More than 700 unique chemicals were injected into oil and gas wells during hydraulic fracturing between January 2011 and February 2013, says an Environmental Protection Agency report. The agency analyzed more than 39,000 chemical disclosures submitted to FracFocus, the nation’s voluntary, industry-backed fracking chemical disclosure registry. Fracking fluid, which is injected deep underground at high pressure to break up tight rock formations to release trapped hydrocarbons, contains about 90% water, 10% proppant consisting of sand or ceramic materials, and less than 1% chemical additives. The chemical identity of some of those additives is protected as confidential business information and not made public, frustrating environmental groups and concerned citizens who want to learn more about the substances. EPA found that 70% of submissions to FracFocus included at least one additive with a chemical identity claimed as a trade secret. Submissions with trade-secret protection claims had, on average, confidentiality claims for five ingredients, the agency reports.