ML20235X487
| ML20235X487 | |
| Person / Time | |
|---|---|
| Site: | 05000000, San Onofre |
| Issue date: | 08/01/1974 |
| From: | Baltz E INTERIOR, DEPT. OF, GEOLOGICAL SURVEY |
| To: | Gammill W US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20235X376 | List:
|
| References | |
| FOIA-87-462 8168, NUDOCS 8710200018 | |
| Download: ML20235X487 (6) | |
Text
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Regulato Docket Fde United States Department of the Interior 1
f:5l GEOLOGICAL SURVEY WASHINGTON, D.C.
20242 4
50-361 50-362 August 1, 1974 i
l 4
Mr. William P. Gamill, Chief Site Analysis Branch Directorate of Licensing U.S. Atomic Energy Comission Washington, D.C.
20545
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Dear Mr. Gamill:
l Enclosed for your infonnation is a draft review of the report
" Analysis of Geologic Features at San Onofre Nuclear Generating Station" (AEC Docket Nos. 50-361 and 50-362).
The review was pre-I pared by Mr. F. A. McKeown and includes also the observations of Mr. R. F. Yerkes.
l l
Sincerely yours,
% 7A 8 Elmer H. Baltz Deputy Chief for Engi eering Geology l
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CD 8710200018 871014 PDR FOIA C 1 o e' SCHARA87-462 PDR..
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1 Draft Frank McKeown July 24, 1974 i
l San Onofre Nuclear Generating Station Units 2 and 3 1
AEC Locket Nos. 50-361 and 50-362 This is a review of a report entitled " Analysis of Geologic Features at San Onofre Nuclear Generating Station" dated July 5, 1974, and received by the U. S. Geolcgical Survey on July 11, 1974.
The report was prepared by FUGRO, Inc., consulting geologists and engineers for the Southern California Edison Company.
FUGR0 prepared the report after investigations of some shear zones and sedimentary features exposed in the course of excavating the pad area for units 2 and 3.
Comments based upon observations made by F. A. McKeown and R. F. Yerkes of the U. S.
Geological Survey are included in this review.
F. A. McKeown visited the site on June 11, 1974, and R. F. Yerkes visited the site on July 15 and 16, 1974.
The report prepared by FUGRO Inc., includes a brief history of l
the discovery of the shear zones and sedimentary features, a synopsis of the stratigraphy and structure of the site, detailed description of l
the shear zones and sedimentary features, a brief discussion of the results of their investigations.
The report also includes 27 drawings, one table, and three appendices.
In ge.neral, the documentation and analysis presented in the report are well done and we concur with the overall conclusions.
However, some minor discrepancies are in the report and some data pertinent to the interpretation of the apparent offset terrace deposits were omitted or not recognized.
Reexamination of data 9
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in the Preliminary Safety Analysis Report (PSAR) also indicates that some data pertinent to the recent investigations were omitted or not recognized.
The most important parts,of the report are the descriptions and analyses of the " planar features" exposed during excavations of the pad areas.
In order to avoid ambiguity these features in this review will be called for whnt they are, namely shear zones.
Although documentation and explanation of the shear zones are important, the apparent offset of terrace deposits at the sea cliff, which was the real cause for detailed investigations, is not explained adequately in the report.
It is mentioned on pages 4 and 15 as erroneously appearing to be a fault, and illustrated in drawings 4 and 5.
The specific reasons to deny the l
offset of the terrace deposits as being a fault are scant and obscure in the report.
The shear zones (planar features) are identified as type A which trend north to N 10' E, and type B which trend N 40' W to N 55' W.
The A shear zones are vertical or dip steeply to the west or east, the B shear zones dip steeply to the southwest.
The type A shear zones occur in 4 principal discontinuous strands that extend from the seacoast to where one of them disappears under terrace deposits at the north side of the excavation.
The type B shear zones occur in 6 principal strands, all of which terminate to the southeast in the excavation; their northwestern extent is unknown, because they extend toward unit one, beyond the limit of grading.
Ihe zones range from less than an inch to as much as 10 inches in width, are bleached white and commonly occur as slight resistant ridges in outcrop.
According to petrographic studies in Appendix A of 4
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N the report the white color is due to angular fize-grained crushed material and "the cementation is the. result of nechanical building of the closely packed fine-grained material." Type A shear zones consistently l
have left lateral displacement and type B shear zones consistently have I
right lateral displacement.
