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select a valid loading rate within such a wide range. between detention time and removal of biochemical Also,little information is given on how other var- oxygen demand (BOD), total suspended solids (TSS), iables such as terrace length and slope can affect ammonia (NH3-N) and total phosphorus (total P). performance. Thus,a more comprehensive and With these relationships, the designer can determine rational design procedure, which takes these factors the detention times needed to achieve the desired into account, is needed to assure that discharge removal efficiency. requirements are met. The specific objectives of this study were to The new design procedure developed in this 1. Develop a method which can be used to pre- report is based on reactor kinetics, a concept dict the hydraulic detention time. familiar to most environmental engineers. In the 2. Determine the removal kinetics for BOD,TSS, case of overland flow, the reactor is the soil surface NH3-N and total P. where v rriious physical, bio 'cal and chemical 3. Validate the detention time and kinetic re- reactions take place. As in conventional process lationships using data from other systems. design, the controlling parameter is detention time. 4. Provide an example using the new design pro- For overland flow,detention time is the average cedure. time a unit volume of water takes to travel from the toD to the bottom o t e terrace. The desired Scope level of treatment can be achieve y controlling Data used in the development of the design pro- the length of time that wastewater remains in con- cedure were obtained from the CRREL overland tact with the soil surface. With this approach, flow test site in Hanover,New Hampshire,during overland flow systems can be constructed for a the 1978 and 1979 growing seasons (April through wide range of site conditions as long as detention October). All the kinetic relationships were Bevel- time requirements are met. This would significantly oped using primary effluent;use of this procedure reduce site preparation costs. for design of overland flow systems receiving a secondary or lagoon effluent will be discussed later Objectives in the report. A design procedure based on detention time re- The hydraulic detention time relationship devel- quires knowledge of two basic relationships. First oped at CRREL was validated using data from the is the hydraulic relationship among application Utica, Mississippi,overland flow site (Peters et al. rate,site characteristics an etention time. With 1981) and the pilot scale system at the University t_Fiis relationship the designer can determine the of California, Davis (Smith et al. 1980).. Data from application rate needed to satisfy detention time several other domestic and foreign overland flow requirements. Second is the kinetic relationship systems were used to validate the kinetic relationships. B.e m (29)/ I---2.9m (9.i�) .r,..�./I, ..... .,, .....\. ....mal-� .._... .. Seq lion / BeStlon •9e bion �` ' Bar face Floes _ 1t meBasin ��'s Primary irk., 4. �Jn l� _ ..��.-.vd ,gyp ,T/vl-a ,• Naslevcler Runoff • Figure 2. Schematic of CRREL overland flow test site. 2