Uranium Investigation in an Alluvial Aquifer with DP Methods Wes McCall, PG Tom Christy, PE Geoprobe Systems Tom Christopherson, Prgrm. Mgr. Well Stds. Howard Isaacs, Prgrm. Mgr. Mon. & Compliance Nebraska, DHHS HPT logging at Clarks

GWMR Vol. 29, No. 1, pp Winter 2009 Salina Journal April 24, 2008 Page A5 Salina, KS EPA Radionuclides Rule amendment establishes MCL for Uranium at 30 ug/l (mass) Why ?

Where ? Village of Clarks Merrick County, NE Alluvial deposits of the Platte River Local bedrock is the Niobrara Chalk. Nebraska Geologic Bedrock Map after Burchett & Pabian, 1991.

Background on Clarks PWS Wells Old, shallow wells in town abandoned due to natural Uranium between ug/L Two new, deeper PWS wells installed outside of town after test wells indicate U nondetect New north PWS well exceeds U MCL at initial sampling event Short time later south PWS well exceeds U MCL New Clarks PWS South

New Wells South PWS well and 4” test well construction based on drillers logs Gravel Pack Concrete Bentonite Seal Depth (feet) psi PWS 4” Test

How ? Hypothesis: Elevated oxygen in zone(s) of aquifer leading to dissolution of Uranium into the groundwater HPT logging for hydrogeology HPT logs guide well placement Install wells using DP methods Develop wells Low flow sampling - DHHS Nebraska DHHS Lab analysis Geoprobe Model 8040 advances 2.25” rods for DP well installation

Hydraulic Profiling Tool (HPT) Logs Geoprobe 6625 Unit advanced HPT probe to obtain logs

HPT Operational Theory Hammer or push probe at constant rate (2cm/sec) Inject water at low flow rate (~300ml/min) Measure injection pressure with in-line transducer Flow Water

HPT Probe Injection Screen E-log Wenner Array

Basics of an HPT Log (South PWS Well) Flow Electrical Conductance – EC (mS/m) Higher EC >>> clay Lower EC >>> sand/gravel Pressure (psi /100 max) Higher P >>> lower perm Lower P >>> higher perm Hydrostatic P >>> rising baseline Flow (ml/min) --- ~ constant Higher flow >>> higher perm Lower flow >>> lower perm Depth (ft) Pressure EC

N A4 A3 A2 A1 B1 B2 B3 B4 B5 PWS Well South (Pumping) 4” Test Well South PWS Well North (Inactive) 4” Test Well North C1 C2 PWS wells are ~500ft apart DP wells separated by ~5 ft Site Sketch Map (not to scale) HPT log locations DP Wells Gravel Pad

HPT Cross Section C1-C2 Looking NW C1C2 Presence and thickness of silt-clay layers varies vertically and laterally across the area. Most clay layers are not continuous.

Selected Screen Intervals A-Group Wells Depth (ft) Pressure (psi) A1 = A4 = A3 = A2 = Use HPT logs to guide screen interval selection. Lower Pressure intervals = sand & gravel. Target sand layers between larger clay layers/lenses

Selected Screen Intervals B-Group Wells Depth (ft) Pressure (psi) B1 = B4 = B3 = B2 = B5 = Does ground water chemistry change with depth? DO? ORP? Uranium ? Cations & Anions?

Setting the DP Wells Drive Cap O-Ring Seals Probe Rod (2.25” OD x 1.5” ID) Expendable/Anchor Point (ASTM D6725)

Protector DP Well Construction Tremie Grouting 25% solids bentonite grout ¾” PVC Grout barrier: fm natural collapse Nominal ¾” Prepacked Screen x 5ft (not to scale)

DP Well Initial Development Development with Check Valve Set within Screen Check valve Early purge water

Low Flow Sampling with Mechanical Bladder Pump Final Development : with Mechanical Bladder Pump Monitor Water Quality Parameters

N A4 A3 A2 A1 B1 B2 B3 B4 B5 PWS Well South (Pumping) 4” Test Well South PWS Well North (Inactive) 4” Test Well North C1 C2 DP wells separated by ~5 ft Site Sketch Map (not to scale) HPT log locations DP Wells Gravel Pad

A-Group & South 4” Well A4 S4” A1 A2 A3 Sp Cnd = 1043 uS/cm Sp Cnd = 698 Sp Cnd = 530 Sp Cnd = 405 Sp Cnd = 1115 DO < 0.1 mg/l all wells ORP ~ -200 to -300 mV all DP wells

B5 N4” B4 B3 B2 B1 Sp Cnd = 770 Sp Cnd = 805 Sp Cnd = 795 Sp Cnd = 605 Sp Cnd = 372 Sp Cnd = 885 uS/cm B-Group & N. 4” Well DO < 0.1 mg/l all wells ORP ~ -200 to -350 mV all wells Where’s the DO ?

A4 S4” A1 A2 A3 A-Group & S. 4” Wells Uranium Data (ug/L) U = 32.2 U = 15.1 U = < 1 U = 168

B5 N4” B4 B3 B2 B1 U = 15.1 U = 1.8 U = 1.3 U = 376 U = 98.7 U = 124 B-Group & N. 4” Wells Uranium Data (ug/L)

What does this mean ?

Low permeability layer(s) South PWS & 4” Test Well Construction With HPT Log Both filter packs penetrate low permeability layers allowing for “short circuiting” Filter packs behave as a preferential flow path. U = 376 ug/l U = 98.7 ug/l U = ND

Summary - Conclusions HPT logs provide detailed information on hydrogeology DP wells yield discrete interval samples for water quality assessment Uranium can be mobile in low DO and low ORP environments … dependent on water chemistry Uranium distribution at this site is heterogeneous in vertical and horizontal dimensions Investigate before Investing Uranium ?

Low DO and Low ORP … DO < 0.1 mg/l in all wells ORP ranges from ~ -200 to -300mV Uranium geochemistry indicates it should be reduced (U+4) and form insoluble precipitates (Pitchblende/Urananite) But … Why is Uranium Mobile here? NE DHHS Team samples DP wells with Mechanical Bladder Pump

Increase in pCO 2 lowers ORP (Eh) at which U +4 oxidizes to U +6 Sufficient CO2 will lower this to < -300mV Iron and Manganese can behave as electron acceptors for U +4 oxidation to U +6 Available Calcium can result in formation of soluble Ca-U-CO 3 complexes

Geochemistry at the Clarks Well Field … Geochemistry in the local aquifer is consistent with having uranium in solution even with low DO and Low Eh conditions observed.

A-Group & S. 4” Wells Sodium & Sulfate (mg/L) A4 S4” A1 A2 A3 Na = 98.1 SO 4 = 239 Na = 43.7 SO 4 = 121 Na = 39.8 SO 4 = 113 Na = 22.1 SO 4 = 46.4 Na = 107 SO 4 = 257

B-Group & N. 4” Well Sodium & Sulfate (mg/L) B5 N4” B4 B3 B2 B1 Na = 56.8 SO 4 = 136 Na = 66.8 SO 4 = 180 Na = 72.9 SO 4 = 160 Na = 45.7 SO 4 = 149 Na = 29.4 SO 4 = 98.7 Na = 67.9 SO 4 = 170