North Indian Bend Wash
The North Indian Bend Wash (NIBW) site is the northern portion of the area designated as the Indian Bend Wash (IBW) Superfund site. The site is located in Scottsdale, Arizona, and the site is bounded by McDonald Drive to the north, Pima Road to the east, 68th Street to the west, and the Salt River to the south. The plume boundary varies and may extend beyond the site boundary but remains part of the Superfund site in its entirety.
The Consent Decree (CD), that the U.S. Environmental Protection Agency (EPA) has entered into with those responsible for the groundwater contamination at the site, identified Motorola as the main responsible party. The majority of the cleanup activities are being addressed by a combination of responsible companies referred to as the “Participating Companies” (PCs).
The NIBW Granular Activated Carbon Treatment Facility (NGTF) was completed in 2013. A pipeline is currently under construction which will connect the NGTF to the Chapparal Water Treatment Plant, allowing the City of Scottsdale beneficial use of the treated water. The Upper Aquifer Unit (UAU) the shallowest aquifer has made progress in clean-up and was able to abandon 30 monitoring wells in 2013.
In 2014, the pipeline connecting the NGTF to the Chapparal Water Treatment Plant was completed and is in full operation now. Well 71A, part of the CGTF, has been completed and is in operation to pump groundwater for treatment at the facility with the cleaned water servicing the City of Scottsdale residents.
1981 - 1983: The IBW site was listed on EPA's NPL on September 8, 1983 after the City of Scottsdale detected volatile organic compounds in municipal wells in the Scottsdale area in 1981.
1984 - 1991: The EPA began a remedial investigation (RI) of the site in two phases, referred to as operable units (OU). The RI and the feasibility study (FS) for OU1 (middle and lower aquifers) began in July 1984 and were completed in April 1988. The RI/FS for OU2 (shallow aquifer and soil contamination) was completed in 1991.
1988: In September, a Record of Decision (ROD) selected a remedy for the middle and lower alluvial units of the groundwater. The OU1, also designated the Scottsdale Operable Unit, involved operation of a groundwater treatment facility located at Pima Park (Thomas Road and 88th Street), and known as the City of Scottsdale Central Groundwater Treatment Facility (CGTF). The facility treats groundwater from four City of Scottsdale production wells by air-stripping. The treated water is added to Scottsdale's public water distribution system.
1991: In September, EPA issued a ROD for OU2 to address contamination in the upper alluvial unit (UAU) of groundwater and contaminated soils. This ROD required soil vapor extraction (SVE) and groundwater treatment systems at several source areas, particularly Areas 7 and 12. The OU1 remedy failed to contain the lower alluvial unit (LAU) groundwater plume. Hydrogeologic data indicated that the plume was migrating to the north and would threaten the Paradise Valley well field.
1994: The PCs, in cooperation with the Paradise Valley Water Company, constructed the Miller Road Treatment Facility (MRTF) at the northern end of the groundwater plume. The MRTF pumps and treats groundwater, and supplies treated water to the Salt River Project (SRP) Arizona Canal and to the Paradise Valley distribution system. Additionally, Motorola and Siemens voluntarily installed on-site groundwater treatment systems at both areas 7 and 12 to treat middle alluvial unit (MAU) groundwater at the source areas.
1995 - 2000: The OU1 Consent Decree (CD) required the PCs to conduct a feasibility study addendum (FSA) to determine the effectiveness of the OU1 remedy and to recommend a final remedy. In 1995, the PCs initiated the FSA process including the completion of a site-wide groundwater flow and transport model. The final FSA was received in November 2000.
2001: In April, the EPA issued a proposed plan. The proposed plan announced the required public meeting, which took place on May 9th. EPA formally selected a remedy in the amended ROD which was received by Arizona Department of Environmental Quality (ADEQ) in July. ADEQ concurred with the remedy as described in the amended ROD, and the EPA signed the ROD in September.
2001 - 2003: The Amended Consent Decree (ACD) became final with the approval of the federal court on June 5, 2003. The ACD was the result of an Amended Record of Decision (AROD) which was prescribed during 2001. The AROD resulted in EPA, ADEQ and the PCs negotiating the ACD. The purpose of the ACD was to include treatment facilities which were constructed by Motorola outside of the authority of the RODs (MRTF, Area 7 & Area 12). The ACD serves as the implementation vehicle of the ROD.
