Product Quality

CalRecycle regulations (Title 14, CCR, Division 7, Subchapter 3.1) require that compost produced by commercial scale composting operations and facilities protect public health and safety.  This includes testing product quality, including metal concentrations, physical contamination levels, and pathogen levels.  Compost purchasers require additional information from suppliers in order to ensure the product meets specific needs, such as for erosion control or specific crops.  The quality of compost and mulch products can be determined by testing for specific characteristics, including pH, soluble salts, nutrient content, organic matter, maturity, stability, and physical contaminants (i.e., inerts, including glass, metal, and plastic).  Appropriate ranges for specific characteristics depend on the type of application.

Specifications

Compost and mulch specifications identify the value ranges for parameters that ensure products meeting these values are suitable for a given use.  Caltrans incorporates CalRecycle’s product quality standards for metals and pathogens, but its physical contaminant requirements may differ slightly.  Caltrans specifications require that compost meet the values shown in the following tables:

 

Quality characteristicTest methodaRequirement
FineMedium/Coarse
pHTMECC 04.11-A
6-8.5
6-8.5
Soluble salts (dS/m)TMECC 04.10-A
0-100-10
Moisture Content (% dry weight)TMECC 03.09-A 25-6025-60

Organic matter content (% dry weight)

TMECC 05.07-A 30-7030-100
Maturity (seed emergence)
(% relative to positive control)
TMECC 05.05-A
80 or above80 or above
Maturity (seedling vigor)
(% relative to positive control)
TMECC 05.05-A
80 or above
80 or above
Stability (mg CO2-C/g OM per day)TMECC 05.08-B
5 or below8 or below
Pathogen
Salmonella (most probable number per 4 grams dry weight basis)
TMECC 07.01-B
< 3< 3
Pathogen
Fecal coliform (most probable number per gram dry weight basis)
TMECC 07.01-B
< 1,000< 1,000
Physical contaminants (% dry weight)
Plastic, glass, and metal
TMECC 02.02-C

Combined Total:

< 0.5

Combined Total:

< 1.0

Film plastic (% dry weight)TMECC 02.02-C

Combined Total:

< 0.1%

Combined Total:

< 0.1%

a TMECC refers to Test Methods for the Examination of Composting and Compost, published by the United States Department of Agriculture and the United States Compost Council (USCC).

The particle size must comply with the requirements shown in the following table:

Quality characteristicTest methodaRequirement
MinMax
Gradation Fine:(dry weight % passing)
1-inch sieve
3/8-inch sieve
TMECC 02.02-B
100
95
--
--
Gradation Medium:(dry weight % passing)
2-inch sieve
3/8-inch sieve
TMECC 02.02-B
95
40
--
55
Gradation Coarse:(dry weight % passing)
3-inch sieve
3/8-inch sieve
TMECC 02.02-B 95
25
--
35
a TMECC refers to Test Methods for the Examination of Composting and Compost, published by the United States Department of Agriculture and the United States Compost Council (USCC).

How to Verify that Compost and Mulch Products Meet Specifications  

In order to verify that compost and mulch products meet a given specification, test for the parameters identified in the specification in accordance with standardized methodologies, such as the Test Methods for the Examination of Compost and Composting (TMECC) used for purposes of the United States Composting Council’s Seal of Testing Assurance (STA) program.  The STA program requires compost be tested by an approved laboratory capable of performing all the specified methods and meeting other program requirements.  A laboratory approved through the STA program tests submitted compost samples in accordance with the TMECC.  The laboratory sends a Technical Data Sheet containing the results to the person that submitted the sample.  Note that the Technical Data Sheet verifies that the compost sample submitted for testing meets the above Caltrans specification for a fine gradation of compost as all parameters are within the ranges identified in its specifications.

Resources

Compost and Mulch Specifications

  • Caltrans Standard Specifications. The California Department of Transportation (Caltrans) website has Standard Specifications and related information.
  • Caltrans Erosion Control Toolbox. The Caltrans website has resources for project managers including specifications, publications, compost calculators, and event schedules.

How to Find the Right Product