Table 1.

Geological and Hydrogeochemical Characteristics of Bedrock Aquifers Containing Arsenic

Province/State	Geologic Formations (Fms)	Rock		Hydrochemistry	Groundwater w/Chemistry			References
		n	Max As mg/kg		n	Max As µg/L	% >10 µg/L As
Nova Scotia	Meta-sedimentary rocks (slates, greywackes and quartzites) of the Halifax and Goldenville Groups of the marine-deposited Cambrian-Lower Ordovician Meguma Supergroup, regionally metamorphosed to the greenschist facies during the Devonian period. Arsenic as arsenian pyrite in quartz veins once mined for gold. The 95th percentile [As] in well water in each of the five bedrock regions are: metamorphic (65 µg/L), plutonic (34 µg/L), sedimentary (10 µg/L), carbonate/evaporite (9.0 µg/L), and volcanic region (3.0 µg/L)	55	>1,000	Ca-HCO3 or Na-Cl type, pH 8.0–8.6, no DO, >90% As as AsIII, Fe 0.05 mg/L – 0.17 mg/L	3	365	100	Bottomley, 1984; Dummer et al., this issue
New Brunswick	Harvey Fm with volcanic tuff overlain by thick deposits of Carboniferous sandstone and other clastic rocks. Magnetite contains As. As risk ranks from high in black shale, coal, high-Fe sedimentary rock, moderate and moderate-low in extrusive igneous and marine sedimentary rocks, to low in intrusive igenous and non-marine sedimentary rocks	124	275	Ca-Cl type, pH 7.0, DO 1.7 mg/L, >90% As as AsIII, Fe 0.07 mg/L	1	146	100	Bottomley, 1984; Klassen et al., 2009
Maine	Ordovician Penobscot Fm with sulfidic, carbonaceous, thinly bedded, alternating schist and quartzite with rare limestone and calcareous sandstone intruded by Silurian plutons of the Northport Granite, the Shaw Brook Diorite and a diorite porphyry. Pyrites from sulphidic bedrock contain 436 – 1290 mg/kg of As.	22	126a	Ca-HCO3, Na(Ca)-HCO3 (high As) types, pH 5.8 – 8.1, low pE, 30% – 96% As as AsIII, Fe <0.1 – 8.8 mg/L mostly as FeII	35	1990	69	Lipfert 2006; Lipfert et al., 2006; Ayuso and Foley 2008
Maine	Five Fms of the Central Maine terrane displayed high to low groundwater arsenic occurrence rates in the order of Ss (Sangerville, 42%), Sw (Waterville, 39%), SOv (Vassalboro, 24%), D (Devonian Granite Intrusions, 15%) and OZc (Ordovician-Cambrian volcanic rocks of Cushing Fm, 9%).Three meta-sedimentary Fms (Ss, Sw, SOv) were Silurian interbedded calcareous pelite and sandstone, some with limestone or calc-silicates. Pyrites contain up to 1944 mg/kg of As, averaging 706 ± 451 mg/kg (n = 115).	76	138	Elevated [As] are more frequently observed in samples with high pH, low DO, and low nitrate. Median [Fe] = 0.11 mg/L	1,113	325	31	Yang et al., 2009; Yang et al., 2012; Yang et al. this issue and O'Shea et al. this issue
New Hampshire	Part of the Central Maine terrane consisted of meta-sedimentary rocks of the Silurian Rangeley Fm (calcareous metapelites) and the Littleton Fm intruded by the NH Plutonic Series (Kinsman, Bethlehem and Spaulding) in early Devonian. Partial melting of the Rangeley and Littleton Fms led to the emplacement of Concord Granites. During the late stages of emplacement, pegmatites and graphite-containing veins formed from metamorphism and melting of the Rangeley Fm, enriching the incompatible elements including As. As-bearing minerals include arsenopyrite (FeAsS) and its alteration products nanocrystalline magnetite and westerveldite.	212	150b	High As (>38 ug/L) water has low Fe (<0.8 mg/L), variable DO, pH 7– 8, variable pE, 0% – 100% As as AsIII	127	398	62	Peters and Blum 2003; Peters et al., 2006; Utsunomiya et al., 2003
