Response to Public Comment

Listed below are summaries of comments by the Citizens Education Project followed by a response from USGS. The summary of each comment is linked to the original document submitted by the Citizens Education Project.

Comments from the Citizens Education Project

Complete letter from the Citizens Education Project (pdf)

CEP1.  Application of inappropriate and misleading methodology

“A  previous US Geological Survey study had determined that the method employed by BARCASS for estimating water balance and recharge (PRISM) is not appropriate for use in eastern Nevada, particularly in mountainous areas. The method has never been verified as accurately simulating precipitation in eastern Nevada. One study (Jeton et al 2005) goes so far as to say that that the PRISM method used to estimate climate input to drive the model ‘is a black box whose details can not be examined.’ Meyers 

This is a significant error since BARCASS states:” Differences between estimates for this study and previous estimates primarily are attributed to variations in the applied methods.” … Additionally, recharge estimates for this study tend to be higher and discharge estimates tend to be lower than previous estimates  Pg. 85. This admission is particularly disturbing when the wrong methodology may have been used by BARCASS in the first place. 

RESPONSE

The intent in the statement “Differences between estimates for this study and previous estimates primarily are attributed to variations in the applied methods such as neglecting hydraulic connections between adjacent HAs” does not imply that past methodologies were wrong. Previous analyses were based on a different precipitation map and many of the earlier water budgets were assumed to be in balance even when the recharge estimates using the Maxey-Eakin method and discharge estimates from field mapping of phreatophytes were not equal. The following text was added to the summary report regarding the PRISM map. “PRISM estimated precipitation was compared to measured precipitation at 155 stations in Nevada and Utah. Annual measured precipitation for these stations averaged 12 inches and was about 1 inch less than the PRISM estimates. Differences between measured precipitation and PRISM estimates had a standard deviation of 4 inches.  Therefore errors resulting from using PRISM to distribute precipitation in the BCM were considered negligible.”

CEP2.  Reliance on methodologies with high degrees of uncertainty

“Recharge Estimates BARCASS updated the estimates from the recon reports using physically based models of the basins. Recharge was based on a basin characterization model (BCM), a water balance analysis of precipitation, ET, soil water storage and runoff for the unsaturated soil above the groundwater table conducted for each of many small cells spread across the basins. Parameters include estimated soil and geologic properties based on remote sensing and climate input is from the PRISM model. The model was solved for recharge... Each parameter and input value is an estimate which includes a significant amount of uncertainty”. Meyers 

RESPONSE

The authors freely admit throughout the report that uncertainty arises from lack of hydrologic data needed to calibrate the input parameters. This study had neither the time or money to drill and hydraulically test the numerous test holes needed to better quantify properties, particularly of the carbonate-rock aquifer. Rather, the emphasis of this study was to refine the hydrogeologic framework, to apply the BCM to regionally evaluate recharge, to verify (calibrate) published ET estimates for the predominant vegetation type (shrub), and to apply geochemical modeling methods to support the hypothesized movement and exchange of ground water among HAs.  The hydrologic study begin conducted for the EIS may reduce uncertainty in estimated values for the water-budget components by evaluating a regional ground-water flow systems bounded by divides.

CEP3. Conclusions unsupported by data

“Interbasin Flow. Because the recharge and discharge were estimated independently, they are not equal and the USGS assumed the difference to be interbasin flow. The BARCASS flow estimates may actually have a higher variability than previous estimates because BARCASS relies on models with many uncertain parameters and inputs. The models are not calibrated or verified.” Meyers

RESPONSE

Few of the previous estimates, particularly the reconnaissance reports, quantify uncertainty, making it difficult to assess the relative error between the current and previous estimates. Qualifying statements such as the following are included in the report text, “Although some uncertainty exists on estimated differences between annual recharge and pre-development discharge, the prevalence of hydrographic areas where recharge exceeds discharge and a significant quantity of subsurface outflow from the entire study area are not unexpected”.  Permeable carbonate rocks form much of the highest mountain ranges; this, coupled with higher precipitation and consequently recharge, make it conceivable that these ranges are the source for regional ground-water flow.

CEP4. Inappropriate use of data

“BARCASS used recent literature values from four separate reports to determine the average ET rate to apply to different types of phreatophytic vegetation (BARCASS, page 54). The range is shown on Figure 27 of BARCASS. Figure 27 also shows a single line for "area-weighted average-annual ET rate" which is confusing because it implies there is a single value per ET unit used for the entire BARCASS area. As discussed in the previous paragraph, it appears that a range was used for some ET units rather than a single value;” Meyers 

A table with values from each literature source showing the value that could be used for each ET unit from that source would be more useful than the range shown on Figure 27. Our review of the sources suggests that ET units in those sources may have significantly varied from those described in BARCASS or the ET report. In other words, BARCASS may have used inappropriate ET units.”  Meyers 

RESPONSE

ET rates used to estimate ground-water discharge are given in appendix A. Text revisions now reference appendix A.

