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CALIFORNIA REGIONATER QUALITY CONTROL BOARD CENTRAL VALLEY RE N 3443 Routier Road, Suite A Sacramento, CA 95827-3098 Phone (916) 255-3000 FAX (916) 255-3015 16 October 1997 Mr. Stephen Chen Department of Public Works City of Stockton 425 N. El Dorado Street Stockton, CA 95202-1997 nt1�i�� Pete`Wilson, Governor We have reviewed the work plan submitted by Camp Dresser & McKee Inc. (CDM) for additional groundwater investigation and corrective actions at the Austin Road Landfill. The report satisfies our 7 March 1997 request for an amended report of waste discharge due to confirmed VOC detections in certain monitoring wells. The general approach outlined in the workplan is appropriate, but a few clarifications are necessary. The location of Transect 1 is intended to define the northern boundary of the plume. The influence of NCYA supply wells on the plume is unknown and we believe it is important to know where the plume is relative to these wells. Unless CDM is certain that Transect 1 in combination with their other studies will yield this information, we suggest that the transect location be shifted to the west or another transect added to better delineate the western portion of the northern edge of the plume. The discussion of Hydropunch sampling explains that water samples will generally be collected from the upper and lower aquifers in each boring. In the previous investigation, samples from the upper aquifer were collected near the water table surface which at that time was commonly above the sandy portion of the aquifer. This sampling strategy left open the possibility that VOCs could have migrated farther in the deeper, coarser portion of the upper aquifer. CDM needs to address this issue in their sampling plan. Finally, CDM notes that well head treatment or alternative water supplies could be used to protect local groundwater consumers. We concur that such options could be important, but note that they would not relieve the City of its responsibility under Title 27 and State Board Policy 92-49 to clean up pollutants in the aquifer. Recycled Paper Our mission is to preserve and enhance the quality of California's water resources, and ensure their proper allocation and efficient use for the benefit of present and future generations.