Central Valley Regional Water Quality Control Board fileCalifornia Regional Water Quality Control Board Central Valley Region Board Meeting – 31 May and 1 June 2018 Response To Written

California Regional Water Quality Control Board Central Valley Region

Board Meeting – 31 May and 1 June 2018

Response To Written Comments For Tentative Waste Discharge Requirements For

Union Mine Landfill Class II Landfill, Closed Class III Landfill and Class II Surface Impoundment

Operation, Maintenance, Closure, and Post-Closure Maintenance El Dorado County

At a public hearing scheduled for 31 May and 1 June 2018, the Central Valley Regional Water Quality Control Board (Central Valley Water Board) will consider adoption of Waste Discharge Requirements (WDRs) for discharges from the Union Mine Landfill (facility) located in El Dorado County. This document contains responses to written comments received from interested parties regarding the tentative WDRs. Written comments from interested parties were required by public notice to be received by the Central Valley Water Board by 20 April 2018 to receive consideration. El Dorado County (Discharger), who owns and runs the Facility, was the only interested party to submit comments. Written comments from the Discharger that were received on 18 April 2018 are summarized below, followed by the responses of Central Valley Water Board staff. Based on the comments, Central Valley Water Board staff revised the tentative WDRs and Monitoring and Reporting Program (MRP) and made minor changes to correct typographical errors. Additionally, Central Valley Water Board staff added some clarifying language, which is detailed in the comment section below. A clarification meeting was held at the Central Valley Water Board between Water Board staff and the Discharger on 19 April 2018. This Response to Written Comments letter also includes responses to additional clarification comments provided by the Discharger during the 19 April 2018 meeting. During addressing the comments, numbering of the WDRs and MRP contents got changed from the tentative order. The new number of the content is provided in parenthesis following the old number in the tentative order.

EL DORADO COUNTY (DISCHARGER) COMMENTS On 18 April 2018, the Discharger provided comments regarding the tentative WDRs and Monitoring and Reporting Program. These comments are provided in italics below, along with Central Valley Water Board staff’s responses.

COMMENTS ON WDR FINDINGS Page 2, Finding 4: Typo "MWU-1" should be "WMU-1".

Response: Staff incorporated the comment by changing “MWU-1” to “WMU-1” in fourth sentence of Finding 4. REASON: Typographical correction. PROPOSED REVISION: Finding 4 to read “The Facility is on a 321.6-acre property located at 5700 Union Mine Road, El Dorado County, CA. The 41.3-acre landfill is comprised of a 35.3-acre unlined Class III Old landfill WMU and a 6.0-acre lined Class II Expansion landfill WMU. The Class II surface impoundment area is 0.84 acres. The Class II Expansion landfill WMU and Class III Old Landfill WMU of the Facility are designated as WMU-1 and the Class II surface impoundment is designated

Response to Comments - 2 - Union Mine Landfill

as WMU-2. The existing permitted WMU-1 and WMU-2 areas are shown in Attachment B. The Facility is comprised of Assessor’s Parcel Numbers (APN) 092-011-17, -20 and -21.”

Page 2, Finding 4: Parcel No. need '0' (092-); Missing APN 092-011-17; Delete 092-011-028- BLM combined parcel not county owned

Response: Finding 4 is based on the APNs provided in section 3.D of Joint Technical Document (JTD) rev 2018 and the APNs are 92-011-20, -21 and -28. APNs provided in section 1.A.1 of the JTD rev 2018 are 92-011-20 and -21. Staff incorporated the comment by changing “92-011-20, -21 and -28” to “092-011-17, -20, and -21”. REASON: To provide correct and accurate information. PROPOSED REVISION: See proposed revision to previous comment.

Page 3, Finding 7, Table Line 1: 36.3 ac and 34.1 ac - most recent map shows 35.3 and 33.1 respectively

Response: Section 1.B of JTD rev 2018 says that “34.1 acres of the Class III Old Landfill Area closed in accordance with CCR Title 23, Title 14, and current Title 27. The closed 34.1 acres includes 13.6 acres closed in 2007 and 20.5 acres (comprised of 4.9 acres closed in 1997 and 14.6 acres closed in 1998. An additional acre was added to these two areas to account for the surface areas of slopes).” A similar description can be found in the monitoring reports as well. Staff incorporated the comment by changing “36.3 acres” and “34.1 acres” to “35.3 acres” and “33.1 acres” in row 1 of Finding 7 table. Staff also changed “14.6 acres including an 1-acre sloped area” to “14.6 acres and a 1-acre sloped area” in row 3 of the table. REASON: To provide correct and accurate information. PROPOSED REVISION: Unit Area Liner/LCRS1 Components Unit Classification &

Status

Class III Old landfill WMU

35.3 acres (total)

Unlined, constructed over native materials.

Class III, filled and closed 33.1 acres as of 2006. The remaining 2.2 acre has an interim cover.

4.9 acre Final cover top to bottom: a one-foot thick vegetative layer, a one-foot thick low permeability layer and two-foot thick foundation layer.

Closed during October 1997

14.6 acres and a 1-acre sloped area

Final cover top to bottom: a one-foot thick vegetative layer, GCL 2, and two-foot thick foundation layer.

Closed during fall 1998


Unit Area Liner/LCRS1 Components Unit Classification & Status

13.6 acres including 0.6-acre inactive landfill area

Final cover top to bottom: one-foot thick vegetative soil layer, a drainage layer of double-side geotextile fabric, a 60-mil LLDPE 3 geomembrane, and existing interim cover (two-foot minimum thick clay/foundation layer with maximum hydraulic conductivity of 1 x 10-7 cm/sec4) to provide foundation layer

Closed in November 2007

Page 4, Finding 9 (8): Acreage 34.1 or 33.1- see above comment

Response: Staff incorporated the comment by changing “34.1 acres” to “33.1 acres” in first line of Finding 9. REASON: To provide correct and accurate information. PROPOSED REVISION: Finding 9(8) to read “On-site facilities at the Union Mine Landfill property include: 33.1 acres of the closed Class III Old landfill WMU, 2.2 acres of Class III Old landfill WMU with interim cover and 6 acres of active Class II Expansion landfill WMU; …”

Page 6, Finding 22 (21): "Corrugated pipe" should be PVC. There is no LRCS sump between Class II landfill and Class II pond.

Response: Section 8.C.2 of JTD rev 2018 says that “The LCS on the north perimeter of the Class III Old Landfill Area consists of a perforated corrugated polyethylene (CPE) pipe in a gravel filled trench. This LCS is located at the toe of the slope where the CPE pipe conveys the collected leachate to the Class II Surface Impoundment via a solid wall CPE pipe, and is described in the Construction Report,...” Staff incorporated the comment by changing “Corrugated polyethylene (PE) pipe” to “polyvinyl chloride (PVC) pipe”, and “Leachate from the Class II Expansion landfill WMU is collected through the LCRS pipes to LCRS sump and conveyed through a solid wall pipe…” to “Leachate from the Class II Expansion landfill WMU is collected through the perforated high density polyethylene (HDPE) LCRS pipes and conveyed through a solid wall HDPE pipe…” REASON: To provide correct and accurate information. PROPOSED REVISION: Finding 22 (21) to read “Leachate from the unlined Class III Old landfill WMU is collected through the toe-drain constructed at the toe of the Class III Old landfill WMU slope. The toe-drain consists of a perforated polyvinyl chloride (PVC) pipe in a gravel filled trench. The perforated pipe transitions to a solid wall PVC pipe at the end of the toe-drain to convey the leachate to the Class II surface impoundment by gravity flow. Leachate from the Class II Expansion landfill WMU is collected through the perforated high density polyethylene (HDPE) LCRS pipes and conveyed through a solid wall HDPE pipe to the Class II surface impoundment by gravity flow. Total leachate flow discharged from the WMU-1 to the Class II surface impoundment is measured monthly and 808,060 gallons of leachate was discharged to the Class II surface impoundment in 2017, as reported in “Fall 2017 Semiannual Monitoring Report”. Table in Finding 24 shows the constituents presence in the landfill WMUs leachate.”


Page 8, Finding 25 (24) Table: Typo "zink".

Response: Staff incorporated the comment by changing text “Zink” to “Zinc”. Staff also made changes to the “Background Groundwater Data” column to address Discharger’s comment to Finding 74 (73). REASON: 1) Typographical correction, and 2) MRP R5-2006-0020 allowed the Discharger to update concentration limits at least annually. The Discharger annually updated the concentration limits. The Central Valley Water Board requested the Discharger to submit an updated WQPS due to the concerns with elevated concentration limits proposed for monitoring parameters in Spring 2016 Semiannual Monitoring Report. In response to the request, the Discharger proposed a new statistical method and concentration limits for monitoring parameters in Fall 2017 Semiannual Monitoring Report. The Central Valley Water Board staff is reviewing the proposed statistical method and the concentration limits. The Central Valley Water Board has not issued an approval letter for proposed concentration limits in the past. To address the Discharger’s comment to Finding 74, these WDRs use the concentration limits proposed in Fall 2017 Semiannual Monitoring Report since the last approved concentration limits are not available. However, Title 27 §20400 (b) allows the Central Valley Water Board to approve, modify or disapprove each proposed limit and each proposed statement. PROPOSED REVISION: Finding 25 (24) table change to read “….

