Supporting Information for Measurement of Dissolved H 2, O 2, and CO 2 in Groundwater Using Passive Samplers For Gas Chromatographic Analyses

Transcription

1 Supporting Information for Measurement of Dissolved H 2, O 2, and CO 2 in Groundwater Using Passive Samplers For Gas Chromatographic Analyses B. P. Spalding* and D. B. Watson Environmental Sciences Division Oak Ridge National Laboratory P.O. Box 2006 Oak Ridge, Tennessee *Corresponding author: phone (865) ; fax (865) ; spaldingbp@ornl.gov Submitted to: Environmental Science & Technology Prepared: August 2006 Summary (2 Tables, 23 Figures, 4 text pages with detailed descriptions of methods and materials) This Supporting Information contains an illustrative calculation of differential outgassing of a binary H 2 /CO 2 system during changing pressure when pumping water from depth with 1 atm hydrostatic pressure (Table S-1). Pictures of the passive sampler devices (Figure S-1), gas sampling equipment (Figures S-2 and S-3), and the sealed bottles employed for laboratory incubations (Figure S-4) are presented. Also presented are gas chromatographic calibration data (Figure S-5 and Table S-2), a typical GC chromatogram of gas analyses (Figure S-6), passive sampler kinetics for He uptake and O 2 release (Figure S-7), and results for H 2 and O 2 concentrations in all eleven groundwater monitoring wells in the impacted area over an eight month period (Figures S-9 through S- 13). Concurrent water table elevation changes over eight months for seven monitoring wells in the impacted area are presented in Figure S-14. Data on H 2 concentrations in six additional sealed bottles of groundwater are presented (Figure S-15). Plan views of all monitoring well locations (Figures S-16 through S-21) and a vertical profile of groundwater elevation relative to screened intervals of monitoring wells (Figure S-8) are also presented. Hydrogen and oxygen gas survey data in many additional wells in the FRC area are presented in Table S-3. A photograph of the S-3 ponds prior to closure in 1986 is presented in Figure S-22 and a design cross-section for the multilayer cap over the S-3 ponds is depicted in Figure S-23. SI - 1

2 Supplemental Methods and Materials (Detailed Descriptions) Gas Chromatographic Conditions - The chromatograph was controlled by an HP Pavilion PC using a USB connection and PeakSimple software to control and record all chromatographic data files. The injector port was maintained at 30ºC while the column oven was maintained at slightly above (36ºC) room temperature so that stable isothermal conditions could be attained. All samples were applied by direct injection on the column using a syringe. A 30 foot long x 1/8 stainless steel tubing column packed with 100/120 mesh HayeSep DB solid phase (Alltech Chromatography) was employed with a carrier gas pressure of 19 psi which maintained a flow rate of 5 cm 3 /min. Under these chromatographic conditions, approximately 18 minutes was required to elute the desired fixed gases (He, Ne, H 2, and O 2 ) in samples and standards. Alternately, when analysis of CO 2 was desired, the column flow rate was increased to10 cm 3 /min by increasing the carrier gas pressure and the column oven temperature was increased to 100ºC to constrain CO 2 to elute within a convenient total run time of 18 min. Gas samples and standards were injected using glass 0.5-mL-capacity gastight syringes (VICI, Series A-2) with shutoff valves and teflon male Luer tips for interchanging injection needles and silicone tubing when the syringe was used as a passive gas sampler. Gas Analytical Calibrations Calibrations of the peak area (millivolt-seconds) with the injected amount of each gas (µl at room temperature and ambient atmospheric pressure) were prepared using standard two-component gas mixtures (100 ppm or 1% H 2 in N 2, Scott Specialty Gases), single component gases (He, Ne, and CO 2, Linde Gases ), or for O 2, ambient air (20.9% O 2 ). Measured volumes of the desired gases were transferred into gastight syringes and subsequently filled to their total volume (0.500 ml) with room air so that a constant gas volume was routinely injected. Linear regressions were performed for peak area versus amount (µl) of each gas with at least five concentrations within the linear range. A blank and the highest standard for a calibration series was run at least weekly although the response of both the TCD and RGD did not vary significantly over the eight month period of this investigation. The concentration of gas in a sample or standard was computed from the amount (µl) detected and divided by the total injected volume (usually L) to express its concentration in ppmv (µl/l). Passive Samplers and Procedures The basic passive fixed-gas groundwater sampler was based on the passive sampler developed by Sanford et al. (1996) with some significant adaptations. Rather than storing the collected gas from groundwater using a customsoldered copper tube chamber fitted with a spring-loaded bicycle tube valve (Sanford et al. 1996), a gastight syringe was substituted with its plunger preset to its maximum volume (500 µl) and its push valve open. Although the sampler of Sanford et al. (1996) worked well for sampling and analyses of noble gases (He and Ne), the metallic copper would likely react with water or acidic water yielding device-generated H 2 gas; the present sampler needed to be constructed with only inert materials (glass, Teflon, polypropylene, and stainless steel) relative to H 2 generation. The device of Sanford et al. (1996) also required considerable secondary gas transfer and handling for GC application which could by obviated by using a syringe as the in situ sample chamber for direct transfer to the GC. These gastight syringes are constructed only with non-hydrogen generating materials (teflon, plastic, and stainless steel). A short length (2.5 in) of ¼-inch SI - 2

