A new technique for rapid measurement of continuous soil moisture characteristic curves

The soil moisture characteristic (SMC) curve of a soil describes the relationship between the soil suction (tension in the soil pore water) and its water content. The majority of traditional methods used to obtain SMC curves involve gathering individual point measurements of soil water content over a range of applied soil suctions, and then fitting a curve through these points. Each point measurement requires at least a day of testing to gather, leading to a total testing time of weeks to assemble the whole SMC curve. This paper presents a technique to obtain a complete, continuous SMC curve in a total preparation and testing time of 3–5 days. During evaporative drying of the soil specimen under examination, a digital laboratory balance and a high-capacity tensiometer, both connected to a data acquisition system, monitor continuous pore water loss and suction data respectively. The tensiometer is composed of a pressure transducer for suction measurement and an extremely fine porous ceramic that interfaces between the specimen and the transducer. To date, the technique has been successfully applied to resedimented, non-clay soils. Experimental results from the new method are in agreement with results from capillary fall tests. The paper also provides some insight into tensiometer behaviour and features of SMC curves

Implications of fecal bacteria input from latrine-polluted ponds for wells in sandy aquifers.

Ponds receiving latrine effluents may serve as sources of fecal contamination to shallow aquifers tapped by millions of tube-wells in Bangladesh. To test this hypothesis, transects of monitoring wells radiating away from four ponds were installed in a shallow sandy aquifer underlying a densely populated village and monitored for 14 months. Two of the ponds extended to medium sand. Another pond was sited within silty sand and the last in silt. The fecal indicator bacterium E. coli was rarely detected along the transects during the dry season and was only detected near the ponds extending to medium sand up to 7 m away during the monsoon. A log-linear decline in E. coli and Bacteroidales concentrations with distance along the transects in the early monsoon indicates that ponds excavated in medium sand were the likely source of contamination. Spatial removal rates ranged from 0.5 to 1.3 log(10)/m. After the ponds were artificially filled with groundwater to simulate the impact of a rain storm, E. coli levels increased near a pond recently excavated in medium sand, but no others. These observations show that adjacent sediment grain-size and how recently a pond was excavated influence the how much fecal contamination ponds receiving latrine effluents contribute to neighboring groundwater