March 2016

Fukushima Daiichi nuclear accident
Groundwater under the site
Situation in January 2016
This document is based on publicly available information on the situation of the Fukushima Daiichi plant.

I.

Background: three different areas to be considered

In order to understand the sources of radioactive contamination of the groundwater under the site,
three different areas should be considered:-The "inlet channel" area, known as “Turbine Building east side” on TEPCO website, is locatednext to the harbour and includes the water intakes of Units 1 to 4. Shortly after the accident,
highly radioactive water from the reactors filled several trenches and passages and then spilled
into the harbour;-

The "nuclear buildings" area, comprising in particular Reactors 1 to 4 and the related buildings
housing the turbines. The basements of these buildings are filled with highly radioactive reactor
cooling water (of the order of 70,000 m 3). In addition, they receive significant inflows ofgroundwater (about 200 m3/day);-

The "storage" area, located upstream of the reactors. Created after the accident to manage thehighly radioactive water pumped on the site1, this tank installation area occupies a surface area
5 times larger than that of the nuclear buildings. To date, approximately 750,000 m 3 ofradioactive water are stored there.

View of the various areas of the site

1

See the information note on the management of radioactive water.

Groundwater flows naturally from the inland toward the ocean into 3 main sandstone layers. TEPCO
estimates that around 1 000 m3/day circulate under the nuclear buildings area. This flow is divided
between the shallow aquifer (Permeable Levels 1 and 2 in the figure below) with 700 m3/day andthe confined aquifer (Permeable Level 3 in the figure below) with 300 m3/day.
Thus, if no particular action is taken, any groundwater contamination at the Fukushima Daiichi sitewould eventually reach the ocean.

Source TEPCO – Geological context of the site
The distance between the contamination source and the sea is the main parameter in terms of time
to reach the ocean. In addition, the rate of contamination migration in the groundwater depends on
the radionuclides, since they may interact more or less strongly with the sandstone layers. Thus,tritium (3H), which does not interact, travels at the groundwater velocity (1 m/day in order ofmagnitude). Strontium travels slower (1 m/month in order of magnitude) and caesium is evenslower (a few cm/day or less).
Under these conditions, the presence of one or more of these radionuclides in the groundwater
gives an indication of the proximity of the radioactive water leaks into the ground. Closer to thesource of contamination, high concentrations of caesium, strontium and tritium are detected.
Further downstream, concentrations decrease and only strontium and tritium are detected, andthen only tritium.

II.

The inlet channel area (east side of Turbine Building Units 1 to 4)

Shortly after the accident in March 2011, the reactor cooling water flowed into the turbine building,filled several trenches (underground tunnels and vertical shafts containing pipes [green] in thefigure below, power cables trenches [yellow] in the figure below), reached the water intakes andwas released directly into the harbour. This highly radioactive water contaminates the harbour
sediment and water, as well as contaminating the soil and groundwater near the water intakes.
In order to limit direct releases into the ocean, TEPCO blocked the mains trenches vertical shaftswith crushed stones and concrete in April-May 2011. The releases into the harbour then continued
diffusely with the natural flow of contaminated groundwater, particularly between the water
intakes of Units 1 and 2.

2/7

As from December 2012, TEPCO started to install piezometers to characterise the groundwatercontamination between the reactors and the sea. In the second half of 2013, this network wasdensified and contamination monitoring was set up. Around 50 piezometers were thus installeddownstream from the reactors, thirty of which are monitored at least once per week.

