1

 September 17, 2012 

John Russell, Project Manager 

Lost Creek Uranium ISR Project 

Bureau of Land Management, Rawlins F.O. 

P.O. Box 2407 

Rawlins, WY 82301-2407 

Via email to Lost_Crk_Mine_WY@blm.gov

 

Dear Mr. Russell: 

The following are the additional comments of Biodiversity Conservation Alliance, Californians 

for Western Wilderness, and Western Watersheds Project on the Lost Creek In Situ Leaching 

Uranium Project Final EIS. These comments supplement our comments during the Draft EIS 

comment period. We ask BLM to respond to both sets of comments pursuant to NEPA’s 

mandates during the course of this NEPA process. In our Draft EIS comments we included a 

great deal of applicable scientific findings, which we will not repeat here, but we do ask BLM to 

examine in detail each scientific article cited in the Literature Cited section of these comments. 

In addition, we would have BLM review our comments on the Nuclear Regulatory Commission 

NEPA process for this same project, which we have attached to our FEIS comments as 

Attachment 1. These comments supplement our Draft EIS comments, and we ask BLM to 

respond to both sets of comments to the extent that the agency has not already done so. 

Analysis of traffic impacts in the EIS is invalid 

BLM reports a sevenfold increase in estimated tractor-trailer traffic, from 2-5 tractor-trailers per 

week as published in the Draft EIS to 2-5 tractor-trailers per day, attributing this to “an error in 

reporting.” FEIS Appendix F-34. The impacts analysis for sage grouse and other sensitive 

wildlife is predicated on the lower level of traffic, and does not appear to have been adjusted to 

reflect the greater level of traffic disclosed in the FEIS Response to Comments. BLM has not 

shown that it has adjusted its Impacts Analysis sections for various sensitive resources (e.g., air 

quality, wildlife) to reflect the actual much heavier amount of truck traffic that has been 

disclosed in the Response to Comments section of the FEIS. 

BLM concedes “The major concern regarding the East and West Access Roads is their location 

with respect to sage-grouse leks.” FEIS 2-94. Both proposed access roads do pass through 0.6-

mile buffers for active leks. FEIS at 2-96. BLM notes that WDFG “determined” that 

reconstructing the proposed East and West Access Roads would have less impact than 

constructing or reconstructing other roads for access. Id. However, WGFD did no actual data 

P.O. Box 1512, Laramie, WY 82073 (307) 742-7978 fax: 742-7989 

Working to Protect Native Species and Their Habitats 
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analysis nor did they rely on any scientific information in reaching this “determination;” it was 

merely an opinion. We find this determination arbitrary and capricious of WGFD, and it merits 

little deference in the FEIS process. During the EQC process, WGFD used the original traffic 

data presented in the Draft EIS, not the increased heavy truck traffic disclosed in the FEIS, 

invalidating their conclusions by way of analyzing a level of traffic that is inapplicable to the 

project presently before the BLM for consideration. WGFD considered one eighteen-wheeler per 

day along these access routes. FEIS at 2-96. In fact, the real traffic estimate later amended by 

BLM in the FEIS is 2-5 eighteen wheelers per day plus 50 SUVs per day (FEIS at Appendix F34), a level of traffic not considered by WGFD. In addition, WGFD never considered both of the 

alternate access routes proposed by BCA, which were recommended subsequent to the WDEQ 

permitting process, and thus BLM cannot rely on WGFD recommendations to evaluate these 

alternate routes against proposed East and West Access Roads. Given that both of these main 

haul roads are within 2.0 miles of active sage grouse leks, and indeed within 0.6 miles, this is 

problematic in light of state and federal policy regarding Core Area impacts management. 

Impacts analysis for sage grouse was flawed 

Four occupied and active leks are within 2 miles of the project. FEIS at 3.8-29. BLM addresses 

only alternate access routes presented prior to the BLM’s EIS in the state process that did not 

account for newly identified sage grouse leks, not alternate routes that DO account for newly 

identified leks, as recommended by BCA in our Draft EIS comments. FEIS at 2-98. This failure 

to examine this reasonable alternative violates NEPA. 

There is an overlap between noise restriction hours in EO 2011-5 and project activities, between 

7 and 8 am. FEIS at F-34. Sooner and Sooner Oil Leks are within 1000 feet of the access roads, 

BLM claims that other leks will have “negligible noise impacts.” Id. By extension, noise impacts 

at the Sooner and Sooner Oil leks will be non-negligible. According to BLM, “Given that the 

Sooner and Sooner Oil Leks are within 1,000 feet of Sooner Road, traffic increases along this 

road could impact lek attendance at these leks.” FEIS at F-34. 

There is no “action alternative” that would comply with WY IM 2012-019. This IM limits 

drilling pads or mining locations to an average of one per 640 acres. See FEIS at ES-6. It is 

abundantly clear that the drilling pads for this project will be spaced at a density approaching 100 

per square mile in developed areas. The Mine Unit 1 diagram provided shows 43 sites for 

monitoring wells alone. FEIS at Figure 3.6-5. The DDCT cannot be used to dilute well density, 

and the consideration that all of the various pods of wellsites be pooled together and considered a 

single wellpad is arbitrary and capricious and circumvents the intent and black-letter direction of 

state and federal core area protection policies. 

Figure 2.1-4 shows the configuration of monitoring wells in a “typical mine unit.” FEIS at 2-8, 2-

9. Twenty production wells and 40 injection wells are expected for each header house. Id. In 

addition, there is one monitor well every four acres, spaced 500 feet apart along the perimeter. 

Id. Is there one header house per mine unit? Presumably so; this should be disclosed. The 

specific number of mine units are considered “conceptual” at this point. Id. Layout of mine units 

would occur later, as part of the WDEQ-LQD permitting process. FEIS at 2-28. In order to 

approve the project and take the legally required “hard look,” the number of mine units should be 
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determined with finality, disclosed in the FEIS, and their impacts on site-specific sensitive 

resources such as sage grouse leks, occupied pygmy rabbit habitat, and Wyoming pocket gopher 

occupied burrow complexes should be evaluated. 

BLM has failed to assess the effectiveness of mitigation measures 

BLM relies on mitigation measures for sage grouse contained in IM 2012-019 and state 

Executive Order 2011-5, but the effectiveness of these measures has never been established, and 

all available science points to the conclusion that they are inadequate. BLM needs to undertake 

an analysis of the mitigation measures in these two policy documents to determine the level of 

impact to sage grouse populations when these measures are applied in the context of an in situ 

uranium project, as well as more generally, in order to meet NEPA requirements in this regard. 

Maximum 5% surface disturbance within DDCT area 

In terms of surface disturbance, the EIS claims that the level of impact is consistent with limits 

prescribed under the state’s Density Disturbance Calculation Tool (DDCT). FEIS at 4.9-26. The 

BLM asserts that WGFD “approved the way the analysis was carried out” and found that “the 

results indicated that the surface disturbance resulting from the Project was in line with the SGIT 

stipulations.” Id. However, the EIS includes no analysis of what this level of impact in terms of 

percentage of land surface disturbed would have on sage grouse. And the state SGIT likewise 

never analyzed what the impact of having 5 percent of the land area within a DDCT zone would 

have on sage grouse, nor did the agency even consult the applicable science to see if there was 

any rational basis for selecting the prescribed threshold. The DDCT process has a crippling flaw: 

Instead of examining the density of impacts on a per-square-mile basis in the area to be 

developed, it expands the land area far beyond the Project Area boundary, thereby masking 

ecologically damaging levels of surface disturbance by adding in undeveloped lands far away 

from the project in question. Thus, BLM calculated using the DDCT that the percentage of land 

undergoing surface disturbance would be 0.9% (FEIS at 4.9-27), while the actual percentage of 

the Project Area that would undergo surface disturbance would be 345 acres in a 4,254-acre 

Permit Area (FEIS at ES-2), which amounts to 8.1% surface disturbance within the Permit Area. 

And even this index is skewed conservatively, because much of the peripheral acreage of the 

Permit Area is not slated for any surface disturbance or activity at all. See project footprint in 

FEIS at Figure 4.9-3. Of note, it appears that the DDCT analysis was undertaken using the actual 

acreage of project area disturbed, but for the sites per square mile analysis, it appears that an 

arbitrary line was drawn around the collective perimeter of all well sites (FEIS at 4.9-32). What 

would be the acreage under the DDCT if the “one-site” approach espoused in this sectionb of the 

FEIS was applied to the DDCT analysis? The complete absence of any analysis of the level of 

impact to be experienced at this threshold of percentage of land disturbed is a violation of 

NEPA’s hard look requirements and also a failure to examine the adequacy of mitigation 

measures pursuant to NEPA. 

According to BLM, “the area of impacted vegetation at any one time should be less than eight 

percent due to the sequential nature of the Mine Unit Development as well as ongoing 

Restoration and Reclamation.” FEIS at 4.2-5. This statement addresses the percent disturbance at 

any one time, rather than the cumulative surface disturbance over the life of the project. This is a 

key distinction, because once surface disturbance occurs, it will take 80 to 100 years for 
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sagebrush to recolonize and return to a mature state where it will fully function as sage grouse 

habitat. At no point has BLM (or WGFD, for that matter) made the assertion that 8.1% surface 

disturbance within a project area will avoid significant impacts on sage grouse populations as 

long as there is a significant expanse of undeveloped sage grouse habitat on adjacent lands. 

Indeed, an examination of the available science on industrial impacts to sage grouse (including 

studies cited by BLM in the FEIS) includes studies where similar intensities of wellfields have 

been developed adjacent to unimpacted sage grouse habitat, and the result has been both 

displacement of sage grouse and population decreases. 

No Surface Occupancy buffer of 0.6 mile around active leks 

BLM claims that the Project complies with the Executive Order requirement that No Surface 

Occupancy measures apply within 0.6 mile of active sage grouse leks. In fact, the project does 

not comply with this measure – both the East and West Access Roads are proposed for 

reconstruction from two-track trails to major haul roads within 0.6 mile of active leks. While a 

0.6-mile buffer around the leks is asserted to be the ‘loafing area’ for males during lekking 

periods, it does nothing to protect nesting habitat around the lek (which can extend out to 5.3 

miles), and BLM has never even presented scientific data that industrial development 0.6 mile 

for the lek site, at the edge of the ‘loafing area,’ will avoid any impacts even to loafing males, 

much less nesting and breeding females. The WGFD argued that upgrading the East and West 

Access Roads would create less impacts to sage grouse than alternate routes considered during 

the WDEQ state permitting process. FEIS at 4.9-29. But WGFD never considered the impacts 

compared to the two access routes recommended by BCA, which were proffered at the Draft EIS 

stage, after the WDEQ process was completed. Thus, application of the 0.6-mile buffer is 

arbitrary and capricious. 

But even if the Project did comply with the 0.6-mile lek buffer requirement, neither the BLM nor 

WGFD or any other agency has ever analyzed the effectiveness of this mitigation measure. In 

our own research, we have been able to track down this spurious lek buffer distance only to 

reports that it corresponds to the 0.6-mile loafing area for male sage grouse around the lek during 

the breeding season. But there have never been any tests to determine that if a wellsite or other 

facility is sited exactly 0.6 mile from the lek’s periphery (which is allowable under this standard), 

that there would be no significant impact on loafing male sage grouse during the breeding season 

(let alone impacts on breeding females, impacts on nesting females – which concentrate their 

nesting on lands within 4 to 5 miles of the lek). Indeed, the best available science has indeed 

tested how far from the lek industrial facilities – including oil and gas wells quite similar in their 

effects as the uranium wells proposed under this project – must be to reduce their impacts to 

insignificance. Indeed, the available scientific studies suggest that the 0.6-mile buffer is woefully 

inadequate to prevent major impacts to sage grouse populations. 

