NC0004308_SOC Application Add Info_20200818

Badin Business Park
Outfall 005 Compliance
Management Plan Update
August 18, 2020
Meeting Overview
2
Introductions
Objectives:
Apprise NCDEQ of BBP’s progress towards Outfall 005 compliance
Present proposed remedy & review path forward
Agenda:
Conceptual model for Outfall 005 drainage basin
Overview of collected field data
Pumping scenario analysis
Proposed solution
Path forward
General Site Layout
3
Conceptual Site Model –005 Basin
4
General:
−Drains approximately 46 acres (Shown in White)
−Consists of stormwater runoff and infiltrated groundwater
−Discharge of process water & ancillary wastewaters discontinued
with Smelter closure in 2010
Structure:
−Comprised of 3 main sewer branches
−Combined discharge flows to Little Mountain Creek via a roadside
ditch adjacent to Highway 740
Water Quality:
−Surface runoff has limited fluoride concentrations
−Bulk of fluoride mass entering as infiltrating shallow groundwater
along the eastern branch
−Infiltrating groundwater maintains a baseflow component which is
diluted by storm flows.
Outfall 005
Roadside Ditch
Little Mountain Creek
•West (red)•East (orange)•Central (yellow)
Overview of 2019-2020 Field Data Collection
5
Objectives
−Characterize water quality and flow from each
area contributing to Outfall 005
−Evaluate variability of effluent concentrations
under different hydrologic conditions
−Quantify magnitudes and temporal variability of
flows for Outfall 005 and Little Mountain Creek
Locations and types of data collected
−Continuous flow data in LMC at Hwy 740,
Outfall 005, and each of the 3 major branches of
the Outfall 005 sewer
−Samples collected at each flow monitoring
location for several storms and analyzed for
fluoride and cyanide
Findings from Field Data Collection –Outfall 005 Flow
6
Flows during December through May averaged 170 gpm with a median flow of 77 gpm
Peak flows during intense storms exceeded 3,000 gpm several times (max = 6,400)
Dry weather flows during summer are <10 gpm
-Monitoring offline due to equipment failure
-System modified to monitor higher flowrates
Findings from Field Data Collection –Little Mountain Creek
7
Flows during December through May averaged 7,400 gpm with a median flow of 1,961 gpm
Peak flows from intense storms exceeded 300K gpm several times (max = 325K)
Dry weather flows during summer have stayed above 100 gpm
-Monitoring offline due to equipment failure
-Monitoring location modified
Outfall 005 Fluoride & Cyanide Concentration
8
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.00
0.50
1.00
1.50
2.00
2.50
3.00
Cyanide (mg/l)Fluoride (mg/l)Fluoride CN - EPA 335.4"
CN - ASTM 7511
Initial
Dilution
Potential
Flushing
Small Storm Event (<0.5 in)Larger Storm Event (1.75 in)
Findings from Field Data Collection –Fluoride
9
Range of fluoride values at
Outfall 005 from storm
sampling: 0.47 –2.5
Range of fluoride values at
Outfall 005 from most recent
two years of DMRs: 0.92 –3.3
Range of fluoride values in Little
Mtn. Creek: 0.047 to 0.15
Within the 1st hour of event
Findings from Field Data Collection –Cyanide
10
Samples were analyzed with EPA 335.4 method and ASTM D7511 method
Results from ASTM method at Outfall 005 were all below chronic criterion
Laboratory NC certification for ASTM method is complete
−Utilized for DMR reporting beginning in July
Outfall 005
Cyanide from
ASTM Method
Outfall 005
Cyanide from
EPA Method
# of samples 56 57
Minimum < 2 µg/L < 2.5 µg/L
Median < 2 µg/L 5.2 µg/L
Maximum 2.7 µg/L 26.0 µg/L
Outfall 005
Cyanide from
ASTM Method
Outfall 005
Cyanide from
EPA Method
# of samples 6 14
Minimum < 6 µg/L < 5 µg/L
Median 3.3 µg/L < 10 µg/L
Maximum 14 µg/L 32.0 µg/L
DMR Data (since beginning of 2020) Study Results
Factors Leading to Evaluating Pumping Scenarios
Outfall 005 Compliance Approach
11
The work to date has yielded improvements, but effluent concentrations exceed current
permit limits at times. How can the 005 discharge be managed (i.e., when and where) to
meet water quality standards in the receiving waters?
Little Mountain Creek has considerable assimilative capacity during wet weather (LMC
drainage area is approx. 78 times as large as 005 drainage area)
Outfall 012 (Badin Lake) has unused assimilative capacity during dry weather (currently
discharges only in response to storms)
Three pumping scenarios were identified and evaluated; these scenarios consist of pumping
different amounts of water from the Outfall 005 drainage area to Badin Lake.
