Groundwater treatment proposal for MTBE removal, Jan 2002

NYC 9/11 Public Portal Document

Page 2 of 2 Process Description WTC - Moretrench American

Bag Filter System

The bag filter system is design to remove suspended solids. There is no discharge limit for suspend solids however, over time the solids will collect in the packing of the stripping tower and reduce its efficiency. The bag filter to be provided is a Rosedale Multibag Filter. The housing holds 6 separate bags. The maximum flow rate through the unit is 1,000 gpm, however, we oversize this unit in terms of flow to extend the time between bag change outs. We intend to use 10 micron filter bags. A bypass is provided so that flow can be diverted around the housing during bag change out. From the bag filter the water moves to the top of the air stripping tower.

Air Stripping Tower

The air stripping tower is design to remove the MTBE from the water. The water is directed to the top of the air stripping tower. The water cascades through packing media inside the tower while air from a fan is blown into the base of the tower. The intermixing and redistribution of the air/water stream takes place repeatedly as the as the air and water travel in opposite directions through the packing. This contact between the two phases accomplishes the mass transfer of MTBE in water to air.

The clean water drops into a sump and will flow by gravity to the discharge point estimated to be 50 feet away without significant elevation change. A flow meter will be provided to record discharge quantities to the sewer.

The air, which now is contaminated with MTBE will be collected at the top of the tower and removed from the air stream using a vapor phase carbon box adsorber.

Vapor Phase Box Adsorber and Carbon

The carbon usage rate as calculated by US Filter Corporation is 101 pounds per day at 90% relative humidity. The box adsorber to be provided holds 20,000 pounds of carbon. Given the usage rate the carbon will have to be changed every 190 days. Sample ports will be installed within the carbon bed to aid in determining carbon break through. When a change out is required it is our intent to exchange the box adsorbers with a new one as opposed to removing spent carbon and replacing with new onsite, however we will need access to the adsorber by a lift truck. The spent carbon will be reactivated at US Filters Arizona Facility.

Control System

The control system will consist of on/off pump floats for the control of the water level in the equalization tank. A high level float will also be installed to shut down the sump pumps in the event of a high water level in the equalization tank.

A high level float will also be installed in the sump of the air stripping tower to turn of the feed pumps in the event of a high level in the sump which would be caused by a clogged discharge pipe GROUND/WATER TREATMENT & TECHNOLOGY, INC.

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