Incomplete impacts analyses for other BLM Sensitive Species 

Pygmy rabbit active habitat and locations are mapped for the project area. FEIS at 3.8-54. Yet 

there do not seem to be alternatives that would avoid mapped pygmy rabbit habitat. The impacts 

analysis is sparse to nonexistent (see FEIS at 4.9-43), evading NEPA’s hard look requirements. 
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Wyoming pocket gopher locations are mapped for the project, and overlapped with predicted 

project activities in at least a crude way. FEIS at 3.8-57. The impacts analysis is sparse to 

nonexistent (see FEIS at 4.9-43), evading NEPA’s hard look requirements. 

Groundwater and Surface Water Impacts 

We remain concerned about the potential for contaminated fluids to be spilled at the surface into 

drainage channels that connect during stormwater events to playas, lakes, and wetlands to the 

southwest. In these types of uranium mining operations, leaks are “common” and the most 

common sources of leaks are outlined in the FEIS at page 4.6-6. The BLM FEIS references the 

NRC EIS for Lost Creek for more detail on surface leaks and their potential impacts to surface 

waters. But while the NRC EIS mentions in passing the possibility of leaks and spills (NRC 

DEIS at 4-23), it in no way evaluates the possibility of a leak or spill from a well sited in or near 

an ephemeral well channel on downstream lakes, playas, and/or wetlands (see NRC DEIS at 4-

26). BLM’s impacts analysis does not consider the potential impacts of a surface leaks and 

contamination that occurs during a rainfall event during which surface water flows could carry 

contaminated fluids far to the southwest via ephemeral drainage channels. In general, wells will 

be sited 20 feet from ephemeral drainage channels, but in rare instances, wells may even be 

installed within or immediately beside an ephemeral drainage channel. FEIS at 4.6-3. This puts 

facilities at grave risk for immediate transport of spilled fluids to downstream locations distant 

from the Project Area. 

The upper portion of the Battle Springs formation is where the uranium mineralization occurs in 

the permit area. FEIS at 3.3-11. The aquifers in the Battle Springs formation are comprised of 

thick deposits (typically 100 feet) of sandstone interbedded with shale layers that serve as 

aquitards or aquicludes, with the result that different sandstone member are separated vertically 

(but not necessarily horizontally). FEIS at 3.3-13. There is an anticline (the Lost Soldier 

Anticline) to the northeast of the Project area, with a steep southwest dip toward the Project area, 

but the dip is reduced to three degrees in the Project Area itself. FEIS at 3.3-14. According to 

BLM, “The main discharge area for the Battle Springs/Wasatch aquifer system is to a series of 

lakes, springs, and playa lake beds near the center of the [Great Divide] Basin.” FEIS at 3.6-1. 

This aquifer is among “[t]he most important water-bearing aquifers within the Basin....” FEIS at 

3.6-4. The Lost Creek Fault, which traverses the Project Area, slows but does not halt 

groundwater flow (FEIS at 3.6-34); mine units for the project will be located on both sides of this 

fault (see FEIS at Figure 3.6-14). “From the permit area, the potentiometric surface dips 

southwest” toward the lakes, playas and wetlands to the south and southwest of the project area. 

FEIS at 3.6-6. For the Project Area itself, “Based on the potentiometric surface map, 

groundwater is inferred to flow to the west-southwest, generally consistent with the regional flow 

system.” FEIS at 3.6-22. Beyond these inferences, the FEIS does not present information on 

groundwater flows to the south and west. 

There are several mapped springs on Battle Springs Flat on the BLM’s South Pass 1:100,000 

scale topographic map. Battle Spring Draw leads to this flat, and is the primary surface 

watershed in the Project Area. See FEIS at 3.5-3. Attachment 3 is the Bedrock Geology Map 

from a USGS report called Water Resources of Sweetwater County, Wyoming, Scientific 

Investigations Report 2004-5214, by Jon P. Mason and Kirk A. Miller. This map clearly shows 
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that the Battle Spring formation, overlain in places by Quaternary sand and playa deposits, is the 

underlying bedrock for T24N R 94W, the township that contains these springs. This USGS 

report did not provide any baseline groundwater quality data for these springs (testing only wells 

in this area), and the BLM’s FEIS didn’t provide them either. These springs are also in proximity 

to seasonal lakes and wetlands that are part of the Chain Lakes complex, likely feeding into these 

seasonal lakes and wetlands. Heller et al. (2010) lumped together the Battle Springs Flat and 

Chain Lakes Flat playas and described them as being underlain by several formations, including 

the Battle Springs formation specifically. See Attachment 2. It is possible that hyporheic flows 

from the Battle Springs formation may feed into these playa lakes and wetlands, but BLM’s 

impacts analysis does not consider nor evaluate this possibility. Indeed, BLM’s analysis of 

potentially affected wetlands is limited to the Project Area itself. FEIS at 3.5-18. Circle Bar Lake 

and the Chain Lakes proper, located in 23/93 and 23/92, are part of the Chain Lakes Wildlife 

Habitat Management Area under the Rawlins RMP. These are also clearly underlain by the 

Battle Springs formation surface outcrop, as can be seen in Attachment 3. Groundwater flows 

generally from northeast to southwest through the Battle Springs formation, from the project area 

toward the playa lakes found in the WHMA. We are concerned that groundwater contamination 

from excursions within the Project Area will result in significant impacts to wetlands, playas, and 

lakes to the south and southwest of the Project Area through hyporheic flows of groundwater, 

resulting in unmitigated loss of wetland function in violation of Executive Orders 11990 and 

11988. 

BLM continues to emphasize the lack of hydraulic connection between the target formation and 

surface waters within the project area (FEIS at 4.7-1), but is still turning a blind eye to the real 

issue, which is where the target aquifer connects with springs outside the Project Area. BLM’s 

description of surface water uses is limited to lands within 3 miles of the Project Area boundary. 

FEIS at 3.5-11. BLM also proposes not to monitor these springs in its off-site groundwater 

monitoring protocols. FEIS at 4.7-11. The Affected Environment section of the FEIS fails to 

disclose which of the neighboring springs are fed by the target aquifer. See FEIS at 3.6-4. Water 

quality in the Battle Springs aquifer in and near the project area is considered comparatively 

high. FEIS at 3.6-49. This high water quality would be expected to be degraded with the 

injection of lixiviants, which themselves may be toxic, as well as the liberation of uranium, a 

major source of radioactivity. Appendix F of the FEIS also contains no response to the comments 

of BCA et al. in this regard. 

Radioactive contaminants have an extremely long half-life, measured in thousands of years. In 

addition, the lixiviant is expected to liberate various heavy metals (FEIS at 4.7-17, 4.7-30), 

which can also be toxic. Although water quality is already low in target formations, injection of 

lixiviant will decrease water quality there significantly. FEIS at 4.7-31. BLM notes that a release 

of pregnant lixiviant into the DE Horizon groundwater through a spill would result in impacts 

that “would be high and long-term.” FEIS at 4.7-21. This is the same fluid that will be produced 

in the target horizons as a matter of course, and the fluid that would be released in the event of an 

excursion. Despite the fact that the mine units will be ringed by monitoring wells, “excursions” 

can and do occur on a regular basis at in situ uranium mines (due to factors outlined in the FEIS 

at 4.7-31). See Appendices 1, 2, and 3 to these comments for examples of the excursion records 

of similar in situ uranium leaching projects in Wyoming. So it should be expected that 
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contaminated groundwater will at some point (maybe more than once) be released into the Battle 

Springs aquifers and be carried wherever groundwater flows take them. How long does it take 

for groundwater in the Project Area to reach the lakes, wetlands, and playas at the center of the 

Great Divide Basin, where the Battle Springs formation crops out at the surface? If contaminants 

are injected, or radioactive compounds are liberated through the use of lixiviants in the Project 

Area, where would groundwater flows carry them in terms of the discharge area at the surface? 

These questions remain unanswered by the EIS (despite the fact that BCA has previously raised 

them and BLM has a responsibility to respond to comments made at the Draft EIS stage), an 

indication that the legally required ‘hard look’ has not occurred. 

BLM discloses various potential chemicals used in lixiviants for the project (FEIS at 4.7-17), but 

does not evaluate the levels of toxicity or potential environmental impacts for these compounds. 

This fails NEPA’s ‘hard look’ standards. 

While BLM proposes a methodology to deal with “excursions,” or release of contaminated fluids 

beyond the monitoring wells (FEIS at 4.7-4), by definition BLM and the Project Proponent will 

be unable to determine the geographic extent of the excursion once it gets past the ring of 

monitoring wells because there will be no system to track such groundwater excursions beyond 

the monitoring well ring. Nor does BLM provide any impact analysis for the off-site potential 

impacts of such a contaminant plume. 

We also remain concerned that wellbores, both for injection wells and for older, uncontrolled 

wellbores that already exist in the Project Area, will lead to cross-contamination of deeper 

aquifers by pregnant lixiviant. All wells for this project appear to be open-hole completions, 

lacking casing. BLM expects “mud filter cake” to seal the wellbores and prevent crosscontamination (FEIS at 4.7-21), but provides no evidence that drilling muds can or will seal an 

open-bore well completed through the target formation to deeper aquifers. In addition, BLM does 

not analyze the extent to which previously existing wellbores, which are legion (see FEIS at 

Figure 3.4-15), will serve as avenues for cross-contamination through shale layers between target 

strata where uranium will be placed into solution and other aquifers. 

The expected drawdown of groundwater is also expected to extend at least 3 miles from the 

Project Area boundary. FEIS at Figure 4.7-2. What will be the impact of the drawdown of 

aquifers feeding lakes, playas, wetlands and springs to the south and southwest of the Project 

Area, as described above? BLM’s impacts analysis does not appear to address this issue. 

Conclusion 

Overall, the approval of this project demonstrates the BLM’s willingness to go to great lengths to 

approve industrial projects inside Core Areas that are fundamentally inconsistent with Core Area 

conservation principles. In approving projects like this, BLM demonstrates the inadequacy of the 

Core Area policy as a conservation measure to protect sage grouse, and illustrate the problem 

that even in Core Areas, sage grouse habitats function can be reduced to zero by an industrial 

project. BLM needs to require that the project proponent utilize directional drilling and well 

clustering (for monitoring, injection, and production wells) such that a maximum wellpad density 

of one wellpad per square mile is achieved for the project. If this proves infeasible, then BLM 
8

should withhold approval of the project rather than approve a project that very clearly will have 

strongly detrimental impacts on sage grouse populations within the Core Area. The U.S. Fish and 

Wildlife Service will be making a determination prior to 2015 on whether Core Area protections 

constitute “adequate conservation measures” to avert Threatened or Endangered Species listing, 

and BLM’s handling of this project thus far undermines the credibility of Core Area protections, 

and indeed indicates that federal and state agencies are willing to go to great lengths to avoid 

applying even the meager and inadequate conservation measures committed to in the state’s Core 

Area policy. If the Core Area protections are never applied in practice, then the Core Area policy 

is merely a paper exercise that has no impact on the ground, and cannot be relied upon as an 

alternate path to Endangered Species Act protections. BLM should remain aware that a negative 

Endangered Species listing in 2015 is likely to be scrutinized in the courts, and that the agency 

needs to be on its best behavior lest it build the record that Core Area protections are being 

skirted when industrial projects are proposed in Core Area lands. Thus, BLM would be wise to 

deny approval to the Lost Creek in situ project until it is substantially modified to comply with 

the intent of the Core Area policy, and will lower impacts to sage grouse below the threshold of 

significance through measures that have the support of the best available science. There are also 

unanswered questions remaining regarding the impacts that will occur to groundwater and to 

groundwater-fed springs and lakes to the south of the project area. 

Please address all of these issues prior to issuing a Decision for the project. 

Respectfully yours, 

Erik Molvar 

Signing on behalf of 

Michael J. Painter, Coordinator 

Californians for Western Wilderness 

P.O. Box 210474 

San Francisco, CA 94121-0474 

415-752-3911 

Jonathan B Ratner 

WWP – Wyoming Office 

PO Box 1160 

Pinedale, WY 82941 

Tel: 877-746-3628 

Fax: 208-475-4702 
9

Appendix 1: Spills and excursions from Uranium One Christiansen Ranch/Willow 

Creek/Irigary ISL project, site last visited 9/3/12.

