AVI has found that many physical and chemical parameters controlling contaminant fate and transport and cleanup are common to a wide range of sites. For example, soil permeability and its relationship to site stratigraphy is an important control to the rate and direction of contaminant migration, cleanup, and risk. Capillary soil properties are another lithologically controlled parameter that strongly influences immiscible phase and unsaturated fluid and vapor flow. Therefore, although every site is unique, there are similar conditions to be defined.

Based on this observation, AVI developed a menu of predefined scopes of work to measure and use these parameters to assess site closure strategies. The scopes are organized into three levels with fixed fees. As the levels increase, the scopes of work become more technically comprehensive and focussed on specific site closure objectives. AVI's fixed fee technical services help clients reliably plan their site closure programs while providing a flexible but controlled work scope. Additional work, if needed, can be added on to the previous level with a minimum of effort and cost.  It is interesting to note that AVI's effort levels (1992) are very analogous to the RBCA approach (1994, 1995), but were developed several years before the publication of the ASTM risk methodology.  This is the beauty of science; its underlying logic should lead people independently to the same conclusions.

Level I Tasks

Level I tasks provide the experienced client with specific hydrogeologic parameters derived from site testing using technically rigorous methods. The deliverable for a Level I task is a data and parameter summary. Hydrogeologic interpretations other than parameter derivation are left to the client. For example, a Level I aquifer test provides calculated transmissivity, storativity and other appropriate hydrogeologic parameters along with draw-down data and analyses. The report briefly describes field procedures but does not correlate the results of the test to the geologic environment.

AVI has found that Level I work is useful because of AVI's cost effectiveness in field procedures and computational analyses, as well as our technically rigorous methods. We can provide top quality hydrogeologic data at up to one-half the cost of most providers. However, because of the technical capabilities of AVI's hydrogeologic team, the best value of this service level may be the technical defensibility and rigor of the data and parameter derivations.

Level II Tasks

Level II tasks include the scope of Level I tasks, but further evaluate the hydrogeologic data to bracket key remediation, transport, risk, or site closure expectations. The evaluations assume that the bulk formation parameters (e.g., typical aquifer or SVE test hydraulic parameters) used are generally representative of site conditions.  Although anisotropy and simple geologic layering can be considered, refined evaluations of heterogeneity are not provided. Likewise, general contaminant properties might be considered, such as gasoline versus diesel, but site specific distributions of different compounds are not addressed quantitatively. Level II calculations provide an excellent physical basis to consider certain cleanup strategies or possible fate and transport or risk conditions.

For example, a Level II Soil Capillary Report includes the raw capillary characteristic parameters provided in a Level I report, but also includes calculation of specific hydrocarbon volume (volume per unit area), vertical saturation distribution, and hydrocarbon relative permeability. Calculations are based on the raw capillary data, free product thickness measurements provided by the client, and fluid properties taken from literature (Figures 1and 2). The Level II Soil Capillary Report provides technically founded free product saturation information unlike the erroneous free product thickness exaggeration calculations that have become an industry accepted standard. This information can be used by the client or lead consultant to estimate free product migration and recovery targets under various remedial strategies.

A second example, a Level II Soil Vapor Extraction (SVE) Test Report, includes the Level I field testing and reporting scope, but also provides a quantitative basis to evaluate the likely effectiveness of the method at a particular site. It provides analyses that can be used to determine cleanup well spacing as a function of cleanup time (Figure 3). The Level II SVE also provides engineering data necessary for full scale system design, such as total vapor flow from the well field and radius of cleanup. Note that the radius of clean up is very different from the industry standard radius of influence approach. The standard radius of influence approach is not based on vapor and chemical flux and cannot provide a time dependent analysis of remedial effectiveness or be used for wellfield design and optimization.

Level III Tasks

Level III tasks provide modeling analyses of chemical fate and transport and remedial strategies. These calculations can explicitly account for contaminant type and distribution and the effects of horizontal and vertical heterogeneity on contaminant transport and cleanup. These calculations can provide a basis for passive remedial closure (no action) when appropriate. For example, a Level III SVE Test Report can evaluate different cleanup scenarios at a site with a heterogeneous distribution of hydrocarbons and compare the results to risk-based goals (Figures 4-7). As seen in the figures, this type of well field optimization evaluation translates to cost savings by identifying the number of wells required to achieve time and contaminant concentration closure goals.

Because lithologic heterogeneity can be critical control factors in the fate and transport of contaminants, AVI has developed the capability to objectively record lithologic variability at existing cased monitor wells through electromagnetic surveying (Figure 8). This capability is particularly valuable at sites where subjective geologic logs have been recorded by several geologists. This method provides AVI with the ability to assign nonuniform hydrogeologic parameters across a site in a cost effective and technically defensible manner, but without intrusive drilling and soil sampling methods. This distribution is then used in quantitative evaluations.