ML20198G395

Discusses 760506 Geological Reconnaissance of Facility Sites & Locations in Region Around Site.No Apparent Structural Anomalies Found in Exposed Soils,Which Tends to Confirm SER Conclusions Re Little Faulting in Soil Strata

ML20198G395
Person / Time
Site:	Washington Public Power Supply System
Issue date:	06/02/1976
From:	Mcmullen R Office of Nuclear Reactor Regulation
To:	Stepp J Office of Nuclear Reactor Regulation
References
CON-WNP-1121 NUDOCS 8605290541
Download: ML20198G395 (3)

Text

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' J. C. Stepp, Chief, Geology and Seismology Branch, DSE I THRU: H. Lefevre, Acting Section Leader, GSB, DSE l GE0 LOGICAL RECONNAISSANCE OF WPPSS 1 ? 4 SITES

,! On May 6,1976, D. Tillson, W. Aiel, and A. Hosler of Wash.

Public Power Supply Services (WPPSS) and R. McMullen, flRC, conducted a geological reconnaissance to the WPPSS-1 and 4 sites

, and certain locations in the region around the site.

The first location visited was an unnamed doubly plunging anticlinal hill just southeast of Badger Mountain, which is part of the Rattlesnake Wallula topographic lineament. The Rattlesnake-Wallula lineament is considered the controlling tectonic structure for defining the Safe Shutdown Earthquake for the WPPSS 1, 2 and 4 nuclear sites. WPPSS's geological consultant, FUGRO, had mapped certain locations along the Rattlesnake-Wallula lineament north of Wallula Gap to detemine whether or not faulting, which exists from Wallula Gap southward was present to the north as suggested by Bingham et. al. (1971).

The stratigraphy as shown on FUGR0's map could be interpreted as showing a fault contact on the nortneast side of the hill southeast of Badger Mountain. Subsequent mapping by UPPSS and Shannon and Wilson geologists indicate that the anoma!ous contact on the map was the result of a mapping error and not to the presence of a fault. .

We examined basalt outcrops and basalt float in this location.

The stratigraphic sequence from bottom to top is the Pomona flow,

- the Elephant Mountain flow, and the Ice Harbor flow, with the

possible presence of a thin section of the Rattlesnake Ridge '

interbeded between the Pomona and Elephant Mountain. It was

- difficult to distinguish between the different flows by briefly examining the float and the limited number of outcrops. We also examined a quarry on one of the hills of the Horn Rapids Lincament to the east, where a thick section of the Elephant Mountain flow was exposed.

' It was not possible from this brief reconnaissance for me to detemine whether or not there was stratigraphic continuity around the north-east side of the hill. I suggested that the mapping error in the M .

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! the data supporting the change. WPPSS plans to do this as j soon as the field data has been analyzed.

! We next examined the excavation for WPPSS-4. The stratigraphic section there fmm bottom .to top consists of the Ringold fomation

, of late Pliocene - early Pleistocene age, a zone of reworked Ringold sands and gravels, a thick sequence of bedded glacio-fluvial sands and gravels, and a thin mantle of aeolian sand.

Although the stratigraphy is complicated by numerous channels and extensive crossbedding, the Applicant has identified several .-

individual stratigraphic zones which can be traced at about the same elevation arsund the walls of the excavation.. /,

Sections are being mapped at 50 feet intervals and at each

change of material. There is no evidence of faulting of the materials exposed in the excavation.

Several weeks ago the Applicant had reported that artesian groundwater was flowing from a drill hole in the bottom of the excavation. The hole had been cased to ground surface and left open to serve as an observation well during the investigation period. When the excavation was nearly down to grade someone inadvertently removed the upper portion of the casing. The hole remained open, as the base of the excavation was well below

, the piezometric head of the confined aquifer sgroundwater flowed continuously onto the excavation floor. With great difficulty, I

the Applicant found the top of the casing at a depth of 26 feet

below base of excavation. Using combined techniques of dewatering l

fmm perimeter holes and chemical grouting into perimeter holes.

l the Applicar.t significantly reduced the flow. The hole will be l grouted and all material that could have been affected by the flow i  :

will be removed and the resulting excavation will be backfilled j with concrete and Category I backfill.

1 I We visited the Unit 1 site, but construction is well underway and

! there were relatively few exposures of the soil around the facility.

Detailed photographs of the WPPSS-1 excavation had been provided to the staff several months ago. The excavation was geologically l l mapped and these data will be presented in the FSAR.

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Although the examination of the geology in the excavations was i brief, there were no apparent structural anomalies in the exposed soils. This would tend to confirm our conclusions

! stated in the SER that there is little likelihood that there is i faulting within the soil strata beneath the site.

I I Richard B. McMullen, Geologist l Geology and Seismology Branch

. Division of Site Safety and Environmental Analysis cc: J. Stepp i

H. Lefevre

. T. Cox

! R. McMullen R. Morris, USGS Distribution: '

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