Spook Hill Flood Retarding Structure (FRS) is a structural plan element of a Watershed Work Plan, prepared by the Natural Resources Conservation Service (NRCS; formerly Soil Conservation Service) in January 1963, for the Buckhorn-Mesa Watershed Project located in Maricopa and Pinal counties, Arizona. The Flood Control District of Maricopa County (District) operates and maintains the Buckhorn-Mesa Watershed Project, which is an integrated system of floodwater retarding structures and floodways. Spook Hill FRS was constructed and completed by NRCS in 1980 with the District as the local sponsor. The Arizona Department of Water Resources (ADWR) is the jurisdictional agency for dam safety for Spook Hill FRS. Spook Hill FRS was designed as a dam to impound floodwaters for a 100-year flood event and direct flows in excess of the 100-year flood event through an emergency spillway. Flows collected by the Apache Junction FRS and Signal Butte FRS are discharged from the Signal Butte Floodway into the Spook Hill FRS which, in conjunction with runoff from the Spook Hill FRS watershed, are conveyed north by the Spook Hill Floodway to the Salt River.
The SR-202L Freeway is a major element of the Maricopa Association of Governments (MAG) adopted Regional Freeway System in the East Valley of Maricopa County. The Federal Highway Administration approved a Final Environmental Impact Statement (FEIS) in 1999 for the SR-202L Freeway corridor between Country Club Drive (SR-87) and Highway US60. The SR-202L, as designed, would pass over Power Road, the Central Arizona Project (CAP) Canal, and the north end of Spook Hill FRS. The freeway would be located adjacent to and within the flood pool of Spook Hill FRS. The freeway would again pass over the Spook Hill FRS and CAP Canal, at the south end of the Spook Hill FRS and transition to become a depressed freeway at University Drive.
ADOT completed modifications to the Spook Hill FRS to accommodate construction of the freeway. Major modifications included the relocation of a 900-foot section of the Spook Hill FRS embankment at the McDowell Road crossing, construction of a new principal spillway, removal of the existing principal spillway, and relocation of the low flow channel to accommodate the freeway mainline. Additional modifications by ADOT included a levee within the existing flood pool to protect the freeway from flood events, excavation within the impoundment area to replace lost flood storage due to freeway construction, realignment of a section of the Signal Butte Floodway outlet, construction of improvements requested by the District which included a crack control central filter along the full length of the Spook Hill FRS embankment and the repair of erosion gullies on the slopes of the embankment, both of which were identified as dam safety deficiencies.