Laserfiche WebLink
1 <br /> GRANITE CONSTRUCTION FACILITY <br /> WKA No 2088 08 <br /> August 18, 1999 <br /> Page 6 <br /> approximately 0 001 feet/foot(Plate No 4) Laboratory test results for the water samples <br /> obtained from monitoring wells MW1, MW2, and MW4 revealed no detectable concentrations of <br /> TPH as gasoline, BTEX, or oxygenate compounds at or above the laboratory method detection <br /> limit However, detectable concentrations of TPH as gasoline(68 µg/1) and Tert-Butanol <br />' (14 pg/l ) were detected in the water sample obtained from MW3 BTEX and the other <br /> oxygenate compounds Methyl tert-Butyl Ether, Di-isopropyl Ether, Ethyl tert-Butyl Ether, and <br /> Tert-Amyl methyl were not reported in MW3 at or above laboratory method detection limits A <br /> historical summary of groundwater elevations and results of laboratory analysis obtained from <br /> the wells are summarized in Tables 7 and 8,respectively <br />' Risk-Based Corrective Action Evaluation and Fate and Transport Model <br /> In January 1997 a Risk-Based Corrective Action (RBCA) and a one-dimensional finite difference <br />' vadose zone leaching model (VLEACH)were performed on the site based on existing site <br /> conditions at that time Results of RBCA analysis indicates that the benzene upper confidence <br /> limit(UCL) concentrations in subsurface soil in the vicinity of the former USTs is below the <br /> risk-based screening levels (RBShs) of 16 mg/kg The remaining UCL concentrations for non- <br /> carcinogenic compounds are below the residual saturation concentrations and are therefore not a <br /> significant heath risk The Total Pathway Carcinogenic Risk for the levels of benzene in <br /> subsurface soil 14 x 10-7 , well below the target risk of 1 x 10-6 (1 in 1,000,000) The Hazard <br /> Index for non-carcinogenic compounds is 4 4 x 10-5 ,well below the Hazard Index standard of <br /> 10 Groundwater UCL concentrations are below the solubility concentrations for BTEX <br />' constituents Results of the VLEACH model predicted that napththalene (diesel) impact to <br /> groundwater at year 10 is 1 597 x 10-6 grams per year. <br /> Sensitive Receptor Survey <br />' As part of our review for site closure, we performed a sensitive survey receptor for the <br /> P Y <br />' surrounding area within 2,000 feet of the property boundary The purpose of this survey was to <br /> identify significant pathways in which contamination released from the former underground <br /> storage tanks may travel to come in contact with humans or wildlife <br /> 1 <br /> `�W <br />' WALLACE•KUHL <br /> R,cycied Pape, &ASSOCIATES INC <br />