WATER QUALITY ASSESSMENT AND MICROSCOPIC PARTICULATE ANALYSIS (MPA) DATA REPORT

Transcription

1 Big Sky County Water & Sewer District No. 363 WATER QUALITY ASSESSMENT AND MICROSCOPIC PARTICULATE ANALYSIS (MPA) DATA REPORT LLC November 2008

2 , LLC 6595 Bear Claw Lane Bozeman, MT Tel (406) Fax (406) WATER QUALITY ASSESSMENT AND MICROSCOPIC PARTICULATE ANALYSIS (MPA) DATA REPORT MOUNTAIN WELL NOS. 1, 2 AND 3 PWSID NO Prepared for: Big Sky County Water and Sewer District No. 363 Big Sky, Montana November 13, 2008 Groundwater Development and Management Services

3 November 13, 2008 Page i TABLE OF CONTENTS 1 INTRODUCTION WELL CONSTRUCTION WATER QUALITY ASSESSMENT Water Temperature ph Conductivity Turbidity E. Coli WQA Interpretations MICROSCOPIC PARTICULATE ANALYSIS CONCLUSIONS & RECOMMENDATIONS...5 LIST OF TABLES 2-1 Well Construction Data 3-1 MPA Data Summary LIST OF FIGURES 1-1 Location Map 3-1 Temperature Time History Plots 3-2 ph Time History Plots 3-3 Conductivity Time History Plots 3-4 Turbidity Time History Plots LIST OF APPENDICES A B Well Logs MPA Lab Reports

4 November 13, 2008 Page 1 1 INTRODUCTION This report presents data collected by the Big Sky County Water and Sewer District No. 363 (District) to investigate direct influence of surface water on Mountain Well Nos. 1, 2, and 3. These wells are sources of supply to the Mountain Village public water system (PWSID 2385) owned and operated by the District. Figure 1-1 shows the locations of Mountain Well Nos. 1, 2, and 3 at Mountain Village in Big Sky, Montana. This work was undertaken due to a request by Montana DEQ that the District evaluate the wells for direct surface water influence. Sources of supply that are groundwater under the direct influence of surface water (GUDISWA) are considered risk-equivalent to surface water and must comply with the Surface Water Treatment Rule and subsequent related rules. Findings presented in this report show the subject wells have low risk of direct surface water influence, and therefore fulfill the requirements for source classification as groundwater. As per ARM , the State of Montana adopted DEQ Circular PWS-5 (2002 Edition) as the standard by which GUDISWA determinations are made. According to PWS-5, GUDISWA evaluations begin with a Preliminary Assessment (PA), and then proceed to a Water Quality Assessment (WQA) and Microscopic Particulate Analysis (MPA). DEQ completed the Preliminary Assessment for the subject wells, finding that additional evaluation was necessary. The District submitted a Sampling Plan (July 26, 2007) to DEQ for approval of data collection to fulfill the WQA and MPA data collection. DEQ approved the Sampling Plan on July 31, 2007 (Letter from James Consort to Ron Edwards). The District collected data from fall 2007 to fall WQA data were collected using field and benchtop grade instruments. MPA samples were collected and analyzed as per the Consensus Method for Determining Groundwaters Under the Direct Influence of Surface Water Using Microscopic Particulate Analysis, USEPA, October WELL CONSTRUCTION Mountain Well Nos. 1, 2, and 3 were constructed in 1972 by the same driller using very similar construction in all three wells. By today s standard, they are good quality constructions with grouted surface seals, steel casing, and stainless steel well screens. Well logs included in Appendix A show that there is substantial thickness of low permeability clay-bound gravel between the screen intervals and shallow groundwater. The only lacking aspect of the well constructions is the depth of the surface seals, which for some reason was limited to 16 feet, whereas the minimum standard applied today is 18 feet. There is no clear technical argument to support that significantly greater risk is realized by the 16 foot seals versus 18 foot seals under the circumstances. Had the seals been built to 18 feet, the Preliminary Assessment would have resulted in groundwater classification, and no further GUDISWA determination would have been required (this determination based on the Preliminary Assessment scoring has been applied to numerous wells statewide and is the primary purpose of the PA screen).

