For the past 2 years, if you’ve asked me what I’m currently working on, I almost certainly started talking to you about the automatic percolation tester (or auto-perc tester). It’s a project that’s been my main focus at EMI over the past 2 years. I shared about it a fair bit during our last home assignment (in late 2023). At that point, I thought the project was wrapping up and that I’d just have a few last issues to resolve when I got back to Uganda. Well, here we are in 2025 (just one year late), and I’m pleased to say that 2 weeks ago, we delivered a device to each EMI office that requested one! For those that haven’t heard about the auto-perc tester (or need a refresher), I figured I’d use this newsletter to share a bit about the device and how we hope to see it impact the work that EMI does around the world.
A good starting point is understanding what a percolation test is and its purpose. Perc tests are used to determine a soil’s permeability to water, to understand how quickly water can be absorbed and transmitted through the soil. EMI performs perc tests on almost every site that we work on. It’s especially important for design septic systems as it allows the civil engineers to properly size tanks and leach fields to handle the expected throughput.
The test essentially involves digging a 6 inch hole with an auger to the depth that needs to be tested (typically about 1 meter deep). The hole then needs to be saturated with water, which involves maintaining a set depth of water in the hole until the surrounding soil. The test protocol that EMI uses calls for a minimum 4-hour saturation. After the soil is saturated, the hole is filled with water to 150mm and allowed to drain to 50mm. The depth is measured throughout this to determine the drainage rate. This is repeated several times to ensure that the drainage rate is consistent.
In 2018, the R&D team was asked to investigate some issues on a large campus that we had constructed. They were reporting issues with high groundwater and problems with their septic system. During the investigation, the R&D team found a lot of inconsistencies in the procedures used for the various perc tests that had been done and large discrepancies in the results. This made it impossible to determine what had gone wrong. Were the inconsistencies in the test results due to variations in the soil, or because of the variations in the various tests performed? The R&D team decided to investigate the impact of those variations by performing hundreds of perc tests. The results of those tests was written up in an EMI tech article in 2020.
The conclusion was that we need to be consistent with our percolation tests as an organization. Small changes in the test protocol can have significant impacts on the results. The problem that remained was figuring out how to ensure that the EMI standard is followed on every project site worldwide. It’s (relatively) straightforward to train our staff, but the issue really comes in when we have volunteers performing the perc tests. This is quite common as perc tests are often performed on project trips. These are 1–2-week, design-intensive trips where we bring in volunteers from around the world to do an initial masterplan/design of a project site. This means that it often falls on a volunteer to perform the test. The issue is that there are lot of conflicting perc test protocols worldwide, and the volunteer often ends up defaulting back to the test protocol that they’re familiar with (especially when the EMI protocol is more time/labor intensive).
As engineers, the solution to this problem seems clear: remove the human element wherever possible. So, we set out to design a device that would automatically perform the test with as little human intervention as possible. Essentially, the idea is that if we make the easiest possible option (an automated test) follow the EMI protocol, then everyone is going to want to follow that protocol. There is also another huge benefit: this saves a lot of time for our civil engineers. Project trips are often under serious time constraints. They have to present a master plan to the client, often from nothing, in as little as a week. But important design decisions need perc test results, so the civil engineers end up standing by a test hole for a full day, pouring water in a hole and measuring the water level. By automating this process, we are freeing up those civil engineers to do more tests and be more involved in the design process. We hope that this will lead to more cohesion between the architects and civil engineers, resulting in better designs coming out of our project trips.
So how did we do it? Stay tuned for our next newsletter, where I’ll go into detail on the design and fabrication process of how we turned this idea into an actual product that is going to be used around the world.
Arensen Update
Sage Elizabeth Arensen was born in November! She was born here in Kampala, at the same clinic that Jamie was born. Everything went incredibly smoothly, and we are so blessed to have her as part of our family. Hannah’s sister and Bruce’s mom were able to visit in January/February, and we’re excited for the rest of our friends and family to meet her this summer.
With the arrival of Sage, Hannah has decided to stay at home full time for this season. She’s still staff with EMI and plans to work on the occasional project, support software trainings, and provide drawing/design review. But she won’t have a set schedule in the office. This is quite a big transition for her, but she loves that she gets to be a full time stay at home mom.
We’re going on home assignment this summer! We’ll be splitting our time between Northern VA, Corning NY, and Minneapolis MN, and we’d love to see you. We’ll send an update when we have a more concrete schedule, but we’re currently planning to be there from mid-June to mid-September.
Pray With Us
We are so grateful for your prayers and support! Please join us in prayer and praise for the following:
Prayer requests:
- Pray for Sage’s citizenship interview and passport application. We just received an interview date for June 2; pray that everything goes smoothly and that there aren’t any delays for receiving her passport before we go on home assignment.
- Pray for Hannah’s continued transition to be at home full time. There are a lot of different things pulling for her time; pray for wisdom on where to focus this season.
- Pray for wisdom as we navigate raising little girls cross-culturally. There are so many blessings to raising children here, but it comes with a new set of challenges when it comes ensuring health and safety.
- Pray for the EMI Uganda office as we are anticipating some major changes, the least of all being a new director in the coming months!
Praises:
- Praise God for the birth of Sage!
- Praise God for the completion of the Perc Tester project!
- We are grateful to have seen so many projects completed this past year. Praise God for all of our amazing ministry partners who are serving those in need and spreading the gospel through schools, hospitals, and places of refuge.
Stay Connected
Each year, EMI’s people complete over 100 development projects which serve the poor and proclaim the Gospel of Jesus Christ. To keep these design services affordable for Christian ministries, professionals like the Arensen’s on EMI’s staff are responsible for raising their own salaries. We are so grateful for God’s provision through the generosity of donors. Would you prayerfully consider partnering with the great things God is doing through the Arensen’s ministry at EMI?