COMPLIANCE INFO_1991-2006 - Laserfiche WebLink

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9 0 Technical Memorandum -3- March 31, 1992 Comparison of the sludge metals data with the California Department of Health Services (DHS), Title 22 limits indicates that the sludge is non-hazardous. The total metals results in Table 2 are average values from 1987 through 1990. These values are used to calculate cumulative sludge metals loading on the 210 acre agricultural land. Sludge Disposal Dried digested sludge is land spread on the 210 acre agricultural land. Because of the nutrient content of the sludge, it is beneficially utilized as a soil amendment to grow various crops. A summary of the sludge nutrient analysis conducted in July 1991 is presented in Table 3. The farmland is leased to a local farmer who cultivates alfalfa, corn and barley. It should be noted that crop selection and farming schedule is determined by the farmer. From 1984 through 1988, liquid sludge was applied on the site. In 1989, following construction of new sludge processing facilities, sludge from the drying beds was applied on the land. A schematic of the site is presented in Figure 3. Summary of the historical unit loading rates is included in Table 1. Nitrogen Loading Land application rates of sludge and effluent on agricultural land is limited by the nitrogen uptake of the crops grown. The application rate should be lower than the crop uptake rate to prevent leaching of excess nitrogen into the groundwater. The nutrient (nitrogen, phosphorous and potassium) requirements for barley, corn and alfalfa are shown in Table 4. A summary of the nitrogen loading from sludge application acres on 210 acres is presented in Table 5. As shown in Table 5, the 1990 unit loading based on utilizing 68 acres for sludge application corresponds to 170 lbs/acre. As stated earlier, the farmer cultivates barley, corn and alfalfa. For this analysis, it is assumed that a combination of one or more of the crops are grown to yield one harvest per year. Comparison of the crop nitrogen uptake rates in Table 4 with the actual sludge nitrogen loading rates, indicates that the crop nitrogen utilization requirements exceed the sludge application rates. Therefore,the sludge application rates are much lower than crop nitrogen requirements. Since the entire 303 acre agricultural land is used for effluent disposal and 210 acres are used for sludge application,the effluent nitrogen concentration also contributes to the total nitrogen loading on the fields. A summary of the historical effluent nitrogen application rates is presented in Table 6. In these calculations, the 1990 effluent nitrogen concentration of 25 mg/L is used. It is assumed that the effluent is applied over the entire 303 acre agricultural site. In 1989 and 1990, annual equivalent flows corresponding to 2.26 mgd and 3.24 mgd, respectively, were land applied. The remainder of the flows were discharged in the winter months to the San Joaquin River. From the data presented in Table 6, 1990 effluent nitrogen that was land applied was 814 lbs/acre. In order to conduct a nitrogen balance on the site, it is assumed that the nitrogen uptake of the crops farmed in 1990 is 600 lbs/acre. This value is believed to be representative of the average crop production on the land in 1989 and 19%.