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1. What are the health risks presented by the landfill water?

There are no known health risks from the groundwater. The groundwater is located over 600 feet below ground surface (ft bgs) and there is no exposure pathway to this water.

The water is not part of the potable (drinkable) water supply.

The nearest drinking water wells are over 1 mile to the southeast and are screened at a much deeper (more than 1,000 feet below ground surface) level. These are City of Phoenix wells that are regularly tested for safe drinking water parameters.

2. When did Maricopa County first learn of the contamination?

As was required by law in 1993, the County installed 2 down gradient groundwater wells (south and southeast of the landfill) and began to monitor these wells along with an already existing up gradient well (north of the landfill). Each well is located on County property. In December 1997, trichloroethene (TCE) above the Aquifer Water Quality Standard of 5.0 micrograms per liter (ug/L) was found in the monitoring wells.

3. How was it determined that the landfill was/is the source for the contamination?

The County is required by law to regularly sample the monitoring wells. In December 1997, TCE above the Aquifer Water Quality Standard of 5.0 micrograms per liter (ug/L) was found in the monitoring wells. The County reviewed historical information and did not find any other potential TCE source up gradient of the landfill.

4. Who is liable for any monitoring or clean up?

The Consent Order from the Arizona Department of Environmental Quality (ADEQ) requires that Maricopa County is responsible for monitoring and remediating the groundwater contamination, if necessary.

5. Are there test wells surrounding the landfill?

There is an up gradient monitoring well (PW-1) to the north of the landfill on County property. There are also two down gradient wells located to the south (MW-2) and southeast (MW-1) of the landfill on County property. In 2007, MW-1 became inoperable and MW-3 was installed as a replacement well for MW-1. MW-3 is located to the southeast of the landfill on Dove Valley HOA property and was installed to evaluate the down gradient extent of contamination.

Additional test wells downgradient of the landfill were installed on the City of Phoenix Sonoran Preserve from 2010 through 2012; these include MW-4 through MW-7. Additionally, there is one test well (MW-8) located on Bureau of Land Management property, to the north of the Dove Valley Ranch Golf Course.

6. Is the contaminated water used for consumer drinking by DVR residents or any other Phoenix area residents?

No. Drinking water for Phoenix residents is supplied by the City of Phoenix from other sources. The City is required to regularly test the water they supply to citizens and to make the testing information available to citizens.

7. If it is not potable (drinkable) water, what is the water used for?

At this time, the water is not used for anything. Arizona protects all aquifers and treats all groundwater as if it might be used as drinking water and thus requires remediation of contaminated groundwater.

8. What work are we doing and why is it important to do it now?

Full-scale soil vapor extraction (SVE) operations at the site were initiated in September 2015 to remove TCE from the zone of the subsurface that is located above groundwater. SVE is important because it removes the source of the contamination that is reaching groundwater. In July 2016, installation of a groundwater extraction well began. After testing of this well to evaluate how much water is available for extraction, design of the full-scale groundwater treatment system can begin. Construction of the groundwater treatment system is scheduled for summer of 2017. The full-scale groundwater treatment system is important to remediate the groundwater impacted by TCE.

9. Is Maricopa County committed to remediate the problem once the extent of the plume is identified?

Yes. In addition to being under a Consent Order to perform remediation after characterization is completed, Maricopa County is working with ADEQ to implement the preferred remediation remedy outlined in the Remedial Action Plan (RAP).

10. Based on what is currently known about the contaminated water, what are the typical corrective actions? Would corrective action be taken on the landfill? If so, what might be done?

As part of the Remedial Action Plan (RAP) assessment, we looked at the effectiveness of potential corrective measures that meet the requirements of the Resource Conservation and Recovery Act (RCRA) and address the site-specific objectives of protecting human health and the environment. Based on this analysis, Maricopa County’s preferred remedy for the site is the on-site extraction remedy with off-site injection, although an on-Site injection well scenario was also retained as a contingency measure. We came to this conclusion after comparing the practicability, risk, cost, and benefit or value of each alternative.

Physical components of the on-site extraction remedy consist principally of a new pump and treat (P&T) system located in the southern portion of the property. This includes a groundwater extraction well, piping, groundwater treatment equipment, and an injection well (located either on-site or off-site) to recharge clean, treated water back into the aquifer. There will also be one new off-site monitoring well to test for any impacted groundwater that may not be contained by the P&T system and a soil vapor extraction system located in the northern portion of the site. The SVE system includes multiple vapor extraction wells and air treatment equipment. This cleanup operation is expected to last 30 years.