ML19341A889
| ML19341A889 | |
| Person / Time | |
|---|---|
| Issue date: | 12/29/1980 |
| From: | Scarano R NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Strong T WASHINGTON, STATE OF |
| References | |
| REF-WM-33 NUDOCS 8101290010 | |
| Download: ML19341A889 (22) | |
Text
WY
'o UNITED STATES 8'
k NUCLEAR REGULATORY COMMISSION
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WASHINGTON, D. C. 20555 a
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I"h Mr. T. R. Strong te Department of Social and Health Services ce..'g g* w ///
State of Washington
@#/ ~. $/Q Olympia, Washington 98504 QT;fCG
Dear Mr. Strong:
Enclosed are NRC responses to comments on those sections of the DEIS for the Proposed Dawn Mining Company Mill Tailings Expansion Project which we prepared, as well as a marked-up copy of the DEIS indicating changes to be made for the FEIS.
In preparing this material, we evaluated and considered all information submitted by Dawn since transmittal of our August,1980 report.
In addition to those changes to the DEIS no'ted in the enclosure, we feel that a change in Table 9.1 ( not prepared by NRC) is imperative.
We suggest that Table 9.1 be amended to also require analysis of ground-water for non-radiological chemical constituents.
If we can be of further assistance or if you have any questions on the enclosed material, please feel free to contact me.
Sincerely, W
/
Ross A. Scarano, Chief Uranium Recovery Licensing Branch Division of Waste Management
Enclosures:
As Stated
[
810.129 o djQ
T-Response to Coments on NRC Input for DEIS - Dawn Mining Company Mill Tailing Expansion Project O
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d.9 Response to EPA Coments on NRC Input for 4
DEIS - Dawn Mining Company Mill Tailings f'
Expansion Project 7
2 COMMENT:
~~
a Page 2-3, Item 2.3, first paragraph. The last sentence says that groundwater flow is reported to be " modest." This is in apparent contradiction to page F-2 (paragraph 3) where the groundwater flow in this zone is referred'to as "significant."
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RESPONSE
The description of groundwater flow in Section 2 for the purpose of the assessment of the proposed below grade pit was not intended to be quantitative since no seepage is expected from the pit. The proposed pit is above the water table and fully lined. The groundwater regime will be quantitatively defined as part of the environmental assessment associated with the Dawn Mining Company license renewal which will evaluate in detail seepage from the existing impoundment.
It should be noted that Appendix F of the DEIS is a report by a Dawn Mining Company consultant and will be deleted from the FEIS since it does not necessarily reflect the position of DSHS or NRC staff.
COMMENT:
Page 3-2.
The figure indicates that Dawn has very little property left between dike edges and the property lines.
I understand that other states have required mill operators to acquire sufficient real estate to provide a buffer zone in which to work to clean up spilis or windblown tailings. Based on studies at other mills we would expect to find land areas contaminated by windblown tailings which would be 3-4. times the area of the tailings piles.
RESPONSE
The staff's position is as stated in Criterion 8 of Appendix A to 10 CFR 40:
" Milling operations shall be conducted so that all airborne effluent releases are reduced to levels as low as is reasonably achievable. The primary means of accomplishing this shall be by means of emission controls.
Institutional controls, such as extending the site boundary and exclusion area, may be employed to ensure that offsite exposure limits are met, but only after all practicable measures have been taken to control emissions at the source." Dawn will be required by license condition to control blowing of tailings through implementation of a documented interim stabilization program.
If weekly inspections, which are required as part of this program, or environmental monitoring show the program to be ineffective, then the need for a better control program and/or extension of the site restricted area-boundary will be considered.
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. COMMENT:
Page 4-4, F.
I would regard the applicant's reported stack emission rates (page A-4) of 0.0015 f/ hour (dryer) and 0.0011 !/ hour as extremely unusual. We have measured the emission rates (using standard EPA methods and equipment) from all of the New Mexico uranium mills and from one Colorado mill (see attached). Only in one new mill have we seen one measurement on a dryer stack as low as the numbers reported by the applicant. 0lder mills and even a second new mill more typically had emission rates which were a few hundred times those reported by the applicant. Obviously, if the emission rates are on the average higher than reported, offsite exposures are elevated accordingly.
