What have we learned (so far) from the Plano and Frisco chlorine burn results?

(1) When we compare each city’s January 2018 & 2019 PRE-chlorine burn TTHMs, there is little difference. However, when we compare their 2018 & 2019 MID-chlorine burn TTHMs, we see some significant increases this year.

When we averaged the 2018 independent test results and the most recent set of 2019 independent test results for each city, here’s what we found:

  • Plano’s average chlorine burn TTHMs increased from 73.1 ppb to 91.9 ppb.
  • Frisco’s average chlorine burn TTHMs increased from 80 ppb to 93 ppb (99.6 ppb if we count the highest concentration of TTHMs regardless of date)

(2) While Frisco provided more *rounds* of tests, Plano tested at the same point in the chlorine burn (3 weeks & 2 days) both years, making it easier to compare apples to apples.

(3) Plano tested at the pump stations (Frisco did not), which is where we saw some of the most dramatic increases. Why is that?