Using Multimedia Modeling to Expedite Site Characterization

GOAL, SCOPE AND BACKGROUND: This paper uses two case studies of U.S. Department of Energy nuclear weapons complex installations to illustrate the integration of expedited site characterization (ESC) and multimedia modeling in the remedial action decision making process. CONCEPTUAL SITE MODELS, MULTIMEDIA MODELS, AND EXPEDITED SITE CHARACTERIZATION: Conceptual site models outline assumptions about contaminates and the spatial/temporal distribution of potential receptors. Multimedia models simulate contaminant transport and fate through multiple environmental media, estimate potential human exposure via specific exposure pathways, and estimate the risk of cancer and non-cancer health outcomes. ESC relies on using monitoring data to quantify the key components of an initial conceptual site model that is modified iteratively using the multimedia model. CASE STUDIES: Two case studies are presented that used the ESC approach: Los Alamos National Laboratory (LANL) and Pantex. LANL released radionuclides, metals, and organic compounds, into canyons surrounding the facility. The Pantex Plant has past waste management operations which included burning chemical wastes in unlined pits, burying wastes in unlined landfills, and discharging plant wastewaters into on-site surface waters. CONCLUSIONS: The case studies indicate that using multimedia models with the ESC approach can inform assessors about what, where, and how much site characterization data needs to be collected to reduce the uncertainty associated with risk assessment. Lowering the degree of uncertainty reduces the time and cost associated with assessing potential risk and increases the confidence that decision makers have in the assessments performed.     

Evaluation of leachate composition by multivariate data analysis (MVDA)

Landfills generate emissions in the form of gas and leachate. The emissions are often measured within monitoring programmes. It is likely that the requirements of such monitoring programmes can be extended in the future, particularly in light of the increased interest in specific organic substances. Multivariate data analyses (MVDA) have been used to evaluate the possibility of predicting the content of specific organic substances from more common analyses. The results indicate that this is possible for a specific leachate. MVDA can also be used to reduce the number of analyses performed within existing monitoring programmes while retaining information about all the variables formerly included in the programmes.     

Evaluation of groundwater and soil pollution in a landfill area using electrical resistivity imaging survey

Landfills are sources of groundwater and soil pollution due to the production of leachate and its migration through refuse. This study was conducted in order to determine the extent of groundwater and soil pollution within and around the landfill of Seri Petaling located in the State of Selangor, Malaysia. The condition of nearby surface water was also determined. An electrical resistivity imaging survey was used to investigate the leachate production within the landfill. Groundwater geochemistry was carried out and chemical analysis of water samples was conducted upstream and downstream of the landfill. Surface water was also analyzed in order to determine its quality. Soil chemical analysis was performed on soil samples taken from different locations within and around the landfill in the vadose zone (unsaturated zone) and below the water table (in the soil saturated zone). The resistivity image along line L–L₁ indicated the presence of large zones of decomposed waste bodies saturated with highly conducting leachate. Analysis of trace elements indicated their presence in very low concentrations and did not reflect any sign of heavy metal pollution of ground and surface water or of soil. Major ions represented by Na, K, and Cl were found in anomalous concentrations in the groundwater of the downstream bore hole, where they are 99.1%, 99.2%, and 99.4%, respectively, higher compared to the upstream bore hole. Electrical conductivity (EC) was also found in anomalous concentration downstream. Ca and Mg ions represent the water hardness (which is comparatively high downstream). There is a general trend of pollution towards the downstream area. Sulfates (SO₄) and nitrates (NO₃) are found in the area in low concentrations, even below the WHO standards for drinking water, but are significantly higher in the surface water compared to the groundwater. Phosphate (PO₄) and nitrite (NO₂), although present in low levels, are significantly higher at the downstream. There is no significant difference in the amount of fluoride (F) in the different locations. In the soil vadose zone, heavy metals were found to be in their typical normal ranges and within the background concentrations. Soil exchangeable bases were significantly higher in the soil saturated zone compared to the vadose zone, and no significant difference was obtained in the levels of inorganic pollutants. With the exception of Cd, the concentration ranges of all trace elements (Cu, Zn, Cr, Pb, and Ni) of Seri Petaling landfill soils were below the upper limits of baseline concentrations published from different sources.     

GIS环境下大区域工程场地地震液化势的二维概率评价方法

用具有概率意义的饱和砂土抗液化强度经验公式来对大区域场地进行地震液化势二维概率评价;在GIS软件ArcGIS的支持下,将取样钻孔处的液化势评价结果等价于数字高程模型(Digital Elevation Model,DEM)中的高程,利用ArcGIS空间分析模块中的Kriging插值法估计大区域场地的地震液化范围。研究表明:将Kriging法应用于岩土工程地质特征的统计推断,有助于揭示勘探孔以外的地层信息,对于大区域场地地震液化范围的判别是一个较好的手段;利用ArcGIS空间分析模块中的Kriging法,通过已勘察点的信息(液化势)来估计未勘测点的土层液化势,能够较好地区划出场地地震液化势的空间分布特征。     

