ML20215K879
| ML20215K879 | |
| Person / Time | |
|---|---|
| Issue date: | 03/31/1983 |
| From: | Odonnell E NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | Conti E, Dayal R, Fischer J BROOKHAVEN NATIONAL LABORATORY, INTERIOR, DEPT. OF, GEOLOGICAL SURVEY, NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| Shared Package | |
| ML20215G205 | List: |
| References | |
| FOIA-87-235 NUDOCS 8706250476 | |
| Download: ML20215K879 (44) | |
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MAR 31 1983
' Those on the Attached Distribution
Dear Panel 'iembers:
Attached for your information and use is a copy of the panel's report on " Initial Research Observations at Maxey Flats Which are Relevant l to Site Closure". We want to thank you for your contributions during our meeting in Reston and for your review comments on the early drafts of the report. We are still planning to go foreward with the Comprehensive Report which will integrate and assess the significant findings of the research conducted at :laxey Flats and we will contact you further on that report.
Sincerely, sw s. w d h _._ a /C Edward O'Donnell Waste Manag'ement Branch Division of Health, Siting, and Waste Management Office of Nuclear Regulatory Research
Enclosure:
As stated i
8706250476 870616 PDR FOIA i MINTONB7-235 PDR
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)R2?*** H p + m ~ 3 INITIAL RESEARCH OBSERVATIONS AT MAXEY FLATS WHICH ARE RELEVANT TO SITE CLOSURE Deliberations of.a Research Panel
-'. Convened November 30 and December 1, 1982 Reston, Virg' inia Panel Chairman: Jared J. Davis, NRC, Office of Nuclear Regulatory Research Panel Members: Enrico F. Conti, NRC, Office of Nuclear Regulatory Research Ramdsh Dayal, Brookhaven National Laboratory John Fischer, U. S. Geological Survey John F. Kendig, NRC, Office of State Programs Doyle Mills, Commonwealth of Kentuckp Edward O'Donnell, NRC, Office of Nuclear. Regulatory Research.
Roger Pennifill, NRC, Office of Nuclear Material Safety and Safeguards Richard W. Perkins, Pacific Northwest Laboratory i W. L. Polzer, Los Alamos National Laboratory l David E. Robertson, Pacific Northwest Laboratory John B. Robertson, U.S. Geological Survey Robert Schneider, U.S. Geological Survey Robert K. Schulz, University of California, Berkeley e.
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m INITIAL REVIEW 0F RESEARCH OBSERVATIONS AT MAXEY FLATS
, WHICH ARE RELEVANT TO SITE CL'05URE 1 INTRODUCTION During the past few years, the U.S. Nuclear Regulatory Commission (NRC) has conducted research at the Maxey Flats LLW Disposal Facility. to determine the processes which are occurring relative ,to degradation of radioactive materials within the burial trenches, the chemical and physical characteristics of the trench leachates and the key geochemical controls governing.the leachate char-acteristics, the chemical forms of the leached radionuclides, the mobility .of these radionuclides, their subsurface and surface transport processes, the l biological uptake, the development,of environmental monitoring strategies, and other factors which influence the long-term fate of the radionuclides. In addition, the U.S. Geological Survey (USGS) has conducted extensive hydrogeo-logical studies which have provided insight into the possible mechanisms of water movement. The Commonwealth of Kentucky has carried out extensive moni-toring programs of environmental radioactivity levels both in their private j laboratories and under contract with their past and present site operation l
contractors.
The primary objective of the present and future management of the Maxey Flats Disposal Facility should be to insure the protection of the general population living near the site from releases of radioactive materials. This will require a reasonable isolation of the radioactive wastes contained on site, such that .
any radioactive materials released to the environs do not result in an annual dose to man that exceeds recommended regulatory limits throughout the institu- 1 tional and passive control phases of the site. In addition, the ALARA concept of maintaining radionuclide releases to the environs as low as reasonably achievable should continue to be an integral part of the management plan.
Studies currently sponsored by the NRC which are investigating Maxey Flats include the following:
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o Geochemical evaluation of isotope migration at LLW sites (Brookhaven National Laboratory) o Burial ground -site survey (Commonwealth of Kentucky) l o Waste radionuclide migration in soils at the Max'ey Flats shallow land burial site (Los Alamos National Laboratory) o Chemical species of migrating radionuclides at shallow land burial sites (Pacific Northwest Laboratory) o Study of unsaturated zone hydrology at Maxey Flats (University of California - Berkeley)
On November 30 and December 1, 1982, a pane'l of researchers and administrators (see cover page) was convened at the USGS National Headquarters in Reston, Virginia, to outline and summarize the available information on Maxey Flats which is pertinent to closure of the disposal f acility. This report is the result of those deliberations and is an initial resource document which can be used by the, Commonwealth of Kentucky to assist them in developing a' closure plan for the site. This document is not intended to provide a plan of actions that should be taken to close the site. Instead, it examines available data, summarizes important observations, and draws conclusions relating to those observations. It is intended to provide an initial review of research observa-tions which are relevant to site closure. A more extensive review of those observations and the past and current research relative to site closure is under way and will be published later.
2 STATEMENT OF THE PROBLEM Observations to date show that water infiltration and accumulation in the waste trenches has been the primary problem at Maxey Flats. Since the waste trenches are located in media of low-hydraulic conductivity, water that infiltrates through the trench cap accumulates in the trenches and was overflowed in the past. This is referred to as the " bathtub effect." The accumulated water e
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accelerates the degradation and dissolution of the waste material, helps l mobilize the radionuclides, and acts as a driving force for subsurface trans- >1 port of the' radionuclides. If the trenches fil1 and overflow, then radionu-clides can be transported directly to the surface. The large inventory )
(presently about 300,000 curies) of tritium in Trench 31, which exists as , I mobile tritiated water, is of major concern during the first 100 years of closure when institutional control may'be needed because it could be trans-ported offsite in the groundwater flow. Thus, continued accumulation of water n in the waste trenches, particularly during the short term (abo'ut 100 years),
is undesirable.
The panel identified at least 14 specific issues which should be considered in developing a closure plan for the Maxey Flats disposal facility (see Section 3),
all of which gener' ally stem from the following site conditions:
o Subsidence of waste trench covers l
l o Water accumulation in the trenches -J o Waste trench leachate contains high tritium concentrations and' complexed forms of other radionuclides o Complicated hydrogeology, including fracture flow, which makes prediction of subsurface radionuclide. transport and radiol'ogical surveillance difficult All of the available data relating to these conditions which seemed pertinent 1 to site closure were examined to provide a summary lof .important observations.
These observations were then interpreted in the form of conclusions which addressed the various problems relating to site closure, and which would be essential to consider in developing a decommissioning plan for the site. 4 03/22/83' ~3 'MAXEY. FLATS RESEAR'CH OBSERV.
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3 SITE CHARACTERISTICS
- Maxey Flats is an isolated plateau in northeastern Kentucky approximately 19 km from the City of Morehead. The radioactive waste b'urial cite is located on'the plateau about 90 to 122 meters above the su'rrouncing valleys. Radioactive, waste
, burial at Maxey Flats began in 1963. Completed trknches at the site vary from 6 to 12 meters deep (20 to 35 feet) and occupy an area of about 0.08 square kilometers (25 acres). As of January 1978 0.13 million cubic meters (4.75 million cubic feet) of nuclear waste consisting of approximately 2.4 million curies of byproduct material, 431 kg of special nuclear material, S41,769 kg of source material and a'pproximately 63 kg of plutonium, had been buried there.
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Rocks exposed in the Maxey Flats area consist of nearly horizontal bedded siitstones, mudstones, sandstones, and shales of Mississippian, Late Devonian to Silurian Ages including, in descending order, the Nancy and Farmers Members of the Borden Formation, Sunbury, Bedford, and Ohio Shales, and upper part of the Crab Orchard Formation. The total thickness of these rocks is about 98 meters. All radioactive wastes are buried in the Nancy Member. The Nancy Member is predominantly a silty shale with a few lenses of siltstone 2-12 cm thick and a 25-100 cm thick sandstone bed that, forms the bottom of many trenches.
Because of its. induration, coly a few trenches pass through this sandstone.