3 OD by 1/8-inch ID silicone tubing (McMaster-Carr 51135K163), plugged with either 1/8- inch black silicone stopper (McMaster-Carr 9277K37) or polypropylene tubing cap (AllTech 4021) at one end, was substituted for the 10.6-cm-long, sand-filled, 0.79-cm OD by 0.48-cm ID silicone tubing, fitted with a bicycle valve cap (Stanford et al. 1996). Our smaller diameter silicone tubing allowed a watertight slip fit directly onto the male Luer fitting of the syringe. The gas volume of our passive sample totaled to1 ml with half that volume accounted within the syringe. The effective diameter of the syringe s push valve limited its use to well casings greater than 3/4"-inch ID. For wells greater than 2-inch ID, samplers were tethered to measured lengths of nylon line sufficient to place the syringes within the screened depth interval of the well using their buoyant weight to submerge them to this depth within groundwater with testing by feel. For the many wells less than 2-inch ID where buoyant tethering proved difficult, syringes were attached to a measured length of polyethylene tubing (1/4-inch OD), using short pieces of duct tape, and simply pushed to the desired depth of the screened interval. Passive samplers were routinely used in pairs to provide replication as well as to provide at least one analysis if one sample were mishandled. Construction details, materials, and elevations of all wells at the FRC are readily available ( with most wells constructed of polyvinyl chloride (PVC). In no case, were any wells employed in this study which contained hydrogen-generating materials (steel or iron). For wells with ID s of ¾-inch or less, the standard gastight syringe was too large in diameter to fit in the well. For most of these smaller diameter wells, standard 1-mL volume polypropylene disposable syringes (Becton-Dickenson ) with male Luer fittings were substituted after removing their standard finger-gripping processes with a scissors; two polypropylene samplers were routinely attached with duct tape in a stacked configuration near the end of a premeasured length of ¼-inch OD polyethylene tubing enabling the samplers to be pushed to the depth of the screened interval. For occasional ½-inch ID wells, these polypropylene syringes were trimmed to even smaller OD by removing the standard thumb plate on the plunger with a scissors; these syringes were taped to a short length of stainless steel wire looped through the end of a desired length of ¼-inch OD polyethylene tubing to push two stacked syringes to the depth of screened interval of the well. Both types of passive samplers are depicted in Figure S-1. Initially, each syringe was filled with air, which allowed its starting O 2 to diffuse into surrounding groundwater to attain its lower O 2 equilibrium concentration. Passive samplers were generally immersed in groundwater within the screened interval of a monitoring well for a minimum of two days but, most frequently, for a 7-day interval. Times and dates of immersion and removal from each well were recorded. Depths to groundwater from a known reference elevation (top-of-casing) were obtained at both the time of immersion and removal using a small-diameter electrical buzzer-sounding water level instrument (SolInst Mini 101). Verifications of total well depth were also performed periodically using the same instrument to probe by feel to the bottom of the well. Upon removal, the valve was immediately closed on all gastight syringes. For the disposable polypropylene syringes, immediately on removal from a well, the silicone tubing was removed and replaced with tight-fitting Luer-lock polypropylene cap (Becton- Dickenson ) for transport to the analytical laboratory approximately 7-miles SI - 3

