Advanced Earth Sciences, Inc. (AES) provided geotechnical investigation and design services to evaluate the stability of slopes below the Long Beach Water Department’s Alamitos Reservoir Site that includes 23 above-ground steel tanks located on a terrace up to 65 feet above Pacific Coast Highway and adjacent developments.

The geotechnical investigation included three tasks: a. to evaluate the impact of proposed excavation for apartment complex near the toe of the slope below the water tanks; b. to evaluate surficial stability of the reservoir slopes at the western and southwestern perimeters where slopes had experienced slumping and erosion damage from past heavy rains; and c. to install a monitoring system to detect any leakage from the water tanks and pipelines, and the impact such leakage would have on the stability of the slopes and groundwater conditions in the neighboring apartment complexes.

AES performed a geotechnical investigation by drilling, logging and sampling five bucket auger borings up to 90 feet deep. Based on the results of geotechnical investigation and laboratory testing, AES performed stability analyses for the southeastern slope of the reservoir to evaluate the static and dynamic factors of safety and to evaluate the Developer’s design of the retaining wall and shoring system for excavation for the proposed apartment complex. The shoring and support systems reviewed included drilled piers, soldier piles, tie-back anchors and retaining wall.

For the surficial stability of the areas of erosion and slumps from past heavy rains, AES performed a slope stability evaluation and prepared plans, specifications and cost estimate for stabilization fills using geogrids. The package was submitted to the Water Department for possible future bid documents.

For evaluation of impact of potential leakage from the tanks on adjacent developments, AES completed installation of two deep monitoring wells to 230 foot depth for future monitoring of groundwater levels and water quality. The program also included installation of 15 shallow neutron probe access tubes to monitor changes in soil moisture content at shallow depths due to potential leakage and to obtain an advance warning of any impacts on adjacent developments.