I believe we have suggested in reviews of previous drafts of this EIS that the actual data be made available in the EIS for review.
Page 4-16.
In view of the apparent difficulty in 40 CFR 190 compliance, I would strongly suggest reevaluation of the reported yellowcake packaging and drying emission rate data.
RESPONSE
The dryer and packaging stack emission rates used in the radiological assessment were based on data submitted to the NRC in a January 30, 1980 report by Alsid, Snowden and Associates for Dawn Mining Company
. entitled, " Atmospheric Emission Evaluation, Dawn Mining Radionuclide Release Rates, Ford, Washington." A copy of the table from this report giving data on yellowcake releases is attached. Although the reported releases are low, the staff regards the data as representative based on the following:
a.
The mill throughput of 430 metric tons of ore per day is very low'in comparision to other mills, b.
The magnitude of the reported releases is not unique in the industry (e.g., Schio Mill, Seboyeta, New Mexico).
c.
The Dawn process does not produce a fine dry yellowcake powder typical of most mills but instead produces yellowcake pellets. The pelletizing process used by Dawn Mining Company in their drying and packaging was observed during a February 1980 NRC site visit and found to be extremely clean and dust free in comparison to the typical drying and packaging operation at uranium mills.
COMMENT:
Page 5-3.
I would suggest that the data reported for the UNC Churenrock dam failure may be partially in error. The reported figure for solids released is based on an engineering survey of the
. ~
eroded area of the solid tailings ' beach.
It does not take into consideration the suspended solids contained in the liquid fraction released. As indicated on page 5-2 and footnote, it is usually assumed that equal weights of solids and liquids are released.
Thgs would indicate the solids loss would have been more nearly 9 X 10 pounds for the Churchrock dike break.
RESPONSE
As indicated in the comment, the data for the solids released from the Churchrock dam failure as presented in Table 5.1 did not account for the suspended solids in the liquid released.
Based on available total dissolved solids data, the table has been revised to account for this.
COMMENT:
Page 5-4.
The values in this table differ by a factor of 100 from those given on page 7-4 (which appear more reasonable).
Suggest checking units.
RESPONSE
t Table 5.2 has been revised to correct the typographical errors in the concentration units.
J
FISULTS SUMMAR'Y 5
DAUN MINING AT TORD, WA Septc=b2r 25, 1979
+
(2)
(1)
PARTICULATE URANIUM (3)
[
SAMPLE ASA ASA PARTICULATE EMISSION FILEASE RADIONUCLI"Z ID LAB SAMPLING CONCENTRATION,
- RATE, RATE, RELEASE R.C,
'(ORIGIN)
RUN #
(GR/SCF)
(L3/MP)
(gs/HP)
(n C1/HR)
[
M Crusher
- M '
,g,
Exhaust 4149 1
.013 1.476 yh; e
Crusher
- 3.,
Exhaus:
u159 2
.001 0.125
?.
AVERAGE
.007
.801 10.165 a
^
Barrel 3
Filling 7
- .xhaust 4169 1
.008
.054 l
i l
2~
3arrel Tilling l3 Exhaus 4179 2
.007
.051
- r. -
Ra-l.60 AVERAGE
.008
.053 0.425 Th-l.27
@x r
l
- 3
.;\\
a Agitator
]1
=
Exhaust 4189-1 1
.001
.020
-4q Atitate.
[,
Exhaust 4189-2 2
.006
.112 Ra-6.12 if
~
AVERAGE
.004
.066 0.210 Th-6.99
- 9 ;
.n,
_l.
I h
5 Dryer Exhaust 4199-1 1
.006
.060
-9
' Ni i
Dryer Exhaust
'4199-2 2
.004
.036 3
Ra-23.9,7 d}
AVERAGE
.005
.048 0.679 Th-19.97 j
.3 S
4 1
5e l3 N
!g (1) GR/SCF (@68' F,1.'O am press., dry)
Sj (av 9
lb-car:g.)
