front of the "windows" in the chamber sides and therefore eliminate the whole sidewall area of the trench as an infiltration surface. Which theory is correct? Proba- bly neither. But the fact is, use of these systems is reasonably wide- spread, and they do work with or without gravel along the sides. Design Each section of gallery has a given bottom area, depending on its length and width. Sizing of the chamber should be done using a table for the bottom areas required for conventional trenches. If you believe the first theory above, consider the chambers as deep trenches for purposes of sizing. If you believe the second theory, size the chamber bottom areas as you would a bed. If you have no idea, follow the manufacturer's instructions and ask for a three-year warranty. Materials Buy two end chambers and enough open-ended chambers to add up to the bottom area you need. ONSITE WASTEWATER DISPOSAL Construction If the height and width of the chambers are enough greater than the dimensions of your expired conventional trench system, you can do a "root canal." Dig out the old system to the point that you can no longer see any evidence of the effects of sewage on the soil. Level the bottom, place the chamber sections, hook up the inlet pipe, and backfill - but not with the excavated (clogged) soil. Don't backfill with coarse sand, which might flow into the cham- bers through the side holes, reduce the storage volume, and cause a depression at the soil surface. Gravel would be one choice, and medium soils (such as sandy clay, loam, or silty clay) are another. Operation and Maintenance Operation and maintenance procedures for leaching chambers are the same as for conventional absorption systems. Modifications of Conventional Systems ALTERNATING DRAIN FIELDS Application Alternating fields are simply two or more full-size or smaller absorption fields (of any type) which are alternately put into service and taken out of service by means of a valve or diversion box (Figure 6.1). There is evidence that a period of resting is