2002: In October, negotiation and approval of the final ACD were completed. All of the parties signed the ACD for the final groundwater remedy. The ACD was lodged with the district court in Phoenix, Arizona on October 31st. On November 19 and 20th, EPA and ADEQ conducted inspections of the MRTF, CGTF, Area 7 and Area 12 remediation sites. The inspections were conducted in order to certify the treatment facilities are operational and functional.
2004: In February, the PCs and the EPA and ADEQ entered an informal dispute relating to the requirements to maintain air emission control systems at the NIBW ground water treatment facilities.
2006: EPA announced that all physical construction of cleanup systems was complete. Soil cleanup is expected to be complete in the next five years and groundwater cleanup an additional 30 years. EPA and the PCs independently conducted risk assessments to determine the relative risk associated with the possibility of removing the air emission controls that are part of the current groundwater treatment systems. EPA and ADEQ determined that the air emission control systems must remain in service at that time, and agreed to look at the air emission data in March 2007.
2007: The City of Scottsdale began demolition of buildings at the former Rolamech facility at Area 7 and completed by the end of 2007. EPA and ADEQ worked with Maricopa County Air Quality Department (MCAQD) to determine if air emission controls for the air stripping groundwater treatment systems could be removed and still be protective for human health and the environment. ADEQ and MCAQD issued letters stating that the air emission controls cannot be removed.
In early 2007, the Agency for Toxic Substances and Disease Registry (ATSDR) agreed to conduct a public health evaluation of potential past exposures to contaminants in the municipal drinking water system in the site that may have occurred before the system’s contaminated wells were closed in 1981. ATSDR completed a public health assessment of the site in 1989 in accordance with the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) of 1980, as amended. ATSDR gathered additional relevant and applicable data about the site’s groundwater and municipal water to further evaluate the past exposures. ATSDR issued a report called a public health consultation which described whether the exposures have any public health implications. The lead environmental health scientist for this site was Dr. Jane Zhu. If you have a question or need more information, please contact her at 800-CDC-INFO, or visit the ATSDR website.
In October, water treated at the MRTF from Well PCX-1 was directed to Tower 2 for nine days while the normally used Tower 3 was under inspection. On October 16th a trichloroethene (TCE) exceedance occurred from the MRTF. On this date, samples were taken which contained 14 parts per billion (ppb) of TCE exiting the treatment facility. Due to laboratory communications and equipment failures, this was not reported to the EPA or ADEQ until November 9th. Samples taken of the water leaving the MRTF on October 8th, and October 22nd showed no detection of TCE. Water from the treatment facility was mixed with water coming from the Arizona American Water Company’s (AAWC) arsenic treatment facility, and so it was calculated that the contamination entering the drinking water system met safe drinking water standards. EPA and ADEQ directed the NIBW PCs to conduct a thorough third-party review of the plant and its operations.
2008: On January 16th, an operator returning to the MRTF found that the blower operating in the treatment tower was not operating. The operator re-started the blower but the plant was shut down at approximately 9:00 A.M. It was found that the plant had been running without the blower operating since approximately 2:30 P.M. on January 15th. Between the times that the blower turned off and the time the plant was shut down, approximately 3,639,000 gallons of water was delivered from the MRTF to the AAWC. Water with up to 22 ppb of TCE was delivered to the Paradise Valley customers of AAWC. In agreement with the EPA, ADEQ, and Maricopa County, the MRTF was shut down pending an investigation and modifications to the plant. The plant was examined by a third-party consultant who re-evaluated both the plant infrastructure and its operating methods. The plant was re-started on April 25th with the following important modifications to the plant and its operations:
The Arizona Department of Health Services stated that there was no public health hazard because of the low rate of exposure to the tap water.
In July, a study was conducted at the Hohokam Elementary School to determine if past irrigation had resulted in contamination to the school grounds. Two separate sampling events occurred; one on July 3rd, and the other on October 10th. Sampling was conducted by the NIBW PCs through a contractor with oversight by ADEQ and consultants for the EPA. Sampling was done of both soil and soil gas at the site. No threat to public health was found in a review completed by ATSDR. Also in July, the NIBW PCs presented a draft Long-Term Operations Work Plan. A revised work plan was submitted in November.
A complete third-party engineering review and rehabilitation of the CGTF was completed. No significant concerns were found and modifications to the plant operating system were completed to bring the technology up to current levels.
2009: On April 20th the NIBW PCs, working with EPCOR (formerly AAWC), EPA and ADEQ, began a rehabilitation of the MRTF.
2010: Rehabilitation of the MRTF was completed by the NIBW PCs. The five Year Review (FYR) process began which includes interviews with stakeholders and community members as well as site inspections to aid in the assessment of the remedy effectiveness.
