A sediment control is a practice or device designed to keep eroded soil on a construction site, so that it does not wash off and cause water pollution to a nearby stream, river, lake, or sea. Sediment controls are usually employed together with erosion controls, which are designed to prevent or minimize erosion and thus reduce the need for sediment controls. Sediment controls are generally designed to be temporary measures, however, some can be used for storm water management purposes. [1]
Treatment of silt impacted water using equipment and chemical addition, commonly called an active treatment system, is a relatively new form of sediment control for the construction industry. These systems are designed to reduce Total Suspended Solids (TSS) from entering nearby water bodies where silt pollution can be of environmental concern. Sediment-laden stormwater is collected and or pumped, and a chemical flocculant is added to aide in clarification. Types of flocculant include;
Extreme caution should be observed when using cationic flocculants like chitosan or positively charged polyacrylamide or polyDADMAC which cause hypoxia in fish. The use of anionic,negatively charged, flocculants is best practice on open loop treatment systems to ensure the protection aquatic habitat, fish and invertebrates.
The water is then either filtered (sand or cartridge filter,) or settled (lamella clarifier or weir tank) prior to discharge. Chemical sediment control is currently used on some construction sites around the United States and Europe, typically larger sites where there is a high potential for damage to nearby streams. [3] Another active treatment system design uses electrocoagulation to flocculate suspended particles in the stormwater, followed by a filtration stage. [4] Active treatment systems require technical expertise to operate effectively as multiple types of equipment are utilized.
Chemical treatment of water to remove sediment may also be accomplished passively. Passive treatment systems use the energy of water flowing by gravity through ditches, canals, culverts or other constructed conveyances to effect treatment. Self dosing products, such as Gel Flocculants, are placed in the flowing water where sediment particles, colloids and flow energy combine to release the required dosage, thereby creating heavy flocs which can then be easily filtered or settled. Natural woven fibers like jute are often used in ditch bottoms to act as filtration media. Silt retention mats can also be placed insitu to capture floccules. Sedimentation ponds are often utilized as a deposition area to clarify the water and concentrate the material. Mining, heavy construction and other industries have used passive systems for more than twenty years. These types of systems are low carbon as no external power source is needed, they require little skill to operate, minimal maintenance and are effective at reducing Total Suspended Solids, some heavy metals and the nutrient phosphorus.
Stormwater treatment can also be achieved passively. Stormwater management facilities (SWMF's) are generally designed Stokes' law to remove particulate matter larger than 40 micron in size, or to detain water to reduce downstream flooding. However, regulation on the effluent from SWMF's is becoming more stringent, as the detrimental impact from nutrients like Phosphorus either dissolved from (fertilizers), or bound to sediment particles from construction or agriculture runoff, cause algae and toxic cyanobacteria (aka Blue-green algae) blooms in receiving lakes. Cyanotoxin is of particular concern as many drinking water treatment plants can not effectively remove this toxin. In a recent municipal stormwater treatment study [5] , an advanced sedimentation technology was used passively in large diameter stormwater mains upstream of SWMF's to remove an average of 90% of TSS and phosphorus during a near 50 year rain event.
All states in the U.S. have laws requiring installation of erosion and sediment controls (ESCs) on construction sites of a specified size. Federal regulations require ESCs on sites 1 acre (0.40 ha) and larger. Smaller sites which are part of a common plan of development (e.g. a residential subdivision) are also required to have ESCs. [6] In some states, non-contiguous sites under 1-acre (4,000 m2) are also required to have ESCs. For example, the State of Maryland requires ESCs on sites of 5,000 sq ft (460 m2) or more. [7] The sediment controls must be installed before the beginning of land disturbance (i.e. land clearing, grubbing and grading) and must be maintained during the entire disturbance phase of construction. Approval for use of any chemical flocculant must be obtained prior to its deployment.
Stormwater, also written storm water, is water that originates from precipitation (storm), including heavy rain and meltwater from hail and snow. Stormwater can soak into the soil (infiltrate) and become groundwater, be stored on depressed land surface in ponds and puddles, evaporate back into the atmosphere, or contribute to surface runoff. Most runoff is conveyed directly as surface water to nearby streams, rivers or other large water bodies without treatment.
