These tests describe the organic load, nutrients, solids and oils in wastewater, surface water and other environmental samples. Concentrations are reported in milligrams per liter (mg/L) unless a test says otherwise. Each test below names the reference method and how the measurement works.
| Test | Method |
|---|---|
| Biochemical oxygen demand (BOD) | Standard Methods 5210 B |
| Chemical oxygen demand (COD) | EPA Method 410.4 |
| Total organic carbon (TOC) and dissolved organic carbon (DOC) | Standard Methods 5310 B |
| Ammonia | EPA Method 350.1 |
| Total Kjeldahl nitrogen (TKN) | EPA Method 351.2 |
| Nitrate plus nitrite (NOx) and nitrite by colorimetry | EPA Method 353.2; nitrite alone also by Standard Methods 4500-NO2 B |
| Total persulfate nitrogen (TPN) | Standard Methods 4500-N C |
| Orthophosphate | Standard Methods 4500-P E |
| Total phosphorus | Standard Methods 4500-P F |
| Total solids | Standard Methods 2540 B |
| Total dissolved solids (TDS) | Standard Methods 2540 C |
| Total suspended solids (TSS) | Standard Methods 2540 D |
| Volatile solids | EPA Method 160.4 |
| Settleable solids | EPA Method 160.5 |
| Oil and grease (HEM) and non-polar material (SGT-HEM) | EPA Method 1664 |
Oxygen demand and organic carbon
Standard Methods 5210 B. The sample, or a dilution of it, is incubated in the dark at 20 °C for 5 days, and the drop in dissolved oxygen is the biochemical oxygen demand: the oxygen used by microorganisms breaking down the organic matter present. Carbonaceous BOD (cBOD) is the same test with a nitrification inhibitor added, so oxygen used to oxidize ammonia is not counted. Reported as mg/L of oxygen.
EPA Method 410.4. The sample is heated with dichromate in a sealed tube at 150 °C for two hours and the result is read by spectrophotometry. Soluble COD is measured on a filtered portion and ff-COD on a flocculated and filtered portion; tell us which you need and we agree the preparation with you. Reported as mg/L oxygen equivalent.
Standard Methods 5310 B, high-temperature combustion: organic carbon is converted to carbon dioxide, which is measured. A low-level option is available for clean waters. Dissolved organic carbon is TOC on a filtered portion of the sample. Reported as mg/L of carbon. Solid samples can also be tested; the preparation and reporting basis are confirmed when you order.
Nitrogen
EPA Method 350.1. The sample is buffered and distilled, and the ammonia collected is measured by an automated colorimetric (phenate) reaction. Reported as mg/L ammonia as nitrogen (NH3-N).
EPA Method 351.2. Sulfuric acid digestion converts organic nitrogen and ammonia to ammonium, which is then measured by colorimetry. TKN is organic nitrogen plus ammonia; some industrial nitrogen compounds are not converted by the digestion. Reported as mg/L nitrogen.
EPA Method 353.2. A filtered sample passes through a copper-cadmium column that reduces nitrate to nitrite, and the total nitrite is measured by a color-forming (diazotization) reaction; running it without the reduction gives nitrite alone. Nitrite alone is also measured by the manual colorimetric method Standard Methods 4500-NO2 B. Reported as mg/L nitrogen. These are different from the ion chromatography method in the anions section.
Standard Methods 4500-N C, persulfate method: the sample is digested with persulfate, which converts organic nitrogen, ammonia and nitrite to nitrate, and the nitrate is then measured. The result is total nitrogen: organic nitrogen, ammonia, nitrite and nitrate together. Standard Methods notes that the digestion is not effective in wastes with a high organic load and directs diluting such samples and reanalyzing until the results from two dilutions agree. Expressed as mg/L nitrogen.
Phosphorus
Standard Methods 4500-P E, the manual single-reagent ascorbic acid method: phosphate reacts with molybdate and antimony and is reduced by ascorbic acid to a blue color measured by spectrophotometry. Only the orthophosphate form reacts. A low-level option is available. Tell us whether you need total or dissolved (filtered) orthophosphate. Reported as mg/L phosphorus (P).
Standard Methods 4500-P F: the sample is digested so all forms of phosphorus become orthophosphate, which is then measured by the automated ascorbic acid method. Low-level and dissolved low-level options are available; dissolved phosphorus is measured on a filtered portion. Reported as mg/L phosphorus (P).
Solids
Standard Methods 2540 B: a well-mixed portion of the sample is evaporated and dried to constant weight at 103 to 105 °C. Total solids are the suspended and dissolved material together. Reported as mg/L.
Standard Methods 2540 C: the sample is filtered through a glass fiber filter, and the filtrate is evaporated and dried to constant weight at 180 °C. Reported as mg/L.
Standard Methods 2540 D: the material retained on a glass fiber filter is washed and dried to constant weight at 103 to 105 °C. Reported as mg/L.
EPA Method 160.4: the residue from a total, dissolved or suspended solids test is ignited at 550 °C, and the weight lost is the volatile solids, a rough measure of organic matter. Tell us which residue the result should be based on. Reported as mg/L.
EPA Method 160.5: the volume of material that settles from one liter of sample in an Imhoff cone is read directly. Floating material is not included. Reported as mL/L.
Oil and grease
EPA Method 1664. The acidified sample is extracted with n-hexane, the solvent is removed, and the extracted material is weighed: this is n-hexane extractable material (HEM), or oil and grease. Treating the extract with silica gel removes polar material, and what remains is silica gel treated HEM (SGT-HEM), the non-polar fraction often requested as total petroleum hydrocarbon. Both results are defined by the method rather than by a specific compound. Reported as mg/L.
For a permit or compliance sample, tell us the program before you sample: the method has to be one that program accepts. Contact us for containers and sampling instructions before you collect the sample. Other water tests are available upon request.
The method numbers on this page follow the published EPA and Standard Methods designations. These references describe the methods; the TNI LAMS registry lists each method’s code and revision.
Questions about a sample or a method, call 360-967-7010 or email [email protected].
