In Situ Remediation of a 1km PCE Plume in Finland

We are ‘in the woods’ as they say here in Finland, in Mukko. Lappeenranta, in the South of Finand, carrying out an in situ remediation of chlorinated solvent contaminated groundwater. This is a part of a Government driven project, which consists of 4 different cases in Finland that are all contaminated by chlorinated solvents.

Nordic Envicon Finland is the main Contractor here, and we use REGENESIS technology and their design and chemicals, and RGS Nordic from Sweden is doing the injection work. We are three companies doing the work together and I am project leader of the whole case. So actually, we have 3 cases now in Finland going on.”

The legacy contamination found at Mukko, Lappeenranta, was caused by the historic activities of a former metal processing facility in the 1990s, where occasional spills and leakages resulted in the contamination of the soils and groundwater with PCE of up to 1500 ug/l.

Mikko Kotro, Nordic Envicon: “ How this was found, this contamination, was that we have 1 kilometre from the source area there is a water abstraction well for the municipal water supply. And there was found some PCE in couple of micrograms.”

After upto 5ug/L PCE was detected in the abstraction well  a series of site investigations were undertaken by environmental consultants Pöyry, and later Ramboll. It was found that the local geology consists of a glacial formation with a series of valleys, which channels the groundwater flow, resulting in a flow rate 2,000m/yr.

Jack Shore (REGENESIS): “This site is unusual in that we are dealing with a kilometre long PCE plume that is only about 20 meters wide. Now that’s unusual because you would normally expect some daughter products being produced as that PCE is broken down in the groundwater. But that’s not happening here because we are dealing with an incredibly fast flowing, highly aerobic, aquifer, that is preventing the degradation of PCE. To overcome this challenge, we decided to deploy an integrated treatment strategy. “

RGS Nordic and REGENESIS first worked together to develop the design. The results is a two-pronged approach:  ERD in the source area to achieve a significant contaminant mass reduction, and in situ sorption and enhanced biodegradation in the plume area, to protect the drinking water abstraction well. The source treatment was carried out in Autumn: REGENESIS electron donor 3-D Microemulsion (3DMe) together with BDI Plus, our bioaugmentation technology, were injected to stimulate and enhance the Reductive Dechlorination process.

Ulf Brännholm, RGS Nordic: “We started to inject between 7 and 13 meters below ground level, and we injected 3DMe and BDI. It went very well. We injected about 8,000 L per point.“

Now it is spring and the 2nd phase of the works are being carried out: the injection of PlumeStop colloidal activated carbon in a barrier formation, together with HRC: a high viscosity, low volume electron donor.  We’re injecting this in the plume area, around 700m downgradient from the source zone.

Jack Shore (REGENESIS): “ This Plumestop barrier is a liquid activated carbon that is being installed to mitigate against the further off-site migration of PCE impacting a municipal drinking water well. “

Access to this injection location was not easy because immediately beyond the source area is a dual carriage way and railway line, followed by a dense forest.  A new road and side road had to be constructed in the forest to provide access for the works. The weather conditions added another challenge.

Ulf Brännholm (RGS Nordic): “One of the challenges in this area was the snow. You see, there is snow still.  but now it’s warm and it’s melting very good. And it’s going very good to inject for the moment. The injection area is approximately 50meters, it is 15 points we’re going to inject. We are injecting between 13 and 20m below ground.“

By overcoming the site and weather conditions, good progress has been made on site.

Mikko Kotro (Nordic Envicon): “We’re expecting it to take up at least a month, maybe a month and a half and then start the monitoring process which means that we are taking groundwater samples, let’s say every 3 to 4 months. And after a couple of years, 2 to 3 years, we expect the results to be as expected. (The goal is to protect the abstraction well (and) there is no set limit values for the concentrations but there’s a goal to (minimise the concentrations, and) lower the concentrations at least 60 to 80%. )”

This site may prove a useful template for other legacy sites with fast flowing aquifers in Finland, contaminated with chlorinated solvents at depth.