Delaware Engineering, D.P.C.
28 Madison Avenue Extension Albany, New York 12203
Tel: 518.452.1290 Fax: 518.452.1335
July 11, 2025
The Honorable Mayor Karen Smythe Village of Red Hook 7467 S Broadway, Red Hook, NY 12571
Subject: Village of Red Hook WWTP – May 2025 Sewer Report
Dear Mayor Smythe:
Significant mechanical repairs and operational changes were performed at the WWTP in May 2025 by the Village’s DPW and our staff that resulted in the UV units returning to operation on May 13, 2025 and the Old Plant being placed in operation on May 28, 2025.
In May, the hydraulics of the WWTP and the internal hydraulics of the Purestream treatment unit were tested to determine if the plant can operate as designed and/or as provided. Our conclusion is that it cannot and that modifications are needed to operate the plant and meet the discharge limits.
The major items that need modification include replacing the EQ pumps by removing the three 35 gpm pumps and replacing them with two 25 gpm pumps and increasing the available EQ/Surge tank capacity to allow for this lower flow rate.
The lower influent pumping flow rate is needed because the Purestream plant cannot operate at a flow rate above 35 gpm or the mixed liquor suspended solids (MLSS) “the bugs” are flushed out of the system causing permit violations. From the Basis of Design report, it was anticipated by the design engineers that the Purestream plant could handle flows up to 70 gpm for several hours without any effect on treatment. Similarly, the downstream sand filter cannot operate successfully at flows between 35 and 70 gpm.
The failure in the Purestream plant is the design of the clarifier and the return sludge pumping system. Per their literature, their design provides a shallow hopper clarifier that requires a 4 to 1 ration of return sludge flow to forward flow to provide settlement and avoid the MLSS from being washed out. The system provided has an air lift pump that is capable of a 1 to 1 ratio. We added submersible pumps to provide the specified 4 to 1 flow ratio and the system still did not work as promoted. This deficiency in the internal hydraulics of the Purestream plant makes its very difficult to operate the plant and requires additional vigilance by the operator.
This disconnect between the installed influent pumping capacity and the treatment unit’s hydraulic capacity was the reason the previous operator could not grow a MLSS population that is needed for treatment.
Additionally, the MLSS requires sufficient air to grow to a population that is needed for full treatment. By operating the WWTP, we determined that the air provided by the Pureshtream system is only half of what is needed to operate the plant. We were able to overcome this deficiency by using both blowers at maximum speed. This means the plant does not have the standby spare blower (air) capacity that is needed to meet code. To address this issue, the spare sand filter blower will be piped to the aeration tank blower’s header piping.
223 Main Street Goshen, New York 10924 845.615-9232
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16 East Market Street Red Hook, NY 12571 518.452.1290
Delaware Engineering, D.P.C.
To return the UV units to operation, we had to abandon the Evoqua control board and install a generic control system. The UV lights and the UV units are capable of disinfecting the effluent but the units need to be kept clean for the fecal coliform limit to be met. Cleaning a minim of once per week is needed.
The effluent water quality has improved from April’s but the WWTP has not improved enough to meet all the effluent limits.
The following data is extracted from the DMR reports attached to this letter.
|Parameter|Units|Result Old Plant|Result New Plant|Limit| |---|---|---|---|---| |Average Day Flow|mgd|.020|.033|0.025/0.05 (1) max| |Total Suspended Solids (TSS)|mg/L|10.7|43.4|10 max| |CarbonaceousBOD5 (5-Day)|mg/L|4.6|7.5|5max| |Total AmmoniaNitrogen(asN)|mg/L|1.4|15.24|1.8 (2)max| |UOD|Mg/l|22.8|84.6|34 max| |Fecal Coliform|MPN/100|<1|2500|200 (3) max| |Dissolved Oxygen|mg/L|9.04|7.1|7min|
Notes:
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Outfall 1A (New Plant) has a monthly average flow limit of 50,000 gpd and outfall 1B (Old Plant) has a monthly average flow limit of 25,000 gpd.
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The limit for Total Ammonia Nitrogen (as N) is 0.98 mg/L from June 1[st] to October 31[st] and 1.81 mg/L from November 1[st] and May 31[st] .
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The limit for Fecal Coliform is regulated as 200 No./ 100m over a 30-Day geometric mean and 400 No./ 100m over a 7-Day geometric mean.
Please call me at 518-452-1290 if you have any questions.
Sincerely,
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Roberto Flores, P.E.
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