U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2009–1143

Groundwater Restoration at Uranium In-Situ Recovery 

Mines, South Texas Coastal Plain

Groundwater Restoration at Uranium 

In-Situ Recovery Mines, South Texas 

Coastal Plain

By Susan Hall

Open-File Report 2009–1143

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2009

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Suggested citation:

Hall, Susan, 2009, Groundwater restoration at uranium in-situ recovery mines, south 

Texas coastal plain: U.S. Geological Survey Open-File Report 2009–1143, 32 p.
 

Introduction 

This talk was presented by U.S. Geological Survey (USGS) geologist Susan Hall on May 11, 

2009, at the Uranium 2009 conference in Keystone, Colorado, and on May 12, 2009, as part 

of an underground injection control track presentation at the Texas Commission on 

Environmental Quality (TCEQ) Environmental Trade Fair and Conference in Austin, Texas. 

Texas has been the location of the greatest number of uranium in Texas has been the location of the greatest number of uranium in -situ recovery (ISR) mines situ recovery (ISR) mines 

in the United States and was the incubator for the development of alkaline leach 

technology in this country. For that reason, the author chose to focus on the effectiveness 

of restoration at ISR mines by examining legacy mines developed in Texas. The best source 

for accurate information about restoration at Texas ISR mines is housed at the TCEQ offices 

in Austin. The bulk of this research is an analysis of those records. 

1 
USGS Uranium ISR Studies 

The USGS initiated a study of the effects on groundwater by ISR mining in 2008 in response 

to increased activity in uranium exploration and mining and the increasing number of 

applications for ISR mines to the U.S. Nuclear Regulatory Commission. USGS geologists 

were particularly intrigued with the widespread assertion that “Groundwater has never 

been returned to baseline at any ISR mine.” 

USGS ISR studies are broken down into three phases: 

1. Compilation of forensic chemistry: the examination of legacy projects. 

2. Investigations of groundwater chemistry over time. 

3. Development of improved restoration techniques. 

The USGS is nearing completion of Phase 1, the forensic chemistry portion of our project, 

and these are some of the interim results of this work. The search for a suitable field site 

and funding to evaluate long-term impacts and natural attenuation of groundwater in ISR 

well fields (Phase 2) is underway, and preliminary testing of new restoration technologies 

for ISR well fields (Phase 3) has begun. 

2 
 

Outline of Presentation 

To determine the effectiveness of groundwater restoration at ISR mines, the following 

topics will be addressed: 

1. The establishment of baseline and restoration goals. 

2. Effectiveness of groundwater restoration Effectiveness of groundwater restoration. 

3. Long-term stability of well fields. 

4. An evaluation of best restoration technologies, including: 

(a) Pump and treat techniques (Texas), 

(b) The addition of reductants (Wyoming and New Mexico), and 

(c) Bioremediation (Nebraska and Wyoming). 

3 
 

Background 

The United States has been steadily producing uranium using ISR mining since the mid1970s. In April 2009 there were four active mines in the United States (red markers): 

Cameco’s Smith Ranch/Highland property in Wyoming and Crow Butte mine in Nebraska, 

and Mestena Uranium’s Alta Mesa mine and URI’s Kingsville Dome mine, both located in 

Texas. 

Most uranium production from ISR mines has come from mines in Wyoming and Texas 

(green markers), with only pilot projects testing mining and restoration techniques 

developed in New Mexico (Crown Point, Mobil) and Colorado (Grover, Wyoming Minerals). 

More than 20 ISR mines anticipate or have begun the process of applying for licensing 

(yellow markers). 

According to the Energy Information Agency, the United States imported 82 percent of its 

uranium in 2007 (Energy Information Agency, 2009) and 38 percent of U.S. uranium 

reserves are classified as ISR amenable (Nuclear Energy Agency, 2008). Thus, the safe and 

effective use of ISR technology in mining uranium deposits is a potentially critical element 

in the movement towards energy independence in the United States 

4 
Texas Coastal Plain Uranium District 

Historically, uranium in Texas has been produced from Tertiary units along the southwest 

coastal plain. Uranium was first mined from a series of open-pit deposits developed in the 

Whitsett Formation (Jackson Group) and Catahoula Formation, starting in the late 1950s, 

when uranium was discovered during radiometric surveys in support of oil and gas 

exploration in Texas. 

