Groundwater collection systems

There are three common methods for groundwater collection using pumping systems a well point system, a gravity drain system, and in combination with injection wells. 

The well point system is the most economical method of groundwater collection where the water table is less than 3 m and the contaminant is less 9 m below the surface. 

The main purpose of recharging water into an aquifer is to elevate the hydraulic gradient to promote the movement of groundwater towards the collection system, thus enhance the efficiency of pumping. 

The facility would use a dry scrubber system for emission control, which would eliminate the need for wastewater treatment. Any water from emission control and from decontamination procedures would be treated in the on-site groundwater treatment system. The residual soil and collected ash is assumed to be nonhazardous and can be disposed of in a solid waste disposal facility in compliance with subtitle D of RCRA. In the event that they cannot be delisted due to the presence of metals, the residuals will be managed as part of the closure of Area 2 shown in Figure 16.21 (lead-contaminated soil). 

Other disposal options for the sewage sludge are landfill, dumping at sea (forbidden in the EU since 1998) [30], and incineration. The most popular for solid waste disposal is landfill. However, many of the disposal sites are open dumps without protective barriers or leachate-collection systems, which represent a potential risk to the quality of the nearby groundwater. 

The purpose of this chapter is not to promote the replacement of traditional physically based methods of assessing groundwater-lake systems with isotopic methods, but rather to demonstrate the utility of isotopic techniques. Physically based methods can provide more detailed information on the spatial and temporal variability of a groundwater-lake system than isotopic approaches can provide. Regardless of the method chosen, however, an adequate number of piezometers is necessary to ensure that groundwater samples are collected from upgradient areas. 

Groundwater contamination was significantly less than that dociunented at other refineries. In part, this finding can be explained by a combination of the original refinery construction methods (atypical of most older refineries), lack of petroleum spills, and the passive action of the refinery s underground sewer system, in which groundwater collects and flows to the wastewater treatment plant. 

Monitor the performance of the system and match monitored performance against that expected. "Trigger" conditions may be developed (e.g. level of leachate mounding and concentration of contaminants in the leachate concentrations at volume of fluid collected from secondary collection systems) such that back-up measures can be implemented once a failure of part of the system has been detected, and before conditions have been established which will ultimately cause contamination of groundwater. 

Modern landfill facilities, waste lagoons, and leachate ponds use geotextiles in their key designed systems to contain wastes within the facility. The main designed systems are groundwater and gas collection systems underneath the base liner system, typically consisting of a leak detection system and a leachate collection and removal system, and within the final cover system to collect gas and water below and above the barrier system, respectively. 

Subsurface drains are essentially permeable barriers designed to intercept the groundwater flow. The water must be collected at a low point and pumped or drained by gravity to the treatment system (Figure 8). Subsurface drains can also be used to isolate a waste disposal area by intercepting the flow of uncontaminated groundwater before it enters into a contaminated site. 

The use of a drain system permits the quick construction of a collection/removal system which also serves as a barrier for leachate from large, shallow sites. At the Sylvester hazardous waste site in Nashua, New Hampshire, a groundwater interception and recirculation system was installed as a method to retard further spread of the leachate plume until a remedial cleanup action could be implemented. The system was operated for 1 year until a containment wall and cap were constructed over the 20-acre site (McAneny, 1985). 

Passive perimeter gas control systems are designed to alter the path of contaminant flow through the use of trenches or wells, and typically include synthetic flexible membrane liners (FMLs) and/or natural clays as containment materials. The membrane is held in place by a backfilled trench, the depth of which is determined by the distance to a limiting structure, such as groundwater or bedrock. A permeable trench installation functions to direct lateral migration to the surface, where the gases can be vented (if acceptable) or collected and conveyed to a treatment system (Figure 10a and 10b). 

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