Mean annual precipitation at Maxey Flats is about 115 cm. (This value is the average of the annual precipitation at Farmers, Kentucky for 1948-1977.) Infil-trating rainfall is temporarily stored in regolith on the hilltop, deeper unweathered bedrock beneath the hilltop, and in colluvium and soil on hillsides.
t Discharge occurs by lateral flow from the reg'olith and bedrock to the sides of hills or to alluvium in valley bottoms. Well yields are low in all rock forma-tions at Maxey Flats, and most groundwater movement is through secondary openings, particularly through fractures (Zehner, 1979). The groundwater system'at Maxey Flats is probably unconfined, and recharge occurs by (1) infiltration of rain-fall into the regolith, and (2) vertical unsaturated flow from the regolith at the top uf the hill to saturateo zones in the Farmers Memb'er and Ohio Shale.
Some recharge could occur as lateral flow to rock from hillsides, but the
- For a more detailed description of the site characteristics and history, see Clancy et al., 1981, and Zehner, 1979.
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D significance of this method of recharge is not known at this time. Thus the very low permeability'of the regolith and unweathered rock beneath Maxey Flats results. in water accumulation in the waste-filled trenches.
4 SPECIFIC ISSUES TO BE CONSIDERED IN DEVELOPING A CLOSURE PLAN FOR THE MAXEY FLATS LLW DISPOSAL FACILITY l
There are numerous issues that need to be considered in developing a closure plan for the Maxey Flats Disposal Facility. These include some problems that result from the high rainfall, the percolation of water through the trench caps, the impermeability of the media in which trenches were excavated which results in the accumulation of water, and the.possible overflow of trench leachate through the trench caps. Key issues and problems which have been identified are summarized below.
(1) Water infiltration and accumulation in trenches.
I (2) Relatively high radionuclide concentrations, especially tritium, in trench leachate. l (3) Subsidence of trench covers.
(4) Uncertainties as to the waste forms which are readily'leachable.
(5) Trench water chemistry which enhances radionuclide mobility.
(6) Subsurface migration of radionuclides and other leachate constituents.
(7) Complex hydrogeology that complicates the prediction of migration patterns.
(8) Surface contamination associated with site operations.
(9) Offsite transport of radiontclides by surface runoff.
(10) Erosion processes that threaten the integrity of the site, 03/22/83 5 MAXEY-FLATS RESEARCH OBSERV 1
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(11) Dispersion of tritium and possibly other radionuclides in the evaporator plume.
, (12) Biological pathways and uptake of radionuclides. -
(13) Lack of effective monitoring methods.
(14) Nonradiological toxic materials in waste trenches.
In the following section, each of these problem areas is briefly discussed and j 1
the relevance of the problems to site closure is considered. l J
- 1. Water Infiltration and Accumulation in Trenches l
Water infiltraticr. and accumulation in the waste-filled trenches has been a l i
problem at Maxey riats. The problem has been aggravated by subsidence, which results in the pe* iodic failure of trench caps even though they have been repaired many times. The permeability of the geologic mecia in which the trenches are located is relatively low, partic-ularly when contrasted with the trench caps. Infiltratica through the trench caps has greatly exceeded the rate of subsurface transport of water from the trenches. To avoid excessive accumulation, the water in trenches is periodic-ally pumped and disposed of by evaporation. A long-term solution to the- I accumulation of water in the trenches must include a means of avoiding water infiltration.
Recent remedial action by Kentucky involving land surface buildup, surface l
. drainage construction surface regrading, and installation of a temporary plastic cover (PVC) over approximately_3/4 of the burial trenches in 1981-82 )
a has greatly reduced water infiltration into the waste burial trenches. This reduction of infiltration has been demonstrated by reduced increase in trench water levels and decreased soil moisture content in the top 0.9 to 1.5 meters of soil in areas where the plastic cover did not contain h9 es.
1 However, the water level in some of the PVC covered trenches has continued to increase although at a much slower rate (Mills, October 27, 1982, verbal communication),.
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presumably due to infiltration of water through uncovered areas such as road- l ways, and via leakage through the plastic cover part'icularly near drain areas. l The decreased infiltration of water into some of the waste trenches has caused I increased tritium concentrations in the trench leachates due to limited dilu-r tion of the tritium leaking from waste containers. Such leachates now contain i tritium concentrations above the levels permitted for processing t'brough the l evaporator, used at Maxey Flats to dispose of trench water, unless they are diluted with less contaminated water. This has inhibited the ability to dewater j i
these trenches. 8 9
The outflow of groundwater through the bottom of the trenches to the rocks immediately beneath them has been estimated by the USGS (Zehner, verbal ,
a communication October 26, 1983) to be only about 0.03 cm per year. Therefore, j an impermeable cover would have to restrict water infiltration in the region of the trenches to no more than 0.03 cm per year to prevent the eventual accu- ;
mulation of water in the trenches. Since the average annual precipitation at the site is 115 cn/yr, an impermeable cover would have to be about 99.98%
effective to prevent water accumulation in the trenches. g
- 2. Subsidence of Trench Covers '
Trench covers need to be designed to provide structural integrity which will j prevent surface water penetration. Subsidence of trench covers may,be a problem that will require continual monitoring and appropriate remedial action ,
for the next several decades. Any permanent decommissioning of the Maxey Flats I
j site will have to contend with this as a potential, yet real long-term problem.
Subsidence could structurally damage either an engineered impermeable cover i
(e.g., asphalt surface or concrete tiles), or a contoured vegetated cover. This j could allow water to infiltrate into the waste trenches and could possibly l i
result in the transport of radioactive and nonradioactive contaminants offsite.
l Therefore, it appears inevitable that some maintenance will be required for the
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short term (up to 100 years) to limit infiltration into waste trenches unless !
the material in the, trenches can be stabilized. 1 I
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- 3. Radionuclide Concentration in Trench Leachate Some of the radionuclides contained in the waste forms buried in the trenches tre highly leachable, which has resulted in conside'rable amounts of several 4 i
radionuclides (Sr-90, CS-137, Pu) accumulating in the trench leachate. Anpther important source is tritium which escapes into the trench water as buried tritium containers fail. The concentrations of tritium in leachate range up to l 105 pCi/f. Concentrations of up to the Ci/2 range occur for several other {
1 radionuclides (e.g., Sr-90). Consideration should be given to methods which l
'g could minimize the leachability of radionuclides from these wastes. Such tech-t l
I niques as in situ waste solidification may be useful; however, it is clear that if infiltration of water could be completely stopped, and if the trenches could be completely dewatered, then fur ther leaching of the waste would probably be ]
eliminated.
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- 4. Uncertainties As To Waste Forms Which Are Readily Leachable This topic is closely related to item 3. The fact that the waste was not solidified prior to disposal has resulted in some radionuclides being disposed of in readily leachable forms. For example, many of the decontamination ,
reagents which contain complexing substances were disposed of in containers which have subsequently failed. Thus, soluble and mobile forms of plutonium and some other radionuclides are present in trench leachate and can possibly migrate by subterranean routes in. groundwater.
- 5. Trench Water Chemistry Which Enhances Radionuclide Solubility This topic is directly related to items 3 and 4. The waste leachate is highly anoxic, which results in plutonium being mainly in the Pu*3 and Pu*4 valence state. These chemical forms of plutonium are readily complexed by EDTA and perhaps other complexing a' gents which are present in decontamination solutions.
These complexing agents, together with container and waste degration products
. including carboxylic acids, enh'ance the solubility of plutonium, Co-60, Cs-137, Sr-90, and perhaps other radionuclides.
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- 6. Subsurface Migration of Radionuclides and Other Leachate Constituents Subsurface migration of radionuclides appears to be mainly through fractures in the rock. Because this is a relatively slow process, compared to surface flow, the opportunity for long distance migration seems rather limited. How-ever, movement of radionuclides by subsurface transport is difficult to trace and the extent of subsurface migration has not yet been fully established.
Recent observations based on tritium in the leaves of trees growing around the site perimeter, and concentrations in monitoring Wells 11E and 13E suggest that some subsurface transport of tritiu'm to offsite locations (particularly near Trench 31) has already occurred (PNL, 1982 unpublished data). This correlates with the lateral flow rate of the onsite groundwater which has been observed by the USGS, near Trench 46 to be as much as 14 to 17 meters per year (Zehner, October 26, 1982, verbal communication). However, the relative contributions of tritium in the discharge plume from the evaporator, which has been used to dispose of trench water, and surface pathways have not yet been fully assessed.
Within the saturated conditions of the trenches the waste trench leachates are strongly anoxic. The radionuclides that are dissolved in trench water and groundwater have been observed to be present in organic complexed chemical forms.
