ML20235V780
| ML20235V780 | |
| Person / Time | |
|---|---|
| Issue date: | 10/13/1983 |
| From: | Higginbotham L NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Nussbaumer D NRC OFFICE OF STATE PROGRAMS (OSP) |
| Shared Package | |
| ML20235U845 | List:
|
| References | |
| FOIA-87-235 NUDOCS 8707230305 | |
| Download: ML20235V780 (9) | |
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. Distribution _:WM83653
.- NMSS r/f 201.6/SMN/83/20/3 OCT 131983 WMLU r/f N l REBrowning ;
MBell SMNeuder PHLohaus I
DMartin J0 Bunting MEMORANDUM FOR: Dcn A. Nussbaumer, Assistant Director Office of State Programs FROM: Leo B. Higginbotham, Chief Low-Level and Uranium Projects Branch Division of Waste Management
SUBJECT:
DECOMMISSIONING PLAN FOR MAXEY FLATS We have reviewed the draf t of the Decommissioning Plan for the Maxey Flats Dispocal Site, Task 3: Evaluation of Alternatives. Our comments are enclosed. Dr. Stan Neuder is the Brancn Technical contact for this project. Please contact him at 427-4607 should any questions arise.
~~ifEalsidedW ori Leo B. Higginbotham, Chief Low-Level and Uranium Projects Branch Division of Waste Management
Enclosure:
As stated i .
CFC : WMLU TI:WMLU WMLU -
.....:._____70: , , __________ :____________'__.....____.:___
NAME . SMNe der:db;PHLohaus :17titj inbotham : :
DATE :83/10/03 10/ /83 : :
- 10/g/83 /
G707230305 870717 d PDR FOIA MINTON87-235 PDR J, .
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l Specific Coments On The Maxey Flats Decommissioning Plan, (Task 3).
- 1. Page 8, Intruder Performance Standard:
" Ensure protection of any individual" to what degree?
- 2. Page 17, 2.2.1.8 Monitoring systemi i
There are many other reasons for monitoring which were not (
mentioned. For example, to verify confinement, to detect changes, i to indicate trends, to identify potentially problematic situations, i to project doses, etc.
- 3. Page 17-20, Environmental Surveillance Programs:
- a. These tables appear to be listings of generic surveillance programs rather than site-specific programs to Maxey Flats. Were )
these programs in place at Maxey Flats? Note that these programs l were not recommended by the NRC for the Kentucky site and indeed may not be totally applicable. These monitoring programs first appeared in NUREG/CR-0570, Addendum, July 1981 for j reference disposal sites.
- b. Much of this discussion is not applicable to decommission j (e.g., establish baseline information, list of pre-operational )
monitoring activity, etc.). I
- c. Conspicuously absent are (i) a non-radiological curveil'ece !
program and (ii) a surveillance program during th c'cccrrissici.iq activities.
4 Page 20, Table 2-5., Post-Operational surveillance:
. Mfire tN post-u rnticr.al perico m ti.ru of the active cr c passive institutional control periods.
- b. Here again, the post-operational surveillance program appears t.o be generic rather than site specific to Maxey Flats. Components of an in-place monitoring program woulo ordinarily be continued into the active institutional control period. i
- 5. Page 21, Deep dynamic comoaction: ]
The word "only" in the last sentence of the phge, which reads
"... densification of Maxey Flats trenches require only the development of methods to control potential releases of j radioactivity and personnel exposure," is grossly misleading. 1 Densification procedures with pile removal may lead to major l radiological and non-radiological hazards off site as well as on site. The control of potential releases will not be readily achieved. Indeed, pile removal may present insurmountable l
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1 2-radiation control problems (See Item 42).
l 6. Page 25. Structural cap Clarify the extent of structural concrete caps. Are they to be above tne trenches only? Explain " bridge over the trenches." Is tne cap to be baluw' grade, on the-soil surface or raised above the sarface? Give examples and briefly explain what kind of cover will protect the cap in the long-term.
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- 7. P_ ape 26, Clay cap:
The bentonite clay layer will.pnly remain relatively impermeable as long as it is kept ut. This limithtion condition'should be-included in tha discussion to clarify why the bentonite layer must i be protected. It should also be noted that root systems can cause localized drying of the bentonite with attendent shrinking'and infilling of the cracks by non-bentonite soi): This_may effectively destroy the relative impermeability of the cap.
- 8. Page 39-40, Trench inventories:
What are the units associated with the given quantities? What are the dates of these inventories? The curie contents listed in Tables 2-8 and 2-9 do not seem to be in agreement. (e.g.3 it appears that 4 Trench 001 has 306 Ci according to Table 2-9 but only a few mci j according to Table 2-8). 1
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- 9. Page 42, Table 2-10, Radiological source term: l l
(a) units missing on all quantities.
(b) define " source term," and how used in the study.
(c) Where were the measurements made? (e.g., adjacent to trench, site boundary, etc.).
- 10. Page 45, Table 3-1, Pctential accidents:
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i (a) what is the basis or tource of information regarding " frequency" of various accident occurrences?
(b) define " performance scenario." ;
- 11. Page 46, next to last paragraph, Careful control over quality:
Give details or exar.ples of quality control of the positive trench drains.
- 12. Page 47, 3.1.3, Observation period:
(a) What specifically is to be observed and whyi a - __________________A.____m -
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(b) What is the duration of the observation period?
