A PROACTIVE APPROACH TO MANAGING NUTRIENT LOADS IN LAS VEGAS BAY AND LAKE MEAD

Flows through the Las Vegas Wash and into Lake Mead have increased proportionally with population expansion in the Las Vegas Valley. Growth of the gaming and entertainment industry, industrial development, and the fact that people are moving to Las Vegas as a place to retire, has resulted in the Las Vegas Valley growing from approximately 450,000 people to over 1,600,000 people during the past two decades.In 1956, the Las Vegas Valley wastewater treatment plants began discharging effluents into the Las Vegas Wash and Lake Mead system. By 1979 the State of Nevada had entered into consent agreements establishing effluent limitations for the Las Vegas Wash and Lake Mead. Through the 1980s and 1990s strategies to increase the level of treatment became increasingly aggressive, but the water quality in the Las Vegas Wash and the Las Vegas Bay continued to deteriorate. In the mid 1990s the Nevada Division of Environmental Protection (NDEP) listed the Las Vegas Wash and the Inner Las Vegas Bay as impaired waters under Section 303(d) of the Clean Water Act and established total maximum daily loads (TMDLs) for total phosphorus (TP) and ammonia to protect the water quality of Lake Mead, which is both the primary source of drinking water and the major water recreational area for the Las Vegas Valley.The dischargers responded to the 303(d) listing with an aggressive program designed to meet all regulatory requirements, which resulted in the Las Vegas Wash and the Inner Las Vegas Bay being removed from Nevada's listing of impaired waters. However, the NDEP left the TMDLs in place and in ensuing NPDES permits added additional constituents to be removed from the wastewater treatment plants' effluents.Water quality in the Las Vegas Bay and Lake Mead has continued to be an issue of concern as the non-point source flows continue to grow with the increase in urbanization. In response to concerns voiced over water quality issues in the Las Vegas Wash and Lake Mead, several groups and committees have been formed since the late 1990s including local, state, and federal agencies, as well as concerned citizens and environmental groups, to help direct development of a long-term solution for protecting water quality.In 1999, the Clean Water Coalition (CWC) commissioned the Alternate Discharge Study (ADS) to address present and future water quality and environmental issues associated with continued discharge of effluent into the Las Vegas Wash and Lake Mead. The CWC identified the need to seek alternatives that could include moving all, or the majority, of the highly treated effluent out of the Las Vegas Wash to an alternate receiving area in Boulder Basin. Ultimately, four alternatives were retained for further water quality modeling and evaluation which included:• An alternate effluent receiving area upstream of Hoover Dam within Boulder Basin• Discharge of effluent downstream of Hoover Dam• Discharge of effluent at or near The Narrows• Continue to discharge effluent in the Las Vegas Wash with process improvements at the wastewater treatment facilities for increased removal of TP and other pollutantsThrough a process of meetings with an Environmental Impact Statement Compliance Team (EIS-CT) and regulatory agencies, interested water user agencies down stream of Lake Mead, and the local, State, and Federal agencies with administrative, recreational, wildlife and water quality responsibilities within Lake Mead, a preferred alternative was selected which included:• An Effluent Interceptor that will connect the three wastewater treatment facilities to a common pipeline that will de-couple all or a selected portion of the effluent from the Las Vegas Wash. This pipeline will provide a bypass of the Wash to a tunnel through the River Mountains, maintaining the integrity of the highly treated effluent while transporting it to the Boulder Islands alternate receiving area.• At the terminus of the River Mountain Tunnel a Hydro-power facility will recover 8 to 13 Mega-watts of electrical power from the transported effluent for use at the Alfred Merritt Smith water treatment facility, approximately one quarter mile away.• From the hydro-power facility, the effluent will be transported through a series of pipelines to a location in the vicinity of the Boulder Islands. The diffuser will have the capability to optimize the velocity of the effluent being released to limit the growth of algae under varying conditions.• The local, State and Federal agencies will adopt an Adaptive Management Plan that will have the ability to manage the placement of the effluent between the Wash and the diffuser, vary the velocity of the effluent release, vary the location of the discharge by diverting effluent between two or three of the six effluent pipelines, and, if necessary, have the treatment facilities lower the effluent TP concentrations through optimization of the individual treatment processes. Initially, the treatment facilities will be expected to remove TP to at least 0.2 mg/L, a level that a treatment facility study showed to be achievable with minor modification to existing facilities.