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Evaluating Collector Well Designs

Sonoma County Water Agency

WHPA developed a new simulation model to describe groundwater flow in the vicinity of Ranney® Collector Wells. The model has been used in all phases of well field analysis:

determining the spacing and lateral arm design of horizontal collector wells that maximize yield and water quality
determining the value of longer microtunneled laterals (as compared to standard pushed laterals) in an existing well
optimizing water quality in a well field that includes a large collector well.

The Sonoma County Water Agency built a new Ranney® Collector Well in the outwash aquifer along the Russian River. This well includes a set of radial arms that were pushed into the aquifer with hydraulic jacks and a single, larger diameter collector arm that was installed directly towards the river with a customized mud-rotary horizontal drilling technique. Initial tests of the new, longer lateral arm suggest that it will produce a very high volume of water into the collector well caisson. It is not clear how a new longer arm might interact with the existing operation. There are three important questions that were addressed:

How much additional water can be produced by this longer arm?
Would any increase in total production be at the expense of production in the other arms of the well?
How does the length of the new arm relate to potential production in this arm?

Our work showed hydraulic resistance inside the lateral arm could be a significant factor in determining how much more water could be pumped by the longer arm. New modeling is being done for the Agency to determine the best approach to developing the narrow alluvial aquifer of the Russian River.