Figure 27 is considered appropriate for the audience of the summary report. ET units described in the summary and ET reports are not inappropriate. Initially, the range in ET rate for each of the 10 ET units was from the literature. Subsequently, the ranges were modified using ET rate measurements made in the study area, and differences in vegetation density identified from satellite imagery using a MSAVI. Figure 27 shows where measured ET rates fall along the range and provides evidence that the ET rates developed for the selected ET units are in fact very reasonable. Readers are referred to Smith and others (2007) for additional and more detailed information on the selection and delineation process. This expanded information is not considered pertinent to a summary report and can easily be found elsewhere. The relation between MSAVI and measured ET rates is illustrated in Moreo and others (2007), another report often referenced throughout the summary report.

CEP5. Insufficient data

BARCASS has been handicapped by a lack of data that might have been provided by BARCASS Two. One of the many areas where more information is needed is in the Confusion Range to estimate the flow east through the Snake Valley. This flow may be the primary inflow to the Fish Springs Flat basin which features the substantial discharge at Fish Springs. Considering the importance of the Wildlife Refuge at Fish Springs, this omission from the BARCASS is especially troubling. 

RESPONSE

We agree but without a phase 2 study many of the uncertainties described in the summary report can not be eliminated or reduced.

CEP6. Reliance on faulty or deficient scientific models

BARCASS relies on faulty and at times misleading data collected in periods of high precipitation atypical of the normal rainfall for the area.” The “PRISM” model used in the study does not allow for interflow between cells. Water that exceeds the percolation capacity of the underlying bedrock remains as excess soil water until it percolates when in reality it would flow downgradient where it might become available for recharge or be lost to ET….The rainfall input using the “PRISM” method overestimates precipitation by from 6 to 15 percent over a substantial portion of the BARCASS study area.   Meyers 

RESPONSE

The period of analysis of precipitation was lengthened from the shorter period (1970-2004) to the longer period (1895-2006) eliminating the problem of evaluating a non-representative (higher precipitation period). Comparisons between measured precipitation at 155 stations and PRISM differed by about 1 inch and had a standard deviation of 4 inches. 

CEP7.  Vague or incomplete reporting of data collection

“BARCASS determined ET rates for 10 units ranging from playa soil to marshland. The ET Rate table in Appendix A shows different rates for marshland, meadowland, grassland, dense desert shrubland, moderately dense desert shrubland. However, for moist bare soil, open water, dry playa and irrigated lands, the same rate is used for all basins and subareas. Many micrometeorological factors are at play and would cause the ET rate to vary for a specific ET unit for different subareas. However, these factors affect the evaporation from all ET units, not just the six mentioned. The USGS makes no effort to explain how the different rates were determined and why site conditions would cause variation in some of the ET units but not in the others.” Meyers  Myers suggests that ET units in those sources may have significantly varied from those described in BARCASS because they used the wrong ET units in the report. 

RESPONSE

ET estimated from the ET units referred to as “bare soil, open water, dry playa, and recently irrigated cropland—historically mixed phreatophytes” accounts for about 10 percent of ET from the study area. Data are very limited for these ET units. The ET rates developed for these ET units represent our best estimates of the long-term annual ET based on the limited data available. Additionally, the effects of depth to water and soil texture on ET rates in these areas are not well understood.  Ninety percent of the estimated ET is from the shrubland and riparian ET units. A range of ET rates could be assigned for these ET units because more data were available, particularly the ET rates measured directly by the USGS for this study. Given the confidence in these high-quality data (albeit only 1 year at six sites), a range of ET rates was developed in conjunction with remote sensing and fieldwork that varied with vegetation density.

