Water Quality Program Facility-specific preliminary determination Water quality standard variance for chloride City of Worthington - MN0031186 / ...
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Water Quality Program
Facility-specific preliminary determination
Water quality standard variance for chloride
City of Worthington
Worthington Wastewater Treatment Plant (WWTP)
MN0031186 / AI 13820
A. City of Worthington Issue Statement
The chloride standard is located in Minn. R. 7050.0222 subp 2. A variance is a temporary change in a
state water quality standard for a specified pollutant and its associated water quality-based effluent
limit (WQBEL) that reflects the highest attainable condition (HAC) for a permittee during the term of
the variance (Minn. R. 7050.0190). All other applicable standards not addressed in this variance
request remain applicable, and the underlying standard for chloride remains applicable. Compliance
with the chloride water quality standard is not feasible because controls more stringent than those
required by sections 301(b) and 306 of the Clean Water Act (CWA) would result in a substantial and
widespread economic and social impact to the community. Upon review of the application, MPCA
staff have determined that the City of Worthington (Permittee) has satisfied the conditions
necessary to grant a variance and, as a result, recommends the Commissioner grant the variance
and include variance conditions in the Permittee’s National Pollutant Discharge Elimination
System/State Disposal System (NPDES/SDS) permit No. MN0031186. The City of Worthington
Wastewater Treatment Facility (WWTP) discharges to Okabena Creek.
B. Worthington WWTP MN0040738
The City of Worthington is located in Nobles County in Southwest Minnesota. The City is located at
the intersection of Interstate Highway 90 and State Highway 60. Land usage surrounding
Worthington is largely agricultural. Worthington WWTP (Facility) is located in the NW ¼ of the NE
1/4, Section 13, T102N R40W, Worthington, Nobles County, Minnesota. This is a Class A facility that
consists of two equalization basins, screening, grit removal, grease removal by aeration, two
primary clarifiers, one first-stage trickling filter, one second-stage trickling filter, four intermediate
clarifiers, two third-stage tricking filters in parallel, five final clarifiers, disinfection (chlorination) and
post aeration. Liquid alum is used for precipitation of phosphorus and biosolids are treated in two
anaerobic sludge digesters, stored as needed in two sludge lagoons, and land applied. The total
number of households served by Worthington WWTP is 4,335. The Facility has a continuousdischarge (SD001) with an average wet weather design flow (AWWDF) of 4.0 million gallons per day (mgd). This permit includes an increase of the design average dry flow to 2.15 MGD but maintains the AWWF. This facility discharges to Okabena Creek (County Ditch No. 12) in the Des Moines River Headwaters with a water ID (WID) of 07100001-540. This waterbody is a Class 7,3C, 4A, 4B, 5, 6 water, considered a low resource value water (LRVW). A chloride impairment exists in Okabena Creek (Elk Cr to Division Cr) at the WID of 07100001-602. This was listed as impaired in 2018 and is approximately 11 miles downstream of Worthington WWTP outfall. The current Effluent Limits Review shows a draft chloride waste load allocation (WLA) of 7,673 lbs/day (3,480 kg/day). C. Factor 6-substantial and widespread economic and social impacts The variance is being pursued because compliance with the WQBELs would result in substantial and widespread social and economic impacts. The municipality used the alternatives analysis and eligibility tool developed by MPCA upon recommendations made the Chloride Working group. This was a group convened by MPCA Commissioner Stine to study the growing problem of chloride in wastewater. This group of eight municipal representatives and two consultant engineers made recommendations that were approved in June 2017. Based on end-of-pipe reverse osmosis and evaporation & crystallization as a tertiary method of treatment, the calculator shows the final limit would cost 5.1% of the median household income (MHI). 