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The proposed site for the overland flow system is adjusted wetted area is 30 ha (74 acres). The non- on a hillside next to a river. As shown in Figure 11, wetted area needed for buildings, access roads and the eastern half of the site has a general slope of 4% buffer zones would add another 10 ha based on the while the slope of the western half is 8%. The length assumption that the wetted area is 75%of the sum of each terrace is assumed to be 50 m (160 ft). From of wetted and non-wetted areas (Aly et al. 1979). eq 16, The area needed for a storage pond is estimated to be 20.0 ha. This estimate is based on a storage _ 0.078 50 volume of 667,750 m3 which includes 567,750 m3 Q (0.04)1/3 60 for storing wastewater and 100,000 m3 for storing precipitation during winter. The storage needed for =0.190 m' hr' for the 4%slope wastewater was calculated by multiplying the design flow (3785 m' day') by the number of storage and days (150 days, November thru March). The depth of the storage pond was assumed to be 3.5 m. Summing _ 0.078 (50 the wetted, non-wetted and storage pond areas, the 9 (0.08)1/3 60 total area of the overland flow facility is 60 ha (148 acres). A possible configuration of the terraces for =0.151 m' hr' m' for the 8%slope. this overland flow system is shown in Figure 12. With an application season of 28 weeks per year COMPARISON WITH THE TRADITIONAL (April through October) and an application cycle of DESIGN APPROACH 10 hours daily for 5 days per week, the annual operating time is 1400 hrs. Also, the runoff coeffic- ient calculated from eq 17 is 0.8. The annual appli- As indicated earlier in this report the traditional cation rate Qa to each terrace can now be calculated design procedure is to calculate the wetted area from eq 15: based solely on hydraulic loading rate. For an over- land flow system receiving primary or pond effluent, _ (0.190 the procedure is to select a hydraulic loading ranging Qa — \0 8 1400 from 6.4 to 20 cm/wk. Using the same design flow and application season as in the previous design ex- 332.5 m3 yr' rn' for the 4%slope ample,the required wetted area would range from 27 to 85 ha. Recall that the wetted area predicted _`0.151\ by the rational procedure presented in this report Qa— 0 8 f 1400 was 27 ha,which is the least amount of land pre- dicted by the traditional approach. Therefore a = 264.3 m3 yr' m' for the 8%slope. system designed according to the traditional procedure will require more land,especially if the designer se- lf the annual design flow is 1.38 x 106 m' and leets a conservative loading rate. For example, it the precipitation minus evaporation volume from would be reasonable to assume that the designer the holding pond is 0.15 x 106 m3, the total water would choose a loading rate in the middle of the volume applied to the overland flow site is 1.53 x 106 range. For a hydraulic loading rate of 15 cm/wk, m3 yr'. If this volume is divided equally, the waste- the land area required would be approximately 40 water applied to each half of the site is 0.77 x 106 ha or 501/6 greater than that required by the rational m3 yr'. With an annual application rate of 332.5 procedure. In this case the cost of a traditionally m3 yr' m', the total width of terrace needed on designed system would be about 50%higher. the 4%slope is 2,316 m. Likewise, the total width Beyond the monetary benefits just described, the of terrace needed on the 8%slope is 2,913 m. If rational procedure presented here is based on the the length of each terrace is 50 m then the combined fundamental process design concept of detention wetted area needed for treatment is 27 ha (67 acres). time. This concept is familiar to most designers, Additional wetted area will be needed to handle which makes overland flow more appealing as a wastewater flows during harvest operations. If three treatment alternative. Also, this procedure allows harvests per year and a drying period of one week the designer to tailor each site according to existing per harvest are planned, the wetted area should be site conditions and discharge requirements. increased by 11% (3 wks/28 wks)..Therefore the 17