ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

Home Browse Search

total mercury loading to the Delta from tributary inputs. The Sacramento Basin(Sacramento River and Yolo Bypass)contributes 80%or more of total mercury fluxing through the Delta. Intra-Delta sources are a very small component of overall loading(CVRWQCB 2006b). The project-specific incremental increase in mercury contributions to Delta waters would be less than measurable(on a concentration basis) and,relative to all other sources of mercury to the Delta,would be negligible. Therefore,based on a review of the above information,this impact is considered to be less than significant. IMPACT Hydrology and Water Quality—Effects of Project Discharges on Pathogens in Receiving Waters. The 4.9-18 project would improve treatment performance for pathogen removal in the treated effluent discharged to the San Joaquin River compared to the existing WQCF operations through the operation of a UV disinfection system. The project would be designed and operated to comply with the NPDES permit limits for total coliform bacteria. Consequently, discharge to the San Joaquin River under the project would contain pathogen levels sufficiently low to be protective of human health. Therefore, this impact is considered less than significant. Levels of pathogens and nonpathogenic organisms that can affect human health are of potential concern with respect to the following beneficial uses: municipal and domestic uses, contact recreation, groundwater recharge, and agricultural supply. Because concentrations of pathogens in ambient waters are generally low, as well as highly varied in characteristic or type and,therefore, difficult to identify, enumerate, and isolate, scientists and public health officials typically monitor nonpathogenic organisms that are associated with fecal contamination, which are more easily sampled and measured. Where wastewater is present,human enteric viruses and other pathogenic organisms may be present, and may constitute a health threat to humans. The proposed effluent limit for total coliform bacteria in the City's tentative NPDES permit is 2.2 MPN/100 ml, which is based on DHS 1987 disinfection guidelines for wastewater. The 1987 DHS wastewater disinfection guidelines for coliform bacteria were developed with the understanding that the presence of these organisms is an indicator of fecal contamination. The DHS guidelines use coliform bacteria to monitor and assess the overall health risks associated with wastewater discharges. These guidelines were developed by DHS to be protective of municipal,recreation, and agricultural uses of surface waters receiving municipal wastewater discharges. The Basin Plan objective for coliform bacteria states that not less than five samples for any 30-day period shall exceed a geometric mean of 200 fecal coliform/100 ml,nor shall more than 10% of the total number of samples taken during any 30-day period exceed 400 fecal coliform/100 ml for waters designated as having a full-contact recreation beneficial use. EPA's current national ambient recommended criteria for bacteria are stated in terms of E. Coli(126/100 ml) and enterococci(33/100 ml), and are for the protection of full-contact recreation. The lowest DHS requirement for total coliform is 2.2 MPN/100 ml,a Title 22 recycled water requirement for unrestricted reuse, such as urban landscape irrigation, irrigation of food crops and storage in recreational impoundments. The project includes the installation of a new UV disinfection system. This system would expose treated effluent to UV rays prior to its discharge to kill pathogens that remain in the wastewater stream after treatment. UV disinfection systems generally achieve a significant removal rate for pathogens. Chorine and UV disinfection both provide similar and adequate disinfection of effluent. Each disinfection process is operated so as to provide the required amount of pathogen kill. UV disinfection has the major advantage of not requiring the addition of chemicals to the effluent in order to achieve the proper level of pathogen kill. The chemicals added in the chlorine disinfection process result in the formation of trihalomethanes (dibromochloromethane and bromodichloromenthane, in particular) and cyanide in the effluent. The city's rationale for implementing UV disinfection is to stop producing THMs and therefore ending the need for dibromochloromethane and bromodichloromenthane effluent limits. Because the project would be designed and operated to comply with the NPDES permit limits for total coliform bacteria, discharge to the San Joaquin River under the project would contain pathogen levels sufficiently low to be protective of human health. Therefore,this impact is considered less than significant. EDAW DER Hydrology and Water Quality 4.9-44 City of Manteca