GLWA-CON-247 - GLWA Southwest Water Treatment Plant – Raw Water Sampling Modifications

The scope of work includes a temporary earth retention system to allow removal and replacement of the upper portion of the existing tunnel access structure. Conical sections of the manhole will be replaced with straight wall sections with a new flat slab top and access hatch. Two submersible well pumps (5.5 gpm each) will be installed within 10-inch diameter casing pipes extending from the top of the tunnel access structure down to the tunnel. The casing pipes will be supported from the access structure walls. 6-inch suction lines will extend from the bottom of the casing, along the top of the raw water tunnel to a point 50 feet upstream of the access structure. Well screens at the end of the suction lines will allow sample collection by the well pumps.
 
Water levels in the well pump casings will be monitored for indication of screen plugging. In case of plugging, connections for back flushing with pressurized water are provided.
 
The well pumps will deliver the raw water sample through buried ¾-inch discharge lines from the tunnel access structure to the basement of the SWWTP building. Inside the building, the lines will combine and be routed to the Process Control and Analytical laboratories on the second floor. Modifications to the laboratory sink in the Process Control laboratory will be completed to incorporate a new sample observation cylinder.