ARCHIVED REPORTS_XR0007005 - Laserfiche WebLink

Home Browse Search

I San Joaquin County Public Health Services - Environmental Health Division (PHS/EHD), subsequently required further assessment of the lateral extent of groundwater contamination Comfort Air appealed this request to the San Joaquin County Board of Supervisors, and was granted permission to install a single well northeast of MW-3 to delineate the down-gradient extent of the dissolved-phase contamination plume On October 12, 1993, one soil boring was drilled at the site The boring was advanced to a depth of 50 feet and completed as groundwater monitoring well MW-4. Hydrocarbon odors were noted in soil samples from 35 to 50 feet Laboratory analysis confirmed the presence of low levels of contamination at 40 and 45 feet (3 10 ppm and 190 ppm TPH as gasoline respectively) On October 19, 1993, the depth to water was measured in all four wells and the I groundwater gradient determined Monitoring well MW-4 was then purged and sampled The gradient was determined to be 0 00057 ft/ft directed N 66° E TPH as gasoline was detected in the water sample at a level of 6,800 ppb, and benzene was detected at 1,400 ppb IThe accepted Maximum Contaminant Level (MCL) for benzene in groundwater is 1 ppb After review of these results, the PHS/EHD issued a directive for further investigation (December 17, 1993) 1) Install additional monitoring wells to completely define the extent of soil and groundwater contamination ' 2) Submit a plan for interim groundwater remediation 3) Continue quarterly monitoring and reporting I4) Prepare a corrective Action Plan (Problem Assessment Report) for soil and groundwater contamination by April 1, 1994 IIn accordance with item 3 of this directive, GeoAudrt has monitored qroundwater quality for the first quarter of 1994, as described below i 3.0 PROCEDURES 3.1 Well Purging and Sampling� g P g On January 25, 1994, the water level in all four (4) wells was measured relative to the top of the casing using a Solinst water level meter (Table 1) The relative piezometric level and hydraulic gradient were determined from these data In accordance with an agreement between the PHS/EHD and Comfort Aar, only MW-4 was sampled 4 I