SUGGESTED SOLUTION: waterra disposable bailers
Bailing monitoring wells is probably one of the oldest methods for developing, purging and sampling in monitoring wells. Bailers are durable and simple to operate and today they are also very inexpensive, so much so that many are considered disposable.
Waterra Disposable Bailers are available in a wide range of sizes and materials, suitable for use in most monitoring wells. Waterra offers bailers in 3 nominal sizes, 0.5" OD, 0.7" OD and 1.5" OD, constructed from either PVC, polyethylene or Teflon. These sizes will fit into most monitoring wells and are suitable for almost any type of contaminated environment.
Well developing with bailers
Monitoring wells can be developed with bailers using a simple method. To develop using a bailer, it is necessary to have the largest diameter bailer that will fit into the monitoring well. In a 2" piezometer this usually requires a 1.5" OD bailer.
Using this method, the bailer is repeatedly lowered into the screened portion of the well and then rapidly pulled upwards. This rapid movement draws water in through the screened portion of the well. These higher velocities will tend to entrain silt particles that may be trapped in the sand pack or screen and draw them into the well. Over time this method will gradually develop the monitoring well. It will also be necessary to remove some of this development water from the well in order to try to remove some of the silt drawn into the well.
The drawback with this method is that it will tend to allow the silt drawn into the well to accumulate in the well and it is very labour intensive.
Well purging with bailers
Monitoring wells can also be purged with the use of a bailer. This is a simple process for lowering the bailer into the well, allowing it to fill completely and then removing it from the well and emptying it and then repeating the process.
Typically, purging a well will require removing a prerequisite number of well volumes. Since the bailer is a known volume, it is a simple matter to calculate the number of times the well must be bailed in order to complete the purging process. The purging process is very tedious, however this can be minimized by using a heavy bailer that will sink faster and also by using nylon bailer cord which also sinks faster than polypropylene cord. The purging process can sometimes also be made easier at wells with above ground completions if the operator can position himself at a height such that he can minimize the amount of reaching above his head he will have to do.
Sampling with bailers
Bailers can be used for collecting samples of groundwater for almost any type of analysis provided that the proper care is taken. In order to ensure sample quality, it is important to minimize the amount a sample is agitated when it is removed from the well. In order to achieve this the bailer should be lowered into the well carefully so that it does not splash when it contacts the water in the well. When the bailer has been lowered to the depth where the sample is to be collected, it should be removed from the well with a constant steady motion. Pulling the bailer up in a series of steps will tend to cycle water through the bailer because of the elastic nature of the bailer cord and the momentum of the water in the bailer. It is important to remove the bailer is a steady motion in order to avoid this. Most operators use an alternating hand over hand motion to lift the bailer from the well, this also helps prevent the cord from becoming tangled.
Once the bailer has been removed from the well, the sample can be removed from the bailer by one of two methods. Some people will decant the sample from the top of the bailer by carefully tipping it into their sample container. The drawback with this method is that it exposes the sample to the atmosphere, which may be undesirable for some types of samples. The weight distribution of the bailer also changes rapidly as the water flows out the top of the bailer and may result in spillage.
Bottom emptying may be preferable for most types of samples. Bottom emptying usually involves inserting a device into the bottom of the bailer after it has been removed from the well. This device gently lifts the ball from the bailers valve seat allowing a stream of water to flow out the bottom of the bailer through the device. This stream is usually regulated such that it is suitable for filling small sample containers such as VOC sample containers. This stream of water is ideal for this type of sampling as the sample's contact with the atmosphere is minimized.
Filtered samples for metals analysis can also be collected from many types of bailers by simply attaching an Inline Disposable field Filter to the outlet of the bottom emptying device and allowing the sample to flow by gravity through the filter.
Free product layer sampling can be done with clear PVC disposable bailers. This is a simple procedure of very slowly lowering the bailer through the product layer but not completely immersing the bailer. Once the bailer has been lowered to the required depth then it can be removed from the well and the product layer can be inspected while it is still in the bailer.
Today, many people prefer to use disposable bailers because of their low cost and the advantages they offer like the elimination of cross contamination. Disposable bailers can also be dedicated to monitoring wells, however this is generally not recommended as there is still a risk that they may become contaminated. Disposable bailers are individually packaged and each contains it's own bottom emptying device.