ML20217M586
| ML20217M586 | |
| Person / Time | |
|---|---|
| Issue date: | 01/29/1992 |
| From: | Surmeier J NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Chernoff A ENERGY, DEPT. OF |
| References | |
| REF-WM-3, TASK-TF, TASK-URFO NUDOCS 9801090229 | |
| Download: ML20217M586 (13) | |
Text
.__ - - -
i hsM / '
SW/FCT/ ADD COMMENTS 8Q[
6 Albert R. Chernoff, Proj::ct Manager M 2 81992 Uranium Mill Tailings Remedial Action Project Office pf72 '/ - [
U.S. Department of Energy Albuquerque Operations Office jm
,tf P.O. Box 5400
~
Albuquerque, New Mexico 87115
Dear Mr. Chernoff:
i The U.S. Nuclear Regulatory Commission (NRC) staff has comp (leted th review of the Falls City, Texas final Remedial Action Plan RAP) dated November, 1991. As a result of this review, the NRC staff concluded that the information provided in the final RAP did not resolve all of the open issues identified in the draft Technical Evaluation Report (dTER).
In addition, the staff identified additional open issues, both technical and editorial. A list showing the current status of al' 2 pen issues (dTER and new) regarding the Falls City Texas RAP is provided as an enclosure to this letter. The NRC staff discussed these open issues with DOE during their telephone conferener call of January 15, 1991.
As you are aware, until these open issues are resolved, the NRC is not Q
prepared to concur in the RAP or the Remedial Action Inspection Plan (RAIP).
I would like to also point out that the issuance of this letter does not alter the NRC staff position that the data can support the Class III Aquifer designation for groundwater at the Falls City, Texas site as discussed in our letter of September 18, 1991. DOE snould provide the information to resolve these open issues in the form of page changes (new information highlighted) to the November,1991 binder version of the RAP, including new cover page inserts.
If you have any questions regarding the information in the enclosure, please contact me at FTS 964-3439 or the NRC Project Manager, Sandra Wastler, at e
FTS 964-2582.
Sincerely, np:nmv m~a: n y John J. Surmeier, Chief
(
Uranium Recovery Branch Division of Low-level Waste Management and Deconnissioning, NMSS
Enclosure:
As stated cc:
P. Mann, DOE /AL D. Lacker, TBRC, Texas G. Gartzke, TBRC Texas Distribution:
Central File #
NMSS r/f LLUR r/f PLohaus RBangart JSurmeier JAustin DGillen DRom BJagannath.
SWastler TJohnson MLayton LJCallan,RIV RHall,RIV,URF0 DJacoby,RIV,URF0 RM)ller WBrach PDR YES X
ACNW YES X
.d SUBJECT ABSTRKCT:
FALLS CITY, TEIAS DDITIONAL OPEN ISSUES OFC :tLUR
- LLUR NAME:S 1r
- DG len
- JSu e er:
CATE:018(/92
- 01/JT/92
- 01/A7/92 :
nnieia8 RECORD COPY 9801090229 920129 PDR WASTE WM-3 rDR
U l
e THE CURRENT STATUS 0F THE OPEN ISSUES IN THE DRAFT TER 0F NARCH 21, 1991, INCLUDING NRC C009 LENT ON 00E'S RESPONSE IN THE NOVEMBER 1991 FINAL REMEDIAL ACTION PLAN The following list provides the current status of each dTER open issue and identifies additional open issues in the Falls City final Remedial Action Plan I
(November,1991) that must be resolved before NRC concurrence can be granted.
l DTER OPEN ISSUES 1.
RESOLVED 2.
RESOLVED 3.
RESOLVED 4.
RESOLVED 5.
The hydraulic conductivity issue has not been addressed. The staff concerns are presented below.
Open item No. 5 in the DTER outlined several concerns the NRC staff had l
regarding the use of laboratory tests to provide representative verification of the constructed radon barrier permeability, along with concerns of compacting the highly plastic clay to the stringently low design permeability. Because of the proposed use of Supplemental Standards, a stringently low design permeability for the radon barrier may not be critical for meeting the ground-water protection regulatory requirements. Regardless, DOE should provide a discussion of the anticipated hydraulic conductivity range that can be realistically achieved under the compaction criteria (as discussed in Mitchell's report) of the design and plasticity of the radon barrier material. DOE should also determine, by a parametric analysis such as the HELP Code, the maximum hydraulic conductivity value that would demonstrate the conservatism of the present design and be as close to the otherwise applicable standards, as required in the Supplemental Standards. DOE should then make the determination that the anticipated hydraulic
]
conductivity, that can be realistically achieved, will comply with the k
provisions of Supplemental Standards.
