PRELIMINARY ASSESSMENT LAS CRUCES PCE DONA ANA COUNTY, NEW MEXICO CERCLIS IDENTIFICATION NUMBER: not assigned 3 November 1997 NEW MEXICO ENVIRONMENT DEPARTMENT GROUND WATER QUALITY BUREAU SUPERFUND OVERSIGHT SECTION Prepared By r\ /] -JlmJSp*- ^r\Jo^\s~+-^*> christopher holmes 000962 PRELIMINARY ASSESSMENT LAS CRUCES PCE Table of Contents 1. INTRODUCTION. ...................................... 1 2. SITE DESCRIPTION, LOCATION, AND WASTE CHARACTERISTICS ........ 1 2.1 Site Description and Location ............................ 1 2.2 Waste Characteristics. ................................ 2 3. GROUND WATER PATHWAY ............................... 3 3.1 Hydrogeologic Setting ................................ 3 3.2 Ground Water Targets ................................ 4 3.2 Ground Water Conclusions. ............................. 4 4. SURFACE WATER PATHWAY. .............................. 5 5. SOIL EXPOSURE AND AIR PATHWAYS. ........................ 5 6. SUMMARY AND CONCLUSIONS ............................. 5 REFERENCES .......................................... 6 List of Tables Table 1 .Tetrachloroethylene concentrations (^g/1) in samples from Las Cruces municipal wells. 2 Table 2. Population served by municipal wells within 4 miles of Las Cruces PCE site.. .... 4 List of Figures Figure 1. Location of Las Cruces PCE Site. ........................... 8 Figure 2. Mesilla Ground-Water Basin.. ............................. 9 Figure 3. Generalized geohydrologic section of the northern Mesilla Basin. .......... 10 000963 Preliminary Assessment Las Graces PCE 3 November 1997 Page 1 1. INTRODUCTION Under the authority of the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA) as amended by the Superfund Amendments and Reauthorization Act of 1986 (SARA), the New Mexico Environment Department, Superfund Oversight Section, conducted a Preliminary Assessment (PA) at the Las Cruces PCE site in Dona Ana County, New Mexico. The purpose of this investigation was to collect information concerning conditions at the Las Cruces PCE site sufficient to assess the threat posed to human health and the environment and determine the need for additional investigation under CERCLA/SARA. The scope of the investigation included a review of existing analytical data and available file information and on-site reconnaissance (19-20 May 1997). A CERCLIS identification number has not been assigned to this site. 2. SITE DESCRIPTION, LOCATION, AND WASTE CHARACTERISTICS 2.1 Site Description and Location The Las Cruces PCE site consists solely of a contaminated ground water plume with no identified source. Tetrachloroethylene also referred to as perchloroethylene (PCE) has been measured hi water samples from four City of Las Cruces municipal wells (Figure 1) (Table 1) (Reference 1). The effected municipal wells are 18, 19, 21, and 27. All four effected wells are located in Las Cruces, in an area approximately 2,500 feet by 4,000 feet (Reference 2). Well 18 is located at 153 North Cottonwood Street (Reference 3). Well 19 is located at 101 South Triviz Drive (Reference 3). Well 21 is located at 671 North Triviz Drive (Reference 3). Well 27 is located at 2025 East Griggs Avenue (Reference 3). The effected wells range from 576 to 730 feet deep (Reference 4). The depth to water in the effected wells ranges from 208 to 250 feet (Reference 4). Tetrachloroethylene has not been detected in water samples from surrounding wells, 10, 20, 26, 28, 54, and 57 (Reference 1). The center of the site was taken to be the latitude, halfway between the north and south most wells and longitude halfway between the east and west most wells. The coordinates of the site are 32° 19' 08" latitude and 106° 45' 16" longitude (Reference 5). The contaminated municipal wells are located Township 23 S, Range 2 E, sections 8 and 9 (Reference 4). The climate of Dona Ana County is arid (Reference 6, page 4). In the basin area along the Rio Grande, temperatures reach 90° F or greater an average of 101 days a year (Reference 6, page 5). Winters are mild. The average daily minimum hi January, the coolest month, is 25°F. The average daily maximum is 57°F (Reference 6, page 5). Potential evaporation and transpiration greatly exceeds rainfall (Reference 6, page 5). 000964 Preliminary Assessment Las Cruces PCE 3 November 1997 Page 2 2.2 Waste Characteristics The Las Cruces PCE site consists solely of a contaminated ground water plume with no identified source. Tetrachloroethylene has consistently been detected in samples from municipal wells 18,21, and 27 (Reference 1). Two water samples from well 18 have contained greater than the federal drinking water standard of 5 /^g/1 for PCE. Existing analytical data is summarized in Table 1. Table 1. Tetrachloroethylene concentrations Qg/1) in samples from Las Cruces municipal wells. Date Well 18 Date Well 19 Date Well 21 Date Well 27 3/13/94 0.0 3/13/94 0.3 8/9/93 0.9 8/9/93 1.4 1/10/95 32.0 5/16/94 0.3 2/17/94 0.8 5/16/94 0.7 2/22/95 1.5 10/3/94 0.0 6/21/94 1.0 10/3/94 0.6 2/27/95 *1. 