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16 <br />36°15' <br />36°!37'30' <br />36' <br />35°52'8G' <br />EXPLANATION <br />Q•iYl)RGGEGLOGIC UNITS <br />IARG)A3iG10.WTE <br />[~ IMIFJ METAIGNEOUS,F"EL51C <br />a:~ IMIIIMEFAIGNEOUS,INTERMEaIATE <br />® {MlM)METAIGNEGUS,MAFIG <br />(MM1(E) METAVGLCANIC, EPICLA5T3~C <br />IM1JF) METAVGLCANIC, FEL51C <br />'IMVIV META40LCANIC, INTERMEDIATE <br />"~ IPHI~ PHYLLIT£ <br />ITRI) 7RIAS51+r 5EDIMENTARY ROCK5 <br />RA08N,13b PICOCURIES <br />PEI1 LlrElt <br />~~"~~ ~ 38.299 ANl7 WE0.L NUMBER <br />~R-1~~® 91Dn • 999AN0 WELL NUMBER <br />OR-104 1,n00-2d99AN0WEL0.NUMBER <br />OEC-1~6® G1~EATER THAN DR EGUAL TD 2,500 <br />pNG WELL NUMBER <br />0 5 ~a r+~iL~s <br />~ -- ' <br />r- <br />0 5 InKILOMETERs <br />Source :Investigation of Ground Water Availability and Quality in Orange County, NC, USGS, 2001 <br />If there is .a geographic area of concern for radon, it is in the south central <br />portion of the County. The wells sampled in the areas west and southwest of <br />Chapel Hill and Carrboro had radon levels in excess of X500 pCi/L. The <br />underlying geology in this area contains several granitic plutans that are <br />relatively "newer" in geologic terms - with a high percentage of feldspar and <br />mica. The largest of these plutons, known as the Farrington pluton, extends <br />south into Chatham County at least as far as the Haw River. This same type of <br />geology was associated with the highest radon readings in Guilford County. <br />Overall, 67% of the wells sampled exceeded the US~PA proposed MCL of <br />300 pCi/L. <br /> <br />7$°15' 79°07'3$' 79° <br />