5.0% of the MHI would be needed to pay for a drinking water lime-softening plant and removal of all point-of-entry ion exchange water softeners. A reverse osmosis drinking water system and removal of all point-of-entry ion exchange water softeners would cost of 3.4% MHI. Pursuing either option of centralized water softening is problematic because the City invested in a connection to Lewis & Clark Regional Water System (LCRWS) on May 7, 2019. The water is blended with locally produced water at a 50:50 ratio. They City has reported the 1.46 MGD of water from LCRWS has been blended with approximately the same amount of local water. With this blending, the water produced is in the range of 290-325 mg/L hardness. This is considered “very hard” by USGS (121 to 180 mg/L hardness as calcium carbonate). In addition, Worthington Public Utilities supplies drinking water through 10 different wells distributed throughout the City making it even more costly to pursue centralized softening at the City-level. D. Highest Attainable Condition (HAC) MPCA has determined the HAC of the receiving water is achieved through alternate effluent limits combined with a Chloride Investigation and Minimization Plan per 40 CFR 131.14(b)(1)(iii). Thus, the alternate limit included in the table below reflects the greatest chloride reductions achievable with the current treatment processes, in conjunction with the implementation of the permittee’s Chloride Investigation and Minimization Plan. Since May 2019, drinking water is a 50:50 ratio blend of water supplied by Lewis & Clark Regional Water System (LCRWS) and local well water. The City reported using 1.46 MGD of water from LCRWS and approximately the same amount from local wells. LCRWS is a conventional lime softening treatment plant with filtration with a current capacity of 32 MGD that services 300,000 people in southeast South Dakota, northwest Iowa and southwest Minnesota. Minerals (iron and
manganese) are removed using lime, and high levels of hardness are reduced to approximately 9
grains per gallon (~154 mg/L hardness). The other sources of drinking water are 10 wells consisting
of water table and buried drift aquifers present within the Quaternary glacial deposits. These wells
are owned and operated by Worthington Public Utilities and have a hardness ranging from 560
mg/L to 1,040 mg/L (Well Head Protection Plan, 3/2018). The combination of softened water from
LCRWS and well water from the City results in a hardness of 290-325 mg/L (17-19 gains per gallon
hardness) distributed to homes.
MPCA has determined that the City is unable to acquire additional water from LCRWS. The water is
simply not available as allocations of the water have been made by various communities. More
water is a possibility but only until LCRWS expands, and this is not planned.
This change in drinking water resulted in changes to the wastewater sent from people’s homes,
with a reduction of chloride at the end-of-pipe. This is likely due to the changes in water softener
use. Therefore, the alternate limit is developed using effluent values collected since May 2019. The
alternate limit is the maximum measured effluent value of 444 milligrams per Liter (mg/L). A
subsequent alternate limit for chloride must not be defined as less stringent than 444 mg/L. In
other words, this limit will never be less restrictive.
Pollutant Parameter SU Alternate Effluent Underlying WQS Underlying WQS
Limit (Daily Calendar Month Daily Max Limit
Maximum) Average Limit
Chloride mg/L 444 mg/L 230 mg/L 281 mg/L
E. Existing Conditions and ambient water quality
The variance alternate limit for chloride is listed above. This reflects the level currently achievable
and will protect existing conditions. Water softeners have been used and have been discharging to
wastewater treatment plants since the 1940’s, meaning chloride has been in the discharge prior to
1978. The alternate limit of 444 mg/L is discussed above. Pollutant reduction required during the
variance term and the maximum alternate limit requires the discharger to aim below this level,
resulting in an overall reduction. All of this will protect existing conditions. Alternate limits will not
allow the Facility to increase its effluent levels of chloride.
The chloride in the receiving water was monitored in 2008, 2009 and 2014. The average chloride
concentration at the downstream ambient monitoring point nearest to the WWTP is 178 mg/L
(S000-240). The average chloride concentration at the next point downstream is 302 mg/L (S000-
269). Both of these points are in the LRVW portion of Okabena Creek. The next downstream point is
in the Class 2 portion of the stream at S001-568 with a dataset all from 2014. This information is
include as Attachment 1 by map and associated data points.
