**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 Keysto ne, 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

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

in the United States and was the incuba tor 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 Te xas ISR mines is housed at the TCEQ offices

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

1USGS 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 exploratio n and mining and the increasing number of applications for ISR mines to the U.S. Nucl ear Regulatory Commission. USGS geologists were particularly intrigued with the widesp read 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, th e forensic chemistry portion of our project,

and these are some of the interim results of th is work. The search for a suitable field site and funding to evaluate long-term impacts a nd natural attenuation of groundwater in ISR well fields (Phase 2) is underway, and prelimin ary testing of new restoration technologies for ISR well fields (Phase 3) has begun.

2Outline 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).

3Background

The United States has been steadily produc ing uranium using ISR mining since the mid

1970s. 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 UR I’s Kingsville Dome mine, both located in

Texas.

Most uranium production from ISR mines ha s 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, th e 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 (Nuc lear Energy Agency, 2008). Thus, the safe and effective use of ISR technology in mining uran ium deposits is a potentially critical element in the movement towards energy independence in the United States

4Texas 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 se ries of open-pit deposits developed in the Whitsett Formation (Jackson Group) and Cataho ula 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. Th e green markers represent closed ISR mines, and the red markers indicate operating ISR mines as of April 2009.

5Along 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:

—Go li ad Format i on ( Tp ); a ser i es of Mi ocene mu d stone, cong l omerates, an d 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.

6TCEQ 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 r oom 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

- checked against original data sheets from the TCEQ data room which database was cross checked against original data sheets from the TCEQ data room
, forms the basis of this research.

TCEQ employees were extremely helpful in allo wing 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 concentr ation 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.

7Table 2 is a copy of the initial restoration tabl e 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.

8All PAAs in Texas have received amended rest oration goals for at least one element after operators have expended a reasonable degree of effort to restore groundwater, as determined by TCEQ regulators, following esta blished 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 restorat ion level actually achieved in the PAAs. As

there are no “ final sample ” data for Zamzow PAA

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

, no information is available to describe the degree to which this well field was restored.

9This 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 repr esent baseline restoration goals for uranium as set by the highest average uranium concentratio n 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 pr ior to release of the PAAs, and green bars represent amended restoration goals for uraniu m. 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 ava ilable 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.

10Baseline 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 we ll 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 Protec tion Agency (USEPA).

In Texas, more than 25 percent of PAAs are char acterized by baseline groundwater above the maximum contaminant level (MCL) for arsenic, cadmium, lead, ra dium, and uranium (shown highlighted on Table 4).

MCL is set b h y t e U.S. Environmenta l Protection Agency ( USEPA; http://www.epa.gov/safewater/contamin ants/index.html ) for those elements with well-established links to negative human health effects. All PAAs contain ra dium 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

p ro ect in Colorado, baseline water showed g ross al ha, g ross beta, radium, and uranium above MCL. In j p Wyoming, averaged values for the Smith Ranch 1, Chr istensen Ranch 2-6, and Irigaray 1-5 mine units were elevated above MCL for cadmium, ch romium, 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 (Cro wn Point), these well fields are characterized by groundwater elevated in multiple MCLs prior to mini ng. 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

.

11Recommended secondary standards are set by th e USEPA for constituents that, in high enough concentrations, negatively affect th e esthetic quality of groundwater, but are not conclusively linked to any negative human he alth 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

.

12Table 6 shows average concentrations and a rang e 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.

13Restoration 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 po st-restoration analyses in the TCEQ records.

In general, at PAAs where post-restoration va lues 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.

14The USEPA-established MCL for uranium in drin king 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 ur anium 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.

15The 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 restorat ion, 55 percent of PAAs exceeded baseline and 45 percent of PAAs were below baseline.

16The MCL for radium ( 226 Ra and 228 Ra) 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.

17The 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.

18The MCL for lead is 0.02 milligram per liter in dr inking 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.

19Although 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 P AAs (Table 7). Of constituents for which secondary standards are established by the USEP A, sulfate increased in the majority of well fields after mining and restoration, wherea s 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 silic a decreased in the majority of well fields after mining and restoration. Statistically, molybdenum decreased in the small majority of well fields after mining.

20Regarding the original question of whether or not groundwater has been restored to baseline in Texas uranium ISR well fields, it wa s observed that no well field for which final sample results were found in TCEQ records re turned 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 Sa ndstone and restored using electrodialysis, shows restored sulfate to 164 percent of baseline Reclamation at O ’

- 2 returned shows restored sulfate to 164 percent of baseline

. Reclamation at O Hern 2 returned constituents with secondary standards or MCLs to baseline values or below.

21Specifically 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 carbonate of 10

. 1 milligrams per liter

, so

‐ restoration elevation these and carbonate milligrams post restoration elevation of

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.

22Long-Term Stability and Natural Attenuation

In Texas, after ISR mining ceased and restor ation 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

- mining and Some well fields monitored for longer periods of time during the post mining and remediation stability period show trends of in creasing analyte concentration, as noted by USGS geologists while examining records at pilot projects in Colorado (Grover), New Mexico (Crown Point), and throughout Wyoming.

23At the Grover, Colorado, pilot test site, pump and treat technologies did not return groundwater to baseline. Analysis of data co llected by Colorado State regulators showed upward-trending uranium, beta activity, radium, TDS, calcium, magnesium, specific conductivity, total hardness, gross alpha, a nd ammonia. Results from individual wells differentiated using solid colored lines are show n above in the time series plot of uranium

concentration. Note that the vertical red lin e 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

.

24During 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 Cr own Point data are not detailed enough to analyze these trends, but the data indicate th at groundwater may not have stabilized when the final samples were collected, similar to the Grover, Colorado, project.

Examples from Grover, Colorado, Crown Poin t, New Mexico, and ISR pilot projects in Wyoming indicate that the 6

- month stability period mandated by Texas ISR rules may not Wyoming indicate that the 6 month stability period mandated by Texas ISR rules may not have been long enough to adequately de termine 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.

25Effectiveness of Restoration Techniques

After mining has ceased, a restoration meth od called groundwater sweep can be used whereby groundwater in a mined aquifer is pum ped 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 H 2 S) have been added to well-field groundwater in an attempt to return groundwater and host rock s to reducing conditions, thereby reversing the effects of oxidizing mining solutions (lixiviants) within the aquifer.

Bioremediation, the stimulation of native bact eria within the aquifer whose life processes
fix metals from solution, is another reme diation technique currently receiving much attention (Long and others, 2008).

26Pump 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.

anium groundwater is Ur in 2 1

, percent 09 baseline groundwater of baseline in well fields using 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.

27Chemical 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 re sults (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 Docu ment, 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.

28Bioremediation

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 of groundwater in Mine Unit 4 remediation groundwater (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 (Na 2 S) 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

e r

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.

29Conclusions

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 da tabase 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, incl uding 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 restor ation 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 de creased. Chemical constituents for which no MCL or secondary standards were set are hi gher 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.

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