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• For each construction area up to 500 square feet - collect 2 composite samples.
   
• For each additional 5,000 square feet of construction area or fraction thereof - collect 1 additional composite sample, up to a maximum of 6 samples for the construction area. [Exception: When soil is excavated before it is sampled, additional samples are necessary from the excavated soil pile (see “How do I collect the samples?”).]

• Choose sample areas where there is the highest potential for contamination within the proposed construction area.
   
• Contamination should be suspected in any area where pesticides or fertilizers have been handled. This would include previous mixing, loading, equipment parking, fertilizer impregnation tower areas, earthen dike interiors, bulk storage areas, equipment repair areas, areas with pesticide staining, dead or barren vegetation areas, scale pits, pesticide container burning areas, runoff ponding areas, water fill sites, along with any areas associated with previous spills.

• Each sample should be a composite sample, taken from an area no larger than 15 feet in diameter. Each composite sample should consist of no more than 6 subsamples from the same depth.
   
• If the planned construction will include significant excavation, collect the samples from below the excavated area. The samples should be collected from the 6-inch interval below the excavation. This could be completed through soil borings to the depth of the planned excavation and then sampling or by excavating the soil that needs to be removed and then sampling the bottom of the excavation. If you choose to excavate the area of construction first and then sample, please be aware that you will need to secure the excavated area and the soil pile while you are awaiting laboratory results and MDA review and approval.

* Note, Minnesota statutes require written approval from the MDA for application of pesticide or fertilizer contaminated media. This means that you MUST have prior written approval from the MDA to spread or otherwise use any excavated soil which you know or suspect might be contaminated with pesticides or fertilizer. 

• If significant excavation is not required for the structure(s), sample from the 0 - 6-inch interval, except in graveled areas where samples should be collected from the base of the gravel to 6 inches below the base of the gravel (gravel is loose gravel and/or stones).
   
• Additional composite soil samples are needed from the soil removed during excavation in order to determine the proper treatment for excavated soil. The soil pile should be mixed before collecting the samples. The following table illustrates the additional number of samples required to evaluate the excavated soil. Refer to MDA guidance document GD11 Soil Sampling Guidance for more information on stockpiling samples.

We suggest samples be analyzed for total Kjeldahl nitrogen (TKN), nitrate-nitrogen, MDA List 1 pesticides, and any other agricultural chemicals that, due to past practices may be present in the area of construction. The MDA List 1 pesticides are listed in Guidance Document 26 Analytical Lists for Pesticide Incident Investigations.