1culate 45 3. 59 10E 6 ug /lb = ( g= -f- --
i g]
l (2) uc-uranium-samole x
x l
ug-particulate sample hr Sa ple defined as that fren ec bined ASA runs j
(avg.)
(3) 10E-9 Curies-sample lb-carticulate
-53.5975 g/lb = nanec s-
= -
x x
g-particulate sample hr-(nCi/h--?
i Radium - 226 and Thorium - 230
Response to Dawn Mining Company Comments on NRC Input for DEIS - Dawn Mining Company Mill Tailings Expansion Project COMMENT:
2.3 Groundwater The D.E.I.S. implies in this section that the groundwater table in the area was determined from one bore hole. This is not the case.
The water table map presented by Dawn in its " Response to E.P.A.
Comments" February,1980, used 24 data points from 10 holes and Chamokane Creek itself to arrive at the contours shown. This water table map is only shown in Appendix F and should probably also be incorporated into this section.
RESPONSE
Section 2.3 of the DEIS has been revised to include a discussion of the development of a groundwater contour map. Appendix F is being deleted from the FEIS, so the figure on groundwater table configura-tion has been added as a new Figure 2.2.
C0KiENT:
3.2.1.2 Settlement The referenced laboratory or field studies have been carried out and subnitted to the D.S.H.S. on November 11, 1980.
RESPONSE
The additional studies requested by the staff have been received and found acceptable, and the results have been incorporated into Section 3.2.1.2 of the FEIS.
COMMENT:
3.2.1.4 Sloce Protection The required rip-rap specifications were submitted to the D.S.H.S.
on September 26, 1980.
RESPONSE
The rip-rap and two stage filter specifications have been received and found acceptable, and they have been incorporated into Section 3.2.1.4 of ths FEIS.
. C0HENT:
3.2.1.5 Under Drain System And Liner A revised set of specifications for the bedding and drain pipe filter was subnitted to the D.S.H.S. on September. 26, 1980.
RESPONSE
The revised set of gradation specifications for the bedding sand and drain pipe filter have been received and found acceptable, and they have been incorporated into Section 3.2.1.5 of the FEIS.
CCXMENT:
3.2.1.7 Construction The Company has previously agreed to provide the notifications and the construction report as suggested on page 3-13.
RESPONSE
The commitments to provide the notifications for inspections and to submit a construction report have been noted in Section 3.2.1.7 of the FEIS.
COHENT:
3.2.1.1 Slope Stability The referenced " Revised Stability Analysis" was submitted to the D.S.H.S. on September 26, 1980.
RESPONSE
The revised stability analysis has been received and found acceptable and the results have been incorporated into Section 3.2.1.1 of the FEIS.
C0HENT:
3.1.4 Underdrain System And Liner l
Figure 3.4. showing the details of liner installation and overlying sand and rip-rap cover have been modified at the request of the D.S.H.S. and N.R.C. and the changes were submitted to the D.S.H.S.
on Septetber 26, 1980.
s i --
RESPONSE
i 3 {
The revised details of the rip-rap, filters, cover sand and liner
..a I
have been incorporated into the FEIS as Figure 3.4a.
d IA 9
COMMENT:
- +f
}
3.2.2 Seeoage Control s-The quality assurance program covering all aspects of liner installation d
was submitted to the D.S.H.S. in July,1980.
3
'5
RESPONSE
j l
In light of Dawn's change in liner materials from Hypalon to High Density Polyethylene, submittal of a revised quality assurance ij program for liner installation (new specifications, testing require-7 cents, etc.) is required as part of the addendum to the pit construction 1
specification document, required by license condition.
4 4i COMMENT:
d V,
3.1.3 and I5 3.2.1.7 Embar
,id Pit Construction a
3' The A.S.T.M. - D1557 test method cited in this section has been d
changed at the request of the D.S.H.S. and N.R.C.