Black crossed mine symbols are uranium properties identified by the USGS Mineral 

Resources Data System database (http://tin.er.usgs.gov/) and show mostly historical openpit mines located near Karnes City, Texas. The green markers represent closed ISR mines, 

and the red markers indicate operating ISR mines as of April 2009. 

5 
Along the

G l

southw

i d

est Tex

i

as co

(

as

)

tal plain,

i

ur

f

anium

i

is mined,

d

using ISR t

l

echniques, from the:

—Goliad Formation (Tp); a series of Miocene mudstone, conglomerates, and

limestones, which is host to seven ISR mines

—Oakville Sandstone and Catahoula Formation (Tm);  Miocene and Oligocene

sandstone, clays, mudstones and Catahoula tuffs hosting 27 mines; 15 mines in the

Oakville Sandstone and 13 mines in the Catahoula Formation

—Whitsett Formation (Te, Jackson Group); Oligocene mudstones, sandstones and

tuffs which host two mines.

Thirty‐six sites were authorized in Texas; seven were never mined (orange triangles), one

was a tailings project (white square), and one was combined with another property. This

leaves 27 mines (green markers) that were developed by construction of 77 well fields,

termed Production Authorization Areas (PAAs) in Texas. The term “well field” and “PAA”

will be used interchangeably throughout this presentation.  Baseline and “amended

restoration” values are available for all 27 mines/ 77 PAAs in TCEQ records.

Currently two mines are active in Texas: the Kingsville Dome mine in Kleberg County,

operated by Uranium Resources International (URI), and the Alta Mesa mine in Brooks

County, operated by Mestena Uranium (red markers). Two mines are in standby or shut

down (green markers): the  Vasquez and Rosita mines, both URI properties in Duval County.

Two ISR mines are in the process of being permitted (yellow markers): Goliad in Goliad

County (Uranium Energy Corporation) and  La Palangana, a South Texas Mining Ventures

property in Duval County.

6
 

 

TCEQ ISR Restoration Database 

The ISR restoration database is housed in the TCEQ offices in Austin, Texas. The database 

consists of binders for each mine in a data room adjacent to regulator offices. TCEQ does 

not represent these data as validated. Official data are on microfiche in an adjacent 

building, but the data are poorly organized and difficult to search. A digital database, 

compiled by a retired TCEQ employee, was also made available to the USGS. This digital 

database was cross database was cross -checked against original data sheets from the TCEQ data room checked against original data sheets from the TCEQ data room, which 

forms the basis of this research. 

TCEQ employees were extremely helpful in allowing the USGS full access to their data and 

copying facilities and were always available to answer questions about the database or 

permitting process. 

This table is a typical data sheet summarizing pre-mining groundwater baseline data for a 

Texas PAA. In Texas, 26 chemical constituents are measured before mining to establish a 

baseline, as shown in Table 1. Restoration values are initially set as baseline, with 

operators selecting the highest average concentration from either the production or mine 

area as their restoration goal. At this Zamzow well field, PAA-1, 0.171 milligram per liter 

uranium was the highest average value from the mine or production area for uranium, as 

highlighted in Table 1. highlighted in Table 1. 

7 
Table 2 is a copy of the initial restoration table for Zamzow PAA-1. Note that the restoration 

goal for uranium in groundwater is set as 0.171 milligram per liter, as highlighted on the 

table, which was the highest average uranium content from the PAA mine area, as shown 

on Table 1. 

8 
 

All PAAs in Texas have received amended restoration goals for at least one element after 

operators have expended a reasonable degree of effort to restore groundwater, as 

determined by TCEQ regulators, following established guidelines. The final restoration table 

for Zamzow PAA-1 shows an amended limit of 3.00 milligrams per liter for uranium. This 

amended restoration value is believed to be a relatively arbitrary value set by the 

regulators, as illustrated by the number of PAAs that set amended values at rounded whole 

numbers that were unrelated to any restoration level actually achieved in the PAAs. As 

there are no there are no “final sample final sample ” data for Zamzow PAA data for Zamzow PAA -1 no information is available to describe 1, no information is available to describe 

the degree to which this well field was restored. 