4 distant. All fixed gas analyses were completed within 8 hours on the day of sample removal and samples in polypropylene syringes were completed within 4 hours of removal. The syringe gas volume was recorded when a needle was interchanged for the silicone sampling tube on the glass gastight syringes or for the plug on the polypropylene syringes immediately prior to injection onto the GC. The plunger on the gastight syringes rarely moved from its pre-immersion setting of ml; the plunger of the plastic syringes frequently moved to a larger volume as it was pushed out by the pressurized gas within the syringe when removed from wells with immersion depths where hydrostatic heads imposed additional pressure. In all cases, the syringe was vented momentarily to the atmosphere prior to injection in the GC so that the injected gas volume was measured at ambient atmospheric pressure. The gastight syringes (See Figure S-1) were reused as passive samplers by replacing the previously-used silicone tubing and plug with new materials. When using polypropylene syringe samplers, all new materials were employed and previously-used sampler components were discarded. All gastight syringes were checked for performance by filling with pure He and injecting on the GC and comparing with the calculated He volume based on peak area with the expected volume; the calculated syringe volumes varied but were generally within 85% of their scribed capacities; the actual rather than the nominal scribed capacity of each syringe was used to calculate the injected gas volume. Syringe capacity performance was checked periodically or whenever plunger resistance changed notably. Kinetics of passive gas sampler equilibration - For the release of O 2 from the starting air within the sampler, the observed O 2 gas concentrations versus time were fit to a similar diffusive equation with the same geometric parameters used in Eq 1 [see main text]: C(O 2 ) t = C(O 2 ) final + {C(O 2 ) initial C(O 2 ) final } exp[ (- D (O2) A t) / (V s L)] [Eq S-1] Where C(O 2 ) t C(O 2 ) final C(O 2 ) initial D (O2) gas phase oxygen concentration in sampler at time t (ppmv) gas phase oxygen concentration in sampler at steady-state (ppmv) initial oxygen concentration in sampler air (209,000 ppmv) effective diffusion coefficient for oxygen in silicone membrane (cm 2 /s) Bubble-stripping groundwater gas sampling Several attempts were made to compare our diffusive sampling of hydrogen gas in FRC groundwaters with the widely-accepted bubble-stripping method (Chapelle et al. 1997) which has evolved into a USEPAsponsored protocol (Weidemeier et al. 1998). In this sponsored bubble-stripping method, groundwater is pumped from a well at a rate of ml/min for 30 minutes through a glass 250-mL gas-sampling bulb initially containing a hydrogen-free 20-mL gas bubble. Thus, the protocol recommends that a relatively large volume of groundwater (12-21 L) be equilibrated with a comparatively small volume of gas and the resulting hydrogen gas will approach a concentration in equilibrium with the initial aqueous dissolved hydrogen concentration. Initially, we employed an adapted 60-mL glass gas-stripping cell (Microseeps Inc., Pittsburg, PA), which very effectively mixes flowing groundwater with the gas bubble using a water-jetting orifice for its inlet, following the manufacturer s SI - 4