(c) What criteria is to be used for determining the duration of the observation period?
(d) How will design performance be evaluated? What are the criteria?
- 13. Page 47, 3.1.4, Active institutional control period:
l What is the rationale for a 100-year active institutional control period?
- 14. Paae 48, 3.3, last few lines, models to evaluate.adequ6cy:
Existing computer or other analytical models are frequently not appropriate for evaluating design adequacy fee many reasons (e.g., gross uncertainties of input parameter values, oversimplification in the mathematical descriptions of '
phenomenological behavior, etc.). Modeling for comparative purpcses would be more appropriate and meaningful.
- 15. Page 51, 4.1, Primary performance requirements:
Add a fourth component, namely " compliance with other stsndards" ;
to the words " waste isolation, safety and long-term perf ormance."
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- 16. Page 55, 4.1.13, ALARA: l Add the word "public" after " general" in that sentence.
- 17. Page 56, 4.1.2.3, Operational safety-occupational:
" Occupational" should include radiological as well as non-radiological regulations. How does this differ with section 4.1.2.1, Operational Safety-Radio'ogical?
- 18. Page 56, 4.1.3.1, _ Active institutional control period: I (a) Here too, as before (item 13), give rationale for "a minimum of 100 years." i (b) What criteria will be used to terminate the active cont'rol period?
19, Page 57, 4.2, Secondary performance requirements:
Site characteristics determination is not a performance requirement.
- 20. Page 59, Table 4-1, Site Characteristics to be determined for decommissioning:
Add to the list: wind speed and stand &N deviations, atmospheric pressure, relative humidity, meteorological and radiological background levels. '
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- 21. Page 66, Manage surface water:
The management of surface water is also closely related to, and influences, ground-water infiltration.
- 22. Page 70-72, 5.1.1, Trench consolidation model:
The model used (Sowers-1973) assumes that settlement due to l decomposition of waste is negligible and that primary consolidation l has been completed. It has not been demonstrated that dynamic consolidation will collapse a significant number of 55-gallon drums or other structural containers. Primary settlement may therefore continue to occur for long periods of time making this modeling-formula inapplicable at Maxey Flats. In' addition, this. formula is an empirical relationship developed on the basis of observations made at sanitary landfills. The applicability of this formula to Maxey Flats has not been demonstrated.
- 23. Page 74, third paragraph, Structural covers:
Here again "structual covers would be able to span areas where formulation conditions in the trenches are poor" needs clarification. Comments made.in item 6, as to the extent of structural caps, apply here as well.
- 24. Page 77, Figure 5-1, Trench design covers for Modeling:
Define symbols SC, CH, and GP which appear in the figure.
Explain " filters."
- 25. Page 81-83, 5.1.4, Trench drain model:
Has this system of trench drains and laterals (channels) ever been tested anywhere? What about long-term maintenance problems? Will these be sources of radioactivity to the environment? What.is the environmental impact of this system? What of the accumulation of radioactivity in the drain materials over time? This system raises many important questions which are not addressed in the document.
- 26. Page 82, Soil inputs:
Parameter values for trench covers (e.g'. hydraulic conductivities)-
- are different from those used in the infiltration modeling. This does not allow for reasonable comparative analysis.
- 27. Page 83, third paragraph, Closed from solutions to the movement of ground water:
The ground-water modeling seems to be superficial in nature. Not enough details are provided to allow for an adequate assessment of the methodology. The term " closed form" in the text leads one to
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believe that a simplistic, one-dimensional flow model was used. The statement "These solutions assume that a phreatic surface forms within the laterals" needs elucidation. What are the real-world j consequences of that assumption? Explain what is meant by j
" behavior of the lateral drainage system." Behavior with respect to what?
- 28. Page 94, 5.1.6.2, Modeling methods:
(a) "... simplified analyses of contaminant transport in the ground I water were made. . ." What are the simplifying assumptions? What are the analyses? Describe the modeling.
(b) "... Ground water measurement through the site rocks was assumed to occur at a rate of 15 meters per year." This statement doesn't make sense. What is moving? Water? leachate? contaminants? If so, which contaminants?
- 29. Page 94, last two paragraphs, Dose calculations:
What scenarios were assumed for the dose calculations? Was NUREG 1.109 used for all calculations? (NUREG 1.109 is primarily applicable to nuclear po.wer plants). What were the radionuclides and source terms used for the calculations? What was assumed about exposure times and ingestion rates?
- 30. Page 95, Table 5-2, Site configuration for dose evaluation:
Define " travel time." For what distance and what radionuclides? Are the values listed for trench infiltration ( 1/10 and 1/100 inch) assumed to apply to the decommissioning period? They do not appear to be conservative estimates. Compare also page 96 of the text, which assumes an infiltration of one inch per year.
- 31. page 96, Discussion of dose calculations:
(a) Large volumes of surface water were apparently used, hence large dilution factors result. A realistic scena'rio would be the nearby drinking water well used by an individual for daily intake. Little i or no dilution may occur. This scenario was not addressed. J (b) Which radionuclides and what concentrations were used for the drinking water scenario and for the consumption of milk?
What are the assumed pathways? Here again, an in-depth review is i not possible because of insufficient information.
- 32. Page 99-100, Sources for costs:
Page 99 makes referer.ce to the use of R. S. Means Construction Costs Data 1983 whereas Page 100 specifies the use of costs being provided by Law Engineering Company (without reference). This is ambiguous and does not permit analysis of cost data.