新疆油田抽汲排液污染控制研究

抽汲排液存在抽汲设备和工具密封性差,对井场环境污染比较严重的问题,为解决抽汲排液对井场造成的污染,分别对抽汲钢丝绳的选择、试油井口防喷盒的密封以及试油抽汲作业规程及其它方面作了研究和应用,使抽汲排液对井场造成的污染得到了较好控制,符合新疆油田创建"绿色油气田"的要求。     

基于PROMETHEEⅡ法的污染场地土壤修复技术筛选及应用

依据当前污染场地土壤修复技术特点以及场地特征,构建4层12指标21方案的污染土壤修复技术决策分析结构,运用多属性决策分析方法——PROMETHEEⅡ偏好排序法,对当前场地修复技术以及典型场地条件进行了客观分析和综合评价,实现基于具体修复目标的污染场地土壤修复技术择优筛选,并采用该方法对虚拟特定污染场地的土壤修复技术筛选进行了实例应用。这为污染场地的治理和修复提供了方法依据和理论参考。     

不同物质对垃圾渗滤液中腐殖酸的吸附研究

垃圾渗滤液是一种有毒有害的高浓度有机废水，其中含大量腐殖酸。腐殖酸具有离子交换能力、吸附能力和脱除杂质能力，因此在很多方面有实用价值。活性碳、土壤、堆肥对废水中的有机物有一定的吸附能力。本文采用正交设计的方法，研究了活性碳、土壤、堆肥在不同温度，液／固，腐殖酸初始浓度的条件下对垃圾渗滤液中腐殖酸的吸附效果。实验结果表明：四种实验因素对吸附剂的吸附能力的影响程度为：吸附剂类型〉腐殖酸的初始浓度〉吸附反应温度〉液固比。在温度为25℃，液固比为50／0．5（mL/g），腐殖酸初始浓度为41．99（mg／L），吸附剂类型为活性碳时，腐殖酸吸附量最大，为40．86mg。同时分析了响应指标随因素的变化趋势。     

生活垃圾填埋产沼的提取净化利用

垃圾填埋是目前我国各城市广为采用的垃圾处理方式，但垃圾填埋产沼以后对沼气的回收利用却不被人们所熟知和重视。由此造成了对可开发利用的二次能源的极大浪费，而沼气对周围环境也造成了严重的污染并对大气臭氧层造成了破坏。本文阐述了垃圾填埋产沼回收的必要性和经济性，对垃圾填埋产沼提取利用、制取汽车压缩气的可行性及工艺流程进行了分析和介绍。     

Effect of soil moisture dynamics on dense nonaqueous phase liquid (DNAPL) spill zone architecture in heterogeneous porous media

The amount, location, and form of NAPL in contaminated vadose zones are controlled by the spatial distribution of water saturation and soil permeability, the NAPL spill scenario, water infiltration events, and vapor transport. To evaluate the effects of these processes, we used the three-phase flow simulator STOMP, which includes a new permeability-liquid saturation-capillary pressure (k-S-P) constitutive model. This new constitutive model considers three NAPL forms: free, residual, and trapped. A 2-D vertical cross-section with five stratigraphic layers was assumed, and simulations were performed for seven cases. The conceptual model of the soil heterogeneity was based upon the stratigraphy at the Hanford carbon tetrachloride (CT) spill site. Some cases considered co-disposal of NAPL with large volumes of wastewater, as also occurred at the Hanford CT site. In these cases, the form and location of NAPL were most strongly influenced by high water discharge rates and NAPL evaporation to the atmosphere. In order to investigate the impact of heterogeneity, the hydraulic conductivity within the lower permeability layer was modeled as a realization of a random field having three different classes. For six extreme cases of 100 realizations, the CT mass that reached the water table varied by a factor of two, and was primarily controlled by the degree of lateral connectivity of the low conductivity class within the lowest permeability layer. The grid size at the top boundary had a dramatic impact on NAPL diffusive flux just after the spill event when the NAPL was present near the ground surface. NAPL evaporation with a fine grid spacing at the top boundary decreased CT mass that reached the water table by 74%, compared to the case with a coarse grid spacing, while barometric pumping had a marginal effect for the case of a continuous NAPL spill scenario considered in this work. For low water infiltration rate scenarios, the distribution of water content prior to a NAPL spill event decreased CT mass that reached the water table by 98% and had a significant impact on the formation of trapped NAPL. For all cases simulated, use of the new constitutive model that allows the formation of residual NAPL increased the amount of NAPL retained in the vadose zone. Density-driven advective gas flow from the ground surface controlled vapor migration in strongly anisotropic layers, causing NAPL mass flux to the lower layer to be reduced. These simulations indicate that consideration of the formation of residual and trapped NAPLs and dynamic boundary conditions (e.g., areas, rates, and periods of different NAPL and water discharge and fluctuations of atmospheric pressure) in the context of full three-phase flow are needed, especially for NAPL spill events at the ground surface. In addition, NAPL evaporation, density-driven gas advection, and NAPL vertical movement enhanced by water flow must be considered in order to predict NAPL distribution and migration in the vadose zone.