Javelin ----Overview----Features----Specifications----
Microhole/Slimhole NMR Logging
Javelin Data Examples
Lawrence, Kansas
Javelin NMR data were acquired at the Geohydrologic Experimental and Monitoring Site (GEMS), a groundwater science test-site that has been extensively studied by the Kansas Geological Survey (KGS). The geologic stratigraphy at this site is well-characterized and is comprised largely of interbedded layers of sands and clayey silts. The Javelin log below clearly distinguishes a sharp transition from silt and clay (short T2) above 11 m to sand (long T2) below 11 m, which is consistent with auxiliary hydrogeologic data from this location.
In addition to the expected transition at 11 m, scientists were surprised to discover signals with long T2 at depths shallower than 5 m. The geology at these depths is known to be silty, however, long signals here indicate the presence of water in large pore spaces or cracks. It is likely that these long signals are associated with water filling large voids left by tree roots or possibly cracks in the well grouting. This interesting example illustrates that Javelin logging is not only useful for determining hydrogeologic information but also for potentially assessing soil stability and the integrity of subsurface engineering.
Cape Cod, Massachusetts
Javelin logs were collected in a multiple boreholes at the Massachusetts Military Reservation (MMR) on Cape Cod. Ongoing contaminant studies at MMR are particularly interested in delineating the location of silt layers interbedded in the mostly sand aquifer. These low permeability silt layers are likely to control the movement of groundwater and migration of contaminant plumes. The Javelin log shown below identifies at least three likely silt zones at 65m, 70–74m, and 82–83m. These zones are evidenced by an increase in bound water content (signal with short T2) and decrease in mobile water content (signal with long T2) over two or more contiguous depth levels. A clay or silt layer may also be present in the unsaturated zone at 12m.
