COMPLIANCE INFO_1992-2001 - Laserfiche WebLink

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When designing a system, it is important to Overland flow method. With this system, take into account seasonal variations of each typical liquid loading rates are from 0.25 to of these factors by evaluating the water bal- 0.7 inch (0.64 to 1.78 centimeters) per day. ance each week or month,as well as annually. For year-round operation, the rate of water loss from the soil.profile limits liquid loading The annual precipitation amount should be rates to 8 to 10 feet(2.5 to 3.0 meters)per year. determined on the basis of the wettest year in To determine the amount of runoff to be ex- ten. Rainfall data are available from State of pected, the water balance should be caculated California Department of Water Resources as follows: bulletins and from local weather stations. ` applied effluent + precipitation The evapotranspiration amount will vary from = evapotranspiration + percolation + runoff. month to month, though the annual ET total should be relatively constant from year to year. Precipitation and evapotranspiration values State of California Department of Water Re- used in designing such a system are deter- sources Bulletin 113-3 gives specific crop mined in the same way as for the Irrigation- water usages (ET requirements) by area for type systems. Percolation will generally be the state. When irrigating in arid climates, it about 0.1 inch (0.25 centimeter) per day or is necessary to leach out salts that accumulate less, dependinglargely on soil type. Percola- in the root zone as a result of evap®transpira- tion rates should be estimated under satu- tion by applying additional water beyond the rated or nearly saturated conditions. The typ- ET requirement (the "leaching fraction"). ical range for runoff values is from 40 percent Leaching fractions for various crops depend of the applied effluent plus precipitation dur- upon the salinity of the applied water and on Ing summer to 80 percent during winter. specific crop tolerances to salt. A 15 percent leaching fraction is generally adequate. Further information is available in FAO Irriga- j oaffiAg rates for organic tion and Drainage Paper No. 29. atter The percolation rate should be based on a As with liquid loading rates, design consid- number of factors including soil charac- erations for organic matter will differ for the teristics, underlying geology, water condi- three systems. tions, length of drying period for satisfactory crop growth, and waste water renovation re- Irrigation method. With an irrigation sys- quirements. tem, a range of 10 to 25 pounds (4.5 to 11.4 kilograms)per acre per day of BOD is accept- Infiltration/percolation method. In an in- able as a guideline. Two pounds (0.9 kilo- filtration/percolation system, the formula for grams) or less per acre per day is applied in a water balance is the same as for irrigation- typical effluent and will not pose a problem of type systems. organic buildup in the soil. Even when pri- mary effluent is used, organic loading rates H The percolation rate should be estimated may exceed 20 pounds (9 kilograms)per acre under saturated soil conditions since it is sig- per day without causing any problems. How- , nificantly reduced when the soil is saturated ever, most irrigation systems include resting for extended periods of time,as it will be with periods (1) to give the soil microbial popula- an infiltration/percolation system. Where tion time to break down organic matter and high rates of effluent are applied intermit- (2) to allow water to drain from the top few tently,percolation is the major disposal factor Inches of soil, thus restoring aerobic condi- and evaporation accounts for 10 percent or tions. The resting period for sprinkler irriga- less of the applied effluent.Where low rates are tion may range from less than a day to 14 days applied an evaporation/percolation.pond may depending primarily on soil type. For surface be needed.Evaporation from the pond surface irrigation, the period can be as long as six Is a significant factor and may be estimated weeks,but is usually between 10 and 20 days. m from available weather data. The length of the resting period will also de 13