White Tanks FRS No. 3 is an existing flood retarding structure (dam) that lies off the eastern flank of the White Tanks Mountains and trends roughly parallel to, and just west of the Beardsley Canal between a projection of Bethany Home Road to the south and Northern Avenue to the north. It was originally constructed by the Soil Conservation Service (SCS), now called the Natural Resources Conservation Service (NRCS), in 1954 as part of the White Tanks Erosion Control Project and was later modified in 1982 and 2002. It is currently operated and maintained by the Flood Control District of Maricopa County (DISTRICT), is under the jurisdiction of the Arizona Department of Water Resources (ADWR), and is classified by ADWR as a high hazard/intermediate dam.

In the early 1990s, studies detected significant settlement, or subsidence, along the centerline of the dam. The results of additional studies indicate that there is, or could be in the future, earth fissures and/or horizontal strain conditions sufficient for fissure development adjacent to or beneath White Tanks FRS No. 3. While the probability of open fissures present in close proximity of the foundation is low, continued strain could produce future fissuring.

In order to mitigate/minimize the risks to the structure due to potential earth fissures, the DISTRICT contracted with the project consultant team to develop alternatives for a modified dam and a realigned dam to replace the function and benefit of the existing structure and to develop a recommendation for a preferred project alternative (either a realigned dam, modification to the existing dam, or replacement of the dam with a basin). EPG was contracted by the DISTRICT, through their on-call contract, to assist in the development of the modified dam and realigned dam alternatives, specifically evaluating opportunities for inclusion of multi-use benefits and the District’s Policy for the Aesthetic Treatment and Landscaping of Flood Control Projects into the formulation of the design. A modified dam alternative was selected. EPG was then selected as part of the consultant engineering team to develop the final plans for the dam modifications. This effort included development of dam alignment; coordination with the future regional trail; design of dam overbuild and borrow areas; cross sectional development for the structure; design of aesthetic treatment for the dam’s structural elements; and preparations of planting/revegetation plans, special provisions, and estimates of probable construction costs. A visibility assessment, 3-D surface models of the proposed structures, simulations, and presentation boards were also developed as a part of the project.