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gent solution in order to remove as• ject we generally,used two men plus sewer system.: In numerous much encrusted material'as possible: the public works director. It usually stances. riser pipes with loose-fitting Following the instructions care- took them 11/2 to 2 hours per manhole. lids or. no.lids at -all were located 1. fully, our department began by mix- Following application of the second where manholes were indicated on ing a fast-setting"plug"material to be'.. coat, a coat of "brush bond white" city sewer maps. These risers were inserted into any holes where water ' was applied over the.patch coat all the capped and-sealed to prevent inflow was present. The plug is a rock-like'. way to the top of the inside of the into the system. material that sets in about 45 seconds manhole. This acrylic modified ce- One final source of inflow was also —needless to say, very little is mixed- ment coating was intended to seal over eliminated:The roof drains of certain at any one time. Just a handful is the porous surface of the brick and buildings in Burlington were found to mixed to a stiff dough-like consistency mortar above the ordinary level of the be illegally tied into..the sanitary and quickly pushed firmly into the water table. Finally, after another 24 sewer system. The town board as- hole or crack. The workers wore hours, a coat of "brush bund grey"' sisted in ordering disconnection of- elbow-length rubber gloves in the was applied over the entire inside these drains from; the community's handling and installing of this material surface of the manhole, completing. sewer system. to avoid possible caustic burns on . the process of sealing the inside of the The final cost in labor and materials bare skin. manhole against water penetration. for the 24 manholes involved in the Once all the holes and cracks with The problem of inflow from the sur- rehabilitation project was approxi- active leaks were sealed and allowed face through the lid of the manhole mately$225 per manhole. In contrast, to dry (usually one day), the second was taken care of in one of two ways. repairing the manholes from the out- "patch plug"was applied to-the entire If the manhole was buried beneath a side would have cost.closer to $300 inside surface of the manhole to a street or in a field and will seldom be each, not including the disruption to height above the ordinary level of the entered, the lid was simply sealed the public that open excavation in the water table. The patch coat was with a thick coat of plastic asphalt roof roadway would have caused. If a applied to the bottom 4 to 6 feet of all coating. If the manhole must be more sewer guard cap was required,it was manholes treated. This 1/4-in. thick accessible, a bowl-shaped fiberglass an extra $100 to supply and install second coat was troweled over the "sewer guard"cap was placed under them. brick to a-firm smooth coat and al- the manhole cover. The seiner.guard We have been constantly checking lowed to dry for 24 hours. The man- has a seal around the lip to prevent the manholes and thus far, even in holes were opened and aired for 24 inflow, a pressure release valve to very wet weather they have been hours before being entered, and left allow air and/or gas from within the holding up well. Significant reduc- open between coats in order to facili- manhole to escape without letting in tions in I&I have been noted much to tate drying and to help prevent the water, and a vacuum compensation the delight of the sewage treatment accumulation of sewer gas. A port- valve to let air into the manhole with plant personnel. ❑❑❑ able air-blower and a safety line at- changes in air pressure. tached to the man doing the work in This completes the manhole re- Acknowledgement. This article is the manhole was a recommended habilitation process. In addition we based on a feature that appeared in safety precaution. Two men working have been using a magnetic dip-type the Winter 1984-1985 issue of Drip,the 20 to 30-minute shifts-were also part of metal locator to attempt to find all publication of the Oklahoma Water the safety requirements. In our pro- manholes and risers in the Burlington and Pollution Control Association. O Preco Industries Ltd a 55 Skyline Drive o Plainview, New York 11.803 . TO L•L FREE: 600645-3.95:4 NEW YORK: 516/935-9100.