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- 33. Page 101, Table 5-6, Cost Bases:
Cost comparisons between the Corps of Engineers,1983 information (NUREG/CR-3144) and Law Engineering show wide descrepencies. (e.g.,
cost of clay cap, cost of flexible liners, etc.).
- 34. Page 104, Modeling discussion:
1 The HELP model is questionable for use in determining exact values ,
of infiltration (.01 inches per year). This probably exceeds the !
limits ~of this model. Very little input data used in the analysis has been provided making an in-depth review impossible. )
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- 35. Page 104, last line:
Describe " filters." ]
- 36. Page 105-106, Figure 6-1 and 6.2:
It may be difficult to obtain' field permeabilities of 7 x 10-10 fgp ]
the lower layer as indicated, unless nearby pure benetonites are used. 7In addition, it may not be possible to compact the local soils to 10~ cm/sec hydraulic conductivity.
- 37. Page 109, 6.1.4, Trench drain model:
(a) Explain how the dreins will be constructed to connect the interior trenches to the surrounding collector trench. !
(b) It is our understanding that several of the disposal- trenches at the site were excavated into the sandstone layers. This will necessitate the excavation of the drains through the sandstone which could be quite expensive. What is the impact of excavating through the sandstone? The estimates for drain infiltration appear quite low unless an engineered cover is used over the drains. Has the cover been assumed?
(c) Provide rationale for seemingly wide drains (10-60 fest).
(d) Explain " drains are more effective in removing large. slugs of water in the trench as apposed to handling continuing water volumes."
(e) How will these deep drains and trenches be maintained?
- 38. Page 110, Table 6-1: '
l (a) Drain infiltration values seem too low unless an engineered cover is in place.
(b) Travel time - for what radionuclides? I (c) What distances are assumed for travel time calculations?
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- 39. Page 111, second paragraph, These results demonstrate: 1 The second paragraph does not follow from the discussion in the previous paragraph.
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- 40. Page 111, third paragraph, A properly constructed drain system:
A " properly constructed drain system" has not been defined.
- 41. Page 114-115, Migration pathway analysis; Table 6-2, Dose calculations:
(a) No details are provided for the dose calculations with regard '
to radionuclides, er.posure periods, exposure scenarios, pathways considered, critical pathways, assumptions used (e.g.,
infiltration, leach rates) etc.
(b) " Dose calculated for all other cases are less than performance !
standards limits." What are the other cases? j (c) ".. these results are preliminary." Why? How will dose '
calculations be refined?
(d) Cases A through F in Table 6-2 have not been defined. What are they? Are they the same as " design concepts" A through F (pp 133) or Wsign options" A. through F (pp.136)?
(e) Again, not enough information has been provided for any analyses.
Table 6-2 is one of the most important pieces of information in the entire study yet lacks the details necessary for analysis.
- 42. Page 116, second paragraph, Dynamic compaction: ;
... dynamic compaction using driven pile. Piles are driven to 7 j meter depth at a spacing of 5 x diameter. The pile are removed as i the work progresses." This is another untested, unproven method j which may readily produce biological, chemical, and radiation '
hazards off site as well as on site. What levels of contamination would be expected on the piles themselves upon removal from the ground? What levels of gaseous activities will be released to the atmosphere? The document does not address hazards nor provide environmental impact assessments. !
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- 43. Page 116, 6.2.2, Positive trench drains.
j (a) Here again, how will the drains be interfaced with existing trenches? See Items No. 37 and 44 (b) What, if anything, would prevent leakage into and out of drains? What would prevent a " bath-tub" effect in the drains, laterals and surrounding collector trench?
(c) The document does not address long-term maintenance problems of the trench drain system.
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- 44. Page 117, 6.2.3, Cutoff trench:
(a) How will the cutoff (collector) trench, at 21 meters down, interface with the drains at 13 meters down?
(b) Explain " stockpiles" (Pgs. 116 and 117).
- 45. Page 118, Table 6-3, Construction costs:
The cost of a ground-water flow barrier was not estimated.
- 46. Py e 132, Design concept A:
Desfgn concept A with a lower barrier of hydraulic conductivity 10' cm/sec will not acnieve the desired infiltration of .01 inches per year according to the graph on page 106.
- 47. Page 133, Table 7-3, Recommended Monitoring:
(a) What is the rationale for monitoring off-site milk? Where are the nearest farms?
(b) This table is not in agreement with Table 2-5 (page 20) for the post-operation period. How do they interface? For example, monitoring of milk, fish and farm crops were not recommended in 3 Table 2-5, but are recommended in Table 7-3.
- 48. Page 134, Design concept D:
(a) Why is the plastic cover placed at the surface?
(b) Why not use plastic in conjunction with designs A or B? l
- 49. Page 134, Design concept F: l How was the 40 year service life for the asphalt membrane liner determined? A PNL document (PNL-4752, DOE /UMT-0064) specifies a j much longer service life. l
- 50. Page 152, top two lines, viability of option C:
Why is there a (premature) inclination to reject option C7 Option C is very viable in that the waste is not disturbed.
