ARCHIVED REPORTS_SHEA HOMES OM TRANSMITTAL LETTER WITH O&M

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Final Operations and Maintenance Plan Neighborhood C,Great Valley Parkway Mountain House,San Joaquin County,California Page 3-1 3.0 REMEDIATION SYSTEM 3.1 REMEDIATION SYSTEM DESCRIPTION The Remediation System comprises a trench excavated into native ground, dieldrin-containing waste soil placed in the trench as engineered fill, and a cover consisting of engineered materials. The encapsulation trench dimensions are approximately 4,060 feet long, 27 to 43 feet wide, and 16 to 18 feet deep, yielding an approximate capacity range of 70,000 cubic yards. The native materials varied from unconsolidated silty clay to weakly consolidated tuffaceous sediments. All waste soil generated from the remediation activities was placed in the trench and encapsulated beneath Great Valley Parkway. The area of Great Valley Parkway that was used for encapsulation is beneath the paved southbound lanes and the landscaped median from 25 feet north of the pipeline easements near Grant Line Road to approximately 1,400 feet north of Grant Line Road measuring 16 to18 feet deep and 43 feet wide. The northern portion of the encapsulation area measured 16 to 18 feet deep and 27 feet wide and includes the southbound lanes (from top of curb to top of curb) and does not include the landscape median. All waste soil was compacted in the encapsulation trench at least to construction specifications of 90 percent compaction. Utility crossings were excavated after primary placement so that the utilities would not be surrounded by impacted waste soil (As-Built Drawings,Appendix A). All impacted waste soil generated from the utility crossings was placed in the southern portions of the encapsulation trench. An orange geotextile marker fabric was placed on top of the dieldrin encasement and at the utility crossings, marking the interface between dieldrin waste soil and non-contaminated native soil. A minimum of one foot of non-contaminated soil was placed on top of the marker fabric and within the utility crossing trenches. Additional soil was placed to finish the subgrade for the roadway, including an additional three feet to accommodate the southern end of Great Valley Parkway where additional clearance was needed over the active pipelines. The waste characterization samples collected from the encapsulation area had dieldrin concentrations ranging from 0.028 milligrams per kilogram (mg/kg) to 0.082 mg/kg. The average concentration of dieldrin in encapsulated waste soil was 0.051 mg/kg. The screening level for sensitive land use is 0.035 mg/kg dieldrin. The total threshold limit concentration for dieldrin in soil that constitutes a California Hazardous Waste is 8.0 mg/kg dieldrin, and discrete samples collected and analyzed during the course of the project were all below the threshold concentration. The final remediation system cover beneath the southbound roadway lanes consists of the orange marker fabric overlain by a minimum of one foot of non-contaminated soil overlain by one foot of aggregate base overlain by six inches of asphalt. In the southern section of the encapsulation area where the area included the median, the cover consists of the orange marker fabric overlain by a minimum of one foot of non- contaminated soil and up to eight feet of non-contaminated soil. Additional hardscape cover includes the concrete curbs plus five to eight feet of soil to fill the median landscape strip. 3.2 REMEDIATION SYSTEM MAINTENANCE Pavement repairs will be the primary maintenance needed, including crack sealing and asphalt patching or replacement. Additional maintenance could include vegetative replacement of landscape components in the median of the southern portion of the encapsulation area. Landscape vegetation could potentially penetrate the warning fabric, and replacement of such vegetation would require implementing soil management plan procedures. Since the utility crossings do not lie within contaminated soil, any maintenance of utilities would not require disturbance of contaminated soil in the encapsulation area. Other maintenance of hardscape materials could include concrete repairs to curbs. �. CONDOR