This water treatment plant was designed to accommodate the requirements of the NPDES Permit issued as part of the construction of the Mill/Bull Tunnel for El Dorado Irrigation District. The plant is a combination of newly patented technologies and conventional treatment technology.


During the contract period at the Mill-Bull tunnel project, a total of 51.5 million gallons of water was treated and released back into nature at the site. The final effluent produced by our water treatment system consistently achieved compliance under the NPDES permit requirements.

Initial Phase of the Water Treatment Process

The treatment process was initiated when a high/low level switch within the Influent Surge Tank triggered the operation of a pump at the interim water storage and sedimentation reservoir located within the existing El Dorado Tunnel. When the 4500-gallon Surge Tank filled with raw influent water, the pump automatically turned off. An emergency overflow pipe was located at the top of the Surge Tank to redirect water back to the tunnel in the event that too much water was pumped to the Surge Tank or the tunnel pump failed to shut off.

Acidification Process

As raw influent entered the Surge Tank, a separate high/low flow control automatically signaled the master control panel to initiate treatment operations. Raw influent was pumped through a series of chemical injector/mixers where a predetermined amount of water treatment additives were injected to the waste stream. The first additive injected (labeled "A" Additive in drawing) was a special patented formulation of carbonic acid and was used to reduce the pH of the raw influent to approximately 2.7. The reduction in pH also served to increase the conductivity to approximately 1000 Mho's.

Housing for Equipment

Ionic State Modification Reactors

Immediately following the acidification, the stream was directed through three separate patented Ionic State Modification Reactors (ISM). The ISM reactors were set at different DC voltage values and had the ability to either oxidize or reduce targeted metals (in this case, specifically manganese, iron and aluminum). Utilization of the ISM technology provided the ability to change the valance states of the target metals in a manner that allowed them to precipitate out of solution using conventional precipitation chemistry.

Additional Water Treatment Additives

As the water exited the ISM reactors, it was injected with a hydroxide solution ("B" Additive) to elevate the pH to approximately 8.5 and an injection of a solution of calcium hypochloride ("C" Additive) immediately followed. This provided approximately 3 ppm of chlorine in the waste stream. Three individual ionic states of manganese were identified in the waste stream. The acidification process altered the first state, the ISM reactors altered the second state and the chlorine attacked the third.

Clarifiers

The waste stream then entered the final injector/mixer where approximately 5 ppm of anionic polymer flocculent were injected. The pretreated water was then directed to the clarifiers. Upon entering the clarifiers, the anionic polymer combined with the cationic charged materials previously injected in a process called "agglomeration". The agglomerated particles formed a heavy floc and settled to the bottom of the clarifier and the clear or "clarified" water decanted from the top.

Effluent Storage and Dwell Tank, Polishing Filters

As the clarified H2O exits the clarifiers, it was directed to a 1500 gallon Effluent Storage Tank where a Sodium Bisulfate based Anti-Chlor compound was injected to remove the previously injected chlorine. The purpose of this tank was to provide a short dwell time for this chemical reaction to occur. A float switch assembly within the Effluent Storage Tank automatically started the Effluent Pump that then directed the clarified water through two Multi-Media Polishing Filters that contained 5 different sizes and types of filtering media. As the polished water exited the filters it was directed through a flow meter and to the discharge pipe and eventually discharged in Spillway #11. A second float switch within the Effluent Tank was installed to automatically shut down the entire treatment plant if a failure was experienced in the Effluent Pump thereby preventing overflow and spill of the clarified water.

Recycling of Water to Tunnel Boring Machine (TBM)

A piping manifold and valve assembly was installed between the Effluent Pump and the Multi-Media Filters to redirect the clarified water to a Recycle Water Storage Tank. The tunnel contractors installed a pump to supply the TBM with clarified water from the Recycled Water Storage Tank. A second pipe was connected from the Canal Siphon Pump to the Recycle Storage Tank to replenish water if the KET plant cannot provide sufficient recycled water for the boring operation. An overflow pipe was installed in the Recycle Water Storage Tank and directed back into the canal should too much water accumulate in the tank.

Spillway Inside Mine


Spillway from Mine Entrance to Housing


Sludge Management System

Periodically, liquid sludge was evacuated from the bottom of the clarifiers and pumped to the 1000-gallon cone-bottom Sludge Decant Tanks. The majority of the settling of the liquid sludge (generally less than .5% solids) occured when it was pumped to Decant Tank #1. As the water within Tank #1 reached the top, it overflowed into the tank #2 to allow for additional solids separation. Excess decant water overflowed from tank #2 back into the Influent Surge Tank where it was reprocessed through the system.

The accumulated solids from the bottom of the decant tanks were periodically pumped through a Filter Press to reduce the thickened sludge to a solid form. The filtrated water from the press was directed back to the Influent Surge Tank for reprocessing in the treatment system.

Sludge Disposal

The product solids were removed from the press and placed in sealed drums for removal and eventual disposal as a classified waste.

Automatic Operation

The Water Treatment System was completely automatic in operation. The design allowed for the system to automatically turn On/Off based upon available raw influent. Several safety features were included to automatically shut the system down for a variety of mechanical failures, low chemical additive levels, tank overflows or other system disruptions. The control panel was connected to a SCADA monitoring system that would automatically notify personnel of system failure during evening hours.

The system was manned 7 days per week. This was necessary in order to monitor pH levels, chemical make-up and daily calibration of monitoring equipment.

Clarifiers


Crystal Clear, Uncontaminated Discharge into Nature

Water Quality

Because of the environmental sensitivity of the area surrounding the Mill/Bull Tunnel Project, stringent discharge requirements were imposed on all waters generated and discharged from the site. The primary metals encountered in the waste stream were Iron, Manganese and Aluminum.

Discharge requirements for these metals are as follows:
· Fe 300 ppb
· Mn 50 ppb
· Al 87 ppb

The metals content of the raw influent varied considerably. These concentrations were impacted by specific activities of the tunnel boring process and by the influence of water due to storm events.

Analysis of the raw influent is as follows:
· Fe 700 ppb to as much as 100,000 ppb
· Mn 240 ppb to as much as 800 ppb
· Al 6100 ppb to as much as 19,000 ppb