ML19309C559

App 2C to TMI-1 PSAR, Groundwater Hydrology. Includes Revisions 1-11

ML19309C559
Person / Time
Site:	Three Mile Island
Issue date:	05/01/1967
From:	JERSEY CENTRAL POWER & LIGHT CO., METROPOLITAN EDISON CO.
To:
References
NUDOCS 8004080779
Download: ML19309C559 (3)

Text

APPENDIX 2C GROUND-WATER HYEROLOGY 1 INTRODUCTION 1.1 GENERAL Three Mile Island Nuclear Station vill be -located on a large island in the Susquehanna River. Purely frem the standpoint of geography, its ground-water conditions are unique, but relatively constant, and predictably controlled by the Susquehanna River, itself. The drainage area of the Susquehanna River extends frem its source at Otsego Lake, Cooperstown, New York, for a distance of 4hh miles , across the States of Pennsylvania and Maryland, and teminates in the Chesapeake Bay. This major water cour:e collects all surface runoff and ground-5 ater seeps as well as their respective centaminants frm a water-shed of e,,,roximately a 27,000 square mile area. Three Mile Island is located about midway along the course of the river and therefore is influenced by the quantity and quality of that portion of the water frem the Susquehanna River watershed upstream frm the island. Average annual rainfall at the site is h0 inches.

1.2 MODE OF OCCURRENCE The bedrock underlying the general area is ccmposed of shales , sandstones ,

and siltstones belonging to the Gettysburg shale of Triassic Age. A vide range in yields occurs within the romation, with the sandstone facies nomally being the best aquifers. Ecvever, in closely jointed or fractured O shales , relatively high yields can occur. The alluvial J.eposits are not believed to be a major source of ground-water in this area.

2 SITE STUDIES Ground-vater was studied at the site by means of:

a. Stand pipes to record elevation and fluctuation of water levels

b. A pu= ping out test to detemine permeability of Se saturated soil

c. A falling head pemeability test to determine pemeability of soil above the water table Ground-water at the proposed station site occurs under water table conditions.

The water table reaches its maximum elevation at the highest topegraphic point in the center of the island and falls off tcvard both the east and vest shores. A variation of only about 5 ft occurs frem either side to the center producing a gradient of approxi=ately 0.6 per cent tcvard the river.

At twenty observation points in and surrounding the plant area, water levels occurred generally at a depth in excess of 15 ft and ranged from lh to 19 ft.

The ground-vater level occurred at a =aximum of 6.2 ft above the top of rock with less than 1 ft of head existing above the soil-rock interface at one q point of observation.

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1 The water level of the Susquehanna River controls Three Mile Island ground-water levels. A rapid rise in the river in response to a heavy rain and thaving of ice jams during Januar/,1967 was seen to produce significant rises in the water levels of observation vells 200 feet frcm the water's edge. Since a positive head exists on the island, any =ovement of ground- l vater frca the plant site vould be tcvard either channel of the river, and vould eventually enter the stream. The river would act as a r.atural boundarf, li=iting the dispersal of grenad-water frcm the island to the river. Teo facters are important in considering the possibility of infiltratica of ,

ground-water into the underlying Gettysburg shale and transmission to en j shore water supplies:

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a. A maxi =um positive head of 6 feet exists above the impervious (relativ to the soils ) Gettysburg for=ation.

b. Ground-water levels are higher on either shore of the river, with hydraulic gradients sloping tcvard the River.

In order fer ground-water to move frem Three Mile Island to the mainland, it would be necessary to reverse the hydraulic gradient on the =ainland, which would necessitate partial devatering of the Susquehanna River.

Further, it is unlikely that river water vould ever significantly infiltrate rocks en either shore, except under sustained high capacity pumping, creating induced infiltration. A natural condition of river water flowing into the ground would not be nomal to this climate and geography.

The length of time required for the ground-water to move to the river is problematical. Teo types of tests have been run to date, in an attempt to establish pemeability of the soils overlying the bedrock. A pumping out test was run on the eastern side of the island and the results detemined indicated the pemeability of the saturated soil zone to be on the order of 10-2 c=/sec. A falling head test was run in the center of the island to detemine the gemeability of unsaturated soil. This test produced a co-efficient of approxi=ately 10-J cm/s ec. These results confi m ed these gemeabilities estimated frca examining the centinuous samples frcm the test borings. Scme change in slope of the water table vill occur due to the varia-tions of the river level and temporary minor reversal of ground-water movement vill prebably result during pericds of high water or during periods of extended drought. Any additional impoundment of water in either channel vould necessaril; have an effect en the direction of ground-water movement and on the sicpe of the water table but in any event the final discharge point vould still be into the river.

1 l 3 AREA WATER WELL DATA l

l Most of the available data on ground-water vells in the Gettysburg shale, at this time, ca::es directly frem the U. S. Geologic Survey water supply paper en the ground-water resources of Olmsted Air Force Base at Middletevn. The base is located apprcximately two and one-half miles north of Three Mile Island.

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s The average strike of the femation in this area is N h3 with dips at angles varying fica 19 to 38 degrees. The rock consists of alternating layers of fine to coarse-grained sandstone, siltstece, and shale.

Ground-vater occurs under artesian conditions at the base. In 20 vells rangin6 frm 300 to 800 feet in depth, specific capacities of the aquifers tapped ranged fra 0.33 to 15.0 and transmissibilities varied frem 1,200 gpd per ft to scmewhat less than 50,000 gpd per ft. The pH of wells tested were frem 6.6 to 8.1, hardness fra 137 to 826 ppn and dissolved solids frem 200 to 1,340 ppn. In Hall's " Ground-vater in Southeastern Pennsylvania", the Brunswick shale (the name applied to the eastern counterpart of the Gettysburg) and the Gettysbu shale were cmbined and included tcgether in tabulations. Of 112 vells surveyed the depths ranged from 18 to 500 feet, with an average depth of 157 feet. Yield ranged frca 0-200 gallons per minute with an average yield of 41. Six analyses were included showing the range of total dissolved solids to be between 201 and 786 ppm, hardness frm 152 to h99 ppm and iron frem 0 5 to h.9 ppm. Since these are fairly deep rock aquifer wells where water chemistry is a function of miner-alogy of the reservoir rocks , one should not expect the alluvial ground-water to be of similar chemical makeup.

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