Diel variations in stream chemistry and isotopic composition of dissolved inorganic carbon,upper Clark Fork River,Montana, USA     

Stephen R. Parker  Christopher H. Gammons  Simon R. Poulson  Michael D. DeGrandpre 《Applied Geochemistry》2007

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Cost Optimization of DNAPL Remediation at Dover Air Force Base Site     

Jonghyun Lee  Xiaoyi Liu  Peter K. Kitanidis  Ungtae Kim  Jack Parker  Aleisa Bloom  Robert Lyon 《Ground Water Monitoring & Remediation》2012,32(2):48-56

This study investigates stochastic optimization of dense nonaqueous phase liquid (DNAPL) remediation design at Dover Air Force Base Area 5 using emulsified vegetable oil (EVO) injection. The Stochastic Cost Optimization Toolkit (SCOToolkit) is used for the study, which couples semianalytical DNAPL source depletion and transport models with parameter estimation, error propagation, and stochastic optimization modules that can consider multiple sources and remediation strategies. Model parameters are calibrated to field data conditions on prior estimates of parameters and their uncertainty. Monte Carlo simulations are then performed to identify optimal remediation decisions that minimize the expected net present value (NPV) cleanup cost while maintaining concentrations at compliance wells under the maximum contaminant level (MCL). The results show that annual operating costs could be reduced by approximately 50% by implementing the identified optimal remediation strategy. We also show that recalibration and reoptimization after 50 years using additional monitoring data could lead to a further 60% reduction in annual operating cost increases the reliability of the proposed remediation actions.  相似文献   

The Effect of Bottle Fill Rate and Pour Technique on the Recovery of Volatile Organics     

Louise Parker  Sanford Britt 《Ground Water Monitoring & Remediation》2012,32(4):78-86

This field study was conducted to examine whether the method or the flow rate (fill rate) used to fill a sample vial affects recovery of volatile organics (VOCs). To our knowledge, there have not been any systematic studies that have examined this issue. For this field study, three fill rates (50 mL/min, 250 mL/min, and ~1 L/min) and three filling methods (top‐pour, side‐pour, and bottom‐fill) were used to fill sample vials. We found that the bottom‐fill method, with the tubing submerged in the sample as it fills, yielded the greatest recovery (i.e., highest concentrations) of VOCs. Little improvement was observed by pouring down the side of a vial vs. simply pouring straight down from the top. We also found that filling the vials at the fastest fill rate (~1 L/min) yielded higher recovery than the slowest fill rate (50 mL/min) using all three filling methods. These results are counter to prevailing guidance and conventional wisdom that slower filling is preferable to faster filling and that pouring down the side of a sample vial is the best practice for VOC sampling. However, because we were unable to randomize the order the samples were collected with respect to fill rate, we recommend a follow‐on study be conducted that will allow us to confirm our findings and better determine which fill rates minimize losses of VOCs  相似文献   

A spreadsheet program for two-well tracer test data analysis     

Tang G  Watson DB  Parker JC  Brooks SC 《Ground water》2012,50(4):614-620

Two-well tracer tests are often conducted to investigate subsurface solute transport in the field. Analyzing breakthrough curves in extraction and monitoring wells using numerical methods is nontrivial due to highly nonuniform flow conditions. We extended approximate analytical solutions for the advection-dispersion equation for an injection-extraction well doublet in a homogeneous confined aquifer under steady-state flow conditions for equal injection and extraction rates with no transverse dispersion and negligible ambient flow, and implemented the solutions in Microsoft Excel using Visual Basic for Application (VBA). Functions were implemented to calculate concentrations in extraction and monitoring wells at any location due to a step or pulse injection. Type curves for a step injection were compared with those calculated by numerically integrating the solution for a pulse injection. The results from the two approaches are similar when the dispersivity is small. As the dispersivity increases, the latter was found to be more accurate but requires more computing time. The code was verified by comparing the results with published-type curves and applied to analyze data from the literature. The method can be used as a first approximation for two-well tracer test design and data analysis, and to check accuracy of numerical solutions. The code and example files are publicly available.  相似文献   

Elevated ammonium concentrations from wastewater discharge depress primary productivity in the Sacramento River and the Northern San Francisco Estuary     

Parker AE  Dugdale RC  Wilkerson FP 《Marine pollution bulletin》2012,64(3):574-586

Primary production in the Northern San Francisco Estuary (SFE) has been declining despite heavy loading of anthropogenic nutrients. The inorganic nitrogen (N) loading comes primarily from municipal wastewater treatment plant (WTP) discharge as ammonium (NH(4)). This study investigated the consequences for river and estuarine phytoplankton of the daily discharge of 15 metric tons NH(4)-N into the Sacramento River that feeds the SFE. Consistent patterns of nutrients and phytoplankton responses were observed during two 150-km transects made in spring 2009. Phytoplankton N productivity shifted from NO(3) use upstream of the WTP to productivity based entirely upon NH(4) downstream. Phytoplankton NH(4) uptake declined downstream of the WTP as NH(4) concentrations increased, suggesting NH(4) inhibition. The reduced total N uptake downstream of the WTP was accompanied by a 60% decline in primary production. These findings indicate that increased anthropogenic NH(4) may decrease estuarine primary production and increase export of NH(4) to the coastal ocean.  相似文献   

Web Services for Dynamic Coloring of UAVSAR Images     

Jun Wang  Marlon Pierce  Andrea Donnellan  Jay Parker 《Pure and Applied Geophysics》2015,172(8):2325-2332

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Characterization and Source History Modeling Using Low‐k Zone Profiles at Two Source Areas          下载免费PDF全文

