EPA On-line Tools for Site Assessment Calculation

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Do you agree with the contouring?

In the tank pit there is a well with a ground water elevation of 90 feet. This well isn't included on the 90 foot ground water contour. This well might be influenced by increased infiltration in the tank pit area, something that is commonly observed. Rather than bend the contour lines around this well, it would be more representative to omit this well from contouring.
The revised contour map shows contour lines for 90.0 ft, 89.8 ft and 89.6 ft. The contours are straight lines, because they fit the observed data and, once the 90 foot level from the tank pit was omitted, there were no data to support the curvature of the lines.
Which way do you expect the contaminants to move?

The water levels, and contours, indicate that the flow is from top to bottom--to the southwest.
Are the wells located so that the plume would be delineated?

There is no data under the roads, so the contour was rightly drawn with question marks. But with the flow going in the direction indicated by the arrows, it's clear that there is no well directly downgradient from the tank pit. Contaminants moving in this direction will be missed. The chemicals may have already reached beyond the area indicated on the map.

How far do the contaminants extend from the tank pit?

Because the wells are not located to capture the downgradient movement of the contaminant, the extent of contamination is not known.

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