Disgrifir y drefn tir halogedig yn Rhan 2A Deddf Diogelu’r Amgylchedd 1990 ac mae'n darparu ffordd o ddelio â'r peryglon y gall tir halogedig eu creu. Disgwylir i Awdurdodau Lleol archwilio'u hardaloedd er mwyn cael hyd i safleoedd o'r fath. Pan fydd yr awdurdod gorfodi'n fodlon bod y tir dan sylw'n cyfateb i'r diffiniad o dir halogedig a ddisgrifir yn y Ddeddf, rhaid iddo ystyried sut y dylai ei adfer. Yna daw'r broses o benderfynu pwy sy'n atebol a sut i gyflawni'r rhwymedigaethau. Sylfaen y drefn tir halogedig yw'r egwyddor mai'r 'llygrwr sy'n talu'. Bydd unrhyw berson a barodd cyflwyno'r sylweddau sydd wedi halogi'r tir neu a wnaeth caniatáu eu cyflwyno yn atebol am ei adfer (cyfeirir ato fel person 'Dosbarth A'). Lle ceir mwy nag un person Dosbarth A, rhennir yr atebolrwydd ymhlith y grŵp. Dim ond os nad oes person Dosbarth A y daw perchennog a/neu feddiannydd y tir yn atebol (cyfeirir ato fel person 'Dosbarth B').
The contaminated land regime set out in Part 2A of the Environmental Protection Act 1990 provides a means of dealing with potential risks posed by contaminated land. Local Authorities are required to inspect their areas with a view to identifying such sites. Once the enforcing authority is satisfied land meets the definition of contaminated land set out in the Act, it must consider how it should be remediated. The process of determining and discharging liabilities follows. The ‘polluter pays’ principle underpins the operation of the contaminated land regime. Any person who caused or knowingly permitted the introduction of the substances by reason of which the land becomes contaminated land is liable for its remediation (referred to as a ‘Class A’ person(s)). Where there is more than one Class A person, liability is apportioned amongst the group. It is only if a Class A person cannot be found that any current owner and/or occupier of the land becomes liable (referred to as a ‘Class B’ person(s)).