Source TEPCO – Top view of the seaside trenches, between Units 1 to 4 and the inlet Channel View of the piezometers - State in September 2015
This monitoring has confirmed the local source of the contamination of this area. The simultaneouspresence of caesium, strontium and tritium in the groundwater indicates the proximity of the leaklocations, with the highest concentrations of caesium (not very mobile) being measured in thevicinity of the trenches. Thus, since 2013 TEPCO has been conducting a work programme spreadover time (emergency measures and then management measures) to limit the contamination ofgroundwater (1) and eliminate diffuse releases into the harbour (2).
(1) To eliminate contamination sources, TEPCO has injected sealants into the ground to prevent
leakages from the seaside trenches, and covered the ground to protect it from rain water
infiltration. After trying to freeze the connections of main trenches to the turbine buildings (Units2, 3 and 4) to stop water exchanges (April-November 2014), TEPCO proceeded to water collection
by a step by step cement filler injection (tunnels, vertical shafts and finally the shafts-turbinebuildings connections) during the 1st half of 2015. These operations led to the pumping and transfer
to the turbine buildings of 11,000 m3 of highly radioactive water. The Unit 1 main trench, whichcontains less radioactive water, was left as it was. TEPCO continues its pumping work in thesecondary trenches network and in the water intake buildings.
(2) To prevent outflow of contaminated water into the harbour, TEPCO has set up additional
provisions for capturing groundwater near the bank:-Three local devices, consisting of a sealing screen made by chemical injection (“groundimprovement”) associated with wells for pumping contaminated groundwater, wereimplemented during the second half of 2013 between water intakes of Units 1 and 2, 2 and 3,and 3 and 4. North of the Unit No. 1 water intake, only one well is used for pumping. Thus, theprogression of the contamination towards the harbour was halted in late 2013, limiting thediffuse releases. Pumping is being continued, in order to reduce the local contamination ofgroundwater;-A second sealing barrier ("sea-side impermeable wall") was established in the harbour, along thebank from April to December 2013. Nearly 900m long and about 35m high, the wall is made ofmetal tubes built in the land from the harbour. It should enable the flows in the shallow anddeep aquifers downstream from the site as a whole to be controlled. In 2014, the space
between the wall and the bank was backfilled and 5 pumping wells (“pits”) were drilled in it
and then tested in August and October 2015 (“groundwater drains”). The closing of the wall wascompleted in October 2015 after the commissioning of the pumping, treatment and release

3/7

device for the groundwater arriving upstream of the wall was announced. However, the rise of
the groundwater behind this wall, now closed, led to a slight tilting of the latter in November
2015. TEPCO then carried out strengthening work and increased the pumping to counteract thisphenomenon.

WallFrom TEPCO data - harbour side sealing barriers (design views, photos of the wall after closing andreinforcements installed following its tilting)After two years of continuous pumping in local devices, the changes in the groundwatercontamination near the harbour are summarized in the following table.
SectorNorth ofPS No. 1
BetweenPS No. 1and 2
BetweenPS No. 2and 3
BetweenPS No. 3and 4

Changes in the maximum readings by sector
Measurement
Tritium
Overall 
Caesium 137
Tritium
Overall 
Caesium 137
OtherTritium
Overall 
Caesium 137
Tritium
Overall 
Caesium 137

2Maximum observed
76,000 Bq/L
330 Bq/L
81 Bq/L
630 000 Bq/L
9,300,000 Bq/L
200 000 Bq/L
54Mn, 60Co, 106Ru, 125Sb
13,000 Bq/L
560 000 Bq/L
110 Bq/L
10,000 Bq/L
8900 Bq/L
520 Bq/L

1st fortnight of 2016
26,000 Bq/L
140 Bq/L
53 Bq/L
69,000 Bq/L
660 000 Bq/L
33,000 Bq/L
54Mn, 60Co, 125Sb
3700 Bq/L
560 000 Bq/L
23 Bq/L
7900 Bq/L
4400 Bq/L
100 Bq/L

Means implemented
1 well discharging
approximately 1 m3/day
Sealing screen and 28 wells
discharging several tens of
m3/daySealing screen and 29 wells
discharging several tens of
m3/daySealing screen and 7 wells
discharging approximately
ten m3/day

