ML20150E891
| ML20150E891 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 01/25/1966 |
| From: | Micheli M PACIFIC GAS & ELECTRIC CO. |
| To: | |
| Shared Package | |
| ML20150E784 | List:
|
| References | |
| FOIA-88-187 5326-65, NUDOCS 8807180036 | |
| Download: ML20150E891 (26) | |
Text
-
Rcport Issuad:.
?
Report No.
5326-65' 1 2 2 5 1936
. Pacific Gas and Electric company 4
-Department of Engineering Research W!.
~DIABLO CANYON NUCLEAR PLANT SITE PPILIMINARY GEOLOGI,C It!VESTIGATION I.
INTRODUCTION This investigation was undertaken to explore the surface geology at Diablo Canyon, San Luis Obispo County, for a proposed nuclear plant site.
The attached geologic maps and cross sections designated as DC-1, DC-2, DC-3, and DC-4, show the
. major geological and structural features of the area covered. A geologic description, photos,,an earthquake f, fault map of California, and conclusions and recommendations y ai9 a1.so included in this report.
Although there is evidence of old and inactive faults in the area, the Diablo Canyon location appears geologically suitable for a Nuclear Generating Plant.
Y
.I 4
i II.
LOCATION AND ACCESSIBILITY The Diablo_ Canyon area is located on the coast, approximately ten railes south-west of San Luis Obispo.
Access to the area is via Highway 101 to Avila Beach and 1
then via a rugged private dirt road, approximately one hour's ride. The proposed i
site is located near the mouth of Diablo Canyon,'which is the only named topographic 4
feature in the mapped area.
The area is covered with low grazing grass (pasture) g J
.cnd can be easily traversed on foot.
It is proposed to locate the reactors, turbine generator, and related facilities on the terrace in the immediate vicinity of Diablo Cove on the south side of Diablo Creek, and to locate the switchyard in a widened section of Diablo Canyon about a quarter mile upstream from the mouth of the canycn.
III. GEOLOGY The mapped area is underlain by sedimentary rocks, marine terrace deposits, and l
minor occurrence of basic intrusive rocks.
The sedimentary rocks occur in the upper Miocene Point Sal Permation and lower Miocene Obispo Formation.
The minor igneous rock, which,instrudes the Point Sal Tormation, is also Miocenic in age.
These geologic units are best exposed in the sea cliffs along the ocean.
Exposures are poor on the adjacent hillside.
At the proposed plant site, the bedrock unito are overlain by a shallow veneer of terrace deposits.
[ :;
1.
Tectonic The major structural features of the area intercept the coast line almost at right angles and are readily seen in the cliffs around Diablo Cove.
a807180036 BOO M D
FOIA "
p N
DALY98-187
~.
Report No.
5326-65 The formations in the area of the reactor site appear-to have been intensely 5'
folded in lost-Miocene time. hiu :erous sheared and faulted areas in the Point Sal
->and Obispo Formations are visible in the near vertical sea cliffs.
The faults are
<usually very small and only those of significance were mapped. The fault planes dip at various angles with small horizontal and vertical displacements, at times l
measurable in the order of one to three feet.
All the mapped faults appear to be old and inactive and of the fold-tault type, originated by a close-folding movement.
The folding thrusts are considered a combination of uplifting and subsequent lateral uovements in a probable south-north directien. The occurrence of this type of tec-tonic movement in the area was probably contemporaneous with the Pilocene orogenic movements of the West Coast.
- 2. Point Sal Tcrmation The Point Sal Formation overlies the Obispo Formation and is overlain in part by marine terrace deposits. The major rock types are dark gray and light brown silty and clay shale and muds?.ones, light-colored tuff and limestone.
Occasional nodules and thin beds of black enert and thin beds of fine-grained sandstone are present.
These various rock types are clearly exposed in the sea cliff to the west and east
(
of Diablo Canyon.
On the hillside to the northeast only outcrops of hard shale and limestone are visible. The various members are well bedded and fairly hard.
The pre-dominant rock type is shale which is exposed in the sea cliffs in alternating beds of nearly uniform thickness, varying from very hard, firm and sparsely. fractured, to weak and minutely fractured, and crushed at times.
The apparent strike of the bedding planes is in a general east-west direction, with local variations due to folding. The beds dip at a high angle, almost vertiet.1 at times, where exposed in the sea cliffs.
Some unrecognizable microfessils including fish bones microfragments, supposedly abundant in this formation, were detected in hand specimen and in one thin section.
- 3. Obispo Formation The Obispo Formation crops out along the coast, south of the plant site and under-lies the Point Sal Formation.
The major rock types in the fornation are light colored, buff and gray tuff, and black shale.
