ML20202D193

Forwards Request for Addl Info Re 850522-23 Field Trip to Foothills of Sierra Nevada Mountains.Observations Made by NRC & State of CA Geologists Do Not Agree W/Util Trip Rept. Resolution Requested

ML20202D193
Person / Time
Site:	Rancho Seco
Issue date:	06/25/1986
From:	Stolz J Office of Nuclear Reactor Regulation
To:	Julie Ward SACRAMENTO MUNICIPAL UTILITY DISTRICT
References
NUDOCS 8607140062
Download: ML20202D193 (27)

Text

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, June 25,1986 Docket No. 50-312 DISTRIBUTION LDocke_t File) RIngram NRC PDR SMiner L PDR GKalman Mr. John E. Ward PBD#6 Rdg NThompson Assistant General Manager, Nuclear (Acting) FMiraglia IAlterman Sacramento Municipal Utility District 0 ELD 6201 S Street ACRS-10 P. O. Box 15830 EJordan ,

Sacramento, California 95813 BGrimes JPartlow

SUBJECT:

RANCHO SEC0 NUCLEAR GENERATING STATION - REPORT ON " REVIEW 0F RECENT GE0 LOGIC AND SEISF0 LOGIC INFORMATION PERTINENT TO SEISMIC SAFETY" As part of our review of your report titled " Review of Recent Geologic and Seismologic Information Pertinent to Seismic Safety", NRC staff members and a California Division of Mines and Geology geologist participated in a field trip to the Sierra Nevada Foothills Fault Zone near Rancho Seco with members of your staff and your consultants. A copy of the staff trip report is attached (Enclosure 2). Observations made on this trip by the NRC staff and the California Division of Mines and Geology geologists are not in agreement with statements in your repor..

In order for us to resolve these differences, we require the additional information outlined in our Request for Additional Information (Enclosure 1).

Within 14 days of receipt of this letter, please provide us with your schedule for responding to this request for additional information.

The reporting and/or recording keeping requirements contained in this letter affect fewer than ten respondents, therefore OMB clearance is not required i under P.L.96-511.

Sincerely,

%JCm C.LL3 y, w m, ,

John F. Stolz, Director PWR Project Directorate #6 Division of PWR Licensing-B

Enclosures:

As Stated cc w/ enclosures:

See next page tsw PBD-6 P > ~PBD-6 PB SMine , an RWeller JS 6/2- 86 6/J.5 86 6/25/86 6/7 /86 g7140062860625 p ADOCK 05000312 PDR

Mr. John E. Ward Rancho Seco Nuclear Generating Sacramento Municipal Utility District Station cc:

Mr. David S. Kaplan, Secretary Sacramento County .

and General Counsel Board of Supervisors Sacramento Municipal Utility 827 7th Street, Room 424 District Sacramento, California 95814 6201 S Street P. O. Box 15830 Ms. Helen Hubbard Sacramento, California 95813 P. O. Box 63 Sunol, California 94586 Thomas Baxter, Esq.

Shaw, Pittman, Potts & Trowbridge 1800 M Street, N.W.

Washington, D.C. 20036 Mr. Ron Columbo Sacramento Municipal Utility District Rancho Seco Nuclear Generating Station 4440 Twin Cities Road Herald, California 95638-9799 Mr. Robert B. Borsum Babcock & Wilcox Nuclear Power Generation Division Suite 220, 7910 Woodmont Avenue Bethesda, Maryland 20814 Resident Inspector / Rancho Seco c/o U. S. N. R. C.

14410 Twin Cities Road Herald, California 95638 Regional Administrator, Region V U.S. Nuclear Regulatory Commission 1450 Maria Lane, Suite 210 Walnut Creek, California 94596 Director Energy Facilities Siting Division Energy Resources Conservation &

Development Commission 1516 - 9th Street Sacramento, California 95814 Mr. Joseph 0. Ward, Chief Radiological Health Branch State Department of Health Services 714 P Street, Office Building #8 Sacramento, California 95814

Enclosure 1 Rancho Seco Nuclear Generating Station Docket 50-312 .

Request for Additional Information

1. What is the nature of the contact observed at stop number 1?* If this contact proves to be a fault, determine its capability as defined in 10 CFR, Part 100, Appendix A, its extent and the magnitude of the largest earthquake of which it is capable.