These results show that the groundwater decontamination is slow, because of the different
migration velocity of the radionuclides through the sandstone layers and the likely continued inflows
from the main trenches until their drainage by TEPCO in the 1st half of 2015. Moreover, an increasein the readings remains possible, as was found in the vicinity of the Unit No. 2 water intake in
November 2015, since the pumping work in the secondary trenches networks and in the water
intake buildings is not yet finished.
Contaminated water pumped by the local devices is returned to the turbine buildings and thus
processed with all of the highly radioactive water.
Groundwater pumped from the land-side of the sea-side impermeable wall, about 100 m3/day (fromthe deep aquifer), is to be mixed with groundwater pumped around the nuclear buildings (see the2TEPCO suspects an overassessment of the highest values for and Caesium 137, due to the presence of contaminatedsuspended solids (SS) in the samples. The role of the SS has been highlighted by the significant differences depending onwhether the measurements are performed with or without prior filtering of the samples.
4/7

next paragraph) for treatment and release into the harbour as long as it is within the permitted
limits3.
With the draining of the trenches, the installation of sealing barriers and pumping wells, TEPCO
considers that it has managed to minimise diffuse releases of contaminated groundwater into
the harbour.

III.

The nuclear building area

TEPCO’s primary goal is to maintain the cooling of the damaged reactors by injecting about
325 m3/day of water, which becomes contaminated upon contact with the fuel and then spreads tothe lower parts of the buildings. Given that the March 2011 earthquake affected the watertightnessof these buildings, TEPCO is forced to keep the level inside the buildings lower than that of thewater table, in order to avoid contaminating the latter. Groundwater thus seeps into the basement(about 200 m3/day) and mixes with contaminated water.
Outside the buildings, monitoring of the water samples taken from the drainage system installedaround them shows a very moderate contamination of the groundwater (around 5000 Bq/L for
tritium downstream from Unit No. 4 and 200 to 500 Bq/L for caesium around Unit No. 2) comparedto the water inside the buildings (of the order of 10 6-107 Bq/L for caesium and 106 Bq/L for tritium).
Thus, there are signs of leaks possibly resulting from the level reached in 2011 by radioactive waterin the nuclear buildings, but no signs of any significant current leak. This finding was confirmed
downstream from the turbine buildings of Units No. 1 to 3 after the installation of 11 piezometers.
In order to prevent groundwater from flowing into the basements of the buildings, without risk ofcontaminating the groundwater, TEPCO conducted the following actions:-Installation of a system of 12 wells to pump up groundwater flowing from the mountain sideupstream of the buildings ("Groundwater bypass"). This system, which has been operational
since the summer of 2013, was implemented in April 2014. It leads to regularly releasing water(about 250 m3/day) after contamination controls3.

-Restoration of 27 drainage pits and construction of 15 new pits around the buildings(" subdrains") to complete the drawdown. Before the accident, this drainage network enabled
the drawdown of the water table in contact with Units No. 1 to 4 by pumping 850 m3/day. Aftera test phase carried out on 14 wells in August 2014, the commissioning of this system and thetreatment and release of water into the harbour were approved by the Japanese regulatory
authority in early 2015 and then by local authorities and associations in September 2015.
Approximately 350 m3/day are pumped from around the buildings and then treated, and mustmeet the same release criteria as the pumped water upstream of the sea-side impermeable wall
mentioned in the previous chapter3;-Search for groundwater seepage areas inside the buildings to carry out sealing work. This longprocess will require a systematic examination of some 800 existing passageways through theouter walls of Units No. 1 to 4;-Deployment of a soil freezing device down to a depth of around thirty meters around Units No. 1to 4 (“land-side impermeable walls”), following the work of a group of experts mandated by theauthorities and several experimental phases. Between June 2014 and October 2015, TEPCO
completed 1552 freezing boreholes and 332 soil temperature monitoring boreholes. Since April
2015, TEPCO has been testing the process at 18 locations (58 holes), on the hill side.