- 51. Page 156, last paragraph, Rockwell-Hanford demonstration:
The demonstration of impact compaction at the Hanford site will not be completed before early to mid 1984 Also trench waste conditions at Hanford are quite different from those at Maxey Flats. 4 Results must be generalized with caution. l l
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3EL 8 983 3201.6/SMN/83/12/06/0 Distribution:
WM file: 3201.6 /
WMEG r/f NMSS r/f REBrowning MEMORANDUM FOR: Donald A. Nussbaumer, Assistant Director MJBell l
' for State Agreements Programs JTGreeves Office of State Programs SMNeuder PLohaus FROM: Leo B. Higginbotham, Chief LBHigginbotham Low-Level and Uranium Projects Branch HJMiller Division of Waste Management, NMSS 0 t ng f3 ,
SUBJECT:
MRKnapp DECOMMISSIONING PLAN FOR MAXEY FLATS PDR We have reviewed the revised draft of the Decommissioning Plan for the Maxey Flats Disposal Site, Task 3: Evaluation of Alternatives. Our comments are enclosed. Dr. Stan Neuder is the technical contact for this pr0 ject. He can be reached at 427-4607 should any questions arise.
Leo B. Higginbotham, Chief Low-Level and Uranium Projects Branch Division of Waste Management
Enclosure:
As stated +
WM PIDlBCI ---
W(_.9 M@A;. C. Docket No._
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PDR LFDR Distibutig: _ . - - - -
1 IEe5tn to WM. 623 SS)
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0FC . WME'G g ,3 . WMEG : WMLU [: WMLh I / : :
_____:.. ____ g __.____________._______ _ _ _ . _ _ _ _ _ . _
NAME :SMNeudFr: Ics: JTGreeves . PLoh s : LHigginbotha[n :
l DATE : 12/ t /83 : 12/ /83 : / /83 : 12/g/83 :
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4 General Comments on Task 3 Decommissioning of M6xey Flats In general, the revised draf t for Task 3 - Evaluation of Decommissioning Alternatives provided specific information that responded to many previously expressed concerns of the reviewers. Technical information in this draft was clearly presented and included sufficient detail needed to assess the proposed decommissioning alternatives and the modeling methodologies.
Although most of the questions raised in our previous reviews of Task 3 have been addressed, several areas of major concern remain.
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l (1) The Proposed Cut-Off Trench and Barrier Wall. The performance of the cut-off trench is uncertain. The potential is there for creating a large " bathtub" if infiltration is not reduced and carefully controlled (See Specific Comments pp. 11, 30-32, 82, 89, 97).
(2) The Proposed Deep Compaction of Existing Waste. Potentially adverse consequences of tnis option incluce releases of hazardous chemicals and radioactivity into the environment, worker exposure, destruction of trench walls, and negative public perception (see Specific Comments pp. 40, 50, 103).
(3) Comparison of Decommissioning Concepts. Methodology for intercomparisons are not describec cespite well-developed listings of associated advantages and disadvantages. The list of l eight proposed Decommissioning Concepts is by no means exhaustive.
I Variations on.some of the Concepts, which may improve the design, I
are not addressed (see Specific Comments pp. vii, 5, 27, 50, 55, 68, 69, 71-2, 86).
(4) Conceptualized Logistics. Performance is based on implied site conditions (i.e. , relatively dry trenches,1/100 inch annual infiltration rate, and that the leach rate will be the same as the infiltration rate). These conditions may not be realized with existing trench water and some trench bottoms below the water table (see Specific Comments pp. 11, 30, 33, 51, 82, 97).
(5) Source Term Assumptions. The assumption that radioactive concentrations in the leachate will remain constant at the present levels found in trenches is questionable. Container degradation and especially deep compaction will substantially increase the source term (see Specific Comments pp. 11, 40, 50, 71-2, 89-90, 94).
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3.?01.6/SMN/83/11/25/0 (6) Modeling Methoddiogies- Little. input and output data has been provided for most of the modeling. Sensitivity analyses were not g quantified. Heavy reliance was placed on limited data. Validation a of some of the models used was not addresseo. Values of several -
important parameters were based on speculative assumptions (see Specific Comments pp. 82-84, 87-89, 106-110, 114-117, 120-122) i (7) Dose Projections. The projected dose is based on currently existing 3 site concitions. Dilution factors were estimated from limited data, I based on currently existing flow patterns. Leachate concentrations !
were assumed to remain at present levels. Stringent controls on i very low infiltration rates were assumed to be achievable. All infiltration were presumed to exit downward into the groundwater.
Since multilayered trench cap and cut-off trench will drastically ]
alter the groundwater flow patterns, most of the assumed modeling j parameter values will change. Dose projections will therefore be different than those specified (see Specific Comments pp. 92, 94, 121, 122, 127).
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l 3201.6/5MN/83/11/25/0 Specific Comments on Task 3 Decommissioning of Maxey Flats i l
Page vii, Last 4 Lines Quantify the basis for the statement that Concepts A and E are most j responsive.
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Page xi, Top Line Define life cycle and why Concepts A, D, and E have the lowest life cycle.
Page xi, Conclusions and Recommendations These conclusions do not fully reflect the broad content and significant findings of the document.
Page 5. 2nd Item The proposed evaluation criteria were never identified as such. Are they l the same as the various " categories" addressed in Chapter 5?
Page 11, 2nd Criteria What is the rationale for the 100 year functional life?