Constituent Unit Concentration CA Primary

MCL

Lowest Applicable

WQO

Background Groundwater

Data a, d

Cla

ss II

Sur

face

Im

poun

dmen

t

Cla

ss II

Sur

face

Im

poun

dmen

t LC

RS

Sum

p

WM

U-1

LC

RS

Pipe

Monitoring Parameters b Alkalinity mg/L 30 49 200 316.7 Bicarbonate mg/L 30 49 200 316.7 Chloride mg/L 19 44 79 250 f 40 Nitrate as Nitrogen

mg/L 1.3 3.2 43 10 CA Primary MCL

1.74

Sulfate mg/L 12 280 83 250 f 198.3 TDS mg/L 100 530 690 500 f 608 Inorganics e ZinkZinc µg/L ND 11 17 Notes: a Monitoring parameter concentration limits from Fall 2017 Semiannual Monitoring Report……”

Page 9, Finding 26 (25): "Discharge_ is a 'designated waste' and ... must be discharged to a Class II WMU". Liquid in sump is not "leachate" as demonstrated by field testing which shows the liquid is consistent

Response to Comments - 5 - Union Mine Landfill with ground water in the vicinity of the Class II surface impoundment. (See comment for finding 77} Liquid from the Class II surface impoundment is treated at the Waste Water Treatment Facility {WWTF}, for which it was designed and built. After treatment, effluent is discharged to either the spray fields located at the facility or to El Dorado Irrigation District (under permit). This practice is covered under the WDR {RS-2006-0019}. In addition, findings 40 and 70 state that arsenic and iron are naturally occurring, therefore the citation of arsenic should be deleted from finding 26.

Response: Finding 26 (25) did not call out the liquid in the Class II surface impoundment LCRS sump as “leachate”. Staff did not incorporate the comment. Staff added clarification to the finding as in proposed revision. PROPOSED REVISION: Finding 26 (25) to read “The analytical data generated from sampling and analysis of leachate from the WMU-1 and liquid from the Class II surface impoundment LCRS sump shows that the concentrations of some of the constituents, including, but not limited to arsenic, nitrate, manganese, sulfate and TDS, exceed the primary MCL or the lowest applicable WQO. Additionally, VOCs were detected in the Class II surface impoundment samples during the second semiannual 2017 monitoring event. The data indicate that some of the discharges to the Class II surface impoundment consist of or contain pollutants that, under ambient environmental conditions at a WMU, could be released in concentrations exceeding applicable water quality objectives or that could reasonably be expected to affect beneficial uses of the waters of the state. Therefore, the discharge is a ‘designated waste’ and as such must be discharged to a Class II WMU as required by Title 27.

Page 9, Finding 27 (26): Concerning erosion at active section of Class II expansion? Spec F.6 SPRR (pg9) Environmental Management Department (EMD) respectfully requests that this item is removed from the WDR. Erosion was a result of severe winter storm conditions as documented by the Colinty and cited by RWQCB and the LEA. The County is already adhering to a compliance plan approved by the LEA and RWQCB. All repair work will be completed by October 2018. Having it in the WDR implies the issue is ongoing, which is not correct. It is a maintenance issue that is being addressed.

Response: The findings in the WDRs document the historical issues at the Facility. Staff added text “As a result of severe winter storm conditions,” to the finding. REASON: To address Discharger’s concern PROPOSED REVISION: Finding 27 (26) to read “…Soil excavated during grading operations for the spray fields was stockpiled along the north edge of the concrete lined Storm Water Diversion Channel and is being used for daily cover in the Class II Expansion landfill WMU. Additionally, the Discharger uses soil acquired from CalTrans for daily and intermediate cover. When the Discharger suspends waste disposal at the Class II Expansion landfill WMU, an intermediate cover is applied across the active section of the Class II Expansion landfill WMU. As a result of severe winter storm conditions, excessive erosion was observed across the entire active section of the Class II Expansion landfill WMU and along the eastern downgradient face of the Class II Expansion landfill WMU during inspection by the Central Valley Water Board staff on 21 November 2017...”

Page 10, Finding 30 (29): ... destructed, plugged and capped ... EMD respectfully requests that "Destructed" should be changed to "Closed" per USDA, Natural Resources Conservation Service - practice code 457.

Response: Staff incorporated the comment by changing text “destructed” to “closed”.


REASON: To use appropriate wording. PROPOSED REVISION: Finding 30 (29) to read “…... Numerous interconnected slopes, shafts, and tunnels exist beneath the active and inactive portions of the disposal site. Three mine tunnels, one mine adit, one stope and one mine shaft are located in the vicinity of the WMU-1 expansion area. In preparation to WMU-I landfill expansion the Springfield shaft collar and the Minerva Tunnel adit were closed, plugged and capped in 1993”

Page 10, Finding 33 (32): Should describe "residential parcels" as "rural residential" as they are zoned.

Response: Staff incorporated the comment by adding text “rural” to “residential parcels”.

REASON: To provide accurate information. PROPOSED REVISION: Finding 33 (32) to read “Land uses within one mile of the Facility include rural residential parcels to the north, east, south and west; and agricultural parcels to the northwest of the Facility. Land owned by the Bureau of Land Management borders the Facility to the north, east and south.”

Page 11, Finding 39 (38): GW depth type - 80' should be 120' (MW10).

Response: The finding was based on the information in section 11.F.1 of JTD rev 2018. Staff incorporated the comment by changing text “80” to “120”. REASON: To provide accurate information. PROPOSED REVISION: Finding 39 (38) to read “Groundwater beneath the Facility occurs in fractured bedrock, valley alluvium, and the underground mine workings. Groundwater flow direction is towards the east and southeast. Groundwater ranges in depth from less than 10 feet to 120 feet below ground surface.”

Page 12, Finding 48 (47): SS-3 (UM-3-spring) -SS-3 is surface water sample location; UM-3 spring is a spring. They are not the same sample location.

Response: Staff incorporated the comment by changing “UM-3” to “Lower” per Central Valley Water Board staff’s letter “Response to Discharger Request to Reconsider Additional Approved Work, Union Mine Landfill, El Dorado County” dated 26 September 2016.

REASON: To provide correct sampling location.

PROPOSED REVISION: Finding 48 (47) to read “The Union Mine Landfill site exhibits springs which flow seasonally or year around as reported by the Discharger. The springs are sampled and monitored per MRP requirements. During the 14 February 2018 site inspection by the Central Valley Water Board staff, springs were observed at monitoring locations SS-1, SS-3 (Lower Spring) and MS-1.”

Page 13, Finding 58 (57): "WMU-1 share a common monitoring system" - please clarify this statement as we are unclear what this means.

Response: Title 27 §20415 (e)(3) states monitoring system for shared system as “If a facility contains contiguous Units, separate ground water monitoring systems are not required for each such Unit if the discharger demonstrates to the satisfaction of the RWQCB that the water quality


monitoring program for each Unit will enable the earliest possible detection and measurement of a release from that Unit”. WMU-1 consists of Class II Expansion landfill WMU and Class III Old landfill WMU. The landfill WMUs do not have separate monitoring system as the Class II surface impoundment has, they share the same monitoring system. Staff did not make any changes to the finding.

Page 14, Finding 62 (61): Typo - "enter" should be "entering".

Response: Staff incorporated the comment by changing text “enter” to “entering” in “Location” column for S-1 and S-2.

REASON: Typographical correction.

PROPOSED REVISION: Finding 62 (61) table to read

Sampling Point Location Type

S-1 In the unnamed tributary prior to entering the west sedimentation basin

Detection

S-2 Outfall discharge from the north sedimentation basin prior to entering Martinez Creek

Detection

Page 15, Finding 64 (63): GW 'drain' should be GW location GWD-3 is noted as a drain but is a spring SS-3 (surface sample location) and UM-3 (spring/seep sample location) are two different sample locations.

Response: Staff incorporated the comment by changing text “Groundwater drain” in “Location” column for GWD-3 to “Spring”. Sampling location of SS-3 is Lower Spring (see response to Finding 48 comment).


PROPOSED REVISION: Finding 64 (63) to read “Monitoring programs at the Union Mine Landfill site also includes monitoring of Pendar Tunnel, groundwater drains and springs. The sampling locations are tabulated in following table and shown in Attachment B:

Sampling Point Location

GWD-1 Union Mine Road underdrain GWD-2 Class II landfill WMU underdrain GWD-3 Spring west of spray fields Pendar Tunnel Discharge from Pendar Tunnel SS-1 Springfield shaft spring SS-2 Springfield shaft pond SS-3 Lower spring to Springfield shaft

Page 15, Finding 67 (66): Detection triggers EMD respectfully requests the insertion "'may' indicate that a release of waste from a Unit has occurred" and Insertion "'potential' release verification testing must be conducted ... ".


