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.. <br />49 <br />Surface 'dater Eudget _ The surface r•,ater balance is stated as <br />I = P + t•1 - Q <br />vrhere I = infiltration, P = precipitation, t1 = snov,melt, and Q = over- <br />land runoff. Accurate estimates of mean monthly runoff are difficult to <br />obtain. Although it is obvious that runoff from the refuse dump occurs, <br />for the purposes of this calculation,. runoff was assumed to be zero. Such <br />a procedure will result in an overestimate of infiltration and, consequently, <br />a "worst case" estimate of deep percolation or subsurface runoff. There- <br />fore, <br />I P + t•1 <br />and I is given in the lefthand column of Table 12 <br />Subsurface 'dater Balance - The equation used for• the monthly accounting of <br />infiltrated vrater is <br /> <br />W= I -Eta-a5 <br />in vrhich 'W is deep percolation, [ is infiltration Eta is actual evapo- <br />ration and a5 is the change in soil moisture storage. The maximum volume <br />per unit area that can be stored in the soil fora prolonged period is the <br />available water capacity, •4;J. The water in the soil, at any particular <br />time, cannot exceed the value of AIJ. If, in any particular month, the sum <br />of infiltrated vrater and stored water exceeds the evaporation requirement, <br />then deep percolation occurs. If the sum of infiltration and stored water <br />is less than the evaporation requirement, then evaporation is limited by <br />this sum. <br />Eecause there is no crop cover on the refuse dump at the present time, <br />the value of stored water, aS, will not change with time (other than the <br />top few centimeters in which evaporation vrill occur). Therefore, <br />,t - I - F a <br />~J <br />