Media of Concern at the ASARCO site in El Paso, Texas
Media of Concern
The facility is located in El Paso County on the Rio Grande floodplain at an elevation approximately 3,600 feet above mean sea level. The surface geology consists of a mix of colluvial sediments from the surrounding mountains and fluvial sediments from the Rio Grande. Typical fluvial sediments can be classified into fine to coarse grain gravel and sand with a mixture of silt and clay all of which are present at the ASARCO El Paso smelter site. The site is built over a series of arroyos which have been filled with either native soils or slag. Slag is a by-product of the smelting process and is considered a solid waste. The thickness of the slag varies across the facility to a maximum of sixty feet. The elements which comprise the Chemicals of Concern (COC) at the El Paso facility include arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), lead (Pb), selenium (Se) and zinc (Zn). The most prevalent COCs are arsenic, lead, and cadmium. The highest on-site surface soil concentrations are arsenic at 17,000 mg/kg; lead at 49,000 mg/kg; and cadmium at 3,500 mg/kg.
Two separate releases have contributed to the groundwater plume at the facility. One source of contamination is attributed to two diesel releases from Leaking Petroleum Storage Tanks (LPSTs) and the metals release is from the plant smelter operations. The diesel and metal plumes are commingled. The groundwater plume is migrating westward towards the Rio Grande.
Diesel Releases from LPSTs
In February 1990, hydrocarbon was observed seeping into the American Canal at several locations. LPST No. 094594 was assigned to the release. ASARCO conducted the investigation, removed contaminated soil, recovered approximately 22,000 gallons of diesel and treated approximately 7,500,000 gallons of diesel-affected groundwater. The release was closed on November 15, 2000.
In March 1990, ASARCO personnel observed visible staining adjacent to the underground piping of an 18,000-gallon diesel tank and dispenser pump. An estimated 62,291 gallons of diesel was released. LPST No. 095897 was assigned to the second release. The tank and all associated piping were dismantled and removed. All impacted soils have been excavated. Based on the latest report, the diesel product is limited to three monitor wells with diesel product ranging from sheen to a thickness of 0.85 feet. A system is currently in place to recover the diesel product. Dissolved-phase concentrations are stable with maximum concentrations of 0.0108 mg/L benzene. Diesel recovery to the maximum extent practicable and protection of potential receptors (e.g. American Canal) are required prior to receiving closure under the TCEQ rules at 30 Texas Administrative Code Chapter 334 (Underground and Aboveground Storage Tanks).
Metals Release from the Smelter Operations
In accordance with the 1996 Agreed Order, ASARCO submitted the first Remedial Investigation (RI) Report on October 9, 1998. Subsequent RI Phase II, III & IV reports were submitted in July 2000, November 2001 and September 2003, respectively. The RI Report indicates the groundwater was impacted by plant operations. Since the process pond water and groundwater are interconnected, the process pond water is most likely the main source for metals in the groundwater. All process ponds have now been closed.
The agency requested ASARCO to sample the groundwater for the following parameters: arsenic, cadmium, chromium, copper, iron, lead, selenium, zinc, pH, specific conductivity and total dissolved solids. After the completion of the groundwater remedial investigation, arsenic, cadmium, chromium, copper, lead and selenium were detected and exceeded federally established drinking water standards. The primary Chemicals of Concern (COCs) in the groundwater are arsenic, lead and cadmium. The federally established drinking water standard is known as the maximum contaminant level (MCL). The MCL is also the state's groundwater standard. The MCL concentrations for arsenic, lead, and cadmium are 0.010 mg/L, 0.015 mg/L and 0.005 mg/L, respectively. The most prevalent COC in the groundwater is arsenic. Currently, the highest concentration of arsenic in the groundwater occurs in onsite well EP-49 with a concentration of 62.5 mg/L, which is above the MCL for arsenic. This well is located on the east side of Paisano Drive. The area of contaminated groundwater is shown in Figure 2.
The aquifer underlying the El Paso site is composed primarily of interbedded and mixed sand, gravel, boulders and bedrock. Depth to groundwater varies and is dependent on the location within the plant area. The depth of groundwater at the plant is 40 to 60 feet below ground surface (bgs). However, the depth to groundwater is approximately 10 feet bgs along the Rio Grande floodplain. The preferred pathway for groundwater flow at the site is via the filled arroyos. In general, the groundwater flow direction is west towards the Rio Grande.
Surface Water Impacted by Contaminated Groundwater
Based on surface water analytical data, the contaminated groundwater appears to have reached the Rio Grande. The latest surface water sampling results are located on the Water Sampling Data web page.