The project involves the approval of the Removal Action Workplan (RAW) for arsenic in soils at the Habitat for Humanity property (Site). The RAW summarized the evaluation of remedial alternatives and proposed remediation consisting of excavation, removal, and offsite disposal of approximately 866 cubic yards (cy) of arsenic contaminated soil to protect human health and the environment.
Excavation of approximately 866 cubic yards of soil with arsenic concentrations above background levels (5 mg/kg) was selected as the removal action. Specific project activities consist of the following:
• Clearing utilities and other underground obstacles prior to initiating soil excavation;
• Excavating and stockpiling approximately 866 cubic yards of impacted soil (depth from 1 to 3.5 feet);
• Conducting confirmation soil sampling and comparing confirmation data to the site-specific arsenic background concentration (cleanup goal), and continuing to excavate until the cleanup goal is achieved;
• Sampling stockpiled soil to classify the hazard level of the waste and to determine the appropriate disposal facility; and
• Transporting the stockpiled soil to the assumed receiving facility, Recology Hay Road landfill.
Excavations will be sloped at a maximum 1:1 ratio to allow ingress/egress. The Site will be graded, leveled, and compacted as part of the planned future construction project; therefore, restoring excavated areas to their original grade or importing backfill material is not part of the removal action.
During all soil-disturbing activities (e.g., excavation, stockpiling, loading), water will be utilized to minimize or prevent generation of airborne dust. Water will be sprayed in work areas prior to daily work activities, during excavation/loading activities, and at truck staging/loading locations. In addition, watering equipment will be continuously available to provide proper dust control as needed. Soil-disturbing activities will be not performed during periods of high winds or during conditions when these activities cannot be prevented from generating visible airborne dust. Trucks will be required to maintain slow speeds (less than 5 miles per hour) while onsite as a dust control measure. A site safety officer will monitor onsite dust conditions that could require cessation of work.
Stockpiled soil will be managed to ensure that stormwater does not cause sediment-laden runoff from the stockpiles and that airborne dust is not generated. Excavated soil will be placed in designated stockpile areas on plastic sheeting. Plastic sheeting will also cover the excavated soil, be secured with weights, and be surrounded with stormwater best management practices (BMPs) such as straw wattles. Stockpiled soil will not be stored onsite longer than 90 days for classifying the hazard level of the waste and determining the appropriate disposal facility.
Soil will be transported for offsite disposal in 20-yard, covered end-dump trailers/trucks. Approximately 72 truck trips will be required to transport the stockpiled soil to the Hay Road Landfill located in Vacaville. Work activities will be limited to hours between 7:00 am and 5:00 pm Monday through Friday, which conforms with the City of Walnut Creek Noise Ordinance. Transportation of excavated soil will occur on arterial streets and freeways approved for truck traffic to minimize noise and traffic impacts in local neighborhoods.
The anticipated start date for this project has not been determined but is expected to begin sometime in the fall of 2020. Project activities will require disturbance of the Site for approximately two to four weeks during which time soil would be excavated and stockpiled.
In the event biological, cultural, or historical resources are discovered during project activities, work will be suspended while a qualified biologist or cultural or historical resource specialist assesses the area and arrangements are made to protect or preserve any resources that are discovered. If human remains are discovered, no further disturbance will occur in the location where the remains are found and the County Coroner will be notified pursuant to the Health and Safety Code, Chapter 2, Section 7050.5.