Colorado authorities will begin sifting through a landfill Tuesday for Kelsey Berreth's remains and other possible evidence in the missing mom's case, according to police.

The search of the Midway Landfill in Fountain, Colorado, is expected to last 16 to 80 days, according to the Woodland Park Police Department.

Investigators have been focusing their attention on the landfill since at least January, when officials from Waste Management told ABC News the Colorado Bureau of Investigation had contacted them "regarding a potential search at Midway Landfill and we are cooperating fully."

Kelsey Berreth is pictured in an undated handout photo.(Woodland Park Police Department) Kelsey Berreth is pictured in an undated handout photo.

Authorities allege Berreth's fiancé and father of her child, Patrick Frazee, killed her at her Woodland Park, Colorado, home on Thanksgiving Day and then burned her body on his property in Florissant, Colorado, according to testimony from investigators at Frazee's preliminary hearing last week.

During the hearing, a law enforcement official said Frazee allegedly told his ex-girlfriend he "scooped Berreth's remains up and was going to take them to the dump or to take them to the river."

Patrick Frazee, the fiance of missing Colorado mother Kelsey Berreth, is pictured in a booking photo released on Dec. 21, 2018.(Teller County Sheriff via KMGH) Patrick Frazee, the fiance of missing Colorado mother Kelsey Berreth, is pictured in a booking photo released on Dec. 21, 2018.

The ex-girlfriend, Krystal Lee Kenney, told investigators she and Frazee burned a black plastic container in a horse trough on Frazee's land after Berreth was killed.

Kenney, who has pleaded guilty to moving the 29-year-old mom's phone from Colorado to Idaho after the alleged crime, told investigators she never saw a body in the fire, but described a "lump" after the plastic melted away, which she believed to be Berreth's remains.

The alleged murder weapon -- a bat -- as well as a mace container, pair of earrings and Berreth's ID card were also burned, according to Frazee's arrest affidavit released Wednesday.

Frazee is charged with two counts of murder and three counts of solicitation to commit murder in his fiancée's death. Teller County prosecutors filed additional charges prior to last week's preliminary hearing, including tampering with a dead body and two sentence enhancers.

Frazee and Berreth's 1-year-old daughter is in temporary custody of Berreth's parents.

Kenney told investigators Frazee said the baby was in the home in another room at the time of the murder.