Sampling 102: 4 Ways to Collect Deep Groundwater Samples During Drilling
Aug 20, 2019 -
If you’re new to environmental services, selecting a deep groundwater sampling method for your project can be overwhelming. There are a variety of factors to consider, including overall depth, geology, budget, suspected contaminant, borehole size, quantity of sample required, drilling method, etc.
In my upcoming webinar, Sampling 101: Methods of Collecting Environmental Samples During Drilling, I’ll discuss different environmental sampling methods, the lithologies for which they’re suited, and share real-life examples of how they’ve worked in the field. If you’d like to learn more about choosing a sampling method, join me next week.
In this blog post, we'll look at four popular groundwater sampling methods that are regularly used with casing advanced drilling systems (like hollow stem auger, sonic, ARCH, ODEX): temporary well installation, ISOFLOW (packer/screen sampler), push ahead groundwater sampler, and SIMULPROBE. Direct push technology is another great way to collect environmental samples in shallow applications but we’ll focus on the deeper applications here.
Temporary Well Installation
Temporary well installation is the simplest of groundwater sampling methods. It’s conducted by using a cased hole to run a small diameter casing with a short, perforated section at the bottom. Add a filter sand, pull back the outer casing, and voila! There is now a well to sample.
The drawbacks of temporary well installation are usually related to the cost. It tends to be more time consuming and thus more expensive. There is also a cost for the temporary well materials and, if contamination is present, development/purge water disposal.
The ISOFLOW is another option for obtaining a high quality, discrete groundwater sample during drilling. This device typically consists of a small section of stainless steel screen that sits below a packer assembly. When the outer casing is pulled back to expose the screen, the packer assembly is lowered into the drill casing to the bottom of the hole. The packer stays in the casing to seal the tool and make sure that only the groundwater can flow through the screen. Once in place, this zone can be developed with pump or bailer and then purged to collect a high quality sample. It can also be used in some applications to provide low flow pump testing information.
ISOFLOW is a great option on sites where a high quality sample is needed, a large volume of sample is required, and where some well pumping information is advantageous. Samples collected by this method are typically less expensive than those collected via temporary well. Drawbacks include purge water disposal and some potential turbidity in the sample.
Push Ahead Groundwater Sampler
There are a variety of push ahead type groundwater samplers on the market, and each has a different twist on the device operation. A push ahead sampler is sometimes referred to as a “Hydropunch,” which was the name of one of the first tools of this type (it is no longer available). These tools are named based on how they work: the tool is driven ahead of the drilling operation, where drilling disturbance has not occurred yet. The drill casing is not moved back for this device; instead, after being driven a distance of 18 to 24 inches, the device is pulled back and/or twisted (there are a variety of ways to open) a short distance to expose a screen. From there, a bailer can be run in the string to collect a water sample. The device is simple, efficient and cost effective.
This sampler is effective on sites that need to collect discrete groundwater samples at the lowest cost possible and where turbidity of the sample is not a concern.
Using the SIMULPROBE is similar to the push ahead method. This tool is driven ahead of the drilling disturbance, and has the ability to collect a soil sample while it collects a groundwater or soil gas sample.
The sampler is prepared with a sheath placed around the driven (lower) end of the sampler. The sheath is perforated at the bottom of the borehole when it hits the competent material at the bottom of the drilling operation. Groundwater is then delivered to a vessel in the tool via some small diameter tubes inside the device. It takes more time to set up, but the SIMULPROBE does collect a good (though turbid) groundwater sample. While more expensive than the push ahead samplers, its ability to collect soil and soil gas samples simultaneously can make it a more cost effective option.
This sampler is ideal for sites where soil, soil gas and ground water samples all need to be collected in the same borehole.
These four groundwater sampling methods are some of the most common—but there are other options. If you’d like to learn more about groundwater and environmental sampling, join me next week for my webinar, Sampling 101: Methods of Collecting Environmental Samples.
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