Land treatment of wastewater 431Water quality
Monitoring of water quality for land application systems is generally more
involved than for conventional treatment systems because non-point discharges
of system effluent into the environment are involved. Monitoring of water
quality at several stages of a land treatment process may be needed for process
control. These stages may be at: the applied wastewater, the renovated water,
and the receiving waters - surface water or groundwater.
The water quality parameters and the frequency of analysis will vary from
site to site depending on the nature of the applied wastewater. The measured
parameters may include:
- Those adversely affect receiving water quality either as drinking
water supply or as irrigation water supply, - Those required by regulatory agencies, and
- Those necessary for system control.
An example of a suggested water quality monitoring program for a large
scale SR system is presented in Table 8.11. Renovated water may be recovered
as runoff in an overland flow system, or as drainage from underdrains, or
groundwater from recovery wells in SR and RI systems.
Groundwater
In groundwater, travel time of constituents is slow and mixing is not as
significant as with surface water. Surface inputs near a sampling well will move
vertically and arrive at the well much sooner than inputs several hundred meters
away from the well. Thus, the groundwater sample represents contributions
from all parts of the surface area with each contribution arriving at the well at a
different time. A groundwater sample may reflect surface inputs, especially
inorganic constituents such as heavy metals, from several years before sampling
and have no association with the land application system. Consequently, it is
imperative to obtain adequate background quality data and to locate sampling
well so that response times are minimized.
If possible, existing background data should be obtained from wells in the
same aquifer both beyond and within the anticipated area of influence of the
land application system.
Wells with the longest history of data are preferable. Monitoring of
background wells should continue after the system is in operation to provide a
base for comparison.
In addition to quality, the depth to groundwater should be measured at the
sampling wells to determine if the hydraulic response of the aquifer is consistent
with what was anticipated. For SR systems, a rise in water table levels to the