You may have noticed as you have driven in and around Colorado neighborhoods that some homes have rectangle (like cutter pipe) external exhaust piping, and others use round piping. That's because physics researchers have studied the flow and dispersal of particles in a fluid (air is a fluid) for scores of years; entire manuals have been written filled with hundreds of numerical tables to aid in the design of flow through various shaped pipes.
Researchers have found out that the flow through various shaped pipes is somewhat counter intuitive. As it turns out, dispersal through cylindrical and oval pipes is nearly identical, and flow through rectangular, not square pipes with an outer measurement of 1.86:1 (or nearly 2:1) in shape provides a nearly identical flow pattern to that of oval and cylindrical piping.
Essentially, with regards to proper functionality, there is very little difference between the round pipes and the rectangular pipes you see in and around your neighborhoods.
USEPA Guidelines clearly indicate that every RADON Mitigation system exhaust stack should be completed at least 12 inches above the roof eave (for externally mounted exhaust fans) or roofline (for attic/internally mounted exhaust fans). International Building Code (IBC) specifies that the stack should normally be completed two feet above the eave or roofline but in no instance should it be completed less than twelve inches above the roofline.
There are many so-called "certified" RADON testers and mitigation installers in Colorado that routinely install the RADON Mitigation system exhaust stack below the eave of the roof. Whatever reason they give, the installation is not to EPA standards and is therefore improperly installed.
The short answer to this question is a resounding YES! No sooner than 1 week after installation and no later than 1 month after installation, your structure should be retested and a follow-up report comparing the before and after analysis results should be presented with a recommendation. Otherwise, how will you know if the RADON Mitigation system is actually mitigating the RADON in your home...? Finally, follow-up testing should be done using Granular Activated Carbon canister(s) [GAC]. GAC will rarely to never give you a false positive test.
This retest should be included in the cost of your mitigation system installation, as should the follow-up report.
If the results of the follow-up show that there is little or no difference between the test results, your RADON Mitigation Professional should make any and all adjustments to make your mitigation system effective. AT NO ADDITIONAL COST TO YOU! If adjustments are made, then another retest should be conducted to prove effectiveness...again, using GAC, AT NO ADDITIONAL COST TO YOU!