Different kinds of systems—familiarly called leaching systems—are used to disperse water within the soil of the earth in connection with subsurface sewage disposal systems (wastewater systems). Those systems can also be used in other applications for receiving, holding and dispersing other waters or liquids, such as receiving stormwater, or for drainage applications.
A traditional leaching system comprises a perforated pipe running through crushed stone contained within a shallow trench. Tar paper or salt hay, laid on top of the crushed stone, has been used to stop the overlying soil from migrating downward over time into the interstices of the crushed stone.
Another type of leaching system comprises interconnected galleries, namely pre-formed concrete chambers having perforated sidewalls. Buried galleries are often surrounded with crushed stone.
Another type of leaching system utilizes molded or thermoformed plastic leaching chambers. The chambers are arranged as strings of interconnected units, often in parallel spaced-apart rows. A typical chamber has an arch shape cross section, a solid top, an open bottom, a multiplicity of corrugations, and perforated sidewalls. Leaching chambers are exemplified by products sold under the Infiltrator® brand name. Geotextile may sometimes be laid onto the plastic leaching chambers to stop fine sand from migrating into the chamber interior. Crushed stone may be placed against the sidewalls of buried chambers.
Still another type of system comprises horizontally-laid cylindrical leaching units comprised of plastic foam beads contained within netting. These are exemplified by products sold under the EZflow® brand name. Typically an EZflow drainage unit is tubular shape, about 10 to 12 inches in diameter and 10 feet long; and it may comprise an integral barrier of geotextile which stops migration of soil downwardly into the spaces amongst the beads. See U.S. Pat. No. 8,256,990 for a description of such kind of product which includes barriers; the disclosure of the patent is hereby incorporated by reference. Alternately, the installer of a drainage unit may provide a separate overlying barrier which is placed onto the unit before the trench containing the unit is backfilled.
While the primary function of a leaching system is to disperse water to the surrounding soil, it is important that leaching systems provide within themselves space for storing water, to handle situations where the in-flow is greater than the rate of outflow to the surrounding soil. Thus, the storage volume per unit length is important.
Generally, leaching system units which are made of plastic are attractive because of low weight and associated ease of transport and installation compared to the older stone-and-trench and concrete gallery systems. Shipping costs can often be a significant factor and in that respect the arch shape cross section leaching chambers are attractive because they nest readily
The height of the leaching unit is also referred to as the profile of the leaching unit. An aim for many applications is to have a leaching unit profile which as low as possible. Low profile units require a shallower trench. That is desirable when the water table or bedrock is not deep since the bottom of a leaching unit should be a certain distance above such features.
Typically there is a regulatory minimum for the overlying soil thickness, usually 6-12 inches, for sanitary reasons. But having overlying soil also reduces the load of a vehicle or the like which is transmitted to the leaching unit. A leaching unit has to be sufficiently strong to resist the weight of overlying soil and other loads, such as motor vehicles which traverse the soil surface.
Inventors have sought to make low profile leaching system units. For example, see the commonly owned low profile leaching chamber described in Moore, U.S. Pat. No. 7,914,230; Ditullio U.S. Pat. No. 6,129,482 and Potts U.S. Pat. No. 7,465,390. Low profile leaching units inherently have less storage capacity per unit length that normal or high profile units; and having good storage capacity can be a regulatory and engineering requirement, particularly when the rate of percolation of water into the soil is low. Thus, it is an aim for any improved unit to have adequate storage volume per unit length.
The leaching units of the above-mentioned prior art systems vary in their load bearing capacity. Generally, arch shape cross section plastic leaching chambers have obtained the requisite strength from a combination of wall thickness, arch shape cross section, corrugations, and ribs. The strength of a plastic bead-within-netting type unit is a function of the crush strength, or compressibility of the bead array.
The present invention is preferably made of plastic. Generally, in a leaching unit which is made of plastic reducing the weight—and therefore the cost of material and shipping—is important to the maker. Product cost is also important: Purchasers are concerned about the cost of providing, by means of a leaching unit, a desired amount of leaching area and a desired amount of storage volume within the system. It is a general object to reduce cost in these contexts.