ML19256E335

Discusses Rept on Aeromagnetic Coverage of Facility

ML19256E335
Person / Time
Site:	Skagit
Issue date:	09/18/1979
From:	Regan R PHOENIX CORP.
To:	Wastler S Office of Nuclear Reactor Regulation
Shared Package
ML19256E326	List: ML19256E328 ML19256E329 ML19256E332 ML19256E335
References
NUDOCS 7911020113
Download: ML19256E335 (3)

Text

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• TWX 710 E334323 Septe=ber 18, 1979 P.s. Sandra Wastler Nuclear Regulatory Co==ission Washington, D.C. 20555

Dear Sandra:

I hope that the final report provides you with the necessary evaluation of the EDCON report. As I stated in that report we generally concur with their findings. However, it must always be re=e=bered that =agnetics is inherently a=biguous and the interpretation of such data is as much an art as a science. Thus there are some aspects of the data interpretation that could be reevaluated in the light of additional information. I'll atte=pt in this letter to answer the additional questions that you posed on some aspects of the magnetic data.

First o.f all I think that a southwesterly dip for the plate contact (or at least the serpentine bodies in the Decatur plate) is equally likely.

This is more consistent with the structure of the isolated ano=alies and l their interpretation (e.g., Ly=an Hill) and seems more geologically plausible as serpentine bodies are either absent or extremely deep (as evidenced by our Figure 1) in the area mapped as Shuksan. I was quite i= pressed with the team of John Whetten and Rick Blakely, and think that their co=bined expertise can best address this problem.

As far as the question of a fault in the Skagit Valley, it seems unlikely especially if it would be buried under only 1,000 feet of =aterial.

It is apparent that the Decatur is definitely not at that depth (if there, it must be extre=ely deep) . If there is some other =aterial there, say with a susceptibility contrast of .001 cgs units, then a fault with a 1,000 foot displace =ent would give considerable ano=alies even at 2,500 depth (less displace =ent would produce less a=plitude anomalies but not in direct pro-portion). Thus the likelihood of a fault in this area see=s low but more strict bounds could be put on any hypothetical fault given the geologicaf conditions and types of rocks involved. With such infor=ation the =agnetic ano=alies could be =odcied.

1259 049 F-21 7911020 //] -

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!b. S:ndra L'astler Fepte:hcr 10, : 7 The B and B f at'lt is a definite linear =apetic feature on the aero-magnetic map, but I concur with EDCON's finding that it is undoubtedly the trace of the plate contact (again if the Decatur were faulted in this region, the downthrown side would have to be qt.ite deep). I guess I keep referring -

to the more magnetic province as the Decatur terrain. This is a result of having talked to k'hetten and having examined the U.S.G.S. regional cap. I think that it shows that this is a coherent unit and that the hypothetical B and B fault in the vicinity of the plant is si= ply the boundary between thi? highly ::p: tic un'.t =d inc itss spatic Shuksan. As I centioned in our report it was dissappointing that EDCON did not consider the U.S.C.S data more.

I have some difficulty in answering your question about che Loveseth fault as we no longer have any of the data to examine. I remember our discussions about it and the mention of some modeling but I also think that sonething led us away fro = the necessity for doing such. I would have to see the data again to connent with any confidence on this. However, you might check to see if this is not associated with the Devil's Mountain fault zone, i.e. , some contact or drag feature.

I hope these answers help in your deliberation. Please do not hesitate to call at any time (I'll try to be more accessible).

Since rely, PHOENIX CORPORATION r

b , Y RobertD.Regan,[h.D.

Director, Earth Sciences Div sion RDR:ke Enclosure F- 22

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