Water pollution is the contamination of water bodies, with a negative impact on their uses. It is usually a result of human activities. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and groundwater. Water pollution results when contaminants mix with these water bodies. Contaminants can come from one of four main sources. These are sewage discharges, industrial activities, agricultural activities, and urban runoff including stormwater. Water pollution may affect either surface water or groundwater. This form of pollution can lead to many problems. One is the degradation of aquatic ecosystems. Another is spreading water-borne diseases when people use polluted water for drinking or irrigation. Water pollution also reduces the ecosystem services such as drinking water provided by the water resource.
A settling basin, settling pond or decant pond is an earthen or concrete structure using sedimentation to remove settleable matter and turbidity from wastewater. The basins are used to control water pollution in diverse industries such as agriculture, aquaculture, and mining. Turbidity is an optical property of water caused by scattering of light by material suspended in that water. Although turbidity often varies directly with weight or volumetric measurements of settleable matter, correlation is complicated by variations in size, shape, refractive index, and specific gravity of suspended matter. Settling ponds may be ineffective at reducing turbidity caused by small particles with specific gravity low enough to be suspended by Brownian motion.
A constructed wetland is an artificial wetland to treat sewage, greywater, stormwater runoff or industrial wastewater. It may also be designed for land reclamation after mining, or as a mitigation step for natural areas lost to land development. Constructed wetlands are engineered systems that use the natural functions of vegetation, soil, and organisms to provide secondary treatment to wastewater. The design of the constructed wetland has to be adjusted according to the type of wastewater to be treated. Constructed wetlands have been used in both centralized and decentralized wastewater systems. Primary treatment is recommended when there is a large amount of suspended solids or soluble organic matter.
In colloidal chemistry, flocculation is a process by which colloidal particles come out of suspension to sediment in the form of floc or flake, either spontaneously or due to the addition of a clarifying agent. The action differs from precipitation in that, prior to flocculation, colloids are merely suspended, under the form of a stable dispersion and are not truly dissolved in solution.
Bioswales are channels designed to concentrate and convey stormwater runoff while removing debris and pollution. Bioswales can also be beneficial in recharging groundwater.
Erosion control is the practice of preventing or controlling wind or water erosion in agriculture, land development, coastal areas, river banks and construction. Effective erosion controls handle surface runoff and are important techniques in preventing water pollution, soil loss, wildlife habitat loss and human property loss.
Nonpoint source (NPS) pollution refers to diffuse contamination of water or air that does not originate from a single discrete source. This type of pollution is often the cumulative effect of small amounts of contaminants gathered from a large area. It is in contrast to point source pollution which results from a single source. Nonpoint source pollution generally results from land runoff, precipitation, atmospheric deposition, drainage, seepage, or hydrological modification where tracing pollution back to a single source is difficult. Nonpoint source water pollution affects a water body from sources such as polluted runoff from agricultural areas draining into a river, or wind-borne debris blowing out to sea. Nonpoint source air pollution affects air quality, from sources such as smokestacks or car tailpipes. Although these pollutants have originated from a point source, the long-range transport ability and multiple sources of the pollutant make it a nonpoint source of pollution; if the discharges were to occur to a body of water or into the atmosphere at a single location, the pollution would be single-point.
Surface runoff is the unconfined flow of water over the ground surface, in contrast to channel runoff. It occurs when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil. This can occur when the soil is saturated by water to its full capacity, and the rain arrives more quickly than the soil can absorb it. Surface runoff often occurs because impervious areas do not allow water to soak into the ground. Furthermore, runoff can occur either through natural or human-made processes.
Siltation is water pollution caused by particulate terrestrial clastic material, with a particle size dominated by silt or clay. It refers both to the increased concentration of suspended sediments and to the increased accumulation of fine sediments on bottoms where they are undesirable. Siltation is most often caused by soil erosion or sediment spill.
