The availability of fresh surface water or groundwater is limited in the James County, VA area, but the demand for drinking water continues to increase. The James City Service Authority (JCSA) contracted Buchart Horn to help address this problem. We designed a groundwater treatment facility for JCSA to desalinate brackish groundwater and produce up to 5.0 MGD of drinking water.
Groundwater is withdrawn from two brackish aquifers, blended, and treated using reverse osmosis for the removal of dissolved salts. Groundwater is withdrawn from the Lower Potomac Aquifer, treated using reverse osmosis membranes for the removal of dissolved salts, and blended with water from the less brackish Middle Potomac Aquifer. Five production wells with individual well houses were constructed at the plant site.
The project schedule was accelerated by obtaining a waiver from Virginia Department of Health (VDH) for the pilot testing requirements. This was accomplished by demonstrating to VDH good quality feed water was available by treating only water from the Lower Potomac Aquifer, and if a reasonably conservative design approach was employed, then pilot testing was not justified.
The project included:
- Drilling and development of five wells in the sand and gravel geology
- Five supply wells, three 1,700 GPM (300 HP) Lower Potomac wells and two 900 GPM (125 HP) Middle Potomac wells. Each well is housed in a 400 SF well house
- High service pumps
- Pre-treatment consisting of cartridge filtration and anti-scalant dosing
- Reverse osmosis (RO) treatment process
- Post-aeration (de-gasification) for radon removal and water stabilization
- Chlorination system and clearwell
- An approximately 13,000 SF building with control room, lunch room, laboratory, maintenance shop, process area, and chemical feed room
- Emergency generator sized to power the entire facility for a water production of 2.5 MGD
- Complete SCADA system fully integrated into JCSA’s existing system wide SCADA system
- Approximately 14,000 feet of 12-inch force main for discharge of the RO concentrate to the James River
Almost 3,000 feet of the force main was constructed using horizontal directional drilling to avoid environmentally sensitive areas. This facility also serves as an emergency control center for all of JCSA’s water and sewer operations. Four skid-mounted RO units were installed with membrane installed in only two for an initial capacity of 2.5 MGD. The membrane cleaning system and all ancillary equipment was sized for the ultimate capacity of 5 MGD. In 2006, we assisted JCSA with the expansion of the facility to a capacity of 5 MGD. The plant has operated at capacity for the past two summer seasons.
Because the facility is located near Historic Williamsburg and adjacent to a school and residential area, the facility had to be unobtrusive and pleasing in appearance. The plant building contains all of the process equipment, and was designed to complement the surrounding community. All outdoor equipment was screened from view. We also performed an abbreviated vulnerability assessment of the treatment facility and site to ensure that appropriate security measures were incorporated into the initial design. In addressing the security system design for this facility, we provided means for routine site and building access control, perimeter monitoring, and intrusion detection. All of these systems are monitored in the control room at the plant and can be remotely accessed through the facility’s SCADA system.