Latest NRC Event Reports referring to Uranium One's Willow Creek (ex Christensen Ranch / 

Irigaray) ISL site in Wyoming: 

• Jun. 30, 2012: 1,500 gallon spill of injection fluid (0.9 ppm U) 

• Jun. 18, 2012: 1,200 gallon spill of recovery fluid (7.5 ppm U) 

• Jun. 18, 2012: 300 gallon spill of injection fluid (1.0 ppm U) 

• Jun. 17, 2012: 500-700 gallon spill of injection fluid (1.4 ppm U) 

• Apr. 20, 2012: 1,020 gallon spill of injection fluid (1.0 ppm U) 

• Apr. 12, 2012: Monitor well placed on excursion status 

• Apr. 3, 2012: Two monitor wells placed on excursion status 

• Mar. 29, 2012: Two monitor wells placed on excursion status 

• Jan. 5, 2012: Monitor well placed on excursion status 

• Dec. 14, 2011: 1,500 gallon spill of RO brine fluid (3.8 mg/L U) 

• Oct. 2, 2011: Aerial release of yellowcake powder 

• Sep. 23, 2011: 4,000 gallon spill of injection fluid (0.87 mg/L U) 

• Aug. 24, 2011: Monitor well placed on excursion status 

• "around August 4 or 5, 2011": approx. 7,000-10,000 gallon spill of NaCl brine solution 

• Jun. 21, 2011: 1,500 gallon spill of injection solution (3.5 ppm U) 

• Apr. 19, 2011: Monitor well placed on excursion status 

• Apr. 12, 2011: Sampling missed for months at 24 monitoring wells, at least 

• Mar. 29, 2011: 1,000 gallon spill of barren injection fluid 

• Mar. 23, 2011: Monitor well placed on excursion status 

• Mar. 8, 2011: Monitor well placed on excursion status 

• Jun 10, 2010: Monitor well placed on excursion status 

• Jun 8, 2010: 1,200 gallon spill of permeate water 

• Jun 3, 2010: Evaporation pond leak 

• Dec 16, 2009: Monitor well placed on excursion status 

• Sep 15, 2009: Monitor well placed on excursion status 

• Mar 12, 2009: Monitor well placed on excursion status 

• Apr 17, 2008: Monitor well placed on excursion status 

• Mar 11, 2008: Two monitor wells placed on excursion status 

• Sep 5, 2007: Monitor well placed on excursion status 

• Apr 25, 2007: Monitor well placed on excursion status 

Find more events under decommissioning issues 

• Jul 22, 2004: Monitor well placed on excursion status 

• Apr 28, 2004: Two leaks detected in evaporation ponds 

• May 31, 2001: Monitor well placed on excursion status 

• Jan 23, 2001: 13,392 Gallon spill of restoration water 
10

• Aug 10, 2000: Monitor well placed on excursion status 

• Oct 28, 1999: Monitor well placed on excursion status 

• Oct 5, 1999: Monitor well placed on excursion status 

• Jul 8, 1999: Monitor well placed on excursion status 

• May 8, 1999: 15,000 Gallon Mining Injection Solution Spill 

• Apr 12, 1999: 32,400 Gallon Injection Solution Spill 

• Apr 3, 1999: 13,000 Gallon Spill of Restoration Water 

• Mar 29, 1999: 23,520 Gallon Mining Injection Solution Spill 

• Mar 26, 1999: 60,918 Gallon Mining Injection Solution Spill 

• Feb 17, 1999: Monitor well placed on excursion status 

• Dec 22, 1998: Monitor well placed on excursion status 

• Nov 19, 1998: Monitor well placed in excursion status 

• Sep 2, 1998: Shallow monitor well is in an excursion status 

• Aug 6, 1998: Ground water monitor well placed in excursion status 

• Jul 22, 1998: Minor leakage of byproduct solution from the evaporation pond 

• Jul 8, 1998: 28,000 Gallons of water containing low level of U3O8 spilled onto ground 

• Mar 5, 1998: Perimeter monitor well in excursion status 

• Oct 3, 1997: Monitor well in excursion status 

• Sep 16, 1997: Spilled 2,440 gallons of waste water containing 78.5 ppm natural uranium 

• Sep 12, 1997: Well in excursion 

• May 16, 1997: Two perimeter monitoring wells in excursion status 

• Mar 12, 1997: Perimeter well in excursion status 

• Dec 31, 1996: Perimeter well in excursion status 

(details on post-Nov.1,1999, events available through ADAMS , Docket No. 04008502) 

Appendix 2: License Violations at Power Resources, Inc. Highland Uranium Project, 

Wyoming, USA. http://www.wise-uranium.org/umopuswy.html#HIGHLVIOL , site last visited 

9/3/12.

• Aug. 8, 2012: Monitor well placed on excursion status 

• Aug. 1, 2012: Monitor well placed on excursion status 

• Mar. 10, 2012: 344 gallon spill of production fluid (4.1 ppm U) 

• Mar. 9, 2012: 1202 gallon spill of injection fluid 

• Mar. 7, 2012: 774 gallon spill of injection fluid 

• Feb. 29, 2012: Monitor well placed on excursion status 

• Jan. 12, 2012: Monitor well placed on excursion status 

• Jun. 16, 2011: Monitor well placed on excursion status 

• Jun. 7, 2011: Monitor well placed on excursion status 

• Mar. 8, 2011: Sampling missed for seven monitoring wells 

• Mar. 8, 2011: Monitor well placed on excursion status 

• Sep. 10, 2010: Monitor well placed on excursion status 

• Jun. 8, 2010: Monitor well placed on excursion status 

• Jan. 29, 2010: 224 gallon spill of injection solutions (1.3 ppm U3O8) 
11

• Jan. 13, 2010: Monitor well placed on excursion status 

• Nov. 23, 2009: Monitor well placed on excursion status 

• Sep. 24, 2009: Release of 90,600 gallons of treated process water 

• July 31, 2009: Monitor well placed on excursion status 

• July 7, 2009: Monitor well failure 

• May 26, 2009: 5050 gallon spill of injection fluid (3 ppm U3O8) 

• May 21, 2009: Monitor well placed on excursion status 

• May 11, 2009: 6500 gallon spill of production solutions (19.8 ppm U3O8) 

• Apr. 16, 2009: Monitor well placed on excursion status 

• Mar. 30, 2009: Monitor well placed on excursion status 

• Feb. 13, 2009: Monitor well placed on excursion status 

• Jan. 10, 2009: 1,820 gallon spill of injection/production water containing 15 ppm 

uranium 

• Nov. 18, 2008: Monitor well placed on excursion status 

• Nov. 12, 2008: Monitor well placed on excursion status 

• July 10, 2007: Monitor well placed on excursion status 

• June 25, 2007: 3747 gallon spill of production fluid (21 ppm U) 

• June 22, 2007: 198,500 gallon [751 cubic meters] spill of injection fluid (8.1 ppm U) 

• May 21, 2007: 700 gallon spill of injection fluid (1.2 ppm U) 

• May 1, 2007: monitor well on excursion status 

• Dec. 30, 2005: 1000 gallon spill of restoration injection fluid, containing approx. 0.7 

mg/L uranium 

• Aug. 30, 2005: 1000 gallon spill of production fluid (15.4 mg/L U) 

• May 17, 2005: 20,700 gallon spill of injection fluid, containing approx. 1.1 mg/L 

uranium 

• Feb. 26, 2005: 3000 gallon spill of production fluid, containing 11.5 mg/L uranium 

• Jan. 10, 2005: 300 gallon spill of injection fluid, containing 1 mg/L uranium 

• Sep. 12, 2004: 1000 gallon spill of production fluid (10.5 mg/L uranium) 

• May 3, 2004: 800-1000 gallon spill of production fluid, containing about 11 mg/L 

uranium 

• Feb. 11, 2004: 400-600 gallon spill of injection fluid (1.3 mg/L U308) 

• Feb. 8, 2004: 500-1000 gallon spill of injection fluid (1.1 mg/L U308) 

• December 20, 2003: Spill of 600 gallons of injection fluid containing approx. 1.5 mg/L of 

uranium 

• October 20, 2003: Spill of 2800 gallons of injection fluid containing approx. 1.5 mg/L of 

uranium 

• September 29, 2003: Spill of 5000 gallons of injection/recirculation fluid containing 

approx. 2.0 mg/L of uranium 

• March 13, 2003: Spill of approx. 1100 gallons of wellfield injection fluid 

• November 7, 2002: Monitor well placed on excursion status 

• July 1, 2002: Monitor well placed on excursion status 

• March 21, 2002: Monitor well placed on excursion status 

• July 7, 1999: Spillage of 3-5 Gallons of Water Containing LSA of Uranium Byproduct 

Material 

• June 1, 1999: Spillage of 4000 Gallons of waste fluid 
12

• Feb. 5, 1999: Monitor well placed on excursion status 

• Feb. 5, 1998: Monitor well placed on excursion status 

> For reports on many more spills, download WY DEQ's spill databases ! 

The Nuclear Regulatory Commission has issued a Notice of Violation to Power Resources, Inc., 

of Denver, Colorado, for violations of NRC requirements at the Highland Uranium Project in 

Converse County, Wyoming. 

Power Resources, Inc. is a wholly owned subsidiary of Cameco Corp. 

Appendix 3: License violations at Smith Ranch in-situ leaching site. http://www.wiseuranium.org/umopuswy.html#SMITHRVIOL, site last visited 9/3/12. 

• Aug. 20, 2012: Monitor well placed on excursion status 

• Dec. 6, 2011: 1,779 gallon spill of injection fluid (0.7 ppm U3O8) 

• Nov. 7, 2011: Leak in East Evaporation Pond 

• Sep. 12, 2011: Monitor well placed on excursion status 

• Aug. 19, 2011: 85 gallon spill of injection fluid 

• Aug. 15, 2011: Leak in East Evaporation Pond (158 mg/L U) 

• July 22, 2011: 53 gallon spill of injection fluid 

• July 8, 2011: 1,190 gallon spill of restoration recovery fluid containing 2.4 ppm U3O8 

• June 13, 2011: Leak in East Evaporation Pond (248 mg/L U) 

• May 19, 2011: 790 gallon spill of solution containing 17 ppm U-nat, spill length 2,112 

feet (644 m), width 3 feet (0.9 m) 

• May 3, 2011: 1,500 gallon spill of production fluid, impacting 12,077 square feet (1,122 

m2

) 

• Sep. 10, 2010: 960 gallon spill of solution containing 1.5 ppm U3O8 

• Jul. 20, 2010: leak in East Storage Pond 

• Jul. 8, 2010: 1,440 gallon spill of injection fluid containing 1 ppm U3O8 

• Nov. 19, 2009: 560 gallon spill of injection solutions containing 1.4 ppm U3O8 

• Aug. 26, 2009: 1,500 gallon spill of injection solutions containing 1.1 ppm U3O8 

• Jun. 11, 2009: 190 gallon spill of injection solutions containing 0.7 ppm U3O8 

• Apr. 23, 2009: leak in East Storage Pond (510 ppm U3O8) 

• Feb. 27, 2009: leak in East Storage Pond (263 ppm U3O8) 

• Feb. 9, 2009: 14,600 gallon spill of production solutions containing 7 ppm U3O8 

• Jan. 9, 2009: 2,169 gallon spill of production solutions containing 11 ppm U3O8 

• Dec. 29, 2008: 1,144 gallon spill of injection fluid containing 0.2 ppm uranium 

• Oct. 30, 2008: 5,500 gallon spill of injection fluid containing 2 ppm uranium 

• Sep. 17, 2008: 16,774 gallon spill of injection fluid 

• Aug. 17, 2008: 7,965 gallon spill of injection fluid containing 1.4 ppm uranium 

• July 24, 2008: 2,887 gallon spill of production water and 12,770 gallon spill of solution 

• Aug. 23, 2007: 11,600 gallon spill of deep disposal well fluid 

• June 27, 2007: 900 gallon spill of injection fluid containing 1.1 ppm uranium 
13