Response: Finding 67 (66) is the standard language in Central Valley Water Board’s WDRs. Staff did not incorporate the comment and did not make any changes to the finding.

Page 16, Finding 70 (69): Reference to finding 41; should be finding 40 (pg 11) concerning naturally occurring As & Fe.

Response: Staff incorporated the comment by changing text “41” to “39”.


PROPOSED REVISION: Finding 70 (69) to read “Arsenic and iron are naturally occurring constituents in groundwater at the Union Mine Landfill site and are not used for detection monitoring for the landfill WMUs. See Finding 39.”.

Page 16/17, Finding 71 (70): Exceedance in MW13 - see following comment for finding 74.

Response: Staff incorporated the Discharger’s comment to Finding 71 by changing the 2015 concentration limits to 2017 concentration limits.

REASON: The Central Valley Water Board has not issued any approval letters to proposed concentration limits in the past. See response to Finding 25 (24) and 74 (73).

PROPOSED REVISION: Finding 71 (70) table to read

Monitoring Parameter

MW-5 MW-6 MW-7 MW-9 MW-10

MW-11

MW-12

MW-13

UM-3 CL a

TDS 290 340 300 290 360 170 510 650 b 290 608 Bicarbonate 210 190 250 250 220 76 210 500 b 220 316.7 Alkalinity 210 190 250 250 220 76 210 500 b 220 316.7 Chloride 2.1 3.8 1.6 1.6 3.5 12 < RL 55 b 21 40 Nitrate-N ND ND ND ND ND ND ND < RL < RL 1.74 Sulfate 37 110 27 27 70 32 32 72 39 198.3 Calcium 70 54 23 29 65 10 61 75 31 168 Magnesium 11 10 4.0 11 8.2 11 23 40 b 14 27.5 Potassium < RL < RL 1.2 1.4 < RL 0.41 7 b 7.1 b 1.3 4.43 Sodium 13 22 62 b 38 17 10 39 36 59 b 55.1 Arsenic 0.0033 0.0025 0.0067 0.0097 0.0067 0.0040 0.140 0.0063 0.004 - Iron ND ND < RL 0.14 0.58 4.0 0.83 0.610 ND -

CL - Concentration Limit ND – Non-detect RL – Reporting limit All concentrations are in mg/L a Fall 2017 Semiannual Monitoring Report b Concentration limit exceedance

Page 18, Finding 74 (73): Quarterly monitoring-See Provision H.16.F (pg45) -MW-11 exceedance for Chloride. Exceedance is based on 2015 limits which were calculated from an abbreviated data set (2006-2015). Limits have been recalculated using historical data (1990's to 2015) and an approved statistical method (EPA's ProUCL program}, showing that there is no exceedance for chloride.

Response to Comments - 9 - Union Mine Landfill RWQCB compliance staff was provided with the revised calculations in December 2016. It is not reasonable to hold EMD accountable to the 2015 limits until "approval" of the updated limits is provided by RWQCB as the methodology was provided to the RWQCB more than one year ago. Furthermore, the 2016 and 2017 Annual Reports were accepted by RWQCB compliance staff leading EMD to believe that the new methodology was acceptable.

Response: Staff incorporated the Discharger’s comment to Finding 74 by deleting the chloride concentration limit exceedance in MW-11 and the reference to 2015 concentration limits. Staff also corrected cross-reference to Finding 58 and added monitoring well WM-10 to monitoring wells that monitor the deeper groundwater zone.

REASON: 1) MW-11 did not show chloride concentration limit exceedance with 2017 concentration limits. 2)MW-10 was added to match with Finding 57 (56) table.

PROPOSED REVISION: Finding 74 (73) to read “Based on the groundwater elevation and the monitoring well screen depth provided in Finding 56, background well MW-6 and MW-10, and detection wells MW-7, MW-9 and UM-3 are monitoring the groundwater quality in the deeper groundwater zone. The Discharger installed monitoring wells MW-12 and MW-13 to monitor the shallow groundwater in the vicinity of MW-9 in October 2016. MW-13 is 47.6 feet deep and the screen interval is 29 to 46 ft from the top of the casing. During the last sampling event, this monitoring well had 1.5 feet of water column. The depth and/or screen depth of MW-13 may not be adequate to yield a representative sample of groundwater quality. The Discharger shall monitor the groundwater elevation quarterly, and lower the screen interval as described in Provision H.16.F. Additionally, monitoring well MW-11 is 80 feet deep with a screen interval from 58 to 78 feet from the top of the casing and pump inlet depth located 77.50 feet below the top of the casing. The groundwater level in this monitoring well historically varied between 37 and 51 feet from top of casing. Title 27 §20415 (b)(1)(B) requires the monitoring points to be installed at appropriate location and depths to yield groundwater samples from uppermost aquifer that represent the quality of groundwater passing the Point of Compliance and to allow for the detection of a release from the unit. The Discharger shall analyze historical groundwater depth variation in each of the detection monitoring wells that monitor the groundwater shallow zone, and evaluate the monitoring well’s depth, screen interval and pump intake depth in compliance with Title 27 requirements, as described in Provision H.16.F

Page 18, Finding 75 (74): Evaluation of vertical and lateral extent of groundwater impact - propose corrective action -See Provision H.16.G (pg46)- Exceedances are based on 2015 limits, which as explained above, are not appropriate to evaluate impacts. EMD respectfully requests that this provision is removed from the tentative WDR. Should monitoring wells MW-7, 9 & UM-3 be destroyed if they are no longer compliance points in the tentative WDR? (See finding 75 of the tentative WDR)

Response: Staff addressed the Discharger’s comment to Finding 75 by comparing second semiannual 2017 sampling event analytical results to 2017 concentration limits.

REASON: The Central Valley Water Board has not issued any approval letters to proposed concentration limits in the past. See response to Finding 25 (24), 71 (70) and 74 (73).

PROPOSED REVISION: Finding 75 (74) to read “Monitoring parameter concentration limit exceedances in down gradient monitoring wells for WMU-1 may indicate that groundwater has been impacted by a release from the WMUs at the site. The following constituent concentration limit exceedances were observed in monitoring wells during second semiannual 2017 sampling event:


a. MW-7 – Sodium b. MW-12 - Potassium c. MW-13 – TDS, bicarbonate, alkalinity, chloride, magnesium and potassium d. UM-3 - Sodium

Concentration limit exceedance for sodium were historically observed in monitoring wells MW-9, MW-7 and UM-3 till 2015. MW-7 shows an increasing trend for sodium concentration based on the data set from 2006 to 2017. MW-9 and UM-3 showed decreasing trends from 2006 to 2014 and show increasing trends after 2014 except the second semiannual 2017 sampling event. Elevated concentrations of chloride, magnesium and potassium were observed in the newly installed monitoring wells MW-12 and MW-13 compared to other detection wells for WMU-1. Although the chloride concentration in MW-12 was below the laboratory reporting limit during the fourth quarter 2017 sampling event, based on the detection history at this location, it may be an anomalous detection. A timeseries plot of chloride and potassium in monitoring well UM-3 show an increasing trend. TDS concentration exceeded EPA recommended water quality criteria for taste and odor (250 mg/L) and even the California secondary MCL for taste and odor (500 mg/L) in MW-12 and MW-13 during second semiannual 2017 sampling event. Additionally, cobalt and zinc (5-year inorganic COCs) were observed at elevated concentrations in MW-11 while other detection monitoring wells for WMU-1 show non-detects for cobalt and zinc during three sampling events from 2006 to 2016. These concentration limit exceedances, increasing trends, and elevated concentrations of monitoring parameters and 5-year inorganic COCs may indicate that groundwater has been impacted by a release from the WMUs at the site. The Discharger shall evaluate the source of these groundwater impacts, the lateral and vertical extent of the groundwater impact or release migration, and propose corrective actions as described in Provision H.16.G.”

Page 19, Finding 76 (117): Competency of Class Ill Old Landfill cover - see Provision H.16.H (pg46) EMD respectfully requests that this provision be removed as it is a compliance issue not a condition of a WDR. Also see Comment for finding 102, pg 24.

Response: Staff did not incorporate the Discharger’s comment to Finding 76. The requirements set in the WDRs are the conditions for the compliance. Staff moved Finding 76 to Finding 117.

REASON: The finding documents the history of the site.

Page 19, Finding 77 (76): Leachate leaking past liner materials - leak test required -see Provision H.16.J (pg47) Class II surface impoundment detection system is not five-feet above groundwater level and at the time of installation, this was acceptable by the RWQCB. Water in LCRS sump has a lower pH (6-7) relative to the high pH (9-10) generally found in the Class II surface impoundment indicating the impoundment is not leaking. The LCRS sump was designed and approved by Water Board in early 1990's and five-foot minimum groundwater clearance was not required back then and therefore should be accepted as is. EMD respectfully requests that this provision is removed from the tentative WDR.

