Each batch of GroCo compost is laboratory tested to ensure it meets Washington State Department of Ecology standards for trace metals and pathogen reduction, known as Exceptional Quality, or EQ.

While GroCo compost is regulated under the state biosolids program, Ecology has also published Interim Compost Guidelines that limit concentrations of trace metals in composts made from other organic residuals. GroCo is well below the limits set for biosolids and composts - see comparison in the following table:

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GroCo is also tested for disease-causing micro-organisms such as bacteria, viruses and parasites. Biosolids treatment kills over 90% of such organisms and composting destroys any that may remain. Laboratory results confirm that these organisms are not found in GroCo and it is a Class A biosolids product.

Biosolids composts may be safely used as a soil conditioner for landscaping, lawns and home gardens.

GroCo also contains plant nutrients such as nitrogen, phosphorus, potassium, iron, calcium, magnesium and zinc. GroCo is not a commercial fertilizer, and nutrient analyses represent an estimate, not a "guaranteed analysis."

Ensuring Compost Quality
Compost producers work to ensure that their products meet the high quality demanded by their customers. For example, in 2002, damage to landscape and garden plants was traced to an herbicide, clopyralid, which had been found in several Washington composts. In response, many composts and ingredients were tested to ensure that sources of contamination were identified. Sources included use of chlopyralid in landscaping, lawns and in weed-free hay and straw grown for livestock use.

Although we did not expect that biosolids or sawdust would contain clopyralid, samples of GroCo compost were laboratory tested and found to contain no clopyralid. GroCo was also tested in plant bioassays conducted by Washington State University and University of Washington, where plants showed no indications of clopyralid damage.

The Washington State Department of Agriculture subsequently banned use of chlopyralid on residential lawns in order to protect compost quality.

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