ML20214D143

Forwards Draft Elevated Gross Beta in Wells at Sheffield Low Level Waste Site. Rept Provides Background Info & Discusses Possible Causes of Elevated Gross Beta Activity. Requests Comments by 861121

ML20214D143
Person / Time
Site:	02700039
Issue date:	11/04/1986
From:	Dale Goode NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS)
To:	Dunkelman M NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS)
References
NUDOCS 8611210375
Download: ML20214D143 (13)

Text

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[fjpturn to WM,6f335[-l- 5, 'f DGoode rf MEMORANDUM FOR: Maxine Dunkelman, Project Manager, WMLU MFliegel D%

FROM: Dan Goode, WMGT

SUBJECT:

ELEVATED GROSS BETA CONCENTRATIONS IN WELL SAMPLES AT SHEFFIELD LLW SITE The Sheffield low-level radioactive waste disposal site operator, U.S. Ecology Inc. (USEI), has recently reported gross beta concentrations above action levels in well 545 near a disposal unit. Detailed analyses by USEI indicates that this is caused by potassium-40, a naturally occurring radionuclide. In response to your verbal request and a request from J. Shaffner, WMLU, I have reviewed well construction information and other data relevant to this observation. The enclosed draft paper provides this background information and discusses possible causes of the elevated gross beta activity.

A deep natural source for potassium-40, and elevated ~ gross beta, is consistent with several observations on the site groundwater chemical composition. Gross beta increases in samples from deeper wells, and is often high in samples which indicate only background concentrr.tions of tritium. This would indicate that the elevated gross beta is not caused by releases from the shallow disposal units. However, the levels of gross beta (assumed to be caused by potassium-40) are inconsistent with measured potassium ion concentrations and the natural ratio of potassium-40 to stable potassium. Thus, although isotopic analyses indicate that the gross beta is caused by potassium-40, this level of potassium-40 activity does not appear consistent with a natural source.

Further review of available data may clarify the cause of these observed levels.

This observation illustrates some problems with using gross beta as a screening parameter for LLW site monitoring. In particular, determination of background and action levels may be very difficult, if other sites exhibit similar variations. Further investigation may be warranted on the general applicability of gross beta to groundwater monitoring at LLW sites.

Please provide any comments on the enclosed draft paper to me by 21 Nov 86.

Dan Goode, WMGT

Enclosure:

Draft background paper 8611210375 861104 JFC .

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4 DANG BETA BACKGROUND DRAFT 86/11/04 ELEVATED GROSS BETA IN WELLS AT THE SHEFFIELD LLW SITE

_ INTRODUCTION Elevated gross beta radioactivity was recently reported by US Ecology Inc.

(USEI) for a water sample from a monitoring well close to a disposal unit.

Detailed isotopic analysis by the operator indicates that the gross beta is caused by potassium-40 activity (see Appendix A). Analysis of samples from two adjacent, but shallower, wells indicate background levels of gross beta and tritium in one and slightly elevated tritium only in the other. The purpose of this paper is to present background information, including previous monitoring data, and to discuss possible causes of elevated gross beta in well 545.

MONITORING DATA In September 1986 USEI reported that the gross beta concentration in well 545 was above action levels (900-1300 pCi/1; see Appendix A). Tritium was reported to be at background levels. Well 545 is adjacent to the east end of Trench 18 (T18) (Figure 1). Two other wells within tens of ft of 545 were also sampled -

520 and 544. Both tritium and gross beta were reported to be at background levels in 520, the shallowest well (Figure 2). However, tritium was slightly elevated in 544 (2100 pCi/1), which is intermediate in depth. Detailed isotopic analysis by the operator indicates that the gross beta is caused by potassium-40 (K-40) activity (see appendix A). However, the interpretation of the isotpic analysis is subject to some uncertainty due to interference and other factors.

Previous measurements at these three wells are generally consistent with the recent results. Although the gross beta level in 545 has not previously been as high as 900 pCi/1, it has been much higher than the level in either 544 or 520 for some time (Figure 3). High gross beta (290 pCi/1) was previously reported by Weiss and Colombo (1980) for well 520 for a sample taken in June 1977 although most measurements are at background levels or below the reportint limit (about 3 pCi/l). Shallow well 519 at the opposite (west) end of T18 also previously contained gross beta above background.