Review -Pumping Scenarios Presented in Nov. 2019 Meeting
12
Scenario A Scenario B Scenario C
Description
Isolate water with
elevated conc’s (must be
less than 40 gpm) and
pump to Badin Lake
Pump up to 40 gpm to
Badin Lake; modify 005
limits based on dilution
in LMC
Pump up to 180 gpm to new,
larger diffuser in Badin Lake;
modify 005 limits based on
dilution in LMC
Pumping rate Up to 40 gpm Up to 40 gpm Up to 180 gpm (approx.)
Modify limits at 005 No Yes Yes
New diffuser in Badin L.No No Yes
Revise mixing zone and
modify limits at 012 No No Yes
The collected field data was utilized to evaluate each of these scenarios
Technical Challenges for Pumping Scenarios
13
Flow rates of water with elevated fluoride concentrations (primarily the subsurface
drain along the east side of the Outfall 005 drainage area) often exceeds 40 gpm
Scenario A is eliminated
Outfall 005 discharges do not meet the current permit limit for fluoride (1.8 mg/L)
at low to moderate flow rates; however, observed concentrations in LMC have met
chronic water quality criteria Scenario B & C are valid options
Pumping more than 40 gpm to Badin Lake would require installing a larger pipe
and diffuser, as well as a revised mixing zone analysis
Uncertainty of jurisdictional status of the roadside ditch that conveys discharges
from Outfall 005 to Little Mountain Creek. Preliminary assessment is the ditch
would be an exempt feature
Proposed Solution
14
The proposed solution is:
Pump up to 40 gpm from Outfall 005 to Outfall 012
during dry periods (Typically June –October)
Flow in excess of 40 gpm will continue to discharge
through Outfall 005
Establish fluoride chronic limit at Outfall 005 to
3.0 mg/L
−Based on critical dilution of 0.7 to 1 in LMC (achieved
99.86% of the time)
Construct pipeline from near Outfall 005 into the
Outfall 012 drainage area
No physical changes or permitting changes to
Outfall 012
Technical Analysis –Long Term Daily Water Balance
15
Long term daily calculations were used to characterize Outfall 005 & Little Mountain
Creek due to limited data availability & no published set of critical conditions (e.g.,
7Q10, 10-yr storm, etc.).
−LMC daily flows estimated as USGS daily flows in Dutchmans Creek multiplied times ratio
of drainage areas (5.62 / 3.44). Period of record was 19 years.
−Outfall 005 daily flows at calculated using SCS Curve Number for surface runoff and “linear
reservoir” for shallow subsurface water (similar to GWLF model). Coefficients in these
calculations were refined based on observed field data.
Dilution ratio in LMC were calculated as flow in LMC divided by discharge from
Outfall 005 (flow at Outfall 005 minus water pumped to Badin Lake).
Watershed Map
16
Long Term Daily Water Balance –Results
17
19 Year Period of Record
Long Term Daily Water Balance –Results
18
Assumptions:
Upstream fluoride concentration was assumed to be constant (0.09 mg/L)
Effluent concentration was assumed to be constant for each trial
Observations:
Ratio of upstream LMC flow to Outfall 005 flow varies greatly on a daily basis
With effluent concentration of 3.0 mg/L, the chronic criterion for fluoride (1.8 mg/L) will be
maintained in LMC about 99.86% or 99.90% of the time with pumping up to 40 gpm or 180
gpm during June –October.
The days when the chronic criterion was predicted to be exceeded in LMC represent scattered,
short term (2 days or less) exposures to concentrations well below the acute fluoride criterion
(24 mg/L).
Long Term Daily Water Balance –Results
19
Path Forward –Schedule
20
Schedule Activity Oct 2019
Proposed Date
Revised Date
(July 2020 Draft SOC)
Site Water Quality & Flow Data Collection May 29, 2020 NA
Model Development & Technical Justification June 09, 2020 NA
Initiate Plans & Specifications for diverting Outfall 005 to Outfall 012 June 17, 2020 June 30, 2020
NPDES Permit Modification Application and Technical Justification Submittal July 27, 2020 NA
NPDES Permit Revision -NCDEQ & EPA Review, Public Comment Period,
Revisions, Final Permit Issuance January 28, 2021 NA
Complete Plans & Specifications NA June 30, 2021
Begin Construction NA October 31, 2021
End Construction, Procurement and Construction of Pumping System October 11, 2021 June 30, 2022
Attain Compliance with the Final Effluent Limitations in the Permit January 10,2022 July 31, 2022
*Current Permit Expires October 31, 2022
The Element of Possibility'