Monitoring approaches for irrigation systems are different than for systems that discharge to streams. The objective of an irrigation site monitoring program is to provide for early detection of problems. In most cases, simple adjustments can be made to the operation to avoid polluting ground or surface water. As a minimum, monitoring should occur at four spots in the system: 1) the treatment plant effluent, 2) storage, 3) irrigation system, 4) soil (and in some cases the vegetation and groundwater). The frequency of monitoring depends on public access to the irrigation site and the system size (Tables 5 and 6).
| Table 5 . Small system monitoring (less than 150,000 gpd) | |||
|---|---|---|---|
| Unrestricted access sites | Restricted access sites | Agricultural sites | |
| Treatment plant | |||
| CBOD5 | Weekly | Weekly | Weekly |
| Total coliform (when irrigating) | Weekly | Weekly | Monthly |
| Flow | Daily | Daily | Daily |
| Storage | |||
| Volume | Weekly | Weekly | Weekly |
| Irrigation system | |||
| Precipitation | Inches/day | Inches/day | Inches/day |
| Wind speed | Application day | Application day | Application day |
| Wind direction | Application day | Application day | Application day |
| Air temperature | Application day | Application day | Application day |
| Irrigation | Inches/day | Inches/day | Inches/day |
| Soil | |||
| Depth to water table | 1 per month | 1 per month | 1 per month |
| Soil temperature | 1 per month | 1 per month | 1 per month |
| Heavy metals | 1 per year | 1 per year | 1 per year |
| Phosphorus | 1 per year | 1 per year | 1 per year |
| Table 6 . Large system monitoring (150,000 to 500,000 gpd) | |||
|---|---|---|---|
| Unrestricted access sites | Restricted access sites | Agricultural sites | |
| Treatment plant | |||
| CBOD5 | 2 per week | 2 per week | 2 per week |
| Total coliform (when irrigating) | 2 per week | 2 per week | 2 per week |
| Flow | Daily | Daily | Daily |
| Total inorganic Nitrogen | Monthly | Monthly | Monthly |
| Storage | |||
| Volume | 2 per week | 2 per week | 2 per week |
| Irrigation system | |||
| Precipitation | Inches/day | Inches/day | Inches/day |
| Wind speed | Application day | Application day | Application day |
| Wind direction | Application day | Application day | Application day |
| Air temperature | Application day | Application day | Application day |
| Irrigation | Inches/day | Inches/day | Inches/day |
| Soil | |||
| Depth to water table | 1 per week | 1 per week | 1 per month |
| Soil temperature | 1 per month | 1 per month | 1 per month |
| Heavy metals | 2 per year | 2 per year | 2 per year |
| Phosphorus | 2 per year | 2 per year | 2 per year |
| Groundwater | |||
| Fecal coliform | 2 per year | 2 per year | 2 per year |
| Chloride | 2 per year | 2 per year | 2 per year |
| Nitrate | 2 per year | 2 per year | 2 per year |
The treatment plant effluent should be monitored to ensure that minimum treatment levels are achieved before it is discharged to the storage facility. The effluent should be monitored for CBOD5 and total coliform bacteria. Treatment systems using chlorine for disinfection may choose to monitor chlorine residual as an early warning for problems in the disinfection system. Total metal analysis is necessary for treatment plants receiving industrial wastewater. The wastewater flow must be monitored.
The storage system requires only limited monitoring. A weekly record of storage volume will help in managing the system to avoid future problems. A simple, easy to read staff gauge with cross-arms is an excellent way to measure liquid levels. Red markings at the top of the gauge give an easy indication that water levels are too high.
For the irrigation system, precipitation and water applied by the system need to be monitored. Simple rain gauges placed in and near the application site can capture both precipitation and irrigation water.
The soil within the irrigation site is one of the integrators of all the material being applied. Soil samples can be analyzed at the Ohio State University Research/Extension Analytical Laboratory (REAL) in Wooster, Ohio. Establish one benchmark site per 10 acres, and collect a soil sample before irrigation begins and each year at the beginning of the application season. For systems over 150,000 gpd, samples should be collected twice a year.
By testing a sample of soil from the same spot each year any possible accumulations of minerals and metals can be monitored. This will act as an early warning for possible surface or ground water contamination. If levels begin to get high, simple adjustments can be made in irrigation scheduling to avoid problems.
The vegetation is a biological integrator of all of the material being applied. Both information on yield and plant tissue nutrient levels can act as an early warning system for problems. Plant tissue samples can also be analyzed at the REAL. Plant tissue tests can reveal nutrient imbalances and the need to add soil amendments such as lime, potassium, or phosphorus.
Groundwater should be monitored up-gradient and down-gradient of large irrigation systems. Monitoring wells should be sampled at the beginning and end of the irrigation season for indicators of wastewater contamination.
Monitoring programs for systems greater than 500,000 gpd would be similar, but need to be developed individually to meet local conditions and wastewater characteristics.
While much of the monitoring occurs during the irrigation period, some monitoring must continue year-round. Records of wastewater flow and storage volumes, for example, need to be recorded throughout the year. Depending on the pretreatment system used, the effluent may also need to be monitored throughout the year.