Current data indicate a correlation between gross beta and depth at this location, as well as other locations at the site. The average gross beta level at several wells from Illinois Dept. of Nuclear Safety (IDNS) files are included in Table 1. Some of the elevations of the top of the screens are:

well 520 - 730 ft; well 544 - 715.8 ft; well 545 - 706.8 ft. The well screen for 520 is 4 ft long and the screens for 544 and 545 are 2 ft long (Foster et al. 1984c). In addition, each screen is in a different lithologic unit (see Figure 2). Other wells which indicate increased gross beta with depth include:

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555, 556, and 557 (north of site boundary); 547 (screened in the same formation as 545); and 535 and 550 (near T23). Some wells, however, indicate relatively

_ higher gross beta in sha'llower formations. These wells include: 519 and 553 -

(west end of T18); and 523 and 540 (near T11).

The recently reported tritium concentrations are also consistent with previous measurements. Results of tritium analyses performed on samples from these wells in 1985 by IDNS are shown in Table 2. As with gross beta, previous ,

samples from well 520 have indicated higher tritium than these recent measurements. Tritium in 520 was as high as 1680'pCi/l in 1978 (NRC 81).

TABLE 2 TRITIUM RESULTS FOR 1985 SAMPLING BY IDNS Well #'s '

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<300 USEI reported that a K-40 (radioactive potassium) concentration of about 600 pCi/1 is responsible for;the elevated beta level in 545 (Appendix A).

Unfortunately, previous samples from these wells '(520, 544, and 545) were not analyzed for K-40 in 1985 by IDNS. The typical detection or reporting limit for K-40 in IDNS records is about 150 pCi/1, so that somewhat elevated levels may go undetected. ,

NATURAL SOURCE As a gross screening measurement, gross beta includes many natural beta-emitting radionuclides. In particular, K-40 appears to be the source of elevated gross beta in well 545. There is some support for this hypothesis in that elemental potassium (K) concentrations are somewhat correlated with depth as is gross beta. However, concentrations of K measured are not sufficient to account for all of the gross beta detected in 545 and other wells.

9 K-40 is a natural isotope with a very long half life (1.3 x 10 yrs). About 0.012 percent of natural K is K-40. From this relationship, it can be calculated that if the concentration of K in solution is 1 mg/1, the concentration of K-40 is .84 pCi/1. Potassium increases with depth at the site, prchably due to dissolution of illites or other minerals in the shale and 4

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o DANG BETA BACKGROUND DRAFT 86/11/04 lacustrine clays beneath the glacial units. Potassium concentrations up to about 20 mg/l have been measured in deeper wells at Sheffield (Foster et al.

1984c), corresponding to about 17 pCi/l K-40. However, gross beta concentrations in these wells have generally been about 400 pCi/l (IDNS files).

Therefore, the observed K concentrations do not support the finding that the gross beta levels are caused by natural K-40.

The operator's recent analyses included pH determinations (Appendix A). The pH increases with depth at several locations (see also Foster et al.1984c). This may be caused by the same process causing elevated levels of gross beta.

Analyses by Piciulo and others (1985) indicate that geochemical conditions at the Carbondale Shale Formation surface are alkaline and strongly reducing.

Perhaps these geochemical properties could be related to the high gross beta levels.

If the gross beta is not from a natural source, it is possibly waste-derived as discussed in the following section.

LLW SOURCE Tritium has migrated from disposal units at Sheffield in several locations. In particular, offsite migration occurs in a pebbly-sand channel from the northeast side of the site to the strip-mine lake. Tritium has previously been detected above background levels in shallow well 519 at the west end of T18, and in 520 and 544. The highest activities reported are about 2 nCi/1, whereas activities in the pebbly-sand channel are about 200 nCi/1. Trench 18, which is isolated from the other trenches, contains very little tritium, less than 0.5 Ci (NRC 81). However, tritium concentrations in the T18 sump have been as high as 500 nC1/1 in 1985 (IDNS files). Most of the approximately 350 curies of activity in T18 is cesium 137 and cobalt 60.

Gross beta is high in samples from the T18 sump. In addition to Cs-137 and Co-60, elevated levels of K-40 are reported. Gross beta levels in monitoring wells vary considerably, but are generally below the action level for the site (60 pCi/1). Previously, a sample from well "V" had an elevated Cs-137 level (Dragonette et al. 1979). This well is near T14A, about 250 ft from T18.

Subsequent monitoring well samples have not indicated significant migration of Cs-137 or other radionuclides.

