Motorola 52nd Street | Site History : Page 3 of 3

OU3

1997: OU3 was formerly part of the East Washington (EW) Area which was listed on the WQARF priority list in 1987. In 1997, the EW site was not re-listed on the new WQARF registry (See OU2 site history). On Nov. 26, 1997, EPA sent a letter to ADEQ creating a third OU and establishing the study area boundaries.

2000: In June, EPA completed its groundwater flow and transport model for the site. One objective of the model was to assess the possibility of contaminants from the companies’ source areas migrating beyond OU2. In February, EPA sent a letter to ADEQ which stated that after conducting its own modeling effort, EPA has concluded that the down gradient boundary (7th Avenue) for the study area is appropriate. EPA further stated that with the available information to date, it appears that Motorola’s releases are not likely to have migrated beyond 7th Avenue.

2001: In December, EPA completed a work plan to conduct a groundwater investigation. Drafts of this work plan were made available to the public for comment.

2002: EPA installed 15 groundwater monitor wells to investigate the nature and extent of groundwater contamination in the area. Monitor wells in clusters of up to three were installed to define the lateral and vertical extent of contamination.

2003: In January, EPA completed a supplement to the work plan to install additional monitor wells that are needed to complete the groundwater investigation. The EPA installed 16 new groundwater monitor wells as part of the on-going groundwater investigation. EPA identified eight facilities in 2003 and four facilities in 2005 that may be potential sources to soil and groundwater contamination. EPA initiated negotiations with PRPs for investigations of soil and groundwater conditions at the facilities identified in 2003. Six agreements were reached and work began.

2005: EPA issued the final March 2004 groundwater monitoring report. The final groundwater investigation report summarizing the finding of the Phase I and Phase II groundwater investigation in OU3 was submitted in Jan.. It provided recommendations for completion of the RI. The RI/FS draft work plan was submitted in April. In Aug., a groundwater monitoring report for the well network in the OU3 study area was submitted. Groundwater monitoring reports are prepared after each semi-annual sampling event.

2007: EPA completed the March 2007 groundwater monitoring report which was finalized in September 2007. Several sites within OU3 conducted investigations in 2007 which are described in the individual facility histories below.

2008: EPA completed the September 2007 and February, 2008 groundwater monitoring reports in February and July, 2008, respectively.

2009: On September 22, the EPA signed a Settlement Agreement and AOC with Honeywell and APS to complete an RI/FS for OU3.

2010: In Oct. and Nov., EPA installed seven shallow and intermediate groundwater wells as part of the Phase III OU3 groundwater investigation to help delineate the extent of the groundwater plume. Semi-Annual sampling reports are submitted in March and Sept. of each year.

2011: Groundwater sampling was conducted from the newly installed (Phase 3) wells. The well results were used to generate OU3 plume maps for the Upper Salt River Gravel, Lower Salt River Gravel and Basin Fill. TCE levels continue to show a decline. Three soil vapor monitoring wells were installed and sampled for soil gas.

2012: A soil vapor monitoring well installation report was submitted in January. Groundwater monitoring continued and an aquifer test was completed. Soil Vapor Monitoring Well (SVMW-1) showed soil gas levels above the Soil Gas Human Health Screening levels at the 18 to 20 foot zone and requires further investigation.

2013: Semi-annual groundwater monitoring for the OU3 area continues. New wells were installed. SVMW-1 continues to be investigated and EPA has requested step-outs.

2014: Additional groundwater monitor wells were installed and semi-annual groundwater reporting continues. EPA performed soil gas sampling at select locations during February 2014.
 
2015 - 2018: Annual groundwater monitoring performed and work continued on risk assessment and feasibility study.