Concrete construction methods for water and waste treatment plants differ from one plant to another, with each plant requiring its own unique forming plan. Practically nothing is standard in these plants because they are designed for a variety of capacities, treatment processes, influent characteristics and topographies. Conventional practices must often be drastically revised or even discarded in such construction. Because of the many complex factors that must be considered in the design and construction of either large or small treatment plants, forming is a prime consideration that many make the difference between profit and loss. In preparing an estimate, the concrete contractor must decide between factory-built or jobsite-constructed forms. Possibly the contractor will uses some of each. Modular forms, typically panels 2 feet wide by 4, 6 or 8 feet high, are generally made of steel frame backing with plastic-coated plywood facing so that smooth, dense, attractive concrete surfaces can be cast even after dozens of reuses. Once assembled, the gangs can be moved by crane from one location to the next much more rapidly than hand-set forms. As an example, during construction of the new $22 million meander Watershed Pollution Control Facility at Mineral Ridge, Ohio, gangs measuring about 24 feet wide by 15 to 19 feet high were moved every other day; the job was thus done in half the time that would have been needed with hand-set forms. When a project requires specially fabricated forms that can be used on only one project, the contractor must decide whether to make his own and discard them after use- in which case he has the problem of disposal- or to try to rent specially shaped forms from a commercial fabricator. The form used for all 16 collector troughs at the Scioto River Purification Plant in Columbus, Ohio, is an example of a special form developed by a commercial forms manufacturer. Each of the 20 foot diameter, 6 foot high troughs required 200 cubic yards of concrete. A small carpenter crew placed the form, establishing grade by means of four adjustment screws.