9 
 

This graph of uranium concentration for various Texas PAAs illustrates the relationship 

between baseline, final values, and amended restoration goals in the PAAs where final 

values were available. The blue bars represent baseline restoration goals for uranium as 

set by the highest average uranium concentration in baseline samples from either the mine 

or the production area. Well-field designations are shown on the X-axis of this chart. Red 

bars represent “final values” for uranium prior to release of the PAAs, and green bars 

represent amended restoration goals for uranium. There is no clear relationship between 

the final value achieved for uranium in groundwater at the PAAs and the amended the final value achieved for uranium in groundwater at the PAAs, and the amended 

restoration goals. Amended restoration goals do not reflect the degree of restoration 

achieved at the PAAs in Texas for which final values are available. Therefore, only those 

fields for which final values were available were chosen for this analysis. 

Only 22 PAAs from 13 mines have final sample values. These 22 PAAs form the basis of the 

study of restoration at these well fields. 

10 
 

Baseline Characterization of Groundwater in U.S. ISR Well Fields 

Baseline standards for all 77 Texas PAAs can be used to characterize Texas ISR well fields that serve as a basis 

of comparison with baseline values determined for other ISR well fields in the United States. The argument is 

commonly made that before mining, groundwater in ISR well fields is so contaminated that it should not be 

used for human consumption. Before mining, these aquifers are typically granted exemptions from the Clean 

Water Act, termed aquifer exemptions, by the U.S. Environmental Protection Agency (USEPA). 

In Texas, more than 25 percent of PAAs are characterized by baseline groundwater above the maximum 

contaminant level (MCL) for arsenic, cadmium, lead, radium, and uranium (shown highlighted on Table 4). 

MCL is set b h y t e U.S. Environmental Protection Agency (USEPA; 

http://www.epa.gov/safewater/contaminants/index.html) for those elements with well-established links to 

negative human health effects. All PAAs contain radium above MCL, and 90 percent contain uranium above 

MCL. Although baseline is artificially elevated in this database because the operator is selecting the highest 

average value within the production or mine area, this value does serve to identify elements of concern in 

these well fields. 

In the Crown Point pilot project in New Mexico, only cadmium was elevated above MCL. At the Grover pilot 

pj ro ect in Colorado, baseline water showed gross alp ha, gross beta, radium, and uranium above MCL. In 

Wyoming, averaged values for the Smith Ranch 1, Christensen Ranch 2-6, and Irigaray 1-5 mine units were 

elevated above MCL for cadmium, chromium, lead, radium, and uranium. 

In Nebraska (Crow Butte mine units 1-5 and the Crow Butte R &D site), average cadmium, lead, radium, and 

uranium were elevated above MCL. Elements above MCL are highlighted in the table. 

With the exception of the New Mexico deposit (Crown Point), these well fields are characterized by 

groundwater elevated in multiple MCLs prior to mining. Radium is almost always elevated above MCL while 

uranium is typically elevated and cadmium and lead commonly elevated. These well fields would require 

pretreatment to be used as a source for drinking water pretreatment to be used as a source for drinking water. 

11 
 

Recommended secondary standards are set by the USEPA for constituents that, in high 

enough concentrations, negatively affect the esthetic quality of groundwater, but are not 

conclusively linked to any negative human health effect. Of those elements for which 

secondary standards are set by the USEPA, iron, sulfate, and total dissolved solids (TDS) are 

commonly elevated above recommended levels in pre-mining water at ISR facilities. 

Chloride and manganese are commonly high in Texas PAAs before mining, while TDS is 

elevated above the recommended standard in all pre-mining Texas PAAs. Elements elevated 

above secondary standards are highlighted in Table 5 above secondary standards are highlighted in Table 5. 

12 
Table 6 shows average concentrations and a range of concentrations in Texas PAAs, within 

pre-mining baseline groundwater for those analytes for which no primary or secondary 

standards have been set by the USEPA. 

