You are here:
ANALYTICAL METHODS FOR FUEL OXYGENATES
Citation:
White, H., B. Lesnik, AND J T. Wilson*. ANALYTICAL METHODS FOR FUEL OXYGENATES. New England Interstate Water Pollution Control Commission, Lowell, MA, 2002.
Description:
MTBE (and potentially any other oxygenate) may be present at any petroleum UST site, whether the release is new or old, virtually anywhere in the United States. Consequently, it is prudent to analyze samples for the entire suite of oxygenates as identified in this protocol (i.e., MTBE, TAME, ETBE, DIPE, TAEE, TAA, and TBA). Samples should be prepared for analysis preferably using EPA Method 5030 (heated to 80? C), although either Method 5021 or Method 5032 may be used if the laboratory can demonstrate appropriate performance with these methods. The determinative analytical method used should either be EPA Method 8260 or 8015, or another method that provides confirmatory identification of all of the fuel oxygenates and can be demonstrated to meet project data quality objectives. The determinative method should be calibrated for the entire suite of oxygenates and these analytes should be reported for every sample analyzed. With the understanding that ethanol and methanol are potentially present at fuel release sites, it is also advisable to have samples analyzed for these alcohol oxygenates using appropriate preparative and determinative methods as well. After all of the oxygenates present at a site (if any) have been identified and their concentration and extent determined, future analysis can then be focused appropriately.
The protocol described above enables determination of all of the common oxygenates and BTEX at levels of regulatory interest. Routine use of this protocol will greatly improve the quality of the data that are reported, which in turn will enable better decisions to be made, which ultimately will result in more effective utilization of available resources. EPA Method 8260 provides confirmatory identification of the analytes, however the method is more expensive and there may be a temptation to substitute methods that do not provide confirmatory identification. This temptation should be resisted.
To properly implement this protocol, ground water samples should be collected from locations where oxygenates are most likely to occur based on their chemical and physical behavior. Because oxygenates are more soluble than petroleum hydrocarbons and can be more recalcitrant, oxygenate plumes may be longer than typical BTEX plumes. Oxygenate plumes may also ?dive? beneath conventional monitoring wells and migrate undetected until a drinking water source is impacted. To ensure that such plumes aren?t migrating undetected, samples should be collected from a series of discrete sampling points, which draw in ground water only over short vertical intervals. There should be a sufficient number of sampling points to cover the entire vertical distance over which an oxygenate plume may migrate. Generally this means that additional sampling points are required at progressively greater depths below the water table as the down gradient distance from the source increases. Increasing the length of monitoring well screens is not appropriate as this will only dilute the concentration of contaminants in the sample and mask the true concentration in the plume.
To prevent constituents in the samples from being biodegraded during storage and transport, samples should be preserved. To prevent chemical hydrolysis of the ether oxygenates during storage, the samples should be preserved with a base delivered as a salt (TSP), rather than a strong acid, and also refrigerated. Preservation with TSP will also eliminate the possibility of the ethers being hydrolyzed during sample preparation. Stored samples should be refrigerated at 4E C and analyzed within the holding period.