5 operating instructions which are operationally equivalent to the protocol (Weidemeier et al. 1998). An inertial groundwater pump (Waterra SS-10 footvalve), a stainless-steel check-valve, was screwed into the end of a rigid 3/8-inch OD polypropylene tube of sufficient length to reach the screened interval of the desired well. This inertial pump was operated either by hand or by a mechanical arm (Waterra HydroLift Pump 500) attached to the tube to exert an oscillating vertical motion bringing water to the surface without the applied vacuum inherent in peristaltic pumps; such a pump does not place any potentially hydrogen-generating materials in contact with groundwater as it consists only of polypropylene tubing and approximately 5-grams of stainless-steel, i.e., the check-valve. However, for most of the groundwater wells, the 60-mL capacity of this gas stripping cell completely filled with additional gas after pumping as little as 0.5 L of groundwater; moreover, the volume of the stripped gas bubble became indeterminate with additional pumping because effervescing gas continued to pulse through the sample tubing and gasstripping chamber. Eventually, 500-mL capacity glass sampling bulbs were employed, with no initial gas bubble; these were allowed a volume up to about 200 ml of effervescent gas up to collected/trapped when the bulb was positioned horizontally (see Figure S-3); initially the bulb was filled with groundwater, without trapping any gas bubbles, by maintaining it in the vertical position after which it was oriented horizontally to initiate gas collection. A group of six wells were selected for this modified bulb sampling method to span the expected range of hydrogen gas concentrations as measured previously and repeatedly with our passive in situ sampling methods. Only 1-L of groundwater, in excess of the initial 500-mL volume required to fill the bulb, was pumped through the bulb to trap effervescent gas, while the bulb s effluent was collected in a 1-L glass bottle which was tightly capped immediately after filling. Both stopcocks of the glass sampling bulb were closed after 1-L was pumped through it and the bulb returned to the laboratory for analysis. Duplicate gas samples were removed from each bulb with gastight syringes inserted through the sampling port septum and analyzed by the gas chromatographic method described above. Additional 20-mL gas aliquots were also removed, transferred to gastight 40-mL vials, and shipped to an independent analytical laboratory following the sub-sampling protocol for shipment in standard gastight vials (MicroSeeps Inc., Pittsburg, PA); blind blanks and hydrogen standards were embedded in the suite of submitted samples as was a trip blank vial prepared by Microseeps. The transferred 20- ml gas aliquot was allowed to equilibrate to ambient pressure by briefly opening the valve of the transfer syringe to the atmosphere allowing the pressure to dissipate after its removal from the bulb. Several additional bulb samplings were performed over the next few days using 0.5 ml volumes in gastight syringes for GC analyses of H 2, O 2, and CO 2 following the modified GC conditions described above. Separate 500-mL bulb samples were taken to measure the volume of effervescent gas produced during pumping these groundwaters. Gas pressure within the gas sampling bulb was measured by inserting the integral needle probe connected to a 0-25 psi pressure gauge (Alltech 86805) through the septum of the bulb. The bulb was then weighed prior to opening the upper stopcock while holding the bulb vertically; the entire volume of the gas in the bulb was then replaced with distilled water using a syringe inserted through the stopcock, the stopcock was then closed, and weighing was repeated using the net weight gain as a measure of gas volume. The volume of gas at standard pressure was then SI - 5

6 calculated by multiplying these measured gas volume by the ratio of measured excess to ambient pressure (1 atm). Sealed bottle aqueous gas sampling - The full 1-L bottle of pumped groundwater flowing from the bubble stripping bulb, after sealing with a one-hole rubber stopper fitted with 6- mm diameter cylindrical septum, was adjusted to contain a small volume of headspace gas by injecting 4.00 ml of air into the groundwater while maintaining the bottle in a horizontal position. As soon as the gas bubble was positioned within the bottle s sidewall, 4.00 ml of water were removed with the same syringe. After extensive shaking to mix the gas bubble with the groundwater and its small amount of entrained soil, the headspace was sampled initially and periodically thereafter using a gastight syringe for GC analyses. Other samples of pumped groundwater from various wells were collected directly in 1-L narrow-mouth glass bottles, sealed with rubber stoppers containing one septumfilled hole, and periodically sampled after initial adjustment to contain a small volume (3-5 ml) of headspace gas. Such periodic sampling of sealed groundwater bottles allowed the assessment of changes in hydrogen and oxygen gas concentrations during storage under ambient laboratory conditions. A minimal 1-mL headspace volume for sealed bottles was constructed using a septum-filled one-hole rubber stopper with a 2.5-inch length of the same silicone tubing used for the passive samplers described above attached to a 2-cm long nipple of trimmed polypropylene pipette tip inserted into the bottom of the stopper hole; this arrangement allowed complete insertion of the 2.5-inch long needle on a gastight syringe through the septum into the cylindrical 1-mL headspace volume without encountering any water (see Figure S-4). Such facilely accessible 1-mL headspace volumes allowed gas sampling of sealed groundwater samples. SI - 6

