Monday, November 30, 2015

What Makes a Good Monitoring Well?

Aquifer conditions are dynamic and therefore water levels can fluctuate because of drought, recharge, and pumping.  Monitor wells help track these changes and inform policy to help protect water supplies and spring flow for all users.  After all, groundwater is a shared resource.
We often get asked the question, what makes a good monitor well? In short, the answer is that a well that is representative of the aquifer we are interested in. But, while water levels can be measured in most wells, the nature of the geology and well construction usually limits the potential for a well to be used for monitoring purposes.
Diagram of a typical well headAt the surface, groundwater wells can appear  similar, however  individual wells--even neighboring ones--can be constructed in very different ways.  For example, different depths of wells, or different depths of the casing influences production rates and water quality.  Well records (e.g. driller's logs, geophysical logs, video logs) are key to understanding a well's construction.
Drillers use a variety of construction methods to balance sufficient quantity (yield) with good (a relative term) water quality.  The Edwards and Trinity Aquifers are each made up of many layers of rock.  Water quantity and quality can vary from layer to layer.  The location and depth of a well, and how it is constructed, determine what rock units that well can access and therefore influence its yield and quality. The construction of a well such as its casing depth, amount of cement, and/or packers can seal off undesirable layers. At the same time, the well is left open or screened at selected intervals to allow water to enter the well at the desired layers.
Every well should have a driller's log that documents well depth, well construction, pump setting, and an initial water level.  In 2003, all well drillers were required to submit this information online, so data on wells drilled in the last 12 years is much more accessible. In sensitive areas, a more detailed geophysical log is often required to inform the well construction and to limit the mixing of undesirable waters between aquifers (and into the well).
On the top of the well (called well head), most contain a 1/2" or 3/4" hole that can allows the measurement of the water level in the well (also called an observation port). To prevent debris or contaminants from entering the well, this port is usually plugged by a blue plastic square-head nut. The water level can be measured through that port using either an eline (electric measuring tape; reliable but time-consuming) or a sonic meter (bounces a sound wave off water surface; fast but requires verification).
District staff maintain over 30 continuous water level monitoring sites in the Edwards and Trinity aquifers. A pressure transducer and the cable installed in a domestic well with a drop tube.Many of the wells are domestic wells that are in use.  These sites are equipped with a probe (a pressure transducer) that is programmed to measure the water level hourly.  Staff stop by to download the data about once a quarter, or more frequently for a specific study. These monitoring wells are plumbed with a drop pipe that keeps the pressure transducer and cable away from the pipe that brings water to the surface and the pump wires. Monitoring does not interfere with operation of the well.
Everyone benefits from an efficient monitoring network.  Optimal monitor wells are representative of the aquifer and area we are interested in learning about. Monitor wells need good construction information (logs) and must be readily accessible. Many thanks to all of the well owners who allow this essential access to water level data, respond to conservation requests, and responsibly use and maintain their wells.  We are all in this together.
Useful links:
Geologic diagram of aquifer layers (stratigraphic column)

Thursday, November 5, 2015

Pouring It On

             For many in Central Texas, the morning before Halloween was much more frightening than the holiday itself. An historic flood, larger than the previous Halloween 2013 and Memorial Day 2015 events, occurred as a large front of heavy rain and thunderstorms swept across the region early Friday.
USGS Stream Gage on Onion Creek at Twin Creeks Road:

Halloween 2013: Gage Height: 20ft; Discharge: 12,000 cfs
Memorial Day 2015: Gage Height: 22ft; Discharge: 17,000 cfs
Halloween 2015: Gage Height: 28ft; Discharge: 45,000 cfs

In Buda, the final rain total reached an astounding 18.46 inches. Surrounding areas, including Kyle, San Marcos, Wimberley and Onion Creek all reported between 11” and 16”. In addition to punishing rain totals, the storm generated three tornadoes and a great deal of property damage.

What made this flood so much more significant than the aforementioned 2013 and ‘15 events? In this case, huge amounts of rainfall were concentrated in a shorter period of time. In addition, the ground in Central Texas was relatively dry prior to this year’s Halloween flood than the months preceding the two earlier events. In dryer conditions, heavy rain doesn’t immediately infiltrate below ground; rather, there is a kind of shock from sudden intense rainfall which results
in surface flow rather than penetration. Potentially-devastating flash floods are sure to follow. 

On the other hand, the Highland lakes saw significant rises in water level, counter to perennial dread about its historical low water levels. Recharge to the Edwards Aquifer hit overdrive, as recharge sites like Anitoch cave (pictured below) submerged.

We recognize that this relief is accompanied by devastation. We’re grateful for the responders who helped evacuate those who experienced this downpour as a disaster. We send care and encouragement to those reeling from yet another assault on their homes and loved ones by extreme flood events.

For information on the response and resources available in Austin and surrounding areas, visit

In the wake of flood events, it may be necessary to take extra precautions like boiling drinking water from your private well. Take a look at to find out more.