Pushp Pal Singh was fined $7,500 for the offences, which occurred at the High River plant between February and March of 2012.
Singh added a substance which reduced the amount of phosphorus before waste-water samples were sent to an external laboratory for analysis.
Excessive phosphorus can reduce oxygen in water and hurt aquatic life.
Singh met with Cargill officials a month later and admitted that he tampered with the samples.
Cargill notified Alberta Environment and was later fined $80,000 for failing to immediately report what had happened