Sunday, October 25, 2020

The Well Went Dry.

How long will it take to refill?

A common question I get from people who think their well has gone dry is how long will it take to refill. Depending on why it went dry, the answer could be tomorrow, when the drought is over, or never. First, make sure that your well has gone dry. The  problem could be:
  1. Equipment failure,
  2. Well failure, or
  3. Diminished aquifer
Check the equipment and power first. Then actually measure the water level (a well service company can do it with a sonic sounder gun or electric probe) recharge rate  in your well should be done before you spend money replacing equipment or thinking of drilling a new well. The recharge can be estimated by water level recoveryafter pumping. It is best to use the recovery yield rates to compare to the rates from previous recovery tests since the recovery yield rate tends to decrease logarithmically as the water level rises because the decreasing difference in head between the well and the adjacent aquifer. However, in fractured rock aquifers as seen around here, the water-level recovery is a straight line in the early period because most of the inflow is from discrete exposed fractures discharging freely above the water level. The well yield may be estimated from this straight-line portion of the graph.

In a well, a diminished water supply can be caused by drop in water level in the well due to drought or over pumping of the aquifer, or the well itself could be failing in several other ways. Even if an aquifer is sound a well may go dry due to encrustation of fractures in a bedrock well or collapse in a well drilled in sandy soils.

I have occasionally gotten a call from someone new to well ownership who watered their lawn and did several loads of laundry and found the limit of their well supply when their well ran out of water. (A top loading washing machine uses about 51 gallons of water and a front loader uses 27 gallons.) What is happening is the well recharge is often less than the pumping rate and they simply kept pumping the water stored within the well bore itself to make up the difference...until the water level falls below the pump. If the well still has a healthy recharge it will only be a matter of hours before it refills. The well bore hole will fill overnight with as much water as it can still produce.  Depending on how much storage your well has (how deep it is) and how much water the well can still produce (if it is stable) it may be adequate with water conservation and demand management.   

This low flow to the well can be caused by drop in water level in the well due to drought (temporary) or over pumping of the aquifer, or the well could be failing due to a buildup of dirt, sediment and gravel reducing the flow to the well (these problems may be fixable). There are times that the steel casing that lines the first 40-60 feet of a well does not extend deep enough and the well walls crumble over time filling the well with dirt and gravel. One or more of these factors could be the cause of a well going dry.

Private wells draw their water from groundwater. Geology, climate, weather, land use and many other factors determine the quantity of groundwater that is available. The water level in your well depends on a number of things, such as the depth of the well, the type (confined or unconfined) of aquifer the well draws from, the amount of pumping that occurs in this aquifer, and the amount of recharge occurring.

Within Prince William County Virginia there are several distinct geologic provinces that will have different groundwater characteristics. The northwestern part of Prince William County down the hill from Bull Run Mountain, consists of sedimentary rocks of the Culpeper Basin. The predominant rock types are conglomerates, sandstones, siltstones, shales, and argillaceous limestones. This geology tends to have moderate to excellent water-bearing potential because it is a fractured rock system with very little overburden. The highest reported yields in the county are from wells in this geology. In other parts of the county there are deep wells in the diabase that tend to have reliable lower yields.

The water level in a groundwater wells naturally fluctuates during the year. Groundwater levels tend to be highest in the early spring after winter snowmelt and spring rainfall when the groundwater is recharged. Groundwater levels begin to fall in May and typically continue to decline during summer as plants and trees use the available shallow groundwater to grow and streamflow draws water. Natural groundwater levels usually reach their lowest point in late September or October when fall rains begin to recharge the groundwater again. If an aquifer is being used up, then despite the seasonal cycles the water level will continue to decrease and ultimately impact the well’s ability to supply water.

If your water loss seems to be from failure of the well itself, the first step is to call a well driller and measure the water level and recharge rate of the well. That information will tell you what you are dealing with and what choices you have to fix the problem. For the next steps

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