ARCHIVED REPORTS XR0012691 - Laserfiche WebLink

Home Browse Search

a Ground water samples were collected from all borings and tested for purgeable hydrocarbons (EPA method 602) and gasoline (using GC/FID). Ground water analytical data is given In Table 2. The perched ground water also displays low concentrations of gasoline and benzene, and slightly higher levels of toluene, xylene, and ethyls benzene. i The highest levels of gasoline and ethyls benzene are in boring#3, benzene and toluene Is in boring #o. and xylene Is in boring #1. Contours of gasolfi-,c In water and soil are shown In Plate 2 and benzene in water in Plate 3. For tie most part, the various components have a similar NE-SW elongated disiribudon pattern, with water contamination being a little more widespread then soil. Xylene in the water h<<s the widest distribution. Cross sections (Figures S, 4 & 5) through the study area show the vertical and lateral distribution of contamination and how they correlate with the analytical data. State allowable limits for the various volatile organic compounds (VOC) detected by lab r analyses during this study are listed in Table 3. Three of the five compounds detected are above the action level set by the state for drinking water or waters with potential i.� domestic use. Even though this shallow water is not used for domestic purposes,the county may require remedial action because of the close proximity of a city well. Surface water eventually percolates down to deeper depths and may be incorporated into s drinking water aquifers. Conclusions The conclusions of this study are briefly listed below. 1) There Is a bimodal distribution of the stratigraphy of the site: sand dominates the upper 7 to 9 feet, while clay dominates below that horizon. 2) The top 3 to 4 feet predominantly contain fill material (sand, silt, clay, & gravel) w plus debris like wood, metal, and cement. 3) The first ground water occurs at the shallow depth of 12.5 to 13 feet. 4) Due to artificial recharge of the ground water from leakage of the irrigation pipes located on the north side of the property, this shallow ground water flows to the south (regional gradient is to the north) and is in abundant supply. 5) Soil contamination is very low and is restricted to a shallow depth (about 10 to 15 feet) in the area around the previous tank location (<5 feet thick & <50 feet radius). Microbial degradation will continue to reduce the contamination level and remove the hydrocarbons from the environment. 6) Ground water contamination is present at very low levels and is restricted to a thin sandy unit about 2 t 3 feet thick (from about 12 to 15 feet in depth). This perched water table is underlain by a fairly impervious clay unit (aquitard) that will __.---.____.___greatly_.retard-vertical-migration-of-both-ground-water-and-the-contaminants.–As-with----------=----:- - —=— soil contamination, the already low contamination levels are steadily decreasing through the microbial degradation process. ;J t3