I would like your assistance.

I have a Client who has a fairly small home with an ASD system, and rents one side of the basement to a tenant. The Renter did a radon test which came back at 5.6 pCi/L and moved out until levels can be brought lower. After speaking with me, Client decided he had more faith in me than original installer and asked for my help. I found and corrected some major errors with the original installation, but have not been able to get concentrations where we want them. Unless noted, there were no significant anomalies with any test data. All test exhibited normal patterns, and all ( with one exception) were done during normal weather conditions for the area. (Please refer to the attached diagrams/tables in the PDF at the bottom.)

Basement is approx. 1000 sq ft, has crushed stone under the floors, and has no garage/carport/porch slab on the upper level. It is a multi-piece modular home where sections are pre-built and bolted together; the center wall is 10" thick (framed). If I remember correctly, exterior walls are poured concrete. There are no below-grade utility penetrations, and no dry traps/drains. House is on City water. Where wall/floor joint was accessible in storage room, Client caulked perimeter. In the rest of the basement it has 1x4 baseboards on concrete floors. He caulked the top and bottom edges of all baseboards. The one variable with which I am not familiar is a free-standing portable A/C unit in the apartment that exhausts through a window. I am unsure whether the exhaust is for heat only, or whether it actually pulls air from the basement (which seems illogical). In any case, tests were done with the Unit off, as it does not run the majority of the time.

Original system had an older RP140 fan which was making some bearing noise, but still moving air pretty freely.
My PFE diagnostics showed that the original system was affecting only 2 of the 4 sub slab areas divide by footers. The PFE did extend across the center footer, (probably because there are plumbing and drain lines that cross the center), but did not reach the front room on either side. As we had pretty good PFE and a relatively small footprint, my solution was to "stitch" the other slab areas to the ones that had good PFE by adding suction points on either side of footers, connected to each other (thanks Bill Brodhead). After stitching slabs, the radon retest at 3.7 pCi/l, but the renter was not satisfied and would not move back in.

We then swapped the fan since the bearings were beginning to fail. As Client was desperate to get the Renters back in, he wanted to just jump to a very powerful fan even though a more energy-efficient one may do the job, so we tried an Eagle Extreme to increase both vacuum and airflow. PFE increased substantially, but radon concentrations also went up to 4.6 pCi/L.

After discussion with my fan supplier, we could not think of a specific instance of it having occurred, but both agreed there was a possibility the strong fan was pulling radon in from outside the foundation somewhere. After swapping the fan to a Maverick (1" w.c. on u-tube), the retest came back at 7.6 pCi/L, but this test had an anomaly where the concentrations spiked up to 30 pCi/L and back down over about 12 hours. Dropping that data, the rest of the test averaged 5.7 pCi/L. Client subsequently did an AirChek test which came back at 4.4 pCi/L.

I admit to being somewhat mystified as to why there is still a radon issue with such good PFE across the slab (-.008 at farthest point from fan.).
Thoughts and questions?
Thanks,