Physicochemical properties and chemical characteristics of water, bed sediment, and mussel tissue from selected streams near the Redleg and Peason Ridge impact areas, Fort Polk Military Reservation, Louisiana, June 2001 - November 2003

At the request of the U.S. Army Joint Readiness Training Center and Fort Polk, the U.S. Geological Survey collected and analyzed water, bed-sediment, and mussel-tissue samples from selected streams near the Redleg impact area (RIA) and Peason Ridge impact areas (PRIA) at the Fort Polk Military Reservation (Reservation), Louisiana. from June 2001 through November 2003. Samples were collected from 13 sites, including 2 reference sites. Water was analyzed for physicochemical properties; water and bed sediment were analyzed for major inorganic ions, cyanide, perchlorate, trace elements, total organic carbon, nutrients, and explosive compounds; and mussel tissue from three sites was analyzed for explosive compounds only. The two reference sites, one near the RIA and one near the PRIA, were selected to provide baseline data for these areas.

Streams near the RIA were acidic and low in buffering capacity. with pH measurements ranging from 5.0 to 6.6. Cation concentrations were less than or equal to E3.3J mg/L (E, estimated; J, method blank contamination; milligrams per liter), and anion concentrations were less than or equal to E7.3 mg/L. Field measurements and major inorganic ions concentrations were similar to the RIA reference site and to previously sampled nearby streams, indicating streams near the RIA were typical of streams near the eastern part of the Main Post.

Streams near the PRIA were slightly acidic to neutral and low in buffering capacity, with pH measurements ranging from 5.7 to 6.9. Cation concentrations were less than or equal to 6.2 mg/L, and anion concentrations were less than or equal to 16 mg/L. Streams near the PRIA were higher than the RIA for most physicochemical properties and constituents, hut typical of streams near the headwaters of the Calcasieu River. All concentrations of sulfate, chloride, and fluoride were less than the U.S. Environmental Protection Agency (USEPA) Secondary Drinking-Water Regulations (SDWR) of 250, 250, and 2.0 mg/L, respectively.

Concentrations of cations calcium, magnesium. and potassium for sites near both the RIA and PRIA were higher in depositional bed-sediment samples than in bulk samples. Higher cation concentrations were likely due to higher clay and organic content in the depositional samples.

The trace elements detected in the highest concentrations in water and bed sediment were aluminum, iron, and manganese. All aluminum concentrations in water were within the range or greater than the USEPA SDWR range from 50 to 200 ug/L (micrograms per liter). All but four iron concentrations in water exceeded the SDWR. Manganese concentrations in seven water samples at the RIA sites and four samples at the PRIA sites were greater than the SDWR. These concentrations of cations were consistent with soil characteristics and low pH measurements of stream water and rainfall in the area. All other trace-element concentrations in water were less than regulatory guidelines and regulations except the USEPA Maximum Contaminant Level Goal of 0 ug/L for arsenic and lead and 0.5 u/L for thallium. Arsenic, lead, and thallium concentrations were similar to those detected in blank samples or those reported for the reference sites.

The Canadian Council of Ministers of the Environment (CCME) has established bed-sediment guidelines for seven trace elements: arsenic, cadmium, chromium, copper, lead, mercury, and zinc. No concentrations exceeded the CCME Probable Effect Level, and only one arsenic concentration of 8.87 mg/kg (milligrams per kilogram), in a depositional sample from one of the RIA sites, exceeded the CCME Interim Sediment Quality Guideline of 5.9 mg/kg.

The median concentrations of total organic carbon in water were 5.3 mg/L at the RIA and 4.0 mg/L at the PRIA, and both concentrations were less than the average dissolved organic carbon concentration of 5.75 mg/L for all world rivers. All detected nutrient concentrations in water were less than USEPA guidelines and regulations. The largest nutrient concentrations in water and bed-sediment samples were total organic nitrogen, measured as total Kjeldahl nitrogen; they included a maximum concentration of 0.53 mg/L in water at the RIA sites, E0.38 mg/L in water at the PRIA sites, 294 mg/kg in hulk bed sediment. and 1,740 mg/kg in depositional bed sediment.

Four explosive compounds, 1,3,5-trinitrobenzene, 2,4,6-trinitrotoluene, RDX (hexahydro-1,3,5-trinitro-1,3,5- triazine), and tetryl, were detected in water near the RIA; one compound, HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7- tetrazocine), was detected in bed sediment near the PRIA; and one compound, nitroglycerin, was detected in mussel tissue near the RIA. The most frequently detected explosive compound, RDX, was detected in 10 water samples from 5 sites near the RIA. Concentrations of explosive compounds in water were less than USEPA Health Advisories available for reference.