The embankment will be compacted to an average of 85% but not less than 30%
.f relative density as determined by A.S.T.M. 0-2049.
-l
RESPONSE
3 i
2,d Dawn's connitment to adhere to the requested compaction critoria revision has been noted and incorporated into Sections 3.1.3 and 2$
]
3.2.1.7 of the FEIS.
4._
COMMENT:
'm
- s 3.2.3.2.1 Failure Modes Associated With Impoundment Elements N
Dawn stated in its September 16, 1980 response to the NRC Environmental
' Assessment that to require at this time a rock cover over the fj i
(
tailings mound would be premature. The Ford, Washington area is f
4 not a desert such as that found in New Mexico.
The dense forest 4
. and underlying grasses surrounding the site is evidence that a proper cover can be established at the site.
Experience with revegetation efforts in the intervening years at the mine site (initiated ir.1980) and on the spoils stockpiles from the new tailings facility will indicate what course of action to take at
)
the time of final tailings reclamation.
Dawn has roughly estimated that to cover the site with one to two feet of rip-rap with rock from the mine will cost in 1980 dollars from $2.5 to 4.9 million. The calculations are as follows:
2 Surface Area:
7497900 ft 3
Volume of Rip-Rap 7497900 x 2 feet = 14995800 ft 3
Conversion to Tons:
14995800 cubic feet + 16 ft / ton =
937238 tons Cost:
Actual 1980 Mining Cost
$1.11/ ton Actual 1980 Hauling Cost 3.15/ ton Estimate Spreading Cost 1.00 Total Cost per Ton
$5.26/ ton Cost for the Project:
937238 x 5.26 = $4,929,869.
Say $4.9 million (If only one foot of rip-rap is used the cost would be $2.5 million.)
Expenditures of this magnitude should be only decided after due consideration and study; not on an opinion that is not substantiated.
RESPONSE
Dawn's estimation of the cost of the required rock cover is somewhat l
inaccurate. The NRC in most cases would require only 6 inches of i
rip-rap over 6 inches of bedding material on the exposed side slopes of the reclaimed area. This would greatly reduce the surface area used by Dawn in the cost estimate (the entire reclaimed area) and in combination with the requirement of one foot thickness would result in a cost estimate much less than Dawn's lower estimate of 2.5 million. A 2-inch thick layer of medium aggregate might be acceptable to the NRC staff for placement on the flat top surface i
of the tailings area.
It is likely that an acceptable medium aggregate could ba found near the site or during excavation of the alluvial materials for the proposed tailings pit. The exact requirements for the rock cover can only be determined after Dawn has shown how the reclamation cover will tie into the cover over the existing impoundment and developed and submitted a plan as required in License Condition No. 1.
, The NRC staff maintains the position that establishment of a fully self-sustaining vegetative cover is unlikely over the long term.
If future studies by the applicant strengthen the case for a cover of this type, it is the staff's recomendation that the option for amendment of the reclamation requirements remain available to Dawn.
4 In the meantime, however, Dawn shall remain bonded for an amount sufficient to include the cost of rock cover of the exposed reclaimed slopes.
COMMENT:
4.
RADIOLOGICAL ASSESSMENT Dawn is currently evaluating the accuracy of this portion of the D.E.I.S. Due to its importance and sophistication, this analysis is not complete at this time. Dawn will coment on this subject at some future time.
The Company agrees with the conclusions outlined in Section 4.9 where the limitations of computer modeling are stated.
Verification of dose estimated must be obtained by actual measurements in the field.
RESPONSE
No response is necessary.
COMMENT:
S.
ENVIRONMENTAL EFFECTS OF ACCIDENTS The method used in the D.E.I.S. to estimate releases from a tailings pipeline failuge is much to conservative.
