SITE INFORMATION AND CORRESPONDENCE_1987-1992

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+ MEMORANDUM CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD - CENTRAL VALLEY REGION 3443 Routier Road Phone: (916) 361-5600 Sacramento, CA 95827-3098 ATSS Phone: 8-495-5600 TO: Antonia K.J. Vorster FROM: John J. Tomko S DATE: 18 December 1989 SIGNATURE: SUBJECT: LINCOLN VILLAGE PHASE II GROUND WATER INVESTIGATION, CITY OF STOCKTON Prase I of the Lincoln Vill ,�gc Center around water investigation was conducted in June 1988. Four shallow zone monitoring wells were installed (MW#1-#4) . MW#4 had 2500 ppb of PCE and 190 ppb of TCE. The other three monitoring wells did not have detectable levels of purgeable halocarbons. See attached map for well locations. The Phase I investigation also included the sampling of soils at the three suspected sources (three dry cleaners) and underneath the site's sewer lines, and the sampling of raw sewage. Soils beneath all three dry cleaners and underneath certain sewer lines contained detectable levels of PCE. Six raw sewage samples were taken from onsite manholes. PCE levels were detected at each manhole at levels one to two orders of magnitude greater than concentrations measured in soil samples. Raw sewage PCE levels were between 5.7 and 32 ppb. The Lincoln Village Center site contains three deep municipal wells. (See attached map.) Lincoln Village Maintenance District Well #1 (LVMD #1) was sampled pursuant to AB1803 in 1984. Water samples from this well contained PCE at 120 ppb and TCE at 14.3 ppb. It was this legislative mandated sampling of municipal wells that precipitated the site's ongoing ground water investigation. PCE was measured in LVMD #6 in 1985 (0.8 ppb) and in 1986 (19.5 ppb) . LVMD #2 did not contain detectable levels of PCE at the time of the Phase I investigation. The likely source of the ground .nater contamination was attributed to the leakage of PCE/TCE contaminated wastewater through joints in the existing onsite sewer lines. The deep zone ground water contamination that was measured in LVMD well #1 and #6 was conjectured as being caused by improper sanitary well seals that provided an artificial conduit for the downward migration of contaminants. This conjecture was based on two observations. One, in 1985 the county televised LVMD#1 and observed that cascading water from a casing separation was occurring. The county installed an 80-foot well seal in this well in 1985 and from that time until the submittal of the Phase I report, PCE was not detected within this well . Two, apparently in 1984 the county installed a PVC liner and a sand pack within the LVMD well #6 to correct a sanding problem. Apparently, the well only had a 40-foot well screen. If this liner was not adequately sealed, then it could be providing a pathway for the downward movement of contaminants. LVMD #6 was shutdown in 1986 and apparently has not been resampled.