Private wells are the source of drinking water for approximately 15% of households in the United States, but these wells are not regulated or monitored by government agencies. The well waters can contain arsenic, a known carcinogen that occurs in groundwater throughout the nation at concentrations that can exceed the Maximum Contaminant Level defined by the U.S. Environmental Protection Agency (10 ppb). In order to reduce arsenic exposure, homeowners can either rely on bottled water for drinking or install in‐house water treatment systems for arsenic removal. Here, we document the arsenic levels associated with these options. We examined 24 different major bottled water brands and found that all have arsenic levels <1.5 parts per billion (ppb), and more than half have levels below our measurement detection limit of 0.005 ppb. For in‐house treatment systems, we examined the performance of arsenic removal by point‐of‐use reverse osmosis filtration, and by whole‐house and point‐of‐use filters containing granulated ferric oxide. Our results show that long‐term (2 years) filtration with granulated ferric oxide reduced arsenic in well water from an initial concentration of 4 to 9 ppb down to <0.005 ppb, validating this technology as an effective form of arsenic remediation for private homes.

Geochemical well logs were obtained through sediments at Sites 815, 817, 820, 822, and 823 of Leg 133. Corrections have been applied to the logs to account for variations in hole size, drilling-fluid composition, and drill-pipe attenuation. Oxide and calcium carbonate weight percentages have been calculated from the processed logs and are compared with the available carbonate measurements from core. Log-derived CaCO 3 measurements correlate well with shipboard CaCO 3 core-derived measurements in each of the logged open-hole intervals.

Geochemical well logging provides a continuous record of the variations in elemental abundances of the major rock-forming oxides of Si, A1, Ca, Fe, Ti, and K, as well as S, Gd, U, Th, and the H and C1 in the formation and pore fluid. Through the additional measurement of the photoelectric capture cross section of the rock, the sum of Mg + Na can also be estimated. Though not as accurate as laboratory analyses of recovered core samples, the log-derived abundances are precise enough to define the degree and extent of alteration, to identify igneous lithostratigraphy, and to calculate integrated chemical exchange between the oceanic crust and seawater. In this paper, the elemental yields from geochemical logging in basalts are calibrated against extensive XRF analyses of cutting samples from the Lamont 2 test well into the diabases of the Palisades Sill, New York. Accuracy and precision of the log-derived analyses are determined in the lower part of the well, and calibration equations are derived, which are then tested against core-derived "standards" from the upper part of the well. The calibrated, log-derived, elemental analyses are within one standard deviation of the core-derived results (except for the Mg + Na curve, which is somewhat noisier). These calibrations are then applied to geochemical logs from the oceanic crustal basalts of Ocean Drilling Program hole 504B, where core recovery was less than 20% of the section. The accuracy and precision of the calibrated, log-derived elemental abundances are tested against core-derived standards from seven dike and sill intervals. Then the corrected elemental analyses are used to derive a mineralogy model for hole 504B that shows the oceanic crust to contain secondary mineralization in the form of celadonites and smectites in the pillow basalts and chlorites in the dikes that are largely confined to fracture and breccia zones. Cyclicity in the AI and other elemental logs was found to vary with the abundances of these alteration products and with eruption and intrusion event boundaries. The geochemical logging data are then used to estimate the integrated chemical exchange resulting from hydrothermal alteration of the oceanic crust that has occurred over the last 5.9 m.y. in hole 504B. The primary change is from Ca loss and Mg gain caused by the reaction of basalt with seawater. A large Si increase found in the transition zone between the pillows and dikes is attributed to precipitation of quartz during mixing of hot, upwelling hydrothermal fluids and cold, downwelling seawater at what was once a major permeability discontinuity. The present low-to-high permeability transition in hole 504B is found 500 m shallower. The K budget requires significant addition to the uppermost pillow basalts both from high-temperature depletion in the lower pillows and dikes and from low-temperature exchange with seawater. The geochemical logs further document that the total chemical exchange between the oceanic crust and seawater is as important to the long-term composition of the ocean...

Elemental analyses of rock compositions have been measured in situ with a geochemical logging tool (GLT) in drillholes through igncous and metamorphic terrains. Comparisons of dry weight percent oxide analyses from laboratory measurements on core samples and the log-derived results demonstrate that accuracics are fair in Ocean Drilling Program Hole 504B basalts, good in Cajon Pass, California granites, and very good in Moodus, Connecticut metamorphic rocks and Palisades, New York diabases. Improved accuracies of GLT measurements are attainable through the use of a boron sleeve to isolate the borehole fluid from wellbore effects, and in smaller diameter, land-based boreholes. Precisions within each well are very good in all cases. That is, only a linear calibration shift was required to bring core and laboratory analyses into general agreement in all cases. Variations in mineralogy, derived from inversion models of the log-derived elemental abundances at each well, produce a lithostratigraphic interpretation that is useful for determining the structure of the oceanic crust (Hole 504B), the fractionation sequence of basaltic intrusions in a new rift basin (Palisades Sill), the deformation history near the San Andreas Fault (Cajon Pass), and the variations in degree of metamorphism across a shallow decollcment surface caused by collision tectonics (Moodus).

A new elemental oxide classification scheme for crystal1ine rocks is developed and applied to geochemical well logs from the Cajon Pass drill hole. This classification scheme takes advantage of measurements of elements taken by a geochemical logging tool string. It uses K20 versus Si~/Al20:3 to distinguish between granites, granodiorites, tonalites, ·syenites, monzonites, diorites, and gabbros. Oxide measurements from cores are used to calibrate the elemental abundances detennined from the well logs. Fro111 these logs, a detailed lithologic column of the core is generated. The lithologic column derived from the well log classification scheme is compared with a lith:llogic column constructed from core samples and well cuttings . In the upper 1295 m of the well, agreement between the two columns is good. Discrepancies occur from 1295 to 2073 m and are. believed to be caused by the occurrence of rock types not distinguished by the classification scheme and/or the occurrence of secondary minerals. Despite these discrepancies, the well log-based classification scheme helps to distinguish changes in rock type and shows potential as an aid to the construction c:llithologic columns in lxreholes of crystalline rocks. The drill hole established an underground laboratory for in situ measurements of the properties near the fault.One of the main objectives of the Cajon Pass project was addressing the "stress/heat flow paradox." Conventional models derived from fault friction experiments [Scholz, 1980] suggest that average shear stress along the San Andreas fault is high (50 MPa). Such high stress should be accompanied by high heat flow. However, none of the approximately 100 s~allow heat-flow measurements taken near the San Andreas fault indicates a frictional heat source associated with the fault [Lachenbruch and Sass, 1980;Zoback et al., 1980]. Rather, the absence of a heat flow anomaly points to shear stress less than 20 MPa, which implies that frictional coupling across the fault is low [Lachenbruch, and Sass, 1988;Zoback et al., 1987]. By drilling a well to seismogenic depths near the San Andreas fault, DOSECC obtained data of both heat flow and stress as a function of depth which could help unravel this paradox. Since the amounts of beat and stress generated along the fault are dependent on rock type, the lithostratigraphy at the core site must be understood before deciphering the beat flow and stress measurements. Consequently, extensive coring and state-of-the-art logging were combined to allow for continuous measurements of the physical and chemical properties of the rock. Roughly 3 % of the total well depth was cored, of which 85% was recovered. Cutting samples were collected at 3-m (10 foot) intervals and log measurements were taken every 0.15 m (6 inches).Geochemical log measurements help to distinguish lithologic changes and geochemical variations that are not apparent in the geophysical log measurements and that are difficult to pinpoint from cuttings and discontinuous cores. The combination of core data, cutti...