Geochemical evidence for Se mobilization by the weathering of pyritic shale, San Joaquin Valley, California, U.S.A

Applied Geochemistry, Vol. 5, pp. 70-'~717, 199t) 0883-2927190 $3.(X) + 0~ Printed in Great Britain Pergamon Press p[c

Geochemical evidence for Se mobilization by the weathering of pyritic shale, San Joaquin Valley, California, U.S.A.

THERESA S. PRESSER U.S. Geological Survey, Menlo Park, CA 94025, U.S.A.

and

WALTER C. SWAIN U.S. Geological Survey, Sacramento, CA 95825, U.S.A.

(Received 2 January 1990; accepted in revised form 26 April 1990)

Abstract--Acidic (pH 4) seeps issue from the weathered Upper Cretaceous-Paleocene marine sedimentary shales of the Moreno Formation in the semi-arid Coast Ranges of California. The chemistry of the acidic solutions is believed to be evidence of current reactions ultimately yielding hydrous sodium and magnesium sulfate salts, e.g. mirabilite and bloedite, from the oxidation of primary pyrite. The selenate form of Se is concentrated in these soluble, salts, which act as temporary geological sinks. Theoretically, the open lattice structures of these hydrous minerals could incorporate the selenate (SeO42 ) anion in the sulfate (SO42) space. When coupled with a semi-arid to arid climate, fractional crystallization and evaporative concentration can occur creating a sodium-sulfate fluid that exceeds the U.S. Environmental Protection Agency limit of 1000/~g 1-1 for a toxic Se waste. The oxidative alkaline conditions necessary to ensure the concentration of soluble selenate are provided in the accompanying marine sandstones of the Panoche and Lodo Formations and the eugeosynclinal Franciscan assemblage. Runoff and extensive mass wasting in the area reflect these processes and provide the mechanisms which transport Sc to the farmlands of the west-central San Joaquin Valley. Subsurface drainage from these soils consequently transports Se to refuge areas in amounts elevated enough to cause a threat to wildlife.

INTRODUCTION

THE GEOLOGICAL setting and climate of the west- central San Joaquin Valley, California, have created soil salinization problems. Agricultural productivity in this arid environment is linked not only to irrigation but also to disposal of drainage water resulting from the leaching of salinized soils. Engineering solutions to save waterlogged agricultural lands have themselves created problems that affect the quality of irrigation return waters. Subsurface agricultural drainage waters have been used in wildlife habitats, namely Kesterson National Wildlife Refuge (KNWR) (Fig. 1), where up to a 64% rate of deformity and death in embryos and hatchlings of wild aquatic birds had been documented in 1983 (PRESSER and OHLENDORF, 1987). The contamination of the ecosystem has developed from naturally occurring Se, in a form that is highly mobile in the environment and that is able to bioaccumulate in the food chain.

In 1984, subsurface drainage water transported from farmlands to KNWR contained up to 1400/~g 1 - j Se, in the selenate form, which was sig- nificantly correlated with sulfate (PRESSER and BARNES, 1985). This concentration of Se exceeds the USEPA (U.S. Environmental Protection Agency) 1000/~g 1- l limit for a toxic waste (U. S. ENVmONMEN- TAL PROXEC~ON AGENCY, 1980). The state of Califor- nia declared the reservoir at KNWR to be a toxic

waste dump in 1986 and it was subsequently drained, filled, and graded in 1989 (NATIONAL RESEARCh COUNCIL, 1989). Although the KNWR facility has been closed, Se remains at elevated concentrations in the shallow groundwater of the west-central San Joaquin Valley (DEVEREL et al., 1984), and continues to be transported to the San Joaquin River and local evaporation ponds (GILLIOM et al., 1989). The USEPA 1987 dissolved Se water quality criteria for the protection of freshwater aquatic life are 5 ~g I- (4d average) and 20/~gl - j (1 h average) (U.S. EN- VIRONMENTAL PROTECTION AGENCY, 1987). it has been suggested that levels for protection of aquatic ecosys- tems be revised downward to 2-5/~gl J total Se (LEMLY and SMITH, 1987).

Geochemically, a cycle similar to that of S has been proposed for Se (SHRIFr, 1964). The characteristics that these cyclable elements have in common are that they exist as gases (H2S and H2Se ) in at least one stage of transformation and that the elements undergo a change in oxidation state (s) ( - 2 - - , 0--, + 4 --~ +6) (KONETZKA, 1977). Steps chemically favored in the cycling of Se include weathering of elemental Se (Se °) or metallic selenides (e.g. ferroselite, FeS½) in the parent rocks or sediments to selenite (SeO~ -2) under acidic and oxidizing conditions and to selenate (SeO42) under alkaline and oxidizing conditions (LAKIN, 1961 ; NATIONAL ACADEMY of SCIENCES, 1976; U.S. ENVIRONMENTAL PROTECTION AGENCY, 1979).

703

704 T.S. Presser and W. C. Swain

t i

'Stockton-") / ) /

i k. - ~, ~ ~ ~ .San Joaquin --1- k San Franosco~.~" "x " > ~

• ~ l~ Los Angeles } ~ Merced"~ ~ 2 L A/

) ~ NuJn ,4,

(X Fresn° ~cb \ 0 Basin \ , ,

~ V i s a l i a )

Drainage Cantua Cr "k ( boundary

"~ ~ Tulare 36 °

-'/. l Basin )

\ ( e ~I\ )

0 50 1 O0 Kilometers t9 ~ ) L ._.z __ [ ~-__ / "~ Q '~

0 50 100 Miles "--- "----.

122 o Delta -h 38 ° ~-.#

h \

o 1 Keslerson ) National _ o . . . . ~_ Wildlife Refuge 7

Study A r e a - - - -

Panoche Cr.

Valley

FIG. 1. Location of the San Joaquin Valley and the study area in California.

Selenite forms stable ferric oxide-selenite (Fe2(OH)aSeO3) complexes causing immobilization of Se (GEERING e t al., 1968; HOWARD, 1977) and selenate forms compounds that are soluble and there- fore mobile (LAKIN, 1961). Previously selenate was thought to be either unstable or not to form (WEDE- POHL, 1970).

Tracing of S and Se contained in the subsurface drainage water at KNWR eventually led to the con- sideration of geological source materials, mainly pyritic (FeS2) sedimentary rocks, in the Coast Ranges (Fig. 1). These shales and sandstones provide the alluvium and abundant soluble minerals that discharge into the San Joaquin Valley from the west. ]'he characteristic landscape instability of these steeply dipping marine shales results in extensive mass wasting in the form of landslides, slumps and debris flows. This erosional material is readily available for transport to the San Joaquin Valley during infrequent large storms.

Increasing concern about the quality of irrigation drainage disposal in similar saline environments has led to investigations in other areas of California, (Tulare Lake Basin and Salton Sea), and in other western states including Montana, Texas, Utah, Wyoming, Arizona and Nevada (SYLVESTER et al., 1988). An observation made by the authors about these studies is that Se clearly was the constituent of concern most frequently detected at elevated levels. [n Kendrick, Wyoming and the Middle Green River

Basin, Utah, Se concentrations in bird liver tissue were similar to or exceeded those found in birds in KNWR. In the Tulare Lake Basin, deformity of waterbird embryos took place up to a rate of 37.5% (SKORUPA and OHLENDORF. 1989).

Our study is the first one of a Se source area, the California Coast Ranges, targeted as a problem area through association with Se-related ecological problems found at KNWR. The study includes 11 Coast Range basins that drain into the western San Joaquin Valley. The study area is bounded on the east by the San Joaquin Valley floor, on the west by the Coast Range divide, on the north by Little Panoche Creek and on the south by Salt Creek (immediately south of Cantua Creek) (Fig. 1). This reconnaissance level study, started in 1984, was designed to examine sources and mobilization processes of Se in the Coast Ranges. These processes are inferred from chemical characteristics and transformations of Se in ground and surface water samples and in efflorescent salt samples. The study led to identification of 17 sulfate minerals and two chemically distinct types of waters important to the study of Se,

SALTS AND WEATHERING CYCLES

The recognition of the correlations between the concentrations of Se, Na and SO 4 in the inflow waters

Se from weathered pyritic shale, San Joaquin Valley, California 705

to KNWR (PRESSER and BARNES, 1985) led to the identification of hydrated evaporative sulfate minerals such as mirabilite (Na2SO 4 • 10 H20 ) and bloedite [MgNa2(SO4) 2 • 4 H20 ] on the valley floor that contain elevated levels of Se (up to 17 ppm). These same soluble sulfate salts were observed to form in the weathering profiles of the pyritic shales of the Coast Ranges to the west of the San Joaquin Valley.

