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DESCRIPTION AND OPERATION OF CRREL loading rates were 13.8 to 46.7 cm wk-'. Each OVERLAND FLOW TEST SITE application rate was evaluated for a period of approx- imately 6 weeks. All sections were operated simul- The CRREL overland flow test site has been in taneously at the same application rate. Because operation since June 1977. This site is 30.5 in of leaks in the membrane along the outside boundary, long x 8.8 m wide (0.03 ha) and graded to a 5% wastewater applications to section A were discon- slope. It is subdivided into three equal sections tinued during 1979. designated A, B and C so that parallel studies can Runoff was collected at the base of each section be conducted. A schematic of the site is shown in in individual galvanized steel catch basins. A small Figure 2. submersible sump pump located in each basin dis- Soil on the site is classified as a Hartland silt loam charged the runoff into a drainage ditch. The volume with sand,silt and clay contents of 5, 72 and 23% of runoff was recorded by flowmeters attached to respectively. The cation exchange capacity is 5 the discharge lines. During this study, the average meq/100 g and the pH is 7.1. Underlying the soil runoff rate was 75,87 and 89%of the application at a depth of 15 cm is a 30.0-mil-thick rubber mem- rate for sections A, B and C respectively. brane,which was installed to prevent downward All measurements of detention time and water percolation. The grass cover on the site is a mixture quality sampling were conducted during periods of of many species including K-31 tall fescue, orchard- hydraulic steady-state operation. The hydraulic grass, Kentucky bluegrass and quackgrass (Palazzo steady-state period began when the runoff rate et al. 1980). The grass was harvested on the average stabilized and it terminated when application was of once every six weeks during the growing season. stopped. A typical runoff hydrograph is shown in Undisinfected primary effluent was applied to Figure 3. In this case the hydraulic steady state the overland flow test site during the entire study. period began 1 hr after commencing application and Perforated plastic pipe was used to distribute waste- terminated 6 hr later when the system was shut water along the top of each section, and a bed of down. The amount of time needed to reach hydraulic crushed stone placed beneath the pipe helped to steady state varied depending on antecedent moisture uniformly disperse the flow. The quality of the conditions. primary effluent is shown in Table 1. Hydraulic detention time was determined by The application rate to each section was monitored measuring the travel time of a chloride tracer. and controlled by means of a constant head weirbox. Chloride was selected as a tracer because it is con- Five application rates ranging from 0.35 to 1.20 m3 servative and easily analyzed. A tracer solution was hr t were tested. The application cycle was 7 hr made by dissolving 94.6 g of sodium chloride in 3 L on, 17 hr off for 5 days per week. At these appli- of distilled water. The sodium chloride solution was cation rates and this cycle, the equivalent hydraulic added as a"slug addition" to the distribution chamber Table 1. Quality of applied primary effluent. Standard No.of Parameter Mean deviation observations BOD (mg L-') 72 23 58 Total suspended sollds(mg L-') 59 30 98 Total Kleldahl nitrogen(TKN) (mg L-') 36 10 32 Ammonia(mg L-' as N) 24 6 99 Nitrate(mg L" as N) 0.05 0.15 98 Total phosphorus ling L-' as P) 6.6 2.2 33 Orthophosphate(mg L-' as P) 4.8 1.4 31 Turbidity (ITU*) 31 13 100 pH 7.2 0.1 100 Specific conductivity (µmhos/cm) 513 105 40 Chloride(mg L-') 28 6 30 Fecal coliforms(no./100 mL) 2.5 X 10' 1.7 x 10° 14 Fecal streptococci(no./100 mL) 02 X 106 0.2 x 10" 7 •)ackson turbidity units 3