Influent
Metro’s discharge permits require that we collect and analyze samples of the wastewater entering (influent) at both RWHTF and NTP for various contaminants.
In Colorado’s discharge permits, the requirements associated with collecting and analyzing samples are called monitoring requirements. In addition to specifying what contaminants need to be monitored, the permits also specify:
The monitoring requirements applicable to the influent of each plant are generally intended to provide the state regulators, the Water Quality Control Division (WQCD) within the Colorado Department of Public Health and Environment (CDPHE) and the EPA with information about the contaminant levels in the wastewater that we need to treat, information about federal and local contaminants of concern that are or may need to be regulated by Metro’s IPP, and part of the information that they need to understand how well we are treating certain contaminants.
Each of Metro’s discharge permits also include a specified “design capacity” rating or amount of flow and contaminant loadings that each plant can treat.
Colorado law requires that the design capacity for POTWs be determined by WQCD engineers. The WQCD engineers base their determination upon technical information that the POTW provides for its facilities and the WQCD’s specific engineering criteria for POTWs.
The design capacity in discharge permits for POTWs is expressed in terms of hydraulic flow (in million gallons per day, MGD) and organic loading (in pounds or tons of 5-day biochemical oxygen demand (BOD5) per day or carbonaceous biochemical oxygen demand (cBOD) per day).
Metro’s specified design capacity for the RWHTF is 220 MGD and 212 tons of BOD5 per day and for NTP is 28.8 MGD and 53,300 lbs. of BOD5 per day.
If the flow and/or organic loading in the wastewater influent exceeds 85% and 90% of the permit specified design capacity Metro’s permits for both RWHTF and NTP include required steps to expand the capacity of the treatment facility. Metro’s discharge permits also include treatment removal requirements for CBOD5 and Total Suspended Solids (TSS). The treatment removal requirement for CBOD5 and TSS for both RWHTF and NTP is 85%; this means that Metro must remove, through its treatment processes, 85% of the CBOD5 and TSS that enters each plant.
Metro is required to conduct the following influent monitoring:
Influent monitoring to provide information about flow and organic loadings received at RWHTF and NTP and how well we are treating certain contaminants:
Influent monitoring to provide information about contaminants that may be of federal concern or local concern for Metro’s IPP:
There is also required influent monitoring for several specific toxic contaminants that are required under federal regulations under 40 CFR 122, Appendix D.