A sand mine off U.S. 421 is looking to expand its footprint onto more than 140 acres of land zoned for heavy industrial development. Situated just south of the border between New Hanover and Pender counties, 421 Sand Mine LLC has operated for more than 20 years, supplying sand to construction companies and local municipalities for beach renourishment and other uses. Now, the company is looking to expand onto an adjacent 144-acre tract.