Page 11, Item (1)
Eliminating lateral flow through the fractures in the sandstone marker beds may generate one large bathtub, even for an infiltration rate of
- 0. 01 i n/yr. What are the assumptions regarding exit pathways for the 1 leachate under the conditions of no lateral flow? What evidence, if any, is there for no accumulation of leachate under the conditions of no lateral-flow?
i Page 14-16, Decommissioning Concept A J Rationale for the indicated thicknesses of the various trench cap layers should be provided. I I
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3201.6/SMN/83/11/25/0 I J
l l Page 14, 2nd Paragraph Does the dynamic compaction option in Concepts A, B, and C imply pile !
driving and surface compaction? I I
J Page 15, Figure 3-1 l 1 (a) It would be difficult to implement as well as maintain the integrity 1 of 6-inch layers in the multilayered trench cap. Bioturbation of the j thin upper layers may be a problem in the long-terir. Recommendations '
l based on experience are that layers be a minimum of 9 to 12 inches thick.
! (b) The compacted fill material should be identified.
l (c) Limestone cobble may not be the best choice. The chemistry of the j cobble should ce considered. If water percolates through the cobble j layer it will pick up HCO3 - from the cobble. The effect on trench water j chemistry is complex, i (d) The lower sand / gravel layers should be designed as a granular filter. Consider standard soil mechanic design procedures for gradation <
of filter materials. l (e) The trench cap represents about 10 feet of relatively heavy ]
overburden load across the entire site. What about possible future settlement of the natural subsoil materials?
Page 18, Figure 3-2
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(a) Cracking may be a major problem with the soil / cement layer. -
(b) A sand layer may need to be edded above the geotextile in order to prevent gravel punctures in the filter fabric.
Page 19. 1st Paragraph I i A geotextile will not minimize root intrusion. ]
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Page 25, Decommissioning Concept E )
l Greater detail should be provided on the physical description and extent of the concrete cap. A 3-dimr.:nsional sketch would help.
Page 26, Figure 3-5 Will localized consolidation and subsidence beneath the concrete cao l cause bowing?
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1 320L 6/SMN/83/11/25/0 l Page 27, Decommissioning Concept F j i
(a) The impression here is that an objective and constructive approach to Concept F has not been presented. Appropriate variations on Concept F will present a more viable option.
(b) The evaporator should be permitted to remain in the event of premature fa:'ure of the selected decommissioning concept.
Page 30, Cut-Off Trench l (a) It would be informative to model the entire cut-off trench rather than just the flow barrier north of the site.
(b) What are the assumptions regarding leachate movement with the cut-off trench in place?
(c) What is the required and expected permeability of the cut-off trench?
(d) Why the need for an additional north wall flow-barrier if the cut-off trench is relatively impermeable?
(e) There is some question about the amount of off-site groundwater flowing in from the north sector. Recharge in that sector and influx to the site should be quantified in order to justify the proposed wall barrier.
Page 31, Cut-Off Trench (a) It would be extremely difficult and expensive to implement a 35-ft deep cut-of f trench of width 12 to 15 f t. Backfill compaction, for example, may need to be implemented by hand in six inch lifts. A l standard slurry wall should be considered. Stability anc soil compaction j in a 35-f t deep trench without support (slurry) will be a major problem.
(b) The backfill compacted site soil represents a " disturbed" soil.
Whatassuranceisthergthatthepermeabilitywillbelessthanthe surroundir.g soils (10 cm/sec)? The concern is that the cut off trench i I may act as a collector of leachate resulting in a large " bathtub." l (c) Consider using a filter f abric or soil filter gradation at all l interfaces. l l (d) How does the ctt-off trench interf ace with the trench cap or concrete cap? I l (e) A 3-dimensior.al sketch of trench configuration would be helpful.
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Define " effectiveness" of the cut-off trench and how effectiveness may be I
monitored.
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3201.6/SMN/83/11/25/0 Page 33, Missing Paragraph Paragraph number 3.2.4.2 is missing.
Page 33, Relocate Sandstone Rubble some of the sandstone rubble may be used for the cobble layer.
Page 33, Borrow Area Soil borrowing may change hydraulic gradients and alter site groundwater flow. This may ultimately alter the dilution factors and projected dose.
Page 33, Add Paragraph An additionai paragraph should be added to discuss current and future water removal operations from the existing trenches and the prevention of further infiltration prior to and during the implementation phase of decommissioning.
Page 35, Demonstration Trench Define and describe the purpose of a demonstration trench and how it relates to existing conditions and the near-term decommissioning?
Page 40. Deep Compaction (a) In addition to the numerous disadvantages associated with deep ccmpaction (e.g., potential releases of toxic cnemicals, gases, and radioactivity, increase in trench leachate concentrations, potential destruction of trench walls, additional fracturing, generation of additional pathways to the environment, hazardous exposure of site workers, etc.) potentially adverse public reaction must be considered.
(b) Composition and compressive strength of landfills are different than those of the low-level waste site.
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Page 41, 3rd Paragraph References are incomplete, j
A 3201.6/SMN/83/11/25/0 Page 43, 4th Paragraph The disadvantages of the two pile-driving procedures are very different.
f- The insi.allation of foundation piles for the concrete treach cap (Concept E) provides a much smaller disadvantage than that associated with pile
'(- driving for deep compaction (Concept A). The major difference is that trench cap foundation piles are r.ot removed whereas the cor.;pacting piles are removed. (See Page 40 comments on deep compaction.)
