10-03-1988 Planning Packet - Laserfiche WebLink

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•* ■« ) for the clean up of ^SI) facility located in italled monitoring wells id horizontal extent of mm m .j ■..-3 Bm msultants, Inc. (Delta) 87 and "Proposed Work installed to remediate t large diameter sump ontaminated water will impounds and then be > 1 m.. iFi ■*r’ smediately west of the d is located in the SW lited States 3eological m no, Minnesota. The initial phase of this Solvent Contamination i was installed and an 4W-4D) and sampling >88. Volatile organic M fi'i ■f. ■v.< A (VCXTs) were identified in monitoring weU MW-4D. The pr«ence of VOCs in MW-4 promote installation of three additional wells proposed in the May 24 work plan. a fl AgPinONAL FBOJECT RESULTS 3.1 General Three additio f**> monitoring wells were installed during Juiw 1988 to further define the extent of VOC contamination. The locations of the new wells (MW-10, MW-II. and MW-12) are shown in Figure 2 along with the locations of previously installed wells. After installation, the new weUs were developed i sampled.hill* 3.1 Soil Borines and Moaitorina Wglll Three additional soil barings were advanced at the site and were completed as monitoring wells. The well locations are shown in Figure 2. The subsurface geology of the site consists of heterogeneous mixture of clay, silt, sand, and gravel The stratigraphy consists of silty clay with intermittent medium to coarse grained sand lenses which are generally less than two feet in width. The sand lenses do not appear to be laterally extensive. Complete lithologic boring logs for the three soil borings are included in Appendix A. Borings MW-10 and MW-11 were each advanced to a depth of 25 feet below the existing grade. Boring MW-12 was advanced to a depth of 55 feet below the existing grade. Each of the three bcrings were completed as monitoring wells. The wells are constructed of low carbcn steel .isers with five foot stainless steel screens. Complete well construction details are given u Appendix B. 3.3. Contaminant Conditions 3.3.1 Soil Contamliiatlon Soil contamination was previously identified in the vicinity of MW-4 and MW-4D; therefore, the upper 21 feet of soil was not sampled during the instaUation of MW-12. Low contaminant concentrations, as detected by the hNu photoionization meter, were detected in an interval between 23 and 35 feet below the ground surface during the drilling of MW-12. A summary of hNu results for borings MW-10, MW-11, and MW-12 is included in Table 1. lonizable gases were not detected in any of the samples after opening the split-spoon. Headspace checks revealed some volatiles in borings MW-11 and MW-12. However, the concentrations (Table 1) are at the lowest detection limit for the hNu which is approximately one part per million. At these concentrations, interferences with water vapors are common and the concentrations must be viewed in this context. Intervals 31 36 41 55 Concent! Sample c Headspa< clo.811