Trench 18 is located in an area where the sands and clayey sands of the Toulon Formation are not saturated. The underlying formations, which are saturated in the area, are believed to have a much lower hydraulic conductivity (Foster et al. 1984a). Because these units are also below the trench bottom, it is expected that if radionuclides were migrating from the disposal unit, tritium

s DANG BETA BACKGROUND DRAFT 86/11/04 would be detected first in the shallow wells near T18. However, the shallowest well (520) has background levels while the intermediate well, 544, has elevated

_ tritium. This may indicate some downward flow in the area of T18, perhaps coupled with a release a tritium from the bottom, and not the side, of T18.

The gross beta level in 544 is at background indicating that beta-emitting nuclides are not migrating to this well.

Two possible explanations for the elevated gross beta in well 545 would include the assumption of migration of beta-emitting radionuclides from the disposal units. For example, the gross beta detected in well 545 could be migrating from a part of the trench bottom distinct from the source of tritium in well 544. The radionuclides would follow a downward flow path, bypassing overlying wells 544 and 520. Recent head gradients may indicate such a downward flow path. As shown in Figure 4, the vertical head gradient in the area of well 545 is usually downward, and was especially high in 1981. Downward migration would also explain the elevated tritium in well 544 which is not present in 520.

A second waste-derived explanation is that well 545 lies in a pathway of radionuclides released from other trenches south of T18. If the weathered shale or bedrock surface acts as a significant conduit for flow (where the sandy clay unit is not saturated) then beta nuclides could be migrating to well 545 via a relatively deep pathway from T14A, or other trenches. A water table contour map by USGS indicates that releases from T14A would generally flow east-northeast. Flow modeling results indicate a more northern flow path (Garklavs and Healy 1986) which would be consistent with this hypothesis. In this area, the pebbly-sand Toulon member is generally not saturated and where it is saturated the unit is more silty than on other portions of the site (Garklavs and Healy 1986). Notably, T14A contains large amounts of Cs-137 and Co-60, and gross beta concentrations in the T14A sump have been as high as 200,000 pC1/1 in 1979. Wells 538, 539, and "V" between T14A and well 545 (Fig.

1) have also exhibited high gross beta. Maximum gross beta concentrations were 1200 pCi/l in 538 (deep) and 600 pCi/1 in 539 (shallow) in 1981 (IDNS files).

Well "V" had a maximum concentration of 100 pCi/1 in 1980 (IDNS files). Well "V" also exhibits high tritium, about 400 nCi/1 in 1985 sampling by IDNS.

Trench 14A also has high levels of Co-60, Cs-137, Sr-90, and K-40. Analyses on three samples from "V" and one sample from 539 taken in 1980-81 by IDNS indicate K-40 levels below the reporting limit.

SUMMARY

AND DISCUSSION Gross beta levels in well 545 which have exceeded action levels are attributed to K-40 by the operator. However, this level of K-40 is not consistent with a natural source and normal ratios between K-40 and stable potassium. The operator's conclusion is supported by the increase in gross beta with depth at

DANG BETA BACKGROUND DRAFT 86/11/04 several, but not all, locations. However, potassium concentrations are not sufficient to account for the K-40 concentrations unless fractionization is

. occurring or a concentrated source is present. Thus, although the operator's analyses indicate the gross beta level is due to K-40, the observed levels are inconsistent with normal natural conditions. Furthermore, high gross beta in shallow wells adjacent to trenches indicate that some beta-emitting radionuclides are migrating from the disposal units.

In general, the use of gross beta as a screening parameter is complicated by the natural occurrence of K-40, and perhaps other natural nuclides, at the Sheffield site. At this time insufficient information exists to establish a background level for gross beta at the site. Furthermore, the gross beta action level should perhaps be adjusted depending on depth of the formation screened.

REFERENCES Dragonette, K., J. Blackburn, and K. Cartwright, Interagency task force report on the proposed decommissioning of the Sheffield nuclear waste disposal site. Report submitted to the U.S. Nuclear Regulatory Commission and the State of Illinois. 1979.

Foster, J.B., J.R. Erickson, and R.W. Healy, Hydrogeology of a low-level radioactive-waste disposal site near Sheffield, Illinois, U.S. Geological Survey Water-Resources Investigations Report 83-4125, 1984a.

Foster, J.B., G. Garklavs, and G.W. Mackey. Hydrogeologic setting east of low-level radioactive-waste disposal site near Sheffield, Illinois, U.S.

Geological Survey Water Resources Investigations Report 84-4183, 1984b.

