Cemex voluntarily ceased operations due to the growing concern within the community, while additional air samples were analyzed.[51] The HSA worked with Cemex to implement engineering controls, such as dust scavenging systems and other dust mitigation procedures. Cemex also made a change in the materials they used, trying to replace current materials with materials lower in chromium.[51] The HSA also monitored the surrounding schools to determine if there were any health risks. Most schools came back with low levels, but in the case of higher levels a contractor was hired to clean up the chromium deposits.[51] This case highlights the previously unrecognized possibility that hexavalent chromium can be released from cement-making.