Some attention has been paid to general effects of salt on soils in arid and semi-arid regions (DRIESSEN and SCHOORE, 1973) and quantitatively predicting salt production in wildland watersheds (WAGENET and JURINAR, 1978), but the study of the relation between the mineralogy of efflorescent salts on shales and soil materials has been limited ( W m ~ m et ai., 1982). Eight hydrated sulfate salts of Na and Mg including mirabilite and bloedite were found by WnI~IG et al. (1982), associated with the Mancos Shale. The Upper Cretaceous marine Mancos Shale is a major contribu- tor to the dissolved mineral load of the Colorado River. As described by EVANGELOU et al. (1984), Na and Mg are preferentially adsorbed by phyllosilicates within the shale and Ca is precipitated as calcite and gypsum following uplift and emergence. This cycle is essentially reversed in the present environment where dispersed gypsum and alkaline earth carbon- ates provide soluble Ca to displace adsorbed Na and Mg.

Fractional crystallization and dissolution during wet and dry cycles of the semi-arid climate in the east- central Coast Ranges could produce brines that deposit different minerals. During evaporation Ca would be eliminated through precipitation as calcite or gypsum, resulting eventually in a Na-Mg-SO4 brine that could deposit bloedite (MURATA, 1977). Trace elements contained in pyritic shales (e.g. Se) could be greatly concentrated by this "pumping effect" in minerals that result from weathering reactions (BARNES, 1986).

Pyrite is considered to be a main source of S in shales. The presence of the soluble sulfate salts such as mirabilite and bloedite show that the weathering chemistry of reduced organic shale (oxidation of sulfides) is largely a reversal of its early diagenetic chemistry (reduction of sulfates) (MURATA, 1977; BERNER, 1984). The general reaction for the weathering of pyrite (KRAUSKOPF, 1967) is:

2FeS 2 + 15/20~ + 4H20--~ Fe20 3 + 4SO42 + 8H +. (1)

Sulfuric acid and ferric oxide or hydrated ferric oxide (limonite) are end products.

Pyrite is disseminated throughout the Coast Range marine sedimentary rocks. It constitutes ~1% of the sandstones and up to 10% of the siltstones and shales (late I. BARNES, USGS, Menlo Park, pers. com- mun.). Physical and chemical weathering of diagenetic sedimentary rocks in the Coast Ranges is extensive and pervasive; no unweathered material was available from the study area. Large amounts of

oxidized iron are seen in veins and joints in the rocks of the study area. In a humid climate, the Fe would be almost all oxidized and precipitated as the oxide; in an arid climate where soluble compounds may per- sist, ferrous sulfate (ferrohexahydrite) and ferric sulfate (jarosite) would also be produced (KRAUSROPF, 1967). Both these minerals have been identified as coatings or crusts on sedimentary rocks of the Coast Ranges and represent the span of oxidation poten- tials for the weathering of the primary Fe-S minerals.

Because of their similar chemical and physical properties, Se can substitute for S (WEDEPOHL, 1970; COLEMAN and DELEVAUX, 1957) such as in the Se analog of pyrite, ferroselite (FeSea). Selenium has been reported in many sulfide minerals. Concen- trations of Se up to 1000 ppm have been reported in remobilized sulfides associated with oxidized sandstone-type U-deposits (DAVIDSON, 1963; COLE- MAN and DELEVAUX, 1957) and concentrations between 50 and 100 ppm in Sudbury pyrite (HAWLEY and NlCHOL, 1959). KRAUSKOPF (1955) cites a maximum of 28 ppm for Se in sedimentary pyrite in his article on enriched concentrations of metals in shales, organic deposits in swamps and semi-arid slopes and basins. The sedimentary deposits most enriched (up to 100 ppm) were the shale units of the Upper Creta- ceous Niobrara and Pierre Formations, which have large surface exposures in North Dakota, South Dakota, Nebraska, Wyoming, Colorado and New Mexico (LAKIN, 1961).

Few analyses of Se are available for water and bedrock from California at the beginning of the study. A reconnaissance in 1941 (LAKIN and BYERS, 1941), including 56 samples of shale and soil from 16 counties, showed an average of 1.4ppm Se. The highest value obtained (28ppm Se) was from the Coast Range Upper Cretaceous Moreno Formation in an area in the northwestern San Joaquin Valley (Hospital Creek). This area contains the same formations found in the west-central San Joaquin Valley, but the rainfall is somewhat higher, providing an increased opportunity for removal rather than accumulation. Recent data (TIDBALL et al., 1989) showed the highest Se concentrations in surficial materials of the San Joaquin Valley were in the interfan area between Panoche and Cantua Creeks.

Significant Se enrichment of geological materials was thought to occur through the increased volcanic activity during the Creataceous Period. DAVIDSON and POWERS (1959) summarize the earlier literature on the primary source of Se. One alternative is that the Se contained in the Niobrara and Pierre Forma- tions was a primary constituent of extrusive and intrusive igneous rocks which were eroded and de- posited into the Cretaceous sea (TRELEASE and BEATH, 1949). A second alternative is that these two formations may have acquired Se from gaseous ema- nations and volcanic dust which accompanied erup- tive activity and which were subsequently washed into the oceans by rainfall (BYERS, 1936; BYERS et al.,


1938). In either case the Cretaceous sea provided an environment in which Se could be biologically concentrated in bottom sediments to yield the enriched shale concentrations seen today (PRESSER and OHLENDORF, 1987). Black shales have been noted as containing elevated concentrations of minor elements (KgAUSKOPF, 1955; VINE and TOURTELOT, 1970), but few reliable Se data are available (DAVID- SON and LAKIN, 1961; LAKIN, 1973; DESBOROUGH et al., 1984).

SETTING

Alluvial deposits in the central and southern part of the western San Joaquin Valley are derived pri- marily from the Coast Ranges of California (Fig. 1). The Coast Ranges evolved as a result of complex folding and faulting of geosynclinal sedimentary rocks of Mesozoic and Tertiary age (DAvis et al., 1959; NORRIS and WEBB, 1976; PRESSER and OHLEN- DORF, 1987). Deformation began in mid-Miocene time and continued at intervals until the mid- Pleistocene, when the mountains were raised to their present heights of 1200-1500 m. The westside alluvial fans are complex, coalescing forms that are characteristic of areas of low, erratic rainfall (MENDENHALL et al., 1917). Heavy precipitation is infrequent, but causes extensive surface runoff, mass wasting and subsurface throughflow piping features. Two types of streams are found in the study area: (1) short ephemeral streams that discharge into interfan areas characterized by debris flows; and (2) larger intermit- tent streams that discharge at the larger fan heads. Flows from these drainages seldom reach the San Joaquin River because of the high permeability of the alluvial fan deposits (DAvis et al., 1959).

The west side of the San Joaquin Valley lies in the rain shadow of the Coast Ranges (DAviS et al., 1959) resulting in annual precipitation of 37.5-50 cm at the higher elevations, while the valley floor receives ~17.5 cm (RANTZ, 1969). Infiltration and recharge occur during the short, winter rainy season; evaporation rates are high, ranging up to 225 cm per year. The daily mean temperature in Jantmry is 2°C, while the maximum summer temperature is 38°C.

COAST RANGE GEOLOGY

Simplified descriptions of the main rocks that appear in the study area are given below by age.

Jurassic

Ultramafic rocks: include ophiolites and serpenti- nites at the base of the Upper Cretaceous and early Tertiary Great Valley sequence (PAGE, 1966). In the

study area, the serpentine core rimmed by Franciscan sandstones was uplifted in stages mostly in late Ceno- zoic time, and was extruded at the surface in the middle Miocene (ECKEL and MYERS 1946; LINN, 1968). Thickness: 600 m.

Late Jurassic to Late Cretaceous

Franciscan assemblage (eugeosynclinal): dominant graywacke, but shale, altered mafic volcanic rocks (greenstone), chert and minor limestone are part of'the assemblage; includes metamorphic rocks of the zeolite, blueschist (glaucophane schist) and eclogite facies. Ultramafic rocks, largely serpenti- nites, are associated with the assemblage, but are now excluded from it (BAILEY et al., 1964). Thick- ness: 1500 m.

The following geological descriptions of sedimentary strata are taken from ANDERSON and PACK (1915) and SULLIVAN et al. (1979).

Late Cretaceous

Panoche Formation (marine): interbedded massive yellow-brown concretionary sandstone and thin gray to black shales and conglomerates; part of Great Valley sequence. Thickness: 1500-6000 m.

