Client: MDEQ Project Management Firm - Earth Tech
Site Location: 420 East M-61, Gladwin, Michigan
Project Dates: 09/00 - Present
Sagasser & Associates, Inc. was subcontracted by a State of Michigan Contract Management firm to complete RI, FAR, FFS, Remedial System Design, and Construction/O&M Oversight for a known contaminated facility. The Site consisted of a former gas station facility with several historical leaking UST systems. Sagasser & Associates, Inc. conducted an extensive RI that included soil characterization (12 soil probe borings), groundwater characterization (11 probe wells and 13 permanent wells), surface water sampling (adjacent drainage and retention ditches), potable well sampling, free product assessment, and vapor assessment.
The soil types generally consisted of silty sand and/or sand to depths on the order of 8 to 10.5 feet below ground surface (bgs), underlain by silty clay. Soil contamination was identified in the immediate vicinity of each UST basin, and in an area of a reported surface spill incident. Groundwater was encountered at the Site at depths on the order of 1 to 4 feet bgs at the time of the RI, and fluctuates significantly at the Site. The groundwater contaminant plume was shown to split in two directions (north/northeast and south/southeast) and reverses flow direction dependent upon aquifer elevation and local influences to groundwater flow. The RI activities identified several acute hazards to include: Soil contamination exceeded the Csat soil concentrations, volatilization to indoor air, drinking water protection, direct contact and GSI protection criteria; groundwater contamination exceeded the volatilization to indoor air, drinking water, direct contact and GSI criteria; and, surface water contamination in the adjacent drainage/retention ditches exceeded GSI criteria.
A focused feasibility study was conducted for the site to address the acute hazards concurrently by developing a remedial approach that incorporates each of the acute hazards to be mitigated. The evaluation of remedial technologies indicated that no one technology would fully eliminate the acute hazards. Based on an evaluation of the existing immediate threats identified at the Site, the technologies available to remediate the Site, and the relative costs for those remedial technologies, a remedial approach was recommended for the Site. The remedial approach included soil excavation, ORC® slurry injection, ORC® sock barrier installation, low flow biosparging, and long term monitoring of groundwater, surface water and indoor air. Institutional controls and risk assessment were also recommended on an “as-needed” basis.
Sagasser & Associates, Inc. designed the remediation system, developed the construction specifications, and oversaw system construction. The project included installation of additional monitor wells, 42 biosparge wells, 100 ORC® injection points, 11 ORC® sock barrier wells, remedial system housing, rotary vane compressor and equipment appurtenances, source area excavation and removal of over 1700 tons of impacted soil, construction oversight, system startup and operation & maintenance (O&M) oversight activities. Numerous reports have been prepared for this project including RI, FAR, Remedial Design, Construction Specifications, Construction Oversight Report, O&M Oversight, Indoor Air Monitoring and Quarterly Monitoring Reports.