5 M id dl e Well #1 For! t es k W # Ga SW #2 lla n Ri Well #2 ti! ve r!! L a k e! Well #3! # ± Well #1 SW #1 0 k y n s L a v i #SW #1 Well sampling location and ID Surface water sampling location and ID Feet Figure 1-1 Sampling Locations

6 November 13, 2008 Page 2 TABLE 2-1 WELL CONSTRUCTION DATA Parameter Mountain Village No. 1 Mountain Village No. 2 Mountain Village No. 3 PWS Source Code Date Installed 8/18/72 8/22/72 8/29/72 Well Location NAD 83 Montana State Plane (m) Well Location, TRS SWSESE 19 6S3E NWNENE 30 6S3E SWNENE 30 6S3E GWIC No Water Right Permit No. 41H H H Total Depth (ft) Screen Interval (ft) Casing Diameter (in) Surface Seal (ft) 16, grout 16, grout 16, grout Static Water Level (ft) Installed Capacity (gpm) Estimated Well Capacity (gpm) A Test Data Q/s/t (gpm/ft/hrs) B 240/14/23 94/6.3/24 114/9.3/24 Specific Capacity (gpm/ft) Aquifer Type Alluvium Alluvium Alluvium A Rate that uses available drawdown in 70 days of continuous pumping. B Test data are reported as the pumping rate (Q), the drawdown (s), and the duration of the test (hours). 3 WATER QUALITY ASSESSMENT Parameters collected for the WQA analysis included temperature, specific conductance (a.k.a. conductivity), ph, and turbidity. Data were collected through fall 2007 until Lake Lavinsky was frozen. Sampling was re-initiated in August 2008 and continued until the end of October when the lake was ice covered. E. Coli was added to the parameter list at Mountain Well No A data CD attached to this report includes the WQA data in electronic form. During 2007, Mountain Well No. 3 was offline as per request of DEQ. Samples were collected by turning the well on with atmospheric discharge. The well was purged for several minutes to ensure it was producing fresh aquifer water. This same sampling protocol was used in 2008 until mid-september. At that time, Well No. 3 was put back online and was sampled during normal runtime. Well Nos. 1 and 2 were online and were sampled during normal runtimes in both 2007 and The WQA sampling was not continued in spring 2008 because the data did not appear to prove a groundwater classification and the District was already performing MPA testing. According to PWS-5, the WQA precedes the MPA phase of GUDISWA data collection. New DEQ staff asked in 2008 that WQA sampling be continued and added E. Coli as a parameter.

7 November 13, 2008 Page Water Temperature Figure 3-1 illustrates temperature data for the three subject wells. The wells show minor fluctuation of a couple degrees centigrade. Surface water temperature fluctuates by approximately 10 C. The data do not indicate a significant visual correlation between groundwater and surface water. The groundwater temperatures are generally consistent among the three wells. This data generally support a groundwater classification. 3.2 ph Water ph data are presented on Figure 3-2. There is significant fluctuation in ph values in both groundwater and surface water, particularly in the lake water during There is an apparent separation of ph values between surface water and groundwater. There is no indication of rapid shifts in groundwater ph in relation to shifts in the ph of surface water. 3.3 Conductivity Water conductivity is at similar levels in surface water and groundwater, with overlap among the data sets. The Middle Fork values show little variation, whereas substantial variation occurs in Lake Lavinsky and the well samples. There are several relatively large fluctuations in the conductivity of groundwater. There are inconsistencies between groundwater and surface water that do not support a correlation between the two water types (e.g., peaks in conductivity at Well 3 that substantially exceed peaks in the Lake). 3.4 Turbidity Water turbidity is very similar among the two surface water sampling sites. Well samples have generally low turbidity, less than 1 NTU. Mountain Well No. 3 has slightly higher turbidity than nos. 1 and 2 possibly due to the intermittent use of the well during most of the sampling period. Low values of turbidity may also be influenced by analysis using a bench-top instrument. 3.5 E. Coli E. Coli was negative in weekly samples from Mountain Well No. 3 collected between July 21, 2008 and October 30, As a warm-blooded intestinal bacteria, E. Coli is used in drinking water quality to assess the presence of fecal contamination of a water supply. The data support no such contamination is present. 3.6 WQA Interpretations Data for temperature appear to indicate limited if any influence of surface water. E. Coli results show Well No. 3 is not impacted by fecal contamination. The other parameters have common fluctuations, although it is not clear as to whether or not surface water influence is the cause. Based on visual examination, there are inconsistencies between the fluctuations in groundwater and those in surface water. In the framework of GUDISWA classification, the WQA is used only to determine if a source can be classified as groundwater and the process can be terminated, prior to collecting MPA samples. In this case, because the District is already collecting MPA samples, the WQA data are not being used to make a case for groundwater classification.

