Nogales Grand Avenue Study Area
The Nogales Grand Avenue study area includes properties surrounding a portion of Grand Avenue running along Nogales Wash, in Nogales, Arizona. The study area is approximately bounded to the north by Ruby-Nogales Road, and to the south by West Mariposa Road.
Valle Verde, under the management of Southwestern Utility Management (SWUM), entered into an agreement with ADEQ to operate a wellhead treatment system on Valle Verde Well #2. Operation of the treatment system began in October 2008.
As of the end of September 2013, the GAC treatment system treated over 220 million gallons of water and removed approximately 3.8 pounds of VOCs. However, since VOCs—and particularly tetrachloroethene (PCE)—have not been detected above the Arizona Aquifer Water Quality Standard (AWQS) in Valle Verde Well #2 during the past two years, ADEQ has decided to discontinue operation of the wellhead treatment system and let the agreement with SWUM expire at the end of September 2015.
ADEQ conducted a public meeting on June 29, 2010 at the Santa Cruz County building. This meeting was to inform the community about the water quality from the treatment system and to provide an update on the investigation.
Late 1980s: Low levels of PCE have been detected in the Nogales Wash area since the late 1980s. Initial investigations and groundwater sampling were initiated by the Santa Cruz County Health Department in late 1986 and early 1987.
1988: Groundwater samples for VOCs were collected from 18 existing groundwater wells in the Nogales Wash area.
1993: Two groundwater monitoring wells were installed just north of the international border and two rounds of samples for VOCs were collected.
1994: A total of 32 groundwater samples were collected for VOCs from existing wells in the Nogales area during the summer of 1994. Wells sampled included groundwater monitoring wells, irrigation wells, public drinking water supply wells, and private drinking water wells.
1997 - 1998: Under a binational agreement between the United States and Mexico, 13 wells in 12 different locations were sampled for VOCs on three separate events. All the wells were within 5 miles north or south of the international border.
2002 - 2003: ADEQ periodically sampled nine wells located just north of the international border for VOCs..
2007 - 2008: Customers of Valle Verde were informed by a public notice mailed on January 19, 2007 that the water system tested above the maximum contaminant level (MCL) for PCE in December 2006. The public notice stated that Valle Verde would test the water quality quarterly; inform the customers when the problem is remedied; provide the required health effects statement; and provide a phone number for customers to obtain a translated copy or to ask questions. Valle Verde stopped supplying water from four of its wells (wells #1, #2, #4 and #7) due to the presence of PCE.
ADEQ periodically sampled four wells located just north of the international border for VOCs in 2007 and 2008. After a December 2007 well survey of the area, 12 additional groundwater samples were collected from wells along the Nogales Wash in the northern part of the City of Nogales (NOC). These samples included irrigation wells, public drinking water supply wells, and private drinking water wells. This limited well survey did detect PCE in some private wells.
In spring 2008, ADEQ signed an agreement with Valle Verde to provide financial assistance to build a treatment system at well #2. This treatment system, which uses GAC to remove PCE, began operation in October 2008 and has been providing water treated to meet all drinking water standards.
In summer 2008, ADEQ signed an agreement with the CON to provide financial assistance to complete a permanent connection between the Valle Verde water system and the CON waste system, which would be used as an emergency water supply if necessary.
2009 - 2010: SWUM continued to operate the treatment system at Valle Verde Well #2. ADEQ continued to provide financial assistance to SWUM to cover operations and maintenance of the treatment system.
2011: Thirty-two private, commercial, and ADEQ installed monitor wells were sampled in the spring of 2011. Analytical results of the sampling showed continued presence of VOCs and PCE in the groundwater in the area, but at lower levels than previous sampling results. None of the wells sampled exceeded the AWQS of 5 microgram per liter (ug/L). In Dec. 2011, 26 wells were sampled. None of the wells sampled in Dec. 2011 exceeded the Arizona AWQS of 5 ug/L for PCE. Additionally, ADEQ provided funding to upgrade the treatment system to meet Santa Cruz County floodplain specifications.
2012: Six new monitoring wells were drilled in January. Thirty-five wells were sampled in March, including the new monitoring wells. None of the wells sampled in March exceeded the Arizona AWQS of 5 ug/L for PCE. As of the end of April, the GAC treatment system at Valle Verde Well #2 had treated over 162 million gallons of water and removed approximately 3.2 pounds of VOCs.
2013: The GAC treatment system continued to operate and as of Oct., Valle Verde Well #2 has treated over 220 million gallons of water and removed 3.8 pounds of VOCs. Due to the lack of detectable PCE concentrations above the AWQS in monitoring wells, along with a decline in overall water levels in the region in 2012, no additional groundwater sampling was completed in 2013.
Groundwater monitoring continued to be performed quarterly; VOCs, including PCE, were not detected above the AWQS.
The current contaminant of concern at the site is PCE. Contaminants of concern at the study area may change as new data become available.
There are potential health risks associated with exposure to PCE, and other VOCs, through drinking contaminated groundwater. A water treatment system is used by Valle Verde on Well #2 to ensure that drinking water meets the drinking water standards. Currently ADEQ is unaware of anyone drinking contaminated water in the study area; if you, or anyone you know, are using a groundwater well in the study area, please contact the ADEQ project manager to get on a mailing list to receive information on any future activity in the area.
The study area is located within the Basin and Range Province of Arizona which is characterized by mountains comprised mostly of intrusive and metamorphic rock of various ages and basins of alluvial sediments.
Hydrogeologic units beneath the area of interest consist of three aquifer units; the Nogales Formation, the Older Alluvium, and the Younger Alluvium. The deepest formation, the Nogales Formation, generally has poor water-bearing characteristics and is not used as a source of water. In the Older Alluvium, well yields are often small. The Younger Alluvium, the shallowest formation, is the most productive aquifer in the region and may have various water bearing strata within the formation.
Groundwater occurs at depths of 30 to 40 feet below the ground surface; corresponding groundwater elevations are 3800 to 3600 feet above mean sea level. The groundwater flow direction is currently to the north-northwest.
*In Arizona, but outside the Tucson area, call toll-free at (888) 271-9302.
Interested parties can review site information here on this page and at the ADEQ Record Center located at 1110 W. Washington Street, Phoenix, Arizona. Please contact (602) 771-4380 or (800) 234-5677 ext. 6027714380 for hours of operation and to schedule an appointment. To review site information at a location near you, please contact the designated Community Involvement Coordinator.