A pesticide screening model was integrated with a geographic information system (GIS) for evaluating the ground water vulnerability to pesticide contamination in Albemarle County, Virginia. The attenuation factor (AF). an index of pesticide mass emission from the vadose zone, was used to evaluate the relative contamination potential of 70 pesticides used in the county. Results for only three pesticides—atrazine, dicamba, and lindane—are discussed in this paper. Spatial (land use, soils, and hydrogeology) and relational (soil and pesticide properties) data layers were combined with the AF model within the GIS environment for spatial computation of AF for actual and 2 m ground water depths. For each pesticide, a ground water vulnerability map with five contamination potential categories (high, medium, low, very low, and unlikely) was generated, based on the spatial distribution of AF for each cell size of 0.27 acre (0.11 ha). To consider the variability in pesticide transport, model simulations were performed for “maximum,”“average,” and “minimum” scenarios of pesticide leaching. Under the average leaching scenario (2 m depth), the three pesticides were found to have very low to low levels of contamination potential in some areas. For maximum leaching scenario (2 m depth), contamination potential of these three pesticides increased to low to medium levels. When actual ground water depth was used, no significant contamination potential was indicated by any of the three pesticides. The modeling approach was evaluated using the data from a limited monitoring study in Albemarle County. Although agreement between the model prediction and actual pesticide detection was observed, extent of the data was not sufficient enough to draw firm conclusions about the model's success in predicting contamination potential. A sensitivity analysis of the methodology revealed that significant uncertainty can be involved in predicting the county‐scale contamination potential. To make better use of this study, it is recommended that a comprehensive pesticide monitoring be undertaken in Albemarle County.
Hypervelocity impact of a rigid spherical projectile with a compressible target material is investigated. Analytic solutions obtained for this problem are based on dynamic cavity expansion and Goodier deep penetration theories and are not restricted, as in previous work, to an incompressible medium. Target compressibility is introduced through a locking approximation for real material behavior under hydrostatic stress. In particular, values of locking density are obtained from Hugoniot curves characterizing homogeneous, isotropic material behavior at different impact velocities. Results of the theory indicate that terminal penetration depth is a function of projectile diameter and mass, and initial density, locking density, yield stress, and strain-hardening modulus of the target material. Using results of the theory, curves are plotted to show the comparison between compressible and incompressible penetration theory for the hypervelocity impact of steel projectiles on an aluminum target. NomenclatureA,D,M = cross section area, diameter, and mass of projectile, respectively a = radius of spherical cavity Bi,Bz = constants related to dynamic pressure, see Eq, (71) b = radius of locked-elastic, locked-plastic spherical shock front Ci = constant of integration E,G = modulus of elasticity and shear modulus, respectively Et = tangent modulus for linear strain-hardening e -bulk strain / = limit of integration f,g = functions of integration k = radius of stress-free, locked-elastic spherical shock front = static pressure term given by Eq. (71) p(t) = dynamic pressure applied to spherical cavity surface as a function of time >># = depth, velocity, and acceleration, respectively, of projectile in target material q Q) v Q = penetration depth and velocity of projectile after completion of shallow penetration phase q t = final penetration depth of projectile r = Eulerian radial coordinate t = time v = outward particle velocity in radial direction Y = yield stress a = material constant given by Eqs. (16), (24) /3 = material constant given by Eq. (40) 8 = material constant given by Eq. (66) ei,e2 = small quantities in the mathematical sense ei = locking strain, ei = -ei = normal strains in radial and circumferential directions, respectively = series expression given by Eq. (54) 0 }( p = equatorial and meridional spherical coordinates, respectively P)PI = density and locking density of target material, respectively o>,<70 = normal stresses inr adial and circumferential directions, respectively Downloaded by UNIVERSITY OF MICHIGAN on February 20, 2015 | http://arc.aiaa.org |
A loafing or sacrifice lot is an area located outside of the free stall barn, where a dairy herd spends several hours per day. Sacrifice lots are usually denuded of vegetation and have high concentrations of manure and urine that can contribute significant amounts of sediment, nutrients, and pathogens to nearby surface waters. In this study, stream water quality impacted by direct runoff from a sacrifice lot was monitored for a period of 20 months. Ambient stream water quality was monitored by grab sampling upstream and downstream of the sacrifice lot. During runoff events, stream water quality downstream of the sacrifice lot was monitored with an automatic sampler. Laboratory analyses were conducted for total suspended solids and nutrients (nitrogen and phosphorus compounds). A grass filter strip (GFS) was installed as a buffer downslope of the sacrifice lot 10 months into the study period. The impact of the buffer strip on the standardized pollutant concentrations and loads was evaluated using the non‐parametric Wilcoxon test. The Wilcoxon test indicated that there was no significant difference (α= 0.05) in the standardized yield of sediment and dissolved pollutants before and after the GFS installation, except for phosphate‐phosphorus and filtered total phosphorus concentrations, and sediment‐bound total phosphorus and total kjeldahl nitrogen loads that decreased significantly. However, load decrease could have been partially caused by the smaller rainfall volumes after the GFS installation as compared to the existing condition.
During crop years 1980–1983, a field study was conducted in southeastern Virginia on a Norfolk loamy fine sand soil to evaluate the effect of irrigation, underrow ripping, and seedbed preparation methods on peanut yields. The seedbeds were prepared conventionally (flat), with a rotary tiller and bed shaper, with a disk bedder, and with a rolling cultivator. Irrigation increased peanut yield only for crop year 1980 peanuts when there was a severe drought. Irrigation decreased yields for the other 3 years when rainfall was near normal. Some of the decrease in yields with irrigation can be attributed to an increase in the severity of several diseases including leafspot, pod rot, and Sclerotinia blight. Underrow ripping and seedbed preparation methods had no significant effect on yield and crop values. The effect of an interaction between underrow ripping and irrigation was indicated. Results from this study and previous studies indicated that underrow ripping does not appear to be an advantageous tillage operation for use in peanut production systems in the Virginia-Carolina area. Comparisons of seedbed preparation methods do not suggest that one method was superior to another method. The inconsistent trends in seedbed methods between years can be attributed to elements other than irrigation or underrow ripping treatments. Further studies need to define irrigation methods and amount of irrigation water to apply for efficient peanut production.
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