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0016 <br /> 79°15' 79"0730' 790 <br /> 36"15' i i <br /> O <br /> OR-111 �------•- - -- <br /> i •�- <br /> I •OR-116 OOR 10) OR-106� <br /> o <br /> I ' <br /> OOR-118 <br /> ORA19 <br /> 0 O R-115 0 OR-111 ! <br /> I I OR-114 ` OR-1080 <br /> OR-131 0 00-110 EXPLANATION <br /> 6 0 O O OR-109 I HYOROGEOLOGIC UNITS <br /> OR-12100R•122 <br /> I OR-112 OR-113 O UTARGIARGILLITE <br /> I O OOR•124 <br /> 36°07'30' V-- 0OR-104 OR-100' F-11(MIFj METAIGNEOUS,FELSIC <br /> I <br /> 0 OR•123 O OR-101 0 ❑IMII!METAIGNEOUS,INTERMEDIATE <br /> i OOR-102 ' D IMIMIMETAIGNEOUS,MARC <br /> i ❑(MVE)METAVOLCANIC,EPICLASTIC <br /> iOOR-120 0OR-98 I CD(MVFIMETAVOLCANIC.FELSIC <br /> I OR-97 <br /> OR-105 OR-89 OR-130' ❑IMVIIMETAVOLCANIC,INTERMEDIATE <br /> i <br /> FOR-95 0 O 01 ❑(PHL)PHYLLITE <br /> OR-87 OR-85 I (-1 ITRII TRIASSIC SEDIMENTARY ROCKS <br /> 0 0' . 99 I RADON PERPLIT ERURIES <br /> 0 <br /> 36°i' OR 92 OR-80 j OR-1000 39.299ANDWELL NUMBER <br /> OR-92 OR-1130 300.999 AND WELL NUMBER <br /> 0 OR-94 OR-81 OR-104 <br /> OR-911 pg.gp 0 ' 0 I,D00.2,499 AND WELL NUMBER <br /> O 0 O O pR-83 OR-1260 GREATER THAN OR EQUAL TO 2,500 <br /> I OR-91 I AND WELL NUMBER <br /> ! , o CPR-84 <br /> '! I OR-129 <br /> O R-93 0 OR•880 0 OR-127 l <br /> i <br /> OR-128 OR-126 I <br /> 35"52'30' ;- ,�• 0 <br /> I I � • <br /> 0 5 10 MILES <br /> 0 5 IOKILUMETERS <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 Carrbor in excess of 2500 i <br /> o had radon levels C L. The <br /> P p / <br /> underlying geology in this area contains several granitic plutons 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 USEPA proposed MCL of <br /> 300 pCi/L. <br /> 9 <br />