Summary of Services

Environmental Evaluation Services (EES) provides technical expertise in support of regulatory, public policy, and litigation issues associated with radioactive and chemical contaminants released to ecosystems, human health and ecological risk assessments, physical disturbances as they affect contaminant transport, remediation of disturbed areas to mitigate contaminant transport, and application of water balance concepts to stabilize landfill and other disturbed sites.

Risk Based Decision Making

The management of risks associated with radioactive and hazardous wastes is one of the major technical, regulatory, and socioeconomic challenges facing society in the coming decades. Projected costs of several hundred billion dollars for cleanup of federal facilities and industry compliance with more restrictive Federal and State environmental regulations dictate that selection of sampling priorities and approaches as well as selection of remediation alternatives be driven by actual rather than perceived risks. This ensures that money is not wasted on actions that provide no added benefit in protecting human health and the environment. Appropriate risk management decisions will rely on credible risk assessment procedures that incorporate our best science and judgment in a format that can be understood and accepted by the general public.

As shown by the diagram below, EES interfaces science and policy through the risk assessment process by integrating scientific information with regulatory and socioeconomic factors that affect the risk management decision. EES uses technical information on the principal components (physical and biological) and functional processes (rates of material and energy flow) that define the relevant ecosystem. EES also uses data on the kinds, amounts, and distribution of stressors present (radioactive and chemical contaminants, and physical / biological disturbances). Both sources of information are integrated using ecological and contaminant transport models to estimate risks to humans and ecosystems.

Developing risk assessment procedures at the beginning of the restoration program creates an iterative framework that allows stakeholders to use pertinent existing data, identify information gaps, target future information needs and evaluate the effects and economic costs of various risk management alternatives.

A technically sound methodology contributes to the development of consistently high quality assessments and scientifically-based regulatory standards. Such an approach also facilitates selection of appropriate and timely remediation strategies which prove both cost effective and acceptable to the public.

Water Balance Concepts for Site Remediation

Covers for radioactive, hazardous, and sanitary waste landfills are mandated by most states and the U.S. Environmental Protection Agency to reduce the potential for transport of buried contaminants into biological pathways. EPA's performance objectives for landfill covers require designs that reduce erosion and downward percolation of water and contaminants to acceptable levels. A range of cover designs representing various complexities and costs have been proposed for landfill closures. Those designs range from multi-layered engineered barriers, such as EPA's clay cap designs, to simple vegetated soil caps that rely primarily on evapotranspiration to manage site water balance. Alternative cap designs are acceptable for hazardous waste and sanitary landfill closures.

There has been renewed interest in vegetated soil caps as an alternative for landfill closures because modeling studies and limited experimental data suggest that they can be effective in controlling site water balance, particularly in arid and semiarid locations. Additionally, vegetated soil caps can be very cost effective compared to more complex, multi-layered designs. In order to fully exploit the potential of soil cap designs for landfill closures, experimental data are needed for a variety of climatic and waste site conditions to evaluate the effect of soil type, soil depth, surface management practice, and vegetation type on site water balance.

EES has conducted a 4-year field study of vegetated soil caps to evaluate the influence of various combinations of vegetation species and gravel covers on runoff, erosion, and soil moisture. The soil cap used in this demonstration simulated a design commonly used at Department of Energy National Laboratories prior to 1990 in that it consisted of a single layer of soil and no engineered barriers.

The demonstration used four treatments as follows: 1) a grass cover; 2) a grass cover with a gravel mulch; 3) a grass and ponderosa pine tree cover; and 4) a grass, ponderosa pine tree and gravel mulch cover. A gravel mulch (~2 cm diameter crushed rock applied 2 cm thick to the ground surface) was used in this demonstration. Previous demonstration by EES, LLC and others have shown that gravel mulches increase plant available soil moisture, herbage yield, and decrease soil erosion.

The results of this EES study (see soil moisture data in following Figure) shows that the types of vegetation cover and surface management practice can affect the hydrologic response of an evapotranspiration waste site cover. The addition of complexity to the vegetation cover by supplementing a grass cover with evergreen trees and/or a gravel mulch reduced erosion and the potential for deep percolation (by as much as 100%). The mechanisms for these decreases include a decoupling of erosion from runoff by protecting the soil surface from impacting raindrops and by enhanced removal of soil moisture through increase biomass production and evapotranspiration.

The feedback between plant and surface cover and soil moisture has important ramifications for strategies of managing water in landfills. EES has shown that the type of vegetation cover with and without a gravel mulch can greatly influence soil moisture status and the potential for deep percolation. EES has also shown that gravel mulches not only control erosion from the cover but that they also markedly reduce the potential for percolation due to the feedback between soil moisture and plant production.

The concepts embodied in the evapotranspiration cover have application to any surface stabilization problem where the potential for deep percolation and contaminants associated with soil moisture exists. EES is uniquely qualified to assist in developing evapotranspiration covers for stabilizing waste sites and in surface reclamation of mine tailings and spoils. We can model such systems and assist in the installation and monitoring of field scale applications. Evapotranspiration covers offer cost effective, long term solutions to site stabilization problem.