• June 19, 2007: 900 gallon spill of fluid containing 41.2 ppm uranium 

• Feb. 19, 2007: 6,000 gallon spill of production fluid (32.5 ppm uranium) 

• Jan. 14, 2007: 5,000 gallon spill of injection fluid (2 ppm uranium) 

• Dec. 13, 2006: 560 gallon spill of injection fluid (2 ppm uranium) 

• Dec. 5, 2006: 10,000 gallon spill of mixed monitor well, restoration and waste fluids (1 

ppm uranium) 

• Nov. 22, 2006: 2,100 gallon spill of mine waste water 

• Feb. 10, 2006: 1,000 gallon spill of production fluid, containing approx. 21 mg/L 

uranium 

• Jan. 9, 2006: 6,240 gallon spill of injection fluid, containing approx. 1.7 mg/L uranium 

• Oct. 21, 2005: 7,041 gallon spill of deep disposal well fluid 

• Oct. 21, 2005: Leak detected in evaporation pond 

• Sep. 2, 2005: 4,500 gallon spill of production fluid, containing approx. 8.6 mg/L uranium 

• Aug. 16, 2005: 1,050 gallon spill of production fluid, containing approx. 2.1 mg/L 

uranium 

• May 31, 2005: 4,700 gallon spill of injection fluid, containing approx. 1.1 mg/L uranium 

• Oct. 9, 2004: 5,000 gallon spill of ground water sweep fluids containing 7 mg/L uranium 

• Sep. 29, 2004: 2,000 gallon spill of injection fluid, containing 1.6 mg/L uranium 

• Sep. 8, 2004: wellfield excursion at Mine Unit 4 monitoring well 

• Sep. 6, 2004: 1,600 gallon spill of injection fluid 

• July 22, 2004: 2,700-5000 gallon spill of production fluid 

• Oct. 15, 2003: 5,000 gallon spill of injection fluid containing about 47 mg/L of U3O8 

• Sep. 29, 2003: 5,000 gallon spill of injection fluid containing about 2 mg/L of U3O8 

• Sep. 6, 2003: 20,800 gallon spill of injection fluid containing about 1.1 mg/L of uranium 

• Feb. 9, 2003: 500 gallon spill of production fluid containing about 2 mg/L of uranium 

• Jul. 30, 2002: 1,480 gallon spill of injection fluid 

• Apr. 25, 2002: 3,500 gallon spill of injection fluid 

• Apr. 24, 2002: 18,000 gallon spill of injection fluid 

• Jan. 4, 2002: 1,800 gallon spill of production fluid containing about 18 ppm U308 

• Dec. 5, 2001: 3,600 gallon spill of injection fluid 

• Oct. 22, 2001: 62,400 gallon spill of injection fluid 

• Jun. 18, 2001: 1,100 gallon spill of deep well disposal fluid 

• Nov. 22, 2000: 1,870 gallon spill of injection fluid 

• Oct. 22, 2000: 11,100 gallon spill of injection fluid 

• Aug. 7, 2000: 780 gallon spill of production fluid 

• Feb. 26, 2000: 3,780 gallon spill of production fluid 

• Jan. 17, 2000: 6,900 gallon spill of production fluid 

• Dec. 31, 1999: 3,000 gallon spill of injection fluid 

(details available through ADAMS , Docket No. 04008964) 
1

January 21, 2010 

 

Chief, Rulemaking and Directives Branch 

U.S. Nuclear Regulatory Commission 

Mail Stop TWB-05-B01 

Washington, DC 20555-0001 

Comments on the Lost Creek ISR project 

To Whom it May Concern: 

The following are the comments of Biodiversity Conservation Alliance on the Lost Creek in-situ 

uranium recovery project. 

The Draft Report for Comment underestimates impacts to several resources due to erroneous 

assumptions and unrealistically optimistic estimates of the effectiveness for mitigation measures 

to be applied. 

Six production units are planned for the project. The production units would overlap in time, 

with up to 2 units on line at any one time. EIS at 2-20. This phased approach is far superior to 

having all pods of wells active at any one time. 

Storage ponds are mentioned, and these would be fenced. See EIS at 4-3. We appreciate the 

netting and fencing requirements to assure that waterfowl, raptors, and/or songbirds would not 

come down to these pond to land or drink and be poisoned by toxins in the holding ponds. 

Sage Grouse 

Six Active sage grouse leks occur within 2 miles of the project t boundary, and the project area 

has been designated a sage grouse Core Area. EIS at 4-47. The Wyoming BLM has a new 

instruction memorandum regarding development within designated sage grouse Core Areas. 

Attachment 1. As this project will be approved almost entirely on BLM lands, we expect the 

project to comply with the directives contained in this policy, and NRC states that the project 

will comply with the Governor’s policy (id.). At present, it does not, as the Governor’s policy 

caps well density at 1 well per 640 acres within Core Areas. 

Figure 2.7 graphically shows the layout of a wellfield. SEIS at 2-11. Between the injection wells, 

producing wells, and interior/perimeter monitoring wells, the total number of wells would total 

104 in the space that appears to be less than a square mile. This is far denser than the one well 

per square mile limit recommended by state and BLM policy. The likely outcome will be the loss 

of habitat function in and near the facilities; Holloran (2005) found that producing gas wells 

during the post-drilling stage that were within 1.9 miles of a sage grouse lek correlated to 

P.O. Box 1512, Laramie, WY 82073 (307) 742-7978 fax: 742-7989

Working to Protect Native Species and Their Habitats
2

reductions in lek attendance among breeding grouse (more than 1 well per section correlated to 

declined in breeding populations as well under this study). We would expect the facilities 

proposed under this ISL project would have a similar level of impact to producing gas wells 

during the production phase of the uranium project. In addition, Holloran (2005) found that 

nesting females avoided areas of high well density (as is proposed under this project) and had 

lower success at raising young than grouse in undeveloped areas. 

A two-mile overhead electrical transmission line accompanies the project. EIS at 2-14. This 

overhead powerline has the potential to serve as a perch for raptors, increasing rates of predation 

on birds and small mammals in the vicinity. Powerlines need to be buried within 3 miles of 

active sage grouse leks and within 1⁄4 mile of active prairie dog colonies. 

NRC states that impacts to sage grouse will be MODERATE to SMALL (EIS at 4-48), but this 

radically underestimates impacts to grouse. The Wyoming Game and Fish Department’s 

recommendations for oil and gas development in sensitive wildlife habitats (WGFD 2009, 

http://gf.state.wy.us/downloads/pdf/OGRecommendationsNovember09.pdf) states that well 

densities greater than 3 wells per mile constitute an impact level that is “extreme” for sage 

grouse even in non-Core areas. The well densities for this ISL facility clearly exceed this 

threshold by a large margin. “LARGE” impacts “are clearly noticeable and are sufficient to 

destabilize important attributes of the resource.” EIS at page xv. Impacts to sage grouse from 

construction and production activities and associated vehicle traffic clearly fall into this category. 

Additional, much stronger mitigation measures will be needed to reduce the level of impact. 

Traffic levels are expected to be 30 to 35 light trucks per day during the construction phase 

decreasing to 20 light trucks per day during production, with 2 to 5 heavy trucks per day 

throughout the course of the project. EIS at 4-8. Holloran (2005) found that as road traffic 

increased, the number of breeding males on affected leks decreased. The level of truck traffic 

shown for this project is likely to have a major negative effect on sage grouse throughout the life 

of the project. 

The sage grouse is rated as Native Species Status 2 (“NSS2”) by the Wyoming Game and Fish 

Department. NSS2 species’ habitats are ranked as “Vital” under the the Wyoming Game and 

Fish Commission’s Mitigation Policy, which states that projects recommends that projects 

should cause “no loss of habitat function.” See Attachment 2. This project appears to fail 

FLPMA’s consistency requirement for state plans and policies in this regard. 

Pygmy Rabbits 

Pygmy rabbits have been documented in the project area. EIS at 3-44. The project will result in 

habitat fragmentation (see EIS at 4-42), which is a major problem for this species. Purcell (2006, 

34) noted, “the conversion of big sagebrush communities to energy production sites within 

southwestern and southcentral Wyoming creates a concern for pygmy rabbits in these regions.” 

NRC states that the extent of pygmy rabbit habitat in the project area is small (approximately 39 

acres, EIS at 4-50); such a small area would be readily avoided by shifting of surface locations of 

project facilities. NRC should require the complete avoidance of pygmy rabbit habitats for the 

purposes of road and well construction as a condition of approval for the project. 
3

Sagebrush Obligate Passerines 

Although the portion of the landscape physically disturbed by roads, wellpads, and pipelines is 

often a relatively small percentage of the overall landscape, GIS analysis of full-field oil and gas 

development incorporating quarter-mile buffers to account for habitat degradation due to edge 

effects indicates that almost 100% of lands within a fully developed gas field are degraded 

(Weller et al. 2002). We would expect a similar result for ISL wellfields. In this way, the 

development of a wellfield results in widespread habitat destruction that extends well beyond the 

acreage of roads and wellpads that are bulldozed in. 

Fragmentation of shrubsteppe habitats has a particularly strong negative impact on birds. Knick 

and Rotenberry (1995) and found that sage sparrows and sage thrashers decreased with 

decreasing patch size and percent sagebrush cover, and reached the following conclusion: 

“Our results demonstrate that fragmentation of shrubsteppe significantly 

influenced the presence of shrub-obligate species. Because of restoration 

difficulties, the disturbance of semiarid shrubsteppe may cause irreversible loss of 

habitat and significant long-term consequences for the conservation of shrubobligate birds” (p. 1059). 

Ingelfinger (2001) found significant declines in nesting songbirds within 100m of gas field roads, 

and also found that sage sparrows declined near pipelines. Kerley (1994) found that 67% of 

songbird species selected for the tallest available sagebrush stands, and nest success was 

associated with 41% shrub cover, while the two nests in 15% shrub cover were both 

unsuccessful. 

Ingelfinger (2001) conducted a study of sagebrush birds in a western Wyoming gas field and 

found that as gravel roads increased, densities of sagebrush obligate birds, Brewer’s sparrows, 

and sage sparrows declined, while horned larks (a grassland species) increased. According to his 

findings, “roads associated with natural gas development negatively impact sagebrush obligate 

passerines. Impacts are greatest along access roads where traffic volume is high” (p. 69), but 

“bird densities are reduced along roadways regardless of traffic volume” (p.71). Kerley (1994) 

found that small patches had fewer shrub-nesting species than large patches, and the green-tailed 

towhee, an interior sagebrush species, was entirely absent from small patches. Remnant patches 

smaller than 1 ha will not support sagebrush shrub-nesting birds (Kerley 1994). 

Sage sparrows, Brewer’s sparrow’s and sage thrashers are BLM Sensitive Species which have 

been documented in the project area. EIS at 4-49. The analysis for passerine birds underestimates 

the true level of impact for these species. NRC contends that passerine birds will be displaced 

during construction activities (EIS at 4-42), which is true as far as it goes, but ignores the fact 

that vehicle traffic and dust will continue to displace passerine birds throughout the production 

life of the wellfields. NRC claims that impacts would not be outside the range of natural 

variability, and that impacts to populations would not be expected (id.), but this is simply an 

inaccurate statement. 
4

Key Wildlife Analysis is Missing 

The EIS references a Lost Creek Environmental Report, but this has not been included as an 

appendix to the EIS. See EIS at 4-3. It would seem that this report contains important 

information which should have been made available to the public for review as part of the NEPA 

process. We request that the NRC please send us a copy of this report as soon as possible. We 

would like to reserve the right to revise and extend our comments based on information 

contained in the report which may not be presented in detail in the EIS. 

Groundwater Impacts 

The impacts of in situ leach (ISL) mining are less visible, but ISL mining, by definition, involves 

the intentional pollution of groundwater, with the hope that the pollution can be extracted 

through the mining process. However, spills and leaks are common at ISL mines, and complete 

clean-up has proved impossible. The possibility of a pipeline rupture could lead to spills of 

lixiviant, either containing uranium or not. EIS at 4-20. In addition, NRC notes that 

“groundwater quality in the production zone is degraded as part of ISR operations.” EIS at 4-33. 

