Fort Collins 2011

I'm back from another well-attended aquifer testing short course held at the headquarters of In-Situ, Inc.on October 5 and 6, 2011 and the sixth consecutive year that we've traveled to Ft. Collins, CO to present Aquifer Testing for Improved Hydrogeologic Site Characterization Featuring AQTESOLV and the In-Situ LevelTROLL.

Analysis of recovery data combining Agarwal method and derivative analysis.

The course covered topics relating to designing, performing and analyzing both slug tests and pumping tests and included hands-on use of AQTESOLV as a teaching tool. As part of my lectures, I spent a good deal of time going over the finer points of diagnostic methods for pumping tests including derivative analysis, a technique widely practiced in the petroleum industry for well test analysis. I further introduced the class to the Agarwal method for analyzing recovery tests which also drew a lot of attention.

Thanks to all who attended the course and to In-Situ for hosting us! I look forward to doing it again next year.

Enhancing Reliability of Slug Test Data Analysis

Data from an overdamped slug test in a well with a fully submerged screen (screen below water table) may exhibit a concave upward appearance on a plot of log normalized head vs. time. The curvature can make analysis by straight-line methods such as Bouwer and Rice (1976) somewhat ambiguous.

Analysis of slug test data using recommended normalized head range.

Butler (1998) suggests matching straight-line slug test solutions to data within recommended normalized head ranges to overcome ambiguity associated with slug test data curvature and thereby enhance the reliability of data analysis. AQTESOLV, advanced software for slug test analysis, includes the recommended normalized head ranges to assist you with visual curve matching.

Learn more about recommended normalized head ranges and slug testing in Aquifer Testing 101 at the AQTESOLV web site.

Summit in Lawrence, Kansas

On today's date in 1969, Neil Armstrong made history by becoming the first man to walk on the moon. Forty-two years later, July 20th marks another red-letter day with the conclusion of the 1^st Lawrence Summit hosted by Jim Butler and attended by Dan Kelleher and myself. The summit met its primary goal of laying the groundwork for future aquifer testing short courses around the world.

GEMS Research Site (Butler et al. 2000)

Unforgettable moments during the visit included a tour of the venerable Kansas Geological Survey and its GEMS research site, a view of the Allen Field House from Jim's bleacher seats ("Rock, Chalk, Jayhawk!") and a reverential pilgrimage to the James Naismith ("Inventor of Basketball") Memorial. Without question, though, the unsurpassed highlight of the summit was the delightful sushi dinner served to perfection by Jim's daughter, Mai. Many thanks to Jim and wife Yun for their warm hospitality throughout the Lawrence Summit!

Agarwal Recovery Method

In yesterday's post, I presented three different methods for analyzing recovery tests. Today, I will focus on the Agarwal recovery method which has been used by petroleum engineers for over 30 years. Agarwal (1980) devised a simple yet powerful data transformation for the interpretation of recovery tests. The transformation, known as Agarwal equivalent time, allows one to analyze recovery data with standard type curves developed for drawdown data.

The following figure illustrates the simplicity of the Agarwal method in the analysis of a recovery test. In this example, I matched the familiar Theis type curve, normally applied to drawdown data, to estimate aquifer properties from recovery test data (USBR 1995).

Agarwal recovery analysis using Theis (1935) solution.

Many different pumping test solutions may be used in conjunction with the Agarwal technique as well as diagnostic methods such as derivative analysis. The figure below shows recovery and derivative data matched together with the Cooper-Jacob straight-line solution.

Agarwal recovery analysis using  Cooper-Jacob (1946) solution with derivative.

Recovery test analysis with the Agarwal equivalent-time method is available in AQTESOLV v4.x. This advanced aquifer test analysis software allows you to estimate aquifer properties by matching both recovery and derivative data together.

Learn more about the Agarwal method in Aquifer Testing 101 at the AQTESOLV web site.

Analyzing Recovery Tests

Did you know that AQTESOLV v4.x provides three different methods for the analysis of recovery tests?

Method 1: Combined analysis of drawdown and recovery data.

Method 2: Analysis of residual drawdown data.

Method 3: Analysis using Agarwal (1980) method.

The foregoing figures illustrate the use of the three recovery test methods in the analysis of a field example reported in the Ground Water Manual (USBR 1995). The results show that one may obtain consistent aquifer property estimates with all three techniques.

Learn more about the three methods of recovery analysis in Aquifer Testing 101 at the AQTESOLV web site.

Groundwater Mounding

Upon its release in 2006, AQTESOLV/Pro v4.0 became the first aquifer testing software to feature groundwater mounding calculators that predict the transient rise and decay of the water table beneath rectangular and circular recharge areas (Hantush 1967). Using AQTESOLV, you may compute the maximum rise of the water table and generate contours of a groundwater mound with ease.

The example plot (above) shows a 3-D contour plot of a groundwater mound developed around a hypothetical rectangular recharge area. Applications for the groundwater mounding calculators in AQTESOLV include infiltration from septic systems and recharge from stormwater impoundments.

Visit the AQTESOLV web site for more information on the Hantush (1967) solutions for groundwater mounding prediction.

ASTM "Standards"

ASTM publishes "standards" on many subjects including aquifer test analysis. ASTM D5912-96 (2004) entitled Standard Test Method for (Analytical Procedure) Determining Hydraulic Conductivity of an Unconfined Aquifer by Overdamped Well Response to Instantaneous Change in Head (Slug) is one such ASTM standard. You'll spend $32 to obtain a copy of this four-page standard from ASTM, but don't expect to get completely accurate information for your investment.

ASTM D5912-96 (2004) describes a widely used method of slug test analysis devised by Bouwer and Rice (1976). The standard contains an equation (ASTM D5912-96 (2004), p. 2, Equation [2]) used in the Bouwer and Rice method to calculate the parameter ln(R_e/r_w) when D (the aquifer thickness) is greater than H (the penetration of the well) as follows:


The ln(R_e/r_w) parameter is used in the Bouwer and Rice method to calculate the hydraulic conductivity K from a slug test.

Unfortunately, the above equation from ASTM D5912-96 (2004) is incorrect. The correct form of this equation (Bouwer and Rice 1976, p. 425, Equation [8]) is written as follows:


As one can see from a comparison the two foregoing equations, the ASTM version misplaces the term L/r_w and leads to a completely erroneous estimate of ln(R_e/r_w).

Am I just nitpicking here? I don't think so. It's hardly unreasonable to expect thorough attention to detail from a publication put forth as a "standard" such as ASTM D5912-96 (2004). Certainly, the basic equations that are central to such a standard should be checked carefully and published without error. ASTM standards purportedly go through a rigorous review process. Yet ASTM D5912-96 (2004), adopted in 1996 and subsequently reapproved in 2004, still contains the flawed equation. One is left to wonder how many other "standards" relied upon for aquifer testing contain similar fundamental errors.