GRO/DRO/1664 Method Overlap
In the interest of simplicity, we wish there was one TPH method that would accurately quantify all types of petroleum contamination. Unfortunately, not only is there no one method for the lighter/volatile and heavier/extractable constituents, some fuels represent a mixture of both volatile and extractable hydrocarbons.
For example, extractable TPH by EPA 8015B (TPH DRO) is normally the best test to perform for # 2 fuel oil (# 2 fuel oil has the same composition as diesel fuel). We have seen situations however where the Volatile TPH test by EPA 8015B (TPH GRO) has yielded higher numbers for a #2 fuel oil spill. There is a logical reason for this discrepancy. Fuel oil is largely composed of semi-volatile compounds. There are however a number of volatile compounds, most of which are lost in the TPH DRO extraction process. The odor you detect from a fresh fuel oil spill is largely these volatile constituents. In a situation where samples are collected from an area above a spill, the TPH GRO test can yield a higher result. This happens because the volatile constituents are migrating upward in the soil column through evaporation and other physical processes.
Most laboratories performing a TPH GRO analysis will quantitate this as petroleum constituents in the gasoline range (which they truly are). This sometimes leads people to erroneously conclude that there is actually gasoline in the samples. At PSS we routinely add a # 2 fuel oil standard to our TPH GRO calibration mix. This allows us to do the TPH GRO test, yet let our clients know if the hydrocarbons we detected are actually in the # 2 fuel oil range.
The TPH DRO analysis can also be used to quanitate # 4 and # 6 range fuel oil. For every fuel weight we analyze, there is an optimal set of GC analytical run profiles that must be utilized to provide the most accurate numbers possible. Additionally, the appropriate standard, # 2, 4 or 6 should be utilized to allow quantitation based on a specific fuel range. In other words, it is not possible to provide the optimal conditions for every fuel range in a single analysis. Consequently, if # 4 or # 6 oil is suspected, a comment in the remarks section of the chain of custody form will help us to select the optimal GC analytical run profile and appropriate standards.
Another example of fuels where the TPH GRO and DRO methods overlap occurs is kerosene and the lighter aviation types such as Jet A. In this case the TPH GRO analysis is normally the best choice unless the fuel in the samples is highly weathered. In which case the TPH DRO analysis may prove useful. Many states regulatory agencies are now requiring that both the TPH GRO and TPH DRO tests be performed on sites contaminated by fresh #2 fuel/diesel and kerosene. They are additionally requiring both tests for most jet fuels such as JP 4 - 8 and Jet A.
As a final note the TPH 1664 methods range of available hydrocarbons overlaps with the TPH DRO analysis. This overlap occurs in the kerosene through # 6 fuel oil range. It should be noted that TPH 1664, is the only procedure that allows the quantitation of hydrocarbons heavier than # 6 such as motor oil, lubrication oils and greases. Both the TPH DRO and TPH 1664 tests are usually recommended for sites contaminated with #3 - 6 fuel oil, hydraulic oil, mineral/dielectric fluids, waste oils and unknown oils.
Please note that waste oil is often contaminated with gasoline from internal combustion engine "blow by" or the tanks content may have been compromised by illegal dumping of petroleum compounds other than waste engine oil. Consequently, the TPH GRO, DRO and 1664 tests are recommended in these situations.
When in doubt, please give us a call to discuss which test(s) or options within specific analyses are most appropriate for your project. Our staff has worked on literally thousands of projects and are happy to share there methodological expertise we have developed.
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Speciation Of Metals: ChromiumSampling Volatiles In Soil by 5035 MTBE - The Next Challenge Utilizing TPH Methods Effectively TPH Method Overlap Specific Petroleum Compound Testing TPH 1664 vs. 413.1 and 418.1 TCLP vs. SPLP Extraction Procedures Analyzing for Metals by ICP/MS ICP/MS Qualitative All Elements Scan