Wednesday, August 06, 2014
Wind Turbines And Groundwater Contamination In Ontario
Last week this warning appeared on Reddit Ontario, and later got picked up at Ontario Wind Resistance:
I've reproduced it below, but its long and a bit technical and if you don't want to read it all then: 1) there has been no contamination yet but there IS a pretty small but not zero chance that flooding, for example, could wash contaminated water down the sides of the utility poles used on the sites mentioned and get into the bedrock aquifer, and; 2) it should all be fixed by next month.
For the longer version, over to Mr. Tomlinson:
As for the posted “warning” you are referencing from reddit.com I can confirm that:
Relatively short answer:
MOECC has a concern relative to the construction methods for the utility poles on this particular project, and has had the proponent for the project, (Dufferin Wind Power), (DWP), modify the construction methods for a substantial number of the poles in the project to prevent surface water from potentially using the caissons, (in this case a 1 m diameter steel casing), that the poles are mounted in, (in the ground), from becoming a conduit into the relatively shallow limestone bedrock that contains the potable water aquifer for the area. In fairness to everyone involved I have a hard time calling the instillation of the various poles as incorrect as neither DWP, or DWP’s consultants or this Ministry, (MOEE), or the Ontario Energy Board, (OEB) who actually gave the approval for the utility pole line picked up that it could become a potential pathway for surface water entering a bedrock aquifer. This type of potential pathway is just not something that is on anybody’s radar until you actually see the instillation and understand the engineering of the system. Having said all that this could be considered as just splitting hairs as MOECC feels that remedial work is necessary.
In short is there a possibility that if the right circumstances come together at the same time that there could be a contamination pathway present? Yes, in some of the locations. Based on that MOECC has asked that remedial work be completed on what has become a substantial number of the poles in the project to prevent them from becoming a potential conduit. Is there, in the opinion of the Guelph District Office of the MOECC, an immediate potential for the contamination of all local wells in the area? No, however based on an abundance of caution it appears prudent to take action to prevent the utility poles in question from becoming a potential source of contamination for a limited number of nearby wells. The proponent, (DWP), was approached to take remedial action, proposed a plan which after some modification is currently being implemented with a target date for completion of 15 September, 2014.
Slightly longer answer with more of the technical issues addressed:
1) Possible conduit:
In order to keep the utility poles standing with the anticipated loads they will be taking the various contractors constructing them in Melancthon Township and to a lesser extent in Amaranth Township have been forced to put down caissons into the relatively shallow limestone bedrock - the caissons are backfilled outside and inside with crushed rock with the pole is inside the caisson. Given that the caissons are in most cases in Melancthon Township bedded into the relatively shallow bedrock, and that a variable number of the sites are subject to the accumulation of surface water in and around the bases of the poles; and this is an agricultural area there is a small but nonetheless actual potential for surface water to travel to and possibly into the fractured limestone bedrock. That scenario is certainly concerning to MOECC.
Once accepting that the potential is there for surface water to travel down the potential conduits, the issue is then will it cause a problem with, in this case, groundwater quality, (remembering that that primary source of potable water in that area is the aquifer contained in the relatively shallow limestone bedrock)? Once looking at the volumes of water involved, the amount of surface water that would be needed to travel down the caisson(s) would have to be extremely large to be able to adversely impact the quantities of water likely to be in the area in the aquifer. Having said all that, it is possible that it can happen, however looking at the construction details of the caissons, they are not particularly efficient pathways for large quantities of water.
3) What is being done:
After assessing the construction methodology of the utility pole bases and concluding that in a limited number of circumstances that the pole bases could cause a conduit for surface water down to or into the relatively shallow fractured limestone bedrock Dufferin Wind Power was approached by MOECC and asked to come up with a methodology and implementation plan to prevent the transmission of surface water down to and\or into the limestone bedrock formation in those potentially vulnerable locations. Dufferin Wind via it’s consultants Dillon Consulting proposed a plan whereby pole bases with a direct connection to or into the limestone bedrock, as well as those that have bases terminating within 2.5 m of the limestone bedrock will be sealed to prevent the transmission of surface water either through the caisson or along the outside of the caisson between it and the hole bored for it.
After discussions and modifications of the plan it has been accepted by MOECC and is now in the process of being implemented by Dufferin Wind and it’s contractors, (at this point none of the actual physical work has been started, however once the work commences it should be completed within a roughly 2 week period). The sealing program consists of the placement of a bentonite clay seal around the outside of the steel caisson to prevent surface water from traveling down the space between the outside of the hole and the caisson, as well as a bentonite clay seal being placed similarly inside the caisson to prevent surface water running down the inside of the caisson to the bedrock. Additionally the vulnerable pole locations will also have the local area around it sloped\landscaped such as to prevent the accumulation of surface water around the immediate area of the pole. All of the 216 poles in the project north of 89 Highway, (Melancthon Township), and 85 of the remaining 174 poles in the project south of 89 Highway, (Amaranth Township), (where the aquifer containing bedrock is deeper and protected by more overburden), will be sealed as described above. The sealing program is slated to be completed by 15 September, 2014.
MOECC’s intention is to, as resources allow, monitor the implementation of the sealing program such that any delays and problems needing MOECC’s attention are addressed as quickly as possible and the program meets it’s stated completion date. It is MOECC’s understanding that the County of Dufferin will have consulting engineers acting for it also observing the implementation of the sealing program.
Please feel free to reproduce and circulate my response.