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 Report Quick Reference Guide

The objectives of the Department of Toxic Substances Control (DTSC) Supplemental Site Investigation (SSI) Report are to document supplemental site characterization activities and identify data gaps for future work in addition to assessing risk and presenting possible remedial action strategies.

SSI Report Content

Include as applicable:

  • Executive Summary – Project objectives, scope of work, main findings.
  • Summary of Site Background
    Location, setting, project contacts, site history.
  • Sampling Activities – Soil gas; matrix and groundwater sampling and analysis; locations and rationale; collection and handling.
  • Sampling Results and Discussion – Sampling results; discussion of investigations completed; site geology; hydrogeology, fate, and transport; updates to Conceptual Site Model (CSM).
  • Risk Evaluation – Exposure pathways and media of concern; evaluations or updates of potential risk to human and ecological receptors; qualitative summary and comparison to screening levels.
  • Risk Evaluation – Exposure pathways and media of concern; evaluations or updates of potential risk to human and ecological receptors; qualitative summary and comparison to screening levels.
  • Summary, Conclusions and Recommendations – Discuss results and comprehensiveness of site characterization(s) for cleanup or interim actions. Make recommendations for next phase of work, if warranted.

SSI Report Tables

Site Data – Summary of historical and current analytical and field-measured data. Use multiple tables, if necessary, to break data out by media type (soil, soil gas, groundwater).

SSI Report Figures

  • Vicinity Map – show property in relation to surrounding region.
  • Site Maps – Identify boundaries, buildings/facilities, historical features, underground storage tanks, locations of hazardous substances, existing well/sampling locations.
  • Cross section(s) – show actual/inferred site-specific geology and hydrogeology.
  • Conceptual Site Model (CSM) – show original CSM and any changes to CSM.

SSI Report Appendices

  • Logs (borehole/test pit, etc.)
  • Permits
  • Laboratory analytical data and chain of custody
  • Sampling and Analysis Plan (SAP)/Quality Assurance Project Plan (QAPP)
  • Field procedures
  • Details of statistical methods
  • Waste manifests

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.