Sampling Methods for Site Characterization

A site characterization is conducted where a hazardous substance has been released, and there is potential for the contamination to reach people or adversely affect the natural ecology. In some cases, site characterization is carried out to provide background 

When site characterizations are complete, they provide accurate information about the presence and distribution of target contaminants in relation to the background environment, thereby facilitating cost-effective and efficient remediation. 

This presentation provides an overview of sampling methods and tools suitable to address most site characterizations. The basic sampling types discussed are the systematic, random, and judgmental sampling approaches. 

In addition to sampling procedures, sampling bias and sampling errors are introduced, leading to some guidance on sample handling, shipping, and chain-of-custody procedures. 

This presentation will focus on sampling methods for soil only. 

---

Catalyst characterization - Characterization of mixed metal oxides was performed by atomic emission spectroscopy with inductively coupled plasma atomisation (ICP-AES) on a CE Instraments Sorptomatic 1990. NH3-TPD was nsed for the characterization of acid site distribntion. SZ (0.3 g) was heated up to 600°C using He (30 ml min ) to remove adsorbed components. Then, the sample was cooled at room temperatnre and satnrated for 2 h with 100 ml min of 8200 ppm NH3 in He as carrier gas. Snbseqnently, the system was flashed with He at a flowrate of 30 ml min for 2 h. The temperatnre was ramped np to 600°C at a rate of 10°C min. A TCD was used to measure the NH3 desorption profile. Textural properties were established from the N2 adsorption isotherm. Snrface area was calcnlated nsing the BET equation and the pore size was calcnlated nsing the BJH method. The resnlts given in Table 33.4 are in good agreement with varions literature data. 

Non-existent samples or reference values Samples may not exist because the plant does not exist yet (it is under construction and has not started up yet), or because the plant does not do any sampling at the process point of interest. Reference values may not exist because the plant lab is not set up to do that particular method, or (worse) there is no established reference method for the analyte of interest. In any of these cases, one is left with a calibration set that contains no samples. There are a number of ways to approach this challenge. If there are samples but no reference values, the plant samples can be sent off-site to be analyzed. The analyte concentration of interest can sometimes be estimated based on process conditions and/or the concentrations of other analytes. (This is one place where fixed covariance can come in handy.) If there is no plant yet, it may be possible to calibrate the analyzer elsewhere (different plant, semi-works, etc.). It may also be possible (or even necessary) to attempt lab value-less calibration, in which one assumes that the concentration of the analyte varies linearly with the height of an absorbance peak characteristic of that analyte (trend analysis). This works only if the spectroscopy of the system is well-characterized and if there are no significant overlaps between peaks and in any case it will only provide qualitative data. 

However it is now clear that acid strength is not a singlevalued function, that different kinds of bases will tend to rank acid strengths differently, depending on their "hardness" or "softness". This is illustrated by the work of Kobayashi (13), who used a spectroscopic method of determining [B]/[BH+] on a sample of silica-alumina titrated with n-butylamine and one titrated with pyridine (Figure 2). Evidently the acidity of indicators and of individual acid sites on solids needs at least two constants for complete characterization of acid strength. 

Treatment with oxalic acid has been described as a method for selective removal of the external acid sites of medium-pore zeolites 61). PER and ZSM-23 zeolites were treated with a 1-M solution of oxalic acid at 353 K overnight 39, 62). The characterization of the acid sites showed that the treated materials had a low number of external acid sites compared with the untreated materials and, when used in n-butene isomerization, they exhibited an improved isobutylene selectivity. It was also observed that acid-treated PER does not have a high selectivity for isobutylene formation. It was inferred (62) that the cavities in ferrierite at the intersections of 8- and 10-ring channels are large enough to accommodate butene dimer intermediates, thus favoring the unselective bimolecular path. In contrast, when the external acid sites are removed from a zeolite with a unidimensional pore system (e.g., ZSM-23), the initial isobutylene selectivity is higher (nearly 80%) than that of the untreated sample. 

---