TABLE OF CONTENTS Land treatment is defined as the controlled application of wastes onto the land surface to achieve a specified level of treatment through natural physical, chemical, and biological processes within the plant-soil-water matrix. The basic wastewater concepts include slow rate (SR), rapid infiltration (RI), and overland flow (OF). These titles were selected to reflect the rate of water movement and the flow path within the process. In addition to these basic wastewater processes, there are criteria in later chapters for combined systems, wetlands and other alternative technologies, on-site and small-scale systems, and land application of biosolids.
The desirable site characteristics for the three wastewater processes are given in Table 2.1. These are not limits to be adhered to rigorously, but rather typical ranges based on successful experience.
| Parameter | Slow rate (SR) | Rapid infiltration (RI) | Overland flow (OF) |
|---|---|---|---|
| Grade | 20%, cultivated site 40%, uncultivated | Not critical | 2 to 8% for final slopes |
| Soil permeability | Moderate | Rapid | Slow to none |
| Groundwater depth | 2 10 ft | 3 ft during application 5 10 ft during drying | Not critical |
| Climate | Winter storage in cold climates | Not critical | Same as SR |
Typical design criteria for the three land treatment processes are compared in Table 2.2. The range of values given represents successful experience in a variety of locations in the United States. Chapters 10, 11, and 12 contain the procedures for developing site-specific criteria for planning, evaluation, and final system design.
