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Tracking reduction of water lead levels in two homes during the Flint Federal Emergency

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Overview

This longitudinal case study tracked lead concentrations at two Flint, Michigan homes with lead service lines over 37 months during and after the Flint water crisis, using parallel sampling by Virginia Tech (high-velocity hose bib) and EPA (kitchen tap at normal flow). The study documents how interruption of corrosion control treatment for 18 months created massive reservoirs of loose lead deposits in lead service lines, how aggressive flushing initially reduced but then failed to sustain reductions, and how lead service line replacement brought lasting improvement while still leaving residual lead in some pipes months afterward.

Key numbers

Home A (kitchen tap, first draw, µg/L):

  • Pre-crisis: 406 µg/L (first sample at 0.1 L); 9.7 µg/L second sample; 6.1 µg/L third sample
  • April 4, 2016 (after enhanced corrosion control treatment): first draw 119.3 µg/L (nearly 8 times the EPA action level)
  • May 31, 2016 (post-”Flush for Flint” campaign): median 11.0 µg/L, range 2.1 to 32.8 µg/L
  • After LSL replacement (February 14, 2017): March 2017 first draw 279.9 µg/L (nearly 19 times the EPA action level, attributable to plumbing disturbance)
  • February 2019: hose bib first draw 59.9 µg/L; all subsequent samples below 5 µg/L

Home B (hose bib, high-velocity, µg/L):

  • April 4, 2016: first draw 31.6 µg/L; subsequent sequential samples 14.5 to 775.9 µg/L during prolonged flushing
  • Maximum single measurement across both homes and all protocols: 1,308 µg/L
  • After LSL replacement (September 28, 2016): March 2017 median 2.5 µg/L
  • February 2019: hose bib first draw 57.1 µg/L after stagnation; all subsequent samples below 5 µg/L

Flint system-wide context (Virginia Tech 5-round sampling): 90th percentile total lead fell from 26.8 µg/L (August 2015) to 7.9 µg/L (August 2017). EPA parallel sampling: average particulate lead fell from 37 µg/L to 9 µg/L at kitchen tap normal flow.

Variability: relative standard deviation across sampling rounds was 52 to 229 percent, 2 to 4 times higher than typical water systems.

Methods (brief)

Sequential 1-L samples from two outlets per home after 6 h or more stagnation. Virginia Tech high-velocity hose bib (12 to 13 L/min) designed to mobilize loose particulate deposits. EPA kitchen tap at normal flow (2 to 3 L/min). ICP-MS Standard Method 3125 B. Minimum reporting level 1.0 µg/L; values below reported as 0.5 µg/L. Laboratory blanks and spikes every 10 samples. Metal ratio fingerprinting (Pb:Zn, lead (Pb):Cu, Pb:Fe, Pb:phosphate) used to identify lead sources.

Evidence fitness

Supports: documenting the dynamics of lead mobilization, flushing response, and recovery following corrosion control failure; demonstrating that high-velocity flushing produces only short-term reduction when pipe deposits are extensive; establishing that LSL replacement is necessary (though not immediately sufficient) for lasting remediation.

Does not support: estimating typical residential water lead exposure in functioning systems; generalizing to utilities without corrosion control failures; applying the extreme concentrations documented here to risk estimates for normal-operating water systems.

Limitations

Two homes in an extreme emergency scenario; not representative of typical residential lead exposure. The crisis-level concentrations reflect 18 months of lost corrosion control in a city with aging infrastructure, a situation that differs qualitatively from background contamination in maintained systems. Parallel sampling protocols (high-velocity hose bib vs. kitchen tap) produce different results by design; the two are not directly comparable measures of a single exposure scenario. Longitudinal home tracking cannot isolate the contribution of specific pipe segments.

Update history

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