7 Differential Out-Gassing Effects (An Illustrative Calculation) - The changing composition of the gas phase in equilibrium with dissolved gas in groundwater during pumping can be illustrated for a simple binary gas (H 2 /CO 2 ) or (H 2 /N 2 ) system using well-established gas solubility data. At 20ºC, the solubility of H 2 in water is 18.2 ml/l/atm, the solubility of N 2 is 15.4 ml/l/atm, while the solubility of CO 2 is notably much larger (878 ml/l/atm); solubility data was taken from Lange s Handbook of Chemistry, 14 th edition but any consistent solubility data could be substituted. The starting conditions are assumed to be 2 atm of total pressure, i.e., at a depth 33.9 ft below water level, and the starting gas composition of each system is assumed to be 1:1 or 50 vol% for each gas with an initially insignificant gas volume (e.g., 1 µl). Using the published gas solubility data, this H 2 /CO 2 system would initially contain 18.2 and 878 ml@stp of H 2 and CO 2, respectively, dissolved in the groundwater at the total pressure of 2 atm (see column 3 in Table S-1). When this water is pumped up to the ground surface where total pressure decreases to 1 atm, calculation of the solubility of both dissolved gases is halved to 9.1 and 439 ml@stp, respectively (column 4 Table S-1). This decrease in dissolved gas would result in the release of 9.1 and 439 ml@stp at equilibrium. This total released volume of gas ( ml) would have a composition of 2 and 98 vol% H 2 and CO 2. The initial 50% H 2 composition for equilibrium gas might approach that measured with an in situ sampler with a minimal total volume. However, an equilibrated and stripped bubble collected at the surface would likely measure only 2% H 2 composition and manifest as a large bubble volume (448 ml) at equilibrium. In contrast, when the H 2 /N 2 system is considered (as illustrated by the lower half of Table S-1), H 2 composition of gas collected during pumping would actually increase slightly from 50 to 54% due to differential out-gassing of the slightly more soluble H 2. This minimal effect results from the similar solubility of H 2 and N 2 in water. Many fixed gases (oxygen, nitrogen, hydrogen, and noble gases) have similar volumetric water solubility and, thus, large differential out-gassing effects would not be expected. However, whenever CO 2 is present at significant concentration (perhaps, greater than 5%), its effect during out-gassing at atmospheric pressure during typical gas-stripping sampling should be expected to be significant. Because CO 2 is a common and abundant component of most soil atmospheres and, thus, probably of most groundwater, such outgassing correction to calculation in situ dissolved gas concentrations may be routinely required. SI - 7

8 Table S-1. Calculations of binary gas phase composition in equilibrium with water during a change in pressure (1 atm) brought about by pumping from a depth of ft. Dissolved In Remaining Released Released Starting Gas 1-L H 2 O Dissolved In Out-Gas Pump to ground surface 1-L H 2 O Volume Composition Gas (vol%) (ml@stp) from 33.9 ft below (ml@stp) (vol%) H CO Dissolved In Remaining Released Released Starting Gas 1-L H 2 O Dissolved In Out-Gas Pump to ground surface 1-L H 2 O Volume Composition Gas (vol%) (ml@stp) from 33.9 ft below (ml@stp) (vol%) H N SI - 8

9 Figure S-1. Syringe-silicone tubing (1/8-inch ID x ¼-inch OD) samplers for passive sampling of dissolved groundwater gasses. The glass gastight is a 0.5-mL capacity (VICI, Series A-2) with integrated valve and the polypropylene syringe is 1.0-mL capacity (Becton-Dickenson ) also shown with its polypropylene closure cap. SI - 9

10 Figure S-2. Carboy (20-L capacity) containing tapwater saturated with either 2% H 2 in air or pure He used to test uptake kinetics of H 2 and He by passive syringe-tubing samplers immersed for various intervals. Saturating gas was delivered to a 50-ft coil of silicone tubing while continuous stirring was maintained. SI - 10

11 Figure S-3. Gas sampling bulb (500 ml capacity) used to collect 124 ml of released gas after pumping 1 L of groundwater from well FW115-2 on April 6, SI - 11