Black chert interbeds are present in minor amounts.
The tuff, which is the predominant rock type, is generally hard.
White when fresh, it weathers to an orange-brown color that makes it clearly distinguishable in outcrop.
The tuff seems to be basically vitric with presence of crystal fragments.
Different types of hard, welded tuff are also present.
The black sh ',, generally well-indur-ated, seems to be more abundant in the cutcrops west of '
lo Canyon.
2-
Raport No.
5326-65
,r q Both the tuff and the shale have undergone some degree of crystallizatien which, at times, renders the shale very hard. These rocks have been subjected to extensive folding movements and like the Point Sal Formation vary from extensively to moderately fractured.
The tuff and the shale are generally well-bedded and trend east-west with a high angle of dip. When the tuff predominates, the shale occurs as interbedde.d rtreaks and lenses.
The contact with the overlying Point Sal Formation is clearly distinguishable along the ocean front.
The two formations appears to be in fault contact along a surface roughly paralleling the coast.
The fault contact probably lies approximately along the dotted contact line shown on drawing DC-1, but its exact location and extent, if it exists, cannot be determined by surface examination.
4.
Terrace Deposits Terrace deposits overlie more than half of the mapped area.
Although mapped as a single unit, they include marine deposits, non-marine talus and slope wash. The deposits range in thickness from a few feet to 30 or perhaps 40 feet at the base of the hill to the northeast.
Slope wash and talus material from the nearby hills account
(,
for some of the greater thickness near the hills.
Over most of the area, these sediments occur as 2 black adobe-like material that contain occasional fragments of rocks of the Point Sal Termation.
Merphologically, this area appears to be a cut terrace. The gentle slope might also indicate a slow rise of the land from the sea with contemporary marine sedimentation.
Typical marine terrace deposits overlying the Obispo Formation are visible only in a few small and localized parts of the mapped area.
They contain essentially flat lying, crudely stratified thin beds of small pebbles alternating with thicker beds of sandy and silty material containing some small rock fragments.
Outside the mapped area, especially west of Diablo Canyon these stratified marine terrace deposits are clearly and centinuously exposed alcng the sea cliff.
They were thoroughly explored, but no sign of any fault movement was detected.
Any minor displacement ( due to faulting) in these stratified deposits, if present, would have been easily observed.
In the immediate vicinity of the proposed reactor site the fields have been cultivated and surface features have been obliterated.
5.
Igneous Intrusive y;
A small intrusive body crops out to the east of Diablo Canyon. The rock which is highly weathered appears to have relict granitic texture. L__
Report No.
5326-65 5
6.
Landslides y.
On the south facing hillside, immediately above the reacter site, bedding planes of the Point Sal formation dip into the hill.
This situation is very favorable to avoidance of slides, and no sliding is to be anticipated in this area.
Several old slides were noted on the north facing slope of Diablo Canyon in an area beginning approximately 1000 ft, upstream from the mouth.
The slides appear to be partially stabilized and there is no evidence of any particularly recent move-The cross sections shown on Drawing DC-4 indicate the general dips found near ment.
the crest and on the south side of the hill, but some surface visual indications would suggest that the dips might be somewhat flatter. These hillsides can be so treated that they will not threaten the proposed switchyard.
This section of Diablo Canyon appears to be the only feasible location for the switchyard, but certain precautions should be observed in design and construction.
SI:eable hill cuts should be avoided.
Whatever level land is required for the switch-t.
yard should be created by filling with provisions for drainage.
Considering the area between Sections C-C and E-E, drawing DC-4, an area approximately 1000 feet square.
could be made with a fill extending across Diablo Canyon whose maximum height would r.
not exceed 80 or 90 feet.
Such a fill, if desired, could be used as a dam to store v
water on Diablo Creek.
IV.
SEISMICITY This area has not been the cource of any strong earthquakes.
See enclosed map from Bulletin No. 116-2, by the Department of Water Resources.
V.
EXPLORATORY TPINCHING On the enclosed aerial photo, the terrace deposits, overlying the fault immediate-ly west of Diablo Canyon, showed indications that might have been suggestive of recent faulting.
To clarify these conditions, only partly visible on the ground, two exploratory trenches were excavated transversally to the projecticn of the fault line.
These trenches were so located that any faultin'g in the terrace' material, if it existed, was certain to be intercepted.
The first trench was excavated approximately 100 feet north of the sea cliff.
The trench was dug to an average depth of 4-1/2 to 5 feet with a maximum of 11 feet at one point.
Exposed in the trench was a black, organic, clayey, adobe-like mater-lal that grades uniformly downward into a gray-greenish type of fat clay.
-4
r 3
.e.
I Report No.
