By Fred Contrada
fcontrada@repub.com

The new environmental technology essentially flushes contamination out of the soil.

NORTHAMPTON - With hungry bacteria and reusable carbon filters, an engineering company is slowly but surely removing a massive plume of gasoline from beneath a busy section of Pleasant Street.

Traffic and business activity haven't had to skip a beat as Penney Engineering, of Mansfield, cleans up the contamination using the latest environmental technology.

The $240,000 project is financed by a $200,000 grant from the federal Environmental Protection Agency and $40,000 from the city, half of which was furnished by a matching state grant.

The contamination was created by gasoline that leaked from underground storage tanks belonging to the former Staab Gas Station. The gas station encompassed the area where Pleasant Street now lies near its intersection with Conz Street, along with land on both sides of the street.

In 1952, the Massachusetts Highway Department acquired part of the Staab property to build Route 5, which coincides with Pleasant Street in that location. The gas station closed in the 1980s and the rest of the property was sold to new owners on either side of the road. Pleasant Journey, a used car business, is located at 459 Pleasant St. A complex that includes Pro Lube Auto Center and Pleasant Street Car Wash is on the other side of the street.

Although the contamination was discovered in 1988, the soil could not be excavated because of the disruption it would create on and around Pleasant Street. With the aid of Penney Engineering, however, the city has found a way to clean the 3,000-square-foot plume without digging up the pavement.

Ralph P. Penney, the company's owner, said he uses a state-of-the-art carbon filtering technique that extracts tiny droplets of gasoline trapped in the soil by vaporizing them. The vapor is then condensed back into liquid in a trailer on site and the filters are cleaned and reused.

As Penney explained it, the gasoline rides up and down with the water table some 10 or more feet underground, creating a "smear zone" of dirty soil. The carbon absorbs the gas in this zone.

In a parallel phase, contaminated groundwater is pumped into a system where it is cleaned, aerated and injected with nutrients that promote the growth of gas-eating bacteria. The water is then reintroduced up-grade from the plume and essentially flushes out the contamination as it moves downhill.

The company set up operations last week, digging trenches on both sides of Pleasant Street and tearing up the pavement in front of Pleasant Street Car Wash. Although the car wash has closed temporarily, business has continued as usual next door at Pro Lube.

"It hasn't hurt business a bit," said owner John Richi.

Penney said the parking lot will be repaved next week and the system will continue operating underground for about two years until the contamination is completely cleaned up.