NC0023884_201 Plan_19940422

April 22, 1994
MEMORANDUM
TO:
FROM: Betsy Johnso THROUGH: Steve Bevington �pQQ
J
Ruth Swanek 2CS
Monica Swihart
SUBJECT: Salisbury 201 Plan
pC.00 2-3$S4
The 201 plan refers to the environmental assessment but that document has only one page about
water quality impacts. There is a great deal of historical water quality information available on
High Rock Lake. In addition, Environmental Sciences has recently completed a water quality
report on High Rock Lake. This report contains data on Grants Creek and Town Creek as well
as the lake data. There is also quite a bit of self -monitoring data on Grants and Town Creek
which should be summarized in the EA.
The no -action alternative should include a discussion of the age of the existing plant and its
operational difficulties. The report should specifically discuss the parameters of concern, i.e.,
oxygen -consuming wastes, toxics, and nutrients. The pretreatment program should also be
discussed. The action alternatives should more clearly discuss how current operational
difficulties will be resolved. Each of the alternatives should address the capability for future
expansion.
The discussion of the pump station and diffuser system is premature. We have reviewed
preliminary designs and stressed that the effluent must be pumped through nozzles on the
diffuser to get a good exit velocity, i.e., approximately 10 ft/sec. At low exit velocities such as 4
ft/sec as mentioned in the 201 plan, there is little initial mixing provided by the diffuser. The
diffuser should achieve an initial dilution of at least 10:1 while not interfering with recreational
uses in the lake headwaters. Additionally, the diffuser will reduce acute impacts of the effluent
and reduce bank attachment of the effluent plume. To date, a design has not been approved.
If you have any questions or comments, please call me at Ext. 508.
cc: Mooresville Regional Office