ARCHIVED REPORTS_XR0011167 - Laserfiche WebLink

Home Browse Search

URS i, Ms. Victoria McCartney Page 4 San Joaquin County Environmental Health Department ARCO 5450 December 22,2005 i ' estimates, tabulated calculations, and a list of conditions and assumptions are presented in Attachment E. Historical soil data suggest initial soil masses of xylene and MtBE were approximately 0.01 pounds each. Historic groundwater data suggest initial groundwater masses of TPHg and benzene were 0.01 pounds and 0.32 pounds, respectively (Attachment E). Toluene, xylene, and tertiary butyl alcohol were also present in concentrations of less than one-one thousandth of a pound in groundwater. The mass estimate for the remaining MtBE is Iess than one-one thousandth of a pound in groundwater (Attachment E). FUTURE IMPACT ON GROUNDWATER AND MAXIMUM PLUME EXTENT Average annual MtBE concentrations in groundwater are shown on Figure 1 in Attachment F for a 99- g g g year prediction. The predicted maximum average concentration was 4.4E-7 mg/L(0.00044 gglL)MTBE in groundwater—essentially, zero predicted impact. SESOIL-$4 was used to predict leachate transport. Average monthly climate parameters were statistically generated using SESOIL-84 for each of the 99 years of the model runs. Mean monthly precipitation was reduced to 10 percent of the SESOIL-generated value to simulate concrete asphalt cover. The average annual groundwater concentrations were calculated using a modified Summers model in the software program UnSAT Suite Plus by Waterloo Hydrogeologic, Inc. SENSITIVE RECEPTORS During the fourth quarter of 2004, URS performed a sensitive receptor survey at the site to identify the locations of water wells (municipal, domestic, and agricultural) within 2,000 feet and surface water bodies, schools,and other receptors within 500 feet of the site. Based on a Department of Water Resources (DWR) well search, no water supply wells were identified within the 2,000-foot radius from the site. Two water supply wells were identified outside the 2,000-foot radius north-northwest and northwest from the site(Figure 1). The California Water Service Company supplies potable water to residents within 2,000 feet of the site. URS contacted Mr. Scott Bailey with the California Water Service Company to discuss water supply well locations within 2,000 feet of the site. URS confirmed that no active California Water Service Company supply wells exist within 2,000 feet of the site. KAWprocessU5 BP ARC01054501Soil Closure 05V7raft of 5450 Closure Report.doc