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 Process sampling
Three 19-L (5-gal) samples were taken simultaneously from the feed slurry
and overflow, and three 4-L (1-gal) samples were taken from the underflow at
five different intervals during processing (1400, 1505, 1525, 1625, and 1715
hours). Samples were captured and transported in new HDPE buckets. Of these,
two from each sampling event were designated for particle size distribution and
contaminant concentration analysis. The remainder of the samples were
designated for particle size distribution only. The field sampling contractor was
responsible for obtaining process samples and packaging and shipping them to
ERDC. The overflow was sampled using a J-shaped diverter of polyvinyl
chloride (PVC) pipe, which was passed through the overflow stream vertically to
obtain a representative sample. The feed stream was sampled from a port welded
onto the outlet from the slurry pump, where the slurry was expected to be
turbulent and therefore well mixed. The line was purged for a few seconds prior
to taking each sample. Underflow samples were captured directly from the
cyclone underflow discharge. The volume of underflow samples was reduced
content of the underflow; 4-L (1-gal) samples were sufficient for all proposed
analysis. Samples designated for chemical analysis were placed in a cooler and
packed in ice for shipment. Samples designated for particle size analysis only
were not refrigerated. Chain-of-custody forms were completed.
A single 19-L (5-gal) sample of the process supply water was also taken to
establish baseline concentrations. It was initially proposed to sample effluent at
the pond discharge during and after processing to verify that no permit
parameters were violated during processing. However, water levels in the pond
were low enough that there was no discharge from the pond at the time of
processing, and the process overflow was passed through a sand drainage bed
prior to being returned to the pond, reducing suspended solids. Dissolved
contaminant levels were therefore measured in the process overflow and
compared to Freshwater Acute Federal water quality criteria (USEPA 1999a). Of
the parameters measured in the overflow having criteria, none exceeded acute
water quality criteria.
Upon arrival at ERDC, the samples were refrigerated, and samples
designated for chemical analysis were quickly processed to meet specified
holding times. The feed and overflow slurry samples designated for chemical
analysis (two field duplicates per stream per sampling time) were sampled while
being stirred to obtain representative samples of the slurry. They were then
centrifuged, and both solids and supernatant collected for chemical analysis.
Percent solids of the underflow samples was much higher, and subsamples were
taken directly from the buckets for chemical and particle size analysis without
centrifuging. Subsamples of all process solids were also taken for water content
and particle size analysis. Due to the difficulty involved in obtaining a
representative subsample from a slurry, slurry samples were allowed to settle for
1
The QAPP describes the technical quality assurance/quality control for specific data
collection, project objectives and organization, sampling design, analytical methods, data
quality indicators, and data review (USEPA 1997, 1998).
22
Chapter 2 Project Description
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