5326-65 The secenc trench was located north of the first, approximately 400 feet from the sea.
It was excavated to an average depth of 4-1/2.to 5 feet with a maximum of 9 feet. The trench was in black, silty, organic, partly clayey, adobe-like material which directly overlies the westerly sloping surface of the Point Sal Termation.
No sign of any fault movement in the terrace deposits was detected in either trench.
VI.
RECOMMENDATIONS In the event that this rite is to be used, and layout and design work is to proceed, a seismic investigation in combination with a drilling and trenching program should be carried out.
These investigations will determine the thickness of the terrace deposits and the extent and location of contacts, faults, and sheared zones in the older rocks.
Approximately five or six continous core bore holes should be drilled in the area of the reactor site to an approximate depth of 60 to 70 feet.
Additional holes may be required.
Some un/ erwater geologic mapping in the immediate vicinity of the coast line should be done for planning of offshore construction.
\\(;c VII.
CONCLUSIONS There are no apparent geological ecnditions which would preclude the constructi-on of a nuclear reactor at this site.
No slide problems are anticipated at the reactor site. There are minor faults present in the older rocks ths.t appear to be old and inactive. No evidence of faulting was detected on the hillsides cr in the recent terrace deposits.
While moderate seismic shaking may be anticipated. rupture is not to be expected.
/
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j M. Micheli,' Geologist W.O.
21935 Distribution:
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Cross Secticns 2 Sheets Geolcgic Maps 2 Sheets Earthquake & Fault Map Photos 5 Sheets s,
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e RICHARD H. JAHN5 2313 BRAM::ER N1Yt MENLO VARK, CALIFO9HIA 94U22
,a December 11, 1965 Mr. F. F. Mautz Chief Civil Engineer Pacific Gas and Electric Company 245 Market Street San Francisco, California 94106 Dear Mr. Hautra This letter is in reference to the brief geologic in-spection of the Diablo Canyon Power Plant Site, San Lui.=
Obispo County, that you and I made on December 1 The most critical portions of this site occupy a broad topographic bench, about 1,000 feet in average width, tha t extends along the irregular coastline.
The bench represents a platform of Pleistocene marine erosion,isto-and is underlain by marine and nonmarine deposits of Ple cene age.
These deposits in turn rest upon a structurally complex assemblare of volcanic and stratified marine sed-imentary rocks of Tertiary age; bedrock exposures are es-sentially continuous along the present seacliff, and are abur. dant along the walls of lower Diablo Canyon.
The bodies of volcanic rocks s'nd the stratification of the associated sedimentar.y rocks are moderately to very steeply inclined, and it is clear that the bedrock section has been affected by large-scale foldinE.
Several faults also can be cbserved, but none of them appears to be large in terms of displacement.
I noted no evidence of fault offsetsinvolvinFthebedrockplatform,i.e.Isistocene the contact between Tertiary bedrock and the overlying P terrace deposits; this suEgests tha t the younrest fault-ing in this coastal area occurred at least 120,000 years ago.
My preliminary opinion is tha t this site can be regarded as feasible for the use under consideration, so far as-geologic factors are concerned.
Additional study, mainly in the form of detailed teologic mapping, is recommended as a necessary basis for making a firm judgment concerning site feasibility, and for establishing the locations of test excavations that would be most useful in working toward a final judgment on site suitability.
I believe tha t two or three days of field work should suffice for the geoloE c mapping of the coastal area, and i
Mr. F.
F. Hautz 2
(
I am prepared to undertake and complete this work during the present month of December.
As per our informal agree-ment, I shall plan to have a formal statement of geologic opinion in your hands by January 1, 1966, and shall fol-low this with a documented report very shortly there-after.
Both the opinion and the report will be based solely upon my own investi ations.
E Best personal regards.
Sincerely yours, w' ch Pichard H. [ s I
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aKHARD N. JANN$
2312 BRANNER DRM AWHLO PARK, CAUPOMA 94026 I
l January-17, 1966 MEMCRANDUM FOR:
Mr. Gorden V. Richards, Pacific Gas and Electric Company FRCM:
Richard b. Jahns
SUBJECT:
Geolo6 c conditions at Diable Canyon Power 1
Plant Site, San Luis Obispo Ccunty As c follow-up to my memorandum of December 11, 1965, addressed to Mr. F. F. Mautz, I am pleased to transmit herewith my preliminary ccnclusions regarding the feasibility, in terms of known geolcE c conditions, i
x of the Diablo Canyon site for construction of a nuclear pcwer plant.
These conclusiens are based upon approx-ima tely three days cf field exsmina tion and geologic mapping, and are offered in advance of a report that will be submitted after the mappint program has been comple-ted.