Response: CCR Title 23 Chapter 15 regulated the discharges of waste to land since 1984 until Title 27, and Chapter 15 §2530 (c) requires 5-feet separation from base of the waste to highest anticipated elevation of underlying groundwater. See Finding 103. The leak detection and collection layer collects liquid that may be leaking through the Class II surface impoundment liner system and acts as an underdrain to collect seasonally rising underlying groundwater. An action leakage rate cannot be established to the Class II surface impoundment geomembrane (primary liner) because of the way that the Class II surface impoundment was constructed. Additionally, it is unclear whether the liquid in the Class II surface impoundment LCRS


sump is leachate or groundwater and there is no reliable vadose zone monitoring to the Class II surface impoundment. Therefore, the Discharger shall perform a leak location test to check whether the Class II surface impoundment geomembrane is leaking. Staff modified Finding 77 as in proposed revision, to clarify the Class II surface impoundment construction and the leak detection and collection layer functions, and to address the Discharger’s concern regarding “leaking” liner.

REASON: To add clarification to the finding.

PROPOSED REVISION: Finding 77 (76) to read “During the second semiannual 2017 sampling event, monitoring well MW-A showed a concentration limit exceedance for potassium. The Discharger suggested that the continuous concentration limit exceedance of potassium at monitoring well MWA is most likely due to the clay liner installed below the Class II surface impoundment. The Class II surface impoundment liner system consists of, top to bottom, a 60-mil HDPE geomembrane, two-foot clay liner and two gravel filled leak detection and collection trenches running the length of the Class II surface impoundment. The leak detection and collection layer collects liquid that may leak through the Class II surface impoundment liner system and acts as an underdrain to collect seasonally rising underlying groundwater. The Class II surface impoundment LCRS sump collects liquid from the leak detection and collection layer. Estimated volume of liquid pumped from the Class II surface impoundment LCRS sump back to the Class II surface impoundment was 2,000 gal in 2017. The leak detection and collection layer may not be collecting all liquid coming in contact with the clay liner. Liquid not collected in the leak detection and collection layer may be passing the Class II surface impoundment LCRS sump and may cause continuous concentration limit exceedance for potassium in MW-A. Further, it is unclear whether the liquid in the Class II surface impoundment LCRS sump is leachate or groundwater. No liquid was collected in the suction lysimeters installed below the Class II surface impoundment leak detection and collection layer. The Discharger reported that the lysimeters L2N and L2S do not collect sufficient liquid for sampling because a significant capillary zone does not develop in the crushed rock fill beneath the Class II surface impoundment. An action leakage rate cannot be established for the Class II surface impoundment geomembrane (primary liner) because of the way that the Class II surface impoundment was constructed. Since there is no reliable vadose zone monitoring for the Class II surface impoundment, the Discharger shall perform a leak location test as described in Provision H.16.K, to check whether the Class II surface impoundment geomembrane liner is leaking.”

Page 20, Finding 80 (79): Results cited are from UM-3 spring. SS-3 has never been sampled because the location is always dry.

Response: Staff incorporated the comment by deleting the analytical results presented in SS-3 column and added text “Not Sampled – Dry”. Staff also changed the 2015 concentration limits to 2017 concentration limits.

REASON: To provide correct information and to address the changes to Finding 68.

PROPOSED REVISION: Table of Finding 80 (79) to read


SS-1 SS-2 SS-3 Concentration Limit (Fall 2017

Semiannual Monitoring Report)

TDS 460 Not Sampled

- Dry

4Not Sampled -

Dry

2251.4

Bicarbonate 290 2 1284.7


Alkalinity 290 2 1284.7 Chloride 59 6 151.5 Nitrate-N < RL < 12.44 Sulfate 96 9 676.7 Calcium 93 9 342.6 Magnesium 26 2 117 Potassium 5.2 5 213.4 Sodium 32 3 132.7 Arsenic 1.4 0 00.11 Iron 14 6 00.275

Page 21, Finding 84 (83)/85 (84): Acreage 36.3 and 34.1 should be 35.3 and 33.1 respectively.

Response: Staff incorporated the comment by changing text “36.3” to “35.3” in Finding 84 (83) and text “34.1” to “33.1” in Finding 85 (84).

REASON: To provide correct information

PROPOSED REVISION: Finding 84 (83) to read “The existing 35.3-acre Class III Old landfill WMU is unlined and constructed over native materials. The Class III Old landfill WMU was sited above-grade over some of the mine's interconnected stopes, shafts and tunnels. This unit no longer accepts wastes.” and Finding 85 (84) to read “According to the 2018 ROWD/JTD, 33..1 acres of the Class III Old landfill WMU have received final cover and 2.2 acres remains to be closed…”

Page 23, Finding 93 (92): There is no sump near the Class II cell or at junction of the leachate pipe and toe drain.

Response: Staff incorporated the comment by changing text “…has a LCRS which discharges leachate collected from base of the WMU to its sump, to where the toe drain along the junction between Class II Expansion and Class III Old landfill WMUs discharges leachate collected from the Class III Old landfill WMU toe.” to “…has a LCRS which consists of perforated HDPE pipes that transition to a solid wall HDPE pipe which discharge leachate collected from the Class II Expansion landfill WMU to the Class II surface impoundment”.

REASON: To present correct information PROPOSED REVISION: Finding 93 (92) to read “The 6.0-acre Class II Expansion landfill WMU constructed in 1996, is lined with a composite liner system as described in Finding 7. The Class II Expansion landfill WMU has a LCRS which consists of perforated HDPE pipes that transition to a solid wall HDPE pipe which discharges leachate collected from the Class II Expansion landfill WMU to the Class II surface impoundment.

Page 24, Finding 102 (101): Measurement of leachate into Class II surface impoundment - see Spec D.10 - Spec D.10 does not exist - Please provide correct citation. Concerning septic waste measurement into Class II surface impoundment: wash out of the septic waste which discharges into the Class II surface impoundment is not easily measurable due to has extremely low, intermittent volume. EMD respectfully requests that the septic waste wash out be estimated as there is no feasible way to measure with instrumentation.

Response: Staff incorporated the comment by changing “... above inflow volumes…” to “…LFG condensate and liquid pumped from the Class II surface impoundment LCRS sump to the Class II surface impoundment…” and “.. Discharge Specification D.10.” to “… Facility Specification C.11”.


REASON: The Discharger explained that the flow volume from the septage truck washout area is very less and it is an intermittent flow. There is no appropriate location to install a flow measuring device. PROPOSED REVISION: Finding 102 (101) to read “Inflow volumes: LFG condensate, liquid from septage truck washout area discharged to the Class II surface impoundment, and liquid pumped from the Class II surface impoundment LCRS sump back to the Class II surface impoundment have not been monitored by the Discharger. The discharger shall measure and record the LFG condensate and liquid pumped from the Class II surface impoundment LCRS sump to the Class II surface impoundment as described in Facility Specification C.11.”

Page 24, Finding 103 (104): Leak detection test required - see Provision H.16.J (pg47) The RWQCB assumes that the Class II surface impoundment is leaking based on the estimated 2,000 gallons removed in 2017. The liquid removed has been demonstrated, by field testing, to be consistent with groundwater in the vicinity of the Class II surface impoundment and not leachate contained within the impoundment. The Class II surface impoundment is emptied and cleaned annually. While empty, the impoundment is inspected and repaired, if necessary. EMD respectfully requests that this finding be amended or removed from the provisions as a leak would be a compliance issue not a requirement of the WDR and there is no credible evidence that the Class II surface impoundment is leaking.

Response: See response to Finding 76. Staff made changes to the finding as in the revision to address the functions of the leak detection and collection layer and removed reference to Provision H.16.J. REASON: See reason to Finding 77 (76).

PROPOSED REVISION: Finding 103 (104) to read “Based on information provided by the Discharger in the JTD/ROWD (2018) and site records, the Class II surface impoundment was not constructed with a LCRS that meets Title 27 §20340 requirements. Title 27 requires the LCRS to be installed between the liners for surface impoundments. Site records do not indicate that there is a secondary liner underlying the two-gravel filled leachate collection trenches that underlay the clay liner. The leachate collection trenches function as a leak detection and collection layer to the Class II surface impoundment liner system and as an underdrain to maintain the separation from the waste to the underlying groundwater.”

Page 24, Finding 104 (103): Five-foot separation from Ground Water - Class II surface impoundment - see Prov. H.16.K (pg48) Five-foot separation was not required when the Class II s0.93urface impoundment was installed in the early 1990's. EMD respectfully requests that this provision is removed from the tentative WDR or revised to recognize that the five-foot separation was not required when the impoundment was constructed.

Response: To incorporate the comment, staff revised the finding as in the proposed revision. Staff deleted Provision H.16.K.

REASON: The Class II surface impoundment was not built with 5-foot separation. The leak detection and collection layer also functions as an engineered alternative to maintain groundwater separation to the waste in Class II surface impoundment.

