DNAPL RESEARCH RELEVANT TO CAMBRIDGE

Removal of or destruction of DNAPL (dense non aqueous phase liquid) in Bedrock is most difficult. The limestone and dolostone Bedrock in Waterloo Region is interspersed with both vertical and horizantal fractures. The issues at both the Middleton wellfield as well as the Bishop St. community are primarily due to the release of chlorinated solvents, which are one particular class of DNAPLS. Unlike creosotes, coal tar and PCB's; chlorinated solvents are generally less viscous meaning they flow more easily and quickly. They are also often denser. These two characteriastics tend to make them flow further deeper and much more quickly. Also their low viscosity helps them move through finer apertures and cracks in both overburden (sand, gravel, clay) as well as in the Bedrock.

Releases of Trichloroethylene and Trichloroethane at Rozell (GE) and Northstar have had horrendous consequences for nearby residents. These DNAPL chemicals have high vapour pressures and change from liquids into vapour in the very shallow unsaturated soil. Residual DNAPL above the water table actually breaks down into a vapour faster than DNAPL below the water table dissolves into groundwater. What I have found difficult to understand is the vapour phase of TCE (trichloroethylene) hundreds of yards downgradient from Bishop St. in the direction of the Grand River. It is my theory that TCE especially has gravity flowed through preferential pathways hundreds of yards from Bishop St. and the most likely preferential pathways would be the gravel bedding that storm sewers draining towards the Grand River are sitting in. This TCE then volatilizes into vapours along the way and migrates up and into basements and other structures.

Meanwhile back at the Middleton wells and their neighbour Canadian General Tower I have found the excuses of their consultants unconvincing. One of these excuses is that TCE is found dissolved in the groundwater at the Middleton wells in higher concentrations than at C.G.T.; therefore they claim that C.G.T. can not be the source. This is nonsense as the dense and very mobile free phase (ie. DNAPL) TCE has flowed downwards long ago and entered the Bedrock and further migrated towards the wellfield. At that point it is probably sitting as a pooled DNAPL in horizantal fractures and slowly dissolving into the groundwater. Meanwhile back at C.G.T. the shallower residual DNAPL has slowly dissolved in the shallow groundwater and discharged into the Grand River. Keep in mind that while contaminant plumes in sand and gravel aquifers are reasonably predictable in their flow direction and concentrations, contaminant flow directions in fractured Bedrock are notoriously difficult to predict. The cracks, fractures and apertures are not predictable.

It is of zero relief or help to affected citizens to know that firstly only DNAPL above the water table is turning into vapours and invading their homes. Similarily it is of zero benefit to know that this DNAPL breaks down faster above the water table than below. I have absolutely no idea how long it takes for these vapours then to naturally exit the shallow overburden although I would guess decades or longer. Additional problems exist with the TCE and TCA (trichloroethane) which enters the Bedrock. The welcoming fractures can be hundreds of metres deep and much wider than required to permit entry of chlorinated solvents including TCE and TCA. In fact TCE is one of the worst chlorinated solvents in Bedrock as it is very dense and very thin and mobile. It is my belief that with or without ISCO (in site chemical oxidation) the TCE will exist in the Bedrock for centuries or longer at both Bishop St. and the Middleton wellfield.

Getting back to ISCO which is being used at the Bishop St. disaster; it is my understanding that these injected chemicals oxidize or break down the TCE and TCA into water and carbon dioxide. In other words they separate the chlorine atoms from the hydrocarbons . Although this is definitely of long term benefit to the groundwater I see little or no benefit whatsoever to the removal or reduction of the vapour phase above the water table. Hence the backyard garden sheds pumping out the vapors from around basements must continue indefinitely. Indefinitely I suspect as stated earlier may be for decades.

This above information while specifically relevant to Cambridge also has some bearing on Elmira. Yes our Bedrock has about 100 feet or more of overburden soils, sands, gravels and clays above it. That being said our polluters are also world class and our Bedrock Aquifer is contaminated although not to the extent that Cambridge is. Here in Elmira although to a lesser extent than Cambridge; we have also managed to dump, spill and bury TCE and TCA. There must be vapour phase contamination in buildings on the Uniroyal/Chemtura site and I also wonder about buildings on and nearby Varnicolor Chemical. Probably tomorrow I will give some further details as to DNAPL behaviour and migration in overburden soils in Elmira versus in Bedrock.