01/07/2011 1

Atmospheric Tritium is a Groundwater Tracer

Water Tritium

Plug Flow Position

What is tritium?

Units for tritiumPicocuries (pCi) – 2 disintegrations per minute

Tritium Unit (TU) – 1 tritium atom in 1018 hydrogen atoms

1 pCi ~ 3 TU

Tritium occurs in rainfall

Tritium in rainfall caused by atmospheric nuclear tests.

Atmospheric tritium range:102 to 10-2 TU

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Tritium (TU)

Near-Suface Groundwater Monitoring Wells

All Chatsworth Fm Monitoring Wells (excludes Area IV)

Area IV Monitoring Wells

<0.09 ± 0.02 TU

0.8 TU

3.4 TU

Atmospheric tritium zone

Atmospheric tritium in recharge water moves along the groundwater flow paths while it is influenced by matrix diffusion and decay.

If the tritium molecules traveled at the same velocity as the groundwater in fractures, then high tritium would be found much deeper.

Monitoring wells across the site sampled for atmospheric tritium.

Conclusion:

The distribution of atmospheric tritium contributes to understanding groundwater flow and the behavior of all types of dissolved contaminants in the Chatsworth Formation bedrock.

Atmospheric 3H in monitoring wells decreases with depth.

Samples collected in 2007 through 2009 and historical values (1987-1998) adjusted for radioactive decay.

Examples from two cluster well locations; smaller tritium concentrations at greater depth.

normal heavy radioactive

3H

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1950 1960 1970 1980 1990 2000 2010

Trit

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Ottawa (Ontario)

Menlo Park (CA)

dotted line = decayed to 2010

CA Precipitation ~5 TU

1950 to 1963

Poster Prepared by Amanda Pierce, G360, June 24, 2011

The tritium movement is much slower than the water because diffusion causes tritium to be transferred from the fracture into the rock matrix.

Radioactive isotope of hydrogen with a decay half-life of 12 years.

0.05 ± 0.02 TU

1.2 TU

1.3 TU

B & C

04/08/2011 1

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Feb‐82

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‐87

Jan‐93

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Well WS‐09AContaminants Detected:TCE, cDCE, tDCE, 1‐1DCE, & VC

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Concen

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FDP‐890Contaminants Detected Historically:TCE, cDCE, tDCE, 1,1DCE & VC

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Mar‐06 Oct‐06 Apr‐07 Nov‐07 Jun‐08 Dec‐08 Jul‐09 Jan‐10

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FDP‐881Contaminants Detected Historically:TCE, cDCE, tDCE & VC

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Oct‐06 Apr‐07 Nov‐07 Jun‐08 Dec‐08 Jul‐09 Jan‐10

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FDP‐882Contaminants Detected Historically:cDCE & tDCE

Seeps are typically a mixture of groundwater from different travel paths and age.

2011 Drilling at Seeps May 10, 2011

SP‐890 Cluster SP‐881 Cluster

SP‐882 Cluster

WS‐09A

FDP‐890

FDP‐882

FDP‐881

154 seeps have been identified along the mountain slopes, 90  have been sampled.

Seeps InvestigationsSeeps on the mountain slopes are being investigated to determine nature of recharge water and where SSFL contaminants could emerge.

Groundwater  samples are collected in bottles  from seeps at points of discharge.

Contaminants have been found at 3 seeps in southwest drainage.

The Shaw Back‐Pack Core Drill was used in May 2011 to core to a maximum depth of 20 feet.

dug hole directly from fracture

from flowing water

Chatsworth Formation

Seep

Overburden

Site

Water Table

Seep

Seep

Seep

Groundwater Flow

ContaminantPlume

Site Boundary

Contaminants were found at on‐site seeps, but not at off‐site seeps.  

Winkie DrillDeeper Drilling ~50 ft

Shaw Back‐Pack Core DrillShallowest Drilling ~20 ft

Portable drilling equipment will be used to install monitoring wells at isolated seep locations.

Well ClusterSeep

Groundwater Flow

ContaminantPlume Well Cluster

Volatilization?

Trapped in the mud?

Because;

• Seep not on plume flow line

•On plume flow line but not arrived

Contaminants are actually at the seep but;

• Loss due to surface volatilization at seep• Trapped in the mud around the seep 

WHY?

Three monitoring well clusters consisting of four wells each were installed in May at on‐site seeps in southwest.

Poster Prepared by Amanda Pierce, G360, revised 8/3/11