Utilization of Electroplating Sludge as Subgrade Backfill Materials: Mechanical and Environmental Risk Evaluation

Table 4

Standard values of soil environmental quality (mg/L).

Heavy metals	Grade I^a	Grade II			Grade III^c
	Natural	pH < 6.5	pH 6.5–7.5	pH > 7.5	pH > 6.5
Cu (farmland)	35	50	100	100	400
Cu (orchard)	—	150	200	200	400

^aLimit values for protecting natural ecology and maintaining the soil quality in the natural setting. ^bLimit values for protecting agricultural productions and human health. ^cLimit values for protecting the normal growth of plants.