The NPDES permit requires that certain tests be made on the effluent on a regular schedule. Effluent testing may include, but is not limited to, flow measurement, temperature, BOD or COD, suspended solids, pH, DO, coliform count, and chlorine residual. Test results must be reported to the regulating agency. Along with the required tests, operators should check the receiving water, especially on small streams and lakes. Laboratory tests and visual checks may show that a problem exists in the receiving water and that something needs to be done. Plant operators cannot usually test large rivers, bays, lakes, and gulfs.
If an effluent containing a toxic substance is accidentally discharged to a receiving water that is used downstream as a drinking water supply, for recreation, or for livestock watering, operators must call the regulating agency and the downstream water users at once. Regulating agencies can then help curb the problem, and drinking water suppliers will have enough time to close their water intake lines until the problem is stopped. This will also warn people in recreation areas and give farmers and ranchers time to move livestock to a safe water supply.
In some areas where there is a shortage of water, wastewater effluent is recycled for industry, recreation, irrigation, and fire control use. Many industries can use treated wastewater for cooling and cleaning. Often this is cheaper for the industry than using potable (drinking) water. Lakes for fishing and boating have been maintained with recycled wastewater. Records show that these man-made lakes are often no more hazardous to the users than natural lakes. Recycled wastewater is seldom used as a drinking water supply.
Monitoring of effluent discharged for recycling is very important. Only by monitoring can the operator be sure that the effluent is good enough to be used. Recycling units may include extended settling and biological stabilization in holding ponds, sand filtering, and disinfection. Quality control is a must since the recycled water must be safe.
Irrigation with wastewater effluent is frequently used in some areas. Before irrigating, it is necessary to consider the contour of the area for irrigation, soil type, ground water table, and potential damage to water supplies. The joint EPA/Army manual, EPA 625/1-77-008 Process Design Manual for Land Treatment of Municipal Wastewater, provides further guidance on this subject.
Hillsides and other areas with steep slopes are not often used for irrigation. Too much runoff may occur. Irrigation equipment is harder to move, control, and maintain. Each area to be used for irrigation should be surveyed by a qualified person. Often, areas with slopes on which normal farm machinery can be used can be irrigated by a sprinkler system or by a jet or spray gun. Terracing and contour furrowing help prevent runoff. Flooding, overland flow, and furrow irrigation may require special work done to the land. This may include leveling, grading, ditches, and dikes.
Soil type and structure affect the rate at which the wastewater can be applied and absorbed. Average loams and sandy loams absorb and filter well. Clay and other types of tight soil are not as good. Deep plowing and chiseling make these soils better for wastewater irrigation. Very sandy or gravelly soils have very high percolation or absorbing qualities. But when these soils are in contact with the ground water table, pollutants may get into underground water supplies before they can be filtered out. Tight, sandy, and gravelly soils can be improved for absorbing and filtering by plowing crops under.
Row crops may be watered by furrow, spray, and/or sprinkler irrigation. Spray irrigation is used where gravity flow is not practical in all parts of an effluent disposal plot or field. There should be gravity flow from one end of the row to the other. A lot of grading is needed to prepare a field for furrow irrigation. Long rows without enough slope will result in boggy parts of the field while other parts will not get enough water. Furrow irrigation on steep slopes may cause too much erosion. Operators in charge of this type of irrigation need special skill and experience to make sure a fairly even amount of water reaches all parts of the field.
Grass crops are often easy to irrigate. The grasslands may be pastures, meadows, parks, turf, or sodded areas of airfields and golf courses. The amount of water applied and how often it is applied are not as important as for row crops. Effluent can be applied to grassland by overland flow, sprinkler heads, or by jet or spray guns. The stems, leaves, and roots of the grasses make a good filter and help prevent rapid runoff. GrassesContinue Reading