1

Practical training on geochemical
investigation:
Geochemical monitoring and water
sampling at the 250 m gallery
August 7th, 2023
Horonobe Underground Research Department
Safety Assessment Research Group
Keisuke Sakuma, Hiroaki Murakami, Fairat Koraphat

2Contents
1. Why is geochemical investigation important?
2. Today's schedule and underground facility
3. Practice in the underground facility
4. Lectures on the Ground3

Why is geochemical investigation required?

• The solubility of radionuclides will be affected by thegroundwater pH and ORP (oxidation-reduction potential),
which are physicochemical parameters.

✓To judge whether groundwater in the repository (candidate)has chemically favorable conditions (Neutral to low-alkalinepH, reductive, low carbonate concentration).

4Groundwater sampling: from the surface• The simplest way:
Pumping water from a borehole

Preliminary
investigation
出典：資源エネルギー庁ウェブサイト
（https://www.enecho.meti.go.jp/category/ele
ctricity_and_gas/nuclear/rw/hlw/hlw01.html）✓ There are several points to be takencare of for the sampling from the groundsurface.

5Groundwater sampling: from the gallery• We can collect water from a borehole.

Detailed
investigation
出典：資源エネルギー庁ウェブサイト
（https://www.enecho.meti.go.jp/category/ele
ctricity_and_gas/nuclear/rw/hlw/hlw01.html）

Water
samplecollection

Borehole

Packer

Water pressure
observation✓ The values of pH and Eh at the ground surface differedfrom those obtained from the in-situ experiment.
✓ This is probably caused by the degassing of CO2 andCH4 during the pumping and subsequent changes inredox conditions in the water.

Objective of this lecture• Measure the correct value of the groundwater• Provide the suitable sampling procedure andaccurate chemical analysis which are required toaccurately characterize groundwater chemistry• Understand the methods and points of caution forobtaining reliable geochemical data on groundwater

6

7Contents
1. Why is geochemical investigation important?
2. Today's schedule and underground facility
3. Practice in the underground facility
4. Lectures on the GroundToday’s schedule of practical training
Group ATime

min.

13:30

15

13:40
13:50
14:00
14:10
14:20
14:30
14:40

14:50
15:00

Group B
ContentLecture↓↓
5
To entrance of URL (by bus)
10To underground (by elevator)↓20Analyzing with sensor↓↓↓
25
Sampling・adding reagents (A)↓↓↓10To the ground↓
5 Back to Yume-chisou-kan (by bus)
Changing clothes

Timemin.

10:30

15

10:40
10:50
11:00
11:10
11:20
11:30
11:40

11:50
12:00

ContentLecture↓↓
5bus
10elevator↓
20
Analyzingwith sensor↓↓
25
Sampling↓↓↓↓
10elevator↓
5bus
Changing clothes

Ventilation shaft
West shaft
East shaft
140 m gallery
250 m gallery

350 m gallery
500 m gallery
Tunnels constructed byMarch 2023.

Layout of Horonobe URL

8

9Today’s sampling point
Ventilation
shaft
WestshaftEastshaft

Ventilation shaft

09-V250-M02
excavation
length:20.0m

Today’s sampling point
140m gallery

East shaft
250m galleryWest shaft
0350m gallery

Layout of Horonobe URL

1020304050m

Geochemical monitoring systemat Horonobe URL• The borehole is sealed off by a packer, which keeps reductive
groundwater in place.
• This system can be used for monitoring pH and ORP without
degassing/contact with the air.
CH4, CO2 O2
16.5
区間11.0 1.0 1.0 1.0 1.0 1.6 (m)区間2

区間3Packer【09-V250-M02】 excavation length: 20m,dip: 0°, borehole diameter: φ76 mm
Electrode in af low-through cell

10

Geochemical monitoring systemat Horonobe URL

11• We can also collect groundwater from a borehole.
• For the reliable geochemical data, the following points should be noted✓ Oxygen intrusion into groundwater✓ Degassing of dissolved gases from groundwater✓ Contamination
CH4, CO2 O2
区間1

1.0 1.0 1.0 1.0 1.0 1.6 (m)
区間2

区間3

Packer
Because of time constraints, we will use thismethod for today’s practice.
(The usual method takes about two weeks tomeasure.)water sampling port