However, as the leachates move away from the trenches, they become more'oxic, resulting in a decrease in pH and an increase in Eh and a series of chemical changes in soil chemistry such as in the partial oxidation of Fe+2 to Fe*3 These changes affect the chemical speciation of the radionuclides, thus affect-ing their migration rates and retention in the surrounding soil. While the full impact of these changes cannot be precisely defined at the present, it
, appears that plutonium retention by the soil is substantially enhanced by the transformation to oxic conditions.
s Another factor which affects the subsurface migration of radionuclides is the presence of chelating agents such as EDTA and other polar organic compounds which can occur in the waste leachates. These substances appear to have com-plexed with plutonium, Co-60, and possibly other radionuclides, thus enhancing their ability to migrate in the onsite groundwater. No subsurface migration e b 03/22/83 9 MAXEY FLATS'RESEARCH OBSERV
l of these radionuclides to the offsite environs has yet been observed with cer-tainty. According to Zehner (written commun.ication February 15, 1983), 1974-75 L Kentucky' Department of Human Resource data showed concentrations of Pu,'Sr-90, and H-3 above world fallout levels, but he noted surface and subsurface routes have not been verified. Currentl,y, except for tritium, radionuclide concentra-tions are at world background levels and some onsite movement away from the waste trenches has been observed. Manganese-54 and Co-60 have migrated over 60 meters at one location (near Tren'ch 46), and Co-60, Sr-90, and plutonium isotopes have moved 7 to 12 meters at other locati.ons (near Trench 27 and near
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Wells UB1 and UB1A).
- 7. Complex Hydrogeology that Complicates the Prediction of Migration Patterns Because of the very complex hydrogeology at the Maxey Flats site, it is 1
extremely difficult to predict migration patterns. Available information !
suggests that in or. der to determine the rate and extent of subsurface migra-tion, it will be necessary to do additional monitoring at the site. 1 The uncertainty in estimating groundwater flow rates is quite high and it is complicated by limited knowledge of the hydrologic properti.es of the strata beneath the site and the patterns, extent, and dimensions of fractures in that
, strata. Observatnns at the experimental trenches near Trench 27, the. Wells UB1 and UB1-A, and rear Trench 46 indicate fracture flow of groundwater at rates up to 17 meters / year. (This estimate comes from the detection ~of Mn-54 and Co-60 migration near Trench 46; Zehner, verbal communication October 26, 1982.) A limited series of laboratory tests of cores from the Nancy ~ Member had c much lower hydraulic conductivities ranging from 0.003 to 1.0 cm/ year (Emcon Associates, 1975). Base flow to the streams adjoining the Maxey Flats (Rock
, Lick Creek, Orip Springs Hollow, and the unnamed stream to the east) is apparently also quite low. Zehner (verbal communication, October 26, 1982) has estimated the discharge of water from the Maxey Flats disposal trenches to the.
rocks immediately beneath them to be.0.03 cm/ year and he estimates that by the
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time this water reaches the streams adjoining the site it will have a mean dilution with water from the colluvium on the hillsides bordering the disposal facility of 2000X.
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- 8. Surface Contamination Associated with Site Operations Observed of fsite contamination of soil and sediment with. traces of C)-6.0 ar.d Pu-238 is apparently the result of surface runoff f' rom'the site whier t r.ir. s -
ported mildly contaminated soil. The onsite soil contamination prcbatly resulted from contamination of surface soil by spillage during the initisi burial operations, erosion of contaminated soil from burial areas whety. waste has been exposed due to insufficient soil cover, from accidental releases of trench leachate during pumping for processing in the evaporator, er ' rom cther surface releases or from fallout from the evaporator plume.
- 9. Offsite Transport of Radionuclides by Surface Runoff The high rainfall at Maxey Flats has caused rapid surface runoff, resulting in I surface transport of contaminants deposited by site operations. Radionuclioes which have been observed offsite (such as Pu and Co-60), with the pM sible l exception of tritium, appear to have most probably resulted from surface flow which results from heavy rainfall on the disturbed soil surface. Unf)rtunately, the offsite surface contamination complicates the problem of defiring subsur-
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face flow. Groundwater discharge may also possibly be contributing to offsite ,
contamination. It will be necessary to develop a measurement protccel which l allows one to distinguish between surface runoff carrying radioactise materials and subsurface transport of radionuclides.
- 10. Erosion Processes that Threaten the Intecrity of the Site The Maxey Flats disposal facility is located on a relatively flat t.p'and and bounded by slopes. Because of this, erosion is a potential hazaro to site integrity and it should be addressed by any long-term site closure plan. It !
Should be noted that any onsite remedial action designed to reduce infiltration will increase surface runoff and the potential for erosion.
03/22/83 11 MAXEY FLATS RESEARCH 0BSEPV -
- 11. Dispersion of Tritium and Possibly Other Radionuclides in the Evaporator Plume l
Virtually all of the tritium in the trench leachate' pumped from the trenches is vented to the atmosphere through the evaporator. This has resulted in a r,ather low but measurable contamination of the immediate environs of the site. Other radionuclides are also present in the evaporator plume, but our observations have shown that deposition of them in the surrounding environmen't are insignif-icant compared to radioactivity from fallout. Thus, while the evaporator plume complicates the background concentrations through the addition of tritium to the environs, it does n'ot contribute significantly to other radioactive contami- l nation and would not appear to present a long-term problem following discon- I
, tinuation of its use and site closure. l
- 12. Biological Pathways and Uptake I l
l Radionuclide transport via biological pathways seems to be minimal at the present time except for tritium. However, levels of other radionuclides in the '
biota may rise if containment f ails and certain rcdionuclides, e.g. , Cs-137 and Sr-90, migrate to areas where they can be intercepted by plant roots and animals, Readily measured concentrations of tritium have been observed in fescue grass grown directly above the waste trenches; and also in the leaves and sap of trees growing near waste trenches containing high tritium levels. While no' serious radiological problems associated with plant uptake appear to exist, the bio-logical uptake pathways may prove to be useful in monitoring subterranean trans-port of radionuclides, particularly tritium.
- 13. Lack of Effective Monitorina Methods' Because of the complex hydrogeology, it is difficult to develop an effective monitoring system for detecting subsurface radionuclide migration. The problem is one of sampling for.radionuclide movement in a fracture flow regime where
- the fracture geometry is imperfectly known. Most fractures are oriented nearly
, vertical so conventional vertical wells,must be supplemented by other methods.
The panel discussed, without making any recommendations, the following methods 03/22/83 12 MAXEY FLATS RESEARCH OBSERV I
which might.be used to monitor radionuclide movement; inclined wells designed to intercept fractures (N.B. inclined wells were recognized as a very expen-1 sive method in which the data gathered might not justify the cost), monitoring I trenches along the perimeter of the site, porous cups, measurements of base flow into the streams adjoining the site during low flow periods, and wells in the colluvium on the slopes bordering the site. Vegetation, particularly trees, could be used'to detect the leading edge of any tritium plume moving offsite.
l 14 Nonradiological Toxic Material in Waste Trenches It has been observed in preliminary measurements that several toxic substances (e.g., barbiturates, chlorinated hydrocarbons) are present in the waste trenches in addition to radionuclides. These toxic substances should be identified and the degree of their movement relative to tritium should be determined. Parti-cular attention should be given to the degree of degradation of toxic materials
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as they move away from disposal trenches and, if desirable, to means of enhanc-ing in situ degradation of those compounds in trenches.
5 OBSERVATIONS AND CONCLUSIONS RELATING TO SITE CLOSURE Much of the research that has been conducted at Maxey Flats by the NRC, USGS, EPA, and others has been of a somewhat generic nature, and has not necessarily been directed toward the specific objective of site closure. However, essen-tially all of this research has addressed problems at Maxey Flats which ar? of concern in the development of a site closure plan. This section of the report summarizes those research observations which appear to be most relevant to site closure. The following observations have served as a basis for developing con-clusions which are of concern to site closure. These observations and conclu-sions are grouped into seven different categories addressing the various problem areas outlined in Section 3.
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4 5.1 Hydrooeology Observations Conclusions
- a. The discharge of water from the A very:small portion of the average disposal trenches to the rocks 115 cm of precipitation perco,lates below them is about 0.03 cm/ year. deeply into bedrock below the trenches. This indicates a very low By the time this water reaches the streams adjoining the site, it will volume of groundwater (and quantity have a mean dilution with water of dissolved radionuclides) in the from the colluvium on the hillsides bedrock beneath the site, bordering the. site 'of 2000X.
- b. Subsurface materials have very An effective groundwater monitoring low primary permeability. However, system would need to be designed to they are frequently fractured, and adequately sample fracture flow.
the fractures transmit water. Accurate modeling of groundwater Virtually all groundwater flow flow within the site boundaries occurs in the fractures. Based on would be very difficult.
radionuclide information at one location, the rate of flow through fractures is estimated to be approximately 14 to 17 meters /yr.
