Backward Source Trace
Trace today's diminished signal back to the original exposure
- Difficulty
- Advanced
- Time to result
- ~months to results
- Steps
- 5
- Confidence
- 94%
Brockovich rejects treating a current environmental reading as if it describes the entire exposure history. She starts with the source document, checks its date, and asks what happened before the reported number. If cleanup, agricultural use, domestic consumption, flow, or dilution has already removed material, a later low value may conceal a far higher earlier concentration. The investigator searches backward for historical measurements, compares datasets, examines terminology that may disguise the hazard, and aligns the reconstructed exposure with the community's use and illness timeline. In the Hinckley example, a 1993 document said most chromium had already been removed while hazardous levels remained, prompting a search for older records. The mechanism turns a static reading into a time-based exposure model and exposes conclusions built on an artificially late starting point.
Origin
Extracted from The Shawn Ryan Show, where Brockovich explains tracing Hinckley's chromium records backward after finding a hazardous 1993 reading despite extensive prior removal.
Core principles
- 01Go back to source documents
- 02Treat today's reading as one point in a changing system
- 03Search for earlier values when the current value reflects prior removal or dilution
- 04Compare datasets and challenge the assumptions behind them
How to run it
- 1
Anchor the current reading
Record the value, date, units, source, and exact language used to describe the substance or condition.
Pro tip Preserve the original document rather than relying on a summary.
Watch out A later reading may not represent the peak exposure.
- 2
Find the changing process
Identify removal, dilution, consumption, discharge, cleanup, or flow that could have changed the value over time.
Pro tip Look for percentages removed and operational records.
Watch out Do not infer a historical value without evidence about the process.
- 3
Trace backward
Search earlier reports, monitoring wells, operating records, and correspondence for prior measurements.
Pro tip Use each dated record to define the next earlier question.
Watch out Keep naturally occurring substances distinct from more hazardous compounds with similar names.
- 4
Cross-check datasets
Compare the responsible party's data with government, scientific, and community records for contradictions or omissions.
Pro tip Recalculate reported figures when the underlying inputs are available.
Watch out A contradiction is a lead that still requires documentation and interpretation.
- 5
Reconstruct exposure
Align historical concentrations with how people used the resource and the period in which effects appeared.
Pro tip Separate measured facts from modeled estimates.
Watch out Do not overstate medical causation beyond the evidence.
In the wild
A 1993 record said monitoring wells still held hazardous hexavalent chromium after 90% had been removed through agricultural and domestic water use. Brockovich asked what the levels had been in 1985, 1983, and 1975, then found earlier records showing much higher dumping levels.
→ The case could evaluate historical exposure rather than relying only on a diminished later measurement.
Common mistakes
Calculating only forward
Projecting from today's lower number can erase the higher values that existed before removal or dilution.
Accepting softened terminology
A generic label can hide the distinction between a naturally occurring element and a hazardous manufactured compound.
Is it for you?
Best for
It is best for investigations where contamination, depletion, cleanup, or dilution changes measurements over time.
Not ideal for
It is not ideal when records are unavailable and no defensible link can be made between past and present measurements.
From the episode
#322 Erin Brockovich - Will AI Data Centers Secretly Drain America’s Water Supply?
Erin Brockovich