Site Mitigation & Restoration Program

We protect and maintain California’s land and places
by setting strict standards for land restoration and cleanup

Supplemental Site Investigation Work Plan Quick Reference Guide

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.

SSI Work Plan Figures

Figures should include a North arrow, scale, legend, measurement units, and annotated clarification as necessary. At a minimum, the following figures should be included:

  • Site plan
  • Regulatory status;
  • Previous investigations’ (PEA, etc.) sampling locations and results
  • Proposed supplemental sampling locations

SSI Work Plan Tables

At a minimum, the following tables should be included:

  • Summary of previous sampling and analysis program
  • Summary of previous detections and findings
  • Summary of previous health risk screening evaluation (PEA)
  • Proposed SSI soil gas/soil/ groundwater sampling program
  • Project schedule

SSI Work Plan Appendices

The following may be included:

  • Field sampling plan
  • Baseline risk assessment work plan
  • Public participation plan
  • Quality assurance plan
  • Health and safety plan

DTSC’s Voluntary Agreements – Assessment and Cleanup Process: 1) Agreement: a) Standard Voluntary Agreement b) California Land Reuse and Revitalization Act Agreement c) Reimbursement Agreement d) Prospective Purchaser Agreement e) Local Agency Oversight Agreement 2) Scoping Meetings a) During negotiation or shortly after agreement execution b) Establishes strong working relationship between DTSC, the Proponent, and the environmental consultant c) Also may be held prior to submitting any documents to DTSC for review 3) Evaluation a) Preliminary Endangerment Assessment (PEA) b) Supplemental Site Investigation c) Remedial Investigation d) Report of Findings Possible End Point 4) Remedy Selection a) Feasibility Study b) Removal Action Work Plan c) Remedial Action Plan d) Response Plan 5) Implementation a) Removal Action Implementation b) Remedial Design c) Remedial Action Implementation d) Response Plan Implementation 6) Certification & Stewardship a) No Further Action b) Certificate of Completion c) Land Use Restriction d) Operation and Maintenance e) Five-Year Review Possible End Point During Remedy Selection, there is a Public Comment Period and California Environmental Quality Act (CEQA). During this entire process, Public Participation Activities and Tribal Consulation is included, as needed. Possible End Points: 1) Based on site evaluation, projects may conclude without need for any further action; 2) Based on site evaluation, projects may conclude with the need for a Land Use Covenant, in which case a public notice process will be implemented through a Preliminary Endangerment Assessment, Report of Findings, or equivalent documents; and 3) Cleanups may either be conducted to unrestricted land use levels, or may require long term stewardships.

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This document is intended to be guidance only and it does not supersede or implement laws or regulations. The information in this advisory is intended solely as guidance and as educational reference material and should not be considered enforceable or regulatory in nature.