Page 45, 1st Paragraph With only 10 percent bentonite, shrinkage and dessication cracking should not be significant. Another clay which is locally available may be useful. The Est111 Shale Member of the Noland Formation is one. This is a local clay that is quite plastic.
Page 45, 3rd Paraoraph
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Here too, use local material such as the Estill Shale.
Page 49, Cut-Off Trench Excavate the cut-off trench under a slurry head.
Page 50, Tcble 4-1, Concept A (a) The degree of the uncertainties associated with the listed items in the " Unknown" column are very significant. In evaluating the decommissioning concepts, the quality of the unknowns must be weighed accordingly. Agreed that this requires a certain amount of subjective judgement, nevertheless sound judgment needs to be exercised.
(b) Add to the list of Disadvantages: Extremely high potential for trench wall rupture and increased radioactivity concentrations in the leachate.
(c) Maintenance, although of a different character, may not be any less vigorous than that of, say, Concept F. An objective evaluation should be made.
(d) The degree of tolerable subsidence needs to be quantified in crder to make objective Concept comparisons.
(e) Under " Disadvantages" add continued long-term custodial care because of vegetation control. Add the same remark to Concepts B through F.
(f) Under " Disadvantages" add potential adverse public reaction to likely release of contaminants.
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1 Page 51, Table 4-1, Concept B Under " Disadvantages":
(a) Deep compaction technology is already known. Perhaps the technology q development refers to methodology necessary to control potentially adverse effects (see Page 40 comments). l (b) Having to replace the cap periodically may cause major problems.
Removal of infiltration controls during ceriods of precipitation may result in sufficient infiltration to re o e months of continuous evaporator use.
Page 55, Table 4-1, Concept F :
i (a) Again, the term " intensive care maintenance" should be quantified .
for comparison / purposes.
(b) Similarly, need to quantify " intensive" monitoring.
(c) Several variations or subsets of Concept F should be evaluated with the same detail. Variations of Concept F will result in a more viat,le decommissioning option than the one presented. For example, subsidence ;
and high infiltration rate may be reduced by appropriate engineering and agronomy methods. Similarly, environmental release via evaporator use ;
may be reduced by improving plant management methods. !
Page 60. Table 4-2 (a) The list number in the table should be 110,943.
(b) Are the given cost estimates for 100 years?
(c) Cost estimates for Concept F appear excessively high. A cost breakdown would be in order.
Page 66, Demonstration Testing .
1 Concept F is being tested, in part, with the lysimeters aY. Maxey Flats. I These tests may be continued in cooperation with other state ?nd/or federal agencies.
Page 68, Table 5-1, Cost Comparison The cost for 90 year institutional control for Concept F is listed as l being about four times as high as that for Cancept A. This cost-estimate should be broken down. Reasons for the large difference in cost is not obvious. 1
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Page 69, 2nd Paragraph 1
(a) Should read " Concept E is considered to provice the best technical solution" rather than "least technical solution."
(b) Concept F shceld rank higher in terms of technical maturity in view of many years of agronomy research.
(c) Details of Concepts comparison methodologies are not provided.
These are key considerations in the evaluation process and should be spelled out. How are "judgements" exercised?
Pages 71-72, Conclusions and Recommendations (a) Conclusion 1 - It is not obvious that the eight Decommissioning Concepts exhaust the range of technologies applicable to Maxey Flats.
(b) The statement that only decommissioning Concepts A through F meet off-site dose criteria has not been justified. For example, Concept H may provide sufficient reduction in infiltration rates to reduce the projected dose to acceptable levels. What is the projected off-site dose under Concept F?
(c) Recommendation a - Before cor,sidering the selection of Concept A, 8, or C it would be essential to " refine the source term" by cor:sidering the increased leachate concentrations and consequent effects on projected off-site dose. The snalysis should be quantified.
Page 81, 2nd Paragraph (e) The environmental consequence of airborne emissions, although
" judged to be of little consequence," should be quantified. Moreover, airborne emissions may be a putential hazard to the inadvertent intruder.
This pathway should be evaluated.
(b) The discussion seems to imply that there is an additional warning barrier other than the cobble layer. If so, what would that be? It is not at all obvious that the system will function properly in the event of animal intrusions into the trench cap layers above the cobt,le.
P_ age 82, Last Paragraph The assumption that "the volume of leachate movement from the trenches is equal to the amount of infiltration into the trenches" appears to be invalid because of the existing " bathtub" effect in many trenches and because the groundwater table in some areas might be BDove the bottom of some trenches. Alternatives to this assumption should be considered carefully since leachate movement directly affects off-site dose.
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2201.6/SMN/83/11/25/0 l Page 83, 2nd and 3rd paragraph (a) The 50 ft/yr groundwater velocity has been deduced from observations at only one trench location. Assuining that 50 ft/yr is the water velocity applicable to the entire site results in a tenuous description of groundwater flow. Calculated concentrations in the alluvial water and projected dose to the individual are all based on this assumed velocity.
l The error bars on the projected dose due to variations in assumed water velocities thould be addressed.
(b) Conceptually, there is no meaning to an " instantaneous release" l velocity. This needs to be defined. The velocity range " instantaneous to 20 ft/yr" does not seem to include the 50 ft/yr value as it should have been. Similar question applies to the 15 ft/3r velocity reported in Table A-5, Page 93.
(c) The results of the sensitivity analysis wefe never given.
