Richard P. Arber Associates, Inc. completed preliminary design, design, and construction phase services for this 1 million gallon per day wastewater treatment plant improvement project. The project was completed in 1996 at a construction cost of $4.1 million. Construction change orders were held to less than 4.1% of the construction cost.

Included in the project were a 230,000-gallon anaerobic digester, centrifuges, and sludge drying beds.

El Portal Wastewater Treatment Plant is owned and operated by the National Park Service and is required to meet the stringent discharge requirements of the pristine Merced River.