Waste rock materials from a closed mine that are at concentrations greater than regulatory standards are being removed to make way for a new housing community in north Peoria.
About 2,560 homes are planned for Mystic at Lake Pleasant Heights, located northeast of Lone Mountain Road and Vistancia Boulevard.
As part of an environmental study, several samples in this area contained elevated concentrations of arsenic, chromium and lead, well above typical background concentrations for Arizona soils, according to Allwyn, a firm that specializes in conducting environmental assessments.
Based on the depths and locations of the test pits on the property, Allwyn estimated the amount of mine waste rock material to be about 40,000 cubic yards in the 6 to 7 acres covered by these materials.
There is little to no health risk unless there is contact with skin or ingestion of contaminated soil, according to documents.
Geo Tek USA has been contracted by the property owner Lake Pleasant (Phoenix) ASLI VIII LLC to remove the materials.
Principal Engineer Chet L. Pearson said prospective homeowners will be made aware of the remediation.
“The builders are not responsible for the environmental contamination, but they are volunteering to clean it up,” he said.
The property owner wants to remove this waste rock to make way for new homes and has created a plan to do so that first must be vetted by the public and then approved by Arizona Department of Environmental Quality.
The work plan to remove this waste was submitted under ADEQ’s voluntary clean up program.
Edward Kavazanjian Jr., professor of Geotechnical Engineering at Arizona State University, said partaking in ADEQ’s clean up program typically means the conditions at a site as they are now being used does not present any threat to public health and safety but that the owner wants to redevelop the site for another higher purpose, and the site does not meet environmental protection standards for that other, higher use.
So, for instance, the site might currently be open space with limited restricted access, but the owner, as in this case, wants to develop it for housing, he said.
“Due to the potential for daily exposure of people who live or work on site, including workers during construction and ultimately the site occupants, the site is subject to a higher standard for environmental protection that may require remedial action — e.g., capping the site with clean soil, excavating and removing impacted soil, or consolidating impacted soil in one location and burying it under clean soil,” Mr. Kavazanjian said.
The public may review and comment on the plan to remove the waste. The comment period runs through Aug. 23.
To learn more about the plan visit the AZDEQ website: http://www.azdeq.gov/public-notice-mystic-lake-pleasant-heights-vrp-site-remedial-action-work-plan-available-comment.
Comments may be submitted as follows:
The work plan involves excavating and consolidating the waste materials under a protective barrier of clean soil called an engineered cap, covering excavated areas with clean soil and demonstrating that all applicable soil and groundwater protection levels are met.
The waste materials at the Mystic site are associated with historic mining activity and previous environmental studies in the area.
The firm will consolidate the mine waste rock piles into a single pile in a smaller area to allow for surrounding development. The consolidated pile will be covered with soil to provide a barrier over the waste rock materials.
David K. Rogers, principal at Voyager Investment Properties, said the time frame for remediation work is undetermined at this time. He said homes in Phase 1 of Mystic at Lake Pleasant are currently under construction and will not be affected by the remediation of the mine area, which is about a mile away.
Once the public comment period closes, the volunteer, in coordination with ADEQ, will prepare and respond to any and all public comments received. If ADEQ approves the final remedial action work plan, the volunteer will then implement the plan with ADEQ oversight and submit a final project report for ADEQ review and approval.
At that point, the volunteer must request a No Further Action decision from ADEQ.
If other requirements are met, a 45-day public notice comment period will be opened for the No Further Action decision from ADEQ. After the close of the public comment period, the volunteer in coordination with ADEQ, will prepare and respond to any and all public comments received. ADEQ, as appropriate, then may issue an final decision.
Philip Haldiman can be reached at 623-876-3697, firstname.lastname@example.org, or on Twitter @philiphaldiman.