SAMPLING/from page 19 samples also need to be chilled, usually between –2° to –6°C (28° to 21°F), Metzger says. So, not only do you need to know what samples need to be chilled, but how you will keep the samples cold. Sometimes a lab will provide you a cooler, but it may also be up to you to keep your samples cold, says Mike Schnieders, president of Water Systems Engineering Inc. in Ottawa, Kansas. If you can, figure out how you will need to sample the well. The sample should be taken as close to the wellhead as possible. Do the homeowners have a sample port on their well? Will you need to collect the sample from a tap inside the house? Is your only option to take a sample once the water has passed through a tank or a treatment system? “Knowing this ahead of time avoids false readings or extra time in either sample collection or sample analysis,” Schnieders says. Tell the homeowner when you plan to take the samples and make sure you allow enough time to collect the samples and, if you’re sending the samples to a lab, that you allow enough time to drop them off or ship them. It’s also a good idea, if you’re using a lab, to give the lab a heads-up, Schnieders says. Each lab may have specific instructions for you to follow. For example, Schnieders’ lab asks for a minimum of one liter of water for each sample, collected from both after the well has been idle overnight and after the well has run for an hour. National Testing Laboratories’ kits also come with a specific set of instructions. It’s best to speak with the lab beforehand, especially if it’s a test you don’t perform often, Schnieders says. “The best projects are when everyone is communicating,” he says. “Everybody has talked about it beforehand. We know what the problem is, and we know what we’re going to test for, the materials are out there, and the contractor has set the time aside and knows what they’re getting into as far as the ease of getting a sample and the type of well.”
Step 3: Collect samples in order. If sampling from multiple wells, the 20/ August 2012 Water Well Journal
U.S. Geological Survey’s National Field Manual for the Collection of WaterQuality Data advises sampling in order from the least contaminated site to the most contaminated to avoid contamination of the samples. Also, if the analytes you’re testing for or your lab requires are “stagnant” water samples from the well, you should take those samples first. Metzger says when taking samples for lead and copper to meet the requirements of the Lead and Copper Rule, the rule requires the water must be sitting in the pipes for at least six hours, preferably overnight. Schnieders says the well should sit idle overnight for at least eight hours. For specific guidance, always defer to any state regulations or the instructions from the kit manufacturer or laboratory. Then, take the samples for analyses requiring water from the aquifer. Metzger says when she’s in the field collecting samples, she takes them in a specific order each time. “Depending on what I’m collecting, I usually collect the metals sample bottle first, then organics—because they sometimes come out of the same bottle,” Metzger says. “I usually collect volatile organic chemicals next, then pesticides and herbicides. I collect bacteria last.”
Step 4: Flush or purge the well to guarantee you’re collecting water from the formation. Before you take samples requiring aquifer water, you’ll need to flush or purge the well to make sure you’re getting water from the formation. If you’re taking a sample from a tap, you should flush the well out to make sure you’re not drawing stagnant water, Schnieders says. “It’s a step that’s commonly overlooked,” he adds. “Whether your sample port is right at the wellhead or is on a tap farther down the line, you want to flush that well.” And, it’s not just a matter of emptying the column pipe and cleaning out the pump. The whole well should be flushed—especially if the well has sat dormant for a long amount of time. You want to flush the standing water column to make sure you’re getting water from the borehole, Schnieders says.
If you have access to the wellhead and well-sampling instrumentation, consider sampling the well via the low-flow purge method. Low-flow purging pumps the well at very low rates (typically around 250 mL/minute), mimicking the natural recharge of the well, while monitoring field measurements such as pH, specific conductance, dissolved oxygen, ORP, temperature, and turbidity. “You’re looking for these parameters to stabilize within a certain value for three consecutive readings taking several minutes apart,” says Laura St. Pierre, product manager with YSI Inc. in Yellow Springs, Ohio. “Once these parameters have stabilized within the regulatory agency’s guidelines, you know you’re getting formation water and you can start taking samples for lab analysis.” Although typically used for monitoring wells, St. Pierre says low-flow purging can yield samples that are representative of the groundwater surrounding the well and not just the water in the well.
Step 5: Collect the samples, taking special care to avoid contamination. In general, you want to take the sample as close to the wellhead as possible. Possible exceptions could include limited or no access to a sample point close to the well or if you want to test what might be in a homeowner’s water lines inside of the house. No matter where the faucet is located, remove any aerators or faucet screens from the tap. Then, turn on the tap and flush it of any debris that has built up around the threads. “Unfortunately, most of the sample taps or sample ports are put in after the fact,” Schnieders says. “They’re difficult to get to or can easily become dirty. Insects or rodents can also get into them.” Once you’ve flushed away debris, disinfect the spigot with a flame, alcohol swab, or a chlorine solution (about 5 to 10 ppb). Then, rinse the spigot again with fresh well water. Before collecting a sample from a tap, let the water run for two to five minutes, then slow your stream to about the size of a pencil to fill the sample bottle.
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