Compositing and storage of air and wastewater samples

The performance of a field study to determine whether any of the 14 New Yor k City water pollution control plants are major sources of air pollution re quired sampling and the analysis of a large number of samples. To reduce th e number of samples for analysis and address the associated storage concern s of the analytical laboratories, the experimental design called for compos iting air and wastewater samples, and for investigating the stability of wa stewater samples. This paper addresses the quality control issues associate d with the compositing and stability components of the experimental design. The study tested the hypothesis that compositing techniques used for air a nd wastewater sampling lead to results that are not unlike those obtained b y conventional grab sampling. The study also tested whether wastewater samp les stored under proper laboratory conditions remain stable for a period lo nger than the conventionally accepted storage period of 2 weeks. Statistica l analyses demonstrated that the hypotheses tested cannot be rejected and, consequently, compositing techniques employed in this study are equivalent to conventional grab sampling and the storage period of samples can be exte nded beyond the accepted 2 week period.