He attempt will be made te document them in this memorandum, but they cen be regarded as subject to no mere than minor chantes, f
1.
Bedrock in the site area is Tertiary in age, and comprises marine shales, sand-stones, and fine-grained tuffaceous sed-iments, along with a considerable var-iety of tuffs.
All these rock types are firm and compact, although they repre-sent a wide ranee in hardness and re-sistance to erosion.
They should be capable cf supporting imposed loads cf
Mr. Gordon V. Richards 2
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the magnitudes that could be antici-pated from elements of a power-plant complex.
2.
The bedrock section has been grossly de-formed, as evidenced by widespread steap dips of both sedir.entary strata j
and volcanic units.
The effects of in-tense small-scale folding and rupturing can be identified locally, especially in parts of the sedimentary section ad-
.io$ ring intrusive masses of the volcanic rt Several sharply-defined faults in 6 erupt parts of the bedrock terrane, but no large zenes of Ecuge or breccia and no other expresciens of large-scale faulting have been recognized.
3 The bedrock is overlain by marine and non-marine terrace deposits of Pleistocene ago.
The base of this terrace secticn rests upon a platform of marine erosien.
the' age of which can be estimated as at least 120,000 years.
Neither this plat-form ner the everlying sequence of ter-race deposits appears to be offset by any fault in che area.
Evidence for such offset was searched for with par-ticular care, notably in the vicinity of recognized faults within the bedrock sectien, but ncne was found.
4.
Landslide masses are not present within the site area, and properly designed cuts and masses of ecmpseted fill shculd introduce no major problems of ground s ta bili ty.
5 Although some local seepate might be en-countered in deep cuts, subsurface water should constitute no more than a ciner nuisance, most of which probably would be temporary.
6.
No large or active fault is kncwn to ex-ist within the site area or in nearby areas.
Moderately severe to severe ground shaking can be expected at the site, however, as s result of major earthquakes along the d'an Andrea s and other act.*ve faults st distances of
Mr. Gordon l'. Richards 3
tens of miles to the east and north-east.
7 The possibility of fault displacement a t the ground surface within the site area durdnt the planned life of a power plant can' be regarded as extremely re-mote.
In ny opinien, the Diablo Canyon Site is a feasible one for the use under consideration, so far as all kncwn geologic f&ctors are concerned.
Results of the inves-tigations completed to date suggest that a progrsm of detailed subsurface exploration, testing, and geologic-seismic analysis would lead to a feverable final judg-ment rugardin6 suitsbility.
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- 2 Geologist l
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RKHARD H. JANNi 2312 BRANNER NVE MENLO PARK, CAUPORNIA 94026
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May 18,1966 I
MEMORANDUM FOR:
Mr. Gordon V. Richards, Pacific Gas and Electric Company FRCM:
Richard E. Jahns
SUBJECT:
Geologic inves tiga tion of Diablo Canyon Pcwer Plant Site, San Luis Obispo County-During the past six months I have been intermit-tently engaged in a study of the Diablo Canyon area in order to determine its feasibility, in terms of geolot c factors, as a site for construction cf a i
nuclear power plant.
Preliminary conclusiens based upon three days ct field work were transmitted to you in a memorandum under date cf January 17, 1966.
Fur-ther examination and mapping, focused en the broad topographic bench tha t extends elont the coastline, was done in March 1966.
No significant chenEes in the conclus$ons offered in my earlier memorendun need be anticipated as a result ef this additienal werk or the apprcximately one more day of field study yet needed' to complete the geologic map.
Detailed 1:apping cf the area has been carried out at a scale of 100 feet to the inch, and field examins-tion of the exposed rock types has been supplemented by micrcscopic examination and other laboratory work.
In evaluating the feasibility of this coastal site fer the projected use, special attentien has been given to:
1.
Pecognizing existing landslides and other expressions of ground instability.
2.
Interpreting lithology and structure cf the rocks in terms of thejr Eeneral bearing s treng ths and future stabil'ty if~ exposed in cuts.
3 Recctnizing faults, tracing their extent and attitude, estima tint their total displacement, and determining the age r
4 Mr. Gordon V. Richards 2
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,7 of their latest movement.
4.
Appraising the seismic activity, during Recent geologic time, in both this and other-parts of California, f.
Estimating the probability of future fault displacement at the surface within the site area.
On the basis of my investigations to da te',
it is my jud ment that the Diablo Canycn Site is a feasible 6
one for the construction of a nuclear power plant.
I expect mo plcra tden,reover, tha t future detailed subsurface e>-
.tes ting of the na tural materials, and final analysis of geologic and seismic data vill firmly estab-lish its suitability for such use and will provide a basis for appropriate design criteris.
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Richcrd h. Ja
.s Geologist i
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