Aquatic-life criteria compared to concentrations of cadmium, copper, lead, and zinc in streams near Fort Polk Military Reservation, Louisiana, December 2015–August 2016

The primary focus of this study was to document cadmium, copper, lead, and zinc concentrations in selected streams near the U.S. Army Joint Readiness Training Center (JRTC) and Fort Polk Military Reservation and to compare those values to Federal and State aquatic-life criteria guidelines. The acute aquatic-life criteria used for this study are as follows: the U.S. Environmental Protection Agency (EPA) aquatic-life criterion maximum concentration (CMC) based on hardness, the EPA CMC for copper based on the biotic ligand model (BLM), and the Louisiana Department of Environmental Quality (LDEQ) acute aquatic-life criteria based on hardness. The chronic aquatic-life criteria used for this study are as follows: the EPA aquatic-life criterion continuous concentration (CCC) based on hardness, the EPA CCC for copper based on the BLM, and the LDEQ chronic aquatic-life criteria based on hardness.

Cadmium was detected in one stream-water sample collected near the Peason Ridge training area, hereinafter referred to as Peason Ridge, and one stream-water sample collected near North and South Fort Polk, hereinafter referred to as the Main Post. A cadmium concentration of an estimated (E) 0.48 microgram per liter (μg/L) in a stream-water sample collected during high stage near Peason Ridge exceeded the EPA CMC of 0.10 μg/L. A second cadmium concentration of E0.33 μg/L in a stream-water sample collected during low stage exceeded the EPA CMC of 0.22 μg/L, and a 4-day average cadmium concentration of E0.16 μg/L exceeded the EPA CCC of 0.14 μg/L.

Copper was detected in 34 stream-water samples collected near Peason Ridge and 22 stream-water samples collected near the Main Post. The EPA acute criteria for copper were exceeded 17 times in stream-water samples collected near Peason Ridge and 19 times in stream-water samples collected near the Main Post. The EPA chronic criteria for copper were exceeded five times in stream-water samples collected near Peason Ridge and seven times in stream-water samples collected near the Main Post.

Lead was detected in 31 stream-water samples collected near Peason Ridge and 16 stream-water samples collected near the Main Post. A concentration of 6.0 μg/L in a stream-water sample collected during high stage at site 2 near Peason Ridge exceeded the EPA CMC of 5.5 μg/L, and a concentration of 4.1 μg/L in a stream-water sample collected during high stage at site 4 near the Main Post exceeded the EPA CMC of 2.9 μg/L. The EPA chronic criteria for lead were exceeded nine times in stream-water samples collected near Peason Ridge and three times in stream-water samples collected near the Main Post. The LDEQ chronic criteria were exceeded two times in stream-water samples near Peason Ridge and none near the Main Post.

Zinc was detected in 35 stream-water samples collected near Peason Ridge and 17 stream-water samples collected near the Main Post. A concentration of 100 μg/L in a stream-water sample collected at site 3 near Peason Ridge exceeded the EPA CMC of 8.9 μg/L and the LDEQ acute aquatic-life criteria of 36 μg/L. One 4-day average zinc concentration, E28 μg/L for stream-water samples collected from site 3 near Peason Ridge, exceeded the EPA CCC of 8.2 μg/L; however, no concentrations of zinc exceeded the LDEQ chronic aquatic-life criteria near Peason Ridge or the Main Post.

The presence of copper, lead, and zinc at concentrations above the calculated acute or chronic aquatic-life criteria for some stream-water samples collected in relatively pristine streams near Peason Ridge and the Main Post indicates that these waters are susceptible to elevated trace element concentrations likely because of low ionic strength and hardness.