Foy Dawn to release the cited 9.2 x 10 gallon of liquid and 1.8 x 10 16 of solids as a result of a pipeline break would take 81 hours9.375e-4 days <br />0.0225 hours <br />1.339286e-4 weeks <br />3.08205e-5 months <br />. Since the tailings line and dam are inspected at least every 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> a more reasonable estimate of the release would be:
Solutions - 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> x 60 min. x 189 gal / min. = 90720 gal.
Solids - 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> x 60 min. x 694 lbs/ min = 333120 lbs.
Even if one were to double these estimates by assuming 16 hours1.851852e-4 days <br />0.00444 hours <br />2.645503e-5 weeks <br />6.088e-6 months <br /> between inspections the releases would still be only 20% of the levels cited for solution and 4% of the levels cited for solids.
In any event, Dawn has agreed on September 14, 1980, to install a flow monitor at the tailings line discharge in 1982 when power will be available at the site.
6-
RESPONSE
It is recognized by the staff that because of small throughput a tailings release due to pipeline failure at the Dawn site would most likely result in volumes less than those based on average historical data. However, it is the staff's objective to require at all sites, timely installation of instrumentation capable of immediate detection of pipeline failures regardless of the size of release. Dawn's plan to delay the installation of such instrumen-tation until 1982 is considered unacceptable. The staff will require that installation of instrumentation be completed by May 1, 1981.
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Response to Coments by Northeast Tri-County Health District on NRC is Input for DEIS - Dawn Mining Company Mill Tailings Expansion Project
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COMMENT:
I
- .t It is our understanding that the anticipated radiation will be 4
alpha type particles. As such the liner should normally provide 7
adequate protection for the groundwater.
However, since the bottom d
of the 70 foot deep pond will only be separated by approximately 30 h
feet of excessively pemeable glacial sands and gravels it seems that more consideration should be given to potential liner leaks.
y:*
The complete exclusion of this possibility, as stated in Section j
4.1, appears to be inappropriate since radiological contamination 3
of a groundwater would definitely have long term, adverse impacts.
1 In other areas of the impact statement (8.3.2 & 10.1.3.2) the i.
possibilities of leakage are briefly addressed.
These impacts, M
however, are to be seemingly mitigated by the fact that the amount j
of contamination would be less than that oosed by the existing, q
unlined ponds.
In the context of the purposes behind SEPA, it does y
not seem to be appropriate to overlook a potential adverse impact
.A on the basis that it is not as severe as an existing situation.
3 This is evident in WAC 197-10-360(3) which states "The question at j
the threshold determination level is not whether the beneficial 9-aspects of a proposal outweigh its adverse impacts upon the quality of the environment."
f f,$
RESPONSE
Based on the type of liner proposed and the requirement for a 1
quality assurance program on liner installation,under nomal operation of the fully lined below grade pit, the staff anticipates that all l,
seepage will be eliminated. Thus, the radiological assessment of g'
the proposed pit does not consider the liquid pathway. However, in accordance with NRC regulations (Appendix A,10 CFR 40), a system 4
i.
for detection of any possible leakage through the liner will be required.
If at any future time leakage is detected, the problem j-will be reviewed and mitigative measures will be taken.
3 Sections 8.3.2 and 10.1.3.2 have been revised in the FEIS to eliminate statements comparing potential adverse impacts of the below grade i
pit to the existing seepage situation.
j l
COMMENT:
[
If the radiation is of a alpha type, why is one of the performance j
objectives for management the reduction of gama radiation (Section j
6.1.5)? I am usuming that the objectives cover radioactive tailings 1
pond management in general and not, specifically, the materials to be found in the Dawn Mining site. However, this should be clarified since the use of an impermeable liner will not restrict the higher J
energy gama radiation.
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RESPONSE
The performance objective referred to applies to emanation of I
radiation through the reclamation cover and deals with gamma radiation since ganna radiation is the most penetrating type of radiation found in uranium mill tailings. Providing sufficient cover to reduce gamma radiation to essentially background will guarantee that alpha radiation from tailings will not penetrate the cover.