Displacements on b:th types range from 0.5 i
i to 4 inches. Where the two types of shear zones intersect they mutually j
offset each other.
i A search for the northwestern extent of B type shear zones resulted a
in a discovery of several other occurrences of similar zones northwest i
of unit one.
No displacement is reported for these occurrences and I
none was apparent to the reviewer. All were truncated by the terrace
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deposits.
An investigation was made to determine whether shear zones i
or fractures similar to type A and B occurred outside of the reactor site.
An abandoned quarry 1.7 miles northwest of the site and the sea cliff near San Onofre Beach were examined.
Both localities had exposures of j
fractures or shear zones which were truncated by terrace deposits.
The origin of the shear zones is suggested from a " theoretical 1
analysis" in appendix B of the report.
Several origins were postulated but the one preferred is that the shear zones resulted from widespread northwest-southeast compressional stresses.
This is a reasonable interpretation.
As mentioned in a previous paragraph description and explanation of the sea cliff exposure of apparent offset of terrace deposits is not treated adequately in the report.
On page 4 of the report, the contact of the marine terrace deposits with the San Mateo formation is described as irregular and of erosional origin and that the sea cliff exposure 3
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I' shows.a type A shear zone overlain by terrace deposits.
This description 1
is correct but incomplete.
Examination of the photograph and sketch-in -
drawing 5 does not convince the reviewer that terrace deposits are not-I offset aginst the. San Mateo formation along shear zone A3 (feature A ).
3 In fact, the sketch shows' shear zone A3 extending almost to the7 top of^
terrace deposits and' separating them from the San Mateo formation.
3 is offset slightly at the base of the deposits; however, the Zone A small amount of offset could be of controversial significance.
The important: aspects of-the information in drawings-4 and 5 relative to the interpretation of the apparent faulting of terrace. deposits is left for the reader to deduce.
The significant information in the-figure thatL is not used in the text of the report is the stratigraphy.
In brief, the sequence of stratigraphic-units in the terrace deposits are not offset across the apparent shear zone.
This information should have been described and utilized in the text.
Another important well-documented observation that is not specifically utilized in the report is that the displacement on A shear. zones is only a few inches in a left lateral sense everywhere over hundreds of feet of-exposure.
This is completely incongruous with the apparent-10-11 feet of vertical displacement of the terrace deposits.
A discrepancy this reviewer notes is-that-the: shear; zone A3 strikes N 38' W and dips 62* SE according to drawing 6. - This strike and dip is assumed to be in error because the dip as plotted in the drawings is to.
the' southwest and the strike is not compatible with trace of A3 plotted
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in drawing 3.
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1, Drawings 4 and 5 in the FUGRO report show 2 terrace (platform) levels.
At the request of the U. S. Geological Survey on July 16, 1974, l
the elevation of the lower terrace was surveyed' and found to be 38 feet' l
e i l
above sea level.
Elevations of bedrock in borings 1, 2, 3, and 4 j
(pl. 2-F, Append. R2B, PSAR). appear to be co-planar with the 38-foot platform at the seacoast.
The profile (Drawing 6, Append. 2A) of the seacliffinthePSARhowever,indicatesthiattheplatformisabout 42.5 feet in the vicinity of the exposure of A'.
Furthermore, only 3
one terrace is shown in the profile.
Within the limits of error of the drawings, the profile appears to show only the 46-foot terrace.
This terrace had been assumed to be the lowermost one and correlative with a terrace about 4 1/2 miles northwest of the site, which has been dated at 70,000-130,000 years before present.
The age of the 38-foot terrace therefore, is not known or else the correlation of terraces is in error.
Considerably more detailed mapping of terraces from the dated terrace southeast to the site would be required to resolve the discrepancy in correlations and ages.
It seems likely however, that the shear zones may be about 100,000 years old or older, because at no place do they j
offset the eroded surface of the San Mateo Formation.
4 In conclusion, the shear zones in the San Mateo Formation and that occur in the excavated area and vicinity of the site do not appear to be capable faults as defined in AEC criteria.
Furthermore, the terrace deposits are not offset as they appear to be but were deposited against a steeply dipping erosional surface-on the San Mateo Formation which may have been controlled by the shear zone in the formation.
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