RE: tritium contamination of Hanford groundwater

["Dukelow, James S Jr" <jim.dukelow@pnl.gov>]

Sandy Perle forwarded to RADSAFE a news article on tritium contamination of
Hanford groundwater:

	<snip>

Thursday February 3 10:43 PM ET 

High Level of Tritium Found  

RICHLAND, Wash. (AP) - A groundwater sample shows the presence of 
tritium at 400 times the federal drinking water standard in a 
monitoring well 3.6 miles from the Columbia River at the Hanford 
nuclear reservation.  

An internal Hanford memo, obtained by the Tri-City Herald, says it 
could take the underground plume as little as three years or as many 
as 30 years to reach the river.  

The U.S. Department of Energy's Pacific Northwest National Laboratory 
and the state officials will begin conducting additional tests on 
Monday at the site.  

``We're hopping on this,'' Mike Thompson, DOE's official in charge of 
groundwater monitoring, said Thursday.  

He hopes to know better in a couple of weeks the concentration of the 
tritium and how serious a threat it poses to the river.  

A tritium concentration of 20,000 picocuries of radiation in one 
liter of water is the federal drinking water limit. The reading at 
the monitoring well was 8 million picocuries.  

	<snip>

JSD comment:

A few years ago I did a back-of-the-envelope calculation to estimate the rate of
groundwater flow off the Hanford site into the Columbia River and the dilution
factor as the groundwater enters the river.

Assuming

a 500 square mile recharge basin,

6" of rainfall per year,

95% evapo-transpiration (i.e., only 5% of the rainfall stays in the ground --
it's a desert here),

and equilibrium conditions (i.e., GW to river = rainfall minus
evapotranspirtation),

gives a flow rate of  11 cubic feet per second groundwater flow to river.

That compares with  117 cubic meters per second low river flow, 3400 cubic
meters per second normal flow, and 19000 cubic meters per second maximum flow.

These three flow rates give dilution factors of approximately  400, 10000, and
100000 respectively for low, normal, and flood flows.

The assumptions on size of recharge basin, rainfall, and evapotranspiration rate
are pretty solid.  The assumption of equilibrium conditions is open to question
since for many years Hanford operations discharged large volumes of slightly
contaminated effluent directly to the ground.  These discharges are the source
of most of the groundwater contamination and were sufficient to produce water
table "mounds" underneath the two processing areas on the reservations high
plateau.  Because of those discharges, which were terminated around 10-15 years
ago, groundwater flow to the river may include a contribution from those water
table "mounds".

These numbers suggest that, even if the high tritium concentrations are not
diluted by surrounding groundwater on their way to the river, the river flow
will be sufficient to dilute the tritium to at or below the federal drinking
water limit.  Some mitigation might be required during times of lowest river
flow.

As a resident of Richland, which gets its water directly out of the river a few
miles downstream from the contamination, I have more than a modest interest in
this issue.

Best regards.

Jim Dukelow
Pacific Northwest National Laboratory
Richland, WA
jim.dukelow@pnl.gov

These comments are mine and have not been reviewed and/or approved by my
management or by the U.S. Department of Energy.
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