Hydraulic and earth engineering – Fluid control – treatment – or containment – Fluid storage in earthen cavity
Reexamination Certificate
2002-02-23
2004-03-23
Will, Thomas B. (Department: 3671)
Hydraulic and earth engineering
Fluid control, treatment, or containment
Fluid storage in earthen cavity
C004S491000, C210S170050, C210S747300, C405S074000, C405S079000
Reexamination Certificate
active
06709199
ABSTRACT:
BACKGROUND OF THE INVENTION
A. Field of the Invention
The field of the present invention relates generally to systems for controlling sediment in earthen basins, such as groundwater recharge and flood control basins. More specifically, the present invention relates to such systems that utilize multiple sloped surfaces through which fluid can continually percolate so as to prevent sediments that would otherwise impede the flow of the fluid through the earthen basin.
B. Background Art
Earthen basins are commonly used to contain water for several purposes including, but not limited to, groundwater recharge of surface water, flood control and containment of municipal, industrial and agricultural waste waters. The function of these basins often rely on, or are enhanced by, the percolation of the contained water through the bottom and sides of the basin. The percolation rate of the basin is primarily controlled by the underlying soil conditions and material and by the amount and type of sediment which has settled on the surface of the basin bottom. The sediment usually becomes the controlling element, often clogging a basin so that pumping the water or fluid from the basin becomes the only economical means of draining the basin for maintenance. The subsequent removal or mixing of this clogging sediment requires light and/or heavy equipment after the basin has adequately dried. The equipment used for basin maintenance can compact the surface material, thereby requiring additional efforts to uncompact the material and return the basin to its maximum infiltration performance levels. The challenge for basin designers and operators has been to develop a low maintenance facility without compromising percolation effectiveness.
It is well known that percolation is at or near the maximum rate for the first several months of operation after initial basin construction or after maintenance of an existing basin because the surface of the basin has not had time to become clogged by sediment materials. The surface clogging sediment results from several sources of fines, including single cell and filamentous algae, silts and clays in the irrigation/recharge water and generated by interbasin erosion (filling and levy erosion. Over time the percolation ability of the basin decreases as the sediment forms a virtually non-impregnable clogging layer. The infiltration clogging effect of the sediment is a serious concern for all industries, businesses and agencies using percolation basins. Accumulated sediments limit the percolation of water through a basin and, without routine mechanical maintenance, the clogging effect will eventually render a basin's percolation ability virtually useless. As explained in more detail below, basin owners and operators have historically used discing, ripping, scraping and combinations thereof to control and/or remove the clogging sediment layer with varying degrees of success. If the sediment was composed of inorganic material, discing or shallow mixing is often ineffective because the near surface becomes clogged with the accumulated fine grained material. If the sediment included sufficient organic material, discing or shallow mixing without routine deep drying cycles is ineffective because the near surface becomes clogged with anaerobic microbes. Scraping and subsequent ripping can be effective, but it is costly and is typically required at least every three years.
Sediments are inorganic and/or organic particles which settle on the surface of the basin during the filling and operation of the basin. The sediments are generated and accumulated via several mechanisms including: (1) release of silt and clay from the native basin material into suspension by turbulence from the filling water in a freshly maintained or newly constructed basin; (2) wave action on the basin's perimeter side slopes; (3) settling of the suspended silt and clay contained in the influent water; and (4) settling of suspended organic materials (i.e., algae and weeds) that grow in the basin. Clays and silt-clays (fines) are deposited as a thin layer on the bottom of the basins. A layer of these fines as thin as one-eighth inch has about as much resistance to infiltration as two feet of silty sands, forty feet of sugar sands and two thousand feet of clean gravel. Over time, organics may also settle to the bottom of the basin. These settled organics also affect the infiltration ability of the basin.
The common methods of maintaining the basin and controlling the clogging effect are expensive and time consuming. All these methods first require that the basin be drained and dried. After drying, heavy equipment is normally used to access and work in the basin's bottom. The draining process sometimes requires pumping the water from the basin when the basin's bottom is significantly clogged. Pumping is also used when the basin's bottom is only somewhat clogged, but time is of the essence. Set forth below is a summary of the various maintenance methods that are used (after first draining the basin).
The “Dry and Crack” Method (also referred to as the “Chip” Method) is often used where the climate is normally hot and dry and the water availability is intermittent or sporadic. It is also used where land for basin construction is abundant and basins can be easily cycled in and out of operation. The surface sediment on the bottom of the basin is allowed to dry and crack to form what are commonly known as “chips,” due to their appearance similarity to potato chips. Once the chips are formed, the basin is generally brought into operation without any mechanical cleaning. Although the permeability of the basin is initially substantially improved, the chips soon resettle and the small spaces between the chips are soon filled with sediment and the basin becomes clogged, requiring the basin to be re-dried. This process is repeated frequently, sometimes as often as twice a month. Periodically, the chips have to be removed by mechanical scraping or raking. The material just under the surface normally becomes compacted, further restricting percolation. Under this method, the operational time of the basin is limited to relatively short periods between refilling of the basin and stopping the influent flow to allow drying. As is well known, the effectiveness of the Chip Method is limited by climate, water availability and available land for multiple basins.
The “Shallow Mix” Method is the desired method when the climate facilitates faster basin drying and time is of the essence for basin maintenance. It is also used when and/or where removal of the sediment is difficult or where the concentration of sediment in the influent water is relatively high, thereby making the Chip Method less viable. The basin bottom is dried longer and deeper than in the Chip Method, forming chips and a moisture content that will allow mechanical equipment, such as a tractor, to drive on the bottom and use a tool, such as a disc, spring tooth, plow or other shallow mixing device, to break-up and mix the chips with the upper surface material. The chips and/or sediments are mixed with the upper surface material to disperse the thin layer of clogging sediment into the upper surface material. The mixing usually takes place within the upper six inches or fifteen centimeters of the basin bottom. This method is more effective than the Chip Method at dispersing the layer of sediment and temporarily improving the permeability of the basin. This process is repeated as needed, typically once a year. Depending on the soil composition and the amount of compaction from the tractor, occasional ripping may be needed to maintain acceptable percolation rates. With repeated mixing of inorganic sediment, the mixed layer becomes increasingly impermeable and must eventually be removed. If the repeated mixing includes the presence of organic sediments, the mixed layer will likely support an active anaerobic condition when the basin is in operation. Anaerobic microbes develop and thrive in oxygen poor environments and in the presence of organic n
Mayo Tara L.
Ryan Richard A.
Will Thomas B.
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