The Dawn tailings are like any other uranium mill tailings and are composed of natural uranium and its daughters along with numerous non-radioactive constituents. The purpose of the synthetic liner is only to eliminate seepage. Ganma radiation which passes through the liner will be attenuated by the ground below and to the sides of the tailings pit.
9
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Response to Cormients of Department of Ecology, 7
State of Washington on NRC Input for DEIS - Dawn Mining
.g Company Mill Tailings Expansion Project i
COMMENT:
The preferred alternative is a lined tailings pond, but there is no discussion of the treatment and disposal of the tailings water mentioned on pages i and 11 of the Sumary and on page 3-14.
Discussion of reasonable alternatives of water disposal should be i
included in the EIS.
There should also be a discussion of leak detection capabilities for a lined pond (i.e., external underdrain
.5 system, additional monitoring wells, leak detection devices, etc.).
j
RESPONSE
i Based on the disposal schedule, which would not require decanting
'I to begin until approximately the fourth year of operation, it is the staff's position that Dawn be required to submit a proposed treatment and disposal plan supported by an evaluation of alternative i
plans within 18 months after the start of tailings disposal.
A safety and environmental evaluation of the plan would then be i
performed by DSHS staff.
In accordance with NRC regulations (10 CFR 40, Appendix A), Dawn will be reauired by license condition to install a system for the i:
detection of possible seepage through the synthetic liner.
Plans
'i for the system must be submitted to the State of Washington for 3
review and approval prior to any construction associated with the below grade pit, other than excavation of in situ materials.
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DEIS Revisions (Inserts) j
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Insert (1)
E Until Dawn has submitted both of the above reclamation plans and they have been reviewed and approved by USHS, the licensee shall not dispose ~
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a t
of tailinas solids in:the.below-grade pit above elevation'1731.
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f.
Insert (2) (Additional License Conditions)
~
- 13. Construction, maintenance, and operation of the'below-grade tailings disposal system at the Dawn site shall be in accordance with the statements, representations, recomendations, and comitments contained in the following documents.
"Geotechnical Design Data, Proposed Tailing Disposal Facility a.
Expansion, Dawn Mining Company, Ford, Washington," Golder Associates, November 2, 1979.
b.
Section 2.1 and 2.2 of " Environmental Impact Statement, Dawn Mining Company Tailings Disposal Facility Expansion Project,"
Dawn Mining Company, July 30, 1979.
" Response to NRC Questions," Dawn Mining Company, July 1980.
c.
d.
September 26, 1980 letter from W. R. Lawrence, Dawn Mining Company to Arden Scroggs, DSHS, State of Washington.
" Dawn Mining Company Contract No. Cl, Excavation and Lining, e.
Tailings Disposal Project," October 1980.
f.
October 31, 1980 letter from Jack Thompson, Dawn Mining Company to Nancy Kirner, DSHS, State of Washington.
- 14. Within 18 months after the start of tailings disposal in the below-grade pit, the licensee shall submit a report, containing the proposed decanting operations and resultant water balance supported by an evaluation of alternative plans, to the State of Washington for review and approval.
In addition, the licensee shall not use the existing impoundment for evaporation of excess water from the below-grade pit without prior approval by DSHS in the form of a license amendment.
- 15. The licensee shall maintain a minimum of 5 feet of freeboard between the impoundment crest and the maximum pond operating level.
- 16. The licensee shall imediately notify the Department of Social and Health Services, State of Washington, by telephone and telegraph of failure in the above-grade impoundments, the below-grade pit, or the tailings discharge, decant or recycle systems which results in a relecse of radioactive material to unrestricted or restricted areas anJ/or of any unusual conditions which if not corrected could lead to such a failure.
- 17. Prior to proceeding with any construction work associated with the below-grade pit, other than excavation of in situ materials, the licensee shall have submitted and received approval by the State of Washington of the following construction details:
a.
The design of a system for detecting any potential leakage through the synthetic liner.
b.
An addendum to " Dawn Mining Company Contract No. Cl, Excavation and Lining Tailings Disposal Project," providing revised quality assurance and construction specification details for the earthwork and the HDPE liner (including details of the methods to be employed to anchor the liner to the crest of the impoundment).