Late Cretaceous to Paleocene

Moreno Formation (marine): foraminiferal and diatomaceous chocolate-brown to maroon platy, friable shales; lower section contains numerous beds of sandstones with concretions and dikes; upper section contains diatomaceous and organic shale more pure than those which occur later; forms extensive collu- vial slopes; type locality is Moreno Gulch; part of Great Valley sequence. Thickness: 300-900 m.

Paleocene and Eocene

Lodo Formation (marine): gray shale or mud- stone; includes Cantua Sandstone Member: yellow- brown sandstone with subordinate beds of gray shale. Thickness: 1500 m.

Eocene and Oligocene

Kreyenhagen Formation (marine): homogeneous white diatomite interbedded with chocolate-brown diatomaceous and foraminiferal shale and clay shale; feldspathic sandstone near base and quartzitic sandstone beds in higher zones. Thickness: 450 m.


Oligocene

Tumey Format ion (marine): assigned to Kreyen- hagen Format ion at times: a succession of brown to tan diatomaceous shale, and gray and buff to brown friable sandstone; base is coarse, pebbly sandstone. Thickness: 480 m.

Minerals were identified by X-ray diffraction. The X-ray analysis was complicated by the transient nature of some of the hydrated salts which underwent structural changes in response to temperature and humidity.

The maps of DmBLEE (1971, 1975) and BARTOW (1988a,b) provided the basic geological framework for the field work.

Miocene (7)

Rocks of Mercury Mines: The New Idria mining district consists of about 20 quicksilver deposits that rim a faul t-bounded core of serpentine and Francis- can rocks which have been extruded through beds of Upper Cretaceous Panoche Format ion (LINN, 1968; ECKEL and MYERS, 1946).

Pliocene and Pleistocene

Tulare Format ion (continental): brown sands, argillaceous sand and mudstones containing gravel lenses; nor thern exposures reflect the influence of the Franciscan; contains the Corcoran Clay M e m b e r which is a homogeneous diatomaceous greenish to bluish silty clay. Thickness: 900 m.

METHODS

Our methods of chemical analysis of waters have been adapted for geochemical environments, complete reference to sampling and methods is given by PRESSER and BARNES (1985). In general: all samples were filtered through 0.45 pm membrane filter; aliquots for anion analysis were left unacidified; and aliquots for cation analysis and trace elemental analysis were acidified with nitric acid to pH < 2. Major cations (Na, K, Ca and Mg) were analyzed by atomic absorption spectrophotometry (AAS) and major anions by colorimetry (B and Si) and ion chromatography (C1 and SO4). Bicarbonate was determined by titration with acid, acidity (H +) was determined by titration with base. The trace elements Se, As and Hg were analyzed by vapor generation AAS, other trace elements were analyzed by sequential inductively coupled argon plasma emission spectrometry.

Initial efforts to isolate the suspected toxicant Se at KNWR were hampered by complex analytical methodology for aqueous samples (PRESSER and BARNES, 1984). Chemical complexities involved both the high salinities present in the water samples and the existence of the different species or oxidation states that are known for Se. The method of choice for the analysis of Se in water and soluble minerals proved to be digestion with potassium persulfate in acid solution, reduction by addition of hydrochloric acid and boiling, hydride generation with heated quartz tube atomiz- ation, and detection by atomic absorption spectrophotometry (PIERCE and BROWN, 1977; GUNN, 1981; NAKAHARA, 1983). Because different sensitivities are exhibited for selenite and selenate in the hydride generation technique, this supposed disadvantage has potential for use in the selective determination of the different oxidation states of Se (PRESSER and BARNES, 1984).

SAMPLING SITES AND DATA

Efflorescent sulfate minerals found in the study area are listed in Table 1. Waters from 11 drainage basins were studied and characteristic examples are presented in Tables 2 through 5. Map numbers identifying specific data site locations are correlated to Fig. 2, which shows the drainages in the study area along with the surface geology of the Moreno Forma- tion. These drainage basins are, f rom north to south: Little Panoche Creek, Moreno Gulch, Escapardo Canyon, Panoche Creek, Griswold Creek, Silver Creek, Tumey Gulch, Arroyo Ciervo, Ar royo Hondo, Cantua Creek and Salt Creek. Collections from the water sampling sites were made several times from 1984 to present; the most representat ive sample is given. The non-seleniferous waters (Tables 2 and 3) are of several types: C1 waters, C I - H C O 3 waters, H C O 3 waters, ultrabasic waters and acid mine drainage. The seleniferous samples (Tables 4 and 5), both acid and alkaline, represent waters from several categories: acid seeps in the Moreno Forma- tion, alkaline ephemeral streams, runoff and integrated watershed. Given in Tables 2 through 5 are location, water chemistry, and water type, salt type associated with the water, and concentrations of Se in water and salt.

Table 1. Efflorescent sulfate minerals identified in the study area

Name Formula

Mirabilite Na2SO4 - 10H20 Thenardite Na/SO4 Bloedite MgNa2(SO4) 2 • 4H20 Konyaite MgNaz(SO4) 2 • 5H20 Loeweite MgNa2(SO4) 2 • 2.5H20 Kieserite MgSO 4 - H20 Starkeyite MgSO 4 - 4H20 Pentabydrite MgSO4 - 5H20 Hexahydrite MgSO4 - 6H20 Epsomite MgSO 4 - 7H20 Ferrohexahydrite FeSO 4 • 6H20 Glauberite NaaCa(SO4)z Hydroglauberite NaloCa3(SO4) s - 6H20 Gypsum CaSO 4 - 2H20 Bassanite CaSO 4 - 0.5H20 Jarosite KFe3(SOa)2(OH)6 Alunite KAI3(SOa)2(OH)6 Burkeite Na6CO3(SO4) 2


Table 2. Locations of non-seleniferous water sampling sites, identified evaporative salts and Se concentrations in salts

Temperature Salts Salt Map # Date Longitude Latitude County (°C) ppm Se type

Chloride waters 1 Salt Creek seep lI 1987-05 120°25'53" 36°22'30 " FR 24 0.5 hi, th 2 Mercey Hot Spring 1984-414 120°51'34" 36°42'12" FR 44 no salt

Chloride-bicarbonate waters 3 Tumey Gulch seep III 4 Little Panoche Creek

1987--115 120°37'20 " 36°31'08" FR 29 2.4 hi, th o ~p u 1984-11 120°50'56" 36 4~ 19 FR 14 no salt

Bicarbonate waters 5 Harris Spring 1987-05 120°31'17" 36°22'47 '' FR 19 0.2 th 6 Mine Creek 1984-11 120051'47 " 36°44'51" FR 15 no salt

Ultrabasic waters 7 Larious Creek 1984-04 8 Clear Creek at San Benito River 1988-04

Acid Mine drainage 9 San Carlos Creek at New Idria

120°42'02 " 36°27'35" SB 21 no salt 120°47'08 " 36°21'31 " SB 15 no salt

1988-04 120°4ll'13 " 36°24'56 " SB 19 0.1 bl, hx <0.1 jr, hx

Map number refers to Fig. 2. Abbreviations: Co. county: FR, Fresno; SB, San Benito; Salts: th, thenardite; hi, halite; bl, bloedite; hx, hexahydrite; jr, jarosite.

Table 3. Selenium concentrations and water chemistry of non-seleniferous waters

TDS* Na 8 0 4 K Mg Ca HCO3+ Cl SiO., B pH Se

Map # ,ug 1-~ Water type mg/t

Chloride waters 1 Salt Creek seep 11 2 Na-CI 8479 2900 530 31 43 25 18511 3100 3.6 50 8.55 2 Mercey Hot Springs <2 Na-CI 2388 8311 4 5.9 <1 40 58 131RI 711 14 8.95

Chloride-bicarbonate waters 3 Tumey Gulch 111 <2 N a - C I - H C O 3 16353 5600 9811 36 51 11 5426 42511 10 45 9.1 4 Little Panoehe Creek <2 Na--CI-HCO 3 1104 200 120 2.8 34 88 367 240 18 5.8 8.61

Bicarbonate waters 5 Harris Spring ~2 Na-HCO~ 844 235 160 1 4 4 433 7 16 <1 8.75 6 MineCreek <2 Na-Ca-Mg-HCO3 881 I10 125 4.4 42 75 398 61) 19 2.9 8.16

Ultrabasic waters 7 Larious Creek 3 Mg-HCO~ 1531 61 150 2.3 2211 12 11135 38 3.1 1.6 9.36 8 Clear Creek at San <2 M g - H C O 3 987 29 63 1.4 135 17 708 26 7.2 <1 8.33

Benito River

Acid Mine drainage 9 San Carlos Creek at New

Idria <2 Fe-Mg-Na-SO4$ 6349 5311 4700 72 3511 325 36§ 300 46 22 3,02

Map number refers to Fig. 2. Abbreviation: TDS, Total dissolved solids. * Calculated. tTotal alkalinity as HCO> SFe = 640 mg I - t . §mg 1 -t H.

