Orange County Branch Newsletter
ASCE OC EWRI
Practical Approaches to Maintaining Injection Well Efficiency
By Nadia Mugisha | EWRI Board Member
On June 6, EWRI was pleased to host a presentation on Practical Approaches to Maintaining Injection Well Efficiency, given by John Bonsangue and Justin McKeever with the Orange County Water District.
The topic was very timely as water use typically increases over summer and water districts are tasked with managing water efficiently. Historically, the Orange County groundwater basin supplies as much as 75% of water demands of North-Central Orange County for different potable water supply wells around the county.
Over time, the overexploitation of the basin’s aquifers led to seawater intrusion. During the 1950s and 60s, in a joint effort, the United States Geological Survey (USGS), California Department of Water Resources (CA DWR), and the Orange County Water District (OCWD) worked together to define the extent of intrusion. As a response to the problem, injection wells were established as a barrier to stop and combat seawater intrusion into the groundwater basin. (See Graph 1: Extent of Intrusion as of 1963 & Graph 2: Intrusion Retreating after the establishment of Injection Wells)
As of today, the OCWD monitors two generations of wells - legacy wells built in 1975 and modern wells built in 1999, 2000, 2003 and 2006. Legacy wells were built by nesting up to four 6” S.S. casings in a 30-inch-diameter borehole, drilled using reverse circulation drilling method, equipped with a louver well screen, with a pressure reverse valve, a process control and system functionality, with an injection flow rate of 1 mgd / 4 zone.
Some modern wells are either a single point or triple well design. Single point wells are built using a 12-inch S.S. casing inside an 18-22-inch borehole, using a reverse circulation drilling method. These modern wells are equipped with a wire wrap S.S. screen, down well flow control valve fully automated, and the injection flow rate is 1 mgd/per casing.
After the establishment of injection wells, production wells on the path of seawater intrusion indicated a retreat and stabilization of the intrusion. This observation was based on the decrease in chloride concentration in the groundwater basin. The next challenge for the district became well maintenance as wells started to clog. Through trial and error, three clogging mechanisms were identified. Organic slim formers, inorganic sources (pipe scaling and particle deposition) and air entrainment. (See Graph 3: Rates of Injection Well Plugging)
To overcome these clogging challenges, downhole flow control valves driven by both pressure and gas levels were added onto modern wells design to vent the gas out and allow wells to breathe. To get rid of organic slime, a jet and airlifting system with 3 - 4 nozzles, 3/32” diameter, at high pressures and velocity is used to flush down dead organic material coating gravel envelope, access port, and well bleeders. The clogging caused by pipe scaling and particle deposition was the hardest to tackle, but after different trials to find a solution, well backwashing was found to be effective.
Currently, to maintain injection wells efficiency, well design includes a camera port/ airline to enable frequent backwashes and allow air venting out of the wells.
The presentation was very informative and the presenters very knowledgeable experts on this topic. They graciously answered audience questions and made the time a personal learning experience for all who attended.