(d) The value assumed for the groundwater velocity is rather critical 1 since the radiological exposure is mainly due to tritium (half-life 12.3 years),
l Page 85, tast Paragraph 1981 reference is incomplete. I Page 86, Table A-2 l j
i Several other radionuclides are present in the inventory (e.g., Ni-63, l C-14, etc.}. Have these been included in dose projections? Add their K d values ti the table.
Page 86, Last Paragraph Should quantify " insensitivity to reasonable variations in porosity and density." Here, again, the results of sensitivity analyses were not given.
Page 87, 2nd Paragraph The purpose for considering dilution factors and input parameters to LADTAP should be provided.
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1 Page 87-89, Dilution Factors i Dilution analyses is based in part on work by Zehner, 1983. How confident can one be about Zehner's data? What would the error-bars on the dilution factors be? Has a sensitivity analysis been performed? If so what are the findings? l 1
i Pace 89-90, Source Term Discussion 1
(a) The assumption that future concentrations of radionuclides in trench leachate will not exceed concentrations which currently exist in the trench leachate is questionable. Wnile no consistent trend of inc easing radionuclides concentration in the trench leachate has been identified to date may be due to the relatively short observation period. Increase in concentrations would be expected over the next few decades as drums and other containers eventually degrade.
(b) More importantly, the assumption of constancy of radionuclides concentration in trench leachate is totally invalid if any one of the Concepts A, B, or C will be used (dynamic compaction options). Dynamic compaction would release radionuclides in the trenches which may initially increase the concentrations 10-fold or more with accompanying incre;ses in projected doses. The concentrations will then steadily decay in time.
(c) The results of (a) and (b) implies a non-conservative assumption in
, the assumed source term. Consequently a more stringent limit on I infiltration rate criteria would be necessary.
Page 91, Table A-4 (a) The 4number, 1.6 x 108 picocuries per liter, next to Cs-137 should be 1.6 x 10 .
(b) Other radionuclides such as C-14 have not been listed.
(c) How might these concentrations change with dynamic compaction?
l Page 92, 1st Paragraph (a) Define the " general population" used for dose projections.
(b) Describe the water pathway scenario for population eose. Is it the surface drinking water pathway only or does it include forage irrigation.
(c) What is the actual and assumed farm and animal population in the vicinity?
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3201.6/5MN/83/11/25/0 Page 52, 4th Paragraph (a) The statement that the " meat and milk pathways were excluded from the groundwater pathway calculations" is not clear, as these pathways are mutually exclusive.
(b) Elaborate on the statement that " exclusion of these pathways results in doses which are approximately one-half the value calculated with all l pathways included." This does not seem to agree with the reported calculational results given in Table A-6, Page 94, where, for example, the groundwater pathway yields 254 mrem / year while the surface water pathways yields 19 mrem / year, a f actor of 13 difference.
(c) The discussion or. pathways in general needs further clarification U.d the assumed parameter values need to be spelled out.
Page 94. Table A-6 (a) It is important to keep in mind that the calculated doses presented in this table are based on the currently existing radionuclides concentrations in the waste trenches. Exe cising Options A, B, or C will significantly increase the dose estimates.
(b) An additional concern is that higher radionuclides concentrations may exist at other site locations and there is some uneasiness with the fact j that dose projections are based on site data at only one ur two locations. The question of higher radionuclides concentrations at other locations should be addressed if sufficient data exists.
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a age 95, Middle Paragraph j l
Since dose results &lmost exclusively from exposure to tritium (half-life 12.3 years) and dose projections are based on current leachate concentrations, it would be appropriate to the overall decommissioning plan to project doses over a 200 to 300 year period under various scenarios (i) co%stant source term, (ii) slowly increasing source term due to container decomposition, (iii) possible change in source term due to selection of Option E, and (iv) sudden, large incrcase in source term I due to selection of Options A, B, or C. Of concern here is that dynamic I compaction (part of Options A, B, and C), will significantly increase the source term and projected doses.
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Pace 95, Lt.st Paracraph (a) The statement that " monitoring data. . indicates that base case dose estimates are high^ should be quantified.
(b) The statement that " calculated doses are larger than will occur" is not necessarily true becau,se (i) major portions of the radionuclides have not as yet leached / arrived at those locations, (ii) monitoring inay not
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3201.6/5MN/83/11/25/0 have detected possible higher concentrations at other nearby locations, and (iii) modeling is based on existing (unccmpacted waste) source terms.
(c) How does one explain the existing discrepancies between estimated and measured concentration data?
(d) It would be appropriate at tnis point to address the appreciable levels of tritium concents ations found in local tree samples. The levels translate to dose rates equaling or exceeding 25 mrem / year due to a hypothetical drinking-water well.
Page 97, 1st Paragraoh (a) How effective is the cut-off trench or low permeability wall expected to be in preventing potential !ateral movement?
(b) Will any trenches be deeper than the flow barrier? If so, how will this affect the dose projection?
(c) Most impcrtant is the fact that the groundwater table in some areas might be above some trench bottoms, rendering a cut-off trench ineffective.
Page 97, 2nd Paragraph Elucidate on " hydrological isolation" and " precipitating agents."
Page 97, 3rd Paragraph Is an infiltration rate of 0.01 inches per year impracticable? What infiltration rates does the modelirg predict for Concep,ts A through H?
Does one concept provide more effective infiltration control thar, another? This is a key question which is not answered li) the infiltration control model results (Page 109-110). The choice of trench cap options will certainly deoend on the ability to meet the 0.01 inches per year.