Vermont	In SW Vermont, Taconic sequence of meta-sedimentary rocks from the carbonaceous slates and phyllites (Ordovician Pawlet/Poultney Fms), the gray to black slate interlayered with limestone and quartzite (mid-Cambrian West Castleton/Hatch Hill Fms), to the gray, green and purple slate and phyllite (Bull/Metawee Fm). Arsenic in pyrite ranged from 53 to 2075 mg/kg.	41	35c	Mostly Na-SO4 type, pH 7 – 9, variable Eh, [As] correlates with [Na] and [SO4],	98	155	22	Ryan et al., 2013; Ryan et al, this issue; Mango and Ryan, this issue
Vermont	In N Vermont, meta-sedimentary rocks, phyllites (Proterozoic-to-Cambrian Hazens Notch and Stowe Fms, the Cambrian Ottauqueechee Fm and the late Cambrian to Ordovician Moretown Fm); originated as marine sediments, then were incorporated into an accretionary prism and subsequently metamorphosed. These rocks now occur in fault contact with each other and with the serpentinized ultramafics. Metamorphosed basaltic volcanic rocks occur as greenstones and amphibolites along faults. As is located in antigorite and magnesite with lesser amounts in magnetite.	107	449 (serpentine); 1,105 (talc-magnesite); 189 (talcchlorite); 190 (metased); 69 (meta-basalt)	Mg–HCO3 type, pH 7.4 – 7.6, three wells sampled were located in recharge zone	3	6.4	0	Ryan et al 2011
Massachusetts	In central MA, probability of As occurrence is high in Neoproterozoic amphibolite-biotite gneiss (Boxford member of the Nashoba Formation 26%, Marlboro Formation 11%, Fish Brook Gneiss 8%), moderate in Silurian plutons (Andover Granite granite 7%, Sharpners Pond Diorite 5%) and phylliteschist (Tadmuck Brook Schist 4%), low in Neoproterozoic schist-gneiss (Nashoba Formation<1) and Silurian schist (parts of the Paxton Formation < 1%). Pyrites (FeS2) contain negligible amounts of As, however, As levels in cobaltites (CoAsS) range from 30 to 50 % of As by weight.				13	478	1,540	Colman, 2011
Connecticut	In northeastern CT (Woodstock), a biotite schist of Hebron Fm intruded by numerous pegmatitic and granitic sills and dikes			CaMg-HC03 type, pH 7.7–8.3, variable DO, low Fe (<0.01 – 0.17 mg/L)	5	40	24	Brown and Chute, 2002
Rhode Island
New Jersey	in NW New Jersey and SE Pennsylvania, the Piedmont Province of the Newark Basin has sedimentary sequences (Upper Triassic and Lower Jurassic 195 – 225 M.A.) with sandstone, black and red mudstone, siltstone and pyrite-containing shale (Lockatong Fm), and red mudstone and siltstone interlayered with black shale (Passaic Fm) intruded by a diabase. Pyrite in the black shale contains up to 40,000 mg/kg As		240	Low DO < 3 mg/L, pH 7.5 – 8.2	94	215	15	Serfes et al 2005
Pennsylvania				pH 6.4 – 7.5, variable Eh, >70% samples mostly As(V), low Fe <0.22 mg/l, low nitrate <400 uM	53	72	23	Peters and Burkert 2008
Pennsylvania	In NW Pennsylvania, the glacial aquifer emerged as the third area in the state with frequent As in groundwater			Alkalinity, pH, sulfate, and TOC were positively correlated w/As. DO and nitrate plus nitrite were negatively correlated	5,023	490	8	Gross and Low, 2013

^aExcluded 4 tourmaline vein samples, one of which has 1,050 mg/kg As

^bExcluded 59 mine samples (max As 10,000 mg/kg), 21 vein samples (max As 622 mg/kg), 15 samples with graphite (max As 622 mg/kg)

^cExcluded 14 samples with pyrite cubes (max As 1,050 mg/kg) and 2 samples with FeOOH (max As 189 mg/kg)