1/1.2 1/9/95 0.0 10/10/94 1.0 5/9/95 0.8 4/12/95 0.5 4/5/95 0.0 1/10/95 0.7 8/18/95 0.0 8/18/95 0.6 8/18/95 0.0 4/5/95 1.3 10/4/95 0.8 10/4/95 0.0 10/4/95 0.0 8/18/95 1.2 2/23/96 mmma^^m1.0 1/9/96 6.4 1/9/96 0.6 10/4/95 1.2 1 7/23/96 0.0 1/9/96 1.1 1 2/21/96 0.8 4/3/96 0.8 5/2/96 1.0 * duplicate samples Tetrachloroethylene is a CERCLA hazardous substance (Reference 7, pages A-722 and A-722). It is a solvent for fats, greases, waxes, rubber, gums, and caffeine (Reference 8, pages 580-581). Uses of PCE include dry cleaning; metal degreasing; removing soot from industrial boilers; heat transfer; and manufacturing fluorocarbons, paint removers, printing inks, trichloroacetic acid and vermifuge (Reference 8, pages 580-581). Under ambient environmental conditions, PCE is a dense npnaqueous phase liquid (DNAPL) chemical (Reference 9, page 3-1). Immiscible fluids, such as PCE, do not completely dissolve in 000965 Preliminary Assessment Las Graces PCE 3 November 1997 Page 3 water but exist as separate liquid and aqueous phases (Reference 9, pages C-2 and C-3). Denser than water NAPLs sink through the saturated zone. The subsurface movement of DNAPL is controlled substantially by the nature of the release; DNAPL density, interfacial tension, and viscosity; capillary forces; and to a lesser extent hydraulic forces (Reference 9, page 2-1). Because of their high density and low viscosity chlorinated solvents such as PCE are highly mobile as a separate phase (Reference 9, page 3-9). 3. GROUND WATER PATHWAY 3.1 Hydrogeologic Setting Las Cruces is located within the Mesilla Ground-Water Basin (Figure 2) (Reference 10, page 3). The Santa Fe Group and flood plain alluvium of the Rio Grande constitute the major aquifer of the Mesilla Ground-Water Basin (Reference 11, page 1). The aquifer is bound by less permeable bedrock (Figure 3) (Reference 11, page 1). The flood plain alluvium is about 4 miles wide along the Rio Grande and 80 feet thick. It generally has a thick basal channel unit consisting of sand and gravel overlain by finer grained flood-plain deposits (Referenc2 e 12, page 28). Horizonta1 l hydraulic conductivities for the river alluvium range from 3.53 x 10" cm/s to 1.23 x 10' cm/s (Reference 11, page 15). The Santa Fe Group is a rock-stratographic unit, classified on the basis of lithology and depositional environment. It consists of unconsolidated to moderately consolidated sedimentary deposits, minor ash-fall volcaniclastics, and other volcanic rocks (Reference 12 page 23). It is approximately 2,500 feet thick (Reference page 12). Dividing the Santa Fe Group into three hydrostratigraphic units facilitates assigning hydraulic properties it (Reference 11, page 13). For the uppe4 r unit of the Santa8 Fe Group, estimates of horizontal hydraulic conductivity range from 7.06 x 10" cm/s to 2.40 x 10~ cm/s (Reference 11, pag4 e 13). Estimates of 2 horizontal hydraulic conductivity for the middle unit range from 3.53 x 10" cm/s to 3.53 x 10~ cm/s (Reference 11, page 13). For the 2 lower unit, estimates of horizontal hydraulic conductivity range from 3.53 x 10"* cm/s to 1.20 x 10' cm/s. From which unit(s) the Las Cruces municipal wells are pumping is currently unknown. The Rio Grande is the primary source of recharge to the aquifer system of the Mesilla basin (Reference 10, page 65). Water moves from the shallow flood plain alluvium to the upper Santa Fe Group through a series of interbedded gravel, sand, and clay lenses (Reference 10, page 65). Thin interbedded clay lenses in the lower part of the flood plain alluvium and upper Santa Fe Group restrict vertical flow. Horizontal permeability usually exceeds vertical permeability by several orders of magnitude because of vertical heterogeneity (Reference 10, page 65). 000966 Preliminary Assessment Las Cruces PCE 3 November 1997 Page 4 3.2 Ground Water Targets Las Cruces is served by two municipal water systems, Las Cruces Municipal Water and Las Cruces East Mesa Water System (Reference). Both water systems are operated by the City of Las Cruces and rely completely on ground water as their source of water. The Las Cruces Municipal Water System is a blended system supplying water from twenty-eight wells to 67,900 people (2,425 people per well) (Reference 13). No single well contributes more than 40% of the total water (Reference 14). The four municipal wells from which samples containing PCE have been collected are operated by the Las Cruces Municipal Water System.