PROPOSED REVISION: Finding 104 (103) to read “The Class II surface impoundment was not


designed, constructed, or is being operated to meet the minimum of 5-feet separation from base of the waste to highest anticipated elevation of the underlying groundwater in accordance with Title 27 §20240 (c) [also CCR Title 23 Chapter 15 §2530 (c)]. However, the Class II surface impoundment was constructed with a leak detection and collection layer that functions as an engineered alternative to maintain groundwater separation. Therefore, the Discharger shall continue to remove liquid from the Class II surface impoundment LCRS sump to maintain liquid level below the leak detection and collection layer discharge pipe elevation in the Class II surface impoundment LCRS sump (Facility Specification C.18).”

Page 27, Finding 117 (118): Require iso-settlement maps every 5-yrs post closure. Title 27, Section 21090 (e)(1) & (2) states: "The RWQCB shall apply the requirements of this paragraph only to a closed landfill which the RWQCB finds is likely to undergo differential settlement of such magnitude as to impair either the Unit's containment features (e.g., final cover) or the free drainage of surface flow. Furthermore, additional iso-settlement maps are not required at 5-year intervals until "At least every five years after completing closure of the landfill [or of the last remaining portion, for landfills undergoing incremental closure ... II There is no evidence that settlement is occurring in the closed portion of the landfill, at a magnitude that would "impair containment features". EMD respectfully requests that 5-year iso-settlement maps are deferred until final closure of the Class II cell. EMD agrees to conduct an initial iso-settlement map of the closed portions, but requests an extension of the date of completion to summer 2019 in order to budget funds.

Response: This is a standard language in Central Valley Water Board’s WDRs. Staff modified Provision H.16.I and MRP Facility Monitoring A.7.c to address the Discharger’s comment.

REASON: The Class III Old landfill WMU is currently partially closed. Every five year iso-settlement shall be performed upon full closure of the Class III Old landfill WMU.

PROPOSED REVISION: Provision H.16.I to read “As detailed in MRP R5-2018-XXXX, iso-settlement survey maps shall be prepared for the closed portion of the Class III landfill WMU (Finding 118)”. And the compliance date was added as “31 October 2019”

Page 28, Finding 120 (121): Cost estimate for Class II surface impoundment closure and establish closure fund - "see Spec. F.2" Section 22221 of Title 27 requires that the operator of a "disposal facility" demonstrate financial responsibility. The leachate control system was not included in the Union Mine Landfill Final Closure Cost estimate because all LCRS improvements will be completed during active operations with no further improvements required at closure. In addition, the County has been operating under the assumption that the Class II Surface lmpoundment would be accepting leachate in perpetuity. Does the RWQCB anticipate the future closure and deconstruction of the impoundment? EMD respectfully requests that this requirement is removed from tentative WDR.

Response: The surface impoundment will need to be eventually closed as a clean closure or as a landfill when the landfill WMUs no longer generate leachate, in accordance with Title 27 §20950 (a) and the Central Valley Water Board shall require the Discharger to establish an irrevocable closure fund with the Central Valley Water Board as beneficiary in accordance with Title 27 §22207 (a). Staff did not incorporate the comment and did not make changes to Finding 120.

REASON: The Discharger shall establish financial assurance for closure of the Class II surface impoundment.


COMMENTS ON WDR PROHIBITIONS, SPECIFICATIONS & TASKS

Page 35, C.4: "Discharger shall post signs about driving on closed portion of landfill" Since the first closure phase of the landfill approximately 22 years ago to the present, EMD is unaware of any prior request by the RWQCB, Ca/Recycle or LEA to post this signage on the landfill. Periodic driving of vehicles by landfill staff is necessary to complete inspections and maintenance. Ruts found during the visit by the RWQCB were associated with unforeseen maintenance issues due to record rainfall in 2017. EMD respectfully requests that this requirement is removed from the WDR.

Response: Staff deleted Facility Specification C.4 since Prohibition 8 states that operation of any equipment on the closed landfill WMUs that will likely damage the landfill cover is prohibited. Facility Specifications were renumbered because of Facility Specification C.4 deletion.

REASON: The comment was discussed with the Discharge who will make situational decisions depending on the condition of the landfill cover.

Page 36, C.15: Record rainfall at facility. This is already required by WDR RS-2006-0019

Response: Comment noted and staff did not make any changes to Facility Specification C.15.

REASON: Facility Specification C.15 is standard language in WDRs. Page 37, C.22 (C.23): Testing of solids from Class II surface impoundment EMD respectfully requests that the RWQCB explain the rationale for testing the solids in the Class II surface impoundment. Solids within the impoundments, after liquids evaporate in the summer months, consist of air borne dirt and dried algae. Solids are disposed of in the Class II expansion cell.

Response: During the meeting on 19 April, the Discharger stated that the Class II surface impoundment is emptied and cleaned before each winter season and the solids are disposed in the Class II Expansion landfill WMU. Staff added a finding after Finding 101 and revised Facility Specification C.22 which is renumbered to C.23

REASON: To document current operational practice at the Facility.

PROPOSED REVISION: Added finding (new Finding 102) to read “The Class II surface impoundment is emptied and cleaned annually before the winter season. The solids removed from the Class II surface impoundment are disposed in Class II Expansion landfill WMU”. Facility Specification C.22 (C.23) to read “Solids that accumulate in the Class II surface impoundment shall be periodically removed to maintain minimum freeboard requirements and to maintain sufficient capacity for surface impoundment leachate and for the discharge of wastes. The removed solids from the Class II surface impoundment shall be disposed in Class II Expansion landfill WMU. ”

Page 40, F.2: By 12/31/2018 Closure C.E. for Class II Surface impoundment to RWQCB; provision H.4.N -typo should be H.16.N (pg50). Date conflicts with H.16.N which states the due date as 2/1/2019.

Response: The Discharger shall submit the cost estimate by 31 December 2018 and establish financial assurance within two months from approval of cost estimate by Central Valley Water Board


staff. Staff corrected reference to Provision H.16.O in Financial Assurance Specification F.2 and changed compliance date for Provision H.16.O.

REASON: Typographical correction

PROPOSED REVISION: Financial Assurance Specification F.2 to read “…, for the Class II surface impoundment closure in at least the approved amount of the current closure cost estimate, adjusted for inflation annually, as detailed in Provision H.16.O.” and Provision H.16.O compliance date to read “Cost estimate by 31 December 2018 and establish financial assurance within two months from approval of cost estimate by Central Valley Water Board staff.”

Page 40, F.6: By 12/31/2018 Corrective Action Cost Estimate for Class II surface impoundment; provision H.4.N -typo -should be H.16.N (pg50). Date conflicts with H.16.N which states the due date as 2/1/2019.

Response: The Discharger shall submit the cost estimate by 31 December 2018 and establish financial assurance within two months from approval of cost estimate by Central Valley Water Board staff. Staff changed reference to Provision H.16.O in Financial Assurance Specification F.6, and changed compliance date for Provision H.16.O.


PROPOSED REVISION: Financial Assurance Specification F.2 to read “…, for the Class II surface impoundment closure in at least the approved amount of the current closure cost estimate, adjusted for inflation annually, as detailed in Provision H.16.O.” and Provision H.16.O compliance date to read “Cost estimate by 31 December 2018 and establish financial assurance within two months from approval of cost estimate by Central Valley Water Board staff.”

COMMENTS ON MRP

Page 5, A.3.a: Typo -"lmpoundment0" should be "lmpoundment”.

Response: Staff incorporated the comment by deleting “0”


PROPOSED REVISION: A.3.a table to read Mon Pt. Unit Where Sump is Located

WMU-1 Leachate Pipe

Pipe at East of Class III Old landfill WMU prior to discharge to the Class II surface impoundment

Class II surface impoundment LCRS sump

East of Class II surface impoundment

Page 7, A.5: S-8 does not exist.

Response: S-8 is a new sampling location added to the revision of MRP. Staff deleted word “current” in section A.5.

PROPOSED REVISION: Section A.5 to read “…The surface water monitoring points for the landfill


are:” Page 8, A.6: SS-3 and UM-3 spring are two separate data collection points. SS-3 has been dry during monitoring events and therefore never sampled.

Response: Staff deleted “UM-3 Spring” in SS-3 of Sampling Point column

REASON: To present correct information.

PROPOSED REVISION: SS-3 sampling location in Sampling Point column to read “SS-3 ” Page 16, C.1.e: RWQCB is reviewing statistical methods; use concentration limits from Fall 2015 for Fall 2017. As stated previously (see comment for finding 74), RWQCB compliance staff was provided with the revised calculations in December 2016. It is not reasonable to hold EMD accountable to the 2015 limits until "approval" of the updated limits is provided by RWQCB as the methodology was provided to the RWQCB more than one year ago. Furthermore, the 2016 and 2017 Annual Reports were accepted by RWQCB compliance staff leading EMD to believe that the new methodology was acceptable. EMD respectfully requests that this condition is removed from the WDR as it is conditional upon approval of the statistical method and may impact future data review associated with the tentative WDR.

