Special Bd. of Aldermen — 10/26/15 Page 10
Ms. Taylor That capped area would be basically open space for anybody that was living there if there was
such a development that could be walked on and used for open space. There wouldn't be any structures that
would be built on that.
Mr. Santos And | just wanted to reiterate that the pictures of the sludge and the movement of this material,
Gerardo had the list of chemicals, the one that by far is the contaminant of concern in terms of the most mass
out there is chromium which is a metal and it is chromium II|, Hexavalent chromium or Chromium 6, is very
toxic and you don’t see that out here. It is Trivalent Chromium, Chrom Ill, low toxicity and there are monitoring
wells within 5 feet of the sludge that don’t have concentrations of chromium above the state standard.
Ms. Taylor In groundwater.
Mr. Santos And again the sludge, as some folks know, the Beazer sites, the Copper site down on the
Merrimack where they have the creosote sludge that is actually migrating through the soil getting up into the
river and we talked about that at the last public meeting and this is a different scenario. They need a cutoff
wall out there, a slurry wall to stop that. We essentially are putting this here to buttress the material that is
there and protect it against floods in the future. The added benefit is it will be impermeable, but that is almost a
secondary.
Ms. Taylor And also just to note that the groundwater flows from up here down to the river, that is typically how
groundwater flows. So | know there were some people in the past that were concerned about groundwater
contaminating their wells or anything like that. It would eventually go to the river, but if we are containing all
this then that material no longer goes to the river. As Darrin said we have monitoring wells right between where
the sludge is and the river, we are not seeing anything. So you know there really is not an issue with
groundwater; we would restrict it either through a town ordinance or groundwater management permit that the
state would issue to make sure nobody would drink the groundwater there. But since everybody is on City
water, there would be no reason for anybody to drink the water anyway.
Alderwoman Kelly
Thank you Mr. President. | actually wanted to know, Ms. Taylor you had said that it was probably more of a risk
to pull it away and contaminating the river during the process, versus the secant wall. | wonder if you could
just unpack that and explain why.
Ms. Taylor Yes sure. | think it is basically very similar to what Darrin was explaining whereas if you have a big
excavator in there you are having a huge hole essentially dug where it is very close to the river. Not only do
you have the river right there and the river bank but you actually have the City sewer system that is right there.
So if you are digging a huge hole right next to that, there’s a greater chance of collapse of not only the river
bank but the actual sewer line. Whereas if you are putting in these shafts, one at a time, there’s virtually no
way to have any of that collapse happen.
Alderman Jette
My concern is the material that is there. You talked about retaining walls around it to contain it. You seem to
hint that maybe you could explain further, what is going to stop it from going down, from the material going
down and into the river that way?
Ms. Taylor Sure. Well the cap that Gerardo explained will be an impermeable cap that is on the top of it. So
there wouldn’t be any infiltration going from say a rainfall event or anything through the cap into the sludge
after this was done. Right now, there is really nothing that is prohibiting that from happening and you are not
seeing any contaminated ground water 5 feet from where the sludge is. But with this, it would be like a geo-
synthetic liner that is essentially impermeable that would be covering all that material so you wouldn’t have any
leakage going inside.
