Attachmt_9_ACE-N.pdf

Attachment 9

USACE Letter to NJDEP - Request to use the on-site gamma spectroscopy analysis data as the basis for release using Th-230 correlation factors

DEPARTMENT OF THE ARMY

Philadelphia District, CORPS OF ENGINEERS Southern New Jersey REO

Welsbach Project Office 130 North Broadway

Gloucester City, NJ 08030

CENAP-EC-CS Serial Letter: NJE-0001 April 26, 2017

Michelle Potter New Jersey Department of Environmental Protection Office of Quality Assurance 401 East State Street PO Box 420 Trenton, NJ 08625-0424

Subject: Request to use the on-site gamma spectroscopy analysis data as the basis for release using Th-230 correlation factors – Welsbach/General Gas Mantle Superfund Project

Dear Ms. Potter:

In regards to the subject project, the US Army Corps of Engineers Welsbach Project Office is requesting approval from the NJDEP for use of the on-site gamma spectroscopy data as the basis for site release using established correlation factors that have been documented and revised over the course of project performance. These correlation factors will be used to determine the Th-230 and total thorium (Th-232 + Th-230) concentrations on a dry weight basis using the on-site gamma spectroscopy results rather than sending all Final Status Survey (FSS) samples off-site for Th-230 analysis by alpha spectroscopy.

This will expedite the remediation process and closure of the site and reduce off-site laboratory costs. For quality assurance purposes, a percentage of the FSS samples will continue to be analyzed by alpha spectroscopy (i.e., 10%) to verify and/or update the correlation factors as necessary.

Th-230 is an alpha emitter and cannot be quantified in the field or by the on-site laboratory. It has been project practice to analyze all FSS samples on-site by gamma spectroscopy and then ship the FSS samples off-site for Th-230 analysis by alpha spectroscopy. Using the on-site and off-site sample results to date, correlation factors have been established for quantifying the Th-230 and total Thorium concentrations based on the Th-232 sample results using the on-site gamma spectroscopy data.

REPLY TO

ATTENTION OF

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Over the project performance, correlation factors have been established and documented to estimate Th-230 concentrations based on the gamma emitting results for Th-232.

These correlations were developed using paired radioisotope concentration results presented in Revision 11 of the Welsbach/General Gas Mantle Superfund Site – Correlation Report, summarized below.

Analyte Correlation Factor Th-232 (< 2 pCi/g) Th-232 (2-10 pCi/g)

Th-230 0.9 0.4 Total Thorium 1.9 1.4

After appreciating the potential impact of Coal Ash Impacted Soils and Non Coal Ash Affected Soils, results for each soil type were subjected to further statistical analysis and it was determined that for low concentrations of Thorium-232, that the two soil types were essentially identical with respect to average (mean) correlation factors, though the absolute ranges (i.e., the extremes of the paired correlation factors) were different. For FSS, only two correlation factors were needed based on analysis of 327 paired results. A detailed analysis of the development of the correlation is provided in the Correlation Report.

Due to the presence of coal ash at the Gloucester Marine Terminal (GMT), a higher background has been established and investigation of paired samples results for Thorium -232 in the range of 2 to 10 pCi/g revealed a discernible difference warranting different correlation factors after examining 431 pairs of data, 325 for Coal Ash Impacted Soils, and 106 for Non Coal Ash affected Soils.

By this letter, six sets of factors useful for project execution are proposed. Four of these factors are similar to the values presented in the table above, indistinguishable from those values were an extra decimal place not provided in the Revision 11 dataset. After re-analyzing the paired results into newly segregated categories for soils in the range of interest [2 < x < 10 pCi/g for Th-232] there was sufficient difference between coal-ash impacted soils from non-coal ash affected soils to promulgate a new set of correlation factors for these soils. A copy of the Correlation Report and retrospective analyses will be provided upon request. As additional data is received, the data will be reviewed and the correlations verified and/or updated as necessary in accordance with the FSS specifications.

For FSS, 6 Correlation Factors (CFs) have been established based on the Th-232 concentrations as summarized in the following Table.

CFs, all soils Th-232 (x < 2 pCi/g) CFs, for 2 soil types: Th-232 (2 ≤ x ≤ 10 pCi/g)

Th-230 0.92 Coal Ash Impacted Soil 0.51 Non Coal Ash Affected Soil 0.43

Total Thorium 1.92 Coal Ash Impacted Soil 1.51 Non Coal Ash Affected Soil 1.45

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For the data associated with the GMT property, data was separated into two principal soil types/substrates (soils affected by coal ash, and other impacted soils not affected by coal ash). The coefficients for all soils above 10 pCi/g are not included in this letter as portable field radiation detection instrumentation is sufficiently sensitive that such material would be detected, excavated and would not be ambiguously within a grey region of sensitivity to identify non-coal ash affected soils (NCAAS) above 10 pCi to as high as 10,000 pCi for natural thorium. .

This office is proposing to use the above correlation factors to estimate the Th-230 and total Thorium concentrations using the on-site gamma spectroscopy data for FSS purposes both at the project wide remediation locations and the GMT property, respectively.

Your response to this request would be greatly appreciated. If you have any questions or require any additional information, please contact David Watters, USACE Health Physicist at David.J.Watters@usace.army.mil or 443-702-6177.

Sincerely, Brian J. Duffy, Contracting Officer’s Representative US Army Corps of Engineers Welsbach Project Office Gloucester City, NJ 08030 Tel. 856-742-5630 Ext.312 Mobile: 215-900-4511

Attachment

CF:

CB&I / Bruce Fox, Project Manager CB&I / Chuck Miscolcy, Field Supervisor CENAP-CT / Hope J. Edge, Contract Specialist CENAP-EC-CS / Brian J. Duffy, COR / Amado S. Domingo, PE, Project Engineer CENAP-DP-IS / Eric Charlier, Project Manager