In addition, excursions of lixiviant or pregnant lixiviant may occur. Id. No examples of 

reclamation that has returned the water to its original condition have been found in the United 

States. In fact, research indicates that mine areas that have been “reclaimed” return to a 

contaminated state. This is because, after the water pumping associated with reclamation ceases, 

contaminated water moves back into the mining area.1

The ISL process uses harsh chemicals collectively known as ‘lixiviant’ to mobilize uranium from 

ore rock and pump it to the surface. EIS at 2-15. Of course, it will be impossible to remove all of 

the lixiviant and mobilized uranium from the formation during production operations, so the fate 

of groundwater in and around the target formations is an important concern. 

The uranium body in question to be tapped for in-situ leaching is the Battle Springs formation, 

which crops out at the surface in the project area and bears uranium to a depth of approximately 

1,150 feet there. EIS at 3-10. It is also faulted by a ‘scissors fault,’ offsetting the uranium-bearing 

strata within the project area. Id. at 3-11. This fault complicates the ability of the operator to 

control flows of lixiviant and also complicates aquifer restoration efforts. EIS at 4-34. 

Due to the thin nature of shale layers being counted on to contain the lixiviant, it is possible that 

vertical confinement of the lixiviant will not be achieved. EIS at 4-34. This leakage between 

 

1

 George Rice. 2006. Effects of URI’s Kingsville Dome Mine on Groundwater Quality. Kleberg County URI 

Citizen Review Board, TX.; Dan Kelley. November 5, 2006. As uranium mines closed, state altered cleanup goals. 

Corpus Christi, TX, Caller-Times; World Information Service on Energy. In-Situ Leaching Decommissioning 

Projects – USA: Texas: General. www.wise-uranium.org/udusail.html. Accessed January 25, 2008; William P. 

Staub. January 9, 1999. Uranium ISL Ground-Water Testimony of William P. Staub, Ph.D. US Nuclear 

Regulatory Commission Docket No. 40-8968-ML. www.sric.org/uranium/WATERDAT.html. Accessedd March 

24, 2008; J.K. Otton and S. Hall. In-situ recovery uranium mining in the United States: Overview of production 

and remediation issues. Lakewood, CO: US Geological Survey; Kenneth S. Wade. 1981. Uranium In Situ Mining 

and Groundwater Quality at the Grover Test Site, Weld County, Colorado. Thesis: Department of Earth Resources: 

Colorado State University. 
5

strata was confirmed by tests in 2007. Id. This increases the likelihood that contamination will 

spread beyond the target formation. 

The EIS discusses liquid wastes such as ‘production bleed’ and how they will be injected 

underground at deep injection wells. What are the chemical constituents of these liquid wastes? 

The EIS provides no information regarding this key point. Do they contain radioactive 

substances? Heavy metals? Caustic acids? The Mesa Verde formation seems to be the injection 

target. EIS at 4-35. We understand that the injection target strata for deep well injection must 

possess water quality equal to or worse than the liquid wastes that will be pumped into them. Is 

this going to be the case for the Lost Creek project, or will wastes be injected into a receiving 

aquifer of higher quality than the wastes? 

Surface Water and Wetland Impacts 

NRC contends that impacts to surface waters would be SMALL because they would occur in the 

Great Divide basin, which has no outlet to the sea and therefore does not contain any statutory 

Waters of the United States. EIS at 4-24. We agree that intermittent and ephemeral stream 

channels, springs and wetlands in the project area or likely to be affected by the project are 

indeed not Waters of the US pursuant to the Clean Water Act. However, the statutory 

classification of stream channels and wetlands has no bearing on the magnitude of environmental 

impact under NEPA. Their classification does not mean that spills or contamination would 

trigger the Clean Water Act’s provisions, but nonetheless NEPA requires that an objective 

assessment of impacts take place, and does not specify a difference between wetlands that are 

Waters of the U.S. versus other wetlands. In addition, Executive Order 11990 requires the federal 

government to minimize to minimize the destruction, degradation, or loss of wetlands (regardless 

of their Clean Water Act status) and to preserve and enhance their natural and beneficial values. 

See http://www.epa.gov/wetlands/regs/eo11990.html. 

The NRC is required to protect floodplains to the extent possible by Executive Order 11988. See

http://www.epa.gov/wetlands/regs/eo11988.html. Battle Spring Draw passes through the project 

area. EIS at 3-13. The EIS states that drainage channels would not be able to be avoided entirely, 

and that well sites are expected to be built right in drainage channels in some cases. EIS at 4-25. 

This would seem to violate Executive orders regarding floodplain management, and we expect 

the NRC to require design of well arrays to ensure that no well site will be located within or 

across a drainage channel. Location of wellpads in drainage channels will certainly result in 

major increases in erosion and sedimentation, and also elevate the risk that any spill that occurs 

at a wellsite will spread downstream along the stream channel. These impacts are readily 

avoidable by shifting the locations of project facilities. NRC needs to prohibit siting of wellpads 

in stream channels and avoid floodplains to the extent possible to comply with EO 11988. 

Historic and Cultural Resources 

Three sites eligible for the National Register of Historic Places have been documented in the 

planning area. EIS at 3-59. NRC concedes that “The visual presence of wells and header houses 

coul also impact the natural setting and overall cultural landscape.” EIS at 4-3. Under the 

National Historic Preservation Act, the federal government must protect not only the sites 

themselves but also their settings. We are concerned that improperly sited wellfields will impose 
6

wellsites, access roads, and other forms of industrial facilities that are inconsistent with 

maintaining the historic settings of the sites in question. With this in mind, wellfields should be 

configured such that facilities do not occur within the viewsheds of NRHP-eligible sites. 

Lost Creek Road needs to be Restored to a Two-track 

The NRC notes that the Lost Creek Road would be upgraded from a two-track to an engineered 

gravel road for the project, and would likely remain as such after the project’s completion. EIS at 

4-24. This road should be required to be reclaimed following cessation of operations, whereupon 

it could revert to a two-track vehicle way. Currently the Red Desert has a large surplus of 

unnecessary engineered roads which contribute needlessly to habitat fragmentation and 

disturbance of wildlife, and there is no reason to perpetuate this project-related impact beyond 

the life of the in-situ uranium recovery. It is doubtful that the county (or any other entity) will 

have the funding to properly maintain such a road, and being abandoned for all practical 

purposes it would be subjected to erosion that may ultimately make it less passable than a twotrack (this happens frequently in the Red Desert). 

Conclusions 

Given the sensitivity of sage grouse Core Areas and the likelihood that this project will impair or 

eliminate the habitat function for sage grouse within and adjacent to the project area, we 

recommend that NRC choose Alternative 2 (the “No Action” alternative ) for this project. Thank 

you for the opportunity to comment, and please send all additional public information concerning 

this project. 

Sincerely yours, 

Erik Molvar 

Wildlife Biologist 

Literature Cited 

Holloran, M.J. 2005. Greater sage-grouse (Centrocercus urophasianus) population response to 

natural gas field development in Wyoming. PhD Dissertation, Univ. of Wyoming, 223 pp. 

Ingelfinger, F.M. 2001. The effects of natural gas development on sagebrush steppe passerines in 

Sublette County, Wyoming. M.S. Thesis, Univ. of Wyoming, 110 pp. 

Kerley, L. 1994. Bird responses to habitat fragmentation caused by sagebrush management in a 

Wyoming sagebrush steppe ecosystem. PhD Dissertation, Univ. of Wyoming, 153 pp. 

Knick, S.T., and J.T. Rotenberry. 1995. Landscape characteristics of fragmented shrubsteppe 

habitats and breeding passerine birds. Conserv. Biol. 9:1059-1071. 
7

Purcell, M.J. 2006. Pygmy rabbit (Brachylagus idahoensis) distribution and habitat selection in 

Wyoming. MS Thesis, Univ. of Wyoming, 160 pp. 

Weller, C., Janice Thomson, P. Morton, and G. Aplet. 2002. Fragmenting our lands: The 

ecological footprint from oil and gas development. Unpublished report, The Wilderness Society, 

24 pp. 
30113 2nd pages / 1 of 8

For permission to copy, contact editing@geosociety.org

© 2010 Geological Society of America

Climate-induced formation of a closed basin: 

Great Divide Basin, Wyoming

Paul L. Heller1,†, Margaret E. McMillan2, and Neil Humphrey1

1

Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071, USA

2

Department of Earth Sciences, University of Arkansas at Little Rock, Little Rock, Arkansas 72204, USA

 1

GSA Bulletin; Month/Month 2010; v. 1xx; no. X/X; p. 000–000; doi: 10.1130/B30113.1; 6 fi gures; 1 table; Data Repository item 2010158.

†

E-mail: heller@uwyo.edu

ABSTRACT

Large closed basins are often associated 

with regions of active tectonics. In contrast, 

we provide the example of the Great Divide 

Basin, in southern Wyoming, where climate 

change, through its impact on erosion and 

fl exure, provides the primary mechanism of 

basin closure. Two- and three-dimensional 

fl exural models that incorporate the effects 

of local basin abandonment due to aridity as 

well as minor extrabasinal extension demonstrate that basin closure with 40 m of basement relief (tilt) could have been achieved 

in the Great Divide Basin under reasonable 

assumptions of sediment rock density and 

fl exural rigidity. The primary drive for basin abandonment was insuffi cient discharge 

that retarded river downcutting. Continued 

erosion in the surrounding drainage led to 

fl exural rebound, against which erosion by 

the outlet from the Great Divide Basin was 

unable to compete. Eventually, the basin 

became detached and isolated from the surrounding drainage, and a few tens of meters 

of differential tilt developed between the basin fl oor and spillover point. An extra amount 

of tilt, up to a few meters, could have been attained by rift shoulder effects associated with 

minor nearby extension outside of the basin 

to the north. Hence, closure of the Great Divide Basin took place with no internal faulting, nor did it require any extrabasinal tectonic activity to force basin closure. Hence, 

basin closure and/or drainage reorganization 

need not record tectonic activity in all cases. 

Differential erosion provides an alternative 

hypothesis that does not refl ect local tectonic 

timing. Our model of the evolution of the 

Great Divide Basin illustrates a mechanism 

by which basins can become closed by climatic effects alone.

INTRODUCTION

Large closed basins are typically associated 

with active tectonism in a variety of settings. 

Examples include Pyramid Lake, Nevada (with 

109 m relief between basin fl oor and spillover 

point), in an extensional setting; Death Valley, 

California (148 m), in a strike-slip setting; and 

Qinghai Lake, north-central China (28 m), in a 

compressional setting. Such basins may be dry or 

contain lakes, depending on water supply (Carroll and Bohacs, 1999). In all cases, closed basin 

formation occurs where rates of sediment supply 

derived from surrounding mountain ranges lag 

behind rates of space created (accommodation) 

by tectonic activity in the basin (Carroll and Bohacs, 1999; Humphrey and Konrad, 2000; GarciaCastellanos, 2007). Accommodation may result 

from basin subsidence or rate of surface uplift of 

a bounding tectonic sill. Typically, closed basins 

are geologically short-lived—once tectonism 

abates, continued sediment supply, coupled with 

erosional downcutting of the spillover point, eventually eliminates topographic barriers to drainage.

The Great Divide Basin of south-central Wyoming (Fig. 1) stands in contrast to closed basins formed in tectonically active settings. The 

basin is a large (~104

 km2), internally drained, 

topographic depression that sits at high elevation 

(2100 m average) astride the U.S. continental 

divide. With tens of meters of closure between 

basin fl oor and spillover point, the basin is as 

large as or larger than most closed basins. In this 

part of the Rocky Mountains, there is thought to 

be little recent tectonic activity (Flanagan and 

Montagne, 1993) and no known recent faulting 

within the basin. As such, an obvious tectonic 

origin of the Great Divide Basin is a diffi cult 

case to make. Alternatively, we suggest here 

that basin closure was primarily the result of an 

isostatic response to the climatically induced 

isolation of the basin from the surrounding 

drainages. Such a mechanism may play a role 

in other closed basins not directly controlled by 

active tectonism along their margins.

