Xenia Rural Water District's North Water Treatment Plant and Well Field Expansion Improvements

Challenge: Faced with reduced well production, increasing demand, and difficult well operations and maintenance, Xenia Rural Water District hired HR Green to evaluate a well field expansion and rehabilitation at their North Water Treatment Plant (WTP) facility.

The existing well field consisted of four shallow alluvial wells along the Des Moines River with nominal capacities ranging from 450 to 550 gpm. Each well was equipped with a constant-speed submersible pump backed up by a portable emergency generator. The wells were placed on an elevated berm for flood protection, with each pitless unit surrounded by a concrete manhole. Xenia found it difficult and expensive to access to the wells for normal operations and maintenance. In addition, the constant speed well pumps provided reduced flexibility for altering treatment flow rates to avoid frequent starts and stops of their lime treatment facilities and associated water quality fluctuations with each restart.

Solution: HR Green initially performed a well field evaluation and analysis to identify possible locations to add an additional well, Well 6. The analysis also evaluated the impact of flood water elevations on each aspect of the well field and improvements needed to improve well access and operations.

Following the evaluation, HR Green designed the following improvements:

• Installation of Well 6, utilizing glass bead filter pack and corrosion-resistant materials, including stainless steel casing and screen and PVC column pipe.
• Installation of individual flow meters and sample ports for each well located in concrete vaults.
• Construction of a new elevated common access drive to all wells, allowing easy access for maintenance and operations while maintaining access above the 100-year flood elevation.
• Full replacement of the well field electrical systems to include individual variable frequency drives (VFDs) on each well pump and a new permanent emergency generator. Electrical facilities were moved to a new location above the 100-year flood elevation and with adequate well separation distances to meet current Iowa DNR requirements.
• Full replacement of the well field control systems to accommodate the new VFDs, including a fully looped fiber optic communications network. New controls and programming allow maximum flexibility for matching a desired treatment rate while maximizing the well field efficiency, allowing groundwater withdrawal to be spread throughout the wellfield regardless of the pumping rates.

During construction, Xenia experienced a complete failure of existing Well No. 4. HR Green quickly evaluated options for redrilling the well to accommodate already designed and installed improvements and then worked with the Contractor to include drilling a replacement well, Well No. 4A, as part of a change order.

Benefit: After fully completing the improvements, Xenia Rural Water District will have a much improved, resilient, and efficient alluvial wellfield to meet operational desires and increased demands.