Based on findings of limited studies during 1989-92, a reconnaissance investigation was conducted in 1993 to assess the effects of the Vermejo Irrigation Project on water quality in the area of the project, including the Maxwell National Wildlife Refuge. This project was part of a U.S. Department of the Interior National Irrigation Water-Quality Program to determine whether irrigation drainage has caused or has the potential to cause significant harmful effects on human health, fish, and wildlife and whether irrigation drainage may adversely affect the suitability of water for other beneficial uses. For this study, samples of water, sediment, and biota were collected from 16 sites in and around the Vermejo Irrigation Project prior to, during the latter part of, and after the 1993 irrigation season (April, August-September, and November, respectively).

No inorganic constituents exceeded U.S. Environmental Protection Agency drinking-water standards. The State of New Mexico standard of 750 micrograms per liter for boron in irrigation water was exceeded at three sites (five samples), though none exceeded the livestock water standard of 5,000 micrograms per liter. Selenium concentrations exceeded the State of New Mexico chronic standard of 2 micrograms per liter for wildlife and fisheries water in at least eight samples from five sites.

Bottom-sediment samples were collected and analyzed for trace elements and compared to concentrations of trace elements in soils of the Western United States. Concentrations of three trace elements at eight sites exceeded the upper values of the expected 95-percent ranges for Western U.S. soils. These included molybdenum at one site, selenium at seven sites, and uranium at four sites.

Cadmium and copper concentrations exceeded the National Contaminant Biomonitoring Program 85th percentile in fish from six sites. Average concentrations of selenium in adult brine flies (33.7 μg/g dry weight) were elevated above concentrations in other invertebrates. Concentrations of other elements were below their respective toxicity levels.

Plants, invertebrates, fish, and fish fillets were collected and analyzed. These analyses were compared to diagnostic criteria and to each other to determine the extent of bioaccumulation of trace elements. Plants contained larger dry weight concentrations of aluminum, arsenic, boron, chromium, iron, lead, magnesium, manganese, nickel, and vanadium than invertebrates and fish. Adult brine flies, gathered from playas, contained larger geometric mean dry weight concentrations of boron, magnesium, and selenium than other invertebrates. Of all samples collected, the largest mercury concentrations were found in fish fillets, although these concentrations were below levels of concern. Mercury and selenium bioaccumulation was evident in various habitats of the study area.

Biological samples from Natural playa, an endemic wetland, and Half playa, a playa that receives additional water through seepage and irrigation delivery canals, generally had elevated concentrations of boron, iron, magnesium, and selenium than samples from reservoir and river sites. Selenium concentrations were lowest in biota from the two reservoir sites, although a wetland immediately downstream from the dam impounding Lake No. 13 (created by seepage from the reservoir) had elevated concentrations of selenium in biota. The geometric mean selenium concentration of whole-fish samples, except those from Lakes No. 13 and No. 14, exceeded the 5-μg/g dry weight selenium concentration that demarcates the approximate lower limit of the threshold range of concentrations that have freen associated with adverse effects on piscine reproduction. Biota collected on and in the area around Maxwell National Wildlife Refuge contained concentrations of selenium that are in the lower range of threshold values that have been associated (dietarily) with risks of avian reproductive abnormalities.

Bottom-sediment samples from two sites downstream from the irrigation project were collected and analyzed for 23 organic compounds (principally organochlorine pesticide residues). Three compounds were detected at the two sites: DDD was found at 0.2 microgram per kilogram, DDE was detected at 0.1 microgram per kilogram at both sites, and chlordane was detected at 1 microgram per kilogram. None of the 28 whole-fish and fillet samples analyzed for PCB and organochlorine pesticide residues contained any of the 23 organic compounds tested for at concentrations higher than the analytical reporting limit (less than 0.01 μg/g wet weight).

Concentrations of inorganic analytes were generally within established guidelines or expected concentrations for water, sediment, and biota. lirigation-return flows were found to be unrelated to adverse effects in biota.