ACTON — One billion gallons of contaminated groundwater continues to spread from the W.R. Grace site through South Acton, with some of the highest contamination levels found under Bellantoni Drive, Knox Trail, Lexington Drive and Lisa Lane.

According to a map presented by the Acton Citizens for Environmental Safety (ACES) to the Board of Selectmen last week, other streets near the contaminated area include Drummer Road, Heritage Road, Independence Road, Laws Brook Road and Old Colony Lane.

Several of the town’s public water supply wells are also in the vicinity of the contaminated groundwater, including the School Street wells — Christofferson, Laws Brook, and Scribner, the latter of which is coming on line for the first time in two years — and Assabet 1 and 2.

Jane Ceraso, the environmental manager for the Acton Water District, said that the School Street wells have the best aeration system in town to reduce contaminants.

" If there was a contaminated plume of six hundred parts per billion, we could reduce it down to less than one part per billion, which is our standard for all volatile organic compounds [VOC]. So we’re okay regarding what our customers are going to get, " Ceraso said. " But we’re still concerned if there is a plume under the ground, and it’s still moving, and it seems to be going into some of the surface water bodies in the area. There are also people in the area who have private wells. "

At the selectmen’s meeting, ACES board member Mary Michelman encouraged the selectmen to look at prohibiting any new private wells within the affected site.

Michelman will be making a presentation to the Board of Health about changing some of the town’s regulations regarding private wells.

" Current health regulations do not even require VOC testing, so a homeowner or business would have no idea they might be using that water for drinking or irrigating their gardens or lawn, and that it might or might not be contaminated, " Michelman said.

Ceraso noted that the problem of contaminated water from private wells goes beyond the W.R. Grace site.

" I hate to say it, but it’s just Massachusetts. We’re pretty badly contaminated, " Ceraso said. " So it’s not just a Grace problem. We really need to protect the people who are drinking from private wells. I get a lot of calls from people with private wells that have contaminated water, and they don’t even know it. So we really need to have regulations that at least let people know that they should be testing for these things on some regular basis. "

As for the W.R. Grace site, the next step is for state and local officials and Grace representatives to agree on how the company will clean up the groundwater to a " fully usable " condition.

" Grace is definitely going to remediate. The question that exists right now is how much do they remediate, and down to what level are we going to hold them to, " Ceraso said. " The Water District feels pretty strongly that the water needs to be cleaned up. We’re anticipating that the definition of ‘fully usable’ that Grace proposes to us will be something that is less than we would like to see, so I think we need to be prepared to come back with a real strong request of them. "

W.R. Grace Co. is expected to present its interpretation of " fully usable " in a letter this month.

" I imagine it’ll probably be the lawyers that eventually work everything out, " Michelman said.

In June, W.R. Grace is expected to issue a report looking at the extent of the contamination on the site; the effectiveness of current remedial efforts; and possible technologies and approaches to utilize.

Other reports will look at risk assessments to the public health and to the environment and wildlife in the area. All of these reports will be available to the public.

After the reports are issued, there will likely be another public meeting in the fall about the Grace property, as there was a large turnout at a public meeting on the company and the contamination issue last November at the high school.

One remediation effort that has been successful so far is an Aquifer Restoration System that was constructed by Grace in 1984 for the southern part of the site.

ACES has been working on the cleanup of the site for 23 years.

The site has been used for industrial purposes since the 1800s. After purchasing the property in 1954, Grace’s manufacturing operations produced a variety of latex and rubber-based products and cellulose battery separators.