Steward has adopted the sample collection, preservation and retention practice of EPA Method 245.7 and 1631.

Labeling

The customer should label all containers using a permanent, completely unambiguous sample labeling system to avoid confusion.

Required Test Volume

Verifying Concentration

A one liter sample is preferred. If subsequent treatability work is done a larger sample is required.

Treatability Study

It is difficult to know in advance exactly how much sample volume is required since the presence of interfering species may require extensive testing. This recommendation assumes that only typical effort will be required.

A 5-10 gal (19-38L) sample is requested for a bench top batch-wise treatability study. Larger quantities can be required, e.g., 10~50 gal (190 L) if additional bench-top Continuous Stirred Tank Reactor (CSTR) tests are needed.

Required Bottle Preparation and Storage

Steward follows EPA method 245.7 and 1631, which requires use of fluoropolymer or borosilicate glass containers with tight-fitting fluoropolymer, fluoropolymer-lined caps is essential.

Cleaning – new bottles

New bottles are cleaned by heating to 65–75C in 4N HCl for at least 48 h. The bottles are cooled, rinsed three times with reagent water, and filled with reagent water containing 1% HCl. These bottles are capped and placed in a clean oven at 60-70C overnight. After cooling, they are rinsed three more times with reagent water, filled with reagent water containing 0.4% (v/v) HCl, and placed in a mercury-free class-100 clean bench until the outside surfaces are dry. The bottles are tightly capped (with a wrench), double-bagged in new polyethylene zip-type bags, and stored in wooden or plastic boxes until use.

Cleaning – used bottles

Used bottles known not to have contained mercury at high (>100 ng/L) levels are cleaned as above, except for only 6–12 h in hot 4N HCl. Bottle blanks should be analyzed to verify the effectiveness of the cleaning procedures.

Testing For Speciation and Dissolved Mercury

A treatability study, when the customer desires to know the relative fraction of dissolved mercury, requires an unfiltered and filtered sample. In an acidic stream this may not be as important but should be done as a precaution since the initial streams are caustic. Testing for dissolved mercury requires the effluent be filtered through a 0.45 micrometer filter at the point of collection. If samples are preserved, they should be filtered first.

Dissolved Mercury - The test solution should be filtered with a 0.45 micrometer filter. If more than 48 hours are expected between sampling and testing the sample should be preserved. Sample volume and containers as discussed previously are recommended.

Total Mercury - The customer should provide a companion, unfiltered solution of the requested volume in specified containers and preservation as discussed previously.

This sample size should be approximately 1 liter. After determination of dissolved mercury we can make a decision about whether further samples for the treatability study require filtration.

Special High Purity, low Mercury Reagents

Most laboratory reagents have significant mercury contamination compared to the values normally sought in a treatment process, so special low mercury reagents must be used. Reagents are always tested upon receipt to verify mercury level.

Sample Preservation

Samples are preserved by adding 5 ml/L of pretested 12 N HCl. Acid-preserved samples are stable for a period of 28 days.

Samples may be shipped to the laboratory unpreserved if they are (1) collected in fluoropolymer bottles, (2) filled to the top with no head space, (3) capped tightly, and (4) maintained at 0–4°C from the time of collection until preservation. The samples must be acid-preserved within 48 h after sampling. Samples for dissolved mercury must be filtered before they are preserved.

Note: Due to the potential for contamination, sample filtration and preservation should be performed in a clean room in the laboratory. However, if circumstances prevent overnight shipment of samples, samples should be filtered and preserved in a designated clean area in the field in accordance with the sampling guidance.

Storage—Sample bottles should be stored in clean (new) polyethylene bags until sample analysis. If properly preserved, samples can be held up to 28 days before analysis. Sample storage and holding time requirements are given at 40 CFR 136.3(e) Table II.

NOTE: If dissolved mercury and total mercury are requested, sample should be preserved AFTER filtration, not before.