Remedial Action Report Construction Phase

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During the construction phase, a rock crusher was used on-site to process clean soil only. Most of the crushed rock was used for the Courthouse Square project. However, near the end of mass excavation some crushed rock was transported off-site to other projects. A majority of the fine material generated by the crusher was transported off-site. 4.3 Dewatering During the construction phase, the static water level in the excavations was observed to range between approximately 12 and 16 feet below street grade. Several excavations, mostly located in the southern portion of the site, required dewatering during construction. The water pumped from excavations was discharged in accordance with the NPDES permit issued during pre-construction. A copy of the permit and a letter from the City of Salem specifying discharge requirements are provided in Appendix B. During construction phase activities completed between April 12, 1999 and June 21, 1999, dewatering was performed using sumps constructed in the vicinity of six Remediated Areas (Areas 2, 6, 19, 21, 22, and 23). Specific sump locations (labeled Sumps 1 through 6) are shown on Figure 4. The dewatering sumps were constructed by placing a large-diameter perforated pipe, wrapped with a geofilter fabric, in the base of excavations. A pump located inside the perforated pipe was used to transfer the water to a treatment system located on Church Street, adjacent to the southeast portion of the Courthouse Square block. Effluent water generated during dewatering was discharged to the storm drain located in the northwest corner of the Church Street and Court Street intersection. The treatment system initially consisted of an oil water separator and two 17,000-gallon sparge tanks. Based on influent monitoring data, one of the sparge tanks was removed from the site on May 20, 1999. Carbon filtration was available onsite to treat non-volatile contaminants in the influent, however, system monitoring data indicated that this treatment was not necessary. In a letter to the DEQ dated May 28, 1999, Century West requested direct discharge of water generated from dewatering operations into the starm drain based on water monitoring data. During a telephone conversation on June 1, 1999, the DEQ approved Century West's request. After DEQ approval, subsurface contamination was discovered in Area 22 requiring reactivation of the treatment system. By June 21, 1999, no further dewatering was necessary in any of the Remediated Areas and the treatment system was deactivated allowing direct discharge for dewatering operations. 4.4 Soil Sampling During the construction phase, Century West collected soil samples for laboratory analysis to: 1) evaluate contaminated soil disposal options; 2) confirm that a sufficient quantity of contaminated soil was removed from excavated areas (confirmation sampling); and 3) evaluate the extent and risk Construction Phase - Remediai Actions - 7- 4080600127 Courthouse Square November 9, 1999