HowTo – Sampling from groundwater fed ponds or springs [50%]

Priority: medium
Updating: rare

This HowTo applies when we sample groundwater that has emerged into a surface water body, typically a pond or springhouse.

Change log:

When Who Comment
2022 05 03 Sp17 First skeleton created.
2023 06 05 Sp17 Minor updates prior to first DEC review.
2023 06 15 Sp17 Convert to Markdown.
2023 07 30 Sp17 Adapt to Quarto.

See also:

1. Objectives

  • Obtain representative samples from surface waters.
  • Obtain field measurements of surface water.
  • Record field data.

2. Quality assurance considerations unique to groundwater fed surface water

Collect samples representing the ground water system before water has been diluted by runoff or rainfall. We are sampling without creating wells thus we lose some representativeness of in-situ groundwater.

3. Equipment needed

  • Dipping or “sucking rod”.
    • The dipping device is a ~6 foot long handle with nalgene bottle cut off to allow scooping.
    • The sucking rod is a chimney sweeping rod segment dedicated to sample collection that can be extended by additional threaded segments, same as used for well surging during development. It has a dedicated hose and a float. This is used in combination with a peristaltic pump.
  • Peristaltic pump, battery powered, Cole Parmer.
  • Standard well sampling hoses can be used to draw a sample from a surface water body using the peristaltic pump; it is better to use the sucking rod.

4. Expendable supplies needed

There is no unique supply needed, beyond what is needed for monitor well sampling on the same trip. (See the HowTo: Sampling road trips that covers supplies used across multiple sites of different kinds.)

5. Sampling location and timing.

When the sampling location is identified originally it must meet the following criteria:

  • Minimal surface water flowing into it. No inlets, except for springs that emerge within a few meters of the shoreline. It may have an outlet.
  • Relatively short residence time after emergence, to limit the influence of surface processes such as strong evaporation or rainfall.
  • Sampling position within the pond should be nearest where groundwater enters the pond, if there is any variation in this. This can be a spring or a seepage face.

Two cases of true surface water sampling and three cases of sampling from other than wells:

  1. Nur-3 upgradient. This is a definite groundwater fed pond that is fed by recharge through the next property to the north. The pond is used by the Nur-3 owner for irrigation. This makes it a possible artificial upgradient source of pesticides used on field crops. We sample near the irrigation intake. We could also sample from the irrigation pipe at the greenhouses. We customarily sample by standing in the shoreline and dipping in containers.
  2. Nur-5 Pond-3. Pond-3 has a seepage face mantled by wet grass. We sample by reaching into the pond with the sucking rod while standing on the seepage face shoreline.
  3. Sod-3 tilebox. This is a rectangular shaft with cover that serves as an access point to remove or replace a lower weir door to control the level of water in the field. We dip the sampling pump’s intake hose into the liquid below the weir when water is flowing there, or above the weir when the water is not flowing and there is water backed up. This is effectively no different from sampling a large diameter well.
  4. Vine-1 Spring. This has a manhole cover before the spring’s emergence in a wetland that we remove partially to insert a peristaltic pump hose. This is clearly a groundwater sample, very similar to the upgradient owner well we sample at VegF-6.
  5. Golf-7, Wells 3 and 4. These are miniature fountains installed by the owner to ease our sampling. They are effectively outlets of freshly pumped groundwater from the pipes that enter into irrigation ponds. We sample by holding a bottle in the fountain. (Obviously all volatile chemicals are lost due to the aeration.) This is clearly a groundwater sample because the emergent water does not mix with the pond before we fill the container.

We do not sample during heavy rain because the rainwater will dilute the groundwater. Light rain is OK.

6. Collecting the sample

6.1 Bottle dip

Immerse the container below the surface a few centimeters or under the fountain. Avoid capturing any floating matter. Rinse once or twice with sample water before filling the container. Take meter readings using the meter cup before or after drawing the sample.

6.2 Peristaltic pump hose, using a sucking rod

Assemble the arm to adequate length for safe operation. String the hose. Activate the pump. Dip the hose tip on the arm into the water body a few inches below the surface. Hold it steady. Draw enough water to waste to first rinse the hose with sample water, then rinse the sample container, dumping it to waste. Finally fill the sample containers; test field parameters using the meter cup before and after drawing the sample. Hose is 1/4” inner diameter thus contains 3.1415928*(1/8)^2*2.54*2.54*100=32 mL per meter of length. To fill a 6m hose thus requires 180 mL, about the same volume as one sample container.

6.3 Peristaltic pump and well hose.

Dangle the hose into the sampling location, taking care not to touch the bottom so we do not draw in any sediment. If any sediment is drawn in, adjust the hose and run the pump to waste until the turbidity clears.

Operate pump to fill containers and make meter readings as in 6.2.

7. Field cleaning

Clean the with deionized washwater brought from Cornell. Clean hoses as in sampling from monitor wells.