Library: Reports: Cleanup: WT

To: Mike Hessling

From: Lowell McBurney, P.E.

Re: Winston Thomas Trickling Filter Water Treatment

Date: 06/03/99

cc: Jim Patrick, Todd Scoville

Per our discussions on June 1, 1998, this memorandum outlines our proposed approach for water treatment and discharge to the City of Bloomington Wastewater Treatment Plant. It is our understanding that this approach is subject to approval by the City of Bloomington Utility (CBU) Board.

In general, the process water will operate in a closed-loop, which includes a 20,000 gallon frac tenk which feeds the wet screen. Wash water is collected beneath the wet screen in a lined sludge box, pumped through two bag filters, and returned to the frac tank. The frac tank is being operated at about half full to provide excess capacity for storm water collected in the process area and trickling filter. Also, makeup water will be added, as necessary, to replace any water lost to evaporation during the wash process.

Under normal operating conditions, we do not anticipate the need to discharge any water to the CBU sewer. Rather. discharges to the CBU sewer will be necessary under the following conditions:

1 . Excess water accumulation due to high stormwater flows; and

2. Disposal of water at the conclusion of the project.

Outlined herein is our proposed plan to treat this water prior to discharge to the CBU sewer. Specifically, we will circulate water through the filtration system and, rather than sending it back to the frac tank currently being used in the system (Frac Tank #1), we will direct it to another frac tank which will serve as a batch treament tank (Frac Tank #2). Once the water has been processed into Frac Tank #2, the water will be sampled and analyzed for PCBs. If the results are less than 10 micrograms per liter, we would propose discharging this water to the CBU sewer. If the results are greater than 10 micrograms per liter, the water will be transferred back to Frac Tank #1, and a carbon treament system will be mobilized to the site. Once the carbon system is in place, we will process this water through the bag filters and carbon system and discharge into Frac Tank #2. At this point, the water will be resampled and, if below 10 micrograms per liter, the water will be released to the CBU sewer. If it is still greater than 10 micrograms per liter, the process will be repeated.

If necessary, we will mobilize additional frac tanks to the site to maintain production in the trickling filter.

Also, no water will be released to the CBU sewer until analytical results are received, and submitted to the City for approval.

We trust that this approach will be acceptable to the City. It provides the appropriate level of treatment based on the concentration of PCBs in the water. Furthermore, it provides the City with definitive data on a batch basis to ensure that all water is being managed properly.

It is out understanding that the CBU Board will be issuing a discharge permit for these activities. We request that our proposed approach, as outlined herein, be presented to the CBU for review and consideration relative to this permit.

Please do not hesitate to contact me with any additional questions.

LWM/mbl