RESULTS AND DISCUSSION

Non-seleni ferous waters

Previously r epo r t ed waters in Cal i fornia in the area of the eas t -cent ra l Coas t Ranges were H C O 3 waters f rom the Franciscan assemblage (BARNES et al., 1973; IRWIN and BARNES, 1975; BARNES et al., 1975); C1 waters f rom the G r e a t Valley sequence of rocks and a zone of h y d r o t h e r m a l a l te ra t ion (Mercey H o t

Spring); u l t rabasic M g - H C O 3 waters f rom serpent i - nites (BARNES et al., 1967; BARNES and O'NEIL, 1969); and acid mine dra inage ( F e - M g - N a - S O 4 water) f rom the oxidat ion of the sulfide ore at the New Idria Mercury Mining District (LINN, 1968). Examples of these waters were invest igated and found to conta in -<3/~g 1 - l of Se (Tables 2 and 3; Fig. 2). For compar i son , STivv (1951) plots of the analyses for these waters show water type and ionic con ten t (Fig. 3). These waters are relat ively dilute except for

Se f r o m w e a t h e r e d pyri t ic shale , San Jo aq u in Val ley, Cal i fornia 709

Tab l e 4. Loca t ions of acid and a lkal ine se len i fe rous w a t e r sampl ing sites, identified e v a p o r a t i v e salts and Se concen t r a t i ons in salts

Temperature Salts Salt Map # Date Longitude Latitude County (°C) ppm Se type

Acid waters Acid seeps in Moreno Formation

10 Arroyo Hondo 11 Tumey Gulch Tributary II

12 Escapardo Canyon 13 Panoche/Silver Creek

confluence 14 MorenoGulch

Alkaline waters Ephemeral Streams

15 Tumey Gulch 1 16 Vallecitos Creek 17 Los Pinos Creek

Runoff* 18 Silver Creek at Panoche Road 19 Panoche Creek a t l -5

1988--04 120o34'06 '' 36024'50" FR 16 1987-05 120°38'01 '' 36°32'11 " FR 24

1988-05 120041'28 " 36°38'27" FR 16 1988-10 120o41'33 " 36o35'59 " FR 27

1989-01 120°44'35 " 36°43'20 " FR 5

12 bl, th 15 th 14 hg

1.1 bl, Iw 2.1 bl, ep

25 bl, gp 1.8 ky, lw, st,

hx

1988---04 120°37'14 " 36031'28" FR 25 11 th, bl, Iw 1989--01 120°47'44 " 36°29'17" SB 14 7.8 th, bk, tr 1984-11 120°46'20 " 36028'35" SB 14 1.9 th, ep

1988---01 120°37'55 " 36o39'03" FR - - no salt - - 1988-01 120°41'01" 36o35'40" FR - - no salt - -

Integrated Watershed 20 Silver Creek headwater seep I 1989-02 120°41'02" 36°28'03" SB 16 0.4 ep, hx 21 Confluence of Vallecitos and Pimental

Creeks 1989--02 120°49'56 " 36°31'01 " SB 15 2.9 th, ky, bl

Map number refers to Fig. 2. Abbreviations: Co., county; FR, Fresno; SB, San Benito; Salts, bl, bloedite; th. thenardite; hg, hydroglauberite; lw, loeweite; ep, epsomite; gp, gypsum; bk, burkeite; tr, trona; ky, konayite; hx, hexahydrite; st, starkeyite. * California Department of Water Resources data except for Se.

T ab l e 5. Se len ium concen t r a t i ons and wa t e r chemis t ry of acid and alkal ine se leni ferous waters

TDS* Na SO 4 K Mg Ca H~" CI SiO 2 B pH Se

M a p # ktgl -] Water type mgl 1

Acid waters Acid seeps in Moreno Formation

10 Arroyo Hondo 11 Tumey Gulch Tributary 11 12 Escapardo Canyon 13 Panoche/Silver Creek

confluence 14 Moreno Gulch

420 Na-SO 4 197 Na-SO 4 42 Mg-Na-SO4 38 Mg-SO 4

87 Mg-SO4

17901 3850 12500 5(I 895 394 10 49744 9850 34500 35 3700 470 16 28332 4200 20500 28 2650 410 31 37358 5400 27500 59 3350 435 9

21159 1350 16(X~(I 30 3250 360 4

150 61 8.0 4.38 1100 89 13. 3.83 425 119 10. 3.60 550 48 16. 4.15

200 62 10. 4.24

Map #

TDS* Na SO 4 K Mg Ca HCO3~ CI SiOe B pH Se

pg I- 1 Water type mg I-

Alkaline waters Ephemeral streams

15 Tumey Gulch I 16 Vallecitos Creek 17 Los Pinos Creek

Runoff§ 18 Silver Creek at Panoche

Road 19 Panoche Creek a t l -5

Integrated watershed 20 Silver Creek head-water

seep I 21 Confluence of Vallecitos

and Pimental Creeks

3500 Na-SO 4 2(I Na-SO4 2916 73(I 1100 6 59 61 708 24 Na-SO 4 5411 1300 3050 5 160 16(I 477

55 Na-Mg-Ca-SO 4 6190 845 3700 19 300 475 205

57 Na-Ca-Mg-SO 4 3710 495 2400 17 170 410 151

141 Na-Mg-SO4 3580 577 1900 6 245 16(I 555

153 Na-SO 4 4356 920 2350 7 145 185 438

159811 44000 88000 2(~1 7550 635 1 4 1 5 18200 2(I 67. 8.57 180 36 6.3 8.91 16(I 13 15. 8.79

95 - - 3.0 7.8

125 - - 2.(I 7.9

8(I 26 5.5 7.68

250 6 9.7 7.96

Map number refers to Fig. 2. Abbreviation: TDS, Total Dissolved Solids. * Calculated. tTotal acidity as H. ~Total alkalinity as HCO 3. §California Department of Water Resources data except for Se.


121 *00'

)6 14

Mercey H o t Springs

I • l ~ Moreno Formation

Water sampling site

\

• Tumey

Panoch,y ",~ Griswold Cr. ~ Silver Cr. ~ .

~18

"'--"~--~e~" 16

STUDY AREA

~15 ~3

"\i COAST RANGE DIVIDE

0 10 20 Kilometers o ..~..~

l i l h l J

0 10 20 Miles

Fm 2. Study area map showing creek drainages, surface geology of the Moreno Formation and locations of water sampling sites listed in Tables 2 through 5.

the extremely concentrated Na-HCO3-CI water at Tumey Gulch III. They are also low in SO 4 except for the water from New Idria.

Seleniferous waters

A c i d waters. Acid waters (Tables 4 and 5; Fig. 2) issuing from landslides in the Moreno Formation in the form of briny, sulfate seeps have elevated levels of Se. These waters provide evidence for oxidation of disseminated pyrite or ferroselite in the weathering of sedimentary rocks, an acid producing reaction (Eqn 1). The pH values for these seep waters range from 3.6 to 4.5. Five examples of these pH seeps were found in widely separated areas of the Moreno For- mation: Arroyo Hondo, 420/~g 1-1 Se; Tumey Gulch Tributary II, 197#gl - l Se; Escapardo Canyon, 42/~gl -~ Se; the confluence area of Silver and Panoche Creeks, 38btg 1 - l Se; and Moreno Gulch, 87/~g 1-1 Se (Fig. 2). Acidity (species titratable with base) range up to 31 mg 1-1 H + and amounts of SO4 up to 34,500 mg/1. Stiff plots of the analyses of the pH 4 seep samples are shown in Fig. 4.

Beside elevated levels of Se, these acid waters contain high levels of dissolved metals (Table 6);

maximum concentrations were 188mg1-I AI, 95mg1-1 Mn, 13mgl -1 Zn, 8.8mg1-1 Ni, and 1.7 mg 1-1 Co. The New Idria Mining District in the area provides an example of acid mine drainage for comparison (pH3); this water contains up to 640 mg1-1 Fe but <2/~gl -I Se.

To determine if H2CO 3 is a contributing factor to the acidity of the pH 4 samples, several headspace gas samples were analyzed (Table 7). These measure- ments allowed the calculation of the partial pressure of carbon dioxide (pCOz) and the concentration of carbonic acid (H2CO3). Concentrations of H2CO3 were low, with a maximum value of 173 mg1-1 measured at Tumey Gulch Tributary seep III. This seep water along with the water at San Carlos Creek at New Idria proved to be anoxic when compared with air-saturated water at 15°C. The analyses also revealed that several of the seeps, notably the upper seep at Arroyo Hondo, contained N20 which may be indicative of microbial activity (PELCZAR et al., 1986).