12 Figure S-4. Typical sample bottles (1-L capacity) used for monitoring gas phase composition dynamics employing a 1-mL volume silicone sampling headspace chamber for access with 0.5-mL gas-tight syringe for direct injection onto gas chromatograph. SI - 12

13 50000 Thermal Conductivity Detector (TCD) Versus Reductive Gas Detector (RGD) For Hydrogen Analyses y = Ln(x) R 2 = RGD Peak Area (units) y = x R 2 = RGD Signal TCD Signal )Log. (RGD Signal )Linear (TCD Signal TCD Peak Area (units) Hydrogen Injected ( STP) 0 Figure S-5. Calibration data for the thermal conductivity detector (TCD) and reductive gas detector (RGD) for simultaneous gas chromatographic measurement of hydrogen using both signals. The RGD signal is linear up to 200 ppmv H 2 (0.1 µl injected in 500 µl, five overlapping points near the origin of the graph) followed by non-linear and less sensitive response at higher concentrations. However, above 200 ppmv, H 2 is detectable by the TCD and is highly linear. SI - 13

14 Figure S-6. Typical gas chromatogram for signals from both the thermal conductivity and reductive gas detectors with peak for hydrogen, oxygen, helium, neon, and unknowns. SI - 14

15 Passive Sampler He Concnetration (ppm v) Helium (mixed) Model Helium Oxygen (mixed) Model Oxygen Passive Sampler O 2 Concentration (ppm v) Time of Immersion in Water (hr) 0 Figure S-7. He and O 2 concentrations in passive syringe-tubing samplers, initially filled with ambient air, after various intervals of immersion in a carboy of He-saturated tapwater. Values for the diffusion coefficients for He and O 2 of 2 x 10-6 and 1.4 x 10-6 cm 2 /s in the silicone tubing material were used in model Equations 1 (main text) and S-1 (Supporting Information) to simulate the kinetics of gas equilibration (r 2 = and 0.995, respectively). SI - 15

16 FRC Area 3 Groundwater Tracer Wells Profile FW113 FW111 FW114 FW106 FW115 Ground Surface FW Elevation (ft) FW FW Water Table Screened Interval FW FW Flow FW FW He & Ne Injection Interval Distance From Well FW106 (ft) Figure S-8. Cross-sectional view of ten groundwater monitoring wells with screened depth intervals and average groundwater elevations in the group used for He/Ne tracer gas and H 2 monitoring. SI - 16

17 Oxygen/FW010 Oxygen/FW112 Hydrogen/FW010 Hydrogen/FW ) - v m p ( O e g r a e v A Oct Oct Nov Dec Jan Feb Mar Apr May-06 Date of Sampling Figure S-9. Dissolved H 2 and O 2 in groundwater of monitoring wells FW010 and FW112 over an eight month period of weekly monitoring with passive gas samplers. SI - 17

18 Gas Phase Hydrogen Dynamics During He/Ne Tracer Injection Hydrogen Equilibria Gas Concnetration (ppm) FW106 FW111 FW113-1 FW113-2 FW113-3 FW Days From Start of He/Ne Injection (October 9, 2005) Figure S-10. Dynamics of equilibrium hydrogen gas in groundwater in six additional monitoring wells during weekly sampling over an eight month period in area around S-3 ponds. Error bars are the standard deviation of duplicate samplers with some error bars smaller than the plotting symbols. SI - 18

19 Gas Phase Oxygen Dynamics During He/Ne Tracer Injection Oxygen Equilibria Gas Concnetration (ppm) FW106 FW FW113-1 FW113-2 FW FW Days From Start of He/Ne Injection (October 9, 2005) Figure S-11. Dynamics of equilibrium oxygen gas in groundwater in six additional monitoring wells during weekly sampling over an eight month period in area around S-3 ponds. Error bars are the standard deviation of duplicate samplers with some error bars smaller than the plotting symbols. SI - 19

