Last week we discussed aquifer hydraulic characteristics and what they mean, this week LWS continues with more on that topic. Aquifer hydraulic characteristics are used for a number of reasons, including estimating:

Aquifer production rates to meet average and peak day demands;

Pump cycle durations, as well as water level recovery times between cycles;
Annual volumetric capability per well;
Boundary conditions that could affect well production over time;
Pump setting depths;
Well and aquifer efficiencies;
Need for rehabilitation and/or re-drill; and
Sustainability of the water supply over time.

Aquifer tests such as constant-rate, constant-head, and falling-head tests can provide most of the information described above. Particularly with constant-rate tests, not only can the hydraulic conductivity and transmissivity be estimated but, if the test is conducted over a long enough period, an assessment can also be made of boundary conditions, either recharge, no-flow, or simply changes in the regional transmissivity. To evaluate boundary conditions it is typically recommended that tests in confined aquifers be conducted for a minimum of 24 hours, while a 72-hour minimum pump test is recommended in unconfined aquifers. Site-specific conditions where boundary conditions are suspected may warrant variations from these minimum recommended timeframes.

Step tests serve a different purpose, as they are necessary to evaluate well and aquifer efficiencies and can also be useful in providing information related to the need to rehabilitate or re-drill a well. When the inverse of the specific capacity is plotted against flow rate for each step, the y-intercept value (B) of the best-fit line is associated with head losses in the aquifer and the slope of the line (C) is associated with the degree of head loss in the well. The lower the y-intercept, the higher the well efficiency. A steeper slope of the line indicates higher head loss in the well, i.e., loss of well efficiency, at higher pumping rates. A low slope indicates that the well losses are low over the range of pumping rates tested. Step test data can also be used to assess not only the current efficiency of the well/aquifer but also whether well rehabilitation is warranted (or a re-drill), particularly if step tests are conducted periodically in a well to allow a comparison of data over time.

step test efficiency evaluation — *Step test efficiency evaluation*

Look for an upcoming LWS blog on the procedures for conducting aquifer testing to develop aquifer hydraulic characteristics, including the data collection requirements and interpretation of step test data. For more information about aquifer testing and what is required in your particular situation, please reach out to Lytle Water Solutions and we will be happy to provide you a proposal tailored to your needs, free of charge. We can be reached at 303-350-4090 or email any of our specialists below.

Bruce Lytle: bruce@lytlewater.com

Chris Fehn: chris@lytlewater.com

Anna Elgqvist: anna@lytlewater.com

Ben Bader: ben@lytlewater.com

Dan Rowe: dan@lytlewater.com