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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />!"'('~"l <br /> <br />EXECUTIVE SUMMARY <br /> <br />BACKGROUJl,l) <br /> <br />The Metro Wastewater Reclamation District (District) provides wastewater transmission and treannent <br />services for most of the Denver metropolitan area. The District's 185 mgd Central Plant discharges <br />effluent to the South Plane River at 64th Avenue, near the beginning of Segment 15. This reach of <br />the river extends 26 miles north to Fort Lupton as shown in Figure ES-l. Land use adjacent to <br />Segment 15 is characterized by heavy commercial/industrial development in the more southerly <br />portion which changes to gravel mining and agricultural use north of 88th A venue. <br /> <br />~egment 15 has been classified by the Colorado Water Quality Control Commission (WQCC) as an <br />...Aquatic Life Warm Water Class 2 stream. The WQCC has set minimum dissolved oxygen levels of <br />5.0 mg/L during May through July and 4.5 mg/L from August through April to sustain aquatic life. <br /> <br />Water quality studies conducted over the past decade have shown that portions of Segment 15 do not <br />meet dissolved oxygen (DO) standards. The Central Plant effluent has been identified as a major <br />.factor in the DO depletion of the river, As a result, the regulatory agencieS required the District to <br />construct nitrification facilities at the Central Plant's 70 mgd North Complex to reduce ammonia as a <br />.potential oxygen~emanding substance in the effluent. These facilities have been operational for about <br />one year (October 1990), and the amount of ammonia discharged has been reduced. Subsequent <br />monitoring data have shown a demonstrated improvement in Segment 15 water quality, <br /> <br />In anticipation that the nitrification facilities in the North Complex would not provide enough <br />treatment to allow the river to meet stream standards, the U.S. Environmental Protection Agency <br />(EPA) required the District to determine the scope, nature, and cost of nitrification/denitrification <br />.facilities for the Central Plant's 115 mgd South Complex. A study completed in 1989 revealed that <br />construction costs could range from $72 to $112 million, plus an increase in annual operation and <br />maintenance costs of $2.0 to $4.5 million, depending upon final effluent ammonia criteria. <br /> <br />Implementation of South Complex nitrification/denitrification would impose a significant financial <br />burden on the District. Before commining funds to additional conventional in.plant improvements, <br /> <br />D-2 <br />