6.
The DOE has revised the strength parameters and the revised parameters are reasonable values.
In addition, the slope stability evaluation uses a very conservative cross section and the resulting factors of safety are higher than the acceptable minimum values. The revised strength parameters and their use in the slope stability evaluation are acceptable to the staff. However, the following aspect of dTER issue 6 (Subitem 5, dTER Section 3.2.5) has not been adequately addressed:
It is stated that composite samples were prepared in the laboratory to represent remolded tailings. However, there is no description of (1) how the three materials (sand, sand-slime, and slime) were mixed in the laboratory, and (2) how this is deemed to 1
i 6
be representative of the tailings after they are relocated in the disposal cell. Since the tailings placement specifications do not place any specific requirements on mixing the tailings before placing them in the disposal cell, it is important to establish the basis on which the relocated tailings tested in the laboratory are representative of the materials placed in the disposal cell.
These aspects of relocated tailings need to be addressed in the RAP.
7.
Draft TER issue 7 addressed concerns regarding the organic contents of the radon barrier material and the tailings (Subitems 6 and 9, dTER Section 3.2.5).
To address subitem 9, DOE has provided a report by Mitchell on the presence of organic material in the radon barrier material. Mitchell's report indicates an organic content ranging from 6.5 to 7% average and that the organics are fully decomposed and appear in mottled pattern. Because of the mottled appearance, Mitchell concludes that the organics are not a continuous vein and are not likely to be flow paths that would result in accelerated flow of water or gas.
However, Mitchell recommends thorough mixing, compaction to a high density, and additional tests to establish the design parameters.
In Q
the final RAP, DOE has neither (1) referred and discussed this report in detail nor (2) followed through the report's recommendations.
Subitem 6, regarding the organic content of tailings was not addressed.
This item was presented in the dTER as follows:
The quantity of tailings to be relocated from piles #3, #4, and #5 is approximately 1,851,100 cy. Only three tests, one for each pile, were conducted to determine their organic contents. Their organic contents were 1.4, 4.8, and 5.5 percent. Using the average of these three values as the organic content of the tailings in the disposal cell is not statistically valid as the samples are not likely to be representative of the relocated tailings.
In remedial action plans for other sites, the organic content of the materials placed in the disposal cell is limited to a maximum of 5 percent, and two out of the three tests indicated O
organic contents of 4.8 and 5.5 percent.
Inclusion of other contaminated or9anic materiais, sucn as coatamiaated vesetation etc., will result in increasing the organic content of the disposal cell. DOE should evaluate this concern in detail and justify the acceptability of their finding.
Removing the organic content requirement from the specifications is not the solution, since the organic content remains in the material.
8.
RESOLVED 9.
DOE's response to the settlement issue is not satisfactory. The revised calculations use only the settlement of slime, beyond the eleven month construction time, in calculating the cracking potential for the radon barrier layer.
Inherent assumption in this method is uniform 2
7 k
b stratigraphy between the locations at which the settlements were calculated. The development of the tailings pile # 7 at this site consisted of starter beras and evaporations ponds resulting in slime surrounded by incompressible bers. Therefore, the amaanMon of uniform stratigraphy between settlement points is not reriistic. Furthermore, the maximum horizontal strain c:A viated u 0.*J percent and the maximum horizontal strain that can be tolerated by the radon barrier material without cracking is 0.15 percent. Considering the closeness of these two numbers and the approximations and assumptions in the graphic method of evaluating horizontal strain in the cracking analysis, the staff considers the radon barrier cracking to be a potential problem. DOE should develop the details of remedial measures mentioned in the RAP, such as placing low-contaminated material above the slime and monitoring settlement to establish the point of near completion of settlement before placing the radon barrier layer. The DOE should submit details of the above options for evaluation by the NRC.
10.
The revised liquefaction analyses does not resolve the concerns that there are still pockets of sand tailings that are susceptible to liquefaction. This is because of the presence of perched water table O
which is likely to be there for a while.
Instead, the DOE has suggested i
leaving or reconstructing the starter beras that confined the tailings in place and would prevent the flow of any liquefied sand. The DOE has not yet documented their solution for this concern. Liquefaction is an open issue.
11.
