr. Steve Parsons at Office of Surface Mining Western Regional Coordinating Center Regarding the "Black Mesa Monitoring Program." August 31.

----. 1998. Memorandum to Director -- Offices of Surface Mining, Reclamation and Enforcement Regarding "Reply to Request to Update Navajo Aquifer Ground-water Flow Model of Black Mesa Area, Arizona." September 9.

----. 1999. Memorandum to DOI Bureau Directors/Staff Regarding "FY 2001 DOI Science Priorities -- Budget Justification." August 16.

Zhu, C., R.K. Waddell, I. Star, and M. Ostrander. 1998. Responses of ground water in the Black Mesa basin, northeastern Arizona, to paleoclimatic changes during the late Pleistocene and Holocene. Geology. February.

^*Prepared for NRDC by LFR Levine-Fricke, a professional hydrogeology firm based in Scottsdale, Arizona.

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