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of leachate flow on UV transmittance. After the leachate flow is reduced, the <br />transmittance will begin to increase. As the leachate flow increases, the UV <br />transmittance would decrease. The level to which the transmittance will decrease <br />depends on how much leachate is fed into the system. <br />After 1,000 hours of run time, the leachate flow rate was again increased to 25 gpm <br />for 100 continuous hours. Shortly before the flow rate was increased the City stopped <br />feeding chlorine into the system. With a leachate flow of 25 gpm into the plant the <br />transmittance decreased to 46% in the effluent stream. This is similar to the <br />transmittance observed during the first test at 25 gpm. With successive tests at 25 <br />gpm of leachate flow the transmittance did not drop below 45%. After 1,171 hours of <br />run time the leachate feed pumps were shut off. 106 hours after the leachate feed <br />pumps were shut off the transmittance increased to 62% which is well within the <br />typical range for domestic wastewater. <br />The pilot study results show the UV transmittance decreases with increase in the <br />leachate flow up to 20 gpm. However, when the leachate flow was increased from 20 <br />gpm to 25 gpm the decrease in transmittance was not as significant. <br />C. WWTF Effluent Flow <br />The City of Elk River continuously monitors the flow into and out of the treatment <br />plant. The total plant flow is generally consistent as shown in Figure 3.3. The average <br />flow during the duration of the pilot study was 1.34 MGD. The wastewater plant flow <br />can be one factor that can influence the treatment of leachate. With higher wastewater <br />flows, the leachate becomes more diluted in the waste stream and will not have as <br />significant of an effect on the transmittance. <br />During the pilot study leachate was pumped at several different flows for different <br />lengths of time. Table 3.1 below shows what percentage of the total flow was leachate <br />and corresponding UV transmittance. This can be helpful in determining how much <br />leachate the system can initially handle in full-scale operation. When the leachate was <br />fed into the system at 25 gpm this equated to 2.7% of the total flow. <br />Prepared by: Bolton & Menk, Inc. Results and Discussion <br />Waste Management/Elk River Leachate Pilot Study I T21.109643 Page 12 <br />