3TEPCO has set itself, in agreement with the authorities and fishing associations, contamination limits below the legal

discharge values set forth in the regulations: less than 1 Bq/L for caesium 137, less than 1500 Bq/L for tritium and less than 3
Bq/L or 5 Bq/L for overall b (essentially strontium) depending on the device. Releases are allowed after TEPCO and a thirdparty organization have confirmed that its quality meets operational targets.
5/7

Source TEPCO – Effect of the "groundwater bypass" and "subdrains" pumping devices before thecommissioning of the soil freezing device.
The results to date of these various devices is detailed below.
-In the case of the "groundwater bypass", there are tritium readings in the pumped water due toleaks from the storage areas (see the next paragraph) and TEPCO has suspended the pumping of
the well exceeding 1500 Bq/L. In addition, bacterial growth in the boreholes causes stoppages
for cleaning. After more than a year of pumping, TEPCO considers that this device has enabled
seepage to be reduced in the buildings from 400 to 300 m 3/day (findings in the summer of2015).

-Pumping was thus commissioned in the drainage pits ("subdrains") around buildings to reduce
seepage into the buildings from 300 to 200 m3/day (findings at the end of 2015 by TEPCO).
However, maintaining a stable water table level around the buildings is made difficult byrainwater infiltrations. In addition, TEPCO expected a reduction in the groundwater flows into
the harbour area, which has not yet been the case.

-In order to freeze soils around the Units 1 to 4, the test phase showed encouraging results.
However, since the month of August and the beginning of the rainy season, increased
groundwater flows have led to a rise of soil temperature in most of the boreholes.

From TEPCO data - soil freezing devices and "subdrains" location.

6/7

IV.

The storage area

Since June 2011, TEPCO has been storing highly radioactive water in tanks installed progressively
upstream of the nuclear buildings. Water treatment enabled TEPCO to reduce their radiologicalcontent4.
In 2013 and 2014, several incidents led to releases of highly radioactive water that reached theshallow aquifer.
TEPCO thus carried out work to limit the occurrence of new spills, reduce their consequences bycontaining leaks or rainwater around the tanks and restoring and monitoring the rainwatercollection network.
After several years of monitoring, the changes in the groundwater contamination in the storage area
are summarized in the following table.
Changes in the maximum readings by sector
Storage Sector

Radionuclide
detected

Maximum
observed

1st fortnight of 2016

Tank R4

Tritium

3,400 Bq/L

570 Bq/L

Tank R6

Tritium

3,800 Bq/L

130 Bq/L

Tanks H4

Tritium
Overall 

790,000 Bq/L
710,000 Bq/L

24,000 Bq/L
9,900 Bq/L

Tanks H6

Tritium
Overall 

7,000 Bq/L
260 Bq/L990 Bq/L
undetectable

Groundwater bypass(Downstream from R4,R6 and H4)

Tritium

3,100 Bq/L

880 Bq/L(No. 10>1,500 Bq/L)

Means implemented
None considerednecessary.
Collection downstream by
the Groundwater bypass
Local pumping between
October and December
2013. Collection by theGroundwater bypass
None considerednecessary
Pumping since April 2014

The levels have fallen significantly, but the closest piezometers still show sharp fluctuations in thereadings after heavy rain periods. Downstream from these areas, only tritium is detectable anddisrupts the functioning of the "groundwater bypass" wells. With levels exceeding 1500 Bq/L, Well
No. 12 was shut down twice between May and August 2014 and Well No. 10 has been shut down
since July 2015 (in November 2015, the readings were still 3,100 Bq/L).
Following the highly radioactive water leaks that occurred in the storage area in 2013 and2014, only tritium is detected downstream. Since the commissioning of the "groundwaterbypass" in April 2014, most contaminated groundwater from this area is captured by thisdevice.
As a conclusion, it appears that the provisions implemented by TEPCO enable the bulk of thegroundwater contamination to be contained within the Fukushima Daiichi plant.

4

See the information note on the management of radioactive water.
7/7