Bridging the GAPs: Approaches to Treating Water On Farms

The second element of validation is on-farm validation. Once critical limits are identified from the initial validation, a grower must then show adherence to those parameters on the farm. These on-farm studies involve collecting data at increased frequencies to demonstrate control over critical parameters. The following scenario includes an example for on-farm validation: A grower monitors free chlorine concentration every 30 minutes at the treatment location and throughout the system to document control. This will help operators understand the lag between adjustments done at the treatment system compared to the last sprinkler head. Water samples are collected before treatment and after treatment and tested for generic E. coli . The percent reduction of E. coli is calculated following the formula below.

Untreated water was found to have 324 CFU E. coli /100 ml

Treated water was found to have 10.5 CFU E. coli /100 ml

In many cases, water sources will have very low populations of E. coli . In these cases, it is also helpful to calculate percent reduction of total coliforms, as they are more frequently present in water sources at higher levels than E. coli . Once a grower shows that he or she can apply the system on the farm and validate that the critical limits are effective, normal operating procedures are followed through written SOPs. The frequency of non-continuous monitoring (free chlorine concentration checks) should be supported from the on-farm validation data. Keep in mind that validation is necessary for both chemical treatments and pesticide devices.

Verification Activities

After proof that the treatment system is effective (validation), verification procedures provide the grower information that the system continues to operate according to his or her plan. These activities are conducted routinely and provide proof that the system continues to control for potential hazards. Verification includes the following activities:

• Calibration of monitoring devices (such as thermometers, pH meters, ORP meters)

Records review

Calibration records

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