DR-4558-CA Final Public Notice

FINAL PUBLIC NOTICE: MCSD Watermain Mad River Crossing Retrofit Project (Phase 1), Humboldt County, California | HMGP 4558-396-059R

The U.S. Department of Homeland Security’s Federal Emergency Management Agency (FEMA) proposes to provide federal financial assistance under the Hazard Mitigation Grant Program to the McKinleyville Community Services District (MCSD) in Humboldt County, California, to provide topographic surveys, engineering design, special studies under the National Environmental Policy Act (NEPA) and California Environmental Quality Act (CEQA), easement acquisition processes, and geotechnical investigations in order to design a new, seismically-resilient secondary pipeline under the Mad River. Pursuant to Executive Order 11988 (Floodplain Management) and FEMA’s implementing regulations at Title 44 of the Code of Federal Regulations Part 9, FEMA hereby provides interested parties with a notice of its final decision and an explanation of the alternatives that were considered. 

The purpose of the proposed action is to investigate reducing seismic hazards to a pipeline under the Mad River. The proposed action involves developing new designs for a pipeline under Mad River through topographic surveys, special studies, and geotechnical investigations to further understand the soil stability in the area for a new pipeline. Geotechnical investigations would include installing borings along the proposed alignment, which would involve ground disturbance. The preliminary survey and engineering design would establish drilling locations, which could be located outside of the MCSD right-of-way, requiring temporary construction easements from adjacent property owners. Drilling would include ten borings extending to depths of 50 to 75 feet and with a diameter between 4 to 6 inches. 

The project area is in the 100-year floodplain as depicted on the FEMA Flood Insurance Rate Map (FIRM) Number 06023C0687F, dated November 4, 2016. The FIRM shows that the project area lies within Zone AE, an area in the regulatory floodway along the Mad River that has a 1-percent probability of flooding every year and where predicted floodwater elevations are roughly 41 feet. 

A map of the project area and its location within the floodplain is available for public inspection. Parties interested in receiving a copy of the map should contact the FEMA Region IX Environmental Officer using contact information provided in this notice. 

Three alternatives were considered to address seismic hazards to the pipeline. Alternative 1 is the No Action alternative. This alternative is to leave the existing MCSD 18-inch, cast iron pipe (CIP) that crosses beneath the Mad River in place as-is. This pipeline is likely corroded, lacks protection, lies within a fault hazard zone, and in the event of failure would leave citizens in the surrounding area without water for an extended period of time. 

Alternative 2 is the proposed action and involves the construction of a redundant watermain crossing under the Mad River to be made of 20-inch outer diameter (OD), 18-inch inner diameter (ID) high-density polyethylene (HDPE) pipe. HDPE is a flexible pipe material that will reduce the likelihood of failure from a large seismic event. The selected location and approach would also ensure the least amount of disturbance to the environment since the above ground disturbed area is relatively small, and the construction footprint will be far enough away from the river so as to not impact the river. 

Alternative 3, the second action alternative, is to provide the redundant watermain without drilling beneath the Mad River. This would involve constructing a suspended aerial crossing of a new pipeline over the Mad River in the same location. While this project is viable, it would require extensive permitting, as construction would likely require access to the river bar and associated disturbance within the river channel. In addition to permitting being more expensive, the construction would also be more expensive than the second proposed alternative. The third alternative would likely require access to the river bar and would involve disturbance within the river channel. The proposed action is therefore environmentally and economically preferred. 

FEMA has determined that the proposed project is the only practicable alternative available; therefore, the proposed action must be located in the floodplain. The proposed action would have no significant adverse impact on the floodplain and would benefit the area by reducing the risk of earthquake damage. Therefore, measures to minimize impacts on the floodplain are not necessary. The McKinleyville Community Services District has declared that the proposed action conforms to local floodplain standards, and would be responsible for the management, construction, and maintenance of the proposed action. 

Based on a desktop review of aerial imagery and the National Wetlands Inventory, there are freshwater forested/shrub wetlands within the project area, along the Mad River. As geotechnical borings would be drilled within the river and on the riverbeds, impacts to wetlands are possible. However, geotechnical borings within the channel would only be conducted when the river bar is dry, minimizing impacts to water quality. Additional information about FEMA’s proposed action may be requested by writing the FEMA Region IX Environmental Officer at FEMA, 1111 Broadway, Suite 1200, Oakland, California 94607, or fema-rix-ehp-documents@fema.dhs.gov. All requests should be received no later than 15 days after publication of this notice. No action will be taken before this date.