2. At stop number 3 on the field trip a N50 W trending topographic lineament approximately a mile north of Comanche Reservoir is delineated by a northeast-facing escarpement in the Mehrten Formation. Coincident with the escarpenent i

is a nearly vertical planar contact between a pebble conglomerate and fine grained layered gray beds. Determine the nature of this contact. If this contact proves to be a fault, determine its capability as defined in 10 CFR, Part 100, Appendix A. its extent and the magnitude of the largest earthquake of which it is capable.

3. The North Jackson Valley lineament was demonstrated to be a fault, based on an exposure in a greenstone quarry on Route 88 south of Ione. Determine if the structure associated with the lineament is capable as defined in 10 CFR, Part 100, Appendix A. If it is, determine its extent and the magnitude of the largest earthquake of which it is capable.

4. There are parallel photolinears close to the China Gulch fault which appear to extend for several miles. Determine if this is a capable structure as defiend in 10 CFR, Part 100, Appendix A, its extent and the magnigtude of the largest earthquake of which it is capable.

• Note - stop numbers refer to stops indicated in the attached report (enclosure 2)

Enclosure 2 California Great Valley-Foothills Fault Zone Field Trip Report Ina B. Alteman, GSB )

1 l

On May 22-23, 1985, NRC staff members, accompanied by Sacramento Municipal Utility District (SMUD) staff members, their geologic consultants, and a geologist from the California Division of Mines and Geology (CDMG), toured the

. eastern part of the Great Valley and the contiguous foothills of the Sierra 1 Nevada Mountains of California in the vicinity of Rancho Seco Nuclear Plant to field check a report of a fault study submitted by SMUD in 1981. A list of participants is included at the end of this report as Attachment 3.

The fault study was requested of SMUD by the NRC because Rancho Seco was built before the Oroville earthquake of 1975. This event occurred about 85 miles

' north of Rancho.Seco on a fault of the Foothills Fault Zone (FFZ), causing surface rupture. At the time Rancho Seco was built, the FFZ was considered a pre-Cenozoic fault zone not capable of localizing earthquakes. The fault study request was for SMUD to evaluate the possibility of capable faulting closer to Rancho Seco that might affect the design of the plant.

The day and a half field trip was to view some fault and linear features closer to the plant that might be related to the FFZ. The mapped fault of the FFZ nearest the plant is 13 miles to the east (Fig.1).

1 Stop 1 On Route 104, about 10 miles east of the site, a roadcut exposed ,

I strata of the Ione Formation that had an unexplained juxtaposition of strikingly different strata in contact along a vertical plane. The Ione is the oldest of the three Tertiary sedimentary units in the eastern Great Valley resting on the Mesozoic island are metamorphic rocks. All of the sediments originated essentially from the Sierra Nevadas and foothills, having been deposited in channels of westward-flowing streams in the Tertiary period. The Ione, disconformably overlain by the Valley Springs Formation, was eroded and channeled so that its upper surface and intraformation bedding are irregular

. rather than planar.

This outcrop at Stop i exposed several' units of the Ione. On the west was an unlayered red clay at road level which changed upward to a cobble conglomerate with a red clay matrix capped by a soil layer above. Height of the roadcut was

. about 15 ft. (Fig. 2).

On the east side of the vertical plane a layered sequence of at least three lithic types contrasted sharply with the massive red clay and cobble units juxtaposed to it. The three lithic types, from lowest to highest were a blocFly medium gray clay unit, about four ft of which was exposed, that was rapidly weathering and undercutting the overlying thin layered light gray 1

ash-like deposit. The thin layered unit was about 6 ft thick. Overlying l this was a brown clay layer similar to the lowest layer on the west side of the vertical contact plane (Fig. 3).

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Although the nature of the contact plane was not obvious, attempts to exhume it ,

with hamer points successfully exposed a nearly vertical, somewhat planar I surface (Fig. 2). No shears or other structures appeared to be related to this plane. However, the layered ash on the east side was characterized by a close-spaced vertical jointing that may strike subparallel or at a low angle to the contact plane (Fig. 4).