The specifications of the radon barrier material have to be revised to reflect the organic content determined in tests run by Mitchell and the DOE's decision on whether to implement recommendations in Mitchell's report on compaction density of radon barrier material. Eliminating the organic content requirement from the specification, as currently proposed by DOE, does not address staff concerns.
In addition, the gradation requirements in the specifications should be revised to reflect the gradation characteristics of the materials tested to develop the design parameters. Any material barely passing the specifications should be similar to the materials used in laboratory tests performed to develop the design parameters. Because the plasticity characteristics 1
O of the radon barrier clay material is an important property in determining its resistance to cracking, the radon barrier material specifications should include a required m'nimum plasticity index.
I 12.
Revisions B and C to the Falls City, Texas, RAIP have addressed the staff concerns and the response is satisfactory. However, consistent with isne 11 above, the RAIP should be revised further to include testing for plasticity index.
13.
RESOLVED 14.
P.ESOLVED 15.
RESOLVED 3
_A 1
16.
RESOLVED 17.
RESOLVED 18.
RESOLVED 19.
RESOLVED 20.
RESOLVED 21.
The " moly" plume discussions (Sectior. 3.8, Page 32, sixth and seventh paragraphs) do not include the information presented to the NRC staff in the July, 1991 response to a previous NRC information request. This information should be incorporated into the RAP.
22.
RESOLVED 23.
FEiOLVED 24.
RESOLVED 25.
(1) RESOLVED (2) The composite samples used to determine dry density for the relocated tailings were sands and sand-slims, yet DOE states that half of the relocated tailings are composed of slimes. The representativeness of the composite samples should be established or the conservatism of the parameter currently used should be demonstrated using the worst case scenario of tailings placement within the disposal cell.
(3) DOE's submittal of 4/30/91 is satisfactory. However, the maps provided in the final RAP (sheets 9 and 10 in calculation 20-439-01-02) include a location 526 in Parcel A and in Parcel B.
DOE's 4/30/91 response located wind-blown sample 526 in Parcel A.
The final RAP l
locates the sample in Parcel B.
DOE should clarify which is the correct response.
O (4) DOE should add to Section 6.3 of the RAS a reference to NUREG/CR-2875 as the source of the experimental procedure used to measure radon diffusion coefficients.
t (5) As provided in the 4/30/91 submittal, DOE should provide the information on Pile 8 in the final RAP.
In response t) the staff comment requesting an explanation of why it is appropr! ate to include the upper two feet of material in the calculations for manation fractions, DOE presented information to justify their conclusion that emanation coefficient is independent of moisture content and activity.
However, there is no supporting data such as the soil type and porosity of the samples. Furthermore, previous studies and models of radon emanations indicates emanation increases with moisture, especially in the 0 - 20 % range. Therefore, DOE's conclusion cannot be verified.
4 i
J
a i
DOE should provide the missing data and justify their interpretation of the data or withdraw their current conclusion.
26.
If the Mitchell report is to be used as a basis for DOE's argument to allow some organics in the radon barrier, then the report needs to be referenced in the Section on radon barrier design and Mitchell's recommendations need to be followed.
In addition, since the estimate of long-term moisture content is based on the organic-dependent Rawls and Brakenseik equation, any change to the estimated organic content based on the Mitchell data need to be factored into the long-term moisture calculations.
See items 7 and 11 for related concerns on organic content.
27.
The radon attenuation analysis should be revisited to determine if any changes in the computer model are required to accurately characterize the system after considering the above comments.
28.
DOE should provide a site-specific procedure, referenced in the RAS, for identifying naturally occurring uranium ore.
Q ADDITIONAL OPEN ISSUES - BASED M THE NOVEMBER 1991 SUBMITTAL 29.
DOE's incorrectly used Roger's empirical equation for estimating long-term moisture content for the contaminant material and the radon material.
In the case of the contaminant material, DOE's proposed values for long-term moisture remain the most conservative when compared to results from the correct usage of Rogers' equations. However, in the case of the radon barrier material, the equation yields a result significantly lower than DOE's value for long-term moisture content. DOE should correct its usage of Rogers' equation.
If DOE chooses to use the present value for long-term moisture content, justification should be provided.
- 30., Section 02090, Well Abandonment: This specification should be modified to address special abandonment procedures for wells identified by DOE as being inadequate because of poor construction or sand pack completions that cross formation boundaries and connect two O
separate permeable zones. Several wells in the Dilworth sand are so identified in the RAP. Abandonment procedures outlined in this specification will not prevent potential cross contamination of separate permeable units.
