Avoiding direct contact between people and disease-causing organisms in wastewater is the goal in reducing health concerns. Several approaches can be used to avoid direct contact. Reliable disinfection to reduce the number of bacteria and other pathogens is one approach. In addition to testing for fecal coliform bacteria, quick tests for chlorine residual can increase confidence in the disinfection system. Restricting irrigation to times of the day or year when people are not present is another way to avoid direct contact. Irrigation only at night or when a facility is closed can be incorporated into the management plan. Establishing buffer areas between the irrigation site and the edge of the field is another approach to avoid contact. Fencing or signs may be needed to help define the buffer area. Figure 3 presents some sample signs. Table 3 lists the fecal coliform limits and buffer area requirements for each category of reuse.
Most domestic wastewater contains low levels of metals. Table 4 lists suggested limits for metals in wastewater for irrigation.
| Table 3. Fecal coliform limits (MPN/100 ml--30 day average) for wastewater reuse | |||
|---|---|---|---|
| Public access buffer area | Unrestricted access sites | Restricted access sites | Agricultural sites |
| None | 23 night application | 23 | 23 |
| 75 feet | - | 23 | 23 |
| 100 feet | - | 200 | 1000 |
| 200 feet | - | 1000 | no disinfection necessary |
| 300 feet | - | - | no disinfection necessary |
| Additional buffer areas need to be observed for fixed features, such as: | |||
| Private water well | 100 feet | ||
| Community water well | 300 feet | ||
| Sink hole | 100 feet | ||
| Drainage way | 50 feet | ||
| Surface water | 50 feet | ||
| Road right-of-way | 100 feet without windbreak using spray irrigation | ||
| 10 feet with windbreak or with flood irrigation | |||
| Property line | 50 feet | ||
| Table 4. Limits for metals in treated wastewater for irrigation | |
|---|---|
| Aluminum | 5.0 mg/l |
| Arsenic | 0.10 |
| Beryllium | 0.10 |
| Boron | 0.75 |
| Cadmium | 0.01 |
| Chromium | 0.1 |
| Cobalt | 0.05 |
| Copper | 0.2 |
| Fluoride | 1.0 |
| Iron | 5.0 |
| Lead | 1.5 |
| Lithium | 2.5 |
| Manganese | 0.2 |
| Molybdenum | 0.01 |
| Nickel | 0.2 |
| Selenium | 0.02 |
| Vanadium | 0.1 |
| Zinc | 2.0 |
|
| Figure 3 Sample signs for wastewater reuse sites. |