13 
 

Restoration Results for Texas PAAs 

Table 7 shows the average value, post-restoration, and baseline ranges of chemical 

constituents for all 22 well fields that have post-restoration analyses in the TCEQ records. 

In general, at PAAs where post-restoration values exceed MCL, the elements elevated in 

baseline values (As, Cd, Pb, Se, Ra, and U) continue to be elevated after mining. 

As compared to baseline values for the PAAs, uranium and selenium are elevated in the 

majority of PAAs. More than half of PAAs show a decrease in As, Cd, Fl, Pb, Hg, nitrate, and 

Ra after mining. 

The following slides examine these trends in detail. 

14 
 

 

The USEPA-established MCL for uranium in drinking water is 0.03 milligram per liter. Ninetyfive percent of Texas PAAs have a baseline value above MCL. Only the Hobson-1 and El 

Mesquite–1 PAAs were below the MCL for uranium and El Mesquite “rounded out” to 

equal MCL. 

Eighty-six percent of Texas PAAs show a final restoration above MCL. In 68 percent of PAAs, 

final value exceeded baseline and in 32 percent of PAAs restoration was below baseline final value exceeded baseline, and in 32 percent of PAAs, restoration was below baseline 

for uranium. 

15 
The MCL for selenium is 0.05 milligram per liter in drinking water. In 18 percent of PAAs, 

baseline of groundwater was above MCL, and in 24 percent of PAAs, the final restoration 

value was above MCL. After mining and restoration, 55 percent of PAAs exceeded baseline 

and 45 percent of PAAs were below baseline. 

16 
The MCL for radium (226Ra and 228Ra) is 5 pCi/L in drinking water. All PAAs are characterized 

by baseline and post-restoration radium concentrations above MCL. 

After mining and restoration, 4 percent of PAAs were above baseline, and 96 percent of 

PAAs were below baseline. 

17 
The MCL for arsenic is 0.01 milligram per liter in drinking water. Before mining, 77 percent 

of PAAs showed arsenic above the MCL, and after restoration 55 percent of PAAs were 

above the MCL. 

After restoration, 18 percent of PAAs exceeded baseline and 82 percent of PAAs were 

below baseline. 

18 
The MCL for lead is 0.02 milligram per liter in drinking water. Eighty-one percent of PAAs 

have baseline levels above MCL, and 18 percent of PAAs are characterized by final 

restoration values above MCL. 

After mining and reclamation, 9 percent of PAAs were above baseline and 91 percent of 

PAAs were below baseline. 

19 
 

Although restoration results vary widely for individual well fields, among the elements with 

an MCL, only selenium and uranium show overall increases in post-restoration 

groundwater in more than 50 percent of PAAs (Table 7). Of constituents for which 

secondary standards are established by the USEPA, sulfate increased in the majority of well 

fields after mining and restoration, whereas chloride, TDS, iron, and manganese decreased 

in the majority of well fields. 

Of those chemical constituents for which there are no established MCLs or secondary Of those chemical constituents for which there are no established MCLs or secondary 

standards, calcium, magnesium, bicarbonate, conductivity, carbonate, alkalinity and 

ammonia increased; sodium, potassium and silica decreased in the majority of well fields 

after mining and restoration. Statistically, molybdenum decreased in the small majority of 

well fields after mining. 

20 
 

Regarding the original question of whether or not groundwater has been restored to 

baseline in Texas uranium ISR well fields, it was observed that no well field for which final 

sample results were found in TCEQ records returned every element to baseline. However, 

two PAAs returned all elements for which USEPA has established MCLs to baseline: the 

O’Hern-2 and Trevino-1 PAAs. 

Trevino-1, which was mined from the Oakville Sandstone and restored using electrodialysis, 

shows restored sulfate to 164 percent of baseline Reclamation at O shows restored sulfate to 164 percent of baseline. Reclamation at O Hern ’ -2 returned 2 returned 

constituents with secondary standards or MCLs to baseline values or below. 

21 
Specifically looking at restoration details from the O’Hern PAA‐2 , this well field was

developed by Cogema from 1979 to1982 in the Catahoula Formation. Groundwater sweep

and reverse osmosis were both used to restore groundwater after mining. Calcium and

carbonate were both slightly elevated above baseline following mining and reclamation, as

shown in Table 8 above.

