Identify one of the key standards for soil and aggregate testing used in the United States.

ASTM, or the American Society for Testing and Materials, is a key standard-setting organization that plays a crucial role in establishing protocols for testing materials, including soil and aggregates, in the United States. ASTM standards provide guidelines for ensuring the reliability and accuracy of testing methods, which is essential for maintaining quality control in construction and engineering projects.

These standards are widely recognized and utilized by engineers, inspectors, and quality assurance personnel to assess the properties and performance of soil and aggregate materials. The ASTM establishes requirements for testing procedures, equipment calibration, and sample preparation, facilitating consistency and safety across various applications in the construction industry.

In contrast, other organizations mentioned, like ISO, focus on international standards, while the EPA is primarily concerned with environmental regulations rather than material testing standards. The ACI provides standards pertinent to concrete but does not encompass the broader scope of soil and aggregate testing like ASTM does. Thus, ASTM is the primary reference for soil and aggregate testing standards in the U.S.