The below advice is based on my assumption following your post that your neighbour's builder has apparently negligently allowed a contaminant to leak onto your land from your neighbour's land.
Stop being nice to these builders, whatever about your neighbours who have been caught up in all this.
This is a very serious matter that may cause great inconvenience in putting it right as other posters have noted, and may well affect your property values if you leave it be.
I endorse the referral to the Environmental Health Officer.
Check and see if there is someone in the local authority dealing specifically with unauthorised and unlicensed spills, deposition of waste and contamination of land. This person may be associated with Environmental Services or the Parks Department.
That's just for a start.
Suss out the other neighbours and see of they have problems as well - the adjoining neighbour on the other side for example - in relation to contamination of their land and neighbours across the way in relation to traffic, noise, dirt and nuisance.
Notify your local residents association to get support when making the contacts listed below [but do ahead regardless] and in case the involved neighbours need a "talking to" to impress on them the seriousness of the situation..
1. Refer this and any other matters which may be relevant to the Health and Safety Authority. This includes whether or not the builders lorries are well-marshalled at delivery time and if they are causing a nuisance on the road. Take particular note of noise, nuisance dust, dirt and general disturbance. Take pictures of the operatives on site if they aren't wearing safety gear - helmets. gloves and boots - and take photos of the site to show if there are no safety signs up and if its not properly secured at night. Request that health and safety check if the builder is insured fully
2. Check the planning permission for a standard condition to keep all roads footpaths and drains clear of rubble, debris etc. If there is no permission the obligation not to obstruct drains or footpaths or make the latter unsafe or impassible still pertains - these are council items which costs money to maintain. There may also be a similar condition referring to protecting other sites or adjoining properties - this would include your site. There may also be a condition restricting working hours - check their times of operation. Write to the Planners about all relevant matters and make them aware of the leak also.
3. Contact Environmental Services as Main Drainage may also need to be informed in case this stuff finds its way into groundwater or sewers.
4. Contact the EPA if you're getting no joy with the local authority.
The builders may have an unhealthy relationship with the Council which will limit their actions.
5. On the strength of the foregoing, Building Control should be notified, requesting they inspect to determine how this leak could have happened if this job was being carried out correctly under Part D Materials and Workmanship.
6. Refer the matter to your solicitor, requesting him to write to the builder and your neighbour outlining your position and confirming that this matter will now be placed before the several offices of the local authority noted above.
7. Contact your local Fire Officer and inform him about a leak of flammable substance onto your land increasing fire risk. Mind you this could be a two edged sword and they may write to you asking you to leave the house.
8. Get your whole family checked by your GP in case there is a particular problem or allergy that you're not aware of yet. If there are health issues with the fumes, you may need to leave the house for a while anyway.
9. Refer the matter to the guards if things get heated. These guys have trespassed on your title with the leak and cleaning this up is likely to cost you money unless they do it or are made do it.
The foregoing will probably shut the site down for a while until the clean up crew get their work done. Ironically you will be helping the builders in the sense that the site as it stands is in a dangerous condition to work in.
ONQ.
[broken link removed]