- 31., Section 02090, Well Abandonment, Page 02090-2: This table identifies the wells scheduled for abandonment. The table should include those Dilworth wells identified in the RAP as being inadequate because of poor construction or inappropriate sand pack lengths. Also, well 617 is scheduled for abandonment.
If the reason for abandonment is its closeness to the completed disposal cell, then well 701 should also be scheduled for abandonment. Drawing No. FCT PS-10-0417 shows two I
wells (B10 and 816) located in tailings piles. Are these wells still existing? If so, they should be included in Table 02090-1 for abandonment.
5
b I
l
- 32. Attachment.
Page 4, Table 1.1, has a table heading for the EPA MCLs that shoulu be removed. Also, is this table meant to be generic or site specific? The table lists all compounds with MCLs, whether the compounds are present at the site or not. The Appendix I and Appendix IX constituents listed appear to be only those compounds that were i
identified (or remotely expected) at the site. This table should be revised.
- 33., Section 3.2, Page 12, fifth paragraph: The statement;
" Pumping tests have shown.......... that there is no vertical hydraulic connection other than leakage....." is not accurate. The tests were too short in duration to demonstrate or disprove any type of vertical hydraulic connection.
It is accurate to state that vertical hydraulic connection was not observed during the short-duration pumping tests.
All references to ' pumping tests demonstrated that there is no vertical i
hydraulic connection' throughout the text should be clarified.
- 34., Section 3.4.3, Page 20, sixth paragraph: Table 3.13 is incorrectly referenced.
O
- 35., Section 3.5.1, Page 24, fourth paragraph: The number of l
monitoring wells at the Hobson site should be included in the text i
discussion.
- 36., Section 3.5.2, Page 25, third paragraph: Table 3.18 is incorrectly referenced.
- 37., Section 3.6, Page 27-28, History of operations: There is no description nor mention of when or who dismantled the mill building and facilities. This section should include such a description.
- 38.. Section 3.6, Page 29, third paragraph: Descriptions of the solution mining indicate that four piles were mined in this manner.
Descriptions on Page 28, fifth paragraph state that five piles were mined in this manner. This inconsistency in the text should be corrected.
O
- 39., Section 3.9, Page 36, third paragraph: Discussions of the
" moly pit" refer back to section 2.0, which does not contain a discussion on the " moly pit".
The text should be corrected to provide the correct reference to the " moly pit" discussion.
- 40., Section 3.9, Page 36, Current aeochemical environment:
Are~the discussions in this subsection restricted to ambient conditions or does it include contaminant geochemistry? Are the geochemical equilibrium simulations restricted to the designated background wells or l
are the 600 series wells included in the database? The 600 series wells I
are useful as supporting evidence (general qualitative). Their use as a part of the computational database is inappropriate from a data-quality verification perspective, since the well construction quality cannot be confirm.d.
In a similar sense, the Hobson data are supporting
(
information and would not be appropriate to use in a computational 6
l l
}
-3 database. Please clarify these points in the text.
- 41., Section 3.9, Page 37, first paragraph: Table 3.20 is incorrectly referenced. The information described in the text is not included in any tables in Attachment 3.
- 42., Section 3.9, Page 39, first paragraph: Input and output i
files to the PHREEQE model were not referenced as a calculation, nor provided as page changes in this submittal. Are the inputs and outputs the same as those submitted in previous RAP draft? If so, are the pre-DOE 600 and 700 series wells included in the data input (see commeni.
40)? Please clarify.
- 43., Figure 3.9: Well 969 is depicted as being questionable for water-level measurements because of construction considerations.
This well is also listed as a background well.
If construction of well 969 is questionable, in any way, it should not be designated as a background well. Text descri modified if this is the case.ptions, tables and figures should be Q
- 44., Figure 3.9 and Table 3.13: Well 679 is shown as questionable on Figure 3.9.
The well is not listed as being questionable on Table 3.13.
Well 679 should be added to Table 3.13 with an appropriate explanation.
- 45., Figure 3.10: This figure needs an notation explaining why i
the ore zones shown in Figure 3.12 corre: pond to the areas with no borehole locations.
- 46., Figures 3.6, 3.17 through 3.25: These figures do not include the TBEG information presented to NRC staff in the August 9, i
1991 meeting. The figures should be revised to include the new information., Figures 3.7 and 3.9; Those two figures include the same water level data from the Dilworth aquifer, but show different contours.
O-These figures should be re-examined and revised for consistency.
47.
Tables 3.17 through 3.21: These tables need to include the number of wells and samples represented in the ranges.
