Mary L. Barrett, Department of Geology & Geography, Centenary College of Louisiana, Shreveport, LA 71104: firstname.lastname@example.org
At the Lake St. John (LSJ) Field, Concordia Parish, LA, dissolved arsenic in shallow groundwater (8 ft to 22 ft below ground surface) occurs in former emergency pit areas associated with tank batteries and with the saltwater injection disposal system. This study uses publically-available geochemical and historic oilfield records to examine the possible origins of elevated groundwater arsenic in three oilfield pits. The study area is composed of two leases historically known as the Applegate lease and the Pan American Insurance Company lease. They were developed and produced beginning in 1942 by the California Company (Standard Oil of California, later Chevron). Both lease areas, in part, have been involved in modern environmental oilfield (legacy) litigation under LA Act 312 legislation initially passed in 2006. This legislative act requires involvement and cleanup oversight (along with the court system) by the Louisiana Office of Conservation (LA OOC) in legacy environmental lawsuits. The legislation has resulted in a large and rapidly-growing public record of high-quality geochemical measurements of various media (groundwater, sediment/soil, solid and liquid wastes) performed by state-certified laboratories. The records (both case files and occasional hearing files) include paper and digital copies and are available at the LA OOC office in Baton Rouge, LA. The LA OOC collections of Lake St. John field litigation are used extensively in this study. Geochemical data were collected by the environmental companies/experts of Pisani & Associates, ICON, and Geosyntec Consultants.
The three studied pits were used in the 1950s – 1980s as emergency pits (periodic usage) and were initially closed in the mid- to late-1980s. The study area and the field are located on the Mississippi River alluvium. The clayey upper section varies from less than 5 ft to over 15 ft in thickness in the study area. The pits were about 6 ft deep. The lowest dissolved arsenic values occur at the Applegate (tank battery) pit area, and values range from non-detect to 0.13 mg/l. Part of this pit’s base was in sand. The highest dissolved arsenic values occur at the Pan American (tank battery) pit area, and values range from non-detect to 0.915 mg/l. This pit’s base was underlain by a few feet of clayey sediment. The Wilcox pit was an emergency pit for the saltwater disposal (SWD) well system, and its dissolved arsenic values range from non-detect up to 0.517 mg/l. This pit’s base was underlain by clayey sediment, also.
Two models have been put forth in the public record to explain elevated shallow groundwater arsenic patterns at the LSJ Field. The first model, a reductive-dissolution model, was put forward by Geosyntec Consultants (2008a, b, c) based on groundwater sampling of one pit six months after pit re-closure (the Applegate pit, first closed about 1984, re-closed 2007). The Geosyntec work has been submitted to the LA OOC records from 2008 through March of 2015. In this model, reducing groundwater conditions related to oily pit wastes or other organics result in adsorbed natural arsenic being released into solution when oxidized iron and manganese species are dissolved. Expected groundwater model conditions include low oxidation-reduction potential (ORP) measurements, and elevated arsenic and elevated iron wholly due to solids dissolution.
Published Louisiana studies indicate that sediment redox conditions influence solubility of arsenic and iron, and this is expected to influence dissolved metal amounts in natural environments (Guo and others, 1997; Miao and others, 2006). But, some dissolved groundwater arsenic below the LSJ field pits is elevated above Pisani & Associates’ interpretation of 0.12 mg/l as the highest naturally-occurring dissolved arsenic value, and the pit values are also above a documented 0.10 mg/l measurement in shallow Mississippi River alluvium groundwater away from the oil field.
The second model was put forward by the author in meeting presentations beginning in October of 2014, and it relies on the geochemical data from the three sampled pits (2006-2015) and the historic record of arsenic corrosion inhibitor usage in the LSJ field. W-41, a patented arsenic-based corrosion inhibitor of Standard Oil of California, was added to well brines and circulated through LSJ field’s unit and lease production systems prior to well injection and disposal in the 1950s. Organic-based (no metals) corrosion inhibitors were being used by the early 1960s.