Response: The staff modified two paragraphs on page 17 as in the revision.

REASON: The staff concurred with Discharger’s comment since the Class III Old landfill WMU is currently partially closed.

PROPOSED REVISION: Section C.1 (page 17) to read “…The Discharger proposed the methods for calculating concentration limits in the Appendix D “Statistical Analysis of Background Data and Development of Site Concentration Limits” of Fall 2017 Semiannual Monitoring Report. The 2017 concentration limits were calculated using Interwell nonparametric 95 percent upper prediction limits with 95 percent coverage based on background data from background monitoring wells MW-5, MW-6 and MW-10 for WMU-1, and parametric 95 percent upper tolerance limit with 95 percent coverage based on background data from background monitoring well MW-C for WMU-2.”

Page 17, C.4: Concentration Limits – pending RWQCB approval of statistical method – See previous comment. As stated previously (see comment for finding 74), RWQCB compliance staff was provided with the revised calculations in December 2016. It is not reasonable to hold EMD accountable to the 2015 limits until "approval" of the updated limits is provided by RWQCB as the methodology was provided to the RWQCB more than one year ago. Furthermore, the 2016 and 2017 Annual Reports were accepted by RWQCB compliance staff leading EMD to believe that the new methodology was acceptable. EMD respectfully requests that this condition is removed from the WDR as it is conditional upon approval of the statistical method and may impact future data review associated with the tentative WDR.

Response: Staff changed concentration limits from 2015 to 2017 and deleted reference to 2015 concentration limits. These WDRs use 2017 concentration limits.

REASON: The Central Valley Water Board has not issued any approvals for proposed concentration limits in the past. Staff concurred with the Discharger’s comment.

PROPOSED REVISION: Section C.4 to read “…As noted above, the Discharger proposed an


update to method of calculating concentration limits and concentration limits for naturally occurring constituents in the Fall 2017 Semiannual Monitoring Report. The concentration limits for select parameters as reported in the Fall 2017 Semiannual Monitoring Report were as follows:


Concentration Limit for MWU-1

Concentration Limit for MWU-2

TDS 608 576

Bicarbonate 316.7 202.8

Alkalinity 316.7 202.8

Chloride 40 73.3

Nitrate-N 1.74 0.97

Sulfate 198.3 156.6

Calcium 168 96.4

Magnesium 27.5 28.1

Potassium 4.43 3.5

Sodium 55.1 38.4 All concentrations are in mg/L

Monitoring Wells Comment: Should monitoring wells MW-7, 9 and UM-3 be destroyed if they are no longer compliance points in the tentative WDR? (see finding 75 of the tentative WDR)

Response: Monitoring wells MW-7, MW-9 and UM-3 would become corrective action monitoring wells upon implementation of any corrective action to the WMU-1.

COMMENTS ON INFORMATION SHEET Page 1, Paragraph 2: 36 acres. Should be approximate 35 acres.

Response: Staff incorporated the comment

REASON: To present correct information

PROPOSED REVISION: First sentence in para 2 to read “The Facility is comprised of three Waste Management Units (WMUs) in all—two separate units for municipal solid waste (MSW Units), 6 and 35 acres in size, and a single 0.8-acre Surface Impoundment with a capacity of 2 million gallons.”

Page 1, Paragraph 4: 36.3 and 34.1 should be 35.3 and 33.1.

Response: Staff incorporated the comment

REASON: To present correct information

PROPOSED REVISION: Paragraph 4 to read “ The 35.3-acre Class III Old landfill WMU is unlined, constructed over native materials and sited above-grade over some of the mine’s interconnected


stopes, shafts and tunnels. This unit no longer accepts wastes and was partially closed in portions since 1997 in accordance with the requlatory requirements at the time of closure. 33.1-acres of this unit was previously closed and 2.2-acres has an interim cover and has not been closed.”

Page 2, Paragraph 1: Class II expansion does not have a sump that collects leachate. Leachate flows directly to the Class II surface impoundment.

Response: Staff modified the paragraph.

REASON: To address the Discharger’s comment and to match with the changes to WDR Finding 94.

PROPOSED REVISION: Page 2, Paragraph 1 to read “The 6.0-acre Class II Expansion landfill WMU constructed in 1996, is lined with a composite liner system. The Class II Expansion landfill WMU has a LCRS which consists of HDPE pipes that transition to a solid wall HDPE pipe which discharges leachate collected from the Class II surface impoundment. This unit was constructed with an underdrain system to maintain the minimum 5 feet separation from waste to the highest anticipated elevation to underlying groundwater and the underdrain …”

Page 2, Paragraph 3: Class II surface impoundment liquid pumped to WWTF and spray fields is not fully accurate. Liquid from the Class II surface impoundment is pumped to the WWTF (per the WWTF WDR RS-2006-0019}, treated along with septic waste, pumped to holding tanks, and then either chlorinated and discharged to the spray fields or not chlorinated and discharged to the El Dorado Irrigation District under permit.

Response: Staff incorporated the Discharger’s comment by changing the paragraph as in the revision.

REASON: To provide correct information

PROPOSED REVISION: Page 2, Paragraph 3 to read “The liquid stored in the Class II surface impoundment is pumped to the onsite WWTP treated along with septic waste, pumped to holding tanks, and then either chlorinated and discharged to the spray fields or not chlorinated and discharged to the El Dorado Irrigation District under separate permit..”

Page 3, Paragraph c: Typo - "requiremetns" should be "requirements"

Response: Staff incorporated the Discharger’s comment.


PROPOSED REVISION: Page 3, c) to read “Updated post-closure maintenance requirements for the partially closed Class III Old landfill WMU”

CENTRAL VALLEY WATER BOARD MODIFICATIONS

Nomenclature: Staff made typographical corrections to the Class II Expansion landfill WMU and Class III Old landfill WMU throughout the WDRs and MRP.

REASON: For consistency of terminology used in the WDRs and MRP. General Corrections: Staff made minor corrections to texts throughout the WDRs and MRP, and the

Response to Comments - 20 - Union Mine Landfill corrections did not change the content of the document.

REASON: For numbering, typographical corrections, consistency, cross-references and readability.

WDRs Page 2, Finding 4: Landfill and WMU areas were corrected per Discharger’s comment to Finding 7.

REASON: To provide correct and accurate information. REVISION: Finding 4 to read “The Facility is on a 321.6-acre property located at 5700 Union Mine Road, El Dorado County, CA. The 41.3-acre landfill is comprised of a 35.3-acre unlined Class III Old landfill WMU and a 6.0-acre lined Class II Expansion landfill WMU. The Class II surface impoundment area is 0.84 acres….”

Page 6, Finding 19 (18): During meeting on 18 April 2018, the Discharger stated that the solids removed from cleaning the Class II surface impoundment before each winter season were disposed of in the Class II Expansion landfill WMU. Staff added solids from the Class II surface impoundment to types of solids disposed at the Class II Expansion landfill WMU. Staff renumbered the findings.

REASON: To add solids types that are allowed to dispose to the Class II Expansion landfill WMU REVISION: Finding 19 (18) to read “The Discharger proposes to continue to discharge non-hazardous solid waste, including non-hazardous de-watered wastewater treatment plant sludge, solids from the Class II surface impoundment and other general non-hazardous solid waste including municipal solid waste, to the lined Class II Expansion landfill WMU. These classified wastes may be discharged only in accordance with Title 27, Resolution 93-62, and Subtitle D as required by this Order.”

Page 7, Finding 23 (22): Staff added functions of the Class II surface impoundment leak detection and collection layer, changed “Provision H.16.I” to “Provision H.16.J” and renumbered the findings.

REASON: To address the Discharger’s comment to Finding 77 REVISION: Finding 23 (22) to read “The leak detection and collection layer underlying the clay liner in the Class II surface impoundment liner system functions as a leak detection and collection layer to the liner system and as an underdrain to maintain separation between the waste and the underlying groundwater. Liquid collected through the leak detection and collection layer is discharged to the LCRS sump, from where the liquid is pumped back to the Class II surface impoundment. The total quantity of liquid pumped from the Class II surface impoundment LCRS sump has not been historically measured. Estimated volume of liquid pumped from the Class II surface impoundment LCRS sump is approximately 2,000 gallons in 2017. The Discharger shall install a flow totalizer to the Class II surface impoundment LCRS sump pump discharge pipe as detailed in Provision H.16.J. The flow rates shall be monitored and reported per the MRP requirements.”

Page 13, Finding 53 (52): Staff changed groundwater elevation variation from “9 feet” to “2 to 14 feet”.

REASON: The groundwater elevation varied approximately 9 ft in monitoring wells in 2017. Looking at last 10 years data, the groundwater elevation varied from 2 to 14 feet. REVISION: Finding 53 (52) to read “Groundwater elevations range from about 1115 feet MSL to 1295.8 feet MSL during second semiannual 2017 monitoring event. Groundwater elevation


seasonally varies approximately 2 to 14 feet in monitoring wells.” Page 16, Finding 69 (68): Staff changed the text as in the Revision to address the Discharger’s comment to Finding 74 and to provide clarification to Central Valley Water Board’s concerns to proposed statistical procedure and concentration limits.