GREAT DIVIDE BASIN

The Great Divide Basin was originally part 

of a foreland basin bounded by the Sevier foldand-thrust belt to the west during Cretaceous–

early Eocene time. In Late Cretaceous time, 

the Laramide orogeny partitioned the foreland 

region into individual basins bounded by narrow basement-cored ranges (Snoke, 1993). This 

event produced the thrust-bounded ranges and 

domal uplifts that surround the Great Divide 

Basin today (Fig. 1). During the early part of the 

Laramide orogeny, the basin was a part of the 

greater Green River Basin (Surdam and Stanley, 

1980). Subsequent relative uplift of the Rock 

Springs Uplift to the west and the Rawlins Uplift to the east (Fig. 1) during Late Cretaceous 

through Paleocene time further defi ned the margins of the Great Divide Basin (Lillegraven et 

al., 2002; Mederos et al., 2005). The basin was 

not closed, however, until at least middle to 

late Miocene time (Hansen, 1986; Lillegraven 

and Ostresh, 1988). Prior to this time, the basin 

drained to the east, into the Platte River system.

Continued, subtle, post-Laramide tectonism 

has affected the Rocky Mountains, including 

regional doming that began after 8 Ma and 

was well on its way by ca. 4 Ma (McMillan et 

al., 2006). Local post-Laramide tectonism and 

volcanism close to the Great Divide Basin include the extensional collapse of the Granite 

Mountains (beginning ca. 11–7 Ma; Anders et 

al., 2009) to the north, the propagation of the 

Rio Grande Rift to the east of the Sierra Madre 

Mountains (beginning 10–8 Ma; Mears, 1998; 

Keller and Baldridge, 1999), and eruption of 

the Leucite Hills (3–0.8 Ma; Lange et al., 2000) 

around the Rock Springs Uplift on the western 

margin of the basin.

It is unclear exactly when the Great Divide 

Basin became isolated from the Platte River 

drainage. Regional studies indicate that the 

basin and adjacent parts of the Northern Platte 

River drainage were buried under >600 m of 

Oligocene–Miocene basin fi ll after the end of 
Heller et al.

2 Geological Society of America Bulletin, Month/Month 2010

30113 2nd pages / 2 of 8

FDF

SDF

KDF

A

A′

2000 2500 3000 3500 4000

Elevation (m)

1000 1500

50 km

Wind River 

Mountains

Rawlins 

Uplift

Rock 

Springs 

Uplift

Ferris 

 Mtns

Seminoe 

 Mtns

Granite Mountains

Sierra 

Madre 

Mountains

Chain Lakes Flat

Separation Flats

Red Desert 

Basin

Green 

Mtns

Wamsutter 

Gap

Sand Gap

Sinclair

Gap

Muddy Gap

Green

River

Basin

N. Platt e

River

Sweetwater River

Hanna

Basin

SL

Sand Creek

Medicine Bow

Mountains

NGMF

SGMF

Park

Range

Rawah

Range

Rawlins

UT

CO

WY

NE

ID

MT Great 

Divide 

Basin

300 km

N. Platte River

Rabbit Ears Range

Leucite

Hills

109° W 108° W

107° W 106° W

42° N

41° N

GDB

Figure 1. Location and topography of the Great Divide Basin (GDB), southern Wyoming. The basin is surrounded by the continental

divide (bold line on inset map). Locations of likely outfl ows for the basin are shown in white. Young faults are shown in red (South Granite Mountain fault—SGMF; North Granite Mountain fault—NGMF). Gray shading shows location of signifi cant sand dune deposits 

(KDF—Killpecker dune fi eld; FDF—Ferris dune fi eld; SDF—Seminoe dune fi eld). SL—Separation Lake, the low point in the Great 

Divide Basin. Arrows indicate fl ow path of river that previously drained the basin. Cross section A-A′ is used for two-dimensional fl exural model (Fig. 2).
Climate control of closed basin formation

Geological Society of America Bulletin, Month/Month 2010 3

30113 2nd pages / 3 of 8

the Laramide orogeny (McMillan et al., 2006). 

These alluvial deposits in areas surrounding the 

basin reach an elevation of ~2200 m, roughly 

250 m above the present spillover point out of 

the basin. The switch from net aggradation to 

net incision of Laramide basins in this part of 

the Rocky Mountains took place after 6.75 Ma, 

the age of tuffs found at the base of the Moonstone Formation, located just north of the study 

area in the Granite Mountain block (Anders et 

al., 2009). Incision of the lowest 100 m of the 

Great Divide Basin took place over the past 

1 m.y., based on the dates and elevations of lava 

fl ows found in the Leucite Hills, along the western edge of the basin (Lange et al., 2000). Abandonment of through-going drainage in the basin 

took place prior to 7 ka, the age of sand dunes 

shrouding the basin fl oor. Hence, closure of the 

Great Divide Basin by a few tens of meters took 

place between 1 Ma and 7 ka.

Today, the Great Divide Basin’s internal 

drainage consists of ephemeral streams that 

fl ow into large playas and small perennial lakes, 

or disappear beneath active eolian sand dune 

and sheet deposits. These arid landforms are 

consistent with modern conditions of low mean 

precipitation and high mean evaporation rates. 

Sand dune fi elds cross into the basin on its western margin, occur on the leeward side of many 

playas within the basin, and blanket the basin’s 

northeastern margin (Fig. 1). Dune fi elds trend 

west to east, parallel to the prevailing westerly 

wind direction. Winds blow on average 25 km/h 

in summer and 36 km/h in winter from the west 

southwest (Martner and Marwitz, 1982). The 

largest fi elds include the Killpecker, Seminoe, 

and Ferris dunes (Fig. 1). The dune fi elds are 

as old as latest Pleistocene and have been active throughout the Holocene, with periods of 

activity coinciding with periglacial conditions 

(Mayer and Mahan, 2004). Sedimentary and 

geomorphic evidence from study of the Ferris 

dune fi eld suggests that wind strength, intensity, 

and direction have not varied much since the 

end of the Pleistocene (Gaylord, 1982).

Large playas coincide with the lowest elevations in the basin and broadly defi ne three subbasins separated by ridges of resistant fi ne-grained 

sedimentary rocks. The three subbasins include 

the northwest-southeast–trending Red Desert 

Basin, an east-west–trending longitudinal valley 

made up of the Lost Creek Basin, Battle Spring 

Flat, and Chain Lakes Flat (hereafter identifi ed 

collectively as the Chain Lakes Flat), and the 

northwest-southeast–trending Separation Flats 

(Fig. 1). The Red Desert Basin and Chain Lakes 

Flat are underlain by the predominantly fl uvial 

and lacustrine deposits of the Tertiary Battle 

Spring, Wasatch, and Green River formations 

(Bradley, 1964). Separation Flats is underlain 

by Upper Cretaceous marine rocks of the Steele 

Shale, Cody Shale, Mesaverde, and Niobrara 

Formations (Barlow, 1953; Bayley, 1968).

TOPOGRAPHY

In order to determine where the Great Divide 

Basin drained prior to closure, we compiled a 

data set including elevations of divides and 

other potential overfl ow points, drainages, and 

possible burial of such features by eolian sand 

accumulations from a variety of sources including elevations from U.S. Geological Survey 

(USGS) digital elevation models (DEMs; 30 m 

resolution), spot elevations using mappinggrade Trimble differential GPS unit (DGPS) 

(20 cm resolution after postprocessing), available geologic mapping, and well-log data from 

the Wyoming Oil and Gas Conservation Commission and Wyoming State Geological Survey.

The average elevation of the Great Divide Basin is 2100 m above mean sea level. Total relief 

within the basin is signifi cant at ~1100 m difference between the highest point along the crest 

of the Ferris Mountains (3050 m) and the lowest 

point in Separation Flats (1947 m). However, 

on average, the basin is quite fl at. Over 80% 

of the basin area falls within the 1947–2150 m 

elevation range, and less than 4% of the basin 

area is above 2300 m above mean sea level. It 

is important to note that there is very little high 

topography, and therefore mountain drainage, 

in the Great Divide Basin catchment (Fig. 1). 

In contrast, the North Platte drainage, bounding the east and north sides of the basin, drains 

much of the high topography in this part of the 

central Rocky Mountains.

Low points in each of the subbasins occur 

at 2005 m in the Red Desert Basin, 1970 m in 

the Chain Lakes Flat, and 1947 m in Separation 

Flats. The lowest points within each subbasin 

step down in a generally west-to-east pattern. 

Similarly, the spillover points today between 

the subbasins step down from west to east from 

2038 m between Red Desert Basin and Chain 

Lakes Flat, to 2005 m between Chain Lakes Flat 

and Separation Flats, to 1996 m between Separation Flats and the North Platte drainage (Fig. 1).

The lowest gaps along the basin divide (Fig. 1) 

include Wamsutter Gap (2051 m), Muddy Gap 

(2066 m), Sinclair Gap (1996 m), and Sand Gap 

(2097 m). The fi rst three sites have exposed Cretaceous bedrock at the surface, and thus these 

are minimum spillover elevations. At the Sand 

Gap site, however, the minimum elevation is located among sand dunes within the Ferris dune 

fi eld. Sand dunes have blown over Sand Gap and 

migrated partway down Sand Creek to the north 

(Fig. 1). Bedrock exposed among the dunes at 

Sand Gap is at an elevation of 1990 m, which is 

slightly lower than the elevation of the divide at 

Sinclair Gap. The largest horizontal distance between bedrock exposures in the Sand Gap area 

is ~120 m. Therefore, it is possible that sand 

hides a buried, narrow valley beneath which 

bedrock basement may be somewhat lower.

Sand Gap seems the most likely outfl ow 

from the Great Divide Basin. Not only is bedrock somewhat lower here than at other candidate areas, but Sand Creek, which runs through 

Sand Gap to join the North Platte River (Fig. 1), 

has well-developed and extensive high terraces 

several meters above the current small creek. 

Bedrock clasts among terrace remnants suggest 

signifi cant outfl ow through Sand Creek. These 

terraces have been partially buried by migrating 

sand dunes. Thus, a river clearly fl owed through 

the gap prior to the period of Holocene drying. Projection of terrace surfaces suggests that 

the spillover point at Sand Gap was not much 

below 1990 m. The maximum relief between 

the lowest spot in the basin, Separation Lake 

(at 1947 m), and the bedrock overfl ow at Sand 

Gap (1990 m) is 43 m. These sites are located 

roughly 30 km from each other. It is unclear 

what generated this closure.

ORIGIN OF BASIN CLOSURE

While there is no known tectonic activity 

along the northern basin margin, there is evidence of young normal faulting farther to the 

north, along the northern fl ank of the Ferris 

and Seminoe mountains. Love (1970) describes 

a west-northwest–trending normal fault, the 

South Granite Mountain fault (SGMF, Fig. 1) 

that bounds the southern edge of the Granite 

Mountain block. The structure is near vertical, 

probably becoming listric with depth (Blackstone, 1991) and places Miocene age deposits (Moonstone Formation) against basement 

rocks. Displacement along the fault reaches up 

to 610 m at the far west end of the South Granite Mountain fault (Love, 1970). However, cross 

sections constrained by well data indicate offset 

is closer to 200 m around the location of Sand 

Creek (Love, 1970; Blackstone, 1991). Subparallel faulting along the northern margin of the 

block (North Granite Mountain fault; Fig. 1) 

indicates that the Granite Mountains sit in a graben (Love, 1970). Available age constraints indicate that normal faulting began between ca. 11 

and 7 Ma, and may be continuing today (Anders et al., 2009). Along the northern fl ank of 

the Seminoe Mountains, to the east of Great Divide Basin, truncated spurs provide geomorphic 

evidence of offset along the fault (Jaworowski, 

1985). However, no similar topography is seen 

in the vicinity of Sand Creek, the proposed outlet of the Great Divide Basin (Fig. 1).
Heller et al.