Oilfields require consideration of all possible anthropogenic sources for arsenic, especially arsenic-based corrosion inhibitors and arsenic-based herbicides. Arsenic was used to inhibit corrosion in oilfield flow systems in two ways: 1) as a production corrosion inhibitor dissolved in circulating oilfield waters and used in U.S. fields in the 1950s (Hill and Davie, 1955) and in the Gulf Coast oilfields from 1949 to at least the late 1950s (Jones, 1955; LA Stream Control Commission, 1957; Gardner, 1963); and 2) as an acid corrosion inhibitor, used in acid well treatments from the mid-1930s into the 1970s. Patents held by Standard Oil of California on the arsenic-based production corrosion inhibitor stated a preferred dissolved arsenic concentration in produced water at 5 ppm after introduction of 10 to 50 ppm at a well, depending on corrosion treatment requirements (calculated as arsenous oxide) (Rohrback and McCloud, 1953; Frisius, 1959).
Examples of forgotten knowledge about arsenic-based corrosion inhibitors are publications of the American Petroleum Institute (API)—while a paper published in 1955 described arsenic-based corrosion inhibitor usage in California fields (Hill and Davie, 1955), publications of 1998 and 2011 did not list this previous arsenic usage as a possible anthropogenic source (API, 1998, 2006). Past arsenic-based herbicide and corrosion usages are also documented in U.S. oilfields by veterinary studies of poisoned cows (Edwards and others, 1979; Morgan and others, 1984; Coppock and others, 1996).
Dissolved iron and chlorides are also elevated in the LSJ field pits’ groundwater. Both old LSJ field brine analyses and published general oilfield corrosion studies indicate that elevated dissolved iron is common in produced brines due to corrosion. The observed geochemical patterns around the heavily-sampled Pan American pit indicate that relative ion mobility in the groundwater is chlorides > iron > arsenic. The ORP values below the pit are slightly reduced as compared to nearby monitoring wells, but elevated pit groundwater arsenic or iron does not vary with ORP. Highest arsenic and iron values are associated with chlorides.
The Applegate pit, first closed in 1984, was sampled sporadically from 2007 to 2015. The lowest dissolved arsenic measurements at the pit were in 2008, 6 months after the Applegate pit was re-closed. Arsenic values suggest an apparent relationship to not only ORP and iron, but also to conductivity (salinity). The 2008 sampling event is interpreted as impacted by the pit re-closure. The groundwater sampling from 2012-2015 contained elevated arsenic and elevated chlorides by the pit, similar to what was present in initial 2007 sampling prior to pit re-closure.
The Geosyntec reductive-dissolution model depends on the presence of oily waste or other organics in an oilfield setting and no anthropogenic sources of arsenic and iron. Publically-available oilfield geochemical data in Louisiana oilfields do not show a common pattern of oily wastes (in pits or otherwise) to elevated dissolved arsenic. This model may be limited in its ability to explain elevated arsenic in old oilfield pits. However, if the elevated groundwater arsenic is related to the 1950s usage of arsenic corrosion inhibitors, then prediction of other potentially-impacted areas is easier. In the LSJ Field, tank battery pits and saltwater disposal well pits of the 1950s operated by the California Company will be of interest.
A 1955 document addressing SWD wells at LSJ field stated that W-41 circulation from production wells controlled corrosion for the SWD wells, indicating that both the unit and non-unit (lease) production systems of the California Company circulated W-41. Thus, the 1950s tank battery pits and the saltwater well (SWD) pits are expected to have been exposed to waste saltwater elevated to different amounts with dissolved arsenic corrosion inhibitors. Oilfield maps and historic aerial photography of 1955, 1959 and 1960 were used to find and map the tank battery and SWD well pits. Other pits were also noted (reserve/drilling pits, well/burn pits, high-pressure gas blowdown pits), but these individual well-associated pit types are less-likely to contain a large saltwater impact. These other pits were not mapped as probably having an elevated arsenic signature related to 1950s production wells producing saltwater.
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