The solution-mineral-equilibrium program SOL- MNEQ (KHARAKA and BARNES, 1973; KHARAKA et al., 1988) was used to determine that the pH 4 seep waters are not saturated with calcite because of the low pH, but that they are near to equilibrium with gypsum ( -0 .1 kcal). In the Tumey Gulch Tributary II seep waters, however, the presence and solubility


Non-seleniferous Waters

Salt Creek seep II 2pg/I So

Mercey Hot Springs <2pg/I Se

Tumey Gulch III <2pg/I Se

Ca HCO 3 or H Na SO 4

< J

\

250 125 125 250 Little<2Ppag:l s°Ch: Creek ~

Harris Spring <2p.g/I Se ~ J

Mine Creek ~ ~ , / / / <21,tg/I Se

Larious Creek 3pg/I Se f

Clear Creek @ San Benito River ~ J r.-. ~ - ~ - ~ - ~ ' <2p.g/I Se

San Carlos Creek @ New Idria / :==.._ / <21ag/I Se

I : ., : ,. I . . . . . . . . i : : : ; i

16o sb . . . . . . . . 5'0 16o

moq/l meq/l

FIG. 3. Variations in water type, ionic content and Se concentration for non-seleniferous waters.

of mirabilite (or an equally soluble Mg or mixed Na and Mg sulfate) seems to be controlling the Se content. An undersaturation for mirabilite of -1 .5 kcal in these waters approaches a value seen in an alkaline water that is precipitating mirabilite ( -1 .4kcal) . These values indicate that the minerals formed may be impure or that the thermochemical solubility or aqueous species complexation data used for mirabilite are slightly inaccurate and thus show a negative deviation from AG = 0 at equilibrium.

Limited information available on other source areas associated with Se contamination, show one pH 4.5 seep near the Sun River Project (Montana) containing 580btg1-1 Se (KNAPTON et al . , 1988). Major ion water chemistry data were not available.

Alka l i ne waters. A second type of seleniferous water (Tables 4 and 5; Fig. 2) is represented by an evaporatively concentrated alkaline (pH 8.6) ephemeral stream in Tumey Gulch (Tumey Gulch I).

Although it takes some acid to produce ferric iron from ferrous iron (STUMM and MORGAN, 1981), neutralization drives Eqn 1 to the right. For the ephemeral stream-water, a concentration range of 2100-3500 pg 1 -I Se was found. This concentration of Se is approximately an order of magnitude greater than other concentrations measured in water in the study area and exceeds the USEPA Se criterion (U.S. ENVIRONMENTAL PROTECTION AGENCY, 1980) for a toxic waste (> 1000/~g 1- l ). Tumey Gulch is one drainage to the south of Panoche Creek (Fig. 2) and it receives ~-17.5 cm of rainfall yearly; flows issuing from it rarely reach the valley floor, making this a mainly closed system. The site of the ephemeral alkaline stream is about 0.4 km away from the pH 4 seep in a tributary of Tumey Gulch containing ~200/~g 1-1 Se (Tables 2 and 3). Geologically similar to the acid site, the alkaline site is dominated by the Moreno Formation but the stream water is strongly buffered by HCO3-water derived from the Lodo

712 T . S . P resse r a nd W. C. Swain

Seleniferous Acid Waters

Ca HCO 3 or H Na SO 4 Mg CI

Arroyo Hondo 420p.g/I Se

Tumey Gulch tributary II 197p.g/I Se

Escepardo Canyon y 42p.g/l Se

Panoche/Silver Creek confluences ~ 381ag/I Se

Moreno Gulch ~ 87gg/I Se

I I, I I I I I I 800 400 400 800

meq/I meq/I FIG. 4. Var ia t ions in w a t e r type , ionic con ten t and Se concen t r a t ion for se leni ferous acid waters .

Ta b l e 6. T r a c e e l e m e n t concen t ra t ions for acid and a lkal ine s a m p l e s * t

Se As Hg Fe AI Mn Ni Co Cu Cd Zn Cr Be

pH ~gl -~ mgl t

Ti

Arroyo Hondo 4.4 420 <1 <0.1 0.3 72 31 Tumey Gulch Tributary seep 3.8 197 <1 <0.1 (I.4 1(16 95

II Escapardo Canyon 3.6 42 2 <0.1 0.4 188 88 New ldria mine drainage 3.0 <2 4 <0.1 640 88 10

6.0 0.8 <0.03 0.08 9 <0.04 0.038 0.06 8.3 1.2 0.08 0.09 11 <0.04 0.039 0.09

8.8 1.7 0.05 0.03 13 1.4 0.6 <0.03 0.10 3

0.03 0.070 0.09 0.07 <0.003 <0.03

Tumey Gulch I 8.6 3500 8 - - 0.1 <0.3 1 0.6 <0.1 0.4 <0.(13 <0.1 <0.04 <0.003 <(/.03 Mercey Hot Springs 9.0 <2 <1 0.1 <0.1 <0.3 <0.1 <0.1 <0.1 <0.03 <0.03 <0.1 <0.04 <0.003 <0.03 Silver Creek headwater seep 7.6 83 <1 - - <0.1 <0.3 2 <0.1 <0.1 <0.03 <0.03 0.1 <0.04 <11.003 <0.03

II

*Pb and Mo concentrations were all <0.3 mg 1-1 . tV concentrations were all <0.04 mg 1 -I .

Tab l e 7. G a s chemis t ry of acid seep he a ds pa c e samples (Samples ana lyzed by W. C. Evans , U .S . Geolog ica l Survey , Men lo Pa rk , Cal i fornia)

N 2 02 Ar CH 4 CO 2 N20 Temperature Se pCO 2 H2CO 3

(°C) /~g I-i k~moles kg- l solution arm. mg 1-i

Tumey Gulch Tributary Pool IIl 16 Seep Ill 14

San Carlos Creek at New ldria 22

Escapardo Canyon 16

Arroyo Hondo Lower seep 16 Uper seep 16

Air saturated water at sea 15 level at 15°C *

5 649 303 17.9 0.06 638 <0.1 0.0165 40 6 685 20.2 15 .1 <(I.(/6 274(I 14.9 0.0722 173

<2 848 0,2 21.4 <0.06 30.6 <0.1 0.0206 19.6

42 760 327 19.9 <0.06 197 6.5 0.0053 12.4

420 932 380 21.3 <0.06 469 18.3 0.0122 29.5 42(1 719 584 19.3 <0.08 1290 94.1 0.0182 80.4

- - 587 315 15.4 - - 14.7 - - 0.11003

* Based on data from EMMERICH et al . , (1977).


Formation. The ephemeral stream has an alkalinity of up to 1415 mg1-1 H C O 3. The water is ~ 2 M in Na2SO 4 salt and precipitates mirabilite upon stand- ing (undersaturation - 1 . 4 kcal). A Stiff plot for the anlysis of this sample is shown in Fig. 5.

A theoretical description and examples of the oxidation/reduction process for Se are given by LAKIN (1961) and are summarized below. The oxidation to Se ÷ 4 takes places easily. The insoluble basic ferric selenite (Fe2(OH)4SeO3) may form. The presence of 12 ppm of Se in acid Hawaiian soils under an annual rainfall of about 250 cm is an example of the occurrence and insolubility of this Fe-Se compound. In acid conditions (pH 1), the oxidation potential for selenite (+4) to selenate (+6) is high but as the pH increases the oxidation can occur through oxyge- nated water. If the selenite were distributed in porous alkaline moist media, its oxidation by air might proceed at a measurable rate.

By differential analysis (PRESSER and BARNES, 1984), the Se in the alkaline seep waters sampled in our study was found to be in the selenate state. The buffering capacity of the Lodo Formation along with that of the Panoche and Franciscan Formations, which were also found to be high in HCO3, provides an alkaline, oxidizing environment ensuring the concentration and mobility of Se as selenate.

There are clear differences between the pH 4 and

the pH 8 waters shown in Table 6 with regard to mobilized metals; as compared with p H 4 seep waters, concentrations of metals in pH 8 waters are very low. The analysis of the alkaline hydrothermal water at Mercey Hot Spring, which contains 0.1/~g 1-1 Hg, is included for comparison.