The groundwater system is highly nonuniform (Zehner, 1979).
5.2 Unsaturated Zone Hydrologic Transport Observations Conclusions
- a. From relative soil moisture The accumulation of water in the readings, tritium movement, trenches (bathtub effect) is cau. sed rapid response of water levels in by the. permeability of the trench trenches to rainf all ' events, and caps which permitted water infiltra-organic tracer movement, it was- tion into the trenches accompanied f
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Observations Conclusions found that the principal mode of by relatively impermeable undisturbed Jy water, entry into the trenches was material between and beneath the k.,, by percolation through the trench trenches. In order to inhibit
- cover and that little occurred by surface water infiltration into the lateral movement within the soil trenches, an effective trench cover profile. It was also found that must be' designed and constructed.
the vertical permeability of the Trench cap design must address-undisturbed soil profile 8 meters controlling permeability and from Trench 19-S was very low subsidence.
-(Schulz, 1982 UC8 Ref. 3).
5.3 Waste Form and Leachate Characteristics Observations Conclusions
- a. Most trench wastes exhibit a Trench waste compositions reflect a strongly developed anoxic regime, cGmbination of two processes: (1) characterized by high alkalinity interaction'between the waste-and and NH , and low S04 2 , N05 ,and accumulated water, and (2) the effects dissolved oxygen s High concentra- of bacterial decomposition'of organic I tions of waste-derived components, matter. The' extent to which trench such as radionuclides, Fe2 +, dis- wastes are modified r. elative to the solved organic carbon, etc., were groundwater reflects the' length of also observed (BNL Ref. 1; L@ L; time that water is.in-contact with the PNL). waste, groundwater chemistry, and the- I intensity of bacterial' action.
- b. Water in the experheental trenches Indicates possible transport by 41 located about fe.8 meters from subsurface flow from nearby trenches Trench 27 exhibits an anoxic water and_ suggests that radionuclides.
chemistry (low 50 4 2 , high alkalinity, may have migrated beyond the experi-y and Fe2 +) and the presence of radio - mental t'rench location. -
nuclides, the concentrations of which f}
are intermediate between the trench j
.leachates (26 and 27) and well water
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(UB1-A) (BNL Reference 1).
03/22/83 15 1 MAXEY_ FLATS RESEARCH OBSERV.
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Observations Conclusions
- c. Groundwater becomes more oxic These changes indicate that the
{- with increasing lateral distances in situ trench water chemisi,ry is
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up to about 3 meters from the highly sensitive to conditions that waste-filled trenches. Exposure are encountered as the water poves of strongly anoxic trench waters away from the immediate trench to oxygen initiates a series of . vicinity. These changes affect the irreversible changes such as chemical speciation of the radio- l partial oxidation of Fe + to Fe *,
2 3 nuclides, generally reducing their and also decrease in pH and solubility and thus affecting their increase in Eh (BNL Ref. 2, 3; migration rates and retention in
. LANL; PNL), the surrounding soil.
, c. Numerous organic compounds have The presence of these compounds can been identified in CH 2Cl 2 and enhance the migration of some radio- l CHCl 3 extracts of trench waters. nuclides that may leach from buried Some of these compounds are known wastes.
, to act as chelating agents for '1 radionuclides (BNL Ref. 1; PNL). l
- e. Plutonium has been observed to occur The mobility of plutonium and Co-60 mainly as an anionic complex and in is probably enhanced by forming the +3 or +4 valence states in both soluble EDTA complexes.
trench leachate and water from onsite monitoring locations. Generally good correlation was observed between plutonium, Co-60, and EDTA in leachate sampled from experimental wells about 4-7 m from Trench 27 (PNL).
- f. Plutonium in trench leachate Plutonium is probably migrating exists in true solution and not as as a soluble EDTA complex and colloids (Cleveland, and Rees, 1981). not as a colloid.
f f
b j 03/22/83 16 MAXEY-FLATS RESEARCH 085ERV 1
s . .
't s t .
Observations Conclusions
- g. Small, but measurable amounts of Pu Pu has migrated in onsite ground-J were found in porous sampling cups water at distances up to 7,6 meters
~
installed up to 7.6 meters from from Trench 19-5.-
Trench 19-S (LANL). . l
- h. Sr-90 and CS-137 generally showed good The Sr-90 and Cs-137 that is migrat- l correlation with carboxylic acids in ing is probably associated with 1 leachate sampled from experiscental carboxylic acid complexes or salts wells located about 4-7 m from in onsite subsurface waters. 1 Trench 27 (PNL),
l
- i. Toxic chemicals, including barbitu- Because of the hazards and mobility ;
i rates and chlorinated hydrocarbons, of certain nonradiological toxic have been observed in trench leach- chemicals found at or near EPA ates (PNL; BNL), and other toxic limits, they need to be considered chemicals (pesticides) are known to in a site closure plan. I have been placed in the burial trenches at Maxey Flats (Mills).
- j. Leachate collected at different Mixing of leachates within indi-dewatering sumps and depths within vidual trenches is often minimal.
a trench commonly has different This variability in leachate compo-radionuclide concentrations as a sition compounds the problem of result of the variability of wasta describing the source term which disposed of in different parts of is important if selected remedial the trenches. This variability is actions are needed for specific compounded by internal dams in the trenches or parts of trenches, trenches resulting from operations.
3, e
6 4
't 03/22/83 17 MAXEY FLATS RESEARCH'08 SERV
^,
7
, .. l Observations Conclusions j l
- k. Recent site operations have revealed. There presently is not adequate j d the presence of several areas knowledge of the thickness of cover )
where waste is within inches of the over all trench areas at Maxey Flats.
1 ground surface. In at least two There is no assurance that wastes I instances, the waste had been are indeed buried with'the re' quired 3 covered with lead sheets to reduce 1 meter soil cover. Thus, any onsite surface radiation exposure rates surface recontouring (i.e., rebuild- ,
)
(Mills). ,
ing) should be carefully planned and '
monitored. Erosion of the surface must also be minim'ized.
i o
. 1. Under present license restrictions, Since_several trenches now'contain' l the evaporator system is limited leachate with tritium concentrations l to processing leachate with tritium for in excess of these limits, the
'. concentrations not exceeding 7 pCi/m2, leachate requires dilution prior to
, this translates to the current processing or redesign of the evapo-tritium emission rate permitted for rator to meet existing emission the evaporator (Mills), requirements,
- m. Tritium was the most abundant radio- Chemically bound as HTO, tritium nuclide in the trench leachates has the greatest migration. potential y L; studied by BNL (BNL Reference 1.) of any radionuclide. d
- n. Trench 20 contains tritium con- ' Substantial quantities (100,000's of j centrations ranging from'34 to liters) of leachate from Trench 30 1 45 pCi/mf'(1982 data, Mills). will need to be diluted with water containing low concentrations of tritium if the practice of dissipating tritium through the evaporator is continued.
3 i
. , \
r lI LO3/22/83 18 MAXEYFLAYS.RESEARCHOBSERV
.~ _ --
a l
5.4 Subsurface Transport of Radionuclides l l
l Observations Conclusions l
. isotopes above background have been of radionuclides from trenches approx-observed in wells UB1 and UB1-A, imately 10 meters away. Transport is together with organic compounds that through the fractured lower sandstone are also present in nearby trenches marker bed which is at the base of
(.8NL; Ref. 1 USGS). most trenches at the site (Zehner written communication, February 14, 1983). l l
l
- b. Excavation of experimental trenches Lateral transport of radionuclides by parillel to Trench 27 resulted in subsurface flow may occur over short a rapid (hours to days) inflow of distances in a relatively rapid time water containing trench leachate, frame, if open fractures exist, presumably by fracture flow. The distance between trenches ranged from 4-7 meters (PNL Ref. 1).
- c. The data from the experimental This may be the r.esult of organic trenches and Trench 27 indicate that complexation of the radionuclides, adsorption does not markedly reduce of chemical saturation of the radionuclide concentrations over exchange sites by components of the short distances (4-7m) (PNL Ref.1), trench leachate, or of too little contact time with the exchange sites,
- d. Pumping of leachate from the trenches The flow of leachate between trenches does not rapidly affect the level of is small in volume when compared to leachate in an adjacent trench the total leachate volume in the (Mills). trench.