Foster, J.B., G. Garklavs, and G.W. Mackey. Geologic and hydrologic data collected during 1976-1983 at the Sheffield low-level radioactive waste disposal site and adjacent areas, Sheffield, Illinois. U.S. Geological Survey Open File Report 83-926, 1984c.

Garklavs, G., and R.W. Healy, Ground water flow and tritium movement at a low-level radioactive-waste disposal site near Sheffield, Illinois, U.S.

Geological Survey Water-Resources Investigations Report 85-DRAFT,1985.

(has been approved for publication, 1986)

Illinois Department of Nuclear Safety files, radiological analyses at the Sheffield LLW site, compiled by Yvonne Young, WMLU, NRC.

- s DANG BETA BACKGROUND DRAFT 86/11/04 MacKenzie, D.R., J.F. Smalley, C.R. Kempf, and R.E. Barletta, Evaluation of the radioactive inventory in, and estimation of isotopic release from, the waste in eight trenches at the Sheffield low-level waste burial site, U.S.

Nuclear Regulatory Commission NUREG/CR-3865,1985.

Nuclear Regulatory Commission. Interim environmental appraisal, Sheffield low-level radioactive waste disposal facility, Sheffield, Illinois.

Unpublished report prepared by Low-level Waste Licensing Branch, Division of Waste Management. 1981.

Piciulo, P.L., C.E. Shea, and R.E. Barletta, Analyses of soils from an area adjacent to the low-level radioactive waste disposal site at Sheffield, Illinois, USNRC NUREG/CR-4069, 1985.

Weiss, A.J., and P. Columbo, Evaluation of isotope migration - land burial, U.S. Nuclear Regulatory Commission, NUREG/CR-1289,1980.

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r\@ gGilg\MDATE:

S. V. Wright September 29, 1986 TO:

FROM: E. D. Martinez M REF: l USGS Well 545 at Sheffield Facility CC: TSB, RES, MSC

SUBJECT:

RBR, RLA, fB

. SI File  ;

i Telephone conversation with Dr. Hewitt Jetter on September 23 and 25, 1986 concerning USGS Well 545 show that the gross beta activity in the sample is due to potassium -40.

Teledyne has performed gross beta analysis on three separate samples. These zamples were also analyzed for gross beta minus potassium -40. The second method consisted of a precipitation method which will precipitate all beta emitters except potassium -40. The results are as follows. All analysis performed on the dissolved fraction.

Gross Beta Minus Gross Beta Potassium -40 Teledyne Sample 1 (pCi/L) (pCi/L) 72577 910 1 30 Less than MDA

• 76774 1300 1 100 Less than MDA

• 77064 990 1 20 Less than MDA *

• MDA = minimum detectable activity.

Teledyne also performed an evaluation of the beta activity, as normally analyzed and calculated based on Cesium - 137 versus a potassium -40, instrument efficiency. This evaluation showed that the gross beta activity (Teledyne 677064 collected 9/17/86) was 990 1 20 pCi/1 based on Cesium -137 and 678 pCi/l based on potassium -40. The gamma spectral analysis showed that the sample had a potassium -40 activity of 635 1 52 pCi/1 potassium -40. A comparison of the gamma result for potassium -40 and the gross beta based on potassium -40 are in good agreement.

Specific analysis for Strontium -90 and Technicium -99 showed that no activity was detected above the MDA's of 2 pCi/l and 4pCi/1, respectively.

The site collected samples from well 545 and T-18 east sump for pH analysis.

Samples were taken prior to and after voiding the well of three casing volumes. These results are:

1

. < t U. S. ECOLUGY, INC.

August 1, 1986 ,

PAGE 2 j ELEV. TOP ELEV. TOP ID. 7-31-86 11-13-81 ,

No. SUMP SUMP REMARKS PIPE GROUND PIPE GROUND sump 18S 760.02 758.7 760.33 - Note 2 Sump 18E 759.67 757.5 759.69 - Note 3 Note 2: 7-31-86 Top of Plain End Pipe, 3" PVC, Low side with cap and adaptor removed.

Depth to water 17'-9 1/2", 7-31-86 9 3:30 PM Note 3: 7-31-86 Top of Plain End Pipe, 6" PVC, Low side with cap removed. Depth to water 16'-3", 7-31-86 9 3:40 PM i

If you have further questions regarding the data, please feel free to call.

Very truly yours, DAILY & ASSOCIATES, ENGINEERS, INC.

tis E. Michels, P.E.

Vice President OEM/ALH:su cc: Hal Hackett .

Louisville i

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