The aquifer overlying O’Hern‐2 is characterized by an average calcium of 27 milligrams per

liter and carbonate carbonate of 10.1 milligrams milligrams per liter, so post‐restoration restoration elevation elevation of these

elements in the O’Hern‐2 PAA seems inconsequential in the scheme of local

hydrochemistry. No final values for bicarbonate or alkalinity were reported, so the specific

degree to which this PAA was restored is unknown.

There is a notation in the TCEQ database that O’Hern PAA‐3 did not receive any

amendments. However, this could not be corroborated by TCEQ records.

22
 

Long-Term Stability and Natural Attenuation 

In Texas, after ISR mining ceased and restoration of the well fields was completed, PAAs 

were monitored for a minimum of 6 months. This period of monitoring has recently been 

increased to one year if no amendments to the restoration table are requested, and to two 

years if the operator requests an amendment to the restoration table. 

Some well fields monitored for longer periods of time during the post Some well fields monitored for longer periods of time during the post -mining and mining and 

remediation stability period show trends of increasing analyte concentration, as noted by 

USGS geologists while examining records at pilot projects in Colorado (Grover), New 

Mexico (Crown Point), and throughout Wyoming. 

23 
 

At the Grover, Colorado, pilot test site, pump and treat technologies did not return 

groundwater to baseline. Analysis of data collected by Colorado State regulators showed 

upward-trending uranium, beta activity, radium, TDS, calcium, magnesium, specific 

conductivity, total hardness, gross alpha, and ammonia. Results from individual wells 

differentiated using solid colored lines are shown above in the time series plot of uranium 

concentration. Note that the vertical red line indicates the end of the 6-month stabilization 

period required for Texas PAAs. These increasing concentrations of analytes indicate 

groundwater may not have stabilized when the Grover well field was released groundwater may not have stabilized when the Grover well field was released. 

24 
 

During the one-year stabilization period that followed restoration at Mobil’s Crown Point, 

New Mexico ISR pilot project, both upward and downward trends in various chemical 

constituents were noted (Mobil, 1981). The Crown Point data are not detailed enough to 

analyze these trends, but the data indicate that groundwater may not have stabilized when 

the final samples were collected, similar to the Grover, Colorado, project. 

Examples from Grover, Colorado, Crown Point, New Mexico, and ISR pilot projects in 

Wyoming indicate that the 6 Wyoming indicate that the 6 -month stability period mandated by Texas ISR rules may not month stability period mandated by Texas ISR rules may not 

have been long enough to adequately determine if groundwater in well fields had 

stabilized. Recent rule changes in Texas allow for longer term monitoring and could yield 

valuable data about the chemical stability of groundwater after ISR mining. 

25 
Effectiveness of Restoration Techniques 

After mining has ceased, a restoration method called groundwater sweep can be used 

whereby groundwater in a mined aquifer is pumped from the well field either to a deeper 

aquifer, an adjacent well field where mining is being initiated, or to surface ponds where it 

is allowed to evaporate. Local groundwater then “sweeps in” to replace the displaced 

water. This is typically the first method of restoration applied to a well field (Mays, 1994). 

Reverse osmosis and ion exchange are methods of removing contaminants from 

groundwater in well fields. The cleaned water is then reinjected into the well fields (Mays, 

1994). 

Reducing agents (H, NaS and H2S) have been added to well-field groundwater in an 

attempt to return groundwater and host rocks to reducing conditions, thereby reversing 

the effects of oxidizing mining solutions (lixiviants) within the aquifer. 

Bioremediation, the stimulation of native bacteria within the aquifer whose life processes 

fix metals from solution, is another remediation technique currently receiving much 

attention (Long and others, 2008). 

26 
Pump and Treat Technology

Texas provides a database that can be used to examine the effectiveness of the “pump and

treat” technologies of groundwater sweep, reverse osmosis, ion exchange, and

electrodialysis. Historically, pump and treat techniques were the only restoration

techniques used in ISR mines developed in Texas.

