Pumps, purging wells

When the well depth or diameter is unknown or a water-level measurement is not possible, purging should be carried out by pumping the well for a pre-determined period of time (e.g., at least 30min). Measurement of groundwater parameters should be monitored at intervals during the purging process and at the time of sample collection (Figure 3). 

Electric Used for purging wells only Centrifugal pump Difficult after highly contaminated samples No limit Relatively shallow (to 75 ft)... 

Most of the wells sampled were fitted with a standard Bangladesh number 6 hand pump. Each well was purged prior to sampling by pumping approximately one stroke per foot of well depth. The water sample was filtered through a 0.2 pm membrane filter into a plastic 30 ml bottle and acidified to 1% with concentrated Analytical Grade nitric acid. 

An application of electrokinetics that serves to illustrate a number of chemical effects is that of electroosmotic purging of contaminated liquids from soils (Shapiro Probstein 1993). A dc electric field is applied across electrode pairs in the ground and under the action of the field, the contaminants in the liquid phase in the soil are moved by electroosmosis to one set of electrodes, typically the cathodes. The electric field simultaneously draws in a noncontaminating liquid to help wash and treat the soil to enhance the restoration process. The contaminated effluent is then removed by pumping from wells surrounding the cathodes. 

In cases where wells have a screened or open-hole interval partially submerged below the water table and a pump is going to be used for both purging and sampling, the pump should be placed at the midpoint between the top of the water table and the bottom of the screen. If different equipment is going to be used for purging and sampling of the well, the pump should be placed at the top of the water column. ... 

Periodic monitoring points should include extraction, injection, and monitoring points. When sampling injection wells, the injection system should be shut down for approximately 24 h to allow ambient conditions to be reestablished. Monitoring wells should be purged and sampled according to standard procedures. Extracted fluid material (pumped water) can be sampled by the same procedures as collecting a surface water sample. 

Wells constructed with perforations and an open unsaturated zone are an efficient procedure to introduce air into the subsurface. A vacuum pump attached to a central well(s) will draw air through the soil to purge the existing soil atmosphere with fresh air. Three commonly used scenarios for bioventing are shown in Figure 10.10. 

The mechanical contractor is usually also responsible for providing adequate pressurized water supply, drainage (with special provisions for low-level areas of the closed-loop water system), bypasses, an electrical supply (typically 110 V, 1 phase, but also 3 phase where temporary pumps are required), HVAC system air purge vents, as well as other facilities, such as site access, toilets, security, and equipment handling systems. 

To purge a well with a pump and sample it with a bailer, we follow these steps Well volume measurements... 

Remove the pump from the well. (If not sampling with a bailer, go to Step 5 of low-flow micro-purge technique, described below in Chapter 3.6.2.4.)... 

Lower the intake of the pump and a dissolved oxygen meter probe into the well slightly above or in the middle of the screened interval. Purge the well at a rate 300-500 milliliter/minute (ml/min). Check the water level periodically to monitor the drawdown, which should not exceed 4-8 in. If the pumping rate is unknown, measure the evacuated volume in a graduated container and monitor the time to establish the rate. 

Submersible centrifugal pumps are now available with integral packers that allow the screened interval of the well to be isolated from the stagnant column above, thus negating purging requirements and reducing sampling times and costs. 

The level of the water in a well is measured to provide data for groundwater flow direction calculations and to calculate purge volumes required for a particular well. If a low-flow sampling protocol is used, the water level is also measured during pumping to ensure that there is minimal drawdown of the stagnant water column. 

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