David T. Adamson  Steven W. Chapman  Shahla K. Farhat  Beth L. Parker  Phillip deBlanc  Charles J. Newell 《Ground Water Monitoring & Remediation》2015,35(2):52-69

Like tree rings, high‐resolution soil sampling of low‐permeability (low‐k) zones can be used to evaluate the style of source history at contaminated sites (i.e., historical pattern of concentration and composition vs. time since releases occurred at the interface with the low‐k zone). This is valuable for the development of conceptual site model (CSM) and can serve as an important line of evidence supporting monitored natural attenuation (MNA) as a long‐term remedy. Source histories were successfully reconstructed at two sites at Naval Air Station Jacksonville using a simple one‐dimensional (1D) model. The plume arrival time and historical composition were reconstructed from the time initial releases that were suspected to occur decades earlier. At the first site (Building 106), the source reconstructions showed relatively constant source concentrations, but significant attenuation over time in the downgradient plume in the transmissive zone, suggesting MNA may not be an appropriate remedy if source control is a requirement, but attenuation processes are clearly helping to maintain plume stability and reduce risk. At the second site (Building 780), source concentrations in the transmissive zone showed an approximately a one order of magnitude over time, but apparently less attenuation in the downgradient plume. The source reconstruction method appeared to reflect site remediation efforts (excavation, soil vapor extraction) implemented in the 1990s. Finally, a detailed analysis using molecular biological tools, carbon isotopes, and by‐products suggests that most degradation activity is associated with high‐k zones but not with low‐k zones at these source areas. Overall, the source reconstruction methodology provided insight into historical concentration trends not obtainable otherwise given the limited long‐term monitoring data.  相似文献   

A model study of tide- and wind-induced mixing in the Columbia River Estuary and plume     

Parker MacCready  Neil S. Banas  Barbara M. Hickey  Edward P. Dever  Yonggang Liu 《Continental Shelf Research》2009

A numerical simulation of circulation in the Columbia River estuary and plume during the summer of 2004 is used to explore the mixing involved as river water is transformed into shelf water. The model is forced with realistic river flow, tides, wind stress, surface heat flux, and ocean boundary conditions. Simulated currents and water properties on the shelf near the mouth are compared with records from three moorings (all in 72 m of water) and five CTD sections. The model is found to have reasonable skill; statistically significant correlations between observed and modeled surface currents, temperature, and salinity are all 0.42–0.72 for the mooring records. Equations for the tidally averaged, volume-integrated mechanical energy budget (kinetic and potential) are derived, with attention to the effects of: (i) Reynolds averaging, (ii) a time varying volume due to the free surface, and (iii) dissipation very close to the bottom. It is found that convergence of tidal pressure work is the most important forcing term in the estuary. In the far field plume (which has a volume 15 times greater than that of the estuary), the net forcing is weaker than that in the estuary, and may be due to either tidal currents or wind stress depending on the time period considered. These forcings lead to irreversible mixing of the stratification (buoyancy flux) that turns river water into shelf water. This occurs in both the plume and estuary, but appears to be more efficient (17% vs. 5%), and somewhat greater (4.2 MW vs. 3.3 MW), in plume vs. estuary. This demonstrates the importance of both wind and tidal forcing to watermass transformation, and the need to consider the estuary and plume as part of a single system.  相似文献   

Nitrogen mineralization across an atmospheric nitrogen deposition gradient in Southern California deserts     

L.E. Rao  D.R. Parker  A. Bytnerowicz  E.B. Allen 《Journal of Arid Environments》2009,73(10):920-930

Dry nitrogen deposition is common in arid ecosystems near urban and agricultural centers, yet its impacts on natural environments are relatively understudied. We examined the effects of N deposition on soil N mineralization across a depositional gradient at Joshua Tree National Park. We hypothesized that N deposition affects N mineralization by promoting exotic grass invasion and increasing soil carbon and nitrogen. These relationships were tested through a laboratory incubation on soils collected from sixteen sites where atmospheric N, soil characteristics, and annual vegetation were measured. Mineralization parameters modeled using the Gompertz model were compared to soil C, soil N, estimated soil N from deposition, and percent cover of exotic and native annuals. Calculated soil N from deposition was directly correlated with measured soil C and N and decreasing C:N ratios, which were associated with increased total amounts of mineralized N. However, no effects of soil C or N, and thus N deposition, were observed on mineralization rates. Exotic grasses, but not native forbs or total annual cover, increased with soil C, soil N, and total mineralized N, suggesting that exotic grasses and N deposition are correlated and associated with increasing total C and N in the interspace soils at polluted locations.  相似文献   

A Forward Modeling Approach for Interpreting Impeller Flow Logs     

by Alison H. Parker  L. Jared West  Noelle E. Odling  Richard T. Bown 《Ground water》2010,48(1):79-91

A rigorous and practical approach for interpretation of impeller flow log data to determine vertical variations in hydraulic conductivity is presented and applied to two well logs from a Chalk aquifer in England. Impeller flow logging involves measuring vertical flow speed in a pumped well and using changes in flow with depth to infer the locations and magnitudes of inflows into the well. However, the measured flow logs are typically noisy, which leads to spurious hydraulic conductivity values where simplistic interpretation approaches are applied. In this study, a new method for interpretation is presented, which first defines a series of physical models for hydraulic conductivity variation with depth and then fits the models to the data, using a regression technique. Some of the models will be rejected as they are physically unrealistic. The best model is then selected from the remaining models using a maximum likelihood approach. This balances model complexity against fit, for example, using Akaike's Information Criterion.  相似文献