The licensee's consultants suggested the possibility that the contact plane was  ;

an erosion surface or other surface irregularity upon which these units of Ione had deposited. Deposition on surface irregularities is characteristic of all three Tertiary fonnations, as they were deposited by high energy streams which produced cut and fill and channelling depositional characteristics.

r There was, however, no attempt to detennine if some linear coincided with this

. . feature.

Some skepticism was voiced about the depositional nature of the contact because of its planar and vertical character. The similarity of the lowest red unit on the west of the contact and the highest unit on the east and the close spaced jointing also added to the doubt concerning the depositional contact interpretation, and indicated the need for further investigation to ascertain whether or not it is a fault.

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Stop 2 On Rt. 124 just south of Ione, a town about 11 miles east of the l plant, another roadcut offered still further examples of Ione Fonnation stratigraphy. This exposure also exposed three distin'ctive lithic units (Fig.

5). The lowest unit is a blocky gray clay unit similar to the lowest unit at Stop 1, but with occasional thin laminae. It is overlain by a very white, l cross-bedded sandstone. The sandstone in turn is overlain by an irregularly j layered sandstone with alternating iron-rich layers which stand out in relief I because of their relatively higher resistance to weathering. The upper two units were seen the next day involved in the China Gulch faulting close to Comanche Reservoir.

The thickness of the strata varied because of the wedge-shaped character of the deposits. The exposure was about 20 ft. high.

. Stop 3 On a north-south road leading to a marina, about a mile north of the reservoir, we looked for evidence for a northwest-trending fault that had been mapped by A. Bartow of the USGS and that is on the new geologic map of the Sacramento 2' sheet. This was where Bartow had found small offsets coincident with a photolinear, according to a recent phone conversation. In the Rancho Seco Foothills Fault report, the licensee's consultant indicated there was no evidence for the existence of this fault.

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Walking south on the north-south road, we observed a roadcut on the west side of the road about 6-8 ft high where abrupt changes of lithology occurred over a short distance along approximately vertical contacts.' Large cobblestone beds were juxtaposed against a pebble conglomerate, and a few tens of feet further south along the cut, fine gray ash beds were juxtaposed against a pebble conglomerate. Although the nature of these contacts was not detemined, further south about 100m the contact between a pebble conglomerate on the south side and the fine layered gray beds on the north side was a planar, nearly vertical surface striking approximately N50'W (Fig. 6) in which a green clay gouge a few nn thick with downdip slickensides on the clay were present(Fig.7).

Attempts to trace this vertical surface and determine its extent were unsuccessful, partly because of time constraints.

The licensee's c'o nsultants were not certain of the identity of all the units but sumised that the pebble and cobble beds, being the upper strata, were of

~t he Mehrten Fomation, the youngest of the Tertiary units in this area.

The ash beds could also be Mehrten or Valley Springs Fomation, which underlies the Mehrten stratigraphically. Thus, the age, amount of offset, and extent of this fault are uncertain.

6 -

This fault exposure is approximately 12 mi from Rancho Seco, but the fault strikes directly towards the plant and, as its northwestward extent is unknown, it is uncertain how close to Rancho Seco this fault may continue.

On a map it appears that, projected northwestward, it could coincide with the Rancho Seco lineament identified by the licensee's consultant as lineament number 9, which passes less than .5 mi to the east of the plant.

Stop 4 Attempts to view field aspects of the North Jackson Lineament were frustrated by lack of exposure of strata associated with the linear, and fenced in private lands that the linear crosses. A greenstone quarry on Rte.

88, south of Ione, through which the linear passes, was faulted in an orientation coincident with the lineament, striking N45'W and dipping steeply tothenorthwest(Fig.8). The fault was in Mesozoic volcanics. There are no younger strata above the volcanics of the quarry, so no age deterinination

, could be made of the faultirig.

Stop 5 On a north-south road near the northeastern end of Comanche Reservoir,

. a fault in a roadcut in China Gulch was mapped by Woodward-Clyde. The exposure, about 15 ft high in bedrock, juxtaposes entirely different lithic units at the fault which strikes N45W and dips steeply to the east. The fault has down to the east movenent, with complexities indicative of multiple movements (Fig.9). The dominant lithology on the downdropped (east) side of the fault is the white crossbedded sandstone of the Ione For1 nation seen at Stop 2 with the overlying thin bedded, differentially weathered sandstone with rusted ironstone interbeds. On the west the lithology was an unlayered blocky

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clay unit similar to the unit underlying the white crossbedded sandstone at Stop 2. At this outcrop, however, thers was no indication of the stra'tigraphic relationship between the units on either side of the fault, other than the assumption that the downdropped units stratigraphically overlie the blocky clay unit.