- 48. : The source of the information presented in Table 3.5 should be referenced. Are these data from published literature, or historic information from 600 series wells?
- 49. : There is an apparent contradiction with information present in Attachment 4. Page 43, Section 3.6, Second paragraph states
"... use of background water from the Deweesville/Conquista aquifer
....... would not present a threat to health of livestock drinking the water....."; whereas, Page 41,Section 3.5.2, Third paragraph says,
"..... whereas the Deweesville/Conquista aquifer shows a potential adverse health effects from these uses (stock and garden) due to highly 7
i
i a
elevated uranium concentrations." Please clarify this contradiction.
- 50. : DOE should incorporate a description of an alternative program for post-closure monitoring in the RAP. Details of the program can be included in the Long-Tern Surveillance Plan. Wording similar to that in the last paragraph of page 5-1, Revision A, DOE Draft Guidance on Surveillance and Maintenance and Long-Term Care Details of the program could be used in the RAP. Additional information on the implementation of the program would also be necessary.
The monitoring is needed as a mechanism to initiate ground-water corrective action (if needed) and demonstrate disposal cell performance.
The NRC staff views that Supplemental Standards are applied on a case-by-case basis, and that the specific elements of the standards are dependant on site-specific conditions. The elements of the Supplemental Standards can include proposals of alternative specific stand &rds, as well as proposals of alternative methods to "come as close to the otherwise applicable standards."
Post-closure monitoring was required in some of the previous RAPS where Q
supplemental standards were applied, because site-specific conditions dictated the need for some form of monitoring to be protective of human health or the environment.
In other cases, site conditions did not warrant post-closure monitoring, if site conditions would remain unchanged. A detailed discussion of the NRC staff position is provided in the attached pages.
O 8
4 a
APPLICATION 0F SUPPLEMENTAL STAfSARDS FOR WATER RES0URCE PROTECTION AT UNTRAP SITES In Subparts A and B, ground-water monitoring serves as a mechanism for verifying the disposal cell performance and thus protection of human health
'i and environment, and also serves as a mechanism for initiating corrective action when the disposal cell components fail to perform according to design criteria.
Applying supplemental standards at an UMTRAP site without a monitoring or verification mechanism may compromise the verification of cell performance, and will not provide a method for initiating corrective action, if needed in the future to protect human health and the environment.
l The NRC staff recognizes that supplemental standards are applied in lieu of the standards in Subparts A and B, under the specific conditions listed in
$192.21. Ultimately, when $192.21(g) (Class III ground water) is invoked, the following requirements must be met:
O 1.
The implementing agencies shall select and perform actions that come as close to meeting the otherwise applicable standard as is-reasonable under the circumstances (6192.22(a)).
2.
The implementing agencies must apply any remedial actions for the restoration of contaminated ground water that is required to l
assure, at a minimum, protection of human health and the environment ($192.22(d)).
In addition, 192.22(c) provides for the implementing agencies to make a specific determination at a specific site concerning remedial actions for any provision of $192.21 that qualifies the use of supplemental standards.
l O Site-specific determinations for concurrence have been made by the NRC staff l
on all UMTRAP sites for which DOE invoked supplemental standards. The l
criteria used to make these site-specific determinations are listed above, as provided by $192.22 (a) through (d). A brief summary of the UMTRAP sites that used supplemental standards for water resource protection is provided below.
Ground-water monitoring was excluded in some instances and is being performed in others. The use of Supplemental Standards for each of these sites was evaluated on a case-by-case basis, with the appropriateness of ground-water monitoring determined according to the site-specific conditions.
The Remedial Action Plans for these sites were reviewed by the NRC staff.
I
Class III designation of uppermost aquifer, monitoring excluded e
Vitro disposal cell - Clive. Utah : This remediation was completed before the proposed revised EPA regulations were l
published; however, the site-specific technical review of the l
disposal cell siting and characterization encompassed many of the j
supplemental standard concepts that are currently included in the regulation. The uppermost aquifer meets the Class III designation l
by TDS exceeding 10,000 ppe. Ground-water monitoring was not proposed, primarily because of the extremely low likelihood of adverse impact to human health and the environment.
There are no surface-water discharge points near the disposal cell and the I
nearest potential ground-water receptor is beyond the 1000 year ground-water travel-time distance, under the most conservative assumptions. Future development of the saline ground water in the area is highly unlikely.
e Snook site - Snook. Wyomina: Supplemental Standards were applied to this site, since the uppermost aquifer met the Class III designation due to widespread ambient contacination (cre zones).
