Main Trunk No. 1 is currently exposed across Grayson Creek due to erosion activities over the last 70 years, so the span across the creek is no longer structurally sound. Therefore, removal of this 39- inch pipe is environmentally beneficial since it reduces the possibility of a sewage event into waters of the State. Additionally, the routine desilting maintenance activities of the Flood Control District are limited with this pipe crossing, so removal provides a public benefit by, potentially, allowing improvements to the channel' s capacity. As central Contra Costa County was developed, two additional interceptors, the A -Line (90-inch diameter) and A -Line Relief Interceptor (102-inch diameter), were constructed in the early 60s and 90s, respectively; therefore Main Trunk No. 1 is not needed for influent capacity since the two interceptors provide sufficient hydraulic capacity to accommodate peak dry weather flows (PDWF) and average wet weather flows AWWF), which been re -verified with the updated hydraulic model in 2023.During their construction, junction structures were installed to divert flow from Main Trunk No. 1 near, current -day, Target and Buchanan Golf Course, and which will be the upstream limit for abandonment of Main Trunk No. 1. However, Main Trunk No. 1 was not abandoned at that time since staff were aware of the Contra Costa Transportation Authority's interchange improvement project and anticipated needing Main Trunk No. 1 for bypassing when the 84-inch portion of the A -Line along Berry would have to be relocated. As the final phase of the interchange improvement project is imminent, preparations to abandon Main Trunk No. 1 may now proceed.