Release of contaminants from a heterogeneously fractured low permeability unit underlying a DNAPL source zone.

The invasion of DNAPL into fractured low permeability deposits results in the formation of secondary source zones that represent a long-term source of VOCs to adjacent aquifers. We present data from a site underlain by a fractured mudstone contaminated with TCE DNAPL that was poised for release following remediation of the overlying aquifer. Observations of contaminant distributions and fracture networks from the site and a nearby mudstone exposure respectively, enabled prediction of the imminent aquifer recontamination. The fractures, likely formed by gypsum dissolution, were characterised by fracture apertures and spacings that ranged from 0.01 to 49 mm and 0.047 to 3.37 m (10th and 90th percentile values) respectively. Numerical model results show that prediction of outward mass flux in the first year was highly variable (8 to 32 g/m²/d for an initial constant concentration with depth profile) and dependent on both the fracture spacing and aperture and the contaminant distribution. However after 1 year, assuming a heterogeneous distribution of fractures, mass flux was predictable within a narrow range of values (at 20 years; 0.04-0.08 g/m²/d). Similar results were obtained from more typical fracture networks with spacings of 0.1 to 0.5 m and apertures of 10 to 100 µm. These results suggest that when considering potential recontamination in a bounding aquifer, fracture characterisation may not be necessary and instead the focus should be on determining the surface area contributing contaminant mass to an aquifer, the contaminant concentration depth profiles, the hydraulic properties of the receiving aquifer and the elapsed time since aquifer remediation.

Hydrogeophysical imaging of deposit heterogeneity and groundwater chemistry changes during DNAPL source zone bioremediation.

Robust characterization and monitoring of dense nonaqueous phase liquid (DNAPL) source zones is essential for designing effective remediation strategies, and for assessing the efficacy of treatment. In this study high-resolution cross-hole electrical resistivity tomography (ERT) was evaluated as a means of monitoring a field-scale in-situ bioremediation experiment, in which emulsified vegetable oil (EVO) electron donor was injected into a trichloroethene source zone. Baseline ERT scans delineated the geometry of the interface between the contaminated alluvial aquifer and the underlying mudstone bedrock, and also the extent of drilling-induced physical heterogeneity. Time-lapse ERT images revealed major preferential flow pathways in the source and plume zones, which were corroborated by multiple lines of evidence, including geochemical monitoring and hydraulic testing using high density multilevel sampler arrays within the geophysical imaging planes. These pathways were shown to control the spatial distribution of the injected EVO, and a bicarbonate buffer introduced into the cell for pH control. Resistivity signatures were observed within the preferential flow pathways that were consistent with elevated chloride levels, providing tentative evidence from ERT of the biodegradation of chlorinated solvents.

Decreased bone anabolic effect of basic fibroblast growth factor at fatty marrow sites in ovariectomized rats.

The purpose of the study was to compare the bone anabolic effects of basic fibroblast growth factor (bFGF) at hematopoietic (red) and fatty (yellow) marrow sites in ovariectomized (ovx) rats. Female Sprague Dawley rats were subjected to ovariectomy or sham surgery at 3 months of age and maintained untreated for 2 months after surgery. Three groups of ovx rats were then injected intravenously with bFGF for 14 days at a dose of 200 microg/kg body weight. One group of bFGF-treated OVX rats was killed at the end of the treatment period, whereas the other two groups were killed at 7 or 14 days after withdrawal of bFGF treatment. Another group of ovx rats and a group of sham-operated control rats were treated intravenously with vehicle alone for 14 days. The proximal tibia and first lumbar vertebra, bone sites with hematopoietic marrow, as well as the distal tibia and caudal vertebra, bone sites with primarily fatty marrow, were processed undecalcified for quantitative bone histomorphometry. At the hematopoietic marrow sites, bFGF treatment induced a marked accumulation of osteoid, which calcified during the withdrawal period to result in a significant increase in cancellous bone volume. Osteoblast and osteoid surfaces were increased by at least a factor of 10 at these sites in bFGF-treated ovx rats before declining rapidly during the withdrawal period. In contrast, osteoid volume was negligible in the fatty marrow sites of bFGF-treated ovx rats. Although these animals exhibited a nonsignificant trend for increased cancellous bone volume in the fatty distal tibia during the withdrawal period, no such trend was observed in the fatty caudal vertebra. Indices of bone formation (osteoblast and osteoid surfaces) were significantly increased by bFGF treatment in the fatty distal tibia, which retained some small pockets of hematopoietic cells, but not to the same great extent as in the skeletal sites with hematopoietic marrow. Furthermore, not even a trend for increased osteoblast and osteoid surfaces was observed in the fatty caudal vertebra of bFGF-treated ovx rats. These findings indicate that bFGF is a strong bone anabolic agent at skeletal sites with hematopoietic marrow, but the stimulatory effects of the growth factor on bone formation are greatly attenuated at fatty marrow sites.

Purchasing with vision.

Although the new NHS has brought new tasks and opportunities to providers, the really new role, and the critical one, is that of purchasers. Bob Dearden outlines the six inter-related functions which purchasers need to get right.