Sunoco Pipeline LP will temporarily relocate five Chester County families whose backyards were damaged last month after sinkholes developed along the Mariner East 1 pipeline, forcing the company to shut down operations over safety concerns after its bare pipeline was exposed.

The company offered last week to temporarily relocate the families on Lisa Drive in Exton for up to the six weeks that it estimates it will take to conduct geotechnical studies in their backyards, where Sunoco's construction of a second Mariner East pipeline caused sinkholes to develop.

The Pennsylvania Public Utility Commission (PUC) ordered Sunoco to shut down the existing pipeline on March 7 until remedial action was taken. At the time, Sunoco estimated the Mariner East 1 pipeline would be out of service for 10 to 14 days.

But the shutdown of the 8-inch-diameter pipeline, which transports as much as 70,000 barrels a day of Marcellus Shale natural gas liquids such as propane to a terminal in Marcus Hook, now appears to be more likely to stretch into May, forcing Sunoco's customers to seek other outlets for their products. Sunoco Pipeline is owned by Energy Transfer Partners (ETP), a giant Texas pipeline operator.

Sunoco began preparatory work Friday for its "geotechnical data-collection activities," installing plastic mats to protect the ground from equipment rutting. In a letter to residents, the company said the studies would involve making "small excavations" every 35 feet to confirm the location of the pipeline, followed by other work, "including the use of small auger drills to obtain core samples to identify subsurface voids, if any, in the area."

"We are working with the PUC and appropriate agencies to complete the necessary testing and remediation in order to ensure integrity of the pipeline before putting it back into service," ETP spokeswoman Lisa Dillinger said in an email. "The preliminary investigations do not indicate any impacts from the subsurface area to any of the homes along Lisa Drive."

Dillinger said the company is working with individual residents to arrange relocations and offered a per diem reimbursement for food during the scheduled work. The offer remains open to any homeowner to accept while the work is underway, the company said in its letter.

"They're trying to get us out of here for a couple of months," T.J. Allen, a Lisa Drive resident whose backyard is largely taken over by survey posts, an orange safety fence demarcating the pipeline route. "They have to do a lot of construction."

Sunoco responded in early March by filling the sinkholes with several truckloads of flowable grout. The geotechnical studies may shed light on whether the remedial work successfully stabilized the underground.

The sinkholes are the latest complication to bedevil Sunoco's Mariner East system, which involves the construction of two additional pipelines alongside the 300-mile-long Mariner East 1 pipeline. Sunoco agreed in February to pay a fine of $12.6 million to resume underground drilling on the project.

Many of Sunoco's problems are related to its use of horizontal directional drilling (HDD) to install large sections of the Mariner East 2 pipeline, which was supposed to avoid the disruptions of conventional open-trenching construction method. HDD involves boring a hole through which the pipeline is pulled, but the method uses water and bentonite clay drilling fluid linked to a number of problems, including sinkholes, fouled private water wells, and leaks of drilling fluid.

The PUC issued its emergency order shutting down the pipeline after its investigators said the sinkholes "could have catastrophic results" if not repaired. The original 8-inch-diameter pipeline Mariner East 1 pipeline went into service in 1931 to carry motor fuel and was converted to natural gas liquids in 2014.

Russell and Mary March of Lisa Drive, along with another area resident, filed suit last month accusing Sunoco of negligence for using HDD and failing to conduct adequate surveys before starting work. The suit, filed in Philadelphia Common Pleas Court by King of Prussia personal-injury lawyer Andrew Neuwirth, seeks class-action status.