344 ENVIRONMF!NTAL ENGINEERING
Groundwater. To prevent contamination of groundwater supplies, the owners
and operators of a solid waste disposal facility must comply with one or more of five
design and operational requirements: (1) utilize natural hydrogeologic conditions like
underlying confining strata to block flow to aquifers, (2) collect and properly dispose of
leachak by installing natural or synthetic liners, (3) reduce the infiltration of rainwater
into the solid waste with correct cover material, (4) divert contaminated groundwater
or leachate from groundwater supplies, and (5) conduct groundwater monitoring and
testing procedures.
Land Used for Food or Forage Crops. Federal guidelines attempt to regulate
the potential movement of heavy metals and synthetic organics, principally polychlori-
nated biphenyl (PCB), from solid waste into crops that are part of the human food chain.
Qpically, the solid waste of concern here is sludge from municipal wastewater treat-
ment facilities. To control heavy metals, the regulations give the operator of such
disposal facilities two options to follow: the controlled application approach and the
dedicated facility approach. The operator electing the controlled application approach
must conform with an annual application rate of cadmium from solid waste. Cadmium
is controlled basically as a function of time and the type of crop to be grown. A
cadmium addition of 2.0 kgma (1.8 lblacre) is allowed for all food-chain crops other
than tobacco, leafy vegetables, and root crops grown for human consumption. An appli-
cation rate of 0.5 kgha (0.45 lblacre) is in force for these accumulator crops. Under
this option, the operator must conform to a cumulative limit on the amount of cadmium
that may be disposed of on food-chain land. This cumulative limit is a function of the
cation exchange capacity (CEC) of the soil and the background soil pH. At low pH
and low CEC, a maximum cumulative application rate of 5.0 kgha (4.50 lb/acre) is
allowed, whereas at high CEC and soils with high or near neutral pH levels, a 20 kgha
(1 8 lb/acre) amount is allowed. The theory is that in soils of high CEC and high pH,
the cadmium remains bound in the soil and is not taken up by the plants. All operators
electing this option must ensure that the pH of the solid waste and soil mixture is 6.5
or greater at the time of application.
The second option open to food-chain landspreaders is the dedicated facility
approach. This option is distinguished from the fist option by its reliance on out-
put control, or crop management as opposed to input control, or limiting the amounts
of cadmium that may be applied to the soil. This second cadmium control option is
designed specifically for facilities with the resources and the capabilities to closely
manage and monitor the performance of their respective operations. The requirements
under this option include: (1) only growing animal feed crops, (2) the pH of the solid
waste and soil mixture is 6.5 or greater at the time of application, (3) there is a facility
operating plan that demonstrates how the animal feed will be distributed to preclude
direct ingestion by humans, and (4) there are deed notifications for future property
owners that the property has received solid wastes at high cadmium application rates
and that food-chain crops should not be grown owing to a possible health hazard.
Solid waste with PCB concentrations greater than or equal to 10mgkg of dry
weight must be incorporated in the soil when applied to land used for producing animal
feed, unless the PCB concentration is found to be less than 1.5 mg/kg fat basis in the
produced milk. By requiring soil incorporation, the solid waste regulations attempt to