Disinfection CT (USEPA SWTR)

CT achieved (C * t10) compared to USEPA SWTR Guidance Manual required CT for 3-log Giardia inactivation by temperature and pH. Bundled <= 0.4 mg/L free-chlorine table; state primacy agency table governs final compliance.

CT_achieved (mg-min/L) = chlorine_mg_l * t10_minutes. CT_required from bilinear interpolation of SWTR Table A-1 (free chlorine, 3-log Giardia, <=0.4 mg/L band) over the 6 temperature x 4 pH grid. 4-log virus pass is inferred from the Giardia result (free-chlorine 3-log Giardia is more stringent than 4-log virus), not from a separate Table E-1 lookup.

USEPA Surface Water Treatment Rule Guidance Manual EPA 815-R-99-014, Tables A-1 and E-1 (public domain).

epa.gov/dwreginfo/surface-water-treatment-rules.

Estimate. Operator of record and primacy agency govern.

Field names used by the API: chlorine_mg_l, t10_minutes, temperature_C, pH, CT_achieved, CT_required_3log_Giardia, pass_3log_giardia, pass_4log_virus

• Lookup table SWTR Table A-1 free-chlorine 3-log Giardia, <=0.4 mg/L band, 6 temperatures (0.5-25 C) x 4 pH (6.0-9.0)USEPA EPA 815-R-99-014
• t10 contact time input is the tracer-derived t10, not the theoretical detention timeSWTR Guidance Manual procedure
• Virus credit 4-log virus inactivation passes when CT_achieved exceeds the SWTR Table E-1 simplified value at the input temperature and pHUSEPA EPA 815-R-99-014 Table E-1
• Chlorine band applicable to free chlorine residual <=0.4 mg/L; higher residuals warn (the higher-residual bands of Table A-1 are not bundled in this screen)spec-v9 §E.2