California Regional Water Quality Control Board San Francisco Bay Region
January 4, 2002
File No: 2342.04(WBH)

Mr. David Cerini, Owner Petaluma Mushroom Farm 782 Thompson Lane Petaluma, CA 94952

Subject: Work Plan for Site Characterization of the Petaluma Mushroom Farm - Petaluma Mushroom Farm, 782 Thompson Lane, Petaluma, Sonoma County

Dear Mr. Cerini:

We have reviewed the Site Characterization Work Plan (Work Plan) prepared and submitted on your behalf by EBA Engineering in response to Cleanup and Abatement Order (GAO) No. 00105. We have determined that certain components of the Work Plan are deficient and need to be expanded, as described below.

1) Pursuant to Provision B.3 of the CAO you are required to evaluate and characterize the presence of applicable nutrients, pesticides, and any other pollutants that may be present in the facility's wastewater in the groundwater beneath and downgradient of the disposal field and wastewater holding pond. The Work Plan proposes to forego characterization of the groundwater conditions at the site if the analytical results of shallow soil samples collected from the disposal field indicate low levels of pesticides. However, given that wastewater has not been applied to the disposal field for more than a year, and that the half life in soil of three of the four pesticides used at the facility range from only four to ten weeks, the residual concentrations of pesticides in shallow soil may not be indicative of nutrient and pesticide impacts to groundwater. Moreover, the facility's wastewater holding pond is unlined and poses a significant threat to groundwater.

Therefore, you are required to submit a proposal for characterization of the groundwater, that includes a site-specific analysis of the geologic and hydrogeologic conditions, and installation of a sufficient number of appropriately located, screened and developed groundwater monitoring wells. This should include installation of at least one upgradient reference well. The groundwater wells should be appropriately surveyed and their groundwater levels established, such that the groundwater gradient at the site can be determined and included in the results of the site characterization. Groundwater samples from the monitoring wells must be analyzed for the four pesticides used by the facility and for conductivity, nitrate, total ammonia, and total kjeldhal nitrogen.

Based on the results of this hydrogeologic/groundwater investigation, the potential for contamination of any domestic water supply wells at neighboring residences needs to be evaluated. The Work Plan must be expanded to include a description of the approach that will be used to evaluate potential impacts to nearby domestic wells based on the results of the hydrogeologic/groundwater pollution investigation.

2) The Work Plan proposes to analyze soil samples for pesticides only. Soil samples must also be analyzed for nitrate, total ammonia, and total kjeldhal nitrogen.

3) Work Plan Table 2 - Summary of Laboratory Testing Program identifies unionized ammonia as one of the analytical parameters to be examined in wastewater and surface water samples. While unionized ammonia is an appropriate and important parameter to evaluate due to its acute toxicity to aquatic life, concentrations of total ammonia must also be determined and reported for wastewater and surface water samples.

4) The Work Plan proposal for investigating the presence and extent of soil pollution in the north-adjacent disposal field must be expanded to include at least one more sampling location on the northern property boundary within the swale located due north of the wastewater holding pond. The additional sample location(s) is needed because excessive wastewater and polluted runoff discharged to the north-adjacent disposal field would drain to this swale which flows to the north onto the neighboring property.Regional Board staff has observed ponded wastewater and polluted runoff in this swale extending a significant distance onto the neighbor's property to the north. It is our understanding that this neighbor to the north has stopped using her domestic well due to high levels of nitrogen in the well water.

5) The Work Plan proposes to place on hold the soil samples to be collected from a depth of thirty-six inches-below ground surface (BGS), until the analytical results from the eight inch-BGS samples are evaluated. Placing the deeper soil samples on hold as proposed is acceptable only for the samples collected from the three soil sample locations in the western portion of the north-adjacent disposal field, which historically received the least amount of wastewater discharge. Each of the thirty-six inch-BGS soil samples collected from within the swale and along the eastern portion of the north-adjacent disposal field must be analyzed, irrespective of the analytical results from the shallower samples from those locations.

6) Provision B.3 of the CAO requires the investigation of soils within the Marin Creek channel. Contrary to the requirements of Provision B.3, the Work Plan only proposes to collect surface water samples from the creek channel. During several site inspections, Regional Board staff discovered wastewater and polluted runoff from the facility being discharged directly to Marin Creek. Wastewater at the facility contains a large amount of settleable solid waste material. Accordingly, sediments within the channel should be sampled at depths of approximately eight and sixteen inches along the centerline of the creek, at the sampling stations identified as MC-1, MC-2, MC-3 and at an additional intermediate location to be established approximately midway between MC-2 and MC-3. Each of the sediment samples collected at these four creek channel locations at both depths must be analyzed for the four pesticides used by the facility and for nitrate, total ammonia, and total kjeldhal nitrogen.

You are hereby required to submit a revised Work Plan pursuant to CAO Provision B.3 that incorporates the items identified herein no later than January 28, 2002. Also, the deadlines associated with CAO Provision B.4 (requiring the submittal of the results of an approved soil and groundwater pollution investigation) and Provision B.5 (requiring the submittal of a Remedial Action Plan as necessary) are hereby extended to April 1, 2002. Any additional extension of these deadlines must be approved in writing by Regional Board staff.

If you have any questions regarding this matter, please contact Carmen Fewless at (510) 6222316 [email at] or William Hurley at (510) 622-2364 [email at].

Bruce H. Wolfe, acting E.O., for
Loretta K. Barsamian
Executive Officer

Cc: Ms. Tracy Tesconi
Sonoma County Permit and Resource Management Department 2550 Ventura Avenue
Santa Rosa, CA 95403-2829

Mr. Jeff Holtzman, Assistant District Attorney Sonoma County District Attorney's Office 2300 County Center Drive
Suite B 170
Santa Rosa, CA 95403

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