WORK PLANS - Laserfiche WebLink

Home Browse Search

A S S O C I A T E S I N C 2.22 Hydrogeology The average depth to groundwater measured in the monitoring wells has ranged from approximately 45.3 feet bgs in June 2000 to approximately 56.4 feet bgs in October 2003. The �f groundwater gradient is relatively flat, historically ranging from 0.0005 to 0.001 f1/ft. The groundwater flow direction has varied but has been predominantly to the southwest. A rose I. I ' diagram showing historical groundwater direction and magnitude is shown on Figure 5. 3.0 EXTENT OF PETROLEUM IMPACTED SOIL AND GROUNDWATER 3_1 Soil ` Laboratory analytical data from previous soil investigations indicated petroleum hydrocarbon L constituents were detected in soil samples collected from soil borings advanced in the vicinity of 1. the former UST location (borings SB3 and MW1), and in borings MW2 and VEW3 advanced south of the former UST location. The highest concentration of TPHg, 1,900 milligrams per d L kilogram, was reported in the soil sample collected from SB3 at a depth of 20 feet bgs. Based on the laboratory analytical data, petroleum impacted soil extends from 15 to 45.5 feet bgs in the vicinity of the former UST location and at VEW3. Low concentrations of petroleum Law.) hydrocarbons were detected in soil samples collected from MW2 at depths of 40.5 and 50.5 feet bgs. The petroleum hydrocarbon concentrations appear to attenuate with depth and do not appear to extend to the water table at its current depth. Analytical data from soil samples collected at the site are summarized in Table 2. The estimated extent of petroleum impacted soil is shown on Figure 3. Mass balance calculations were performed for TPHg and BTEX in soil. it �. is estimated that there is a mass of 21.4 lbs of combined BTEX constituents and a mass of 180.7 pounds of TPHg. Mass balance calculations are included in Appendix A. L3_2 Groundwater 4 Laboratory analytical results of groundwater samples collected at the site on October 20, 2003, Lindicated petroleum .hydrocarbons were detected in the groundwater samples collected from MWl and MW2. MTBE was detected in the groundwater sample collected from MW at a + concentration of 7.1 micrograms per liter (pg/L). TPHg, benzene, toluene, and MTBE were L detected in the groundwater sample collected from MW2 at concentrations of 190 pg/L, 1.2 µg/L, 2.5 µg/L, and 21 pg/L, respectively. I L + Groundwater samples collected from wells MW3, MW4, MWS, MW6, and MW7 did not contain concentrations of TPHg, total petroleum hydrocarbons quantified as diesel fuel (TPHd), total petroleum hydrocarbons quantified as kerosene (TPHk), BTEX constituents, or fuel oxygenates at or above the laboratory reporting limits. Analytical data for groundwater samples collected at i the site are summarized in Table 3. The estimated extent of petroleum impacted groundwater is L shown on Figure 5. Because of the low concentrations and limited extent of TPHg, benzene, LS:1Environmenta11625771SCMCAPAdddoc 3