WHCRWA Water Supply Project Pump Station

Project Background

The West Harris County Regional Water Authority (WHCRWA) provides surface water to 67 water plants, with 46 districts having transitioned to surface water. The Harris-Galveston Subsidence District (HGSD) and Fort Bend Subsidence District (FBSD) are regulatory agencies that work with Houston-area regional water authorities and government entities to reduce the risk of subsidence, which refers to ground sinking caused by water extraction. These agencies have mandated that all water suppliers in Harris, Fort Bend, and Galveston counties decrease groundwater pumping starting in 2025 and beyond.

To comply with groundwater reduction mandates and combat subsidence, WHCRWA has partnered with the North Fort Bend Water Authority (NFBWA) on the Surface Water Supply Project (SWSP). This joint initiative will shift the region’s dependence on groundwater to surface water by utilizing the City of Houston’s Northeast Water Purification Plan to deliver water from Lake Houston to retail water providers in each district. Over 55 miles of large-diameter pipelines and two large pump stations are being constructed as part of this project.

HVJ has been providing geotechnical and construction material testing services for the central pump station.

The Problem

The project required several large, heavily loaded prestressed concrete storage tanks, each up to 264 feet in diameter, placed on soft clay soils. The geotechnical design for the tank foundation called for a cost-effective solution because the tanks and their connecting pipes have a low tolerance for movement.

During construction, the contractor faced difficulties in passing the proof roll of the existing ground. They excavated a few feet and backfilled with fill soil, but the proof rolling showed a stable subgrade had still not been achieved.

Our Solution

Our team performed comprehensive settlement analyses using consolidation tests for each soil layer, accounting for the interaction of the multiple tanks. Our solution of five to six feet of surface soft soil replacement cost-effectively ensures that the soft clay soil will not adversely affect the storage tank foundation.

To address the challenge of achieving the proof rolling requirement, our geotechnical engineer inspected the site and identified a small swale area that could have backfilled without compaction control. We coordinated with the contractor to excavate down to the bottom of the swale area using the site survey data, allowing the excavated soil to dry. They then backfilled in an 8-inch lift to the final grade level. This enabled them to perform the final proof on the ground surface before proceeding with subsequent subgrade work.

The Results

Our solutions helped keep the project on budget and on schedule. We eliminated the need for costly deep foundation requirements during the tank design phase. By resolving problems promptly on-site, we also avoided the necessity of bringing in expensive select fill material to meet the proof rolling requirements. The delivery of water through the newly built pipelines is scheduled to begin in 2026.

WHCRWA Water Supply Project Pump Station

Project Background

The Problem

The Goal

Our Solution

HVJ Associates, Inc.

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