No abstract

Current literature values of 2,4,6-trinitrotoluene (TNT) solubility in water vary widely from 100 to 200 mg/L at room temperature. We investigated the effects of temperature and pH on the solubility of both reference TNT and field neat TNT obtained from the Alabama Army Ammunition Plant (AAAP), Childersburg, AL. The TNT solubility determined from this study was significantly lower than that of Taylor and Rinkenbach, which was cited by several reference chemical handbooks and articles. However, the values reported by the Merck Index and the Lange's Handbook of Chemistry compared well with our values. TNT solubility dropped rapidly as the pH increased. Three unknown HPLC peaks were observed at high pH, indicating a possibility of forming unknown transformation products. Both reference and field neat TNT solubility agreed well. A semiempirical solubility correlation was developed to predict the solubility of TNT at a temperature range from 6 °C to 42 °C.

Solute transport from soil to overland flow is an important source of nonpoint pollution and was investigated through tracer studies in the laboratory and at an outdoor laboratory catchment. The depth of surface water interaction with soil, defined as the mixing zone is a useful value for approximate estimation of potential solute transport into surface water under rainfall. It was measured in the laboratory for a noninfiltration case (0.90 to 1.0 cm) and estimated through mass balance modeling for an infiltration case (0.52 and 0.73 cm). At an outdoor laboratory catchment, mixing zones were calculated through calibration of a numerical model that describes unsteady, uniform, infiltration and chemical transport. Overland flow was simulated using kinematic wave theory. Mixing zone depths ranged from 0.47 to 1.02 cm and were a linear function of rainfall intensity. Also, the fraction of solute present in the mixing zone at the time of ponding which was extracted into overland flow was a linear function of the initial soil moisture content. A steady state analytical approximation of the solute transport model was also developed which overpredicted solute transport into overland flow by 1 to 60%.

No abstract

Sampling frequency for a water quality monitoring network is presented, and for illustrative purposes the criterion is applied to the Massachusetts portion of the Connecticut River basin. The proposed frequency criterion is based upon the assumption that the primary objectives of future river quality monitoring networks are the determination of ambient water quality conditions and an assessment of yearly trends rather than detection of stream or effluent standards violations. The sampling frequency criterion is derived as a function of the random variability of the river flow. The criterion is specifically related to the magnitude of the expected half width of the confidence interval of the mean of the random component of the annual statistic‐mean log river flow. The appropriate sampling intervals (at each sampling station within the river basin) are determined by specifying equality of this confidence interval half width, which insures a uniform reliability of the annual statistic.

No abstract

One of the main mechanisms of failure of levees is a phenomenon called ''piping,'' which generally begins with the formation of a sand boil at the leeward side of the levee, and has been frequently observed to proceed upstream along the base of the levee through a slit formation. The issue of most important concern is to estimate the critical head that could promote the occurrence of piping. Considering the flow through porous media and coupling it with Bernoulli's equation and a critical tractive stress condition, a model is developed for the critical head. Using appropriate transformations, the proposed model takes on a form which supports Bligh's empirical findings. Another model based on critical velocity is also developed to estimate the critical head. The functional form of these two models is evaluated using the critical head versus porosity data from a number of laboratory studies conducted in the Netherlands. These models were found to perform better than did Terzaghi's model.

In the usual case of infiltration into a soil, the flow resistance of the expelled air is negligible compared with the resistance of the water to flow. If the air escape route deeper into the medium is blocked by an impermeable barrier, however, the air will be trapped and its pressure will increase as the water fills the pores. This back‐pressure of the air will decrease the infiltration rate, and if there is a horizontal, truly impermeable barrier at some depth the interface may eventually stop moving. In the analytic approach to the problem it is assumed that the medium is saturated to the wetting front and that all capillary forces are acting at the water‐air interface. Experiments with vertical columns of glass beads and fine sands generally verified the analysis, but it was observed that for mediums with particles larger than 0.30 mm diameter the air escaped upward into the atmosphere through the wetted medium and the interface kept moving downward.