8 20 MTN-1 MTN-2 MTN-3 Water Temperature (C) Lake Lavinsky Middle Fork 5 0 9/1 9/8 9/15 9/22 9/29 10/6 10/13 10/20 10/27 11/3 11/10 Year MTN-1 MTN-2 MTN-3 Lake Lavinsky Middle Fork Water Temperature (C) /1 8/8 8/15 8/22 8/29 9/5 9/12 9/19 9/26 10/3 10/10 10/17 10/24 10/31 Year 2008 Figure 3-1 Temperature Time History Plots

9 9.5 MTN-1 MTN-2 MNT-3 Lake Lavinsky Middle Fork 9.0 ph (Standard Units) /1 9/8 9/15 9/22 9/29 10/6 10/13 10/20 10/27 11/3 11/10 Year MTN-1 MTN-2 MTN-3 Lake Lavinsky Middle Fork ph (Standard Units) /1 8/8 8/15 8/22 8/29 9/5 9/12 9/19 9/26 10/3 10/10 10/17 10/24 10/31 Year 2008 Figure 3-3 ph Time History Plots

10 350 MTN-1 MTN-2 Specific Conductance (us/cm, 25C) MNT-3 Lake Lavinsky Middle Fork /1 9/8 9/15 9/22 9/29 10/6 10/13 10/20 10/27 11/3 11/10 Year MTN-1 MTN-2 Specific Conductance (us/cm, 25C) MTN-3 Lake Lavinsky Middle Fork 50 8/1 8/8 8/15 8/22 8/29 9/5 9/12 9/19 9/26 10/3 10/10 10/17 10/24 10/31 Year 2008 Figure 3-2 Conductivity Time History Plots

11 10 1 Turbidity (NTU) 0.1 MTN-1 MTN-2 MNT-3 Lake Lavinsky Middle Fork /1 9/8 9/15 9/22 9/29 10/6 10/13 10/20 10/27 11/3 11/10 Year Turbidity (NTU) 0.1 MTN-1 MTN-2 MTN-3 Lake Lavinsky Middle Fork /1 8/8 8/15 8/22 8/29 9/5 9/12 9/19 9/26 10/3 10/10 10/17 10/24 10/31 Year 2008 Figure 3-4 Turbidity Time History Plots

12 November 13, 2008 Page 4 4 MICROSCOPIC PARTICULATE ANALYSIS Most states use the MPA as the final determination of GUDISWA for existing water supply wells, and Montana has taken this same approach. The MPA analysis performs counts of bio-indicator classes occurring in the sample which are known to be present in surface water. Based on these counts, a score is assigned and equated to risk of surface water contamination. A low risk is assigned for a score less than 10. Moderate risk corresponds to scores from 10 to 19. Scores of 20 or higher are high risk. Normally, an occurrence of two consecutive low scores will result in classification as groundwater. Other scores will result in additional MPA sampling. One or more high risk scores will normally result in classification as GUDISWA. MPA samples were collected for all three wells in October 2007 and then again in May A third MPA sample was collected from Mountain Well No. 3 in October 2008, after the well had been online for approximately 30-days. Laboratory reports are provided in Appendix B 2. Table 4-1 summarizes the scores and risk levels for each sample. The MPA data overwhelmingly support a groundwater classification for Mountain Village Well Nos. 1, 2, and 3. Scores of zero indicate that no bio-indicators were present, which is unusual for groundwater that is hydraulically connected to surface water, even when substantial natural filtration is occurring. The score of five for Mountain Well No. 1 is still solidly in the Low risk category (upper limit of 9). Some states have modified the MPA scoring and would have scored this sample as 0, designating the two algae and one rotifer as non-significant (NS) instead of rare (R). TABLE 4-1 MPA DATA SUMMARY Date Parameter Mountain Village No. 1 Mountain Village No. 2 Mountain Village No. 3 October 2007 Score Risk Low Low Low May 2008 Score Risk Low Low Low October 2008 Score Risk Low 2 The report for May 2008 was first issued with an error, indicating a score of 7 for Mountain Well No. 1. This report was later corrected to a score of 5.

13 November 13, 2008 Page 5 5 CONCLUSIONS & RECOMMENDATIONS The wells are located in proximity to surface water based on horizontal offset, but the intakes are separated from surface water by significant barrier layers consisting of clay and clay-bound gravel, deposited as glacial till on top of the alluvial aquifer. The wells are within a watershed that receives 35 to 40 inches per year of precipitation, providing sufficient aquifer recharge to meet the entire production volume of the wells. Historical use of the wells for more than 25 years in an un-chlorinated water system supports that source water is not impacted by surface water, and is likely dominated by or is entirely groundwater. MPA data collected from the wells have resulted in consistent Low risk scores from multiple samples. Such results are the established precedent for groundwater classification in Montana and other states nationwide. The fact that no bio-indicators were present in all but one sample supports that little if any surface water is present in the well discharge. There is no technical basis within the existing framework for GUDISWA evaluation that would refute a groundwater classification or support further data collection. To this end, the wells should be classified as groundwater by DEQ, and the GUDISWA evaluation terminated.

14 APPENDIX A WELL LOGS

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18 APPENDIX B MPA LAB REPORTS

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