Although the Tumey Gulch drainage is considered to be unique, other examples of alkaline ephemeral streams at Vallecitos (tributary to Griswold Creek) and Los Pinos (tributary to Silver Creek) Creeks were sampled. Waters at these two sites (Tables 4 and 5) contain lesser amounts of Se (20-24/~g1-1, respectively) and are N a - S O 4 type waters whose H C O 3

concentrations range from 477 to 708mgl - l Although salt efflorescences are found at both sites, these sites are dominated geologically by Quaternary deposits rather than the Moreno Formation as at Tumey Gulch. Stiff plots for these analyses are shown in Fig. 5.

Transport waters. The remaining waters investi- gated (Tables 4 and 5; Fig. 2) are representative of the extent of Se transport from the described mobilization processes. Examples are given of runoff from the two major drainages (Silver and Panoche Creeks) and regional ground water as indicated by seeps at the headwaters of Silver and Griswold Creeks (confluence of Vallecitos and Pimental Creeks). The

Seleniferous Alkaline Waters

FIG. 5.

Ca

Na Mg

Tumey G u l c h ~ ~ - - 350011g/I Se

Vallecitos Creek 20Ag/I Se

LOS Pinos Creek 241~g/I Se

Silver Creek at Panoche Road 55pg/1 Se

Panoche Creek at I-5 F - - \ 57~g/I Se

H C O 3 o r H

so 4 cI

, i i I t i i i J i , t I , ~ i i {

2 0 0 0 1 0 0 0 1 0 0 0 2 0 0 0

Silver Creek headwaters seep I ~ 141 p.g/I Se

Confluence of Vallecitos & Pimental Creeks ~ /

153p.g/I Se ~--~... . . . . .~ ,

I I I I I l I l

80 40 40 80 meq/I meq/t

Variations in water type, ionic content and Se concentration for se]eniferous alkaline waters.


latter sites are associated with structural synclines in the upper reaches of the Panoche Creek drainage and thus represent integrated watershed samples encom- passing the geological section from Jurassic to Mio- cene. These transport waters are dominated by Na-SO 4 and contain elevated levels of Se. The runoff water samples, taken at the peak of the hydrograph, contain 55-57 ~g 1-1 Se and approximately 10% sus- pended solids. The integrated watershed samples from Silver and Griswold Creeks contain 141/~g 1-1 and 153/~g1-1 Se, respectively. The analyses for these waters are depicted in Fig. 5.

Sulfate minerals

The sulfate regime in the east central Coast Ranges is readily recognized by the prevalence of Na- and Mg-SO 4 salts as efflorescences on rock surfaces and evaporites at water interfaces. The chemistry of KNWR waters (PRESSER and BARNES, 1985) implies that the complex array and interrelations of sulfate minerals are important factors in the study of Se sources. Seventeen sulfate minerals, with up to 10 waters of hydration, were identified from saline geological formations in the study area (Table 1). The- nardite (dehydrated mirabilite) and bloedite were the dominant minerals found by X-ray diffraction (Tables 2 and 4). Even though care was taken to preserve the natural state of the minerals and to X- ray immediately upon return, the hydrous minerals are labile, and dehydration took place in the labora- tory and on the mount used for X-ray diffraction, resulting in intermediates being found. For example, the newly identified mineral konyaite (VAN DOES- BURG et al. 1982; SHAYAN and LANCUCKI, 1984) was found in mixtures with other salts: it dehydrates to bloedite and loeweite.

Concentrations of Se in examples of evaporites collected at each water sampling site are given in Tables 2 and 4. Utilizing differential analysis (PRESSER and BARNES, 1984), Se in the Na- and Mg-SO 4 salts was found to be in the selenate state. The hydrous Na- and Mg-SO 4 minerals have an open lattice structure which could theoretically incorporate the selenate (SeO42) anion in the sulfate (SO42) space. This replacement would cause an enrichment of Se and thus provide a temporary geological sink for Se.

Evaporites that contain the highest Se (up to 25 ppm Se), are associated with drainage from the shale-rich Moreno Formation. In Tumey Gulch they contain up to 15 ppm Se and at Arroyo Hondo up to 14 ppm Se. The evaporites associated with the acid seeps in the Moreno Formation average 7.0 ppm Se. At the toe of one landslide in the Moreno Formation, an extensive layer of thenardite 7.5 cm thick has developed; the salt contains 4 ppm Se. In contrast, the sandstones of the Lodo Formation issue massive amounts of sodium and magnesium sulfate salt

(~125 m 2 at a thickness of 5 cm) into the Panoche- Silver Creek drainage, but little Se is found (<2/~g1-1 in water and <0 .5ppm in evaporites). Salts from the sandstones of the Panoche Formation, while being predominantly halite, contain minor amounts of loeweite which were found to contain <0.1 ppm Se.

In comparison with Na- and Mg-SO 4 salts, gypsum, the principal Ca-SO4 mineral represented, does not seem to tolerate the substitution of selenate, measuring <0.5 ppm Se in various samples. This could be an exclusionary and consequently a concen- trating mechanism for Se in Na- and Mg-SO4 brines, salts, and soil solutions.

Identification of the hydrous sulfate mineral hydroglauberite, Nal0Ca3(SO4)8.6 H20 (Table 4), suggests a link between the disparate Ca and Na geochemical regimes with regard to Se. It was identified in evaporite crusts from Tumey Gulch that contain up to 14 ppm Se. It shows a distinct crystalline habit (acicular crystals radiating from a central nu- cleus) and is observed to break down to gypsum with increases in moisture. At the original mineral occurrence (FLEmCnER, 1970), it was found associated with halite and mirabilite along with polyhalite and astra- khanite.

Efflorescent salt crusts form on shales exposed at the surface. When analyzed, they were always found to be enriched in Se when compared with those shales. From selected shale samples of the weathered Moreno Formation, it was found that 95% of the Se was soluble and that it was in the selenate state.

Solute sources and further studies

Isotopic analyses of blSO and 6 D for these seleniferous water samples and those additionally collected for Se reconnaissance are plotted in Fig. 6. and show evaporative concentration of the spatially and chemically divergent ground- and surface waters. These points fall on an evaporative trend line with a corre- lation coefficient of 0.93, indicating a single source for the waters. This suggests that the solute chemistry of the brines is controlled and/or modified by solution-reprecipitation processes of surficial and subsurface evaporites rather than the mixing of distinct water sources. The most evaporatively concentrated sample, Tumey Gulch I ephermeral stream, also has the highest Se concentration.

Solute sources are also predicted through calculation of normative salt assemblages for these waters (BoDINE and JONES, 1986). The assemblages found, thenardite, bloedite and glauberite, indicate oxidation of sulfide minerals to sulfuric acid in meteoric water followed by weathering of Na-, Mg- and Ca- silicates or alumino-silicates.

In a parallel study, we are collecting data on the Se content of the different geological units. Preliminary data suggest that the Upper Cretaceous-


' ' ' I . . . . I . . . . I . . . . I '

0

~20 •

-40

-60

-80

100

-10 -5 0 5

~80 (%0)

FIG. 6. Variations in ~D and 6180 for study area waters. The results are expressed in 0/00 measured relative to Standard Mean Ocean Water (SMOW); the Meteoric Water Line (MWL) is plotted for reference (CRAIG, 1961).

Locally derived meteoric waters are denoted by x's.

Paleocene Moreno Format ion and the Eocene- Oligocene Kreyenhagen Format ion contain elevated levels of Se, as compared with the Upper Cretaceous Panoche Format ion, the Pa leocene-Eocene Lodo Formation, the Plio-Pleistocene Tulare Format ion and non-marine rocks. Surficial exposures this extensive of the Moreno and Kreyenhagen Format ions are not seen to the north or to the south of the area implicated to be the source of Se at K N W R .

As a representat ion of unweathered material , pyrite was obtained from cuttings from a 4900 m well located on the San Joaquin Valley Floor, outside the study area, near Mendota . The well encompasses the geological section from Tert iary non-marine rocks to the Uppe r Cretaceous Panoche Formation. Prelimi- nary analysis on a small sample set f rom seven different intervals shows that pyrite samples are enriched in Se when compared with whole rock samples.

