In the quarry are employed both Temple drills and ordinary large sized pneumatic drills, the latter supplied from three compressors with a combined capacity of 4500 cu. ft. of free air per minute, in the central power station, at which are also transformers to step down from the transmission line voltage. At the concrete block yard is an elevated platform, mounted on rails, spanning the space occupied by block forms and carrying several small mixers which discharge directly into the forms. A traveling crane stacks the blocks when they have hardened sufficiently to be handled, and also loads them on cars for transportation to the dam. Installed on the dam for the purpose of setting masonry are thirteen derricks of the same type as those in the quarry each with a 75-h.p. induction motor handling the fall and boom fall lines and an additional 11-h.p. motor for operating the swinging gear. The derricks on the masonry lift the stone and some of the concrete from cars running along each side of the dam. At present the lift is 20 ft. to 25 ft. The purchased alternating current operates the drills, the derricks in the quarry, the crushing and screening plant, the concrete block yard, the derricks on the dam and doubtless some miscellaneous services as shops, water supply, lighting, etc. The current performs no part of transporting the materials from sand pit and quarry to the crushing plant or to the dam. The two 1861-ft., 10-ton, traversing cableways with400-h.p. engines, although at one time used on the excavation, are now used only to handle and move plant. The mixers are of the gravity type. For the month ending Sept. 24, 1913, 760 cu. yd. mass concrete, 49,850 cu. yd. cyclopean concrete, 2630 cu. yd. concrete blocks or a total of 53,240 cu. yd. of masonry was laid, using about 312,000 kw.-hours of electric power as metered at line voltage. During the above period the drills performed more than a corresponding amount of work as many holes are drilled ahead of the other quarrying operations. The block yard also manufactured blocks ahead of requirements. On the other hand, the output of the crushing plant was somewhat below the normal corresponding requirement as a large stock of crushed stone that was on hand early in the season was being exhausted.
A comparison between any of the above performances must necessarily be very rough. Nevertheless they may be of interest and as fair to one performance as to the other. Thus at the New Croton there was a large amount of pumping but it was probably completed before the time when the work was in full progress. The stone was hauled nearly or quite twice as far as at Olive Bridge, and a large part of it was delivered on cars at such an elevation that the derricks had to raise it considerably; on the other hand (until later when the embankment and core wall were replaced by cyclopean concrete) no crushing was done as the rubble was entirely laid up with mortar. Assuming that during the winter season little work was done and only a small amount of coal used, then the 10,000 tons per year might mean 1100 to 1200 tons per month during the busy season. At Olive Bridge dam we cannot say just how much of the coal consumed was chargeable to work not connected with the masonry dam, but it was certainly considerable. Roughly it might be said that at Olive Bridge nearly twice the masonry progress was accomplished as at New Croton with the same amount of fuel. Something like the above difference would be expected from the fact that at the New Croton the fuel was burned in a large number of small detached boilers instead of at a central power plant; also from the fact that the materials were delivered at a low elevation. With the quarry 6 miles distant and outside of the reservoir, it would seem that a route might have been selected such that the stone might have been delivered at the top of the dam, and a comparatively small amount of power subsequently used to deliver it via cableways to the derricks. However, at that time the cableway was not appreciated or worked to the extent that it has been since. One further difference in conditions should be noted, that at the New Croton the .quarrying methods had to be such that a large percentage of face stones could be gotten out. This resulted in a higher cost of quarrying and quite possibly accounted for additional power more than would be used at Olive Bridge in the block yard.
To compare the two dams where electric power has been used: At Roosevelt the quarry derricks quarried the rubble and face stone, did necessary handling and turning for the cutters, passed the stone and waste to points under the cableways. Cableways delivered all material to the masonry derricks. Mixing was done by power instead of gravity. Cement and sand were brought to the dam via tramway. At Kensico the electric power may be credited with quarrying, loading cars (except that much of the loading of crusher material is done by steam shovel), crushing, making the face blocks and setting the masonry. All transportation was done by steam locomotives. The shop, camp and miscellaneous services to the credit of the electric power in each case may be roughly taken as proportional. Then at Roosevelt quarry and masonry derricks, crushing, mixing, cableways, cement and sand tramway compare with Kensico quarry and masonry derricks, crushing and concrete block yard. At Roosevelt were laid 18,328 cu. yd. per month with 148,512 h.p.-hours of power delivered to distribution system; at Kensico were laid 53,000 cu. yd. of masonry with 312,000 k.w.-hours purchased, which at say 97 per cent, transformer efficiency = 405,538 h.p.-hours delivered to machines. In brief, Kensico laid 2.89 times the Roosevelt masonry at a consumption of 2.73 times the power.
At the Roosevelt dam the quarries were much more favorable but on the other hand more large stone was used, including the face stone - 40 per cent, of the masonry as compared with 27 per cent, at Kensico. Roosevelt mixed the concrete and transported all materials. Kensico did no mixing (except in block yard), no transporting and not all of the loading in the quarry. Some power was lost through the system of delivery of materials whereby they have to be subsequently elevated again, although as yet the masonry is not high enough to make this a serious item.
When considering either of the above comparisons it should be borne in mind that the New Croton masonry contained 50 per cent, of large stone, the Roosevelt 40 per cent., and the Olive Bridge and Kensico 25 per cent, to 27 per cent. Other things being equal, the larger percentage of large stone involves additional quarry cost and probably power; also in setting the masonry it involves additional cost and undoubtedly more power. It is more work for the derrick to set a cu. yd. of stone, as frequently stones have to be lifted and set a second time; probably also concrete blocks are more easily set than face stone.