20 20000 Equilibrium Hydrogen Gas in Groundwater (ppm v) Feb-06 4-Mar Mar Apr-06 3-May May Jun-06 Sampling Date FW115-3 FW115-2 FW115-1 Figure S-12. Dynamics of equilibrium hydrogen gas in groundwater in three additional monitoring wells during weekly sampling over a three month period in area around S-3 ponds. Error bars are the standard deviation of duplicate samplers with some error bars smaller than the plotting symbols. SI - 20

21 80000 Equilibrium Oxygen Gas in Groundwater (ppm v) FW115-3 FW115-2 FW Feb-06 4-Mar Mar Apr-06 3-May May Jun-06 Sampling Date Figure S-13. Dynamics of equilibrium oxygen gas in groundwater in three additional monitoring wells during weekly sampling over a three month period in area around S-3 ponds. Error bars are the standard deviation of duplicate samplers with some error bars smaller than the plotting symbols. SI - 21

22 Water Levels in FRC Area 3 Tracer Test Wells Water Elevation (ft) FW106 FW111 FW112 FW113-1 FW113-2 FW113-3 FW Days from Start of He/Ne Injection (October 9, 2005) Figure S-14. Groundwater elevations in seven monitoring wells during interval of observing elevated hydrogen concentrations in groundwater (vertical line indicates time of peak hydrogen concentrations). SI - 22

23 Hydrogen In Sealed Bottles of Groundwater From Six Wells Hydrogen Gas Concnetration (ppm-v) Time After Sealing Bottle (hours) FW010 FW106 FW112 FW113-1 FW115-1 FW115-2 Figure S-15. Hydrogen gas concentrations in 1-L sealed bottles of groundwater sampled from six wells collected on April 6, 2006, as effluent from 500-mL capacity bubblestripping glass sampling bulbs. SI - 23

24 Figure S-16. Location of monitoring wells examined for H 2 concentrations in groundwater around the 3.7-acre closed and capped S-3 ponds impoundment. SI - 24

25 Figure S-17. Plan view of groundwater well locations in the USDOE Field Research Center, areas 3 and 4, immediately west of the parking pad covering the former S-3 liquid waste disposal ponds. Inset area is enlarged in the Figure S-18. SI - 25

26 Figure S-18. Inset locations from Figure S-17 of well locations employed for survey of equilibrium H 2 gas concentrations in groundwater. This is the area of pilot-scale in situ uranium-immobilization project recently reported by Wu et al. (2006). SI - 26

27 Figure S-19. Plan view of groundwater monitoring well locations within area 2 of the FRC containing several wells used for survey of equilibrium H 2 gas concentrations. SI - 27

28 Figure S-20. Locations of groundwater monitoring wells in FRC Area 1. SI - 28

29 Figure S-21. Location of groundwater monitoring wells in FRC Area 5, east of S3 ponds parking pad. SI - 29

30 Figure S-22. Photograph of S-3 ponds in 1986 prior to closure (from Stone 1990). SI - 30

31 Figure S-23. Design of the 4-acre multi-component infiltration barrier placed over the S- 3 ponds impoundment area in 1990 (from Stone 1990). SI - 31

32 Table S-2. Gas chromatographic detection of fixed gases using a 30-ft x 1/8-inch diameter HayeSepDB 100/120 mesh packed column with N 2 carrier gas at 5.0 ml/min with sequential thermal conductivity and reductive gas detector signals. Average Minimum Minimum Detection Limit Typical Gas Linear Peak Retention Peak Area Detectable Concentration Atmospheric Chromatographic Calibration Equation Regression Time Detectable Amount in 0.5 ml Concentration Gas Species Detector (µl H sample) R 2 (min) (mv-sec) (µl@stp) (ppmv) (ppmv) Helium TC (Area x 5.33E-02) ± Neon TC (Area x 2.276E-01) ± Hydrogen RG (Area x 7.64E-06) ± Hydrogen TC (Area x 2.97E-02) ± Oxygen TC (Area x 8.81E-01) ± Carbon Dioxide TC (Area x 3.812) ± at 2 x base flow rate SI - 32

