2015-04-28 – USACE – EPA – Review of West Lake Landfill Radon Flux Analysis

2015-04-28 - USACE - EPA - Review of West Lake Landfill Radon Flux Analysis

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April28, 2015
Mr. Brad Vann, Remedial Project Manager
Environmental Protection Agency Region 7
11201 Renner Boulevard
Lenexa, KS 66219
Dear Mr. Vann:
Per your request, The U.S. Army Corps of Engineers (USACE) has reviewed the Responsible
Party’s (RP’s) Radon Flux Analysis provided in Attachment A of their October 2014 Isolation
Barrier Alternatives Analysis Report. The purpose of this review was to identify assumptions
made by the RPs in their radon exposure and risk calculations and identify standard geotechnical
analyses or other tests that could be performed on core samples to verify the assumptions made
and utilized in the RP’s calculations and modeling.
In the October 2014 report, the RPs used the RAECOM model to calculate radon exposure and
risk. The following parameters that are inputs into the RAECOM model were assumed in the
RP ‘s report:
• Change in soil density
• Change in soil porosity
• Change in soil moisture content
• Radon emanation fraction of soil
• Rate of settlement
Fallowing are the geotechnical tests that would provide information that could be utilized to
confirm the RP’s assumptions:
• Soil dry density testing (ASTM D 7263 Laboratory Determination of Density (Unit
Weight) of Soil Specimens) could be conducted using existing cores to verify the density
of 1.4 g/cm3 utilized in the RP’s modeling effort.
The dry density could then be used to calculate the void ratio, which would be used to
calculate porosity. This number would confirm the porosity of 67% utilized for layer 1 of
the RP’s modeling effort and would confirm the change in soil porosity assumed in the
RP’s model that reflected an SSE.
• Moisture content testing (ASTM D 2216 Standard Test Method for Lab Determination of
Moisture Content) could be conducted to verify the initial moisture content of25%
WLLFOIA4312- 001 – 0059044
West Lake Core Testing Alternatives
April28, 2015
utilized in the RP’s modeling effort. Newly obtained cores would be necessary in order
to obtain accurate current moisture content. After heating is applied to simulate an SSE,
the resulting moisture content measurement would allow for confirmation of the 20%
reduction assumed by the RPs in their modeling effort.
Other geotechnical tests that may be of value:
• ASTMD 6539 Measurement of the Permeability ofUnsaturated Porous Materials by
Flowing Air. While this test wouldn’t confirm the RP’s parameter assumptions directly
input into the RAECOM model; it could potentially be used to better calculate the landfill
gas flow rate and radon retention time. These parameters would be used to estimate the
radon concentration in the landfill gas emission stack. The test could be conducted under
baseline conditions and after drying the core to measure the change in airflow when the
pore spaces are not filled with water.
• ASTM D 4318 Standard Test Method for Liquid Limit, Plastic Limit, and Plastic Index
of Soils (Atterberg Limits) and ASTM D 421/422 Test Method for Grain Size analysis of
Soils- washed sieve analysis. While these two tests will not directly confirm parameters
input into the RP’s modeling program, it is useful to know the material type which is
directly related to soil behavior characteristics and may be useful information in the
future, such as designing the IB.
There were no known standard geotechnical tests identified that would allow for confirmation of
the following parameters:
• Radon emanation fraction of soil
• Rate of settlementN olume of landfill gas expelled due to subsidence
Radon emanation fraction of soil (radon emanation coefficient) could be determined through a
specifically-designed laboratory test. Documentation for the RESRAD model references a test
method by Strong and Levins (1982) that determines the radon emanation coefficient by using an
accumulation (ingrowth) chamber, a sampling cylinder, a diaphragm pump, a scintillation cell,
and supporting electronics for the radon measurement. This test could likely be conducted under
baseline conditions and with modification, be subjected to heat to simulate an SSE to determine
if the emanation coefficient changes due to temperature. The resulting coefficient would directly
be entered into RAECOM for the the baseline conditions, and if the coefficient changes under
temperature, for the SSE conditions.
The volume of landfill gas expelled due to subsidence is a parameter that would be extremely
difficult to reproduce in a laboratory environment. Field scale testing would likely be extremely
time-consuming and costly.
It should also be noted that when the RPs revise their calculations, in addition to incorporating
the parameters confirmed by any core testing conducted, they should also incorporate the most
recent RIM investigation results and utilize temperatures that are reflective of the SSE event in
the south quarry. Additionally, the link the RPs provided in Section 2.1 of their October 2014
report for the web-based radon calculator (Wise Uranium Project:
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West Lake Core Testing Alternatives
April28, 2015
=..:::===.::.~===’ 2011) is no longer active. That link should be updated in the next report
addressing their approach so that their radon flux calculations may be verified.
If you have questions, please call me at 816-246-5660.
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Robyn Kiefer
Project Manager
WLLFOIA4312- 001 – 0059046