Monday, November 15, 2010

Around the Sound: Rayonier groundwater sampling

By Steve Teel, Hydrogeologist

If you’ve walked by or ridden your bike down the Olympic Discovery Trail recently, you may have seen trucks at the Rayonier gate and people out on the property. Work is underway, but what’s actually going on at the property?

One of Rayonier’s main tasks is collecting groundwater samples. They are looking for contamination in the water that sits under the ground’s surface. To do this, they use a special type of well.

Groundwater sampling wells

The wells are drilled from the ground surface straight down into groundwater. On the Rayonier property, the depth to groundwater varies from about 3 to 17 feet. Groundwater depths can change throughout the year, so the well must be deep enough to reach the lowest groundwater levels.

The well casing can be plastic or metal. The upper part of the well casing is solid, but the lower part—the screen—has slits to allow water into the well (see diagram). Materials such as concrete and clay are used to seal around the outside of the solid casing. Also, sand is placed around the outside of the screen to make sure that it does not become plugged with silt or clay.

Taking a sample

The sampler first cleans the well of any stagnant water and waits for fresh groundwater to flow into the well. The sample can then be pumped up or a container can be dipped into the water.

The samples are processed, labeled and sent to the lab for analysis. The lab will look for the level of contaminants such as pesticides, metals, petroleum-related chemicals, and more.

Here are some photos of the sampling process...

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