Colorado River Basin Study Comments--Southern Nevada Water Authority

Comments on the Colorado River Basin Study prepared by the the Western Water Policy Review Advisory Commission

Study of existing information concerning water quality within Lake Mead

The purpose of Task 010A15M of the Southern Nevada Water Authority (SNWA) Treatment and Transmission Facility (TTF) contract is to conduct a study of existing information concerning water quality within Lake Mead and identify additional water quality studies that are needed to supplement existing data. The objective of this task is not to discuss treatability of the raw water source; this is addressed by Task 010A18M, Define Water Treatment Requirements. In addition, a narrative on the effect of pending Safe Drinking Water Act amendments and a determination of treated water quality goals is included in Task 010A16M, Review Safe Drinking Water Act (SDWA) Regulatory Impacts. Lake Mead has the largest surface area of any reservoir in the Northern Hemisphere. Bordered by Arizona and Nevada, the lake was created by the impoundment of the Colorado River behind Hoover Dam. The dam was constructed in 1935 to control flooding and provide a dependable water source, which now supplies about 20 million people in the desert Southwest and Los Angeles metropolitan area. The Bureau of Reclamation manages the water resources of the reservoir, and the National Park Service administers the recreation facilities at the reservoir

Comparison of water quality, zooplankton density, and cover in razorback sucker (Xyrauchen texanus [Abbott]) spawning areas of Lake Mead and Lake Mohave

Las Vegas Bay and Echo Bay in Lake Mead have small, self-sustaining populations of razorback sucker (Xyrauchen texanus [Abbot]). Increased productivity and cover have been hypothesized as reasons for successful recruitment of razorback sucker in Lake Mead. Conversely, reproduction has been documented on Lake Mohave, another lower Colorado River reservoir, but no recruitment has been observed. In 2000, BIO-WEST, Inc. was contracted by the Southern Nevada Water Authority to design and implement a study to examine nutrient levels, zooplankton density, and cover in areas with and without razorback sucker recruitment success. We sampled Echo Bay, Las Vegas Bay, and Trail Rapids Bay on Lake Mead, along with the Arizona Bay and Tequila Cove areas on Lake Mohave. The Lake Mohave locations were chosen because they are known to have razorback sucker reproduction, but no recruitment. During the first year of the study, we found that Las Vegas Bay had higher nutrient levels than all other locations. However, the amount of cover seemed to be the only factor distinguishing Las Vegas Bay and Echo Bay from the other three locations. We hypothesized that increased cover may provide larval and juvenile sucker with protection from predation by normative fishes. We suggested that the long-term lake level fluctuations in Lake Mead may be responsible for the increased cover and suggested continued studies to find links between environmental conditions and razorback sucker recruitment. In 2001 we collected information on water quality and nutrients, zooplankton density, and cover at Las Vegas Bay, Echo Bay, and Trail Rapids Bay in Lake Mead and the Arizona Bay and Tequila Cove areas of Lake Mohave. As in 2000, Las Vegas Bay had higher nutrient levels than all other locations. Overall, most sites had higher ammonium and phosphate levels in 2001. The 2000 results showed no real trends in zooplankton density, but in 2001 we found that Las Vegas Bay and Tequila Cove had a higher zooplankton density than the other locations. Zooplankton density was substantially higher at Las Vegas Bay, Tequila Cove, and Arizona Bay in 2001 versus 2000. Cover was substantially reduced at Echo Bay and Las Vegas Bay in 2001. In May 2001 no significant differences were seen in percent cover at any of the locations. Lake level lowered over 24 feet from March 2000 to May 2001, and left much of the submerged vegetation that provided cover in 2000 dry on shore. However, turbidity, which also provides cover, was significantly higher at Las Vegas Bay and Echo Bay than the other study locations. We recommend continuing and potentially expanding the study in future years. Cataloguing the conditions present in different years, under different lake elevations, and correlating them with the presence of a strong razorback sucker year class should identify what suite of factors is important in allowing razorback sucker recruitment in Lake Mead. Information on factors necessary for recruitment would assist in managing for the recovery of the species in the Lower Colorado River system

Interagency Lake Mead and Las Vegas Wash monitoring program: Standard operating procedures manual

A number of agencies sample Lake Mead and the Las Vegas Wash on a routine basis at several locations. In order to share and properly interpret the data, the Bureau of Reclamation, Southern Nevada Water Authority and the three Wastewater Treatment Facilities (City of Las Vegas, Clark County Sanitation District and City of Henderson) formed a committee to examine sampling and analytical protocols and to share information with the goal of maximizing the data quality. The group first met in April 1997. It was agreed that an effort should be made to discuss and compare specific sampling and analytical techniques so the data can be compared and the differences in techniques and data can be defined. It was also agreed that future work would be coordinated as much as possible to provide for the most cost-effective water quality sampling and to facilitate the sharing of data. The intent of this document is to provide a comprehensive source of information that will allow the participating agencies, and other interested parties, to access information regarding sampling locations, sampling schedules, and analytical methodology

A case-control study of determinants for high and low dental caries prevalence in Nevada youth

<p>Abstract</p> <p>Background</p> <p>The main purpose of this study was to compare the 30% of Nevada Youth who presented with the highest Decayed Missing and Filled Teeth (DMFT) index to a cohort who were caries free and to national NHANES data. Secondly, to explore the factors associated with higher caries prevalence in those with the highest DMFT scores compared to the caries-free group.</p> <p>Methods</p> <p>Over 4000 adolescents between ages 12 and 19 (Case Group: N = 2124; Control Group: N = 2045) received oral health screenings conducted in public/private middle and high schools in Nevada in 2008/2009 academic year. Caries prevalence was computed (Untreated decay scores [D-Score] and DMFT scores) for the 30% of Nevada Youth who presented with the highest DMFT score (case group) and compared to the control group (caries-free) and to national averages. Bivariate and multivariate logistic regression was used to analyze the relationship between selected variables and caries prevalence.</p> <p>Results</p> <p>A majority of the sample was non-Hispanic (62%), non-smokers (80%), and had dental insurance (70%). With the exception of gender, significant differences in mean D-scores were found in seven of the eight variables. All variables produced significant differences between the case and control groups in mean DMFT Scores. With the exception of smoking status, there were significant differences in seven of the eight variables in the bivariate logistic regression. All of the independent variables remained in the multivariate logistic regression model contributing significantly to over 40% of the variation in the increased DMFT status. The strongest predictors for the high DMFT status were racial background, age, fluoridated community, and applied sealants respectively. Gender, second hand smoke, insurance status, and tobacco use were significant, but to a lesser extent.</p> <p>Conclusions</p> <p>Findings from this study will aid in creating educational programs and other primary and secondary interventions to help promote oral health for Nevada youth, especially focusing on the subgroup that presents with the highest mean DMFT scores.</p

Metering Secondary Water in Residential Irrigation Systems

With rapid growth and limited water supplies, many water systems throughout the United States, in particular those in western states, are aware of the need for water conservation. Supplying secondary water is an approach that reduces demand on potable water and allows for more connections. However, unmetered secondary water use has resulted in an increase in overall water use. The regulation of secondary water would provide utilities increased control of water supplies and would allow residential users to actively conserve water used for outdoor purposes. The authors explore current practices that water suppliers are using, including filtration and innovative meter designs, to conserve precious water resources. Their experiences show that not only is secondary metering a future necessity, it is also a current possibility. Water suppliers can use this information to learn from the experiences of other systems and plan the future of their own distribution systems