REASON: To add clarification to the finding. REVISION: Finding 69 (68) to read “The Discharger submitted a Water Quality Protection Standard (1998 WQPS) report in 1998 proposing statistical data analysis methods to calculate concentration limits for each monitored constituent in accordance with Title 27. The 1998 WQPS report proposed to use interwell data analysis to calculate tolerance interval for the monitored constituents. MRP R5-2006-0020 allowed the Discharger to update the concentration limits at least annually. The Discharger annually updated concentration limits and presented them in second semiannual monitoring reports until 2015. In 2015, proposed concentration limits for chloride, nitrate-N and potassium at the WMU-1 were 60 percent lower than the previous 5 years average. The Discharger again updated concentration limits in Spring 2016 and concentration limits for the WMU-1 were higher than last 5-year average before 2015, by 300 percent for chloride and 550 percent for nitrate-N. On 26 September 20161, the Central Valley Water Board requested the Discharger to submit an updated WQPS report based upon concerns with elevated concentration limits proposed by the Discharger in the Spring 2016 Semiannual Monitoring Report. In response to the letter, the Discharger submitted a “Statistical Analysis of Background Data and Development of Site Concentration Limits” report in Appendix D of the Fall 2017 Semiannual Monitoring Report. These WDRs use concentration limits proposed in Fall 2017 Semiannual Monitoring Report, however Title 27 §20400 (b) allows the Central Valley Water Board to approve, modify or disapprove each proposed limit and each proposed statement. The Discharger shall submit an updated WQPS report with the statistical method to be approved by the Central Valley Water Board staff, as described in Provision H.16.E.

Page 18, Finding 72 (71): Staff changed 2015 concentration limits to 2017 concentration limits in Finding 72 (71) Table.

REASON: To address the Discharger’s comment to Findings 71 (70) and 74 (73).

REVISION: Finding 72 (71) table to read Monitoring Parameter

MWA MWC Concentration Limit a

TDS 200 390 576 Bicarbonate 60 140 202.8 Alkalinity 60 140 202.8 Chloride 13 54 73.3 Nitrate-N < RL < RL 0.97 Sulfate 86 99 156.6 Calcium 27 52 96.4 Magnesium 8.2 16 28.1 Potassium 7.7 b 3.3 3.5 Sodium 10 27 38.4 Arsenic < RL 0.0026 - Iron < RL < RL -

1 Letter “Response to Discharger Request to Reconsider Additional Approved Work, Union Mine Landfill, El Dorado County” dated 26 September 2016.


ND – Non-detect RL – Reporting limit All concentrations are in mg/L a Fall 2017 Semiannual Monitoring Report

b Concentration limit exceedance

Page 20, Finding 75: Staff added Finding 75.

REASON: Based on the discussion with the Discharger on 19 April 2018, a conceptual site model will provide a better understanding of the site.

REVISION: Finding 75 to read “Based on the complex hydrogeology of the site, and activities at the site prior to the landfill, developing a conceptual site model will provide a better understanding of the site characteristics, source characteristics, release, transport mechanisms and pathways, actual/potential receptors, and site risks. This Order in Provision H.16.H requires the Discharger to submit a work plan to develop a conceptual site model to determine, but not limited to,

• The nature of shallow zone groundwater flow in the vicinity of the Facility,

• Effect of groundwater flow, elevation and characteristics in fractured bedrock beneath the Facility,

• Effect of groundwater flow and characteristics, if any, from historic mine related features at the Facility.

• The nature of groundwater exhibiting surface expression within the Facility,

• The effect of spray fields associated with the WWTP on local groundwater flow, and

• Effect of a release, if any, from the WMU(s) on local groundwater quality, and findings and results of Provision H.16.G.”

Page 20, Finding 76 (117): Staff moved Finding 76 to Finding 117.

REASON: To move to relevant section for better readability of the WDRs.

Page 22, Finding 78 (77): Staff changed 2015 concentration limit to 2017 concentration limit.

REASON: To address the changes to Finding 69 (68). REVISION: Finding 78 (77) table to read

Parameter GWD-1 GWD-2 GWD-3 Pendar

Tunnel Concentration Limit

(Fall 2017 Semiannual Monitoring Report)

pH 6.58 6.85 Dry Dry - Specific conductance, µmhos/cm

212 375 -

TDS, mg/L 180 280 239.3 Arsenic, mg/L < RL 0.052 Iron, mg/L < RL 0.22 Sulfate, mg/L 57 77 76.5


Page 22, Finding 79 (78): Staff changed the text as in the revision.

REASON: To address the changes from 2015 concentration limits to 2017 concentration limits. REVISION: Finding 79 (78) table to read “Concentration limit exceedance was observed for TDS and sulfate at location GWD-2 which is the Class II Expansion landfill WMU underdrain discharge. The Class II Expansion landfill WMU underdrain was constructed to maintain 5 feet separation from base of the waste to highest anticipated elevation of underlying groundwater required by Title 27 §20240 (c). The monitoring well directly downgradient (approximately 500 feet) to the Class II Expansion landfill WMU is UM-3 which shows a concentration limit exceedance for sodium and increasing concentration trends for chloride and potassium. The Class II Expansion landfill WMU underdrain discharge may indicate that the groundwater quality underlying the Class II Expansion landfill WMU may be impacted by the landfill waste. The GWD-2 will be sampled and analyzed for additional constituents per MRP R5-2018-XXXX.”

Page 25, Finding 94 (93): Staff changed the text of Finding 94 (93) based on the Discharger’s comment to Finding 93 (92).

REASON: To address the changes to Finding 93 (92) and associated requirements in SPRR Facility Specifications E.13 and 14. REVISION: Finding 94 (93) to read “The depth of fluid on the landfill liner shall not exceed 30 centimeters (cm) [40 CFR §258.40 (a)(2)]. The leachate collected from the Class II Expansion landfill WMU LCRS layer is conveyed to the Class II surface impoundment by gravity flow. The Class II Expansion landfill WMU floor slope and elevation difference between the Class II Expansion landfill WMU LCRS and the discharge point at the Class II surface impoundment allow the leachate from the Class II Expansion landfill WMU to drain by gravity flow without head buildup on the primary liner. Title 27 §20340 (d) requires the LCRS to be designed and operated to function without clogging through the schedule closure of the Unit and during the post closure maintenance period. Due to the way of the Class II Expansion landfill WMU LCRS construction, it cannot be tested for its proper operation. However, the LCRS collection pipes were provided with cleanout connections. The Discharger shall propose testing method to check LCRS collection pipes for clogging, as described in Provision H.16.L. .”

Page 24, Finding 99 (98): Staff changed “leachate” to “liquid” to address Discharger’s comment to Finding 26 (25).

REASON: To add clarification to the finding. REVISION: Finding 99 (98) to read “…..The two gravel filled leachate collection trenches function as a leak detection and collection layer to the Class II surface impoundment liner system and discharge collected liquid to the Class II surface impoundment LCRS sump.”

Page 24, Finding 102: Staff added Finding 102 as in the revision to address the changes to Facility Specification C.22.

REASON: To include the current practice at the Facility based on the discussion with the Discharger on 18 April 2018.


REVISION: Finding 102 to read “The Class II surface impoundment is emptied and cleaned annually before the winter season. The solids removed from the Class II surface impoundment are disposed in Class II Expansion landfill WMU.”

Page 24, Finding 109: Staff deleted “…This order continues the approval of that engineered alternative final cover for the Class III Old landfill WMU.”

REASON: The Discharger shall comply with the regulatory requirements available at the time of closure. Final cover with GCL was approved in accordance with Title 14 for the portion of the Class III Old landfill WMU closure constructed in 1998. The last portion of the Class III Old landfill WMU was closed in accordance with Title 27 in 2007. Further, final cover with GCL alone may be more vulnerable to impaired performance due to the combined effects of desiccation cracking, inadequate overburden stress, and loss of plasticity. REVISION: Finding 109 to read “In the fall of 1998, the Discharger installed an engineered alternative final cover on 14.6 acres of the top and eastern sideslopes of the Class III Old landfill WMU in accordance with Title 14. The engineered alternative final cover uses a GCL in place of the prescriptive one-foot thick low permeability barrier layer. The final cover is described in the table to Finding 7. The engineered alternative final cover was approved by the Regional Board in previous WDRs Order No. 98-238.”

Page 30, Finding 117: Staff moved Finding 76 to Finding 117.

REASON: For better readability.

Discharge Specification B.3: Staff added “c. Solids from Class II surface impoundment”.

REASON: To address added Finding 102. REVISION: Discharge Specification B.3 to read “The wastes allowed to be discharged to the Class II Expansion landfill unit are:

a. Non-hazardous, treated and dewatered sludge from the onsite septage and leachate treatment plant,

b. Non-hazardous municipal solid waste generated from onsite facilities, and

c. Solids from the Class II surface impoundment.”