1 03/22/83 19 MAXEY FLATL RESEARCH OBSERV
____m.__.___._______ _ _ _ - - . _
i Observations Conclusions
- e. Subsurface transport of trench leachate i
~
Leachate has been observed to n, flow along the sandstone fracture has been physically observed to occur
< system underlying the site up to via fracture flow. Where unhealed distances of 100 meters (U.S. fractures and hydraulic gradients exist Ecology fide, Zehner written at Maxey Flats there will be readily communication, February 15, 1983). observable fracture flow in strata which exhibit low hydraulic conduc-tivity (see observation 4.2(a) and Section 3 item 6).
- f. Water collected from a seep along Onsite subsurface transport of the wall of Trench 46 during con- radionuclides in trench leachate struction contained H-3, Sr-90, has been observed where the flow Pu-238, Mn-54 and Co-60. These is through fractured rock.
radionuclides were transported by ground water from one of the"other burial trenches at Maxey Flats.
Trench 46 was located 60 meter from the nearest waste-filled trench (U.S. Ecology fide, Zehner written communication, February 15, 1983).
- g. Tritium concentrations in soil Comparisor with tritium concentra-solution at various depths (from tions in the cap over Trench 19-5 O.3 m to 7.6 m) 8 meters away indicates that the evaporator was from Trench 195 are low, and they the source of the water and the low decrease markedly with depth concentration at the 7.6 m depth (Schulz 1982, Ref. 2). shows that the undisturbed profile is quite impermeable to percolat-ing water. Water movement then in both the horizontal and vertical j direction is very slow in the absence of fissures.
, 03/22/83 20 MAXEYFLATSRESEdRCH'0BSERV 2 _ _ _ _ _ _ _ _ _ . _
,,3= . . .
a - - - , - , -
. i- ,- ,.
Observations Conclusions l
- h. Tritium concentrations in the The marked increase in tritium with trench cap of Trench 19-S . depth ,(note observation g) in the increased markedly with increas- trench ~ cap indicates that the waste i
ing depth in the trench cap is the principal source of thre (Schulz 1982, Ref. 2). tritium and not the evaporator.
Tritium from trench leachate would be available for root uptake by plants growing over the trenches.
- i. At Trench 19-5, the ratios of Not all of the complexed plutonium plutonium to tritium decreases as reinains mobile in the soil.
a function of distance away from Trench 19-5 (up to at least 6 m)
(LANL Ref. 2).
- j. In the Trench 19-S study area The data suggest that the sandstone tritium concentrations are higher layer provides a partial barrier to above the sandstone layer than downward movement of water, below (LANL Ref. 2, 3).
- k. Tritium concentrations are higher The data suggest that this inter-above the interface between the face provides for lateral flow of undisturbed profile and the land- infiltrated surface water, fill than below (LANL Ref. 2, 3).
)
- 1. Laboratory studies of Maxey Flats . Complexing by EDTA appears to be a shale and oxic waters which are potentially important mechanism spiked with various organc chelat- that increases mobility of some ing agents showed a decrease in radionuclides such as Co-60, Pu-238, i
sorption coefficients relative to Am-241, and Sr-90. EDTA is likely unspiked waters. EDTA produced the
{
to be present i.n most trenches. ;
most drastic change (BNL Ref. 1).
b 4 03/22/83 21 MAXEY FLATS RESEARCH OBSERV
. o
l <
l 1
i 5_. 5 Radioecological Factors !
l Observations Conclusions j
- a. Fescue grass extracts considerable Sampling of grass for tritium may
, water from the top 2 meters of trench be a useful method for determ.ining 1 i
caps, but except for tritium the the location of poorly recorded (
- v. a. .a. c> >
grass,up very little radioactivity. burial sites. Transpiration by j The tritium concentration in grass plants can provide an effective !
from the caps was about l',000 times means for gradually dissipating greater than in grass sampled 2-3 tritium, meters from the trenches (UCB Ref. 3). ,
- b. Localized areas of elevated tritium 1. Data suggest subsurface flow of in tree leaves have been observed tritium to offsite, although along the west side, down slope from the relative contributions from Trench 31 (high tritium trench). A air and surface pathways have 10X decrease in tritium was observed not been fully evaluated.
between 1981 and 1982 in leaves (PNL, j verbal communication, W. H. Rickard, 2. Trees (leaves and sap) may serve ]
1982), which coincides with the as useful post-closure biological installation of the plastic cover, monitoring devices for trench leachate movement, particularly tritium,
- c. Radionuclide concentrations in off- Measurements made to date indicate site surface soil and vegetation that the site-appears not to have (other than tritium) are essentially been significantly breached by sub-at weapons testing fallout levels in surface transport, except possibly areas free of surface runoff (PNL for tritium. Additional monitoring Ref. 5, 6), sites would be needed to adequately
, assess subsurface transport.
f h
03/22/83 22 MAXEY FLATS RESEARCH OBSERV
g- _, _ . . - - - - _
' ,/
2 ,
Observations Conclus. ions -j i
- d. Surface sediments in drainage areas One source of onsite' surface con- 1 adjacent to trie site contain traces tamination may have been spillage !
7 of Co-60 in concentrations slightly of radionuclides during pumping of
~
, greater than in fallout, but low trinch leachates in 1572. T h.e .
compared to other fallout radio- Co-60 was translocated by. surface nuclides (PNL Ref. 7). runoff into adjacent woods. .
- e. Plutonium-238 attached to' sediments The apparent source of this t
has been observed in excess of back- plutonium has been erosion of '
^'
ground concentrations in offsite contaminated surface soil, drainage areas (east and south drain-age areas) (PNL; EPA; KDHR fide Mills written communication March 14., 1983).
- f. Many operational activities have been Current environmental assessment !
implemented at the site in order to is complicated by past and on-effect stabilization, but the radio - going . site operational activities.
nuclide' concentrations observed off-site have remained reasonably con-
, sistent'(Mills). '
5.6 Engineering Factors i
Observations Conclusions '
- a. Subsidence has been noted to occur on Any site closure plan must address essentially all 'of the trench cap the inevitable problem of continuing covers. This subsidence has been subsidence of trench caps. Subsi-more readily observed since the dence problems could damage an engi-installation of the temporary surface neered and/or vegetated cover which plastic cover. Subsidence has'taken. Could collect precipitation.and the form of small area depressions, enhance water infiltration with
. large area' catastrophic subsidence, :its resultant accumulation.
differential settlement within the trench boundaries, and subsidence.
between the trench contents and-the undisturbed soil' side ~ wall. The
"' ' subsidence .is still continuing' (Mills).
03/22/83' 23 'MAXEY' FLATS.RESEARCH'OBSERV
, )
e ~ -
1 t
Observations Conclusions
- b. -Water levels vary within trenches as The deliberate construction of is observed.by sump liquid level internal trench dams, or those !
measurements even after pum' ping of inadvertently created by waste, liquid from one sump or a series of make trench dewatering difficult sumps from the same trench (mills). to accomplish.
- c. Water levels in trenches which were The temporary plastic surface cover covered with the surface plastic is an effective short-term method have shown reduced increases i~n for significantly redu: og infil-
, water levels when compared to tration and resultant water accu-similar uncovered trenches (Mills). mulation in the short term,
- d. Where perforations were present An impermeable cover must essentially ,
1 in the clastic cover, soil be perfect or the defective cover moisture increased (UCB Ref. 3). will function as a "one-way valve,"
. letting water into the soil but preventing evaporation.
- e. Soil moisture in the upper 0.9 to -
An impermeable cover will permit the 1.5 meters has generally decreased site to be dewatered, and therefore since installing the plastic cover, eventually eliminate subsurface water ;
where the cover is intact (UC8 Ref. 3), and radionuclide transport.
- f. Approximately 2-5 cm of the 115 cm Although only a small percent of total ant..=1 rainfall penetrated into the annual rainfall penetrated into the trenches 'efore installation of the trenches before installation of the plastic cover (UCB Ref. 3), the plastic cover, it still resulted in excessive water accumulation in the trenches because of the low hydraulic conductivity of the media in which the trenches were excavated.
t.
03/22/83' 24 MAXEY FLATS RESEARCH OBSERV.
6 POSTCLOSURE MONITORING l l
l The research studies have identified needs and suggested potential methods for postclosure monitoring needed to assure that the radioactive wastes at Maxey Flats are behaving as predicted. Radiological surveys of the si,te have de. fined the current distribution of radionuclides at the ground surface, in waters of shallow test wells on the site, in the biota surrounding the site, and in l sediment from streams near the site boundaries. The studies indicate that principal radionuclides which need to be considered in developing a monitoring
,. program include H-3, Co-60, Sr-90, Cs-137, Pu-238, Pu-239/240, and Am-241.
