Glass shards from the A.D. 1783 Laki fissure eruption in Iceland have been identified in the GISP2 ice core from Summit, Greenland, at a level just preceding the major acidity/sulfate peak. Detailed reconstruction of ice stratigraphy, coupled with analyses of solid particles from filtered samples, indicate that a small amount of Laki ash was carried via atmospheric transport to Greenland in the summer of 1783, whereas the main aerosol precipitation occurred in the summer and early fall of 1784. Sulfate concentrations in the ice increase slightly during late summer and fall of 1783 and remain steady throughout the winter due to slow oxidation rates during this season in the Arctic. The sulfate concentration rises dramatically in the spring and summer of 1784, producing a massive sulfate peak, previously believed to have accumulated during the summer of 1783 and commonly used as the marker horizon in Greenland ice core studies. The chronology of ash and acid fallout at the GISP2 site suggests that a significant portion of the Laid eruption plume penetrated the tropopause and that aerosol generated from it remained aloft for at least 1 yr after the eruption. Based on comparisons with other glaciochemical seasonal indicators, abnormally cool conditions prevailed at Summit during the summer of 1784. This further supports the claim that a significant volume of sulfate aerosol remained in the Arctic middle atmosphere well after the eruption had ceased.

A microparticle concentration peak in a GISP2 ice core contains volcanic glass shards of rhyolitic composition that correspond in age to the 1479-1480 A.D. Mt. St. Helens Wn eruption. These glass shards are compositionally similar to the Wn tephra and constitute 83% of the total particle population. The shards are very coarse-grained (up to 40 μm diameter), suggesting rapid transport from their source to Greenland. A major sulfate peak in the ice occurs approximately 4 months after deposition of the glass shards. This difference in depositional timing suggests primarily tropospheric transport of the ash and stratospheric transport of the sulfate aerosol. Large-scale climatic perturbations following this eruption were evidently negligible. Glaciochemical seasonal indicators suggest a late-fall to early-winter 1479 A.D. eruption.

Assessing the climatic impact of the A.D. 1783 eruption of Mt. Asama, Japan, is complicated by the concurrent eruption of Laki, Iceland. Estimates of the stratospheric loading of H2SO4 for the A.D. 1108 eruption of Asama derived from the SO42− time series in the GISP2 Greenland ice core indicate a loading of about 10.4 Tg H2SO4 with a resulting stratospheric optical depth of 0.087. Assuming sulfur emissions from the 1783 eruption were only one‐third of the 1108 event yields a H2SO4 loading value of 3.5 Tg and a stratospheric optical depth of only 0.029. These results suggest minimal climatic effects in the Northern Hemisphere from the 1783 Asama eruption, thus any volcanically‐induced cooling in the mid‐1780s is probably due to the Laki eruption.

A pilot study was completed at a fractured crystalline bedrock site using a combination of soil vapor extraction (SVE)

A systematic hydrogeologic site characterization has been completed in a fractured rock flow system, with the objective of identifying contaminant migration and fate pathways from a historical release of 1,1,1‐trichloroethane (TCA). The study integrated hydrogeologic analysis techniques such as borehole geophysical logging, pumping test analysis, and hydrochemical facies analysis to study the impact of a dense nonaqueous phase liquid (DNAPL) in a sparsely fractured crystalline bedrock. The assessment methodology can be divided into two parts: (1) characterization of the source area, where DNAPL is acting as a residual source of TCA, and (2) characterization of the downgradient plume. Reduction in DNAPL mass in the source area has resulted in significant and sustained reductions in downgradient concentrations, suggesting that remediation of fractured crystalline bedrock contaminated with DNAPL is possible and not “technically infeasible.”