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The preliminary designs have been made for a tunnel lined with concrete, of the ordinary horse-shoe aqueduct section, and equivalent in area to a circle of twenty feet in diameter.

A preliminary study had made so plain the importance of obtaining the greatest possible elevation of flow line for the purpose just mentioned and in order that sufficient storage could be had to carry over from a year of large rain fall for use in a year of small rain fall and yet have enough to permit at all times keeping the swampy bed of the basin well covered, that surveys to determine the maximum height of flow line permissable were made in great detail.

Contour lines at all the villages bordering the lake were traced out and all dwellings and other buildings were located out as far as could be affected by the highest possible flow line, and plans for future reference were prepared, as has been already set forth in items 9, 10 and 11 on pages 35 and 36. There land plans form Series "C." Small scale photo-engravings are appended, at end of report, that the information obtained may not become buried from use.

The accompanying drawings, plates 11 to 16, show the outlines of the proposed dam and power-house structures.

BORINGS AT DAM SITES.

Wash borings were promptly undertaken at the several sites which appeared most favorable for a dam. Owing to the lateness of the season the number of holes put down was much less than desired and the contractor who undertook making diamond drill borings to bed rock suffered from a series of financial misfortunes and mechanical accidents, such that he succeeded in putting only a single hole, to the depth of about 100 feet, without reaching ledge.

Mr. Parsons, engineer of the Hudson River Power Co., kindly gave us results of a few similar borings that he had put down.

Samples from these borings have been preserved and forwarded to the office of the State Water Supply Commission at Albany.

A few representative specimens were forwarded for expert examination; one set to one of the experts of the Board of Water Supply, who was engaged in making many hundred deep borings on Long Island; and another set of the same to Prof. W. O. Crosby of Boston, Consulting Geologist to the Metropolitan Water Board of Boston and to the Board of Water Supply of New York city. The reports follow on the next page.

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From my personal examination and from the more complete daily examinations of Mr. Ropes as the work progressed, I believe that all borings thus far made concur in showing the feasibility and safety of the type of dam proposed at this site, but before becoming definitely committed to so important a work, many more borings should be taken.

All borings concur in showing that a deep buried gorge more than a hundred feet deep exists all along under the river bed.

The following is result of expert geological examination of a few of the samples.

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CLASSIFICATION OF SAMPLES FROM TEST PITS AND BORINGS AT SITE OF PROPOSED DAM ON THE SACANDAGA

RIVER, N. Y.

By Walter E. Spear, Division Engineer, B. W. S., Babylon, N. Y.

*Too fine for our sieves,

MASSACHUSETTS INSTITUTE OF TECHNOLOGY.

BOSTON, MASS., GEOLOGICAL DEPT.

Classification of a Few Somples from Sacandaga Dam Site.

MR. JOHN R. FREEMAN, Consulting Engineer, Providence, R. I.:

February 27, 1908.

MY DEAR SIR.- I have examined the samples of earth from the proposed dam site on the Sacandaga river sent me by Mr. Ropes, and beg to report on the same as follows:

Test-pits B and D (on southerly side of dam site B). These two samples are essentially identical. The material is clearly a rather sandy till or bowlder clay, derived by glacial erosion from a granitic bedrock. It is of a highly composite character a heterogeneous mixture of particles ranging in size from gravel to rock flour and clay, the finer grades of sand and rock flour largely predominating. The proportion of true clay is quite small, but still sufficient to yield a firm mass by drying. Although, to the naked eye, the material appears dense or non-porous, it absorbs water rapidly on partial immersion, showing that the interstices are mainly capillary in size, and not sub-capillary, as would be the case in a true clay. It cannot, therefore, be described as impervious; but, I believe, nevertheless, that actual trial, for which these samples are insufficient, would show that the filtration rate is low. Abundant experience has shown that this association of a low filtration rate with a marked degree of perviousness is not unusual, and that it is especially characteristic of rock flour and sandy till. By virtue of its sandy and essentially non-clayey character, this till would yield readily to a stream of water, and thus be found well adapted to excavation and transportation by the hydraulic method. In fact, it may be doubted if earth more suitable for use in this way could be found; since a larger proportion of clay would add to the resistance to excavation without insuring a larger proportion of clay in the re-deposited material.

The marked buff color of these samples is due to oxidation, and indicates that they are probably from near the surface. Or, if from a considerable depth, the color affords additional proof of unusual perviousness for till. The general effect of oxidation, aside from change of color from gray to buff, is to cement the particles and yet leave the structure more open.

Test-pit F at dam site D (adopted site) southerly side. This sample is essentially similar to the preceding, except that the color is gray instead of buff and it has, presumably, come from a greater depth, or at any rate from below the zone of oxidation.

Test-pit G, dam site D, southerly side. This sample is also essentially similar to the preceding, except that it is distinctly more sandy, containing hardly more than a trace of clay. An approximate analysis shows:

Gravel

Coarse and medium sand.

Fine sand

Superfine sand and rock flour.

50 per cent. 25 per cent. 15 per cent. 10 per cent.

This material must have suffered a considerable loss of clay and rock flour by the washing action of water at the time of its deposition. But it is probable that in spite of this its highly composite character gives it a low filtration rate. The buff color is less indicative as to depth than for samples B and D, because of the more sandy and permeable character. But for the angular and unworn ferms of the stones, this might, if judged by so small a sample, be regarded as more properly gravel than till. Field observations are essential to the satisfactory classification of such materials.

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Sample No. 5, on river margin at dam site D, from boring 185 feet deep represents ground from 109 to 185 feet below top of hole. This is essentially a mixture of superfine sand and rock flour (6, 7, 8) without clay. It is modified or washed drift which has been deposited in standing water and under conditions unfavorable to a low uniformity coefficient. Consequently a low filtration rate is safe assumption. Under the conditions stated in previous report (six-inch column and ten-foot head), the filtration would quite surely fall below 500 and possibly below 100 cubic centimeters per hour. In this connection it would be of special interest to know whether this is a dry or a washed sample. To be conservative, I am assuming it to be the former. It is unoxidized (gray instead of buff); but this is what we should expect from its position, well below the water table. It is unoxidized; and its filtration rate must be very low, or practically zero. As a foundation for the proposed dam it may be accepted with entire confidence.

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