Flow-Weighted Two-Source Water Blend
The concentration of two water sources blended together and the split to meet a target -- the calculation when an operator combines wells or intakes to hold a contaminant (nitrate, fluoride, hardness, TDS, chloride) under its limit. Blend = flow-weighted average (Q1 C1 + Q2 C2)/(Q1 + Q2): 500 gpm at 4 mg/L with 300 gpm at 12 = (2,000 + 3,600)/800 = 7.0 mg/L, under a 10 MCL. To hit a target between the two source values, the lower-source fraction is (Chigh - target)/(Chigh - Clow): reaching 8 mg/L from a 4 and a 12 needs (12-8)/(12-4) = 50% clean flow (equal flows). A target outside both source concentrations can't be blended to -- it needs treatment or a third source. A blending screen; source concentrations vary, the SDWA MCL applies, and the state primacy agency and the operator's monitoring govern compliance.
Formula and source
blended_conc = (flow1_gpm x conc1 + flow2_gpm x conc2) / (flow1_gpm + flow2_gpm); required_low_source_pct = 100 x (Chigh - target_conc) / (Chigh - Clow) when the target lies between the two source concentrations.
Flow-weighted source-water blending mass balance (AWWA / WEF operator-certification math), by name; the source concentrations vary over time, the SDWA maximum contaminant level applies, and the state primacy agency and the operator's monitoring govern compliance.
Audience
This tile is built for water operators and the adjacent professions in the Water and Wastewater Operations group. The interactive calculator runs entirely in your browser. No account, no fee, no advertising, no tracking.
Related tools
Posture
Rough Logic answers the math question the working professional asks on the job. The site is a calm, fast, ad-free, account-free, ever-free reference. It does not interpret code. It does not replace the licensed professional. It does not store your inputs. The Authority Having Jurisdiction governs all installations and inspections.