DALLAS (CBSDFW.COM) – A city hold up is keeping federal investigators from testing soil in a northwest Dallas neighborhood. The area is where a natural gas explosion killed a 12-year-old girl last year.

As officials with the Army Corps of Engineers and National Transportation Safety Board (NTSB) continue to investigate how the blast happened, and are set to collect soil samples in the alley and around the neighborhood where young Linda “Michellita” Rogers died.

NTSB investigators were hoping to start getting samples around 9:30 a.m., but the Army Corps of Engineers crew is waiting on a right of way approval from the City of Dallas before they can start.

When testing finally gets underway, soil samples will be collected from four sites — three street corners in the neighborhood and behind the property where the Rogers family home once stood.

CBS 11 News was told this is the first time the Army Corps of Engineers has ever been asked to assist an NTSB investigation. They were called to help because the drilling crew is very familiar with soil in North Texas.

Equipment will be used to dig down approximately 20 feet to get the samples.

The natural gas explosion that killed the 12-year-old last year, happened after neighbors reported multiple natural gas leaks and fires in the neighborhood.

Atmos Energy blames the gas leaks on heavy rainfall, shifting soil and aging steel pipes.

The NTSB will determine what – if any – impact soil conditions had on those gas leaks.

The soil samples collected will be sent to a lab in Arlington and the findings will then be forwarded to the NTSB.

The Army Corps of Engineers says drilling should start this afternoon and be finished by Wednesday.