Boca Ciega Isle is connected to the City of St. Petersburg Beach, Florida, by a bridge. Since the area is surrounded by water, infiltration into the gravity sewer system was evident from the high chloride levels which were measured. Excessive infiltration caused system surcharging along with high maintenance costs for the pipelines, manholes and lift stations. Energy costs associated with pumping this excessive water were high. The City had previously tried to repair certain portions of the collection system by either internal joint grouting, sliplining and/or manhole lining. It was apparent, based on an evaluation of the rehabilitation work conducted, that groundwater migration was occurring after repairs were made. It was therefore decided to use the Sanipor renovation process since it minimizes the chances of water migration by stopping infiltration from the main line, service laterals and the manholes simultaneously. Moreover, the City was also actively addressing infiltration/inflow removal from its wastewater collection system in order to meet certain criteria for an effluent re-use programme. It had previously surveyed these sanitary sewers using CCTV and identified active infiltration along with high chlorides in the effluent. For this project only, individual line sections were isolated by plugging and flow measurements taken using a calibrated V-notch weir to determine the rate of infiltration for each line section. All line sections were hydraulically cleaned and surveyed by CCTV tu quantify leaks and dokument the sewer conditions. Active leaks were observed and dokumented for every line section, with inspection work being conducted during high tide conditions. The sewer section to be repaired was isolated by plugging all incoming and outgoing lines at the manhole.

Service connections were not plugged since there was no risk of flooding any buildings. Once the line sections was isolated, Sanipor's 'S1' solution was dumped by gravity directly from a tanker truck into the line being repaired. In all cases the lines were filled from the downstream manhole to the upstream manhole.

For optimum exfiltration of the S1 solution through the defective areas of the pipe and the manholes and subsequently into the surrounding soils, a hydrostatic head was maintained sufficient to overcome the hydrostatic head exerted from the groundwater. This was done by filling the manhole up as high as possible. The S1 solution remains in the line until at saturates the void areas and surrounding soils in the defective areas - usually 1-2 hours - and minimal exfiltration is observed at the monitoring manhole. The switch-over of solutions is the most critical part of this process. A rapid switch-over minimizes the number of cycles required to effectively seal the entire reach of sewer. High speed submersible pumps were utilized to pump the S1 solution from the downstream manhole back into the tanker truck. Since poor grades were observed in some of the line sections during the preinspection phase, a line 'squeegee' was pulled through the pipe from the upstream manhole to the downstream manhole to remove excess S1 solution. Once the line was emptied, the 'S2' solution was immediately dumped by gravity into the upstream manhole. The S2 solution then exfiltrated and mixed with the resudial S1 solution in the soil and voids. When the two solutions are mixed, stabilisers within each solution react and a strongly polymerised polysilicic acid gel results. Soil particles and sand grains are bonded together to form a cohesive mass which totally encapsulates the defective area and is impermeable to groundwater infiltration. The S2 solution was pumped from the downstream manhole directly into the second tanker using two high speed submersible pumps. Immediately after the removal of the S2 solution, all plugs were removed and the line section was put back into service.

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