Facility Specification C.7: Staff added Facility Specification C.7.

REASON: To address the changes to Finding 94 (93). REVISION: Facility Specification C.7 to read “The Class II Expansion landfill WMU LCRS pipe shall be operated without clogging, to prevent leachate head buildup on the primary liner due to capacity loss of the LCRS pipes”.

Facility Specification C.11: Staff added “…,except septage truck washout liquid,…” to address Discharger’s comment to Finding 102.

REASON: To add clarification to the finding. REVISION: Facility Specification C.11 to read “The Discharger shall measure, monitor and record all inflows, except septage truck washout liquid, to the Class II surface impoundment....”

Response to Comments - 25 - Union Mine Landfill Facility Specification C.19: Staff added a new facility specification to address the changes to Finding 104.

REASON: To address the changes made to Finding 104 (103). REVISION: New Facility Specification C.19 to read “Liquid level in the Class II surface impoundment LCRS sump shall be maintained at or below the leak detection and collection layer discharge pipe elevation in the Class II surface impoundment LCRS sump”.

Facility Specification C.19 (C.20): Staff added “may be” to the specification.

REASON: The Class II surface impoundment does not have a reliable unsaturated zone monitoring because of the way it was constructed. REVISION: Facility Specification C.19 (C.20) to read “If liquid is detected in the suction lysimeter of a Class II surface impoundment may be indicating a leak in the containment structures…”

Closure and Post-Closure Maintenance Specification E.13: Staff corrected cross-reference to Provision from “H.4.B” to “H.16.D”.

REASON: Typographical correction. REVISION: Closure and Post-Closure Maintenance Specification E.13 to read “… The Discharger shall submit the Closure Documents at least 90 days prior to proposed closure of the Class II surface impoundment as detailed in Provision H.16.D.”

Financial Assurance Specification F.4: Staff corrected cross-reference to Provision from “H.16.M” to “H.16.N”.

REASON: Typographical correction. REVISION: Financial Assurance Specification F.4 to read “…described in Provision H.16.N.”

Provision H.16.E: Staff added “Sampling collection and analysis plan” to the provision.

REASON: To include sampling collection and analysis plan to be addressed in WQPS. REVISION: Provision H.16.E. to read “Sampling collection and analysis plan.”

Provision H.16.G: Staff added “and elevated concentrations” to the provision.

REASON: To address the changes to concentration limits. REVISION: Provision H.16.G. to read “The monitoring parameter concentration limit exceedances and elevated concentrations in downgradient groundwater monitoring wells may be an indication of a release from the WMUs at the site...” and Provision H.16.G.1 to read “An evaluation of potential sources and a description of the source determined to be the cause of the observed constituent’s concentration limit exceedance and elevated concentrations.”

Provision H.16.H: Staff added Provision H.16.H as in revision.

REASON: To address inclusion of conceptual site model work plan.


REVISION: Provision H.16.H to read “ H. Conceptual Site Model Work Plan Based on the complex hydrogeology of the site and the activities at the site prior to the landfill, the Discharger shall submit a work plan to develop a Conceptual Site Model to determine, but not limited to:

1. The nature of shallow zone groundwater flow in the vicinity of the Facility. 2. Effect of groundwater flow, elevation and characteristics in fractured bedrock beneath the

Facility. 3. Effect of groundwater flow and characteristics, if any, from historic mine related features at the

Facility. 4. The nature of groundwater exhibiting surface expression within the Facility. 5. The effect of spray fields associated with the WWTP on local groundwater flow. 6. Effect of a release, if any, from the WMU(s) on local groundwater quality, and findings and

results of Provision H.16.G.”

And the compliance date is “31 December 2018”

Provision H.16.L: Staff added Provision H.16.L as in revision.

REASON: To address the changes to Finding 94 (93). REVISION: Provision H.16.L to read “ L. Class II Expansion Landfill WMU LCRS Testing Title 27 §20340 (d) requires LCRSs shall be designed and operated to function without clogging through the scheduled closure of the Unit and during the post closure maintenance period. Due to the way of Class II Expansion landfill WMU LCRS construction, annual LCRS testing cannot be performed. However, the LCRS collection pipes were constructed with cleanouts. The Discharger shall propose testing method(s) and testing frequency for clogging of the LCRS collection pipes, for Central Valley Water Board staff’s review and approval. Upon approval of the testing method, the Discharger shall perform LCRS collection pipe testing at specified frequency.” and the compliance date is “31 December 2018.”

ATTACHMENT B

Staff moved the SS-3 location and edited the call-out, and changed the caption of the attachment to “Site Plan and Monitoring Network”.

MRP

Section A.3.a: Staff modified section A.3.a. to reflect the changes made to Finding 94 (93) of the WDRs. See revision

REASON: To address monitoring and reporting requirements for the Class II Expansion landfill WMU LCRS. REVISION: Section A.3.a to read “The LCRS of the Class III Old landfill WMU consists of toe drains consisting of a gravel-filled trench that runs the length of the north and northeast perimeter of the Class III Old landfill WMU and the junction (southwest of the Class III Old landfill WMU) between the Class III Old and Class II Expansion landfill WMUs. The Class II Expansion landfill WMU was constructed with a LCRS which did not have a testing point to test it for its proper operation. However, the LCRS collection pipes were provided with cleanout connections. The Discharger shall monitor for clogging of the LCRS collection pipe and operate the LCRS pipes without clogging to prevent leachate head buildup on the primary liner due to capacity loss of the LCRS pipes. The leachate collected from the Class II Expansion landfill WMU and Class III Old landfill WMU is combined prior to


discharge to the Class II surface impoundment. The Class II surface impoundment has a geonet leak detection and collection layer which collects liquid leaking through the liner system and groundwater to maintain the separation from the waste to underlying groundwater, and discharges to the Class II surface impoundment LCRS sump. The Discharger shall operate and maintain leachate collection and removal system (LCRS) sumps and conduct monitoring of any detected leachate seeps in accordance with Title 27 and this monitoring program.”

Section A.3.c: Staff modified section A.3.c. to reflect the changes made to Finding 94 (93) of the WDRs. See revision

REASON: To address monitoring and reporting requirements for the Class II Expansion landfill WMU LCRS. REVISION: Section A.3.c to read “LCRS Collection Pipes Testing

The Class II Expansion landfill WMU LCRS cannot be tested for its proper operation because of the way it was constructed. The Discharger shall propose a testing method for clogging of the LCRS collection pipes as described in Provision H.16.L of WDR R5-2018-XXXX. Upon approval of the testing method and testing frequency by the Central Valley Water Board staff, the Discharger shall perform LCRS collection pipes testing for clogging at specified frequency. The results of these tests shall be reported to the Central Valley Water Board in the Annual Monitoring Report following the most recent test and shall include comparisons with earlier tests made under comparable conditions.

Section A.7.c: Staff modified section A.7.c. to address the Discharger’s comment to Finding 117 (118).

REASON: The Class III Old landfill WMU is currently partially closed. The five-year iso-settlement survey shall be conducted upon full closure of the Class III Old landfill WMU. REVISION: Section A.7.c to read “For closed landfill units, the Discharger shall conduct a five-year iso-settlement survey and produce an iso-settlement map accurately depicting the estimated total change in elevation of each portion of the final cover’s low-hydraulic-conductivity layer. For each portion of the landfill, this map shall show the total lowering of the surface elevation of the final cover, relative to the baseline topographic map [Title 27, section 21090(e)(1 & 2)]. Reporting shall be in accordance with Section B.Error! Reference source not found. of this MRP. The iso-settlement survey shall be conducted for the closed portion of the Class III Old landfill WMU in 2019. The five-year iso-settlement survey shall be conducted upon full closure of the Class III Old landfill WMU.”

Section B.1.e: Staff added section B.1.e. to get better understanding of the site.

REVISION: Section B.1.e to read “Cross sections showing the profiles of groundwater elevation, approximate location of the waste bottom elevation and the liner system shall be prepared in the north-south direction and east-west direction for the WMU-1. The monitoring wells locations and depth, screen depth and interval, and pump intake shall also be projected in the cross-sections.”

Section B.1.h: Staff modified section B.1.h. as in revision. Section B.1.h is renumbered to B.1.i.

REASON: The SPRR Facility Specification E.13 does not apply to Class II Expanasion landfill WMU LCRS. REVISION: Section B.1.i to read “An evaluation of the effectiveness of the leachate monitoring and control facilities, and of the run-off/run-on control facilities. ”


Section B.2.g: Staff modified section B.2.g. to reflect the changes made to section A.3.a and c.

REVISION: Section B.2.g to read “The results of the testing of leachate collection and removal systems required under Sections A.3.a and c.”

Section B.7: Staff changed the date to address the Discharger’s comment to Finding 117 (118).

REVISION: Section B.7 to read “…Refer to Section A.Error! Reference source not found. of this MRP, above. The next report is due by 31 October 2019.”