COMPLIANCE INFO_1991-2006 - Laserfiche WebLink

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Technical Memorandum 4- March 31, 1992 If 55 lbs/acre (1990 data) is supplied from the sludge, the remaining crop nitrogen uptake capacity is 545 lbs/acres. The effluent nitrogen application rate of 814 lbs/acre exceeds the available crop nitrogen requirement of 545 lbs/acre. Therefore,effluent application on the site needs to be reduced to meet agronomic nitrogen demands. Heavy Metals Loading The concentration of heavy metals (from Table 2) in sludge is used to calculate the amount of sludge that can be land applied. The cumulative pollutant loading rates used in this analysis are as stated in the Environmental Protection Agency's (EPA)proposed 40 CFR,Part 503 draft sludge regulations. The final regulations are expected to be issued in July 1992. EPA's proposed Cumulative Pollutant Loading Rates (CPLR) is presented in Table 7. For the purpose of this analysis, the calculations are based on 1984 as the start of operations to determine the cumulative pollutant loads that have been applied to the 303 acre site. The remaining capacity of Manteca's agricultural land is calculated based on the total metals applied from the sludge and effluent since 1984. Between 1984 and 1988, sludge was applied as a liquid over the entire 303 acre site. In 1989 and 1990, dried digested sludge was applied on 98 acres and 68 acres, respectively. For the years 1989 and 1990, effluent equivalent to 2.26 mgd and 3.24 mgd, respectively, were applied over the entire 303 acres. A comparison of the actual total metals (effluent and sludge) applied since 1984 and EPA's cumulative pollutant loading rates is presented in Table 8. Results from Table 8 indicate that copper is the contolling parameter that determines the remaining capacity of the agricultural land. At this time, 78 percent of the total capacity of the 303 acre site is available for sludge and effluent application, assuming that only 210 acres of the site is available for sludge application. Based on the results of this analysis, it appears that the past seven years' sludge and effluent application has exhausted 22 percent of the site's useful capacity. PROJECTED SLUDGE AND EFFLUENT APPLICATION RATES Based upon the historical sludge and effluent application data, the future sludge and effluent application rates on the 303 acre site is controlled by the rate of effluent nitrogen applied. A ten-year planning period(1991-2000) is used to determine the projected sludge and effluent loads. In the year 2000, it is assumed that the flows would be 6.95 mgd. Table 9 presents a projection of the sludge and effluent loads that can be land applied in the future. The results in Table 9 indicate that effluent at an annual equivalent of 2.24 mgd can be land applied in 1991. In the year 2000, the effluent application would be reduced to an annual equivalent of 2.15 mgd. It is assumed that sludge is applied on 210 acres of City owned land. Effluent is applied on both the 210 acre City-owned land and the 93-acres of leased land. At these effluent application rates, it is expected that a nitrogen balance with the crop nitrogen uptake requirements would be achieved.