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, 20 June 2001 AGE-NC Project No. 98-0440 _ ' Page 5'of 6 Department,of Water Resources, the regional ground'water flow direction has been toward.the ; northeast. Rose diagrams showing ground water flow direction, flow' direction distribution and gradient for the eight monitoring;events conducted.at the site are illustrated on Figure 5. ,4:4. CONTAMINANT MIGRATION ' s f the 2001 monitoring event, analytical results from ground water samples indicate wells A o h g - MWI, MW2, MW5 and MW6 are impacted with petroleum'hydrocaibons, and'wells MW3 and . MW4 are not impacted. Soil samples collected during the UST removals in August 1989'indicated,, detected in soil samples collected beneath UST No. 4 and UST,No. 5. USTs No. TPH-.g was-'only p . 4 and 5,are located in the east"A on of the site (Figure 2);which'based on,soil sample analyses, is t the main contaminant source area on the site. Monitoring'well MW3 is located to the northwest of the main'.contaminant source area, which has been directly down-gradient three of the last eight monitoring events. However,"samples from MW3 have not contained detectable concentrations of- TPH-g or TPH-d for the.past eight sampling,events. AGE believes this may be due to the greater distance'ofMW3 frorn the main contaminant source area on the site compared to MW5 and MW6. . Proximity coupled with,a north-northeast ground water flow direction exhibited in the past may explain why wells MW2, MW5 and MW6 are impacted with petroleum hydrocarbons and well MW3 is not. Additionally, Sand Zone A and Sand Zorie B may provide-preferred migration routes fol impacted ground water when saturated- Further investigation is needed to determine the extent ; ' of the impacted ground water and the relationship-between the subsurface conditions and the plume 'migration path. 5.0. ' SUMMARY AND CONCLUSIONS = Based on the data collected during this,monitoring period, AGE concludes: • ` Depth to groundwater at the site as'of 15 March'2001.was approximately 1335 feet below ' surface grade with a north-northwesterly flow direction:. • The highest concentration.of dissolved hydrocarbons quantified as TPH-g, TPH-d, and ' generally BTEX compounds extends northeast from USTs No. 4 and 5. Dissolved hydrocarbons were encountered-in,the down-gradient`direction from the former USTs in Samplesfrom monitoring wells MW2, MW5 and MW6.- ' lateral extent of petroleum h drocaibon'impacted-grouiid,water has.not been defined The late p , - y . . toward the northeast beyond MW5 and MW6. The'hydrocarbori plume is fairly wedefined well dened ; to the south, east and west and northwest. Advanced GmEavironmental,Inc.