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r <br /> _ ENVIRONMENTAL HEALTH DEPARTMENT <br /> "\ SAN JOAQUIN COUNTY <br /> . r- +•--u �y C�nit.Supervisor.� <br /> Q. Donna K. Horan,R.E.H.S. Carl Borgman. R.E.H.S. <br /> ;04 East Weher Avenue. Third Floor <br /> I)irector %like HuL=gins.R.E.11 S.. R.D.I. <br /> �- �=� •i ki Olsen, R.E.H.S. Stockton, California 957021-2708 Uuugla>W.Nilson. R.E.II.S- <br /> c P Pru r,tm.IIu uc rr <br /> ,�c FORS <br /> Telephone: 2(_U9) 468-34-10 N1.ttL.ret La,_,orio, R.r.11.s. <br /> 1,auric.k.Cotulla, R.E.H.S. Robert McClellon.R.E.H.S. <br /> - /'rr>snun Afuau rr pad: (��)�) ���-�)l�� Mark Barcellos. R.E.H.S. <br /> MR RUSSEL CHAPIN APR 18 200 <br /> CHAPIN BROTHERS, INC <br /> 1203 N CARLTON AVE <br /> STOCKTON CA 95203 <br /> RE: CHAPIN BROTHERS Site Code: 0850 <br /> 1766 MONTE DIABLO AVENUE <br /> STOCKTON, CA <br /> The San Joaquin County Environmental Health Department (EHD) has received and <br /> reviewed Ground Water Monitoring - Natural Attenuation Work Plan (WP), dated 21 <br /> March 2005, prepared by Advanced GeoEnvironmental, Inc. (AGE). The WP was <br /> prepared in response to the EHD directive letter dated 03 March 2005. <br /> In the WP, AGE gives an abbreviated remediation history of the site and proposes to <br /> monitor the site wells for contaminant concentrations and for natural attenuation <br /> parameters to demonstrate that active natural attenuation of the plume of dissolved <br /> petroleum hydrocarbon contaminants is likely to occur following suspension of the <br /> current ground water extraction and treatment (GWE) system. AGE will also utilize the <br /> data to assess plume stability and degradation. <br /> In response to telephone inquiries from the EHD concerning methods to collect the <br /> natural attenuation data, AGE prepared a work plan addendum, Ground Water Sampling <br /> and Monitoring Natural Attenuation Work Plan Addendum (Addendum), dated 12 April <br /> 2005 and submitted to EHD by e-mail. The Addendum describes monitoring well purging <br /> and sampling methods for obtaining the natural attenuation parameters. The wells will be <br /> purged and sampled utilizing a low-flow pump. <br /> AGE proposes to collect groundwater samples utilizing the low-flow purge technique <br /> from all wells for contaminant analyses and to collect groundwater samples from wells <br /> VW-6, EW-1, EW-2 and EW-3 utilizing the standard purge methods for contaminant <br /> analysis to calibrate the results between the two sampling methods. The EHD <br /> recommends that wells MW-3 and MW-4 be added for this comparison. Comparison of <br /> the analytical results from the samples collected by both methods will provide the basis <br /> for evaluating which sampling technique is appropriate for the site wells. <br /> The EHD recommends utilizing an inline filter to collect samples for manganese and <br /> ferrous iron analysis. The EHD understands that dissolved methane analysis is <br /> expensive and difficult and recommends performing the analysis at a later date if <br /> justified by the other data. In-situ measurements, such as dissolved oxygen and <br />