Implementation of a monitoring program should be done in stages. As data become available the program should be flexible enough to accommodate the changes that data indicate are necessary. The panel made no specific recommendations ~as to methods for monitoring radionuclide migration. The panel noted that_ tritium can be a useful indicator of radionuclide migration in groundwater since it j precedes other nuclides in the moisture front moving away from buried waste.
However, the presence of tritium in itself does not mean that other radionuclides l will follow as they may be in an immobile form or their migration may be attenuated ]
due to geochemical processes. Some other methods which might be employed for monitoring include vertical wells, inclined wells designed to intercept fractures l and/or to measure downward flow into deeper rocks, porous cups, wells in the colluvium on the slopes bordering the site, monitoring trenches along the peri-meter of the site, measurements of base flow into the streams adjoin _ing the site' during low flow periods, and analysis of vegetation. The trees growing around the perimeter of the site may be good indicators of tritium migration from the site but may be inadequate to detect the movement of complexed plutonium.
It appears that, in the very complex hydrogeological system at Maxey Flats, a site closure monitoring plan might well incluce consideration of each of the above methods to help ensure tha,t any subsurface flow, which would lead to movement of contaminated water'offsite, is observed in sufficient time to take
., appropriate remedial action Because of the complex hydrogeology of the site,
~
including the predominance of fracture flow, reliance ihould not be put on only one surveillance method. -.
y A.
03/22/83 ' 25 ~ -
MAXEY FLATS RESEARCH OBSERV t '
.a-
- a
, l j
7 SITE CLOSURE SCENARIOS v.
'After considering all the observations and conclusions based on the available i
j data pertinent to site closure, it was felt that site closure scenarios should
]
be considered for two major time frames. The first time-frame would be' approx-imately the first 100 years of' closure during which institutional control could
('
be provided. In this period water infiltration and accumulation in the waste trenches should be avoided to prevent the offsite transport of tritium and other l short-lived radionuclides via groundwater flow. After about 100 years, the f tritium would have decayed to much lower levels and may no longer be a concern to human exposure (it would be about 0.2%'of original burial activity). ]
1 l
In the first time frame various engineering activities and environmental control
' actions may be undertaken to immobilize the wastes and stabilize the site. This ,
i could include actions to ameliorate any site stabiliza-tion problems that may develop. The institutional control during this per.iod may control access to the site and use of the area; 1A monitoring program will need to be maintained to assure that the site is performing as predicted and in compliance with closure '
requirements, i
The major concerns for the second time frame, the past 100 year period, would j encompass long-term site stability and the potential for offsite migration of long-lived radionuclides (Sr-90, Cs-137, Pu-238) via the groundwater or by overflowing trenches. Plutonium is of major concern since approximately&f63 kg
- s. -
of' plutonium isotopes are buried at the site (Clancy et al.,_1981), ,This plutonium-l has been observed to have migrated for several meters from waste trenches. 1 e
However evidence developed.thus far suggests that the plutonium is absorbed as it moves from the anoxic trench environment to the oxic. soil environment a few meters from the trench. Our current state of knowledge contains a number of ,
important' uncertainties (e.g., unknown environmental lifetime of the organically.
4 complexed radionuclides; changes-in soil retardation factors in going ~from- l anoxic to oxic conditions; complicated.hydrogeology) so that it.is difficult'
~
l f
at this point to predict the amounts of Sr-90, Cs-137, and Pu-238 that would l or could ultimately migrate offsite, it may be that totally insignificant 3
03/29/83 26 MAXEY FLATS RESEARCH OBSERV ;
i u.
s,
.g * ..
6 4 e-amounts of these long-lived radionuclides would leave the site even if unre-stricted' water infiltration occurred. After the 100 year period, tritium
, would have decayed to relatively insignificant levels (0.2% of original burial activity), and it should be possible to allow the siteI to be restored toLthe' indigenous ecosystem or to some limited agricultural use. The panel dis .
cussed the feasibility or advisability of limited use without providing a recommendation.
The panel discussed three general scenarios for the short-term (100 year) decom-missioning phase of the site which are summarized'below. Since it would be j inappropriate for this panel to define and recommend specific decommissioning J', plans, the following should be considered as broad environmental and engineer- J ing concepts in which costs and other soc'ioeconomic and environmental impacts were not considered, and they should not be construed in any way as preferred or even reasonable alternatives. The people involved in developing site closure plans for the Maxey Flats Disposal Facility or any other low-level waste disposal facility are encouraged to examine the numerous alternative plans which are available.
7.1 Leveled Site With Grassland Cover Brief consideration was given to the possibility of restoring the site fto the j original leveled sloping condition with fescue grass' cover as was maintained before the plastic sheeting was installed. This type of cover if' properly
~
'i maintained could be expected to be quite effective in inhibiting water from infiltrating and accumulating in the trenches. However, this method could not adequately restrict the percolation of rain' fall through 'the soil to prevent accumulation of water _in the waste trenches on an annual basis, since the flow through the slopes and bottom of the site is only about 0.3 cm per year. There-fore, it is obvious that a closure method which-will provide more efficient-water management must be considered.
- ~\
e l
j l
l 03/22/83 27 MAXEY FLATS RESEARCH.0BSERV !
ll
.,r . . ..
_ _ = _ -
e.
y 9
7.2 Trenches Mounded and Vegetated (see Figure 1)
A proposed more effective system for controlling water infiltration would involve contouring the surface of the site into a series of mounded rows of appropriate slope to increase runoff but avoid erosion. The grade of'the ,
'. slopes that co.uld be used would be dependent on the characteristics of the
,;. cover selected. The m'aterial covering the slope would be' chosen to reduce infiltration. Examples of materials considered by the panel for covering the ;
j slopes of the mounds included vegetation,. rip rap, or impermeable material such )
as asph' alt, plastic sheeting, or concrete tiles. Additional soil wat'er control j could be achieved by growing small trees or large shrubs on the tops of.the mounds. Trees or shrubs should be selected which develop deep root systems and evergreen species'should be considered because they transpire throughout ,
the year. By this method the precipitation which falls upon mounded trenches, l properly covered with vegetation, would be removed by t'ranspirat' ion and runoff.
The main advantage of this system is that it can inhibit water from getting into the trenches and provides an effective mechanism for removal of water that ,
enters the soil. A negative water balance may be established especially in the l summer months, by the combination of the impermeable cove'-drainage r system and the vegetation. This method could result in.the eventual dewatering of the waste trenches, and eliminate the problem of subsurface migration of radio-nuclides in groundwater to offsite locations. It was felt that one person working full time could maintain such a system. Another advantage of this method is that.it would be relatively easy to eventually let the site return to
~
a natural forest ecosystem after the initial 100 year. period, by which time the tritium will have decayed. Several factors that would needzto be investigated in planning this approach include:
(1) Assessment of uptake of long-lived radionuclides-(e.g., Sr-90 Cs-137, complexed Pu) by the vegetation; (2) Assessment of capabilities of deep-rooted plants to penetrate trenches and transpire infiltrating water; a
03/22/83 28- LMAXEY FLATS:RESEARCH 0BSERV
. c, . . .
.v.
e; Figure 1. ' Trenches Mounded and Vecetated.---The scheme illustrated here is.
. one variation of several possibilities. ~It represents a design to reduce infiltration and to to promote runoff. The plants will serve to r,emove precipitation that may penetrate the covered slopes.
1
{
' COVERED SLOPES to reduce VEGETATION to remove moisture.
by TRANSPIRATION ,
. INFILTRATION
..skv !
7
(% g, $h 'N 'khD LOW MOUNDS to promote DRAINS to remove RUN0FF RUN0FF
.l J
I 1
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-(3) Assessment of effectiveness of vegetation in this system to transpire spil moisture throughout the year; and (4) Assessment of the ability of the plants to survive when exposed to the l toxic chemicals and anoxic conditions in and close to the trenches.
The panel felt that if this cover system was given serious consideration as a short-term (100 year) site closure scenario, it'would be wise to convene a peer review committee to examine such a system in detail. Also, it'may be desirable to devise a small-scale demonstration project'on the site to test the effectiveness of thi's cover system before a full-scale application.