- 18. Prior to the placement of tailings in the below-grade pit, the licensee shall submit a groundwater monitoring program for the below-grade pit to the State of Washington for review and approval.
The report shall include but not be limited to the location, penetratio'n depth and elevations open for groundwater sampling for each well associated with the new pit.
- 19. The licensee shall submit, by May 1,1981, to the State of Washington, plans for meeting the requirements of Regulatory Guide 3.11.1,
" Operational Inspection and Surveillance of Embankment Retention Systems for Uranium Mill Tailings."
Insert (3)
In response to an NRC request, the applicant conducted a second analysis using shear strengths based on standard penetration testing results adjusted for overburden stress (Ref. 61). As expected, there was a reduction in the calculated factors of safety. However, the factors of safety still exceeded the minimum allowable values of Regulatory Guide 3.11.
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Insert (4) 7 In response to the NRC's request to present additional settlement analyses
}
accounting for the deep layer of glacial clays underlying the site, the e$-
licensee performed further field and laboratory investigations. A total I
settlement analysis of the clay layer based on a conservative application 9
of the results of the investigations yielded an estimated maximum differentiaI 3
settlement of 1.9 feet (.58 meters) over a horizontal distance of approximate!y
?
500 feet, and a maximum strain on the HDPE liner of less than 0.1% (Ref.
i 62).
It is not anticipated that the estimated differential settlement c
will have harmful effects on the liner since manufacturer's test data (Ref. 63) indicates that the liner can withstand 30% strain without damage.
p Insert (5) a As specified in Sherard, et. al. (Ref. 9), and recorriended by the NRC, i
the criteria for the riprap layer will be as follows (Ref. 61):
-.e a
a.
The riprap layer thickness will be 18 inches thick measured normal to the slope.
y b.
The maximum rock size in the riprap will be 18 inches and the minimum rock size will be 1 inch.
c.
The minimum average rock size (D50) will be 10 inches.
d.
The riprap will be well graded and placed in such a manner as to 3
avoid excessive segregation of particle sizes.
The riprap will be u' derlain by a two-stage filter to protect the sand n
covering the HDPE liner from erosion. This requires a modification of the original slope design.
Figure 3.4a illustrates the modifications i-required in the upper portion of the slope crest to accommodate the Z
riprap and two-stage filter arrangement. As shown, the riprap layer is i
18 inches thick, the riprap filter is 9 inches thick, the underlying drain pipe filter layer is 9 inches thick and the cover sand layer is 12 i
inches thick. The configuration of slope has also been slightly modified so that the riprap is resting above inplace soil rather than cover sand i
as originally designed. This has been done to improve the long term
?;
integrity of the riprap.
p The gradation specifications for the twostage filter, as presented in Reference 61, have been reviewed and are considered acceptable in meeting g
filter criteria with respect to the overlying riprap and underlying g
cover sand.
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5 ei-Insert (6)
M z.
I Revised gradation specifications have been provided in Reference 61, as requested by the NRC.
In addition to meeting these gradation envelopes, I-the drain pipe filter and bedding / cover sand are required to be well b-graded and to have individual gradation curves approximately parallel to their respective envelopes. The revised gradation specifications are 1
considered acceptable in meeting filter criteria including criteria f
governing segregation of grain sizes.
Insert (7)
[-
5-In accordance with NRC tailings regulations (10 CFR 40, Appendix A), a system will be installed for detection of any possible leakage through the HDPE liner. Prior to installation, the system design will be submitted to the State of Washington for review and approval.
.e Insert (8)
?_
In addition, a construction specification document has been prepared by C
Dawn (Ref. 65). Based on recent changes in the synthetic liner and deficiencies in the document noted by the NRC staff, an addendum to the construction specifications will be submitted to the State of Washington
?f by Dawn Mining Company for review and approval. With regard to the 1
l impoundment construction, cocmitment to implement the following NRC f
l recoamendations has been made by the applicant:
g
\\
i, Insert (9) s Subsequent to the publication of the revised DEIS, Dawn Mining Company
[
submitted a request to change the proposed Hypalon liner to a High y
Density Polyethylene liner of the same thickness.