16.5

or12Contents
1. Why is geochemical investigation important?
2. Today's schedule and underground facility
3. Practice in the underground facility
4. Lectures on the GroundIn-situ groundwater analysis ofphysicochemical parameter

Measuringcup

1. Collect groundwater

pHEC
Temp

ORP

POWER

POWER

2. Dip the electrode connected to each meter

3. Once the values become stabilized, write the physicochemical parameter
Sample nameData, timepH

ORP(mV)

EC(mS/m)Temp.(℃)

13In-situ groundwater analysis of dissolved iron(totaliron, divalent iron) at underground and laboratory

10 mL

10 mL

For a 10 mL reagent【 Total iron 】

10 mL【Group A】

shake

30 mL

For a 25 mL reagent【 Divalent iron 】

30 mL

1. Collect groundwater

For blank

30 mL

30 mL

30 mL

10 mL

2. Add the reagents

2. Add the reagents

At underground

shake

14

In-situ groundwater analysis of dissolved iron(totaliron, divalent iron) at underground and laboratory
For a 10 mL reagent

10 mL

10 mL

【 Total iron 】

10 mL【Group B】

shake

For blank30 mL

1. Collect groundwater

30 mL

For a 25 mL reagent【 Divalent iron 】

30 mL

30 mL

30 mL

10 mL

2. Add the reagentsshake

2. Add the reagents

At undergroundAt laboratory

15

16

Sampling listA(1)

Adding the reagent
at underground

(2)
(3)

(1)
B
Sampling only
(2)

C
Already sampled

(3)
(1)
(2)
(3)

amount
10 mL
10 mL
10 mL
10 mL
10 mL
10 mL
30 mL
30 mL
30 mL
10 mL
10 mL
10 mL
10 mL
10 mL
10 mL
30 mL
30 mL
30 mL
30 mL
10 mL
30 mL
30 mL

RemarkFor total iron

For divalent iron
For blank

For total iron

For divalent iron
For blank
For total iron
For divalent iron
For blank

17

Contents
1. Why is geochemical investigation important?
2. Today's schedule and underground facility
3. Practice in the underground facility
4. Lectures on the Ground18

Analysis of dissolved iron(total iron, divalent iron)Objective• Analyze dissolved iron, which is sensitive to redox reactions➢ Understand the difficulties in assessing the in situ quality of reductive
groundwater
Contents【Lecture】
Absorption spectrophotometry【Practical training】• Analyze the dissolved iron in groundwater• compare and discuss the results of samples with different timings of water
sampling and reagent addition

Analysis of dissolved iron (total iron, divalent iron)Dissolved iron: dissolved and ionized iron (Fe3+, Fe2+) in water
Absorption spectrophotometry (1, 10-phenanthroline method)【Divalent iron, Fe2+】• 1, 10-phenanthroline forms a complex only with Fe2+ (without Fe3+)(giving a reddish-orange color)• Add the reagent to the sample and determine the amount ofcomplexation by absorbance at a wavelength of 510 nm.
【Total iron】• Determined by complexation after reduction of dissolved iron to Fe2+.

Fe2+–Phenanthroline complexes

19Analytical procedure for dissolved iron (total iron, divalent iron)【 Divalent iron】【Blank】【Total iron】

Quartz glass cell

10mL

10mL

Line
(10 mL marker)

2. put 10 mL of the sample

1. put 10 mL of blank

10mL

10mL

Line
(10 mL marker)

10mL

3. wipe the sides of the quartz glass cell.

close the lidzero

4.

measurement

set the blank sample in the absorbance spectrophotometer, measure at 510 nm
wavelength, and press zero 0.
5. set the sample for total iron or divalent iron in the absorbance spectrophotometer,press the measurement button, and note the measurement results.

20

Analysis of dissolved iron (total iron, divalent iron)

Analysis results
Sample name
Data and time of the sample collection
Analysis date
Total iron concentration (ppm)
Divalent iron concentration (ppm)

Key Points for Consideration•Relationship between total iron concentration and divalent iron concentration•Difference in the percentage of divalent iron and the concentration of dissolved iron between
the analysis results of samples immediately after collection and a few days after collection21Summary
For geochemical analysis of groundwater, important
points are the following;✓ Necessary the accurate state of groundwater in the
deep underground✓ Recognize that the geochemical condition changes
by sampling method✓ Prevent the occurrence of artificial influence, suchas oxidation, degassing, and contamination during
sampling

22