A few hundred yards down the road, in the downdip direction of the fault, a second fault in the same strata showed similar characteristics but appeared to have offsets of only about 2 ft. (Fig.10). It suggested the possibility that this and the China Gulch fault are part of a fault zone. Although the licensee's consultants contend that the China Gulch fault can only be traced for .5 mile, this was not demonstrated satisfactorily. The presence of parallel photolinears close to the fault which appeared to extend for at least 7 miles, and the 15 ft minimum offset of the China' Gulch fault demonstrate a ,

need for further investigation to detemine age and extent of this fault.

Stop 6 The eastern boundary of the Mesozoic volcanic rocks that constitute

, the foothills of the Sierra Nevada Mts. is the Melones Fault Zone. A well-known fault of this zone, the Mother Lode Fault, more recently renamed the Poorman Gulch Fault, is about 22 mi from Rancho Seco. It was investigated and trenched by Woodward-Clyde for the Stanislaus site in 1978. Because of their determination that colluvium above the Tertiary strata was offset, that there

was evidence of multiple movement, and that the age of the colluvium was about 100,000 years old, they concluded that this was a capable fault. A visit to the trench site, to see what can be seen of a capable fault in this area, did l not reveal cuch of the nature of the fault. Some subtle top'ographic and

, vegetation linears could be discerned. Adjacent to the fault is a much sheared and fragmented rhyodacite intrusion. It is thought to have intruded the overlying Mehrten Fonnation and to have produced the shears in the Mehrten.

Evidence, however, for the relationship of the igneous body and overlying Tertiary deposits is sparse.

Structures in the slaty rocks exposed in a roadcut close to the fault included 4

folds and faults in the cleavage that suggested multiple deformation of the Mesozoic slates.

Ibe licensee's consultants, although accepting that Tertiary deposits were offset in the trench, argued that none had demonstrated that the trench offsets of Tertiary strata were related to bedrock faults in the Mesozoic rocks a few hundred feet below the trench. The consultants suggested the l

possibility that the shearing and offsets resulted from the igneous intrusion rather than from tectonic faulting.

The representative from CDMG, William A. Bryant, had seen the original trench and was convinced that the colluvium, which post-dates the intrusion, was also offset, supporting tectonic faulting as the cause of shearing and displacement.

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Attempts to examine the Youngs Creek Fault, which was also determined by Woodward Clyde Consultants to have offset Cenozoic strata, were unsuccessful, as there were no exposures in the vicinity and only subtle topographic expression.

Stop 7-8 With little time left of the day and a half field reconnaissance, we walked out two photolinears at the eastern end of Comanche Reservoir. Both were NW-trending, although the more southerly one trended more NNW rather than NW. Both also were linear valleys occupied by streams and appeared to be contacts of Mesozoic metamorphic rocks. The nature of the contacts were obscure, although in the second one, which had limited exposure on a road that led to a bridge across the reservoir, the hard foliated rock graded into more fissile and saprolitic rock as it approached the contact with a more massive unit. The contact was not exposed but the change in character of the foliated unit suggested the possibility of a fault contact.

Neither.of the linears provided enough information to ascertain their origins.

The trip served to confirm only the large amount of uncertainty and the lack of information that characterizes the nature of the FFZ the western limit of Mesozoic faults, and the age limits of faults in the eastern Great Valley that may be associated with the FFZ, closer to the Rancho Seco nuclear power plant than had been previously considered.

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l In sunnary, the following observations suggest a need for more knowledge of the geology of the eastern Great Valley and foothills:

(1) The nature of of the contact of Stop 1 and, if it proves to be a fault, the age of latest movement. This feature was less than 10 mi from the '

plant.

(2) The recognition of faulting at Stop 3, with no knowledge of its age or extent. The fault strikes towards the plant.

(3) The large displacement and suggestion of a fault zone in China Gulch.

The age and extent of this fault have not been detennined.

(4) The nature of the photolinears, and if faults, the age of latest movement and extent. Most of the recent faulting and seismicity in the foothills occurred on reactivated Mesozoic faults.

