TCLP (Toxicity Characteristic Leachate Procedure) and SPLP (Synthetic Precipitate Leachate Procedure) are used to assess the leachability of semi-volatile organic and inorganic parameters.
ZHE (Zero-Headspace Extraction) is used to assess the leachability of volatile analytes whenever analysis of volatiles in leachates (either TCLP or SPLP) are required.
It is also important to understand that these methods represent sample preparation techniques and not analysis.
All three methods are used to characterize the quality of leachates for either solids or multiphased matrix samples and determine whether a material or waste is considered hazardous in nature or not (as compared to provincial waste management criteria).
The difference in classification potentially determines the receiving facility the waste is suitable for (i.e. between a hazardous waste processor and a typical landfill). Alternatively, the data may be used to determine measures to be put in place should soil be required to be temporarily stockpiled on a site.
The principal difference between TCLP and SPLP are;
1. Applicability to real-world scenarios.
2. The pH level at which the extraction is completed.
Much of the analytical approach between these two methods is similar. Once leached, the extract undergoes analysis for target compounds in the same fashion as other routine environmental samples would.
Procedure Comparison
| Comparison Element | Toxicity Charcteristic Leaching Procedure (TCLP) | Synthetic Preciptitate Leaching Procedure (SPLP) | Zero-Headspace Extraction (ZHE) |
| Reference Method | EPA 1311 | EPA 1312 | EPA 1311 |
| Applicability | Landfilling conditions (acetic acid) | Stockpiling (acid rain) | Volatile Compounds only (as applicable under either a TCLP or SPLP request) |
| Multiphase Samples | If >0.5% solid, liquid is separated for use at a later time (may be combined with final leachate for analysis; If <0.5% solids, the liquid, after filtration is considered the extract (or leachate). | Solid material only. | |
| Extraction ratio | 100g of solid sample material + extraction fluid (1:20) | 25g of solid mater + extraction fluid (1:20) | |
| Selection of Extraction Fluid | 5g of sample material is mixed with DI water in a slury, if the pH of this mixture is <5.0, then TCLP Fluid #1 (pH 4.93) is used; if the pH of the slury mixture is >5, then TCLP fluid #2 (pH2.88) is used. | For sample east of the Manitoba/Ontario border, SPLP fluid #1 (pH 4.2) is used, for samples west of the boarder, SPLP Fluid #2 (pH 5.0) is used. | If the ZHE procedure is for a TCLP request, TCLP fluid #1 is used; For a SPLP request, SPLP Fluid #3 (DI water) is used. |
| Duration of Extraction | 18 hours | ||
| Extract filtration | Filtration through a 0.7um glass fiber filter. | Not applicable to the ZHE method (avoids loss of target analytes). | |