S U M M A R Y

The distinctive chemical characteristics of these pH 4 waters, found in close association with the Moreno Format ion in five widely separated locali- ties, suggest that they can be explained as a result of local processes involving a similar mechanism. It is postulated that the pH 4 seeps are surface ex- pressions of transition points in which pyritic marine shale is oxidized, the Se being oxidized with it. With further buffering in the existing H C O 3 regimes of the Coast Ranges, oxidative weather ing conditions are

ensured and Se as selenate continues to be concentrated in the water or in the crystal lattice of hydrous N a - a n d M g - S O 4 evaporites. Theoretically, the open lattice structures of these hydrous minerals could incorporate the selenate (SeOg 2) anion in the sulfate (SO42) space. Thir teen sulfate minerals were identified which act as temporary geological sinks for Se. The saline runoff in the flushing events of winter is also high in Se. This provides evidence for the existence of a second mechanism of mobil ization besides that of the movement of a residual insoluble fraction in particulate mat ter to the valley floor, where it is then oxidized. This second mechanism would involve the movemen t from the Coast Ranges of Se already oxidized to selenate in solution or in readily soluble salts to the valley floor. Evaporat ive concentrat ion would accentuate the latter process; the "pumping effect" of an arid climate producing fractional crystallization could concentrate trace elements , namely Se. A N a - S O 4 fluid which contains a Se concentrat ion that exceeds the U.S. Envi ronmenta l Protect ion Agency limit of 1000pg 1 - l Se for a toxic waste could be produced by such a process. Reduct ive mechanisms in the Se biogeochemical cycle may intervene to immobilize Se, but overall transport of Se remains high enough to cause a threat in the San Joaquin Valley to water quality and hence to the wildlife, fish, human health and beneficial use supported by that water.

Acknowledgments--Members of the U.S. Geological Sur- vey who deserve thanks are: T. L. Fries (Branch of Geo- chemistry) for assistance with trace metal analyses, R. H. Mariner for assistance with X-ray diffraction analyses, W. C. Evans for gas analyses, and L. D. White and Mark Huebner for isotope analyses. Thanks also to J. Cooper and staff of the San Joaquin District of the California Depart- ment of Water Resources, Fresno, California, who provided runoff samples and access to their data.

Editorial handling: Y. K. Kharaka

R E F E R E N C E S

ANDERSON R. and PACK R. W. (1915) Geology and oil resources of the western border of the San Joaquin Valley north of Coalinga, California. U.S. Geol. Surv. Bull. 6113.

BAILEY E. H., IRWIN W. P. and JONES D. L. (1964) Francis- can and related rocks, and their significance in the geology of western California: Calif. Div. of Mines Geol. Bull. 183.

BARNES I. (1986) Sources of selenium. In Selenium and Agricultural Drainage: Implications for San Francisco Bay and the California Environment, Proc. of the 2nd Selenium Symp. (ed. ALICE HOWARD), Berkeley, Califor- nia, March 27 1985, pp. 41-51. The Bay Institute of San Francisco, Tiburon, California.

BARNES I., HINKLE M. E., RAPe J. B., HEROPOULOS C. and VAU(mN W. W. (1973) Chemical composition of naturally occurring fluids in relation to mercury deposits of north-central California. U.S. Geol. Surv. Bull. 1382-A, 1-19.

BARNES 1., IRWIN, W. P. and GIBSON H. A. (1975) Geologic

716 T. S. Presser and W. C. Swain

map showing springs rich in carbon dioxide or chloride in California. U.S. Geol. Surv. Water-Resour. Invest, Open-File Map.

BARNES I., LAMARCHE V. C. Jr and H1MMELBERG G. (1967) Geochemical evidence of present-day serpentinization. Science 156,830-832.

BARNES I. and O'NEIL J. R. (1969) The relationship between fluids in some fresh Alpine-type ultramafics and possible modern serpentinization, western United States. Geol. Soc. Am. Bull. 80, 1947-1960.

BARTOW J. A. (1988a) Preliminary geologic map of the Lillis Ranch quadrangle, California. U.S. Geol. Surv. Open- File Report 88-49.

BARTOW J. A. (1988b) Preliminary geologic map of the Monocline Ridge quadrangle, California. U.S. Geol. Surv. Open-File Report 88-528.

BERNER R. A. (1984) Sedimentary pyrite formation: an update. Geochim. Cosmochim. Acta 48,605-615.

BOD~NE M. W. Jr and JONES B. F. (1986) THE SALT NORM: a quantitative chemical-mineralogical charac- terization of natural waters. U.S. Geol. Surv. Water- Resour. Invest. Report 86-4086.

BYERS H. G. (1936) Selenium occurrence in certain soils in the U.S with a discussion of related topics: second report. U.S. Dept. Agric. Tech. Bull. 530.

BYERS H. G., MILLER, J. T., WILLIAMS, K. T. and LAKIN H. W. (1938) Selenium occurrence in certain soils in the U.S. with a discussion of related topics: third report. U.S. Dept. Agric. Tech. Bull. 601.

COLEMAN R. G. and DELEVAUX M. (1957) Occurrence of selenium in sulfides from some sedimentary rocks of the western United States. Econ. Geol. 52,499-527.

CRAIG H. (1961) Isotope variations in meteoric waters. ,Science 133, 1702-1703.

DAVIDSON D. F. (1963) Selenium in some oxidized sandstone-type uranium deposits. U.S. Geol. Surv. Bull. 1162-C, 1-33.

DAVlDSON D. F. and LAKIN H. W. (1961) Metal content of some black shales of the western United States. U.S. Geol. Surv. Prof. Paper 424, 329-331.

DAVlDSON D. F. and POWERS H. A. (1959) Selenium content of some volcanic rocks from western United States and Hawaiian Islands. U.S. Geol. Surv. Bull. 1084-C.

DAvis G. H., GREEN J. H., OLMSTEAD F. H. and BROWN D. W. (1959) Groundwater conditions and storage capacity in the San Joaquin Valley, California, U.S. Geol. Surv. Water-Supply Paper 1469.

DESBOROUGH G. A., POOLE F. G., HOSE R. K. and GREEN G. N. (1984) Metalliferous oil shale in the Upper Devo- nian Gibellini Facies of the Woodruff Formation, southern Fish Creek Range, Nevada. U.S. Geol. Surv. Bull. 1694, 93-104.

DEVEREL S. J., GILL1OM R. G., FuJn R., IZBICKI J. A. and FIELDS J. C. (1984). Areal distribution of selenium and other inorganic constituents in shallow ground water of the San Luis Drain Service Area, San Joaquin Valley, California: a preliminary study. U.S. Geol. Surv. Water- Resour. Invest. Report 84-4319.

DIBBLEE T. W. (1971) U.S. Geologic maps of seventeen 15- minute quadrangles. U.S. Geol. Surv. Geol. Map.

DmBLEE T. W. (1975) Geologic map of the Pacheco Pass, Hollister, Quien Sabe, Ortigalita Peak, San Benito, Panoche Valley and Tumey Hills quadrangles, San Benito, Santa Clara, Merced, and Fresno counties, Cali- fornia. U.S. Geol. Surv. Open-File Report 75-0394.

DRIESSEN P. M. and SCHOORL R. (1973) Mineralogy and morphology of salt efflorescences on saline soils in the Great Konya Basin, Turkey. Soil Sci. 24, 437-443.

ECKEL E. B. and MYERS W. B. (1946) Quicksilver deposits of the New Idria District, San Benito and Fresno counties, California: State Mineralogist's Report. Cal. J. Mines Geol. 42, 81-124.

EMMERICH W., RUaIN B. and WILCOCK R. J. (1977) Low pressure solubility of gases in liquid water. Chem. Rev. 77,219-262.

EVANGELOU V. P., WHITTIG L. D. and TANJI K. K. (1984) Dissolved mineral salts derived from Mancos Shale. J. Environ. Quality. 13, 146-150.

FLEISCHER M. (1970) New mineral names. Am. Mineral. 55, 317-321.

GEERING H. R., CAREY E. E., JONES L. H. P. and ALLAWAY W. H. (1968) Solubility and redox criteria for the possible forms of selenium in soils. Proc. Am. Soil Sci. Soc. 32, 35- 40.

GIELIOM R. J., BELITZ K., HEIMES F. J., DUBROVSKY N. M., DEVEREL S. J., ElO J. L., FuJn R. and CLIVrON D. G. (1989) Preliminary assessment of sources, distribution of selenium in the San Joaquin Valley, California. U.S. Geol. Surv. Water-Resour. Invest. Report 88-4186.

GtJNN A. M. (1981) The determination of arsenic and selenium in raw and potable waters by hydride generation/atomic absorption spectrometry--a review. Techni- cal Report TR169, Medmenham, Marlow, Bucks, Great Britain, WRC Environmental Protection.

HAWLEY J. E. and NlCHOL I. (1959) Selenium in some Canadian sulfides. Econ. Geol. 54, 608--628.

HOWARD J. H. (1977) Geochemistry of selenium: formation of ferroselite and selenium behavior in the vicinity of oxidizing sulfide and uranium deposits. Geochim. Cos- mochim. Acta 41, 1665-1678.

IRWIN W. P. and BARNES 1. (1975) Effect of geologic structure and metamorphic fluids on seismic behavior of the San Andreas fault system in central and northern California. Geology 3, 713-716.