The receiving water is approximately 11 miles upstream of a water listed as impaired for chloride in
2018. The Draft Des Moines River TMDL Report (Draft TMDL Report) is currently on public notice
until January 6, 2020. The draft Waste Load Allocation for the City of Worthington WWTP is 7,673
lb/day (3,480 kg/day). No other variances exist upstream or downstream of the City of
Worthington. Therefore, there are no additive effects to the water body. However, other
dischargers impact this portion of Okabena Creek and will need to reduce chloride in their dischargein order to comply with the final TMDL. See below for draft WLAs from Table 16 of the
abovementioned Draft TMDL Report.
WLA
New/Revised
Permit Flow Concentration Chloride
WWTP Chloride
Number [cfs] Assumption [lbs/day]1
Permit Limit2
[mg/L]
Brewster WWTP MN0021750 1.997 230 3,831 Yes
Hubbard Feeds Inc - Yes3
MN0033375 0.009 230 17.3
Worthington
Okabena WWTP MN0050288 0.244 230 468 Yes
Worthington Yes
MN0031178 2.16 230 4,143
Industrial WWTP
Yes
Worthington WWTP MN0031186 4 230 7,673
1
WLA calculated using flow (cfs) * concentration (mg/L) * 8.34 (conversion factor) to get WLA (lbs/day)
2
See Section 6.1.4 for discussion of municipal WWTPs and chloride management alternatives
3
WLA may not result in new total chloride effluent limit if the discharge does not have reasonable potential to
cause or contribute to the impairment.
Section 6.1.4 of the Draft TMDL Report states, “During permit issuance or reissuance process,
wastewater discharges will be evaluated for the potential to cause or contribute to violations of the
chloride water quality standard. Water Quality Based Effluent Limits (WQBELs) will be developed for
facilities whose discharges are found to have a reasonable potential to cause or contribute to
chloride above the water quality standards. The WQBELs will be calculated based on low flow
conditions, may vary slightly from the TMDL WLAs and will include concentration based effluent
limitations.” All the facilities listed above are operating under expired permits that have
administratively continued. Considerations will be made when MPCA can begin the reissuance
process related to WQBELs.
The Draft TMDL Report also discusses the flow and ambient sample values. It indicates the chloride
results are higher during low flow conditions which points to point sources as being the primary
source of the impairment. Reductions for all sources will be required to bring the impaired stretch
of Okabena Creek back into compliance. In the case of Worthington WWTP, reductions are required
through this proposed variance and permit reissuance. The final limits comply with the WLA of the
draft TMDL. No increase in existing load is being requested or allowed through this proposed
variance.
F. Protection of human health & endangered species and conformance with antidegradation
Chloride is not considered a pollutant that harms human health at the levels being addressed here.
The variance (alternate limit and source reduction measures) is consistent with the protection of
the public health, safety and welfare. No endangered or threatened species were identified
downstream of the discharge. This variance conforms to MPCA’s antidegradation rules and
procedures (Minn. R. 7050.0250 to 7050.0335). No increase to chloride in the discharge are
requested or approved; the variance will lead to a decrease.G. Term of the Variances
The MPCA proposes a variance term of 15 years. To ensure progress, this variance establishes an
iterative process during which the City must focus on source reduction. Worthington is required to:
1. investigate sources and identify reductions that can be achieved using the best
management practices (BMPs) required in the variance (see draft permit for specific
language);
2. document successful reductions and barriers to success; and
3. adjust BMPs to achieve further reductions.
The variance term allows time for Worthington to conduct a comprehensive investigation of
chloride sources and implementation of chloride reduction actions. In addition, the variance
requires investigation of long-term compliance options. The term of 15 years is reasonable and
appropriate to allow the Permittee to identify sources, evaluate the effectiveness of source control,
and ultimately identify whether there is drinking water or wastewater treatment technology
available to attain compliance with the final limit that would not result in substantial and
widespread negative economic and social impacts. Every five years, at permit renewal, the MPCA
will re-evaluate the conditions of the variance, emerging and available technologies, costs
associated with meeting the final WQBEL, and pollutant minimization strategies. This re-evaluation
ensures that the Permittee is required to reduce chloride to the maximum extent possible. It also
ensures the final effluent limits are met as soon as possible if the conditions under which the
variance was approved have changed.