O Neither ground-water monitoring nor a correct:ye action plan were proposed, because of no historic use and no surface-water discharge points from uppermost aquifer. The low probability of i
future human health and environmental exposure make the credible i
failure scenarios of the disposal cell insignificant. Provisions were placed in the NRC concurrence that monitoring and corrective action may be needed in the future if the site conditions significantly change and present a greater exposure potential than is presently estimated at the site.
e Ambrosia Lake site - Ambrosia Lake. New Mexico : Supplemental Standards were applied to this site, since the uppermost aquifer i
met the Class III designation due to the projected sustained yield l
being less than 150 gpd. No monitoring was proposed, because saturation in uppermost aquifer is totally derived from tailings i
seepage and is of limited extent.
There is no historic water use in the uppermost aquifer, nor in the next lower aquifer. There O
are no surface water discharge points. DOE is monitoring a deeper aquifer that has some domestic and stock use because of the l
vertical hydraulic connection with shallower aquifers by deep mine shafts. Contamination of the deeper aquifers is attributed largely to mining activities.
1 l
Class III designation with monitoring e
Shiorock site - Shierock. New Mexico:
This remediation was also completed before the proposed revised EPA regulations were published; however, the site-specific technical review of the disposal cell siting and characterization encompassed many of the 2
l
4 supplemental standard concepts that are currently included in the regulation. TDS within the uppermost aquifer exceeds 10,000 ppa.
Saturation in the uppermost aquifer is largely derived from tailings seepage and is of limited extent. The pre-milling ambient conditions could not be established through upgradient monitoring. Monitoring of the uppermost aquifer is currently being performed, because the potential discharge from the uppermost aquifer beneath the site could impact the adjacent contaniinated San Juan River alluvial aquifer.
Point of compliance monitoring was also excluded from the remedial action at a disposal site without the invocation of supplemental standards. This was a unique instance and based entirely on the site-specific conditions at the disposal site:
l e
Rifle diso_osal cell - Estes Gulch. Colorado: Supplemental Standards were not used for this site because the great depth to the uppermost aquifer through thick, low-permeability strata is beyond the depth range normally developed for water supply. The l
depth to the uppermost aquifer is well beyond the 1000 year i
ground-water travel-time distance, under realistic conservative l
estimates. There are no current water use in the uppermost aquifer, and no surface water discharge points. The cell design incorporates a bottom sand blanket, finger drains, and monitoring wells to monitor short-duration saturation within the tailings.
l This system will serve to verify disposal cell performance and is viewed as a substitute to POC monitoring, since it addresses the more imminent concern of moisture build-up within the cell.
Ground-water monitoring was included or excluded at the above sites on a case-l by-casa determination, using the site-specific information unique to each site. Generally, ground-water monitoring was not proposed for sites with very low exposure potentials even with credible failure scenarios under current conditions. Monitoring was performed for two cases where supplemental standards were applied, because of the potential impact to human health and the environment. For one site where supplemental standards do not apply, O
compliance ground-water monitoring was inappropriate, but an alternative compliance monitoring approach will be used.
i Falls City. Texas site If the Falls City site met Supplemental Standards according to 9 192.21(g), it i-would likely be due to wide-spread ambient contamination unrelated to milling operations ($ 192.ll(e)(2)). There is some current ground-water use in the uppermost aquifer, although water quality in the area is poor and may meet the Class III (limited use) designation.
Even if supplemental standards were found to apply at the site, an alternative monitoring program is needed at Falls City because of:
(1) the current and proposed ground-water use in the 3
e uppermost aquifer; designed cover perme(2) geotechnical concerns with the ability to achieve the
)
ability of 2 x 10* cm/s using the available soils; and (3) climatic considerations (wetter conditions) conson at the Falls City site.
A credible failure of the disposal cell could present an added exposure potential and degradation to the current conditions at the site. The NRC staff recognizes that a ground-water monitoring program based on set concentration limits is not appropriate for demonstration of disposal cell performance, nor for implementing potential corrective action at a Supplemental Standards site. Othe mise, the application of Subparts A or B would be appropriate. A ground-water monitoring program based on intra-well trend analyses of constituents (both hazardous and major lon) through time for selected background and contaminated wells would provide a method for evaluating cell performance and also provide a mechanism for implementing corrective action. Another alternative monitoring program could involve l
moisture monitoring in the tailings disposal cell to quantify the performance
}
j of the cell components.
l lo i
l I
(
4