Some of these observatier.s are inconsistent with conclusions drawn by the

+1censee in the geologic and seismologic report. They concluded no evidence for faulting at Stops 1 and 3; they concluded that Tertiary strata were not offset along the North Jackson lineament but were unable to demonstrate that l 1

in the field; they concluded the China Gulch fault is only .5 mi long, but l

were unable to demonstrate that it was not a fault zone associated with longer linears nearby; they give the Poonnan Gulch Fault a low probability of being a i

capable fault and are not convinced by the trench observations.

Considering the. differing opinions and the lack of information, it is prudent to suggest that more detailed work be done to resolve the geologic issues in order to provide more confidence in the seismic safety of Rancho Seco.

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t3 k C::llfirnis Th2 Resozrc:;s Ag2ncy Memorandum To Perry Anisoto p.,,, May 29, 1985 crologic Information officer .

William A. Bryant From : Department of Conservation

. Divielen of mines and Geelegy

• sans o seco.e. se . ee essie subject. Rancho Seco Field Trip As per your request of May 17, 1985, I represented DMG at a field inspection of lineaments and faults near Rancho Seco Nuclear Generating Plant on May 22 and 23. Others participating in the field trip included: Ina Alterman and Sid Minor from the NRC David Campbell, Tom Crosbye and Michael Wolff from Bechtel; and Robert Dieterich and two others from SKID.

Rancho Seco had been designed prior to the 1975 M5.7 Oroville earthquake, at a time whan the Foothills fault zone was not considered to be active. In 1980, Priscilla Grew, then Director of the Department of Conservation, requested ,

that the seismic safety of Rancho seco be re-evaluated with respect to activity along the Foothills fault zone. As a result of this request, Bechtel completed a review in March 1981 of geologic and seismologic information pertinent to the seismic safety of Rancho Seco. The report consisted

l primarily of a literature review of investigations along the Foothills fault i zone by Woodward-Clyde Consultants (W.C.C.) and USBR that were conducted for the Auburn Dam study and by W.C.C. for the proposed Stanislaus Nuclear Power

, _ Plant. In addition, Bechtel identified lineaments within a 25-mile radius of Rancho seco, based on evaluation of remote sensing, U-2, and, locally, j large-scale ae' rial photography. suspicious lineaments were field-checked and, 1 with the exception of excavations in 1975 across northeast-trending lineaments I (Dry Creek lineaments) near Rancho Seco, no trenching was performed.

The field trip on May 22 and 23 was conducted in order to familiarize Ina Alterman~with the structure and lithologies along the Foothills fault zone.

Also, the nature and difficulties of evaluating recent faulting in this area where explained. Specifically, Bechtel had raised questions regarding W.C.C. 's evaluation of the Poorman Gulch fault (figure 1). W.C.C. had stated that this was a NRC-capable fault with repeated offsets, including a paleo B soil horizon considered to be at least 100,000yr old. Bechtel stated that W.C.C. had not clearly demonstrated a relationship between offset Pliocene Mehrten Formation and the underlying fault in Mesozoic bedrock. Alterna-tively, Bechtel suggested that the offset Mehrten Formation was perhaps due to the extrusion of nearby late Pliocene rhyodacite domes, a local, nonrecurring phenomenon with no expected future activity. However, Bechtel concluded that a tectonic origin could not be ruled out and that the capability of the Poorman Gulch fault was doubtful but uncertain. Bechtel concluded that a ML 6.0 earthquake originating on the Poorman Gulch fault 20 miles from the Rancho l

Seco site was an appropriately conservative maximum earthquake for assessing l

, the seismic safety of the Rancho Seco plant.

O

u__

t Memo, P.Amimoto Page 2 ,

May 29, 1985 l l

I Lineaments and faults within the 25-mile study area around Rancho Seco that were inspected during the field trip included (see figures 1 and 2):

(1) short, northwest-trending faults north of t'amnche Reservoir mapped by Bartow & Marchand (1979); (2) a northwest-trending, northeast-dipping normal fault in China Gulch that offsets the Eocene Ione Formation a minimum of 15 feet; (3) the North Jackson Valley lineament which passes within 7 miles of Rancho Seco; and (4) additional lineaments observed on U-2 photography by Ina Alterman.