MPCA supports the 15-year variance term while including permit requirements that allow for the
Permittee to request a subsequent variance if compliance with the final WQBELs remain infeasible
and would result in substantial and widespread economic and social impact. This term will also
allow for long-term compliance options.
H. Nonpoint source control
The draft permit includes language to address nonpoint sources of pollution, such as road salt
application. Due to chloride levels increasing in Minnesota waters, MPCA developed a Smart Salting
Assessment tool (SSAt). This web‐based tool will help winter maintenance organizations assess
operations, identify opportunities to reduce salt using proven best management practices and track
progress. Along with this tool are Smart Salting training opportunities. The permit will require City
staff to attend Smart Salting Training and use the Smart Salting Assessment tool (SSAt). The city
staff chosen shall be a decision-maker in road maintenance and become certified within first three
years of permit issuance. This will satisfy the requirement that Permittees with a variance will
implement cost-effective and reasonable best management practices for nonpoint source control
(Minn. R. 7050.0190 subp. 1(B)). This training will also reduce the amount of chloride being
discharged to the WWTP from spring melting events and inflow and infiltration (I&I). Road salt
intrusion is something that a WWTP needs to reduce by maintaining the collection system, and this
training will benefit the WWTP.L. Compliance and Enforcement
It is staff’s job to review submittals to determine compliance and appropriateness of Plans. MPCA has a
monthly meeting to pull together compliance and enforcement (C&E) staff from different regions of the
state to discuss various topics. A standing agenda item will be the level of detail being looked for in
chloride investigation and minimization plans. As more Plans are submitted and reviewed, a guidance
will be developed to help staff review Plans, with an eye toward successes in other Cities. Because this is
the first plan of its kind where success hinges on reductions made far in advance of wastewater reaching
the WWTP, MPCA staff must be aware of the detailed actions planned by the Permittees. First, staff will
assess the permit to see that all permit conditions have been addressed. Second, the assessment/review
will verify the timeline for implementation to determine adequacy in relation to community resources
(for example, staff time financial ability). Should MPCA have questions about the priority of actions or
timeline, MPCA will reach out to Permittees and ask for more information. The hope is to work with
Permittees to update Plans before enforcement becomes necessary.
Should a Regulated Party be in noncompliance with permit conditions, MPCA has the authority to take
compliance and enforcement action. The MPCA has an Enforcement Response Plan (ERP) that describes
how noncompliance situations are handled. The water quality point source standard guidance in the ERP
outlines how non-construction related compliance schedule violations can be addressed. Below is a
table outlining the response actions, including environmental harm and other variables that may impact
the general starting point. The situations and potential responses are intended solely for the guidance of
MPCA staff, and may change based on specific circumstances. As variances become a more common
part of NPDES/SDS permits in the state, MPCA acknowledges that the ERP needs to be updated if non-
compliances with a variance is encountered. Noncompliance with a schedule of compliance activities in
a permit associated with a variance is considered a violation of a water quality standard.
Violation Situation General Starting Point
Minor Major
Non-construction 30 days late, no environmental harm, LOW LOW
Related Schedule nuisance condition, or limit violations
Implementation (i.e. I
& I Study, Water > 30 days late, no environmental harm, LOW NOV
Balance, etc.) nuisance condition, or limit violations
Environmental harm, nuisance condition,
or limit violations NOV APO
> 90 days late = SNC (regardless of enviro
harm/nuisance condition or limit violation)
LOW –Letter of Warning
NOV – Notice of Violation
APO – Administrative Penalty Order
I. . Submittals
The complete application and eligibility tool were submitted on 8/28/2020. Further information was
requested and received on 10/1/2020. A MPCA staff forum was held to discuss this document on
November 4, 2020.J. Conclusions / Recommendations Upon review of the variance request from City of Worthington, MPCA staff have determined that the Permittee has satisfied the conditions necessary to grant the variance. MPCA staff recommend the Commissioner grant the variance and associated alternate effluent limit and Chloride Inventory and Minimization Plan in the MN0031186 permit for Worthington WWTP. A permit has been drafted and attached that includes the variance and additional requirements. Attachment 1. Map showing ambient monitoring results for chloride. Attachment 2. Completed variance request and eligibility tool for City of Worthington – available upon request
Jack Creek, 2Bg, 3C
Jack Creek,
2Bg, 3C
S001-568
Judicial !
