From Leonard Rice Engineering:
A Three-Part Blog Series
To paraphrase Brad Pitt, the first rule of Water Club is that “there is never enough water”. OK, maybe not everywhere, but in the Western United States, there isn’t a truer statement to be had. The states in this region constantly struggle to find balance between an ever-growing population and an ever-dwindling water supply for that population. Municipalities are continually seeking ways to maximize the usage of accessible supplies, which has spawned alternative water resource management solutions like Aquifer Storage and Recovery (ASR). ASR can be achieved through recharge basins, vadose zone wells, or dual purpose wells (Figures 1-3). One of the benefits in storing directly into aquifers is the ability to preserve supplies from evaporating, which typically occurs behind surface reservoirs. ASR is still an evolving science, and there are currently several ASR methods being utilized within the industry, each with benefits and drawbacks.
In this three-part series, we will review ASR as a viable water resources management strategy and how new technologies are improving well efficiencies in recharge and pumping performance. These newer recharge well systems have also become manager/operator friendly, which results in efficient reporting to State Agencies, reducing the labor force, reducing operational and maintenance costs, and provide quick performance data.
Part One: Reverse Siphon Method
Before we dive into the different kinds of recharge methods, let’s take a look at some pitfalls that are common to all ASR wells. We start with the number one issue – clogging. Reading the term clogging and the first word you think of might be an artery, like your heart. Actually, well clogging is a lot like artery clogging and the end result is the same – the equipment stops working, which is not good in either case!
Well clogging typically occurs in three locations: proximal to the well, intermediate (interface between filter pack and aquifer) and distal (exceeding 100 feet beyond the well). Depending on where the well clogs, it can take different forms. Abrasion between grains, air binding, biofilm, cementation and dissolution are all types of clogs found in ASR wells, and all require slightly different solutions to resolve the issue.
The conventional method in reducing air binding/air entrainment clogging in ASR wells is by the installation of a down-hole flow control valve. This valve is attached to the pump assembly and prevents air from the column pipe from binding onto the filter pack and unconsolidated sediments in the aquifer.
An alternative recharge method was developed at the City of Phoenix to reduce air entrainment into the aquifer, ensure easy maintenance, lower operations and maintenance costs, provide an easy operator interface, have the ability to unclog the well with the permanent pump, and increase recharge utilization. This alternative method is called “reverse siphon”. Instead of a valve connected at the bottom of the pump assembly, the controlling valves are positioned at the wellhead infrastructure for system hydraulic balancing, removing air from the column pipe, and for easy maintenance for the operator. This method requires an understanding system hydraulics, programming, and reverse flow testing through line-shaft turbine impellors.
The reverse siphon method entails the following steps:
Pump the well to waste (e.g., sanitary sewer) to expel out particulates accumulated in the well and to remove air from the column pipe. Slowly transition and open the recharge globe valve to deliver the source water to the well and pump to waste system. All purged particulates in the recharge source will go to the pump to waste line. Once the programmed flow rate is achieved on the recharge line, the pump to waste valve will slowly close and the line-shaft turbine pump will shut off and lock into place with the use of a non-reverse ratchet. The recharge source line will flow resources down the well (via system pressure and gravity) and to the pump to waste line. Once the pump to waste line is fully closed, the well is transitioned into recharge mode. This reverse siphon method typically takes 5 to 7 minutes to transition from pump to waste to recharge mode and all valves are automated to open and close with programming developed at the Operator Interface Terminal.
In Part Two: we will continue examining new technologies linked to the “reverse siphon” method. These technologies/advancements build upon better and sustainable well injection performance.