I agree with Tim.I would probably use an RP140 or Hp2133 fan. The smaller energy consumption the better. Take some pressure reading in the slab before and after though. Tony McDonaldDirector of Commercial AccountsA-Z Radon Services11377 Miller Ave NEHartville, OH 44632330.877.5515 Office330.877.8912 Fax From: International Web Resource for Radon Professionals [mailto:RADONPROFESSIONALS@LIST.UIOWA.EDU] On Behalf Of Timothy PittmanSent: Wednesday, May 18, 2011 4:33 PMTo: RADONPROFESSIONALS@LIST.UIOWA.EDUSubject: Re: [RNPROF] Wet clay under slab Should work like a charm. Have had to resort to this method several times. I would assume the french drain pipe "daylights" on each end. You will need to find the ends and install one way backflow type valves. You may not need the high vac fan....most of the time I end up using a high flow type...just check your pressures and size the fan accordingly depending on pressures and leakage. If you are in a cold climate sometimes you may have problems in winter with the valves freezing. Another possible problem is if somebody has tied downspouts or yard drains into this drain line..,that happens quite often. Good luck. Tim PittmanSent from my Verizon Wireless BlackBerryFrom: brian popke Sender: International Web Resource for Radon Professionals Date: Wed, 18 May 2011 14:07:52 -0600To: ReplyTo: brian popke Subject: [RNPROF] Wet clay under slab We're working on a house that had a French Drain installed after the home was built in the 70's. The basement was flooding. We didn't consider using it, the realtor thought it was about 8' from the house. We drilled a suction point in the basement closet the sub strate is very saturated clay, heavier than modeling clay, the kind you make bricks out of. After talking with the home owner we found out the french drain is against the footer on 3 sides of the house, which is the basement. It tested at 5.2 pCi/L. What we think will work is using a higher suction fan GP501 and using the french drain. The french drain was lined with a lot of gravel. Any comments on success/failure of this idea? Thanks!********** RN PROF (Subscription changes - archives) - http://list.uiowa.edu/scripts/wa.exe?SUBED1=RADONPROFESSIONALS&A=1 *********** ********** RN PROF (Subscription changes - archives) - http://list.uiowa.edu/scripts/wa.exe?SUBED1=RADONPROFESSIONALS&A=1 ********************* RN PROF (Subscription changes - archives) - http://list.uiowa.edu/scripts/wa.exe?SUBED1=RADONPROFESSIONALS&A=1 ***********