In many instances, monitoring wells need to be installed to characterize the water quality in the aquifer. However, this may also entail only screening a very small interval so discrete samples can be obtained or the aquifer has very limited production potential. When water quality sampling is key to understanding existing water quality conditions, the introduction of foreign water is not acceptable. As such, developing monitoring wells in a low-producing aquifer so they can sample native groundwater can be challenging.

LWS follows procedures to ensure proper completion of every groundwater well, regardless of the yield of the aquifer system. Typical groundwater well construction includes installation of the well screen, well casing, and filter/gravel pack. After construction, the process of well development must be undertaken to clean the borehole and casing of drilling fluid and fine sediments that were introduced during the drilling process. The primary objectives in well development are to establish optimal well yield that indicates the well has been adequately cleaned, which will also allow representative water quality samples to be obtained.

Widely-used techniques include bailing, over-pumping, jetting, surging and rawhiding. Details about these methods can be found in our blog post about development of the Monument Well 10. Although a seemingly straightforward process, wells will not always develop quickly and easily. Factors that influence the rate of development include the well design specifications (screen slot size, gravel pack thickness, type of gravel pack), the type of drilling fluid, and the nature of the formation. When there is very little formation water to create flow into and out of the well during this process, tailoring development to the aquifer conditions is critical.

Recent work for LWS involved completing multiple monitoring wells in a tight, clayey aquifer, with a primary purpose of collecting water quality samples once the wells were completed. Therefore, it was necessary for the well development to be sufficient to obtain representative samples. An important consideration for all well development operations is that well development should always take the necessary time until the well is essentially clear to provide unrestricted flow and native groundwater is being produced by the well.

For our recent project, once the development process began, initial data were collected to understand the well condition. Water levels were recorded and the saturated casing volume was calculated. Initial pumping of the well commenced to understand the drawdown and recovery rate of water levels. With this information, the necessary development techniques and timeline were further defined.

This initial data collection enabled our team to understand that multiple wells were limited in production to a range of approximately 2 gallons per minute (gpm) to 5 gpm, with one well not even being able to sustain 1 gpm. Knowing the screened interval would not easily accept fluids nor would water levels recover quickly, we re-evaluated our well development plan to increase effectiveness and maintain the project timeline and budget.

Considerations when developing a low-yielding well include:

Which well development techniques should/can be used?
Can water in the well be surged to produce the flow needed to clean the filter/gravel pack?
What is the purpose of these wells?

Introducing foreign water downhole did not comply with site requirements for this project. Therefore, we had to rely on the natural productivity of the wells to assist with development. This led to a difficult process as the low productivity of the aquifer was further hampered initially due to the suspended materials in the well and the gravel pack from the drilling operations.

Each of the wells underwent bailing and surging with the bailer as an initial means for the loosening and removal of water and fine sediments. During bailing, depth-to-water was noted along with observations about the water level recovery rate to understand the water level recovery rates in the wells. Bailing continued until the heavier material had been removed from the well and water level recovery rates had increased and stabilized.

Following this initial step, and with an understanding of the water level recovery rates, a pump was installed downhole to begin purging the well screen and adjacent aquifer. Pumping was necessary to surge the well in short increments, as the well could not sustain high pumping rates for any extended period of time. In fact, production was so limited that, for some wells water levels had to be allowed to recover overnight so there would be a sufficient water column to allow surging of the well with the pump. Surging then continued until the well was producing essentially clear, sand-free water.

From the bailing to the pumping process, water quality parameters were also periodically collected to inform of the development progress. These data assisted in understanding when representative aquifer water quality samples could be obtained. Parameters documented included:

Temperature
Specific conductance
Turbidity
pH

An important property to measure during well development is turbidity. Turbidity refers to the clarity of water and units are nephelometric turbidity units (NTU). Photo 1 shows the turbidity meter used to measure turbidity with suspended and dissolved solids scattering light from a beam.

There are many acceptable methods for the development of wells; however, the appropriate method(s) can vary significantly depending on the purpose(s) of the wells and the aquifer system that is being characterized by the monitoring well system.

If you are in need of a groundwater monitoring plan, water quality sampling plan, and/or analysis of water quality data LWS can help with your water quality needs. Feel free to give us a call (303-350-4090) or email our team members.

Bruce Lytle bruce@lytlewater.com

Chris Fehn chris@lytlewater.com

Ben Bader ben@lytlewater.com

Anna Elgqvist anna@lytlewater.com

Dan Rowe dan@lytlewater.com

Marlena McConville marlena@lytlewater.com