Clean Techniques for Metals

The following photos depict some of the activities and procedures followed in sampling for trace metals [1] in Louisiana waterbodies using clean techniques. It is possible that several of the waterbodies listed as impaired on Louisiana's 303(d) list are listed due to trace metal contamination. The data used to determine impairment was collected by conventional metals sampling and analysis techniques. Recently it has been shown that the trace metal concentrations in many waterbodies were overstated due to sample contamination [2] when using conventional methods. LDEQ is reexamining our metals water quality data using a series of procedures called clean techniques. These sampling and analytical methods were designed to monitor very low concentrations of trace metals in ambient waters and to reduce the sample contamination problem.

The clean technique is a prescribed set of procedures for metals sampling involving field sampling, handling, laboratory analytical methods, and quality assurance/quality control (QA/QC). Using these clean techniques for trace metals sampling will provide Louisiana with more sound and scientifically defensible data.

The project LDEQ is undertaking will involve sampling state waterbodies identified in Louisiana's 303(d) list of impaired waters as not meeting metals criteria. The data collected from clean technique sampling and analysis will be compared to current water quality standards. Those waterbodies deemed as not impaired due to trace metals will be taken off of the 303(d) list (delisted).

 

  1. Water Quality Surveys section Environmental Scientists are shown preparing for clean metals sampling. Clean, non-talc gloves (talc gloves sometimes contain high levels of zinc) are worn at all times to avoid the potential contamination from skin. Multiple layers of clean gloves are often worn because the outer, pair can be shed quickly with minimal disruption to work activity. One person is designated the "clean hands" person this person is responsible for all operations involving contact with the sample bottle and transfer of the sample from the sample collection device to the sample bottle. The other person is designated the "dirty hands" person. He/she is responsible for preparation of the sample equipment (except the container and tubing itself), operation of any machinery, and for all other activities that do not involve direct contact with the sample, container, and tubing.
  2. The scientists create a workstation by placing a layer of plastic over the ground in the area the sample will be taken from to avoid any potential soil contamination. Once the plastic layer is placed down carefully, the scientists will move their equipment to the workstation. This site was carefully chosen along the waterbody to minimize contamination by collecting the sample upwind and as far as possible from metal supports, bridges, wires, and heavily traveled roads.
  3. The designated "dirty hands" person (on the left) opens the cooler containing the sampling equipment and removes the bag containing the resin tubing. The "clean hands" person (on the right) removes the tubing from the bag.

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  1. By way of a peristaltic pump, sample water is collected from the waterbody to the sample bottle through the resin tubing. The "clean hands" person is shown below attaching the tubing to the pump, careful not to touch any portion of the pump. The "dirty hands" person will engage the clamp on the tubing.

 

  1. The tubing is attached to a length of PVC pipe in order to minimize contamination from air and soil sources and to allow collection of a representative sample away from the bank at approximately one meter depth (or half the depth if total depth is less than 2 meters). "Clean hands" holds the inlet end of the tubing against the PVC pipe, and "dirty hands" attaches the tubing to the pipe using plastic tie-wraps. "Dirty hands" immerses pole with tubing in the sampling area to the appropriate depth, turns on the pump and holds the tubing apparatus until purging and sampling are complete, and turns the pump off at appropriate times throughout this process.

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  1. The "dirty hands" person turns the pump on and allows it to run for 5-10 minutes to purge the tubing, and the "clean hands" person holds the outlet end of the tubing.

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  1. The "dirty hands" person removes the sealed plastic bag with the filter in it from the cooler and opens it. The "clean hands" person obtains the filter from the bag and places it at the end of the tubing. Filtered samples are necessary for the determination of dissolved metals rather than total metals. In-stream water quality criteria for metals are based on the dissolved fraction and not total metals.

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  1. It is recommended that there be a minimum of 3 people present during sampling. Two of the scientists are designated "clean hands" and "dirty hands", with the third person in charge of quality control, record keeping, etc. After each sample is collected, the sample number is documented on the field sheet, and any unusual observations concerning the sample and the sampling are documented. Proper record keeping is important and will assist in tracking potential sources of contamination if necessary.

The scientist in the background is taking in-situ [3] measurements for dissolved oxygen (DO), temperature, pH, and conductivity, which is necessary to determine the analytical method .

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  1. The "dirty hands" person retrieves the sealed plastic bag containing the sample bottles from the cooler and opens the outer bag. The "clean hands" person removes the sample bottle from the inner bag. The bottle is opened and the pump is started to provide rinse water for the sample bottle. The sample bottle and cap are rinsed with site water three times.

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  1. The sample bottle is filled with site water, and the "clean hands" person places the cap on the bottle, returns the bottle to the inner plastic bag, and places the inner plastic bag into the outer plastic bag. The scientists must even take care not to breathe directly onto the sample because it has been demonstrated that dental work (mercury amalgam fillings) in the mouth can contaminate samples.

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  1. The "dirty hands" person then seals the outer bag. The double-bagged sample is then placed into a clean, ice-filled cooler for shipment to the laboratory.

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  1. During sampling for metals using clean techniques, samples are also collected for total suspended solids (TSS) and hardness. Hardness levels are used to determine the appropriate in-stream standard for metals. TSS measurements will be used should a TMDL be required because assessment of waterbody data indicated a standards exceedance. TSS affects the metals availability which is accounted for in the TMDL model.

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  1. The picture below provides an example of the same sampling method taking place from a boat. Note that a clean layer of plastic is placed on the working area, and the working area of the boat (usually the bow) is positioned upstream to avoid contamination from the boat itself. In this picture, the scientists are arranging the sampling equipment on the plastic layer covering the boat.

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 [1]Trace metals - For sampling purposes, consist of: arsenic, cadmium, chromium, copper, lead, mercury, nickel, zinc.

 [2]Contamination - Sample contamination can occur from several metal sources not related to actual content of the waterbody. Examples of sources of contamination: metal sampling containers, boats, storage containers, laboratory and sampling equipment, air and soil contamination, surfaces in contact with the sample, etc.

 [3]In-situ - In its original place; unmoved; unexcavated; remaining at the site or in the subsurface.

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