Annual report of the State Board of Health, Lunacy, and Charity of Massachusetts . e drains below runningtraps. The lower manhole on each trunk sewer is provided witha perforated cover, to relieve the other portions of the sewerfrom the pressure caused by heavy surf, and not, as hasbeen suggested, as a fresh-air inlet, for, on the upper side ofeach manhole, is a flap valve or tide gate which would effect-ually prevent any such use being made of the perforatedcover. The sewers and house connections above the lastmanhole on each trunk line (which manhole is intended forthe purpose above describe
Annual report of the State Board of Health, Lunacy, and Charity of Massachusetts . e drains below runningtraps. The lower manhole on each trunk sewer is provided witha perforated cover, to relieve the other portions of the sewerfrom the pressure caused by heavy surf, and not, as hasbeen suggested, as a fresh-air inlet, for, on the upper side ofeach manhole, is a flap valve or tide gate which would effect-ually prevent any such use being made of the perforatedcover. The sewers and house connections above the lastmanhole on each trunk line (which manhole is intended forthe purpose above described) are water-tight, so far as carefulwork can make them. House connections are entered in4-inch Y pipes, and the ventilation for both sewer and housedrain is provided for by a 4-inch pipe, connecting outsideeach and every house, extending from the main drain of eachbuilding just below the running trap, to some point above 234 DEPARTMENT OF HEALTH. [July, Secli oil of Mcijih ole01dhoiuiiig rmttwd ofirrspectioft with jrurro?: Cover rettuwecifo admitT^nJz^7it. Surface of roartwaz/. Sewe? 1883.] THE SEWERAGE OF NAHANT. 235 4& j0 +^j 2-g dt-LT-l \ § k I ?& Sfsouo jo zynj dufu^y •qp s-souojo aw-i d*i}ii»j Ok 236 DEPARTMENT OF HEALTH. [July, the chimneys. (See Fig. 8.) This provides Dot only forthe ventilation of sewer and house drain (the latter is rarelyventilated between the running trap and the sewer, thoughapt to be fouler than any portion of the public sewer), but italso causes each house drain to ventilate its proportion ofthe system, and prevents the usual concentration of the gasesat a few points. All ventilation being above the top of the house, there isvery small chance of annoyance from smell, and so far asknown there has been none noticed at any point save slightlyat the perforated manholes at the foot of the trunk lines,and in three instances from puffing of fresh-air inlets tohouse drains—both of which were disconnected from thesewer a
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