Filtered gravel is one that can sufficiently support the sand layer in the filtration pond　and can perform stable　and efficient cleaning,　and is specified in 1.1 main component, 1.2 quality (physical properties)　and 1.3 quality (leaching property). Must fit.

1. Main component　and quality

1.1 Main component
Filtered gravel is a rounded stone with rounded corners that is obtained by crushing naturally occurring rocks by natural action. Its main components are oxygen　and silicate.

1.2 Quality (physical properties)
Quality (physical properties) shall be tested according to JWWA A 103-4: 2006-2 6.4.1-6.4.3　and shall comply with the provisions of Table 1.

1.3 Quality (exudability)
Quality (exudability) shall be tested according to JWWA A 103-4: 2006-2 6.5　and shall comply with the provisions of Table 1.

● Table 1-Quality

item		Quality regulations	Applicable test clause
Physical properties	Cleaning turbidity (degree)	30　or less	JWWA A 103-4:6.4.1
	density（g/cm3)	2.50　or more in a saturated surface dry state	JWWA A 103-4:6.4.2
	Hydrochloric acid solubility (%)	3.5　or less	JWWA A 103-4:6.4.3
Exudative	taste	Not abnormal	JWWA A 103-4:6.5
	Odor	Not abnormal
	Saturation (degree)	0.5 以下
	Turbidity (degree)	0.2　or less
	Iron　and its compounds (mg/L)	0.03　or less
	Manganese　and its compounds (mg/L)	0.005　or less

2. Appearance　and dimensions

2.1 Appearance
Appearance shall be tested according to JWWA A 103-4: 2006-2 6.6.1　and comply with the provisions of Table 2.

2.2 Dimensions
The dimensions shall be tested according to JWWA A 103-4: 2006-2 6.6.2　and comply with the provisions of Table 2　and the requirements set by the purchaser.

● Table 2-Appearance　and dimensions

item		Appearance　and dimensions	Applicable test clause
appearance	appearance	Hard　and rounded, with little content of flats, impurities, clay, fragile particles, etc.	JWWA A 103-4:6.6.1
Size	Shape of gravel particles (%)	The shape of the gravel particles should be 5 times　or more the major axis　and 2　or less in mass ratio.	JWWA A 103-4:6.6.2
	Mass ratio of particle size (%)	The particle size of the filtered gravel shall be 15　or less in total, which is the sum of the mass ratio of the particle size below the design minimum diameter　and the particle size above the design maximum diameter for each layer.

Quote: Japan Water Works Association Standard JWWA Water Supply Filter Material A-103: 2006-2
Revised on March 30, 2006