RESUMEN
Rapid infiltration basins (RIBs) are effective tools for wastewater treatment and groundwater recharge, but continuous application of wastewater can increase soil P concentrations and subsequently impact groundwater quality. The objectives of this study were to (1) investigate the effects of reclaimed water infiltration rate and "age" of RIBs on soil P concentrations at various depths, and (2) estimate the degree (percentage) of sorption equilibrium reached between effluent P and soil attained during reclaimed water application to different RIBs. The study was conducted in four contrasting cells of a RIB system with up to a 25 year history of secondary wastewater application. Soil samples were collected from 0 to 300 cm depth at 30 cm intervals and analyzed for water extractable phosphorus (WEP) and oxalate extractable P, Al, and Fe concentrations. Water extractable P and P saturation ratio (PSR) values were generally greater in the cells receiving reclaimed water compared to control soils, suggesting that reclaimed water P application can increase soil P concentrations and the risk of P movement to greater depths. Differences between treatment and control samples were more evident in cells with longer histories of reclaimed water application due to greater P loading. Data also indicated considerable spatial variability in WEP concentrations and PSR values, especially within cells from RIBs characterized by fast infiltration rates. This occurs because wastewater-P flows through surface soils much faster than the minimum time required for sorption equilibrium to occur. Studies should be conducted to investigate soil P saturation at deeper depths to assess possible groundwater contamination.
Asunto(s)
Restauración y Remediación Ambiental/métodos , Fósforo/análisis , Contaminantes del Suelo/análisis , Eliminación de Residuos Líquidos/métodos , Contaminantes Químicos del Agua/análisis , Adsorción , Cinética , Fósforo/química , Suelo/química , Contaminantes del Suelo/química , Contaminantes Químicos del Agua/químicaRESUMEN
During moment-based analyses of partitioning tracer tests, systematic errors in volume and concentration measurements propagate to yield errors in the saturation and volume estimates for nonaqueous phase liquid (NAPL). Derived expressions could be applied to help practitioners bracket their estimates of NAPL saturation and volume obtained from such tests. In practice, many of these effects may be overshadowed by other complications experienced in the field. Errors are propagated for systematic constant (offset) volume, proportional volume, and constant (offset) concentration errors. Previous efforts to quantify the impact of these errors were predicated upon the specific assumption that nonpartitioning and partitioning masses were equal. The current work relaxes that assumption and is therefore more general in scope. Through the use of nondimensional concentration, systematic proportional concentration errors do not affect the accuracy of the method. Specific consideration needs to be given to accurate flow measurements and minimizing baseline concentration errors when performing partitioning tracer tests in order to prevent the propagation of systematic errors.
Asunto(s)
Monitoreo del Ambiente/métodos , Contaminación Ambiental/análisis , Residuos Industriales , Trazadores Radiactivos , Contaminantes Químicos del Agua , Modelos Químicos , Modelos Estadísticos , Modelos Teóricos , Reproducibilidad de los Resultados , Contaminantes del Suelo/análisis , Solventes , Factores de Tiempo , Contaminantes del Agua/análisis , Purificación del Agua/métodosRESUMEN
The uncertainty in NAPL volume estimates obtained through partitioning tracers can be quantified as a function of random errors in volume and concentration measurements when moments are calculated from experimentally measured breakthrough curves using the trapezoidal rule for numerical integration. The methodology is based upon standard stochastic methods for random error propagation. Monte Carlo simulations using a synthetic data set derived from the one-dimensional solution of the advective-dispersive equation serve to verify the process. It is shown that the uncertainty in NAPL volume predictions nonlinearly increases as the retardation factor decreases. An important result of this observation is that there is a large degree of uncertainty in using partitioning tracers to conclude NAPL is absent from the swept zone. Under the conditions investigated, random errors in concentration measurements are shown to have a greater impact on NAPL volume uncertainty than random errors in volume measurements, and it is also shown that uncertainty in NAPL volume decreases as the resolution of the breakthrough curves increases. The impact of uncertainty in background retardation (i.e., sorption of partitioning tracers in the absence of NAPL) was also investigated, and it likewise indicated that the relative uncertainty in NAPL volume estimates increases as the retardation factor decreases.