2011: FYR report was approved in the fall. The FYR summarized the remedies at the IBW site are currently protective of human health and the environment, and exposure pathways that could result in unacceptable risks are being controlled. The agencies and NIBW PC’s are negotiating a final long-term remedy for the Miller Road Treatment Facility which is expected to be selected by the end of calendar year.
2012: A final long term remedy for PCX-1 was approved. PCX-1 is currently treated at the MRTF and under the Long-Term Operating Plan has been conditionally approved to discharge to the adjacent SRP canal. A treatment facility is currently under construction with an expected completion date of 2013. The NIBW PC’s continue site monitoring and sampling and have submitted a request to reduce the monitoring well network in the UAU due to the reduction in contamination and comprehensive monitoring of data.
2013: The NIBW Granular Activated Carbon Treatment Facility (NGTF) was completed. A pipeline is currently under construction which will connect the NGTF to the Chapparal Water Treatment Plant, allowing the City of Scottsdale beneficial use of the treated water. 30 UAU monitoring wells were abandoned.
The current contaminants of concern in groundwater include volatile organic compounds (VOCs). VOCs were used as degreasing agents and solvents at various industrial facilities located in the study area. Contaminants of concern at the site may change as new data become available.
Six City of Scottsdale wells are affected by VOCs including TCE and lower levels of tetrachloroethene (PCE), 1,1-dichloroethene (1,1- DCE) and chloroform. TCE is the only VOC quantified in samples from these wells at levels that exceed primary drinking water standards. As mentioned earlier, six of the seven affected wells are not currently operating and the seventh (City of Scottsdale No. 6) is equipped with a VOC treatment system.
Groundwater at the site is used to irrigate various crops and feed livestock. In addition, contaminated groundwater is being treated at the CGTF to drinking water standards and supplied to the City of Scottsdale's municipal water supply. Water from the MRTF well PCX-1 is currently treated to remove TCE and is then discharged to the SRP canal for irrigation use.
The site is underlain by alluvial sediments which can be divided into three hydrostratigraphic units. These units consist of the UAU, the MAU, and the LAU.
The UAU varies in thickness; however, in the vicinity of the study area, the thickness of the UAU is approximately 120 to 160 feet. The UAU consists primarily of sand, coarse gravel, cobbles, and boulders in this area. Groundwater occurs at depths ranging from approximately 90 feet to approximately 130 feet, with up to 40 feet of saturated thickness. The saturated thickness of the unit changes with the time of year, but generally decreases to the north. Groundwater in the UAU appears to be flowing in a west-northwest direction.
The MAU primarily consists of silt, clay, and interbedded fine sands. Relatively thin layers of coarser deposits are scattered throughout the unit. The thickness of the MAU ranges from approximately 360 to 660 feet. Groundwater flow in the MAU appears to be toward the north-northwest in the study area. Water levels in wells perforated in the MAU occur at depths of 140 to 180 feet.
The LAU is less well defined. Samples collected during monitor well installation indicate the unit consists of moderately to well-cemented sands and gravel. The depth of the unit is not well defined; however, it is known that the LAU is underlain by the red unit which consists primarily of fanglomerate, conglomerate, and sandstone. The direction of ground water flow in the LAU is thought to be similar to that of the MAU.
Water level data indicate that there is a downward-directed, vertical hydraulic gradient between the UAU and the MAU, and between the MAU and the LAU. Groundwater quality data indicate contamination at NIBW has occurred from various organic solvents, particularly TCE, PCE, 1,1- DCE, and 1,1,1-trichloroethane (1,1,1-TCA). All of these chemicals have been found in monitor wells at concentrations exceeding state action levels. TCE is the most widespread contaminant with a maximum reported concentration of 2,500 parts per billion (ppb) from a UAU monitor well. The maximum concentration reported from a MAU or LAU monitor well is 700 ppb. TCE has been detected in several municipal wells at concentrations up to 390 ppb and from depths as great as 1,100 feet below land surface.
*In Arizona, but outside the Phoenix area, call toll-free at (800) 234-5677.
Interested parties can review select site documents at the Scottsdale Civic Center Library located at 3839 Drinkwater Boulevard in Scottsdale, AZ, 85251, (480) 312-2474.
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.
The complete official site file can be reviewed at the EPA Region IX, Records Center, Mail Stop SFD-7C, 95 Hawthorne Street, Room 403, San Francisco, CA 94105, (415) 536-2000.