N.H. Code Admin. R. Env-Wq 707.04

Current through Register No. 25, June 20, 2024

Section Env-Wq 707.04 - Basis of Design Report: Project Need

For existing and proposed projects, the basis of design report shall address the need for the project based on a description or analysis of the following:

(a) Conditions requiring improvements;

(b) The design period for the WWTP, which shall be not less than 20 years unless a shorter design period is shown to be more cost effective when taking into consideration construction of additional facilities needed to meet the peak demand of the 20-year design period.

(c) The design period evaluation shall include:

(1) An evaluation of future expansion requirements in excess of the planning period, when laying out and designing major treatment units and WWTP hydraulics;

(2) Design flows for domestic, commercial, industrial and infiltration/inflow (I/I) flows, as applicable;

(3) Stormwater flows, for WWTPs with combined sewers within the service area;

(4) Design flow values, including the following:

a.Annual average flows;

b.Peak hourly flow;

c.Maximum daily flow;

d.Maximum monthly flow;

e.Minimum monthly flow; and

f.Minimum daily flow;

(5) Total influent TSS and BOD₅ loading, calculated as the sum of domestic, commercial, industrial, and septage loads throughout the design period of the WWTP; and

(6) A mass balance, performed as follows:

a.The mass balance shall be prepared for average conditions and appropriate peaking factors used for peak design conditions;

b.The mass balance shall include BOD₅ and TSS loadings for each appropriate process and for all side streams;

c.The mass balance shall include nutrient loadings when the WWTP is designed for nutrient removal; and

d.Sidestream flows returned to the liquid treatment process as the result of sludge, scum, or other floatable matter processing shall be characterized as to solids and organic content, with the characterization being included in the design loadings for both liquid and solids treatment processes;

(d) Relative to WWTP hydraulics, the basis of design report shall address the following:

(1) Hydraulic profiles of each treatment process on the design drawings indicating water surface elevations for peak hourly and annual average design flows against 25-year flood and average levels of the receiving waters;

(2) Hydraulic design under peak hourly flow conditions, including associated sidestream flows, to be passed through the WWTP with the largest or longest flow path of each unit process removed from service;

(3) Design allowance for maximum flows to pass through the WWTP when and if the largest pump or other piece of mechanical equipment is out of service; and

(4) A minimum velocity of 2.0 feet per second at design annual average flow and 1.5 feet per second at minimum flow in channels carrying unsettled wastewater unless wastewater is managed to prevent sedimentation of solids;

(e) Present and proposed future discharge permit limits, if any; and

(f) The effect on the wastewater treatment process of industrial wastes likely to be encountered in the influent waste stream.

N.H. Code Admin. R. Env-Wq 707.04

Adopted byVolume XXXIV Number 46, Filed November 13, 2014, Proposed by #10693, Effective 10/15/2014, Expires10/15/2024.