4 Geological Society of America Bulletin, Month/Month 2010

30113 2nd pages / 4 of 8

Impact of Extrabasinal Tectonics

It is possible that if there were young, signifi -

cant normal fault offset along the South Granite 

Mountain fault, it could have played a role in 

closing the Great Divide Basin. Normal offset 

would not close the basin by building a tectonic 

dam along Sand Creek. In fact, normal fault offset, had it occurred along the drainage, would 

have led to the formation of a knickpoint, and 

would have accelerated erosion along the stream, 

facilitating downcutting. Instead, any signifi cant 

reduction in tectonic load by thinning of the crust 

along the margin of the Granite Mountain graben could lead to fl exural rebound adjacent to the 

graben margins. This phenomenon contributes 

to the formation of “rift shoulders” (Weissel and 

Karner, 1989; Chéry et al., 1992). Tilting to the 

south away from the graben would help provide 

a slope that, under the right conditions, could 

contribute to closing of the Great Divide Basin.

In order to evaluate this mechanism as a 

cause of tilting in the eastern Great Divide Basin, we constructed a simple two-dimensional 

fl exural model using cross sections of the Granite Mountains provided by Love (1970). Twodimensional modeling is appropriate because 

the load, the Granite Mountain graben, is an 

elongate feature, and we are modeling a location 

near the approximate midpoint of the graben 

margin, so that three-dimensional boundary effects are unlikely to play a signifi cant role. The 

geologic history of the Granite Mountain block 

suggests that during, or following, downdrop of 

basement rocks, sedimentation took place. Assuming the South Granite Mountain fault does 

not offset the Moho, the result of the net effect of 

extension and basin fi lling is to replace basement 

rock (density ~2850 kg/m3

) with sedimentary 

rock of density between 2200 and 2500 kg/m3

. 

Thus, density contrast ranges from 350 to 

650 kg/m3

. For simplicity, we assume a rectangular load shape for the graben geometry. Load 

width is the half-width of the graben, which 

along our cross section is 24 km. The elastic 

plate is assumed to be laterally infi nite, and thus 

half the load is compensated for by that part of 

the plate that extends to the north. For fl exural 

rigidity, we assumed values ranging from 1022 to 

1023 N•m. This range includes the best-fi t values 

for the subsidence geometry of the Cretaceous 

foreland basin across southern Wyoming (Jordan, 1981; Liu and Nummedal, 2004). Load 

height is ~200 m based on fault offset of the 

Split Rock Formation along a cross section near 

the modern Sand Creek (Love, 1970; Blackstone, 1991). We calculated the resultant relief 

(tilt) due to rift shoulder development between 

Sand Gap and Separation Lake (Fig. 2), which 

lie 30 km apart from each other. Sand Gap is 

located ~3 km south of the South Granite Mountain fault (Fig. 1). Our estimates of relief were 

calculated for a variety of likely sediment-fi ll 

densities and fl exural rigidities. The tilt between 

Sand Gap and Separation Lake ranges from 

2.5 m and 12.4 m, depending on the assumed 

density and rigidity (Table 1; Fig. 3, white bars). 

Such values fall far short of the required basement tilt of ~40 m that closes the basin.

Role of Climate Change

The Great Divide Basin today is very dry. 

The basin has low mean precipitation rates 

(12–30 cm/yr, avg. 1961–1990; U.S. Department of Commerce, 2005) coupled with high 

mean evaporation rates (>75 cm/yr of shallow 

lake evaporation, avg. 1956–1970; Farnsworth 

et al., 1982). Being on the continental divide, 

16

12

8

4

0

0 10 20 30 40 50 60 70 80 90 100

Deflection (m)

Distance from load center (km)

graben

fill 2400 kg/m3

2500 kg/m3

2300 kg/m3

ρs = 2200 kg/m3

Sand Gap Separation Lake

South Granite

Mountain fault

A A′

Granite

Mountain

block

Great Divide Basin

Figure 2. Calculated fl exural rebound due to graben development 

along the Granite Mountain block. Cross section A-A′ (Fig. 1) 

runs from the Granite Mountain block across the Great Divide 

Basin. Flexural response is calculated for rigidity of 1022.5 N•m and 

assumes that density of sediment fi lling Granite Mountain graben ranges from 2200 to 2500 kg/m3

, replacing material that is 

2850 kg/m3

. Results are calculated for fault offset of 200 m along 

the South Granite Mountain fault. Solid lines are fl exural profi les 

within Great Divide Basin; dashed lines are profi les within Granite Mountain block. Locations of basin spillover (Sand Gap) and 

basin low point (Separation Lake) are shown.

TABLE 1. CALCULATED TILT RESULTING FROM RIFT SHOULDER AND REGIONAL EROSION

Flexural rigidity

and equivalent 

effective elastic 

thickness (EET)

Sedimentary rock

density 

(kg/m3

)

Rift shoulder tilt (relief) 

from Separation Lake to 

Sand Gap

(M)

Erosional tilt (relief) from 

Separation Lake to Sand 

Gap 

(M)

Total 

tilt 

(m)

1022 N•m 2200 12.4 50.6 63.0

(EET = 11.7 km) 2300 10.5 56.6 67.1

2400 8.6 63.7 72.3

2500 6.7 72.0 78.7

1022.5 N•m 2200 6.6 27.1 33.7

(EET = 20.0 km) 2300 5.6 29.7 35.3

2400 4.6 32.6 37.2

2500 3.6 35.9 39.5

1023 N•m 2200 4.7 18.7 23.4

(EET = 25.2 km) 2300 4.0 20.3 24.3

2400 3.3 22.2 25.5

2500 2.5 24.2 29.7
Climate control of closed basin formation

Geological Society of America Bulletin, Month/Month 2010 5

30113 2nd pages / 5 of 8

overall elevations are high; however, there is 

very little relief within the catchment and surrounding range crests. As a result, there is little, 

if any, orographic impact on prevailing westerly 

weather fronts to force precipitation within the 

basin. In contrast, the North Platte River, which 

fl ows just east of the basin, originates in the high 

ranges of northernmost Colorado (Fig. 1). The 

catchment drains high ranges (>3500 m) where 

orographic effects promote high precipitation 

rates (up to >152 cm/yr, avg. 1961–1990; U.S. 

Department of Commerce, 2005), yielding perennial river fl ow.

The stark difference in aridity between the adjacent drainages today raises the possibility that 

change in climate could have impacted the catchments in the past. Specifi cally, we consider the 

impact of differential changes in discharge between the Great Divide Basin and adjacent North 

Platte River drainage during Pleistocene time.

A change in climate alone need not yield any 

change in differential precipitation between 

the Great Divide Basin and North Platte River 

drainages. The nearly ten-fold difference in annual precipitation seen today due primarily to 

orographic effects could well have existed in 

Pleistocene time. In the study area, however, 

Pleistocene glaciation was limited to the headwaters of the North Platte River, with none 

forming along highlands of the Great Divide 

Basin (Pierce, 2004). Meltwater was released as 

glaciers retreated during times of warming climate. This led to periods of high discharge in the 

Platte river drainage and likely increased ero2200 2300 2400 2500 2200 2300 2400 2500

0

10

20

30

40

50

60

70

80

Relief between Sand Gap and Separation Lake (m)

2200230024002500

ρsediment (kg/m3)

D = 1022.5 N•m

D = 1022 N•m

D = 1023 N•m

Will this do?

Figure 3. Calculated relative relief between the low point in the basin (Separation Lake) and the inferred spillover point (Sand Gap) 

due to fl exural response related to unloading. Black bars result 

from removal of deposits along the North Platte River drainage as 

calculated from the three-dimensional (3-D) fl exural model. White 

bars show tilt due to rift shoulder effects from normal faulting 

within the Granite Mountain block. Results are for a range of rigidities (1022, 1022.5, 1023 N•m) and assumed density of sedimentary 

rocks (2200, 2300, 2400, 2500 kg/m3

).

sion. Meanwhile, the absence of glaciers, and 

thereby signifi cant water storage, in the Great 

Divide Basin precluded similar magnitudes of 

stream incision. As a result, rapid downcutting 

along the Platte River during meltwater times 

was not matched in the Great Divide Basin—

the latter of which was left literally high and dry.

Impact of Extrabasinal Erosion

While the North Platte River continued to erode 

down to its present position, the Great Divide 

Basin became abandoned and then closed. The 

North Platte drainage has eroded a deep, wide valley just northeast of the much higher Great Divide 

Basin. It therefore seems possible that the strong 

asymmetry in erosion rates between these drainages may have contributed to closure of the basin 

due to regional isostatic response (i.e., fl exure). 

Was the fl exural uplift due to removal of basin fi ll 

in the North Platte drainage enough to lead to the 

observed differential uplift between Sand Creek 

Pass and Separation Lake?

In order to evaluate the fl exural effect of regional erosion, we applied a three-dimensional 

elastic fl exural model to the northeastern Great 

Divide Basin, in the vicinity of the Sand Gap spillover point. To facilitate model construction, we 

assumed that the elevation of the Platte River near 

where the drainage from the Great Divide Basin 

once fl owed was close to the present elevation 

of the spillover at Sand Gap, i.e., 1990 m. Thus, 

we assume that any incision by the North Platte 

drainage below this elevation took place after the 

Great Divide Basin was no longer connected to 

the Platte River. The removal of material below 

this elevation would then lead to isostatic rebound 

in the area affected by the fl exural effects.

Figure 4 shows the present distribution of the 

1990 m contour surrounding the modern Platte

River. This contour line is assumed to represent 

the limits of Platte River erosion since isolation 

of the Great Divide Basin. We only modeled 

the region shown in Figure 4, an area of 100 × 

120 km. This area includes the northeastern 

limit of the basin and adjacent parts of the North 

Platte River drainage from the towns of Rawlins 

to Casper, Wyoming. This modeled area is closest to the former spillover point at Sand Gap, 

where fl exural impacts would have been greatest. Erosion farther downstream along the North 

Platte River would have added to the calculated 

fl exural response; however, loads farther away 

have exponentially less impact on fl exure in the 

area of interest and are considered to have minimal impact on our results.

To facilitate modeling, we broke this region 

into a series of cylindrical point loads, each 

5 km in diameter (Fig. 4), the removal of which 

leads to fl exural rebound. The height of each 
Heller et al.

6 Geological Society of America Bulletin, Month/Month 2010

30113 2nd pages / 6 of 8

34

Seminoe Mtns

< 50 

50–100 

100–150 

150–200 

200–300 

300–410 

North Fork Platte River

continental

divide

Sand Gap

(1990 m)

Separation Lake

(1947 m)

20 km

Casper

Ferris Mtns

Rawlins

107°30′W 107°W 106°30′W

42°30′N 

42°N

Great Divide

Basin

1990 m

1990 m

Flexure (m)

Figure 4. Area modeled in three-dimensional (3-D) fl exure analysis. The northeast margin of the Great Divide Basin is shaded. The 1990 m contour (thin 

dashed line) is model datum. Incision into datum forms the erosional load for 

model runs. Location and thickness (binned) of eroded cylindrical loads are 

shown by shaded circles. Position of North Fork of the Platte River, continental 

divide, and location of the towns of Rawlins and Casper, Wyoming, are shown.

0

20

40

60

80

100

0

20

40

60

80

100

120

-100

-50

0

50

100

150

200

250

Distance East (km)

Distance North (km)

Deflection (m)

Figure 5. Results of three-dimensional fl exural model. Graph shows position of an originally horizontal datum surface following erosion along the North Platte drainage as described in text and resulting fl exural rebound (D = 1022.5 N•m, ρs

 = 2500 kg/m3). Positions 

of Sand Gap (to the north) and Separation Lake are shown by black disks.

eroded load was determined from the average 

elevation of each 5-km-square grid point over 

which these cylinders were centered. We calculated the difference between average elevation 

of each cell and the 1990 m datum representing 

the preerosion surface. The erosion of each grid 

point is available in the GSA Data Repository,

1

but the general heights of each load, binned, are 

shown in Figure 4.