1. A N500 W-trending topographic lineament north of Camanche Reservoir is delineated by a northeast-facing escarpment in Mahrten Formation, and an alignment of a spring and saddle to the southeast. Coincident with the northeast-facing escarpment was a steeply east-dipping planar contact between conglomerate (Mehrten Formation) and fine grained tuffaceous sandstone (7) (Miocene Valley Springs Formation). It was not clear if

^

this contact was a fault because no shears or gouge were ob. served, but Bechtel representatives agreed that this feature perhaps warranted further investigation. About 100 to 150 meters west of this location, a ,

west-dipping shear, characterized by a Sam-wide clay gouge, separated I conglomerate on the west from fine-grained sandstone on the east. No ,

geomorphic expression of this shear was observed.

2. The fault in China Gulch, first observed by W.C.C., is delineated by a vegetation tonal for about 1/2 mile. Extremely sparse soil overlies the Ione Formation at this roadcut and further evaluation of recent activity could not be made.

3. I was concerned with the North Jackson Valley lineament, as was Alterman, because the feature was demonstrated to be a fault, based on a quarry exposure. Here the fault offsets Mesozoic greenstone; the fault strikes N450W and dips about 650NE. Ione Formation occurs west of the fault in an uncomformable contact with the greenstone, but does not overlie the fault, rendering evaluation of Cenozoic activity at this site impossible. A colluvial deposit overlies the fault, but road grading and quarry operations tend to obscure the bedrock-colluvial relationship.

However, there is no offset of the bedrock surface across the fault, suggesting a lack of late Quaternary activity. Valley Springs Formation occurs across the North Jackson Valley lineament near Dutschke Hill.

Bechtel had observed near-horizontal beds of the Valley Springs Formation within 600 feet of the lineament and concluded that the North Jackson Valley lineament was not a capable fault. However, no outcrops of Valley Springs Formation were observed across the lineament, and I considh that a lack of Cenozoic faulting has not been satifactorily demonstrated.

4. Northwest-trending topographic lineaments (generally linear drajnages) interpreted from U-2 imagery by Alterman were field-checked. Little information with respect to late Cenozoic faulting was observed due to the lack of exposures. Trenching would be necessary in order to better understand the nature of these features.

\- ,

. Memo, P;Amimoto Page 3 May 29, 1985 ..

I informed Alterman that three Fault Evaluation Reports for the Foothills fault zone were prepared by DMG for the Alquist-Priolo Fault Evaluation Program; she indicated that these reports could be useful for reference and requested that copies be sent to her.

Four specific questions were raised by Perry Animoto regarding information pre:ented in the Bechtel reports s .

1) What is the design acceleration for the present facility?

2) What is the mari'eum credible ground acceleration using presently kaown geology?

3) What is the nearest fault trace of the Foothills fault zone to Rancho Seco?

4) Are there any questionable lineaments close to the site?

1. The safe shutdown earthquake design acceleration is 0.25g horizontal.

2. 0.12g for a ML 6.0 evsnt along the Poorman Gulch fault, 20 miles from the site.

3. The westernmost trace nearest to Rancho Seco is the " Spring Valley structure", 13 miles to the east (figure 1); this structure includes the Youngs Creek fault which was trenched by W.C.C. (1977) and offsets Pliocene Mehrten Formation. An overlying paleosol apparently was not

. - offset.

4 This question cannot be completely answered without interpreting aerial photography. However, the North Jackson Valley lineament (7 miles from site), and the Ione-Amador Lake lineae.nt (12 miles from site) are prominent (figure 2). The Ione-Amador Lake linearaent was not field-checked during this inspection due to time constraints, but is delineated by a premiaant west-facing escarpment that forms the contact between Ione Formation and Jurassic metamorphic rocks.

Ina Alterman indicated that she would send a copy of her field trip report to Jim Davis. A complet.e review of the Bechtel report by the NRC will be completed in the future.

U William A. Bryant Associate Geologist WAB:cip cc J. Davis E. Hart R. Sydnor -

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• Attachment 3 List of Participants SMUD Robert Dieterich Rich Myers Roy Deguchi CDMG William A. Bryant Bechtel Michael Wolff Tom Crosby David Campbell NRC Sid Miner

. Ina B. Altennan

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