CEP8. Inconsistencies of method 

Water Balance Method for Estimating Recharge: The BCM report details the Basin Characterization Model, water balance method, used to estimate recharge. The model divides each basin into 890 foot square cells and balances precipitation and ET to estimate recharge on each cell…. In addition to parameter and input uncertainty, various shortcomings of the model technique as described in the BCM report further increase the variance on the estimated recharge [The model] underestimates runoff by effectively spreading the precipitation and snowmelt out over the month. Second, the BCM model ignores interflow between cells. The BCM model retains until the next month any potential recharge that exceeds the maximum recharge capacity which would, in reality, seep downgradient as interflow. It might become available for recharge at that point, or it might be lost to ET. Meyers 

RESPONSE

A consistent method was used by applying a single set of criteria. The distribution of ground-water recharge and first-order estimates of recharge rates were developed using a regional-scale, recharge-accounting model. While the recharge model is not calibrated, it provides a means for evaluating and comparing the processes, properties, and climatic factors that ultimately control the potential for recharge under differing hydrologic conditions (Flint and others, 2004). The BCM is a mathematical deterministic water-balance method that integrates maps of geology, soils, vegetation, air temperature, slope, aspect, potential ET, and precipitation. The model uses many of these data sets and internal computations to estimate the distribution of precipitation, snow accumulation and snowmelt, potential ET, soil-water storage, and bedrock permeability.

CEP9. Incorrect assumptions or assumptions based on faulty data 

Open Water: “The USGS includes groundwater discharge from open water area. Presumably, this means playa lakes and open water in wetlands throughout the valleys. The ET rate ranges from 4.6 to 5.6 ft/ y and is considered to be discharge from groundwater (BARCASS page 54). Open water accounts for just 0.1 percent of all ET units and only a few hundred acres. However, the reality is that not all evaporation from open water sources is from groundwater. Surface runoff, especially during storm periods and snowmelt, reaches the open water areas in these valleys. BARCASS assumes that surface water runoff that reaches "fine-grained playa sediments is assumed to evaporate and for the purpose of the water budget does not contribute to either ground-water recharge or discharge" (BARCASS, page 64). It seems that surface water runoff to any open water area would add to area for ET discharge estimates and that the methods used in BARCASS overestimated GW ET discharge by including surface water evaporation”  Meyers 

RESPONSE

The authors do not consider ground-water discharge by ET to be over-estimated in the BARCAS study primarily because ET units in the areas most likely to change annually or seasonally (open water bodies, marshland, and playa) were delineated using a land-cover classification that used remotely sensed imagery from multiple dates and years (SWReGAP; Smith and others, 2007). The authors feel strongly that that the area delineated as open water is supported primarily by ground water inflow or by springs which are fed by regional ground-water sources. The extent of these “wetter” ET units during anomalously wet years or during wetter periods of the year is not included as part of the delineated unit. In addition, Figure 32 shows the relatively tiny contribution of “open water” unit to ground-water discharge. Therefore, even if ground-water ET discharge is slightly overestimated for the “open water unit,” the overall affect to basin-wide estimates is minimal.

CEP10.  Insufficient Documentation

The report contains errors of documentation and specific errors in maps conversions, graphs, that while minor when taken individually are more serious in the aggregate as they indicate casual attitude toward data collection and reporting data. 

RESPONSE

Please note that the USGS does not take a casual attitude toward data collection and data reporting; however, it is possible that typographical errors can persist in a document even after numerous scientists, illustrators, and editors review the draft.  We have checked all data and interpretations to maintain consistency throughout the report. A thorough verification of values, cross-checking among figures, tables, appendix, and plates has been performed.   

CEP11. Errors of omission

The BARCASS failed to consider a previous report that the current BCM model may overstate recharge. The BARCASS also failed to assess the potential that ground water withdrawal might changed the direction of flows in the Snake Valley. The BARCASS failed to assess the probable impact of the withdrawals on subsurface flows in the Confusion Range, The Wah Wah Valley and on Fish Springs.

RESPONSE

Evaluating potential reversals in the hydraulic gradient within Snake Valley and probable impacts on Wah Wah Valley and Fish Springs resulting from ground-water withdrawals is beyond the scope of the enabling legislation and time and budget constraints of this project.  Potential effects from ground-water pumping are best evaluated using a numerical ground-water flow model. Flow modeling was not an objective of the BARCAS study.

CEP12. Charting errors

The BCM report has a map which shows the precipitation estimated using PRISM for the BARCASS study area (Figure 4). The scale is very hard to read; based on the scale and the amount of blue shown on the map, there are rather large areas in the mountains with more than three feet of precipitation (the top of the scale is 3.5 ft/y, or 42 in/y). Even if the ridges receive this much (they do not), the large area with this amount illustrates how PRISM may overestimate the precipitation.  “BARCASS discusses that the input to the water balance accounting has inherent uncertainties (BARCASS, page 74). However, it does not attempt to put a distribution around the estimated inter-basin flow values. Utilizing the distributions determined for discharge that should be determined for recharge is an error. Failing to do so, the interbasin flow numbers shown on plate 4 will be considered as exact estimates.”  Meyers “Plate 4 shows interbasin flow from the Snake Valley through the Confusion Ranges. This appears to be separate from the inter-basin flow from Snake Valley to the Great Salt Lake Desert. The map shows the entire boundary as likely to transmit groundwater.” Meyers

RESPONSE

Figure 4 imparts the precipitation distribution by scaling values from coolest colors (highest) to warmest colors (lowest).  The size and intensity of cool and warm colors indicate the spatial distribution but is not intended for use for accurately quantifying amounts. Values are presented in appendix A.