The NRC staff reviewed
?
the proposed change and conveyed approval of the HDPE as an acceptable alternative lining material (Ref. 66).
e Y
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t 1
,p
" ^ - - - - ~ - - - - - - - - - - - - - - - ^ ^ ~ - - ^ ^
~. - -. -
Insert (10)
However, by comparing doses from the present and expanded (with the below-grade pit) operations it is evident that the contribution from the below-grade pit is quite small, with the major dose contribution coming from present operations.
Furthermore, as illustrated by Table 4.2, the rafor source of radioactive particulates is the front end of the mill circuit. For example, at the residence (0.6 km NNE) with the highest doses, the doses from the milling operation alone, excluding all tailings contributions, account for 97% of the total lung dose via the inhalation pathway, 93& of the bone dose via the inhalation pathway, and 68% of the bone dose via the begetable pathway.
Insert (11)
As indicated in Table 4.7, maximum individual doses at the " nearest residence" and " nearest residence in the prevailing wind direction" locations are computed to exceed the EPA limits.
However, by comparing doses from the present and expanded (with the below-grade pit) operations, it is evident that the contribution from the below-grade pit is quite small, with the major dose contribution coming from present operations.
Furthermore, as illustrated by Table 4.2, the major source of radioactive particulates is the front end of the mill circuit.
From the analysis performed, therefore, it can be concluded that construction and operation of the new impoundment will have very little bearing on the issue of overall site compliance with 40 CFR 190.
Further evaluation of the doses from the front end of the mill circuit and the need for better effluent control must be considered immediately as part of the license renewal review presently underway, Insert (12) 63.
Wilson, Lee C. and Rouse, Jim V., Envirologic Systems Inc., "Geohydrological and Geochemical Evaluation of Existing and Potential Contaminant Transport from Dawn Mining Co. Tailings Pond, Ford, Washington."
May 2, 1980.
61.
Letter from W. R. Lawrence, Mill Superintendent, Dawn Mining Company to Arden Scroggs, DSHS, State of Washington, September 26, 1980.
62.
Letter from Ronald E. Versaw, Golder Associates to Dawn Mining Company, November 5, 1980.
63.
Letter fror, J. E. Thompson, Resident Manager, Dawn Mining Company to Nancy '.irner, DSHS, State of Washington, October 31, 1980.
=
- Q
,, 3 s
~
ihA 64.
" Dawn Mining Company Response to fiRC Environmental Assessment of
'.t.3 the Dawn Mining Company Proposed Below-Grade Tailings Management 1*4 Plan," September 14, 1980.
[!j 65.
" Dawn Mining Company Contract tio. C1, Excavation and Lining Tailings 19 Disposal Project," October 1980.
,;d
- 66. Letter from Ross A. Scarano, Chief, Uranium Recovery Licensing h["
Branch, US ?IRC, to fiancy Kirner, DSHS, State of Washington, December 3, 1980.
.4 341 Insert (13)
J
,33 B.4 DOSES TO IllDIVIDUALS j
Doses to individuals have been calculated for inhalation, external
)
exposure to air and ground concentrations, and ingestion of vegetables, meat, and milk.
Internal deses are calculated by the staff, using dose y
conversion factors that yield the 50-year dose comitment, that is, the entire dose insult received over a period of 50 years following either inhalation or ingestion. Annual doses given are the 50-year dose comitments resulting from a one-year exposure period.
The one-year exposure period
.a was taken to be the final year of mill operation, when environmental concentrations resulting from plant operations are expected to be near their highest level.
B.4.1 Inhalation doses Inhalation doses have been computed using air concentrations obtained by Eq. B-3 (resuspended air concentrations are included) for particulate materials and the dose conversion factors presented in Table B.5 (refs.
I and 6).
.a
.,,