Focus On Water Division
Nebraska Department of Environmental Quality
Standard Operating Procedure

Water Quality Division
Water Quality Assessment Section - GW

Standard Operating Procedure Number GW-080
Title: Field Filtration of Groundwater Samples
Written Date: September 1, 2000
Approved Date:


Purpose: To filter sediments and other foreign materials out of ground water samples so accurate determination of dissolved metals (Ca, K, Na) is possible during laboratory analysis.

Equipment/Materials Needed:

· Filters, 0.45 m mesh, 47 mm diameter
· Tweezers/tongs
· Squirt bottle filled w/ deionized water
· Filtration funnel w/ magnetic base and rubber stopper
· Hand pump
· Flask, 1000 ml nalgene or equivalent w/ tubing port
· Clear plastic tubing to fit flask port, approximately 2’
· Temporary sample container filled with sample water as per SOP # GW-060
· Sample container (cubitainer) with label and green marking as per SOP # GW-060, Appendix A.

Procedures:
  1. Rinse the filter funnel and flask with distilled water or excess sample water.
  2. Separate the funnel into its top and bottom portions.
  3. In a wind-free environment, use the tweezers to separate a filter disc (white) from its wrapper and protector (blue) and place the filter on the bottom portion of the magnetic funnel. Do not touch the filter with your fingers--fingers can impart oil, dirt, or other contaminants to the filter. A drop of rinse water on the funnel screen (on the bottom portion of the funnel) will help keep the filter in place. Reconnect the top and bottom portion of the funnel. (NOTE: if a filter disc has been left on the screen from the previous sample, be sure to remove it before emplacing the new filter.)
  4. Connect the funnel to the flask by inserting the rubber stopper on the bottom portion of the funnel into the flask neck.
  5. Connect the hand pump and tubing to the flask tubing port.
  6. Pour a small amount (50-100 ml) of sample water into the filter funnel.
  7. Squeeze the hand pump until the sample water is pulled through the filter.
  8. Rinse the flask by swirling the filtered water all around the inside of the flask.
  9. Discard the rinse water.
  10. Fill the funnel with sample water and squeeze the hand pump until the sample water is pulled through the filter. Continue adding sample water until all of it has been filtered.
  11. Rinse the cubitainer labeled with a green mark and green cap (as per SOP # GW-060, Appendix A) by transferring a small amount of filtered water to the cubitainer. Place the cap on the container, swirl the water all around the inside of the sample container and discard the water.
  12. Transfer the remaining sample water from the flask into the cubitainer with the green mark and green cap.
  13. Preserve and store the sample as per SOP # GW-100.
  14. Take the filtration funnel apart and observe the filter paper. Note on the field inventory sheet the presence of any sediment or other contaminants. Leave the filter disc in place until the next sample.
  15. Disassemble the remaining filtration equipment, and secure all equipment for transport to the next sampling site.