Plate 4 does not show interbasin flow magnitude or direction.  It does show recharge, discharge, and differences that are now rounded to fewer significant figures reflecting the imprecision of the estimate.

CEP13. Unexplained discrepancies

“There is an unexplained discrepancy in the total irrigated area in Snake Valley between the value used for ET discharge and the value used for irrigationconsumptive use. (SEE table 4 and Apendix A) Similar discrepancies occur in other valleys (Table 5). The biggest discrepancy is for Lake Valley which has 4360 acres with irrigation but none for ET discharge. In addition to Snake Valley, Spring Valley, Steptoe Valley, and White River Valley have substantially higher acreages for ET discharge than for irrigated consumptive use.” Meyers Parameter and input uncertainty along with the uncertainty imparted by the BCM model assumptions cause a large uncertainty for the overall model predictions which the BARCASS report does not adequately discuss. Concern with the uncertainty is amplified by considering that the same authors using the same model published a separate report just three years ago that had estimated recharge up to 25 percent different (mostly less) than estimated in BARCASS.” Meyers

BARCASS does not even discuss why there is a difference. Such discrepancies are found throughout the report and these errors generally favor of increased water availability. 

RESPONSE

After further review, the authors see no inconsistency among the irrigated cropland acreage reported in the draft summary report (OFR 2007-1156) and supporting publications (DS 273 and SIR 2007-5087). Irrigated acreage based on the water use and acreage worksheets given in appendix A are, in fact, correct. The noted differences are valid, not errors. The acreage reported in the water use worksheet is defined as the acreage of irrigated cropland for 2005 regardless of whether these lands are located inside or outside of ground-water discharge areas. For example, 9,200 acres are reported for Snake Valley and 4,360 acres for Lake Valley. The acreage reported in acreage worksheet is defined as the composite acreage within ground-water discharge areas for the “recently irrigated cropland-historically mixed phreatophyte” ET unit during the year 2000 and/or 2002, and/or 2005.  For example, 9,932 acres are reported for Snake Valley and 0 acres for Lake Valley indicating that in Snake Valley most irrigated acreage is within the ground-water discharge area, and for Lake Valley all irrigated acreage falls outside the ground-water discharge area. Since 9,932 acres were delineated in Snake Valley for the “recently irrigated cropland-historically mixed phreatophyte” ET unit, and only 9,200 acres were identified as actively irrigated cropland in 2005, then there are some fields within the ground-water discharge area that were not actively irrigated in 2005. A table and text was added to the summary report (SIR 2007-5261), and column headings revised in appendix A to help clarify this point.  

Please see the explanation given by the authors on page 15 of the BCM report, “Although recharge estimates presented in this report are an extension of Flint and others, 2004, results may differ due to different climatic data and an improved snow accumulation and snowmelt model used in the current evaluation”.  Additionally, new information incorporated into the BCM for the BARCAS study and specific to the smaller study area as opposed to the earlier, larger regional model (Flint and others, 2004) will always influence model results. If future BCM simulations are done that incorporate new hydrologic and geologic data being collected by SNWA, models results will not be identical to the current results.  This is true of all models due to the non-uniqueness of results.

CEP14. The repeated substitution of hypothesis for fact

We must believe that many of the missing pieces in the puzzle of the Basin and Range Carbonate Aquifer might be answered by BARCASS 2.  This problem has been compounded by the apparent belief that the information we have now is the only data we are ever going to get. In the absence of this information the authors have been forced to substitute a series of educated guesses for hard facts. These estimates may have been made in good faith, but a scientific study can not be based on non-existent data. The BARCASS Report reveals serious gaps in our understanding of the geology and hydrographic features of the study area, these gaps can only be resolved by funding BARCASS 2.

RESPONSE

The authors agree that there are significant data gaps particularly for the carbonate-rock aquifer.  However, we have confidence in the results presented in the summary report due to the fact that numerous methods and techniques were independently used to arrive at our conclusions.  We agree that additional research is needed to improve our understanding of the behavior and response of ground-water systems.