A field study was conducted to determine the applicability of multivariate geostatistical methods to the problem of estimating and simulating pesticide concentrations in groundwater from measured concentrations of nitrate and pesticide, when pesticide is undersampled. Prior to this study, no published attempt had been made to apply multivariate geostatistics to groundwater contamination. The study was divided into two complementary aspects of geostatistics: estimation and simulation. The use of kriging and cokriging to estimate nitrate and the herbicide dimethyl tetrachloroterepthalate (DCPA) contaminant densities is described in Chapter I. Measured concentrations of nitrate and the DCPA were obtained for 42 wells in a shallow unconfined alluvial and basin-fill aquifer in a 16.5 km² agricultural area in eastern Oregon. The correlation coefficient between log(nitrate) and log(DCPA) was 0.74. Isotropic, spherical models were fitted to experimental direct- and cross-semivariograms with correlation ranges and sliding neighborhoods of 4 km. The relative gain for estimates obtained by cokriging ranged from 14 to 34%. Additional sample locations were selected for nitrate and DCPA using the fictitious point method. A simple economic analysis demonstrated that additional nitrate samples would be more beneficial in reducing estimation variances than additional DCPA samples, unless the costs of nitrate and DCPA analysis were identical. These estimates are by definition, the Best Linear Unbiased Estimates (i.e., the estimates with minimized estimation variance), however the requirement of minimized variance smoothes the variability of contaminant values. The application of conditional simulations to groundwater contamination is described in Chapter 11. Conditional simulation allows the degree of fluctuation of nitrate and DCPA between sample points to be assesed. With knowledge of both the 'best' estimates and the of the variability between sample points, nitrate and DCPA groundwater contamination in the study area can be characterized Based on the semivariogram models found in Chapter I, univariate and multivariate conditional simulations of nitrate and DCPA were generated using the turning bands method and the kriging or cokriging system. Kriging was used to condition the univariate simulations, while cokriging was used to cross-correlate and condition the multivariate simulations. The mean of 25 conditional and coconditional simulations at 8 different locations in the study area were generated and compared to kriging and cokriging estimates and 95% confidence intervals. Both conditional and coconditional simulation of the DCPA and nitrate contaminant densities showed large variations when values in different simulations were compared. The fluctuation in values demonstrate the uncertainties in the contaminant distributions when sample sizes are small. As a result of this unkown component, simulated values vary widely. Coconditional simulation displayed the cross-correlation imposed by using the cokriging system to condition the simulations. After 25 simulations, the mean remained unstable indicating that more simulations would be required to enable comparisons with kriging and cokriging estimates. / Graduation date: 1989

This study investigated the use of radon-222 as an in situ partitioning tracer for quantifying nonaqueous phase liquid (NAPL) saturations in the subsurface. Laboratory physical aquifer models (PAMs), field experiments, and numerical simulations were used to investigate radon partitioning in static (no-flow) experiments and in single-well, 'push-pull' tests conducted in non-contaminated and NAPL-contaminated aquifers. Laboratory push-pull tests in a wedge-shaped PAM and field push-pull tests in a NAPL-contaminated aquifer showed that radon was retarded in the presence of NAPL, with retardation manifested in increased dispersion of radon extraction phase breakthrough curves (BTCs). An approximate analytical solution to the governing transport equation and numerical simulations provided estimates of the radon retardation factor (R), which was used to calculate NAPL saturations (S[subscripts n]). Laboratory static and push-pull tests were conducted in a large-scale rectangular PAM before and after NAPL contamination, and after alcohol cosolvent flushing and pump-and-treat remediation. Radon concentrations in static tests were decreased due to partitioning after NAPL contamination and increased after remediation. Push-pull tests showed increased radon retardation after NAPL contamination; radon retardation generally decreased after remediation. Numerical simulations modeling radon as an injected or ex situ partitioning tracer were used to estimate retardation factors and resulted in overestimations of the likely S[subscripts n] in the PAM. Radon partitioning was sensitive to changes in S[subscripts n] in both static and push-pull tests. However, the test results were sensitive to test location, sample size, test design, and heterogeneity in S[subscripts n] distribution. Numerical simulations of hypothetical push-pull tests conducted in a NAPL-contaminated aquifer were used to investigate the influence of homogeneous and heterogeneous S[subscripts n] distributions and initial radon concentrations on radon BTCs and resulting S[subscripts n] calculations. Both of these factors were found to affect radon BTC behavior. A revised method of plotting and interpreting radon BTCs combined with numerical simulations modeling radon as an in situ partitioning tracer (incorporating initial radon concentrations into the model as a function of S[subscripts n]) were used to re-analyze laboratory and field push-pull test BTCs. This method reduced the overestimation of calculated S[subscripts n] values from laboratory tests. / Graduation date: 2003

Radon-222 gas has unique properties allowing it to be used as an indicator for the presence of organic phase liquids in the saturated zone. It naturally occurs in soils. It is radioactive, making quantitative detection straight forward. A noble gas, it is chemically inert and does not react with aquifer media. Finally, radon has an affinity to concentrate in nonaqueous phase liquids. A proposed linear equilibrium partitioning model was tested by batch equilibration with the pore fluid to establish the deficit in aqueous radon concentrations that results from its partitioning into the residual saturation of the organic phase (Soltrol-220). Five sets of experiments were run on columns with 0.0, 1.0, 2.5, 5.0, and 8.0 percent residual soltrol fractions. The model was found to accurately represent the partitioning process. A one-dimensional physical model was run to see if the data from the partitioning experiments could be successfully applied to predict the aqueous radon concentrations in a more complex situation. The results indicate that radon-222 has great potential to be used as a means of detecting and quantifying the presence of residual organic phase liquids in the saturated zone. / Graduation date: 1995

A 4.87 hectare potato field at St. Leonard d'Aston, Quebec was instrumented to measure surface runoff and tile drain flow over the 2 year growing season period, 1989-1990. The soil type was a Ste. Jude sandy loam. Several soil and water parameters and NPK concentrations in runoff were measured. The CREAMS (Chemicals, Runoff and Erosion from Agricultural Management Systems) computer simulation model was validated for the study site. / Observed N concentrations in tile drain flow exceeded the Canadian water quality guideline of 10 mg/L. Observed P concentrations were less than 0.01 mg/L; and K concentrations, for the most part, exceeded 10 mg/L. / CREAMS overpredicted event surface runoff depths, and underpredicted event percolation depths. However, total monthly surface runoff and percolation depths closely matched observed values. / CREAMS overpredicted event nitrate concentrations in tile drain flow. There was a poor match between predicted and observed event nitrate concentrations in tile drain flow (coefficient of predictability, CP$ sb{ rm A}$ = 104.95). However, predicted total monthly nitrate load closely matched observed values (CP$ sb{ rm A}$ = 0.84). Total monthly and seasonal nitrate loads in tile drain flow were underpredicted.

No description available.

Indiana University-Purdue University Indianapolis (IUPUI) / Groundwater monitoring networks are subject to change by budgetary actions and stakeholder initiatives that result in wells being abandoned or added. A strategy for network design is presented that addresses the latter situation. It was developed in response to consensus in the state of Indiana that additional monitoring wells are needed to effectively characterize water availability in aquifer systems throughout the state. The strategic methodology has two primary objectives that guide decision making for new installations: (1) purposive sampling of a diversity of environmental variables having relevance to groundwater recharge, and (2) spatial optimization by means of maximizing geographic distances that separate monitoring wells. Design objectives are integrated in a discrete facility location model known as the p-median problem, and solved to optimality using a mathematical programming package.