GREELEY - A trial that could set far-reaching precedents for Colorado water policy got under way Monday in Greeley.

The scheduled 45-day trial in Division 1 Water Court before Weld Chief Judge Roger Klein is the result of a decision by the state engineer last May to shut down 440 wells in Weld, Adams and Morgan counties. Senior water rights holders feared the well owners - all junior rights holders - would injure their rights to South Platte River basin water supplies.

The case was filed by Central Colorado Water Conservancy District in Greeley on behalf of well owners. On the other side of the dispute are about 20 cities, irrigation and ditch companies, water associations and sanitation districts from Boulder to Sterling who claim that allowing the well owners to pump again in another dry year could jeopardize their ability to serve their residents and clients.

Monday's hearing included opening arguments. Andy Jones, an attorney representing the water district, said the district would present a water replacement plan in which stored water could be used in dry years and replaced in wet years.

Objectors to the case have said they want to be certain that the water district can clearly demonstrate to Judge Klein that any proposed replacement plan can work.

"We have to prove we have replacement water to put back in the South Platte River at the right time and the right place and in the right quantity," said Tom Cech, Central's director.