You might try researching environmental clearance documents (environmental assessments or environmental impact statements) for small arms ranges. They have to address potential contamination of soils and ground water. Look at the listed references and see if there is a source for the data you want. To get you started, here are two "best management practices" manuals:
Best Management Practices for Lead at Outdoor Shooting Ranges
Army Small Arms Training Range Environmental Best Management Practice (BMP) Manual
The first (EPA) manual talks about alternatives to lead shot, starting on p. 67.