Asunto(s)
Monitoreo del Ambiente/métodos , Trazadores Radiactivos , Contaminantes Químicos del Agua/análisis , Simulación por Computador , Contaminación Ambiental , Modelos Estadísticos , Reproducibilidad de los Resultados , Contaminantes del Suelo , Tricloroetileno/análisis , Incertidumbre , Eliminación de Residuos Líquidos , Contaminantes del Agua , Purificación del AguaRESUMEN
BACKGROUND: All-terrain vehicles (ATVs) are popular recreational and utility vehicles. In 1984, Cogbill published an article regarding three-wheelers. These are no longer manufactured, but the injury and death rate with four-wheeled ATVs is high and disproportionately affects young riders. METHODS: We conducted a retrospective review at two Level I trauma centers from January 1994 to April 2003. Statistical analysis was performed using the SAS V8.2 program. Values of p < 0.05 were significant. RESULTS: Two hundred eight patients were identified. There were no differences identified in demographics, mechanism, types of injury, Injury Severity Score (ISS), or Glasgow Coma Scale (GCS) score. Seventy-five percent were male and 84% were white. The mean age was 23 +/- 13 years. The average ISS was 12.3 +/- 9 and the mean GCS score was 13.1 +/- 3.7. Injury mechanisms were loss of stability (33%), separation of rider from ATV (32%), and ATV versus stationary object (27%). ISS for ages 12 to 15 years was significantly higher than for other ages (14.5 vs. 11.5, p = 0.04, Wilcoxon rank sum test) and included more major head injuries (40.4% vs. 21.8%, p = 0.09, Wilcoxon rank sum test). They experienced fewer spinal fractures (3.9% vs. 15.4%, p = 0.03) and pelvic injuries (0% vs. 9%, p = 0.02, Wilcoxon rank sum test). The GCS score in this group was lower (12.3 vs. 13.4, p = 0.03, Wilcoxon rank sum test). CONCLUSION: Adolescent ATV riders have more severe injuries and more head injuries than other age groups. Prevention efforts should target this group.
Asunto(s)
Accidentes de Tránsito/estadística & datos numéricos , Vehículos a Motor Todoterreno/estadística & datos numéricos , Centros Traumatológicos/estadística & datos numéricos , Heridas y Lesiones/epidemiología , Traumatismos Abdominales/epidemiología , Adulto , Factores de Edad , Seguridad de Productos para el Consumidor , Traumatismos Faciales/epidemiología , Femenino , Traumatismos Cerrados de la Cabeza/epidemiología , Humanos , Puntaje de Gravedad del Traumatismo , Masculino , Análisis de Regresión , Estudios Retrospectivos , Estados Unidos/epidemiología , Heridas y Lesiones/prevención & controlRESUMEN
A dense nonaqueous phase liquid (DNAPL) source zone was established within a sheet-pile isolated cell through a controlled release of perchloroethylene (PCE) to evaluate DNAPL remediation by in-situ cosolvent flushing. Ethanol was used as the cosolvent, and the main remedial mechanism was enhanced dissolution based on the phase behavior of the water-ethanol-PCE system. Based on the knowledge of the actual PCE volume introduced into the cell, it was estimated that 83 L of PCE were present at the start of the test. Over a 40-day period, 64% of the PCE was removed by flushing the cell with an alcohol solution of approximately 70% ethanol and 30% water. High removal efficiencies at the end of the test indicated that more PCE could have been removed had it been possible to continue the demonstration. The ethanol solution extracted from the cell was recycled during the test using activated carbon and air stripping treatment. Both of these treatment processes were successful in removing PCE for recycling purposes, with minimal impact on the ethanol content in the treated fluids. Results from pre- and post-flushing partitioning tracer tests overestimated the treatment performance. However, both of these tracer tests missed significant amounts of the PCE present, likely due to inaccessibility of the PCE. The tracer results suggest that some PCE was inaccessible to the ethanol solution which led to the inefficient PCE removal rates observed. The flux-averaged aqueous PCE concentrations measured in the post-flushing tracer test were reduced by a factor of 3 to 4 in the extraction wells that showed the highest PCE removal compared to those concentrations in the pre-flushing tracer test.
Asunto(s)
Etanol/química , Contaminantes del Suelo/aislamiento & purificación , Solventes/química , Contaminantes del Agua/aislamiento & purificación , Contaminantes Ambientales/aislamiento & purificación , Solubilidad , Tetracloroetileno/aislamiento & purificaciónRESUMEN
The partitioning tracer technique for dense nonaqueous phase liquid (DNAPL) characterization was evaluated in an isolated test cell, in which controlled releases of perchloroethylene (PCE) had occurred. Four partitioning tracer tests were conducted, two using an inverted, double five-spot pumping pattern, and two using vertical circulation wells. Two of the four tests were conducted prior to remedial activities, and two were conducted after. Each test was conducted as a "blind test" where researchers conducting the partitioning tracer tests had no knowledge of the volume, method of release, nor resulting spatial distribution of DNAPL. Multiple partitioning tracers were used in each test, and the DNAPL volume estimates varied significantly within each test based on the different partitioning tracers. The tracers with large partitioning coefficients generally predicted a smaller volume of PCE than that expected based on the actual release volume. However, these predictions were made for low DNAPL saturations (average saturation was approximately 0.003), under conditions near the limits of the method's application. Furthermore, there were several factors that may have hindered prediction accuracy, including tracer degradation and remedial fluid interference.