-r 7.3 Hard Impermeable Engineered Cover Over Site Another suggested means of covering the site to prevent water infiltration during the first 100 years of institutional control would be to cover the site with a har.d impermeable engineered cover. Such a cover. would have to limit infiltration to less than 0.3 cm/ year to avoid water accumulation in the trenches. One suggested method would be to cover the site with~an impermeable material such as concrete or asphalt. This material would be laid,out over slopes designed to handle runoff and it would have to include an effective surface drainage system. The advantages of the impermeable cnver are that it would be observable, repairable, resistant.to biological intrusion, and subsidence could be repaired relatively easily. Another: advantage of such a system would be that it would discourage unintentional human intrusion for a long period of time. A serious disadvantage is that any leakage-through the cover would constitute a major problem. Therefore, if'an impermeable cover was used, water levels in trenches would have to_be carefully monitored. For the long term, that is, after_i'nstitutional control has ended, a closure plan for an impermeable engineered cover would have to dea 1 with failure of the engineered cover and reversion of the site to.an indigenous ecosystem. There may'be-considerable uncertainty as to the " smoothness" of.this transition. .For example, the measures taken to increase runoff will increase. erosion. Without~ human-
intervention, this may lead to waste exhumationi 'It would be difficult to
~
transfer the controlled engineered system to a' suitable long-term situation; If, L
03/22/83- 29 MAXEY FLATS LRESEARCH OBSERV
3,
(*
v -1
-o pioneer vegeta-tion was permitted to gradually take over the site it could not i
be expected to be able to accommodate enough of the water falling on the site !
- 3. . to prevent reflooding of burial trenches. For reasons such as these, very care-ful consideration would have to be given to the effect of an engineered cover on the environment, its predicted performance in the absence of institutional controls, and to actions which should be taken to assure'that the first phase of closure can be effectively transferred to the final closure phase.
An impermeable hard cover could be , installed'over the entire site or only over particularly problem waste trenches. For example, about two-thirds of the Maxey i Flat tritium ' inventory r'esides in a singleLtrench, and 'it may be feasible to:
construct an impermeable hard cover over only several of the trenches containing l the high tritium concentrations. If lateral subsurface flow from uncovered areas is not significant, then a partial coverLover the problem areas could possibly be a short-term (100 year) mitigative procedure for preventing signif-icant offsite transport of tritium.
Complimentary to the above schemes (7.1, 7.2,, '7.3), engineering methods should be considered'to immobilize radioactive wastes within the trenches. This could include various methods of impregn; ting the waste-with matrix materials to ,
i reduceradionuclidemigration,incfrporatingtrenchwaterinsolidifyingmate- ;
t ,
rials,orcompactiontoreducegragualsettlingofcoveredtrenches. These methods could be incorporated withiany of the above thr.ee general scenarios.
e 4
'Q %
S 4 03/22/83 <
30 MAXEY' FLATS RESEARCH'0BSERV
1 .
I REFERENCES BML References Czyscinski, K. S., and A. J. Weiss, 1981, Brookhaven National Laboratory,
" Evaluation of Isotope Migration-Land Buriai Water Chemistry at Commercially Operated Low-Level Radioactive Waste Disposal Sites, Status Report, October ;
1979-September 1980," NUREG/CR-1862, BNL-NUREG-51315 (BNL Ref. 1). ;
Pietrzak, R. F., K. S. Czyscinski, and A. J. Weiss, 1982, Brookhaven National Laboratory, " Evaluation of Isotope Migration-Land Burial Water Chemistry at Commercially Operated Low-Level Radioactive Waste Disposal Sites, Status Report, October 1980-September 1981," NUREG/CR-2616, BNL-NUREG-51514 (BNL Ref. 2).
Pietrzak, R. F., R. Dayal, M. T. Kinsley, J Clinton, K. S. Czyscinski, and.
A. J. Weiss, " Trench Water Chemistry at Commercially Operated Low-Level Radio-active Waste Disposal Sites," in Proceedings of the 1982 Annual Meeting of the Materials Research Society, Boston, MA (in press) (BNL Ref. 3).
Commonwealth of Kentucky References Mills, D., and R. Page, 1982, "A Brief Overview of Remedial Actions Necessary at Maxey Flats," in Proceedings of Fourth Annual Participants Information Meet-ing, DOE-LLW Management Program, Oak Ridge National Laboratory ORNL/NFW-82-12.
LANL References 'l ,
l Polzer, W. L., E. H. Essington and E. B. Fowler, 1981, " Migration of Waste Radionuclides Through Soils at Maxey Flats, KY", In: Research Program at Maxey Flats and Consideration of Other Shallow Land Burial Sites, NUREG/CR-1832, PNL-3510, U.S. Nuclear Regulatory Commission, Washington, D.C., March 1981, (LANL Ref. 1).
Polzer, W. L., E. B. Fowler and E. H. Essington, 1982, " Potential for Migration of Waste Radionuclides at the Maxey Flats, KY Shallow Land Burial Site.," In:
Radionuclide Distributions and Migration Mechanisms at Shallow Land Burial Sites, NUREG/CR-2383, U.S. Nuclear Regulatory Commission, Washington, D.C.,
July 1982 (LANL Ref. 2).
Polzer, W. L., E. H. Essington and E. B. Fowler, 1982, " Transport of Waste Radionuclides Through Soil," Draft of Annual Report, FY 1982, Los Alamos National Laboratory, Los Alamos, New Mexico (LANL Ref. 3).
PNL References Kirby, L. J., 1981, " Chemical Species of Migrating Radionuclides at Maxey Flats and Other Shallow Land Burial Sites," In: Research Program at Maxey Flats and Consideration of Other Shallow Land Burial Sites, NUREG/CR-1832, PNL-3510, U.S. Nuclear Regulatory Commission, Washington, D.C., March 1981 (PNL Ref. 1).
03/22/83 31 MAXEY. FLATS RESEARCH OBSERV
4-9' l
Kirby, L. J., C. W. Thomas, A. P., Toste and C. L. Wilkerson, 1982, " Chemical Species of. Radionuclides at Maxey Flat," In: Radionuclide Distributions and l Migration Mechanisms at shallow Land Burial Sites, NUREG/CR-2383, PNL-4067, ;
U.S. Nuclear Regul.atory Commission, Washington, D.C. , July 1982 (PNL-Ref. 2).
Kiraby, L. J., W. H. Rickard and A. P. Toste, 1982, Chemical Species of Migrat-i ing Radionuclides at Commercial Shallow Land Burial Sites. Quarterly Progress Report, April-June 1982, PNL-4432-1, Pacific Northwest Laboratory, Richland, WA., August 1982, (PNL Ref. 3).
Kirby, L. J. and A. P. Toste, 1982, Chemical Species of Migrating Radionuclides at Commercial Shallow Land Burial Sites. Quarterly Report, July-September 1982, PNL-4432-2, Pacific Northwest Laboratory, Richland, WA. , October 1982, (PNL Ref. 4).
Rickard, W. H., L. J. Kirby and M. C. McShane, 1981, "Radioecology Studies at Maxey Flats, Kentucky: Radionuclides in Vegetal Samples" In: Research Program at Maxey Flats and Consideration of Other Shallow Land Burial Sites, NUREG/
CR-1832, PNL-3510, U.S. Nuclear Regulatory Commission, Washington, D.C.,
March 1981, (PNI Ref. 6).
Rickard, W. H., L. J. Kirby and M. C. McShane, 1982, "Radioecology of the Maxey i Flats Site," In: Radionuclide Distributions and Migration Mechanisms at Shallow Land Burial Sites, NUREG/CR-2383, PNL-4067, U.S. Nuclear Regulatory Commission, Washington, D.C. , July 1982, (PNL Ref. 6).
Kirby, L. J., 1982, " Areal Distribution of Radionuclides at Maxey Flats," In:
Radionuclide Distributions and Migration Mechanisms at Shallow Land Burial Sites, NUREG/CR-2383, PNL-4067, U.S. Nuclear Regulatory Commission, Washington, D.C., July 1982, (PNL Ref. 7).
UCB References Schulz, R. K. ,1981, " Study of Unsaturated Zone Hydrology," In: Research !
Program at Maxey Flats and Consideration of Other Shallow land Burial Sites, l NUREG/CR-1832, PNL-3510, U. S. Nuclear Regulatory Commission, Washington, D. C. , ;
March 1981 (UCB Ref. 1). l Schulz, R. K., 1982, " Study of Unsaturated Zone Hydrology at Maxey Flats," In:
t l
Radionuclide Distributions and Migration Mechanisms at Shallow Land Burial Sites, NUREG/CR-2383, PNL-4067, U.S. Nuclear Regulatory Commission, Washington, D.C., July 1982, (UCB Ref. 2).
Schulz, R. K., 1982, " Study of Unsaturated Zone Hydrology at Maxey Flats," in Proceedings of Fourth Annual Participants Information Meeting, DOE LLW Manage-ment Program, Oak Ridge National Laboratory, ORNL/NFW-82-12, pages 423-436, (UCB Ref 3).
