An explosion that shook a few Tracy residents Tuesday, April 24, was related to tests in the hills southwest of Tracy, according to local police.

Dispatchers in the Tracy Police Department said a loud boom reported by three Tracy residents was part of testing conducted by SRI International, a research firm.

According to the company’s website, SRI’s tests include examining missile components, simulating natural gas pipeline ruptures, and calibrating explosives for safety-classification purposes, among others.

SRI representative Ellie Javadi could not provide more specific information about recent activities at the site as of 3:30 p.m. Tuesday.

According to Scott Wilson of Lawrence Livermore National Laboratory, the SRI testing grounds are near the lab’s Site 300, which is a few miles southwest of Tracy in the Altamont hills. Wilson said no tests had been conducted at Site 300 this week.

In town, one woman living near Valpico Road said she and friends living 3 to 5 miles from the testing grounds heard a loud explosion. Two others who reported hearing the boom said their houses shook.