Page 100, 3rd Paragraph Should read " secondary compression occurs." ,
I Page 103, Consolidation Model Results Af ter impact compaction, the model predicts h f t. to lh f t. , long-term ,
settlement. In view of the potentiai radiological hazards, chemical !
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3201.6/5MN/83/11/25/0 hazards, additional costs associated with impact compaction and residual long-term settlement, is compaction a viable design element?
Page 106, Modeling Methods How valid is the HELP model for the present application? The HELP model has several levels of approximation which should be discussed. The EPA uses this model to evaluate surface runoff and drain flow but does not use it to evaluate liner performance. Of special concern is how HELP l handles flow when the layers are only partially saturated. The model may I assume no flow conditions when the soil is not saturated. This assumotion may significantly affect accuracy of prediction when simulating systems with low flux. HELP also ignores vapor flux and might therefore not be appropriate to investigate potential drying of liner layers. These issues should be addressed in the discussion.
i Page 106, Last Line
, It is unclear how the 3 percent slope will be implemented. Will it be across individual trenches, across several trenches or across'the entire site? How readily can 3 percent slopes be. implemented in two-dimensions across an extended area with drains and long-term maintenance requirements? Greater detail is necessary.
Page 109, 2nd Paragraph Synthetic membranes were considered but model output was not presented.
Page 109, 3rd Paragraph Modeling results which indicate that the chosen design is the most effective are not presented to support the conclusion.
Page 110, 2nd Paragraph Data is not presented to support the conclusions.
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! Page 110, 3rd Paragraph Increasing soil layer thickness is straightforward and much more reliable than decreasing its hydraulic conductivity.
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! 3201.6/SMN/83/11/25/0 Page 110, 4th Paragraph The use of the HELP code in this generic analysis is very valuable for comparing alternative designs. The analysis, however, may not be sufficient to predict percolation performance of 0.01 inches / year.
Page 110, 4th and 5th Paragraphs (a) What are the results of the infiltration modeling? Details tre not provided to support conclusions.
(b) Since one is at the limits of the model used, what uncertainties I would be expected in the calculated percolation rate of 0.01 in/yr?
(c) Most importantly, the multi-layered trench cap will effect the piezometric contours. How will the projected off-site doses ce changed from those predicted on the basis of presently existing site conditions?
Pages 114-117, General Discussion 1
(a) More consideration should be given to the fact that drainageways !
will require additional protection against erosion and that the l calculations were done for single trench slopes. The designs shown in Figure B-3 and B-7 indicate slope lengths much longer than 9,75 meters and erosion may increase significantly as a result.
(b) In discussing the HELP model, short drainage pathways were also used. Since the cover will be placed across the entire site, drainage path lengths will be longer and infiltration higher than calculated.
Page 120, 3rd Paragraph (a) The trench excavation option is mentioned but not modeled.
(b) A three-dimensional diagram and additional descriptions would help Does the cut-off trench surropnd the entire site?
Page 129, 5th Paragraph Model input value; should be presented. Was this model " calibrated"?
What is the significance of the geometric mean? A discussion of Zehner's analyses would be helpful.
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3201,6/5MN/83/11/25/0 Page 121, 2nd Daragraph j
(a) Again, model input and rationales are not provided.
(b) L17e 5 should read " constant head boundary."
(c) Results cf sensitivity analysis were not presented.
Page 121, Last Paragraph Radionuclides travel time, dilution factors, and resviting dose l projections were modeled on the basis of currently existing surface and l groundwater flow patterns (Pages 83-97). A low permeability, l mult.ilayered trench cap will not only decrease infiltration of precipitation but will also alter flow patterns because of changes in the direction of the hydraulic gradients. Different flow patterns will I affect dilution factors. The concern here is that other dilution factors should have been usea for establishing infiltration criteria.
Page 122, Groundwater Flow Barrier-Modeling Results Here again, the estimated radionuclides travel time will be altered because the combination of low permeability trench cap and flow barrier t will produce a significant change in hydraulic gradient across the disposal area. It would be more meaningful to ertimate dilution factors and off-site doses with the decommission options in place.
i Pages 124 and 126, Figures A-11-and A-13 l l
(a) It would be extremely helpful to indicate the location of the ]
" equivalent flow barrier" on the figures. j Page 127, 2nd Paragraph l
(a) The flow barrier and up gradient drain will divert the flow away from the waste disposal site. The drop in piezometric head will ultimately affect dilution. Consequent changes in the dilution factors i and dose projections should be addressed and quantified if possible. 4 (b) The quoted values for changes in the piezometric heads are not ,
apparent from the figures.
Pace 127, Assumptions Elaborate on the rationale for, and the consequences of, the two stated assumptions.
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3201.6/5MN/83/11/25/0 Page 127, Last Paragraph The easing of the requirement on infiltration rate will alter the projected dose. Dose estimates over the following 200 to 300 years should be quantified.
Page 141, Fioure B-5 It appears that some waste disposal trenches are located outside the perimeter of the cut-off trench which defeats the purpose of the cut-off trench.
Page 181, Glossary It would be helpful to add (or to refer to the appropriate description page) the following: alluvium, consolidation, void ratio, dilution factor, cut-off trench, barrier wall, upper and lower marker beds, flume, positive trench drain, evaporator, and sump.
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