!
Ditch 76,
2Bm, 3C
Tile Line Judicial
Discharge Ditch 84,
# Okabena
2Bg, 3C
Unnamed Creek,
creek, 2Bg, 3C
2Bm, 3C Unnamed
creek,
2Bm, 3C
Total Facilty Judicial
Discharge Ditch 3,
# 2Bg, 3C
Elk Creek,
2Bg, 3C
S007-892 S000-240
! !
!
Unnamed
creek,
2Bg, 3C
S000-269
!
!
Little Sioux
River, 2Bg, 3C
Main Facility
Discharge Okabena
# Creek, 7
Unnamed
Okabena
Creek, Worthington WWTP creek,
2Bg, 3C
2Bg, 3C
Whisky Ditch,
2Bg, 3C
Lake Judicial
Okabena, Ditch 28,
2Bg, 3C 2Bg, 3C
Judicial Ditch
6 (Lake Okabena Judicial Ditch
Outflow), 2Bg, 3C 13 (Skunk
Creek), 2Bg, 3C
Unnamed
53-0024-02-201 creek,
! Judicial
Ocheda Lake, Ditch 9, 2Bg, 3C
2Bg, 3C 2Bg, 3CSYS_LOC_CSAMPLE_DATE CHEMICA REPORT_REPORT_APPROVAL_CODE S000-240 11/17/2008 Chloride 140 mg/L Final S000-240 2/24/2009 Chloride 204 mg/L Final S000-240 3/25/2009 Chloride 98.5 mg/L Final S000-240 4/22/2009 Chloride 131 mg/L Final S000-240 6/1/2009 Chloride 175 mg/L Final S000-240 8/17/2009 Chloride 188 mg/L Final S000-240 9/14/2009 Chloride 335 mg/L Final S000-240 10/21/2008 Chloride 260 mg/L Final S000-240 5/12/2009 Chloride 69.8 mg/L Final S000-269 6/9/2015 Chloride 145 mg/L Final S000-269 5/7/2014 Chloride 350 mg/L Final S000-269 5/21/2014 Chloride 372 mg/L Final S000-269 6/25/2014 Chloride 129 mg/L Final S000-269 7/7/2014 Chloride 158 mg/L Final S000-269 7/30/2014 Chloride 338 mg/L Final S000-269 8/6/2014 Chloride 398 mg/L Final S000-269 8/26/2014 Chloride 322 mg/L Final S000-269 9/9/2014 Chloride 395 mg/L Final S000-269 9/29/2014 Chloride 411 mg/L Final S001-568 5/7/2014 Chloride 200 mg/L Final S001-568 5/21/2014 Chloride 198 mg/L Final S001-568 6/2/2014 Chloride 137 mg/L Final S001-568 6/25/2014 Chloride 46.5 mg/L Final S001-568 7/7/2014 Chloride 54.7 mg/L Final S001-568 7/30/2014 Chloride 188 mg/L Final S001-568 8/6/2014 Chloride 234 mg/L Final S001-568 8/26/2014 Chloride 109 mg/L Final S001-568 9/9/2014 Chloride 344 mg/L Final S001-568 9/29/2014 Chloride 330 mg/L Final S000-269 9/29/2014 Chloride 413 mg/L Final S001-568 9/29/2014 Chloride 329 mg/L Final
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