Implementation Approach

This section describes the basic method RAAS uses to reach its objective. It relates

the workings of the software in a graphic manner and explains the nature of the user

interface. Depiction of an example "run" wiU help to reinforce these descriptions.

RAAS is developed using the object-oriented software development model (Bohn,

1991) In object-oriented programming, a decision problem is described in units that are

natural to the process (i.e. as objects). Each object has an identity described with data or

equations. The entire problem is thus defined as a set of objects that are linked together.

By passing messages among the objects, the program can represent the decision process as

time progresses. The critical concepts which make object-oriented analysis effective in

describing the remedy selection process are that objects may be arranged hierarchically and

inherit information from their parent object. In addition, specific instances of an object can

be created during program execution to depict the results of different processes (e.g.

instances that show the effects of different clean up technologies on a given waste matrix).

Objects allow modularity in development and facilitate integration of knowledge from

separate experts to emulate the real process~the CERCLA FS process.

Figure 5 shows the basic object-oriented structure used by RAAS to depict the

CERCLA technology screening process (Bohn, 1991). The "cell" object contains the

physical description of the media and the contaminant in that media. It interacts with the

"user interface" object to collect site information. The user interface also supplies

information to the "planner" and "preprocessor" objects in order to control the selection of

the technologies. The "planner" object represents the professional conducting the RI/FS.

The "planner" coordinates and tracks the screening of technologies that will effectively

clean up the site depicted in the "cell" object according to the general response action

(GRA) defined by the user.

Technologies

( Planner J^ X.

User Interface

I Pteiwocessor \

Figure 5. RAAS Object-Oriented Structure.

The GRA is a critical concept in the CERCLA process (EPA, 1988e). GRAs are

general treatment approaches. For example, for a petroleum-contaminated groundwater,

two typical general response actions might be applied. First, a collect-treat-dispose

scenario might be employed such as a pump-and-treat activated carbon system. Second, an

in-situ biological treatment approach might be implemented. GRAs are taken as user input

or can be applied from system defaults. The "preprocessor" object facilitates the

application of technologies which are unique to a particular GRA element (e.g. pumping is

used as the collection component of the GRA). In concert with the preprocessor, the

planner develops a sequence of technologies that solves the entire ti^atment objective

The heart of the technology screening phase of RAAS is the "technology" object.

Once the planner has an accurate representation of the existing conditions and has the user's

objectives for clean up in the form of a GRA, it systematically queries technologies to

develop viable treatment trains. The RAAS methodology uses two distinct processes to

accomplish this task (Pennock, 1991).

The first task is to determine the applicability of a particular technology. This is

shown in Figure 6 (Pennock, 1991). The technology object, which contains a series of

enabling and disabling conditions, is queried relative to the site conditions. Second, the

regulatory object is queried to determine if the technology is applicable in the given site

conditions. The inference object facilitates this rule-based analysis by accepting

knowledge, performing the inference and passing back the answer to the question. The net

result of this sub-system is to determine in a qualitative manner if a technology is

applicable. h Regulatory Object Inference Object Technology Object

IL

Figure 6. RAAS QuaUtative Evaluation for Applicability

The second task is to determine the effectiveness of a given technology in meeting

the clean up objective. Each technology is represented by a set of mass balance equations

which model before and after conditions at the site when a technology is applied (see

section III below). The model of each technology is a coarse numerical approximation

which facilitates screening. Figure 7 shows how the technology object interacts with other

objects to screen for effectiveness (Pennock, 1991). The contaminant, medium and

physical properties which might be encountered in a treatment process. The site object is a

temporary instance of the cell object which shows how the site is altered after one or a

series of technologies has been appUed. The site object tracks all of the critical parameters

so that the "planner" can determine if the technology is effective.

Medium Object Contaminant Object Reaction Object Technology

Figure 7. RAAS Qualitative Evaluation for Effectiveness.

As an example of the RAAS methodology, consider again the petroleum-

contaminated soil. In the initial interaction with the user, the system would query for the

principle contaminants (e.g. benzene or toluene) and the concentration of these

contaminants based on field tests. Additional physical parameters such as soil type and

hydraulic conductivity would also be elicited from the user. Next the GRA would be

determined. For simplicity, assume that the user required that an in-situ bioremediation

scenario be implemented.

In-situ bioremediation requires the ability to place biological agents into the soil and

to provide them nutrients. The GRA might thus be described by two sub-components:

injection and bioremediation. See Figure 8 for a graphic a representation of the process. In

this scenario, the planner would first query the technology object database to select an

injection technology and then query to select a bioremediation technology.

(I)nject (Dreat /\eiobi\ AnaerobK I-l 1-2 Injection Technology List Subobjective T- 1 T-2 T-3 Treatment Technolgy List Final Objective

I I = Feasible Technology ^^ = Infeasible Technology

(I-l)-(T-l)-(T-3) a-l)-(T-2)-(T-5) (I-l)-(T-2)-(T-6)

= Potential Treatment Trains

I

Figure 8. RAAS Technology Screening Process.

Consider the bioremediation technology screening. First assume that two potential

technologies are available: aerobic and anaerobic bioremediation. When the planner

invoked the aerobic treatment, the applicability determination would be made first. Then if

found applicable, the technology object would run the mass balance model for aerobic

bioremediation and compare the residuals to the constraints of the program and those

supplied by the user. If found effective, the planner would link the technology with a

successful injection technology to create a complete treatment train. The resultant treatment

train and any others that are screened as both applicable and effective would be submitted to

the user for further evaluation. Figure 8 shows a result which includes three potential

treatment trains. Each uses the same injection technique but two use aerobic and one uses

anaerobic biodegradation. The user could then interact with RAAS to examine the decision

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