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MEMORANDUM CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD - CENTRAL VALLEY REGION 3443 Routier Road, Suite A Phone: (916) 361-5600 Sacramento, CA 95827-3098 ATSS Phone: 8-495-5600 TO: William H. CrooksU L Q FROM: Cori Condon Executive Officer- 1992 Assoc. Eng. Geologist ENVIRONMENTAL HEALTh, PERMIT/SERVICE �l DATE: 2 July 1992 SIGNATURE: C oyl6n SUBJECT: CITY OF STOCKTON, BANNER ISLAND, STOCKTON, S JOAQUIN COUNTY I have reviewed the Second Phase Subsurface Investigation for the City of Stockton, Banner Island property. The City's property occupies a part of Banner Island which was formerly a ship building facility. The facility was torn down in the seventies and in November 1989, two monitoring wells were installed at the site to assess the subsurface conditions. The results of the laboratory analysis of the water samples showed hazardous levels of cadmium (650 - 2, 100 ppb) and elevated concentrations of arsenic, chromium, lead and selenium in the ground water. The second phase of investigation was carried out in March 1992 in which seven additional monitoring wells were installed. Monitoring and sampling of all of the wells on-site showed the water table gradient is to the north (away from the Deep Water Channel ) and ground water had high concentrations of arsenic, barium, chromium, and selenium. Acetone has also been detected in two of the monitoring wells on the property. The Report includes a survey of water quality of three other sites in the area of Stockton; each of these site also has ground water with concentrations of arsenic, barium, chromium, and selenium above State Primary MCL's. The consultant concludes ground water at the City of Stockton's Banner Island site is consistent with water quality of the south-central Stockton area and that past practices at the site have not caused any ground water degradation. Based on results of this assessment and previous work performed on the site, the consultant also concludes that ground water in the Stockton area is of poor quality due to chlorides and TDS. The average electrical conductivity of the purging water data collected while sampling at the site, is about 842 umhos/cm. Based on State Water Resources Control Board Resolution No. 88-63, all waters of the State are considered suitable, or potentially suitable, fcr municipal or domestic water supply unless the electrical conductivity exceeds 5,000 umhos/cm. Therefore, as outlined in the Basin Plan, it is necessary to consider the ground water at this site as being potentially suitable as a drinking water resource. The high concentrations of metals and occurrence of acetone in the ground water underlying the former ship building yard (traditional users of chemicals, paints, and metals) suggests that these contaminants are from the past operational practices and/or are caused by materials used to build the island itself. If the contamination at this site were naturally occurring, we would expect concentrations to be more consistent across the site. Although the Deep Water Channel was a losing channel during the reporting period, the gradient may reverse during other seasons of the year and these contaminants would be discharging into surface waters, threatening water quality. Therefore, it is necessary to look more closely at the hydraulics of the island to gain a better knowledge of ground water and surface water quality, to determine seasonal or tidal effects upon ground water and drainage systems and to improve our understanding of stratigraphic zones and soil quality.