FIELD DOCUMENTS - Laserfiche WebLink

Home Browse Search

t Subsurface Conditions Four exploratory soil borings were advanced on-site at the locations shown on Figure 3. B1, B2, 63 and B4 were drilled for the site assessment, soil sample chemical analyses and for temporary well installation to evaluate the limits of contamination from the former tank area, if any. The site is underlain by clayey silts, silty clays (silts and clays with high organic content), and peat which locally contain thin very fine grained sand lenses. Very moist to wet soil was detected at depths ranging from 3.5 feet to 7.5 feet bgs to the bottom of each boring. No measurable groundwater was detected in the temporary wells on the date of installation (after approximately one and one half hours). Five days after installation groundwater was measured in each of the four temporary wells at approximately 6.5-feet bgs and is unconfined. Chemical Analysis and Results Four soil and four groundwater samples were analyzed at a state-certified labratory, Priority Environmental Laboratories, Inc., in Milpitas, California. One soil sample was split (B4 S1) and transported under a separate chain-of-custody to Friedman and Bruya, Inc. Environmental Chemists (F&B), in Seattle, Washington. Selected samples were tested for the following: Total Petroleum Hydrocarbons as Gasoline (TPHG), Total Petroleum Hydrocarbons as Diesel (TPHD), by test methods 8015M, and Benzene (B), Toluene (T), Ethybeneze (E), total Xylenes (X) by EPA test methods 8020/602. The results are presented in Table 1 (see Appendix B). Discussion The chemical data from this study and the previous sampling show that contaminants were not detected in soil, and only very low concentrations of TPHG and BTEX occurred in groundwater samples. Groundwater from B4 showed very low levels of TPHG and Benzene was not detected. Benzene exceeds the current MCL by 3.7 parts per billion only at the sample from B3. Groundwater flow was not mapped but is surmised to be unconfined and flow southerly toward the river. In our opinion, these concentrations represent residual contaminants which are depleted in volatile fuel constituents. Groundwater occurs in the predominantly clay and organic sediment. A very slow groundwater motion is inferred from field observations, wherein boreholes accumulated about 3 feet of standing groundwater in 120 hours. The distribution of contaminants suggests only a limited spreading along the capillary fringe in the easterly and southerly directions. The presence of organic material in the sediment, and presence of organic sediments enhances absorption of contaminants and possess low hydraulic conductivity. Consequently there is very little yearly net groundwater motion toward the river, and Benzene was not detected in the apparent downgradient Boring 4 location. Conclusions and Recommendations Four exploratory borings were advanced around the former underground tank location. The suspected source has been removed and contaminated soil removed from the vicinity of this survey has been removed from the site and properly disposed of. The results of this study show the site is underlain by organic rich silts and clay, and very low contaminant concentrations were detected. Very depleted volatile fuel constituents were observed, however those were roughly thirty feet from the river. Groundwater occurs in clayey and organic sediments, and very slow motion is indicated given proximity to the river and borehole observations. In our opinion these residual concentrations should not pose arty threat to the river and should continue to degrade and be absorbed onto the subsurface organic material In our opinion, the contaminants source has been removed and site subsurface has been defined. Negligible potential threats for onsite groundwater and the river are indicated from the data presented herein. Further work is not warranted at this time. Wright proposes that his site be considered a candidate for site closure. Naomie King Trust Project No. 4131 Page 4