33 Table S-3. Hydrogen and oxygen equilibrium gas concentrations in selected monitoring wells at the FRC on various survey dates. Well Number Sampling Dates Hydrogen Gas (ppmv ± STD) Oxygen Gas (ppmv ± STD) Area Map (Figure ) FW511 12/16-20/ ± ,000 ± / Figure S-19 FW504 11/4-9/ ± ,000 ± / Figure S-19 FW504 11/11-15/ ± 17 51,000 ± / Figure S-19 FW504 12/6-12/ ± ,000 ± / Figure S-19 FW007 11/9-11/ ± 20 65,000 ± / Figure S-15 FW007 1/9-18/ ± ,000 ± / Figure S-15 FW008 11/9-11/ ± 12 76,000 ± / Figure S-15 FW008 12/6-12/ ± ,000 ± / Figure S-15 FW008 1/9-18/ ± ,000 ± / Figure S-15 FW009 11/9-11/ ± 14 55,000 ± / Figure S-15 FW009 12/6-12/ ± 95 71,000 ± / Figure S-15 FW009 1/9-18/ ± ,000 ± / Figure S-15 FW025 11/9-11/ ± ,000 ± / Figure S-18 FW025 12/6-12/ ± ,000 ± / Figure S-18 FW025 1/9-18/ ± ,000 ± / Figure S-18 FW023 11/9-11/ ± ,000 ± / Figure S-18 FW023 1/9-18/ ± ,000 ± / Figure S-18 TPB32 1/9-18/ ,500 ± ,000 ± / Figure S-15 TPB32 2/16-20/ ,700 ± ,000 ± / Figure S-15 TPB25 3/20-27/ ± ,000 ± / Figure S-15 FW015 1/19-25/ ± ,000 ± / Figure S-18 FW021 1/19-25/ ± 75 89,000 ± / Figure S-18 FW031 1/19-25/ ± ,000 ± / Figure S-18 FW034 1/19-25/ ± 81 81,000 ± / Figure S-18 TMW05 10/25-27/ ± 18 NA 2 / Figure S-17 TMW07 10/25-27/ ± 0.3 NA 2 / Figure S-17 TMW09 10/25-27/ ± 3.6 NA 2 / Figure S-17 TMW12 10/25-27/ ± 13.2 NA 2 / Figure S-17 FW205 10/25-27/ ± 0.2 NA 2 / Figure S-17 FW217 10/25-27/ ± 31.0 NA 2 / Figure S-17 GW835 11/2-4/ ± 0.4 NA 2 / Figure S-17 FW /2-4/ NA 2 / Figure S-17 PTMW02 11/4-9/ ± 29 36,000 ± / Figure 4 PTMW02 5/26-29/ ± 24 22,000 ± / Figure 4 FW412 11/4-9/ ± ,000 ± / Figure S-15 FW405 11/4-9/ ± 8 60,000 ± / Figure S-15 FW405 2/6-10/ ± ,000 ± / Figure S-15 FW /4-9/ ± ,000 ± / Figure S-15 FW /6-12/ ± ,000 ± / Figure S-15 FW /16-20/ ± ,000 ± / Figure S-15 SI - 33

34 Well Number Sampling Dates Hydrogen Gas (ppmv ± STD) Oxygen Gas (ppmv ± STD) Area Map (Figure ) FW /6-12/ ± ,000 ± / Figure S-15 FW413 11/4-9/ ,700 ± ,000 ± 0 4/ Figure S-15 FW413 12/6-12/2005 9,400 ± ND 45,000 ± ND 4/ Figure S-15 FW413 2/16-20/ ± ,000 ± / Figure S-15 FW110 2/16-20/ ± 15 54,000 ± / Figure S-16 FW110 2/6-10/ ± 66 83,000 ± / Figure S-16 GW243 2/6-10/ ± 30 30,000 ± / Figure S-16 FW /6-10/ ± ,000 ± / Figure S-16 FW /6-10/ ± ,000 ± / Figure S-16 FW /6-10/ ± ,000± / Figure S-16 FW104 2/6-10/ ± ,000 ± / Figure S-16 FW024 2/6-10/ ± ,000 ± / Figure S-16 FW026 2/6-10/ ± ,000 ± / Figure S-16 FW103 2/6-10/ ± ,000 ± 200 4/ Figure S-16 SI - 34