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River Islands Development at Lathrop November 2020 Final Phase 2 Sewer Technical Report Rev 1 #6520 Standards. Low velocities in sewer lines has the potential to lead to increased odor and corrosion issues in the sewer collection system as these conditions create the following environments which promote the rate of hydrogen sulfide odor and corrosion. • Low velocities attribute to longer detention time in the collection system which can decrease the dissolved oxygen of the sewage thus promoting anaerobic bacterial growth contributing to corrosion and odor. • Low velocity can promote less aeration of the sewage due to turbulence, increase solids deposition, and not removing the anaerobic slime buildup beneath the flow line. This is especially a concern with pipes operating at low velocities with larger depths creating a larger wetted surface area. Future sewer infrastructure will be required to be designed in accordance with the newer lower sewer generation rates to reduce the occurrence of low sewer velocities. For the existing Phase I infrastructure designed with the higher 2014 sewer generation rates, the River Islands sewer collection system has the following features to combat potential low velocity conditions. Improvement plans provided by Odell indicate that the larger sewer lines were designed in accordance with the City's Standards and were specified to be constructed of corrosion resistant C900/C905 PVC pipe. LS-A1 is also installed with a Bioxide (nitrate solution) dosing system, which will reduce the potential for anaerobic conditions by promoting anoxic bacterial growth and will be the primary means of combating odor and corrosion issues. The installation of recycled water flushing stations throughout River Islands will allow for operations staff to combat the previously mentioned low velocity conditions by flushing out the larger lines, primarily during interim conditions. At full buildout, flushing of the trunk lines should be considered as a secondary means of combating low sewer velocities as frequent flushing not only wastes recycled water, but also has the potential to affect the wastewater characteristics such as increasing total dissolved solid concentrations. However, during the interim and just after the full buildout of the collection system, the sewer collection system should be monitored for odor and corrosion issues to see if further measures are required. It is recommended that all trunk lines in the future continue to be designed and constructed of corrosion resistant material and the interior of all trunk line manholes be PVC lined or epoxy coated and installed composite corrosion resistant manhole covers. 27