Persons storing or who have stored, distributed, or used agricultural chemicals may have had releases of these chemicals into the environment. To determine if such sites are actually contaminated and the level of concern, the Minnesota Department of Agriculture (MDA) requires a remedial investigation (RI). Corrective actions may also be required, if appropriate.
The objectives of an RI are to identify the:
- likely sources of contamination;
- extent and magnitude of contamination in soil and/or ground water;
- actual or potential impacts relating to the contamination; and
- information needed for designing any necessary corrective actions.
A work plan describing how the RI will be conducted must be submitted to the MDA for approval prior to implementation. MDA approval of the work plan is necessary for the Agricultural Chemical Response and Reimbursement Account Board to approve reimbursement of costs associated with the investigation and any subsequent cleanup (ACRRA.001 Reimbursement of Costs for Agricultural Chemical Incident Cleanups: ACRRA). Once the work plan is approved, investigation activities can proceed. Remedial investigation results must be documented in a Remedial Investigation Report and Corrective Action Plan. A Corrective Action Plan may be required to address or mitigate agricultural chemical contamination impacts. (GD10 Agricultural Chemical Incident Remedial Investigation Report and Corrective Action Plan)
APPROACH TO REMEDIAL INVESTIGATIONS
The following general procedures apply to agricultural chemical incident investigations. MDA staff can modify any of these procedures based on site specific considerations. Environmental consultants and responsible/voluntary parties are encouraged to propose modifications that will achieve effective results while reducing project costs.
Investigations at agricultural chemical facilities should be conducted in a flexible stepped approach whereby the results of preceding steps are used as rationale and justification for subsequent steps. With MDA staff approval, steps may be modified, combined or conducted concurrently at different locations on one facility to best suit the needs of a particular site. All work must be conducted in a safe manner and in accordance with all appropriate local, state, and federal rules and regulations.
STEP I. RI Work Plan Development
The main objectives of the work plan are to identify and document:
- potential source areas and chemicals of concern;
- proposed methods and procedures that will be employed to investigate potential source areas and chemicals of concern; and
- how potential receptors and migration pathways will be identified and investigated.
Attachment 1 is an RI Work Plan outline.
A thorough review of former and current agricultural chemical activities conducted on or near the site is necessary. This review should closely follow the procedures for a Phase I Environmental Site Assessment as outlined in the American Society of Testing & Materials (ASTM) standard E 1527. Also review:
- MDA spills databases, facility files and site file. Add these to the list of environmental record sources to be reviewed under Section 7.2.1.1 of the ASTM standard.
- Property tax files and recorded land title records. Locating and reviewing property tax files and recorded land title records should be done only after all other Standard Historical Sources (listed in Section 7.3.4, ASTM) have been considered and found to be unavailable or deemed not applicable in determining historical use of the property.
- Regional hydrogeologic data.
The consultant shall visit the site to identify sampling areas and site specific concerns or restrictions (preferably with MDA staff) and interview facility personnel prior to submitting the RI work plan.
The work plan must document the results of the site history investigation discussed above. The site history results shall be used to provide the rationale and justification for selecting (or not selecting) potential source areas and chemicals of concern that will be investigated through further sampling and analysis. The work plan shall discuss how the information necessary to complete the Contamination Impacts Survey (see Attachment 2) will be obtained and evaluated. The methods and procedures that are to be utilized to collect remedial investigation data must be identified and discussed in detail. MDA staff will not approve work plans that only reference MDA technical guidance documents when discussing methods and procedures. Any deviations from MDA technical guidance documents should be identified with rationale and justification for the changes proposed.
STEP II. Investigation Of The Likely Contaminated Areas
Once the historical and current use of the property has been evaluated and potential areas of concern have been identified (STEP 1), those areas shall be investigated by collecting and analyzing soil, ground water, and/or surface water samples. Several phases of field work may be required to address the objectives of the RI as noted above. MDA staff should be notified at least two weeks prior to the implementation of field work and may choose to observe the field work and split samples without prior notice.
A. Soil Sampling:
FOCUS. Investigation activities should focus on high risk areas identified in STEP 1. These areas include:
- Any place where small packaged, minibulk, or bulk quantities of agricultural chemicals were delivered, stored, mixed or loaded. This includes the interior of any earthen dike;
- Fertilizer impregnation tower area;
- Equipment parking areas;
- Stained areas;
- Obvious dead, damaged or barren vegetation spots;
- Areas associated with previous spills;
- Pesticide container storage locations;
- Scale pits;
- Locations where pesticide containers have been burned;
- Areas where runoff occurs;
- Water fill sites;
- Seed treatment areas;
- Equipment repair areas;
- Fertilizer production areas (e.g. mobile phosphate reactors); and
- Beneath the floor of dry fertilizer buildings if the floor is cracked
SOIL SAMPLING APPROACH: Sampling consists of at least one surface composite sample, one subsurface composite sample and one subsurface discrete sample from each high risk area and other potential contaminant source areas on the site. Composite samples in each high risk area should consist of 3 to 6 evenly spaced subsamples from an area roughly 15 feet in diameter. Surface composite samples are to be taken 0 to 6 inches below any surficial gravel. Subsurface composites should be collected at a depth of 2-2.5 feet.
One discrete "grab" sample from a depth of 4.5 to 5 feet should be collected near the center or close to the probable source in each surface composite area.
For more information see MDA guidance document GD11 Soil Sampling Guidance.