Best management practices (BMPs) is a term used in the United States and Canada to describe a type of water pollution control. Historically the term has referred to auxiliary pollution controls in the fields of industrial wastewater control and municipal sewage control, while in stormwater management and wetland management, BMPs may refer to a principal control or treatment technique as well.
A silt fence, sometimes (misleadingly) called a "filter fence," is a temporary sediment control device used on construction sites to protect water quality in nearby streams, rivers, lakes and seas from sediment in stormwater runoff. Silt fences are widely used on construction sites in North America and elsewhere, due to their low cost and simple design. However, their effectiveness in controlling sediment can be limited, due to problems with poor installation, proper placement, and/or inadequate maintenance.
Urban runoff is surface runoff of rainwater, landscape irrigation, and car washing created by urbanization. Impervious surfaces are constructed during land development. During rain, storms, and other precipitation events, these surfaces, along with rooftops, carry polluted stormwater to storm drains, instead of allowing the water to percolate through soil. This causes lowering of the water table and flooding since the amount of water that remains on the surface is greater. Most municipal storm sewer systems discharge untreated stormwater to streams, rivers, and bays. This excess water can also make its way into people's properties through basement backups and seepage through building wall and floors.
A sediment basin is a temporary pond built on a construction site to capture eroded or disturbed soil that is washed off during rain storms, and protect the water quality of a nearby stream, river, lake, or bay. The sediment-laden soil settles in the pond before the runoff is discharged. Sediment basins are typically used on construction sites of 5 acres (20,000 m2) or more, where there is sufficient room. They are often used in conjunction with erosion controls and other sediment control practices. On smaller construction sites, where a basin is not practical, sediment traps may be used.
Filter strips, also referred to as buffer strips, are small, edge-of-field tracts of vegetated land that are used to reduce the contamination of surface water. They are primarily used in agriculture to control non-point source pollution, however, they may also be used to reduce sediment in storm water runoff from construction sites. There are several types of filter strips including vegetative filter strips, forested riparian buffers, and wind buffers. In agriculture, they are highly effective in reducing the concentration of nitrogen (N) and phosphorus (P) in runoff into surface water and are also effective in reducing sediment erosion and removing pesticides. This helps to prevent eutrophication and associated fishkills and loss of biodiversity. The use of filter strips is very common in developed countries and is required by law in some areas. The implementation and maintenance of filter strips is inexpensive and their use has been shown to be cost effective.
Point source water pollution comes from discrete conveyances and alters the chemical, biological, and physical characteristics of water. In the United States, it is largely regulated by the Clean Water Act (CWA). Among other things, the Act requires dischargers to obtain a National Pollutant Discharge Elimination System (NPDES) permit to legally discharge pollutants into a water body. However, point source pollution remains an issue in some water bodies, due to some limitations of the Act. Consequently, other regulatory approaches have emerged, such as water quality trading and voluntary community-level efforts.
Water-sensitive urban design (WSUD) is a land planning and engineering design approach which integrates the urban water cycle, including stormwater, groundwater, and wastewater management and water supply, into urban design to minimise environmental degradation and improve aesthetic and recreational appeal. WSUD is a term used in the Middle East and Australia and is similar to low-impact development (LID), a term used in the United States; and Sustainable Drainage System (SuDS), a term used in the United Kingdom.
Clarifying agents are used to remove suspended solids from liquids by inducing flocculation, causing the solids to form larger aggregates that can be easily removed after they either float to the surface or sink to the bottom of the containment vessel.
SNF is one of the largest manufacturers of polyacrylamides. These water-soluble polymers are used as flocculants and coagulants in solid/water separation to recycle water, rheology modifiers and friction reducers. These functionalities have many uses where water is used, in drinking water production, wastewater treatment, mining, paper, enhanced oil recovery, hydraulic fracturing, agriculture, textile and cosmetics.
Industrial stormwater is runoff from precipitation that lands on industrial sites. This runoff is often polluted by materials that are handled or stored on the sites, and the facilities are subject to regulations to control the discharges.
| Authority control databases: National |
|---|
