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EM 1110-1-4001 3 Jun 02 • improve progress toward closure if a chap e or addition of remediation technologies is warranted or if P P �' � g � system can be closed 9-3 Sampling and Analysis a To verify that cleanup criteria have been achieved,the sampling plan described in the SAP will be carred out The sampling is likely to be more exhaustive both spatially and analytically than that used during routine monitoring The DQOs will probably be more rigorous as at this stage the consequences of errors are more serious It will be important when deterimning cleanup confirmation or compliance with ARARs to use sampling techniques that are consistent with those used at system start-up,so that comparisons between the two sets of data are meaningful Quality Assurance/Quality Control (QA/QC) samples, such as field duplicates,equipment blanks,trip blanks, and split samples sent to the USACE QA laboratory,will be an important component of the sampling program Adherence to standard operating procedures,including sample notation and chain-of-custody procedures,is critical at this juncture Table 3-4 lists the topics covered in a SAP b It is important to note that it is NOT appropriate to wait until sampling for"closure" to perform thorough sampling and analysis of key soil venting parameters In order to operate the system optimally,it is critical to frequently monitor parameters such as extracted concentration and flows from individual wells, in-situ soil gas concentrations from vadose zone piezometers,and water table fluctuations A more comprehensive list of routine sampling parameters is found in Chapters 7 and 8 In addition the RSE checklists describe a set of parameters that should be monitored periodically to ensure that the system is operating as intended By maintaining a good database of the "routine" operational data,the practitioner is unlikely to be surprised by the results of the sampling and analyses described in this chapter c Analytical Definitive fixed-laboratory analyses are usually required at this stage Use of standard analytical methods and reference materials to enhance comparability of data over time and across laboratories will make the comparison valid An example of a reference material might be a sample of floating product from a monitoring well in the case of remediation of a gasoline release An aliquot of this product would be analyzed every time a set of field samples was analyzed to indicate differences in analytical response Completion of remediation will be documented by attainment of agreed-upon contaminant concentrations using agreed-upon sampling and analysis methodologies 9-4. Typical Data Trends Usually the most concentrated exhaust stream treated by an SVE system is encountered at the beginning of remediation The typical data trend for vapor phase contaminant concentrations is steeply downward for two to three months,after which concentrations approach asymptotic levels This is graphically depicted for six example sites in Figure 9-1 Some systems are operated intermittently(pulsed)to periodically permit the soil system to equilibrate and introduce additional VOC into the soil air to maximize vapor phase concentrations This may make the air treatment system more efficient,particularly for catalytic combustion treatment systems(see paragraph 8-2) a If the data do not demonstrate an appreciable reduction in vapor phase contaminant concentrations over the first few months of operation,it is possible that NAPL is present and acting as a continuing source of VOC vapors • 9-3