Page 137 - The Engineering Guide to LEED-New Construction Sustainable Construction for Engineers

LEED W ater Ef ficiency 117

OR
OPTION 2
Treat 50% of wastewater on-site to tertiary standards. Treated water must be infiltrated or
used on-site.
Potential Technologies and Strategies
Specify high-efficiency fixtures and dry fixtures such as composting toilet systems and non-
water using urinals to reduce wastewater volumes. Consider reusing stormwater or
greywater for sewage conveyance or on-site wastewater treatment systems (mechanical
and/or natural). Options for on-site wastewater treatment include packaged biological
nutrient removal systems, constructed wetlands, and high-efficiency filtration systems.

LEED 2009 Calculations and Considerations
First, the intent of these two options should be further explored as there are many definitions
for sewage and wastewater. For the purposes of this credit, the volumes used for calculating
either option should be based on “blackwater” volumes. As a default, blackwater is the
water from toilets (water closets) and urinals. Some jurisdictions also include kitchen
sinks and other wastewater sources. If these other sources are included, then they should
be specifically noted in the calculations and the local or state definitions provided in the
submittal. In fact, it is usually easier to obtain this credit if blackwater is defined as the
wastewater from toilets and urinals only. In some senses, this is justified for Option 1 as
kitchen sinks need to use potable water. Therefore, for the calculations as outlined in the
following sections for this credit and for WEc3, it will be assumed that blackwater is
the wastewater from water closets and urinals only. Again, any variances from this should
be specifically outlined and noted in the submittals.
The calculations are based on the usage of the building with both a baseline case
and a design case. The baseline for this credit is always based on the same usage of the
building as the design case, but with water usage rates as established as the baseline in
the Energy Policy Act (EPAct) of 1992.
The number of occupants should be differentiated by gender, by employee occupancies,
and by transient occupancies. There are numerous variations of the occupancies based on
various usages, but the typical assumptions for blackwater generation are as listed in Tables
3.2.1 and 3.2.2. These values have been taken from the LEED-NC 2.2 and 2009 Reference
Guides. They refer to the daily usage for a full-time employee equivalent (FTE) on her or his
shift, for the special definition of transient occupancy for water usage (TOW) which is the
summation of each and every transient occupant in the building during a day (the transient
uses have been further subdivided into student/visitor uses and retail customer uses) and
for residential design occupancies. For residential uses these may be higher for certain uses,
particularly for residential facilities where there are many children or retirees, as they may
be home for more hours during the day. Obviously, for special residential uses such as
retirement or nursing homes, the numbers for daily uses would need to be increased
appropriately. Otherwise, the default values in Table 3.2.1 should be used.
Various special notes are needed for some of the blackwater generation rates listed in
Table 3.2.2. Many of the typical values given for some fixtures in the LEED 2009 Reference
Guide have changed significantly from those listed previously in the LEED 2.2 version and
there are two new acronyms being used; HET for High Efficiency Toilet and HEU for High
Efficiency Urinal. The values listed in Table 3.2.2 are from the 2009 version. In the calculations,
actual flow values should be used for the fixtures as designed. Also, composting toilets and
nonwater urinals do not use water for regular usage. They are not currently customary