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Several areas in Hawaii have background concentrations of unexploded ordnance (UXO) as a consequence of past and current military training. The presence of UXO and the release of their che...

The growing global food security crisis is complicated by the need for increased crop production with less arable land and limited water resources. Reuse of treated wastewater for agricultu...

The complementary relationship areal evapotranspiration (CRAE) model estimates actual evapotranspiration (ET) based on potential and wet environment evapotranspiration rates. The existing C...

Cryptosporidia are opportunistic pathogens, some of which infect humans when ingested in water or food. Filtration through granular media is the primary mechanism to remove them from water....

Nitrification of chloraminated water in distribution systems, particularly in summer time, is a serious problem for some utilities because nitrifying bacteria deplete residual chloramine, a...

Riverbank filtration (RBF) is a simple yet effective treatment technology that uses the natural soil and aquifer media to remove various pollutants from river water during induced infiltrat...

Experiments were performed to evaluate flow and head variations along perforated screens ( 10–30 mm in diameter) using sand tanks which were connected and a perforated screen extended through these tanks to form a model collector well lateral up to 2.6 m in length. Hydraulic heads and discharge along the lateral and production rates of the model collector well were measured as the water level in the well, the lateral length, and diameter, and the hydraulic conductivity of the filter sand were varied. A mathematical model was developed to predict the axial flow velocity distribution and the discharge intensity variation along the lateral using the head distribution. Results showed that the production rate increased as the lateral length and diameter and the drawdown at the well increased. However, the production rate increase was not linearly related to these factors. When larger-diameter laterals were used, the axial flow velocity in the laterals decreased. This caused the hydraulic heads along the latera...

A simulation of the transport of dibromochloropropane (DBCP) and ethylene dibromide (EDB) in the vadose zone and ground water was conducted in the Mililani area of central Oahu, Hawaii to revisit the ground water contamination predictions made by researchers at the University of Hawaii in 1988 for selected wells of the Honolulu Board of Water Supply. Examination of sampled DBCP results in these wells indicated a large discrepancy between the observed and predicted concentrations in 1988. Therefore, a postaudit study was initiated in the same area to assist in better defining projected concentrations of contaminants in well waters in the future. With the new data, different modeling approaches were undertaken for simulating flow and contaminant transport in both the vadose and saturated zones. The new simulations indicate travel times of 14–32 years for contaminants to reach the water table, depending on the location. The approximate recovery time of wells in the study area is expected to occur after the y...

An experiment in Hawaii proves that landfill caps designed as alternatives to those prescribed by law can effectively increase runoff and decrease leachate production, even in humid climates.

A neural network analysis of agrichemical occurrence in groundwater was conducted using data from a pilot study of 192 small-diameter drilled and driven wells and 115 dug and bored wells in Illinois, a regional reconnaissance network of 303 wells across 12 Midwestern states, and a study of 687 domestic wells across Iowa. Potential factors contributing to well contamination (e.g., depth to aquifer material, well depth, and distance to cropland) were investigated. These contributing factors were available in either numeric (actual or categorical) or descriptive (yes or no) format. A method was devised to use the numeric and descriptive values simultaneously. Training of the network was conducted using a standard backpropagation algorithm. Approximately 15% of the data was used for testing. Analysis indicated that training error was quite low for most data. Testing results indicated that it was possible to predict the contamination potential of a well with pesticides. However, predicting the actual level of contamination was more difficult. For pesticide occurrence in drilled and driven wells, the network predictions were good. The performance of the network was poorer for predicting nitrate occurrence in dug and bored wells. Although the data set for Iowa was large, the prediction ability of the trained network was poor, due to descriptive or categorical input parameters, compared with smaller data sets such as that for Illinois, which contained more numeric information.

Many irrigated areas in the United States and abroad overlie unconfined aquifers. The soils are coarse textured with low water-holding capacity, and irrigation water is frequently necessary for crop growth. Many of these areas experience elevated nitrate levels in water from shallow domestic wells. It is often observed that the nitrate plumes are stratified with depth with the highest concentration just near the surface. The irrigation wells are generally screened toward the bottom part of the aquifer where the material is coarse and the available drawdown is greater. Pumpage is typically cyclic but can be somewhat continuous during drought conditions. It is often believed that the floating nitrate plume is recycled by the irrigation wells. Simulations were carried out to show that slight deepening of domestic wells in both stratified and more homogeneous aquifers could eliminate nitrate problems for many domestic wells even in close proximity of irrigation wells.

Assessment of pesticide and nitrate contamination of rural private wells was conducted using artificial neural networks. Data from 192 drilled and driven wells and 115 large-diameter dug and bored wells, available from two earlier studies, were used for training and testing purposes. Four separate models, two for the two well types and one each for pesticide and nitrate, were developed. Parameters such as depth to aquifer material from land surface, well depth, and distance to cropland were used as input parameters, and the concentrations of nitrate or pesticides were the outputs. While the training efficiency of the network reached between 95 and 100% for these four models, the prediction accuracy for the four models ranged from a low of slightly above 50% for nitrate in dug and bored wells to a high of 90% for pesticides in drilled and driven wells. Sensitivity analyses were performed to examine the impact of network architecture, training and testing parameters, and the size and type of input parameter...

Large-scale nitrate contamination of ground water is often observed in irrigated areas where the soils are generally permeable, and nitrate plumes have been reported to occur at shallow depths in unconfined aquifers. It has been hypothesized that these nitrate plumes can be captured by the pumping action of irrigation wells and recycled at the field site. This paper presents results from a field and modeling study investigating the distribution of nitrate in an unconfined sand aquifer in an irrigated system. Results from tracer tests under both natural and forced gradients indicate that irrigation pumping has minor but measurable effects on solute transport. Hydrological and solute transport modeling using various pumping schedules suggests that, in most cases, the influence of irrigation pumping on solute transport will be minimal, even on local scales.