ARCHIVED REPORTS XR0012689 - Laserfiche WebLink

Home Browse Search

M WR 01 M- Work Plan Stewart's Beacon Project No.01-17.1.2 March 12,1940 Fage: 3 To accomplish the dewatering process,a sump was dug in the northeast comer of the excavation to a depth of about 18 feet. An 16 inch diameter slotted casing Has installed in the sump and gravel was filled in around it(Figures 2&3). Approximately 8,000 gallons of water was pumped out of the sump and stored in a 10,000 gallon swing tank this water was tested and found to have 9.8 mg/l gasoluie and a varying amount of aromatic hydrocarbons. The data.that is given in Appendix A,sample number GT-18 water 1. On 4 January 1990, the excavation was dewatered and the hole v:as deepened by digging to a depth of about 14 to 15 feet. This material was first allowed to drain by stacking it at one side of the excavation. It was then stockpiled on site and sampled by composite methods described above. Three composite samples were collected with . . three sampling points per sample. Approximately 150 yds3 of contaminated soil was removed. The lab data is presented in Appendix A,sample numbers GT 18 soil 6 A,B,C to GT-18 soil 8A,B,C The samples contained mainly gasoline and aromatic hydrocarbons(BTX&-E)and some. diesel. It is believed that all of the contaminated soil below the tanks was removed. In situ sampling below the tanks was not practical due to the high Ievel of water saturation. ]excavation %(,is extended to the depth of the lowered water table appraxicnately 14 to 15 feet). The recharge water that came in from the north side of the excavation is believed to have brought in the low amount of hydrocarbons observed in the excavation after it had fully recharged. The sample number is GT18 sump and is presented in Appendix A. 3.0 PROPC 9EU WORK PLAN 3.1 Excavai'on Backfill r E Two iypes of Y.'iterial are proposed to be'used to fill in the old tank excavation. First, pea gravel will be installed at the bottom of the hole and brou&'tt up to the rater table (.-10 feet). This gravel is self packing and wii;'eliminate problems that would occur if native soil was installed into 4 to 5 feet of water. Installed above the pea gravel will be the native soil that has been stockpiled on site for a year, and additional native soil removed from.the new underground tank installation site. Between the two materials a 6 riil.plastic sheeting barrier is proposed to be installed. The native material will be compacted to help prevent settling and the surface will then be covered with asphalt. It should be noted,that evidence suggests that some contaminated soil as left in lace to the north and west of the excavation. The evidence is the contamination touiD in the `' soil bode s on those sides of the excavation (Figure 2). It is believed that all of the