KHARAKA Y. K. and BARNES 1. (1973) SOLMNEQ: solution mineral equilibrium computations. U.S. Geol. Surv. Computer Contrib. WRD-73-002 (NTIS PB-215-899).

KHARAKA Y. K., GUNTER, W. D., AGGARWAL P. K., PER- giNS E. H. and DEBRAAL J. D. (1988) SOLMINEQ.88: a computer program for geochemical modeling for water- rock interactions. U.S. Geol. Surv. Watcr-Resour. Invest. Report 88-4227.

KNAPTON J. R., JONES W. E. and SUTPHIN J. W. (1988) Reconnaissance investigation of water quality, bottom sediment and biota associated with irrigation drainage in the Sun River Area, West-central Montana, 1986-87. U.S. Geol. Surv. Water-Resour. Report 87-4244.

KONETZKA W. A. (1977) Microbiology of metal transformations. In Microorganisms and Minerals" (ed. E. D. WEIN- BERG), pp. 317--342. Marcel Dekker.

KRAOSKOPF K. B. (1955) Sedimentary deposits of rare metals. In Fiftieth Anniversary Volume 1905-1955 Econ- omic Geology (ed. A. M. BATEMAN), pp. 411--462. Econ- omic Publishing Company.

KRAUSKOPF K. B. (1967) Introduction to Geochemistry. McGraw-Hill.

LA~IN H. W. (1961) Geochemistry of selenium in relation to agriculture. In Selenium in Agriculture (eds M. S. ANDER- SON, H. W. LAKIN, K. C. BEESON, F. F. SMITH and E. TnACKER), pp. 3--12. U.S. Dept. of Agric. Handbook 200.

LAKIN H. W. (1973) Selenium in our environment. In Advances in Chemistry (ed. E. L. KOTHNY), Ser. 123, pp. 96-111. American Chemical Society.

LAKIN H. W. and BYERS H. G. (1941) Selenium occurrence in certain soils in the U. S. with a discussion of related topics: U.S. Dept. of Agric. Tech. Bull. 783, 1-27.

LEMLV D. A. and Sr~ITH G. J. (1987) Aquatic cycling of selenium: implications for fish and wildlife. U.S. Fish and Wildlife Leaflet 12.

LINN R. K. (1968) New Idria Mining District. In Ore Deposits of the United States, 1933-1967: The Graton- Sales Volume (ed. J. D. RIDGE), pp. 1624--1649. The American Institute of Mining, Metallurgical and Pet- roleum Engineers Inc.


MENDENHALL W. C., DOLE R. B. and STABLER H. (1917) Ground water of the San Joaquin Valley. U.S. Geol. Surv. Water-Supply Paper 398.

MURATA K. J. (1977) Occurrence of bloedite and related minerals in marine shale of Diablo and Tremblor Ranges, California. J. Res. U.S. Geol. Surv. 5,637-642.

NAKAHARA T. (1983) Applications of hydride generation techniques in atomic absorption, atomic fluorescence, and plasma atomic emission spectroscopy. Prog. Anal. Atom. Spec. 6,163-223.

NATIONAL ACADEMY OF SCIENCES (1976) Selenium: Medical and Biological Effects of Environmental Pollutants. National Academy of Sciences.

NATIONAL RESEARCH COUNCIL (1989) Irrigation-induced Water Quality Problems. National Academy Press.

NORRIS R. M. and WEBB R. W. (1976) Geology of Califor- nia. John Wiley.

PAGE B. (1966) Geology of the Coast ranges of California. In Geology of Northern California (ed. E. BAILEY), Calif. Div. Mines Geol. Bull. 190,255-276.

PELCZAR M. J., CHAN E. C. S and KREIG N. R. (1986) Microbiology, 5th Edn. McGraw-Hill.

PIERCE F. D. and BROWN H. R. (1977) Comparison of inorganic interferences in atomic absorption spectro- metric determination of arsenic and selenium. Anal. (;hem. 49, 1417-1422.

PRESSER T. S. and BARNES I. (1984) Selenium concentrations in waters tributary to and in the vicinity of Kesterson National Wildlife Refuge. Fresno and Merced counties, California. U.S. Geol. Surv. Water-Resour. Invest Report 84-4122.

PRESSER T. S. and BARNES I. (1985) Dissolved constituents including selenium in waters in the vicinity of Kesterson National Wildlife Refuge and the west Grassland, Fresno and Merced counties, California. U.S. Geol. Surv. Water-Resour. Invest Report 85-4220.

PRESSER Z. S. and OHLENDORE H. M. (1987) Biogeochemi- cal cycling of selenium in the San Joaquin Valley, Califor- nia. Environ. Mgm. l l , 805-821.

RANTZ S. E. (1969) Map of the mean annual precipitation in the California Region. U.S. Geol. Surv. Basic Data Comp. scale 1,000,000.

SHAYAN A. and LANCUCKI C. J. (1984) Konyaite in salt efflorescence from a Tertiary marine deposit near Gee- long, Victoria, Australia. Am. J. Soil Sci. Soc. 48, 939- 942.

SHRIFT A. (1964) A selenium cycle in nature? Nature 201, 131/4-1305.

SKORUPA J. P. AND OHLENDORF U. M. (1989) Drain-water contaminants in eggs related to deformities in Tulare Basin waterbirds. U.S. Fish and Wildlife Serv. Res. lnfo. Bull. 89-04, 1-2.

STIFF H. A. Jr (1951) The interpretation of chemical water analysis by means of patterns. J. Petrol. Tech. 3, 15-17.

STUMM WERNER and MORGAN J. J. (1981) Aquatic Chemis- try: An Introduction Emphasizing Chemical Equilibrium in Natural Waters, 2nd Edn. John Wiley.

SULLIVAN P. J., SeOSITO G., STRATHOUSE S. M. and HANSEN C. L. (1979) Geologic nitrogen and the occurrence of high nitrate soils in the western San Joaquin Valley, California Hilgardia 47, 15-49.

SYLVESTER M. A., DEASON J. P., FELTZ H. R. and ENGBERG R. A. (1988) Preliminary results of the Department of the Interior's Drainage Studies. hi Proc. on Planning Now for Irrigation and Drainage, 18-21 July 1988, Lincoln, Nebraska: Irrigation Division, pp. 665~677. American Society of Civil Engineers.

TIDBALL R. R., SEVERSON R. C., MCNEAL J. M. and Wit,son S. A. (1989) Distribution of selenium, mecury, and other elements in soils of the San Joaquin Valley and parts of the San Luis Drain Service Area, California. In Selenium and Agriculture Drainage: Implications for San Francisco Bay and the California Environment, Proc. of the 3rd Selenium Syrup. (ed. ALICE HOWARD), Berkeley, Califor- nia, 15 March 1986, pp. 71-82. The Bay Institute of San Francisco, Tiburon, California.

TRELEASE S. F. and BEATH O. A. (1949) Selenium, its Geological Occurrence and its Biological Effects in Re- lation to Botany, Chemistry, Agriculture, Nutrition and Medicine. Champlain Printers.

U.S. ENVIRONMENTAL PROTECTION AGENCY (1979) Water Related Environmental Fate of 129 Priority Pollutants, Vol. I, pp. 16-1-16-13. (EPA-440/4-79-029a). U.S. En- vironmental Protection Agency.

U.S. ENVIRONMENTAL PROTECTION AGENCY (19801 Hazar- dous waste management system. Fed. Reg. 45 (no. 98), 33063-33285.

U.S. ENVIRONMENTAL PROTECTION AGENCY 11987) Ambient water quality criteria for Se-1987 (EPA;44015-87-0061. U.S. Environmental Protection Agency.

VAN DOESBURG J. D. J., VERGOUWEN L. and VAN DER PLAS L. (19821 Konyaite, Na2Mg(SO4) 2 • 5H20, a new mineral from the Great Konya Basin, Turkey. Am. Mineral. 67, 11135-1038.

VINE J. D. and TOURTELOT E. B. (1970) Geochemistry of black shale deposits--a summary report. Econ. Geol. 65, 253-272.

WAGENET R. J. and JURINAR J. J. (1978) Spatial variability of soluble salt content in a Mancos Shale watershed. Soil Sci. 126,342-349.

WEDEPOHL K. H. (1970)Handbook of Geochemistry. Spr- inger.

WHrFrlG L. D., DEYO A. E. and TANJI K. K. (1982) Evaporite mineral species in Mancos Shale and salt efflor- cscence, upper Colorado River basin Am. J. Soil Sci. Soc. 46,645--651.

Documents

Geochemical evidence for Se mobilization by the weathering of pyritic shale, San Joaquin Valley, California, U.S.A