The Department of Toxic Substances Control (DTSC) requires a Supplemental Site Investigation (SSI) to further delineate impacts encountered during previous investigation(s). The SSI Work Plan describes the proposed investigation and sampling procedures, with consideration of applicable health and safety protocols. The plan is intended to provide a detailed description of the sampling and measurement to be conducted during the SSI implementation, in accordance with ASTM Standard E1903.

Site limitations should be identified, and the plan should:

• incorporate these limitations;
• avoid further impact on the environment, and preclude the site from becoming a pathway for contaminants to migrate;
• clearly state the objectives of the investigation or sampling effort;
• identify the location of each sample or measurement;
• include specific sampling or measuring methods, and
• consider the merits of a quality assurance/quality control (QA/QC) program.

SSI Work Plan Content

• Executive Summary – Help the reader to quickly understand project objectives, scope of work, and all the main findings.
• Introduction – Review property identifiers, location and setting, project contacts, and site history and use.
• Summary of previous site actions – Recap prior assessments and DTSC’s determination.
• Sampling Analytical Results – Evaluate analytical data quality and discuss fate and transport; relate field and lab data with Conceptual Site Model if available.
• Proposed Risk Assessment Process – The Preliminary Endangerment Assessment process may be acceptable.
• Community Profile – A community profile report may be used to meet the public participation requirements.
• Project Schedule – Outline an implementation schedule assuming normal turnaround times.

If previous investigation(s) did not achieve complete delineation of impacts both on- and off-site, then an SSI is necessary. The SSI Work Plan is a road map for implementing the SSI.