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exposed manure heaps west of the spring, but no opportunity for their surface drainage to enter.

Everett, Glendale Spring. – On Spring Street, about five hundred feet from Ferry Street. Spring rises to level of ground, in cemented enclosure five feet square and three feet deep, and is covered. Overflows several thousand gallons a day. The spring is in Mills' meadows, part pasture and part cultivated. Nearest cesspool is about four hundred feet away, and above, i.e., nearer Ferry Street. This cesspool is cemented all around, and overflows through a pipe into a ditch two hundred and twenty-five feet from the spring at nearest point. Several other cesspools within a thousand feet run into this ditch, which is not higher than the spring. A few houses on the other side of Ferry Street have cesspools which overflow on the ground. Large manure heap two hundred and thirty feet from spring, toward Ferry Street.

Swampscott, Moose Hill Spring. — About one hundred and fifty feet north from corner of Columbia Avenue and Beach Avenue. Bricked and cemented well in large bottling house. The water flows through a crevice in ledge, and rises nearly to the level of the ground in an oblong stone basin, about five feet long, two feet wide and three feet deep; surface water excluded; spring said to overflow the year round. The soil in the neighborhood is chiefly gravel with boulders, with underlying ledge. The drainage is from the southwest and west. The spring house is in a grassed lot. There is a cesspool ninety feet south-west on the hillside, and more cesspools and privies on the hill within three hundred feet. There is a stable fifty feet north-west of the spring. Water sold chiefly in Lynn and Swampscott.

ON THE

AMOUNT OF DISSOLVED OXYGEN

CONTAINED IN

WATERS OF PONDS AND RESERVOIRS

AT

DIFFERENT DEPTHS.

BY THOMAS M. DROWN, M.D., CHEMIST OF THE BOARD.

ON THE AMOUNT OF DISSOLVED OXYGEN CONTAINED IN WATERS OF PONDS AND RESERVOIRS AT

DIFFERENT DEPTHS.

The interesting changes in the character of the water of deep ponds, consequent on the stagnation and circulation of the water at different seasons of the year, was discussed in the special report on the Examination of Water Supplies, 1890 (pages 749–767). Investigations of the temperature and composition of the water from different depths in deep ponds showed the presence, in the warmer months, of a stagnant layer of water below a depth of twenty feet from the surface. If the surface of the pond is undisturbed by winds it may reach even to a greater height, say ten feet from the surface. This stagnant layer begins to form in the early part of April, and mingles with the surface water when the circulation of the water takes place in the autumn. This mingling begins in the early part of October and is completed some time in November.

It was stated in the account of this special investigation of deep ponds that the composition of this stagnant water depended upon the amount and character of the impurities in the water, and on the character of the bottom of the pond, whether or not it contained much decomposable organic matter. Thus of seven deep ponds or reservoirs examined it was found that the amount of free ammonia, which may be taken as a measure of the amount of decomposition going on in the stagnant layer, varied from 0.4720 parts per 100,000 in Jamaica Pond, Boston, to 0.0008 parts in the bottom of Reservoir No. 4 of the Boston water supply in Ashland. That the results in these two cases are not accidental is proved by repeated examinations of the deep layers in both of these bodies of water, extending over several years.

The freedom from products of decomposition in the latter case, namely, Reservoir No. 4, is due to the fact that the water is derived from an unpolluted water-shed; that the organic matter which it

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