Our fl exural model assumes the elastic plate 

was infi nite in all directions. Model runs used a 

range of densities of eroded sedimentary rock 

(2200–2500 kg/m3

) and fl exural rigidities (1022–

1023 N•m, equivalent to effective elastic thickness 

of 12–25 km; Table 1). An example of a calculated fl exural response to removal of the eroded 

material using a fl exural rigidity of 1022.5 N•m 

is shown in Figure 5. Both the shape and magnitude of doming associated with regional erosion are shown. In the area of analysis, rebound

generates between 19 and 50 m of relief, depending on assumed fl exural rigidity value and 

the density of eroded material (Table 1). The 

model assumes that topography of the area prior 

to erosion was that of a fl at surface at 1990 m. 

Therefore, we ignore any erosion that might 

have taken place in the preexisting mountains 

surrounding the region, which would only serve 

to increase the possible amount of rebound and 

tilt. Thus, we consider the model response to be 

a minimum estimate at that fl exural rigidity.

DISCUSSION

In order to explain the basin closure with 

~40 m of relief between the basin low point and 

the spillover at Sand Gap by fl exural response, 

either the assumption of low fl exural rigidity is 

required for the erosional model alone, or for 

the combined isostatic effects of regional erosion as well as tilting due to rifting to the north 

(Fig. 3; Table 1). We fi nd that if we use the bestfi t fl exural rigidity determined by analysis of 

Cretaceous foreland basin defl ection in southern Wyoming (1022.5 N•m; Liu and Nummedal, 

2004), we get excellent agreement with the observed relief of basin closure in the Great Divide 

Basin (34–40 m depending upon sedimentary 

rock density assumed; Fig. 3). An increase in 

fl exural rigidity to 1023 N•m yields insuffi cient 

rebound to explain the observed relief (Table 1).

The fl exural model described here has little 

impact on the paleoelevations of the other candidate overfl ow points. The position of Sand 

Gap, in the NE corner of the basin, allows it to 

1

GSA Data Repository item 2010158, Table of 

load magnitudes, is available at http://www. 

geosociety.org/pubs/ft2010.htm or by request to 

 editing@geosociety.org.
Climate control of closed basin formation

Geological Society of America Bulletin, Month/Month 2010 7

30113 2nd pages / 7 of 8

be maximally impacted by both the area of greatest erosion along the North Platte River to the 

northeast and the normal faulting to the north. 

We have not observed any other erosional or tectonic patterns in the vicinity of the other potential overfl ow points around the basin that would 

yield comparable results from fl exural modeling.

It is possible that some additional relief may 

have been generated by local wind defl ation 

in the area of Separation Lake. We have observed occasional ventifact clasts in this part 

of the basin. Wind erosion on the order of 10 m 

would make it possible for the higher rigidity 

to provide a reasonable fi t. Regardless, we fi nd 

it interesting that rigidity of 1022.5 N•m best explains both the Cretaceous subsidence history of 

southern Wyoming as well as our Pleistocene 

to Holocene reconstruction. This suggests there 

has been little net change in regional rigidity 

over the past ~70 m.y. across southern Wyoming, despite the Laramide crustal thickening 

that occurred during this time.

Model of Basin Evolution

Our results suggest that climate, leading to 

low erosion rates in the Great Divide Basin in 

contrast to high erosion rates nearby, coupled 

with an isostatic fl exural response can explain 

basin closure and most of the relief between the 

basin low point and spillover point. A key factor to this interpretation is that the Great Divide 

Basin, once tributary to the North Platte River, 

is arid and has very little potential to integrate 

much precipitation despite its large size. None 

of the ranges surrounding the basin has high 

enough relief to force much orographic precipitation today. In addition, none of the ranges has 

large enough catchment area to provide signifi -

cant discharge to the basin. 

During Pleistocene time, glaciers that formed 

in the headwaters of the North Platte River 

(Fig. 6), but not in the Great Divide Basin, 

provided a means for high discharge during

meltwater events during periods of glacial retreat (e.g., Pelletier, 2009). Accelerated erosion 

along the North Platte River, but not the Great 

Divide Basin outfl ow, led to isolation of the latter from the Platte drainage. Erosion in excess 

of 200 m by the North Platte River led to isostatic rebound that fl exed the northeast corner 

of the Great Divide Basin, creating signifi cant 

relief in the area of the basin outlet (i.e., tens 

of meters), which forced basin closure. Rigidities of the order 1022.5 N•m generated a broad 

doming that affected the entire eastern part of 

the basin as well as nearby areas (Fig. 6). In addition, normal faulting along the Granite Mountain block to the north of the Great Divide Basin 

(SGMF in Fig. 6) that took place sometime in 

the past <11 m.y. encouraged minor back tilting 

due to fl exural rift shoulder effects. This added 

to closed basin relief, albeit to a minor extent.

Finally, windblown dunes formed as a result 

of continued aridifi cation of the central Rockies and adjacent Great Plains over Holocene 

time (Marrs et al., 1987). Dune fi elds are common along the Wyoming Wind Corridor, which 

runs east across the southern half of Wyoming 

including the Great Divide Basin. A discontinuous line of sand dunes can be traced across the 

basin into the area of the basin outlet at Sand 

Gap (Fig. 1). Sand dunes bank around the northeast basin margin and overtop the divide into the 

adjacent Platte River drainage. The dunes add as 

much as an extra ~100 m of relief to the basin 

closure in the area of Sand Gap.

CONCLUSIONS

Two- and three-dimensional fl exural analysis 

suggests that closure of the Great Divide Basin 

was likely due to enhanced erosion in the adjacent North Platte River drainage. Enhancement of 

Figure 6. Key elements for interpretation of climatic cause of closure of the Great Divide Basin. Shaded region shows approximate 

area that underwent fl exural response and unloading due to erosion 

by the North Platte River (assuming fl exural rigidity of 1022.5 N•m) 

as well as thinning of the Granite Mountain block. Heavy dashed 

line follows approximate trace of previous drainage out of Great 

Divide Basin. SC—Sand Creek Gap, SL—Separation Lake.
Heller et al.

8 Geological Society of America Bulletin, Month/Month 2010

30113 2nd pages / 8 of 8

this closure was due to minor extrabasinal tectonic 

impact and the encroachment of sand dunes due 

to increased aridifi cation in Holocene time. In our 

model, differential erosion is caused by increased 

meltwater discharge during periods of deglaciation. Headwaters of the North Platte River were 

glaciated; the Great Divide Basin was not.

Because of the competition between the effects of rift shoulder and erosional tilt, the results 

are not very sensitive to the sediment density assumed. The greater is the sediment density, the 

more erosional rebound plays a role, and the less 

rift shoulder uplift contributes. The amount of 

calculated tilt is sensitive to the fl exure rigidity 

of the lithosphere, producing a good fi t with observed basin relief if a rigidity of 1022.5 N•m is 

used. This value is the best fi t found by Liu and 

Nummedal (2004) in their study of Cretaceous 

foreland basin development across the same part 

of Wyoming. Hence, this suggests that net regional fl exural rigidity has not changed over the 

intervening ~70 m.y.

Isostatic impacts caused by differential erosion may play roles in drainage reorganizations 

and basin closure, and locally enhance structural 

features in a variety of locales (e.g., Simpson, 

2004). Deep incision of the Grand Canyon by 

the Colorado River has led to in excess of 300 m 

of fl exural rebound (Pelletier, 2010). With broad 

wavelength deformation on the scale of 100 km, 

fl exural rebound may have led to drainage reorganization and drainage reversal along the canyon rim. Similarly, Qinghai Lake, the largest lake 

in China, sits near the northeast margin of the 

Tibetan Plateau. The lake sits in a shallow closed 

basin that may owe its origins to basin closure 

due to nearby erosion by the Yellow River.

Our results indicate that the presence of a 

closed basin does not require, nor should be 

taken as proof of, tectonic activity. Flexural response to moderate differential erosion, as seen 

in this analysis, can generate tens of meters of 

tilt over wavelengths of many tens of kilometers. 

Such modest topography is suffi cient to close 

basins in most settings. An even greater degree 

of closure would have occurred if more incision 

had taken place. Although perhaps atypical, it 

seems that under special circumstances, climate 

alone can lead to closed basin formation.

ACKNOWLEDGMENTS

Field assistance was graciously provided by Peter Beland, Max Garnier, Steve Holbrook, and Cliff 

Riebe. We thank Xiangyang Xie for allowing us to 

use his three-dimensional fl exure program, and PASSCAL (IRIS) and Bryan Shuman for use of geophysical equipment used to determine depth to bedrock. 

We benefi ted from discussions with Bryan Shuman 

and reviews by Peter Molnar and Christian Koeberl. 

Funding was made available through the Petroleum 

Research Fund of the American Chemical Society.

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JB094iB10p13919.

MANUSCRIPT RECEIVED 20 JUNE 2009

REVISED MANUSCRIPT RECEIVED 2 FEBRUARY 2010

MANUSCRIPT ACCEPTED 4 FEBRUARY 2010

Printed in the USA
Flaming

Gorge

Reservoir

Big Savery Lakes

41°45′

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108°45 108°30′ 108°15′ 109°15 109°00′ ′

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10 15 20 MILES

20 KILOMETERS

Planimetric base modified from U.S. Dept. of Commerce, Bureau of the Census digital data, 2001

Public land survey system from Wyoming Water Resources Center digital data, 1994

Hydrography modified from USGS National Hydrography Dataset (NHD) digital data, 1999

Lambert Conformal Conic projection

Standard parallels 41° and 42°, central meridian −108°45′

Geology from Love, J.D., and Christiansen, A.C., 1985

108°00 107°45′ ′

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T. 26 N.

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R. 93 W. R. 92 W. R. 91 W. R. 90 W.

R. 98 W. R. 97 W. R. 96 W. R. 95 W. R. 94 W. R. 110 W. R. 109 W. R. 108 W. R. 107 W. R. 106 W. R. 105 W. R. 104 W. R. 103 W. R. 102 W. R. 101 W. R. 100 W. R. 99 W. R. 112 W. R. 111 W.

T. 16 N.

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EXPLANATION

TERTIARY SEDIMENTARY AND IGNEOUS ROCKS

MESOZOIC SEDIMENTARY ROCKS

Miocene rocks

Lance Formation

Bishop Conglomerate

Fox Hills Sandstone and Lewis Shale

White River Formation

Lewis Shale

Ice Point Conglomerate

Almond Formation

Bridger Formation

Ericson Sandstone

Washakie Formation

Mesaverde Group undivided

Mesaverde Group

1 Crooks Gap Conglomerate

Rock Springs Formation

Laney Member

Blair Formation

Green River Formation

Wilkins Peak Member

Cody Shale

Transitional unit between Battle Spring Formation and Wasatch Formation

Cathedral Bluffs Tongue

Main body

Niland Tongue

Luman Tongue

Fort Union Formation

Alluvium and colluvium

Gravel, pediment, and fan deposits

Landslide deposits

Dune sand and loess

Playa lake and other lacustrine deposits

Undivided surficial deposits

Alkalic extrusive and intrusive igneous rocks

Terrace gravel

Battle Spring Formation

QUATERNARY UNCONSOLIDATED DEPOSITS

 AND IGNEOUS ROCKS

Wasatch Formation

Wilkins Peak Member and Tipton Shale Member or Tongue

Baxter Shale

WATER AREAS

Tipton Shale Member or Tongue

CONTACT

FAULT--Dotted where concealed. Bar and ball on downthrown side

THRUST FAULT (CONCEALED)--Sawteeth on upper plate. Thrust 

fault approximately located on the basis of seismic data and drilling

1

The areal extent of the Crooks Gap Conglomerate in Sweetwater 

County is small and not shown on the stratigraphic chart. 

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PLATE 1A. BEDROCK GEOLOGY

SCIENTIFIC INVESTIGATIONS REPORT 2004-5214

Bedrock geology, physiographic and structural features, and stratigraphic chart PLATE 1A

Jon P. Mason and Kirk A. Miller, 2004, Water Resources of Sweetwater County, Wyoming