20131070 Ver 2_More Info Requested_20150521

Strickland, Bev
From: Moore, Andrew W
Sent: Thursday, May 21, 2015 2:13 PM
To: Angelo Accetturo
Cc: Devane, Boyd; davidf.ramsey; Fox, Tim; Davidson, Landon; Price, Zan (George);
Strickland, Bev
Subject: RE: Interim comments on Elk Creek # 13 -1070
This email is to notify you that the Division of Water Resources is putting the subject application on hold until the
information described in the email below is received.
Notice: • po d • and from this address may be IM ' to the North •
Public Records Law and therefore may be disclosed • third parties.
From: Devane, Boyd
Sent: Tuesday, May 19, 2015 2:10 PM
To: Angelo Accetturo
Cc: davidf.ramsey; Fox, Tim; Moore, Andrew W; Davidson, Landon; Price, Zan (George); Strickland, Bev
Subject: Interim comments on Elk Creek # 13 -1070
Although we have not completed our final review of the stormwater plan received by our office on March 13, 2015, we
are writing you now so you can have your engineer get started on making the corrections. While we do recognize that
your engineer did make many of the changes and improvements that we discussed at our February 3rd meeting in
Asheville, there are still some significant engineering calculation errors that need to be corrected and numerous changes
that were not made to the documents. Some of the errors observed and changes that have not been made are:
1. The size of the wet detention pond orifice was not calculated according to our Manual as we specified and a
considerably over -sized orifice was specified. Your plan indicated that a 4" orifice would drain the pond over a
48 hour period. That is not correct. Our quick calculation showed that a 4" orifice would drain the pond in
approximately 8 hours. Some of the reasons for the error were that the .0085 SF orifice calculated by your
1

engineer converts to approximately 1.25" diameter orifice, not 4 inches as was stated. Although 1.25" diameter
seems to be a reasonably close to our estimated number, had we not caught the error, the stormwater would
have never been treated during the life of the project. This is of concern. Furthermore, being one of the most
critical calculations relative to the stormwater treatment device, we would have expected it to be checked
before submittal. As we said in our December 30, 2014 letter, please have your engineer refer to Section 3.5.2
"Orifice Equation" in calculating the estimated drawdown time. In that letter, we specified that the H value
should be divided by three to get an accurate assessment of the average head. His drawing needs correction to
show the "driving head" at 2' not 3' and the average head less than that. His "Calculations" on Sheet 9 of 9
show an incorrect "Orifice Equation" formula. His "Average Head" formula shows a division by 2 although he did
not use an average head but rather the maximum "driving head" in his actual calculation.
2. We were surprised that the specific requests in our July 31, 2014 letter, December 30, 2014 letter and at our
February 3, 2015 meeting regarding the "Water Quality Notes and Calculations" (sheet 9 of 9) have not been
addressed. Again, these are:
a. There is no "filter area" in this plan.
b. The unidentified number (147,580) after the "V" is not the volume. It is the area in SF.
c. The "Volume provided for retention pond is 12,298.33 CF" is an incorrect statement. The supplement
Sheet indicates that the "Volume, temporary pool" is 16,806 CF. The 12,298.33 CF number is probably
the required treatment volume.
3. Although there were some changes made to figures on the "Supporting Calculations" sheet, it still contains
inaccuracies and is still presented in a manner that makes its review difficult. This issue was discussed at our
February meeting but was not addressed. Some of the issues on this page that were discussed but not modified
are:
a. Under "Peak Flow Calculations ", there is still the "DA- 1..... 11 developed area" statement. What
does that statement reference?
b. Also under "Peak Flow °, there is a reference to the "A" being 8.5 acres. We noted that the previous
submittal's 11 acre reference was changed in this submittal to the 8.5 acre number. However, the
calculations below that indicate an 8.0 acre drainage area. Since other calculations in the submittal
were based on 8.0 acres draining to the pond, we assume that these other numbers were an oversight
in the engineer's review. Although the inconsistencies in the project's drainage area may seem minor, it
has been such a significant area of our concern in our correspondence and discussions that we expected
this to be correct in this final submittal.
c. We mentioned in our February meeting that the "Pollutant Removal Calcs: Bioretention" is an
inaccurate heading and should be changed. This was not done.
d. As was in the previous submittal, the misalignment of almost every column with the column headings
makes reviewing the calculations difficult. Please correct.
As we continue our review of the project, we may find other items that are need addressing. We will complete that
review as soon as possible and let you know. If you or your engineer has questions, contact Boyd DeVane at
boyd.devane @ncdenr.gov or at 919 - 807 -6373.
Fil