ESTCP Project #1011, Rhizosphere
Final Report
Sample Collection. To initially characterize the general contaminant distribution at
the site and to find the best location for the demonstration plots, we analyzed an initial set of
samples in a grid pattern by organic vapor analysis. To monitor the bioremediation process, we
used three types of soil samples: 1) grab samples as typically used for ADEC regulatory
purposes, 2) composite samples in which six to eight grab samples are taken on each plot and
thoroughly mixed together, and 3) soil-sock samples to reduce variability. Each sample type is
summarized below. Details are given in Section 9 "Quality Assurance Plan" of our
Demonstration Plan.
Grab samples were taken from four locations of each treatment plot at the start of the
demonstration and at the fall of the subsequent two growing seasons. Each of the four locations
was sampled at a shallow and a deeper depth. These samples were sent, using chain of custody
procedures prior to analyses for GRO, DRO, BTEX, and residual oil using ADEC-approved
methods. These data provided little utility for monitoring the processes.
Composite samples were taken from each treatment plot at the start of the demonstration and at
the spring and fall of the subsequent two growing seasons. The rationale for using a composite
sampling technique is to account for sampling spatial variability by taking sufficient samples in
each treatment plot so that their "mean value" (the composite) better represents the "population",
i.e., the soil in the treatment plot. A total of eight composite samples were obtained from each
treatment plot at each sample time. Each of the eight composite samples were composed of ten
random samples, taken from either a shallow or deeper depth in a treatment plot, and thoroughly
mixed together. These samples were analyzed at CRREL for analysis.
For research-demonstration sites, we used soil-sock samples in an effort to reduce variability.
This approach is not amenable to typical site implementation. The soil sock procedure is a
derivative of that used in litter decomposition studies. Approximately 200 samples were
randomly taken prior to seeding or fertilization and mixed by rotary mixer. These large mixed
samples, generally 10 to 20 ft3 of soil, were then apportioned into fine mesh, cylindrical, open-
topped bags (soil socks) that were buried vertically in the plots from which we had taken the
samples. Sufficient bags were buried so that a soil sock could be removed from each plot at each
sampling time and sacrificed for analysis.
Where the field conditions suggested that there were areas that were different, based on initial
chemical measurements, visual clues, or landscape position, we attempted to use statistical
blocking (Figure 8), so that each "distinct" area included one replication of each of the four
treatments. At each site, the samples taken for the soil socks were obtained from and returned to
the same block.
Soil samples were collected using hand tools, which were decontaminated between samples. The
samples were packaged in sealed bags and placed immediately into pre-cooled coolers with blue
ice. Samples were collected in the spring and fall; the actual sampling dates were subject to
weather conditions at each site.
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