Uranium in groundwater is 2 1,09 percent of baseline baseline in well fields using groundwater groundwater

sweep only, yet is 48 percent of baseline when groundwater sweep is combined with

reverse osmosis (Table 9). Similar trends are shown for arsenic, cadmium, lead, mercury,

and selenium. Trends for fluoride and nitrate are not as clear.

Analysis of patterns in Texas PAAs show restoration using groundwater sweep coupled with

reverse osmosis results in the greatest decrease in concentration of chemical constituents.

These coupled techniques are commonly used in many well‐field restoration projects

nationwide.

27
 

Chemical Reduction 

Inorganic chemical reductants are designed to reverse the effects of oxidizing lixiviant 

solutions on host rock and groundwater. Overall, these techniques when used in 

remediation of U.S. ISR mines, show mixed results (Table 10). Crown Point and Irigaray did 

not appear to significantly benefit from the addition of reductants into groundwater at the 

levels applied (LQD/DEQ Response Document, 2005; Mobil, 1981). Uranium Resources 

International is completing a pilot project in Texas to test the restoration effectiveness of International is completing a pilot project in Texas to test the restoration effectiveness of 

hydrogen gas in removing analytes from groundwater (M. Pelliza, oral commun., May 

2009). Results of this study are not yet available. 

28 
Bioremediation

Nutrients, such as acetate, methanol, and molasses, can be added to groundwater as a

food source to stimulate native bacteria populations. As bacteria populations rise in

response to increased food, metal concentrations decrease in groundwater; however the

exact mechanism is uncertain.

In January 2009, an emulsified oil substrate was added to 6 production wells at the Crow

Butte ISR mine as part of remediation remediation of groundwater groundwater in Mine Unit 4 (NDEQ, 2009). The

first 4 months of preliminary results do not show a significant reduction in uranium. At a

Smith Ranch/Highland ISR remediation project in 2003, methanol and molasses were

added to wells in the Highland B well field, first as a pilot project following chemical

reduction (Na2S) and then in a full‐scale remediation project without prior chemical

reduction (Reimann and Huffman, 2005).  Selenium in groundwater was rapidly reduced in

both the pilot (MP13) and full‐scale (MP20) fields, although uranium concentration initially

increased (see graphs above). Uranium increases noted in groundwater after

bioremediation had been initia

ve). Ur

te

anium

d may

incr

be a

eases

ttribut

not

able

ed

to

in

the

groundw

dissolution

ater aft

of

er

iron

oxyhydroxides and the concomitant release of their contained uranium in response to

increasingly reducing conditions created during bioremediation (Reimann and Huffman,

2005). In subsequent bioremediation projects at Smith Ranch, cheese whey coupled with

methanol has been used as a biostimulant.

The USGS continues to gather and process records from State agencies to track the

effectiveness of these bioremediation methods.

29
 

 

Conclusions 

Can we answer the question: “Has any ISR mine in the United States returned post-mining
 

groundwater to baseline?”
 

Answer: Not based upon analysis of the Texas database because “final value” records were
 

found for only 22 of 77 PAAs (13 of 36 mines). 

We can conclude that in Texas, ISR mines are characterized by high baseline arsenic, 

cadmium lead selenium radium and uranium After mining and restoration for those cadmium, lead, selenium, radium, and uranium. After mining and restoration, for those
 

well fields that reported “final values” in TCEQ records, more than half of the PAAs had
 

lowered levels of many elements, including some that dropped below MCL. 

Of those elements for which MCL is established, the majority of PAAs showed increases in 

uranium and selenium after mining and restoration and decreases in arsenic, cadmium, 

fluoride, lead, mercury, nitrate, and radium to below baseline for the majority of well fields. 

Analytes for which secondary standards have been established show that sulfate is the only 

constituent that increased in the majority of well fields after mining and remediation, 

whereas chloride, TDS, iron, and manganese decreased. Chemical constituents for which 

no MCL or secondary standards were set are higher than baseline for calcium, magnesium, 

bicarbonate, conductivity, alkalinity, and ammonia. Sodium, potassium, silica, and 

molybdenum were lower than baseline in the majority of well fields after mining and 

remediation.
 

30 
31 
32