SOIL SAMPLE COLLECTION: Samples may be collected by any suitable sampling method including hand auger, solid stem auger, hollow stem auger or test trenching. The work plan shall specify exact sampling procedures to ensure the sample is representative of the specified depth interval and not contaminated by soil falling in from above. Sampling at depths within areas previously sampled or excavated shall be noted in the work plan.
DEEP SOIL SAMPLING: Hollow stem auger (HSA) borings, to a depth of 25 feet or the water table, whichever is less, generally will be required in selected potential source areas to evaluate the threat of contamination reaching the ground water, the vertical extent of contamination, and/or to evaluate subsurface stratigraphic formations. Deeper borings may be required at some sites. Soil samples should be collected from HSA borings by split spoon (ASTM D 1586) every 10 feet or less, at changes in lithology and at the water table. Classify soil samples in accordance with ASTM methods D 2487 or D 2488. Soil samples should be held under proper chain of custody and analyzed according to MDA staff preapproval.
Soil borings should not be a conduit for the vertical migration of contamination. Borings should not penetrate through confining layers below saturated zones or connect aquifers and shall be immediately grouted in accordance with the Minnesota Department of Health (MDH) water well construction code (MN Rules Chapter 4725).
SOIL SAMPLE ANALYSIS: Composite samples from the 2-2.5 foot interval are to be analyzed immediately. The 2-2.5 foot interval is analyzed first, in high risk areas, because past experience suggests that the surface sample in high risk areas is very likely to be contaminated. The surface composite and 4.5 foot discrete samples are to be held frozen under proper chain of custody for long term storage.
Analytical data of the 2-2.5 foot samples and a map showing sampling locations should be forwarded to the MDA project staff by both mail and fax IMMEDIATELY upon receiving it from the laboratory. MDA staff will then contact the consultant and responsible party to discuss the analysis of frozen samples. If the 2-2.5 foot sample is found to be contaminated above the cleanup goals for the site, the deep discreet sample is usually analyzed to determine the vertical extent of contamination. MDA staff will accept analytical data from frozen samples properly stored for a period of up to six months.
If the 2-2.5 foot sample is not contaminated above the cleanup goals for the site, the surface composite is usually analyzed to determine if there is contamination above 2 feet. Proposals to analyze the deep discrete or the surface composite sample initially will be considered on a case by case basis.
SOIL ANALYTICAL PARAMETERS: The MDA has standard analytical lists for use in pesticide incident investigations. In general most soil samples are analyzed for MDA List 1 pesticides (neutral extractables). See MDA guidance document GD26 Analytical Lists for Pesticide Incident Investigations. Analysis of site specific pesticides, based on the history of chemicals stored or used at the site, may also be required. Nitrate-nitrogen and TKN analysis will be required in those areas where fertilizer contamination is suspected. If practicable, analytical costs may be reduced by targeting previously identified contaminants of concern. However, confirmation sampling for the full MDA List 1 parameters will be required.
B. Ground Water Sampling:
FOCUS: Monitoring wells may be required at sites depending on the extent and magnitude of contamination and site specific hydrogeology.
MONITORING WELLS: A minimum of three wells are necessary to define the ground water flow direction. At most facilities, four or more wells will be required to adequately assess ground water below the facility. Monitoring well locations (approximate), well design, well drilling methods, well development methods and well sampling methods must be reviewed and preapproved by MDA staff. Monitoring wells should be constructed with polyvinyl chloride, stainless or low carbon steel depending upon the contaminant of concern. Monitoring wells intended to intercept the water table or perched water should be constructed to allow for seasonal fluctuations in water levels. Monitoring wells must comply with the MDH water well construction code (MN Rules Chapter 4725).
Slug or plug tests should be conducted in all monitoring wells to estimate the horizontal hydraulic conductivity of the screened formations. In order to obtain accurate results, slug or plug tests should be conducted on undisturbed wells before water samples are collected. Data evaluation techniques should be selected appropriately and be based on whether the saturated formation is confined or unconfined.
POTABLE WELLS: Potable wells on and near the site should be sampled as soon as it appears that there is a reasonable likelihood that ground water may be contaminated, based on the site hydrogeology, past practices and analytical data. This could be as early as the start of Step II. Contact MDA staff if there is any concern about potable wells and prior to sampling off site wells.
For more information on ground water sampling see MDA guidance document GD12 Ground Water Sampling Guidance.
C. Handling and Transport of Samples
All samples must be collected, transported and stored in accordance with applicable EPA, DOT and MDA approved procedures including chain of custody. QA/QC plans and analytical methods from commercial laboratories analyzing standard List 1,2 & 3 compounds must be approved by MDA. Lists of commercial laboratories with approved QA/QC plans are provided in MDA guidance document GD23 Pre-approved Commercial Laboratories: Fixed Base and Mobile.
Step III. Remedial Investigation Report
After field work is completed, an Agricultural Chemical Incident RI must be submitted to the MDA (GD10 Agricultural Chemical Remedial Investigation Report and Corrective Action Plan). If RI activities do not accomplish the RI objectives, additional activities and reports may be necessary. The contamination impacts survey (Attachment 2) should be completed, submitted, and discussed in the RI report.
The report should be a comprehensive document. All data used, such as geological logs, well construction logs, and laboratory data should be reproduced in the appropriate tables and appendices, without referring to previous reports.
CLOSURE
Once the site is investigated and potentially remediated to MDA staff satisfaction, the site will be closed.
MDA Contact
651-201-6061 • Fax: 651-201-6112
Pesticide & Fertilizer Management Division
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