A resident in the rural mountains of West Virginia notices a yellow-orange foam

Question

A resident in the rural mountains of West Virginia notices a yellow-orange foam forming at the opening in the ground where the stream that runs through their backyard originates .

a) What is the source of the color, and the solid precipitate that accompanies it, and how was it formed? Use chemical equations to explain your answer. What other issues might there be with the water quality (besides the precipitate) in this stream? Explain

b) Speculate the causes that might be behind the appearance of this pollutant. Is it likely to be naturally occurring or from an anthropogenic source?

c) What are the negative effects of the precipitate, and other pollutants, on the surface and groundwater locally as well as further downstream?

d) Discuss possible methods for remediation of the contaminants Who is responsible for this remediation?

Explanation / Answer

a) The effluents discharged by industrial units located along the stream is discharging their pollutants without treatment directly into the stream water. The colour is due to. Lead(II) iodide, lead chromate and Chromate of potassium, Aluminium . Formation of a precipitate indicates the occurrence of a chemical reaction.E.G.Fe3+(aq)+NO3(aq)+Na+(aq)+3OH(aq)Fe(OH)3(s)+Na+(aq)+NO3(aq).Precipitation reactions occur when cations and anions in aqueous solution combine to form an insoluble ionic solid i.e. precipitate. Not all aqueous reactions form precipitates. Precipitates are insoluble ionic solid products of a reaction, formed when certain cations and anions combine in an aqueous solution. The determining factors of the formation of a precipitate can vary. Some chemical reactions depend on temperature, whereas others are dependent only on solution concentration. The solids produced in precipitate reactions are crystalline solids, and can be suspended throughout the liquid or fall to the bottom of the solution. The remaining fluid is supernatant liquid. The two components of the mixture (precipitate and supernate) can be separated by various methods, such as filtration, centrifuging, or decanting.

Arsenic is a widely dispersed element in the Earth's crust and exists at an average concentration of approximately 5 mg/kg. There are many possible routes of human exposure to arsenic from both natural and anthropogenic sources. Arsenic occurs as a constituent in more than 200 minerals, although it primarily exists as arsenopyrite and as a constituent in several other sulfide minerals. The introduction of arsenic into drinking water can occur as a result of its natural geological presence in local bedrock.

b) Arsenic pollution, the cause can almost always is traced to mining or mining-related activities. Mechanisms by which arsenic is released from minerals are varied and are accounted for by many (bio) geochemical processes: oxidation of arsenic-bearing sulfides, desorption from oxides and hydroxides, reductive dissolution, evaporative concentration, leaching from sulfides by carbonate, and microbial mobilization. By environmental degradation pollutants are directly or indirectly discharged into water bodies without adequate treatment to remove harmful compounds.

c)Humans have long used air, land and water resources as ‘sinks’ into which we dispose of the wastes we generate. These disposal practices leave most wastes inadequately treated, thereby causing pollution. This in turn affects precipitation, surface waters, and groundwater , as well as degrading ecosystems . The sources of pollution that impact our water resources can develop at different scales (local, regional and global) but can generally be categorized. Identification of source types and level of pollution is a prerequisite to assessing the risk of the pollution being created to both the aquatic systems and, through that system, to humans and the environment. With the knowledge of the principal sources of the pollution, the appropriate mitigation strategy can be identified to reduce the impact of impurities on the water resources. Landscape, sedimentation, pollution, over-abstraction and climate change are primarily the result of human actions. Sediments occur in water bodies both naturally and as a result of various human actions. When they occur excessively, they can dramatically change our water resources. Sediments occur in water mainly as a direct response to land-use changes and agricultural practices, although sediment loads can occur naturally in poorly vegetated terrains and most commonly in arid and semi-arid climates following high-intensity rainfall. Atmospheric contamination from industrial plants and vehicle emissions leads to dry and wet deposition. This causes acidic conditions to develop in surface water and groundwater sources and at the same time leads to the destruction of ecosystems. Acid deposition impairs the water quality of lakes and streams by lowering pH levels (i.e. increasing acidity), decreasing acid-neutralizing capacity, and increasing aluminum concentrations.

d)Remediation of contaminated sites is necessary in order to facilitate the remediation process and avoid undue delays. The most important aspects of the approach include site characterization, risk assessment, and selection of an effective remedial action. The most conventional method for groundwater remediation has been the pump and treat method. A network of extraction wells are designed to extract the groundwater. The groundwater is pumped to the surface and treated through an activated carbon process and re-injected into the ground to enhance hydraulic control and to flush the contamination zone. Monitoring the treatment included measuring groundwater elevations and collecting groundwater samples for analysis. Monitoring the pump system aims at maintaining a steady flow through extraction wells. Soil flushing involves pumping flushing solution into groundwater via injection wells. In general, a permeable wall containing an appropriate reactive material is placed across the path of a contaminant plume. As contaminated water passes through the wall, the contaminants are either removed or degraded. Remediation of contaminated groundwater is critical in order to protect human health and the environment. It is of the utmost importance to properly characterize the site, and such a characterization includes defining the site’s geology, hydrology, and contamination, potential releases to the environment, and locations and demographics of nearby populations. Several technologies exist for the remediation of contaminated groundwater. These technologies include pump and treat, air sparging, in-situ flushing, permeable reactive barriers, monitored natural attenuation, and bioremediation. Many of these technologies are used in combination or other innovative technologies are being developed. Remediation technology for a particular site is selected based on the site specific hydrogeologic and contaminant conditions, desired cleanup levels, remedial time, and cost.The beneficiary group must be constituted and several IEC programs must be conducted to educate the beneficiary and they may be made responsible to protect their water.

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