03/22/83 32 MAXEYFLATSRESEARCHOBSERN l l
l
=ewax f
Radioactivit,y called M&e r ...
normal at Maxey Flats r=. m.
,,. r_
py trVINGSTON TAY1.OR g7 ./ , , ,,, g g, C 0 ". .". . .:". P. u' F. . .'.' E
^ ^ u **e**- suestion pt.federst ageoese,s that "e O* *:It .- 1. . m FRANKFORT. Ity. - Ometals of een bete es," Mrs. swtpast asM. . -
GCT she said she wested to get me te- Tre the state Department ter Nesta .formones te me smees esesmas.
services seM yesterday met their M mes.blefore their e4ecnoe recess, q pg y ,, .i- g
- c,g weekly moeisertes of me Mesey Flats radioecWee westedisposal site pects' it may3wigart sakt that be noe .1e6e'le getshe sus- ,
dews 80 censest levels et redleeC* se approprietion le the currest ll'ity.
Cesium med cobelt - Only eistd year's federal badgW het met she W me 23 samples were )ested for "We ve seen se cesium med estalt.
chaage." emed Dr. Robert W. Yosessigelneset adu hopen federalsect emoneytests are *fterun eve we#-sernpees deputy commhedoner ter commese, tuany be availehes. from po(sts receMag direct surface fy health services, Niestywelee percent of me radio-dretamar from the sete. sad es any Department effletals said mey before the alte was closed camesenve other samples weste esseped attests le which3eseral Mezer Flaes leformation that Naturel Resoorteshave tried womeet asecem . show devstedto met tod6 eceMiy, the efrom redb set.oretate sources, some Deperta esoe<emar:4 sdortsk saw.
ad EsMrseawatal Pmmetlen Sec tem la me 11.5. and pyssendose - No sweary JacWe swtgart referred to et 'reest, she said..
a sept. 34 eeos conference, Mrs, swigart. osed the Noelear tests speemcefly ser serenstem sad Mrs. Swisert este men "la recent wita ' inthrv Ceiendesles. Agms es Qum have year bebeve done ser at
" sets seoeftertog data ... has be foceweter esmptos.the *refred'cdtfe ,,,, ,,,,3,,,,csume from sue ,,,,,,,,y, they have not goe to show that redsoective materv er ta The more generst tests two se aff (6. b ,seedes tressau C - g a, e nwagtd6r me*e rediatloe tneportmentcenfor - pg ,wh as fw spee and bete trescaos tremah undergreed chan- ,, ,,,, ,, se ecoyny se= = toe.sech - from w 48 that woo JedJoe "This contentested water com- ,seds on med e, seed .e Ma r 4 -
totes radioecuve seatertet imeledtes \pige, ggge every two weeks. DIC#d' " m ' e ,,,,6,,s es,d' '
testem. streetenet. ceesit. pteteelem taw.teoutts se 33 sempees estlect. - Mrs. Swigart seM the NRC figures and trmusa." og gepg,3 gewed me mq; are particuJarly dtstrasing because le se intervtow yesterday afteo g,g,g,,, _ gigg ,,,gg,g.131. is me sta hes 'P'"
stroom et east edge of site. Pre- 88 g aad she he nece. Mrs. Swtgart seM her state vtously tabulated reedless at alsple.gm 3 preyesteg senhage has mena were tened om figures fmm Jederal Mnciserseten, RessagggAt.es frees a high et 13A es Ata.
d 23 to acatsch moder receW coetracts dortog isg2 how meted i
miedon messeertog whics en wtm Bittman Neclear and Devel*P-ta difternet leestloes fWest these of low et 33 en Apre S. yhe lert tabu. g % gg, me state healsk departrust, leted reedtag won 114 se Atts 2. Under the carrest contrac1 with Emw reading 8.8. to 7%s DMk h SWW W effective last
-1 hoew they (health emeists) are 4% mnes west et esta. July W ao Mc speet." Mrs. Swtgart sold. "This .
MozimutapermiselMe coteestro. g43,,3,1,. ,,Estunen,. ,,4 ,y4 ,w.,,,,, ,,,ette doesn't or la say way renect en thesa t6ea: 33,000. Taas standard hea been,,,c,, ,,, ,,,,,,,,,,,3,g ,,gg4 their meanerteg" Mrs. swtgart die est neones the &ptedJan eso by seeersteg the Nuclear ,,,,, , g,,,y pg, ,,
to Stagelatory sectsee as- 'yhe redkDm secdoe of um 9e um one p,ieces and me so.itgures yeseerdey Themfigures poputmem en #w neen seevices perview Deved TLCurb. Wrteum eens are le thousseds et 36coctries cominges a he me stow ma**cy r*-
partment employees who cae com P" #8'fd = esw W the sue, on-put these have boet et a sympo. Cniest - N4ft reedlag 1. a( two - pervtsor Dee Hephes said, dem said, in Wastgestem tb4s week, she stream locatices et the' east edge et Mrs, swtgart esid es Sept. "l4. and the atte. %
,,,g, y,,gerday, that eves the fig-On Moedey seersing me "techeb law fondlag 4, et **eetal let** erus se sh4ch de b tWyleg "do not cat people" trem both departuneets tions- ' preerst as tausediate heeltla hea-are a "gettegemer med snare tafer. Maximum permisethee edecentre . ord."
== Man a she sets. $
ties: 39,300. (Utfts are plcoevetes Mrs. swtsort hw sold mM me east pu tuer.)
M t permaneet soluttoa et Mazer Plats - a tovw and wens to ser- Cohett - 3tish reedlag 3, et e rowed the barled weste sostertal - Arteam at me seth east utge.
(Aw reedlag 6, et several loce* ,
could 8 MAW 0e-vseer freen $38 edalse to 847 goes.
' her She occh yesteedsty met Mealmuss peradasthes
- man' entre- i Sept.14 s tsome 30,000. (Ustes ese p6cocertes via se eye e,tatemeses were made per 18ter.)
a8 speramen.ord t to settses me fed-
, "wesem ,,,,,,,, h,eap per ,g,g ser pee k.___iCteseth . ,, pg 1 j
cr .
Date ROUTING AND TRANSMITTAL SUP 9/8/82 TO: (Name, office symbol, room number, initists Date building Agency / Post) g, Witt Potzer le sG4Amd5 NAY L.A t5 2.
3.
4.
5.
Action File Note and Retum Approvst For Clearance Per Conversation As Requested For Correction Prepare Reply Circulate For Your information See Me Comment investigate Signature Coordination Justify RDAARKS Witt: - -
l Attached is a copy of the material that Doyle Mitte )
gave us on 8/27/82. The tritizen info came from PNL and it tsaa measured this eteraner. For further i information you might contact Doyle Mitte or Rip Kirby. l 1
1 i
DO NOT use this form as a RECORD of approvals, concurrences, disposels,
- clearances, and similar actions FROM: (Name, rnbol, Agency / Post) Room No.---Bldg.
Edward O'Donnett Ph*** N**
sost-to2
- GPo a 1980 o 311-156 (6) OFTIONAL Prescribed FORM OSA 41 (Rev. 7-76)
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O P QBalfelle Pacific Northwest Laboratories I
P.O. Box 999 Richland, Washington U.S.A. 99352 Telephone (509) 376-3286 August 13, 1982 yeie,15 2sn i
Mr. Doyle Mills Office of Special Projects Department for Natural Resources and Environmental Protection Fourth Floor, Capital Plaza Tower Frankfort, Kentucky 40601 f e, 4 c4 Apb n /Am ed A.
Dear Doyle:
,.,, pffg z, i
I am enclosing the tritium data for leaf samples taken during July 1981 and July 1982. With a few exceptions, the samples were taken from large oak trees.
h The 1982 tritium levels are markedly lower along the southern half of the west fence line, giving you an indication of the effectiveness of
' your plastic cover over the waste trenches adjacent to this area. Both sets of data show a peaking in trees sampled near trench 31, indicative of tritium migration there.
Please note that tritium levels in trees near the N340 coordinate below f
the evaporator have remained at about the same level, while adjacent I
sampling points to the south have decreased markedly. Evidently tritium is migrating toward this channel and additional study may be warranted here.
l The tritium concentrations we have measured are well below MPC and should give you no cause for alarm on this issue. The technique we have used is sensitive enough to give an early indication of tritium migration.
Best regards to all.
Very truly yours, b
L. J. Kirby roject Manager Radiological and Inorganic Chemistry Radiological Sciences Department cc: hO'Donnel)/NRC,'w/cattach.
l l
)I
.. _ . - _ _ _ - .