Brad D. Lee

Pedogenesis in a wetland meadow and surrounding serpentinitic landslide terrain, northern California, USA

Landslide deposits in serpentinitic terrain of northern California are common, and often support wet meadows, which are strikingly different from the surrounding xeric landscape. These landslide deposits provide an opportunity to observe pedogenic processes across differing moisture conditions and depositional environments in ultramafic terrain. The objective of this study was to assess predominant pedogenic processes by landscape position for a stabilized landslide bench and the surrounding area in serpentinitic terrain. Distributions of dithionite extractable metals and exchangeable cations were compared to interpret processes involved in element redistribution. Landscape positions were defined as the scarp, flanks, foot, and bulge. The foot, which supports a wet meadow, is inundated during a significant part of the year due to water ponding behind the bulge. The forested scarp and flank positions are subject to episodes of erosion, probably following wildfires, thereby delivering sediments to the lower landscape positions. The major pedogenic processes on the slopes of the scarp and flanks include mineral weathering, oxidation, and illuviation of clay, as evidenced by argillic horizons in which Cr- and Al-bearing Fe-oxyhydroxides are concentrated. Serpentine-weathering products are transported from the scarp and flanks to the poorly drained foot where fine sediments and neoformed smectite yield clayey soils. On the foot, cycles of vegetation growth and deposition of sediments, coupled with reducing conditions, result in deep, organic-rich soils.

A Plaster Cast Method for Determining Soil Bulk Density

Abstract The plaster cast method for determining bulk density is an excavation method that uses dental plaster to form a cast of the excavation volume. Bulk density measurements using the plaster cast method were compared against measurements using the clod and core methods. Results from the plaster cast method were not significantly different (P< 0.05) from the clod and core methods for coarse-textured soils with loose consistence and minimal macropores. The plaster cast method is especially useful under soil conditions that limit the use of the clod or core method, such as soils with loose consistence, abundant rock or gravel content, thin horizons, or sloping topography, but may not be suitable for use in soils with abundant macropores.

Amelioration of Physical Strength in Waste Foundry Green Sands for Reuse as a Soil Amendment

To avoid increasing costs of landfill disposal, it has become increasingly important for U.S. foundries to identify beneficial reuses for the 8 to 12 million tons of waste foundry sand (WFS) generated annually. A major drawback to the reuse of some WFSs as a soil amendment is their high soil strength, under dry conditions, where root growth may be limited. Fifteen WFSs were analyzed for strength to rupture using lab-formed clods, exchangeable cations (Na, Mg, Ca), metal oxide concentration (Fe, Mn, Al, Si), cation exchange capacity (CEC), and % clay. Several WFS samples from gray iron foundries demonstrated high strength to rupture values (> 1.5 MPa), and could potentially restrict root growth in amended soils. The percentage of Na-bentonite exhibited a positive correlation (R(2) = 0.84) with strength to rupture values. When WFSs containing more Na-bentonite were saturated with 1 mol L(-1) Ca ions, strength values decreased by approximately 70%. Waste foundry sands containing less Na-bentonite were saturated with 1 mol L(-1) Na ions and exhibited a threefold increase in strength. Additions of gypsum (up to 9.6 g kg(-1) sand) to high strength waste foundry sands also caused decreases in strength. These results indicate that high strength WFSs have properties similar to hardsetting soils which are caused by high Na(+) clay content and can be ameliorated by the addition of Ca(2+).

Identification of Stolen Rare Palm Trees by Soil Morphological and Mineralogical Properties

The San Diego County District Attorneys office requested our help to investigate the theft of palm trees from a private collection of exotic plants. Circumstantial evidence led investigators to the suspects residence where 33 palm trees were found. Because the victim raised all palms from seed in the same potting mix, we compared morphologic and mineralogic properties of soil samples collected from the root balls of palms that were at the victims and suspects residences. Analyses of soil color, reaction with dilute hydrochloric acid, particle size, heavy:light mineral ratios, and mineral speciation of the >2.86 g cm - fine sand fraction, indicated that 25 of 33 soil samples collected from palm trees at the suspects residence were very similar to soil samples from palm trees at the victims residence. After a pretrial hearing at which the soil evidence was presented, the suspect changed his innocent plea to guilty.

Ground conductivity survey of a septic system during and after failure

Editors note: The use of trade names is for descriptive purposes only, and does not imply particular endorsement by the authors or SEG. Many people (e.g., 25% of the U.S. population) use septic systems for wastewater disposal. In the United States, county health departments typically are responsible for overseeing the installation and operation of these systems. Because most systems rely on the soil to absorb the wastewater, special attention is required where the hydraulic permeability of soils may allow contamination to reach either the surface or a nearby aquifer. Electromagnetic induction (EMI) provides an efficient means for observing septic system performance and for guiding costlier onsite investigations. In 2001, the Ft. Wayne–Allen County Health Department identified several failing septic systems in the suburbs of Ft. Wayne, Indiana, U.S., through field observation and water-quality monitoring of nearby streams. One such system had been installed in a fine-textured (35–50% clay) soil of low permeability, and serviced a residence on a two-acre lot. The system was mapped in December 2001 and again in July 2002 with the DUALEM-2 and several other EMI instruments. The DUALEM-2 is designed to measure ground conductivity at low-induction-number (LIN). The instrument contains coils that operate in both the horizontal coplanar (HCP) and perpendicular (PRP) geometries. Transmitter-receiver separation is about 2 m. At LIN, the PRP geometry is sensitive to conductivity fluctuations to a depth of about 1.2 m beneath the instrument, and the HCP geometry is sensitive to a depth of about 3 m. To evaluate the location of the septic system absorption field and contaminant distribution, the instrument was carried at low ground-clearance aligned with north-south traverses spaced at 2-m intervals (Figure 1). Although the surveys progressed along serpentine paths, the transmitter-receiver orientation of the instrument was kept consistent. Continuous measurements were recorded at walking speed (about …