December 22, 2009
Attention: Randy Scherzer, Senior Planner/GIS Coordinator
Re.: Beaver Valley Village: Review of Updated Karst and Hydrogeology Reports
Dear Mr. Scherzer,
As requested, I have completed a review of the updated karst and hydrogeology reports in support of the proposed Kiener subdivision (Beaver Valley Village). I have primarily commented on issues related to karst and karst hydrogeology. The two reports are reviewed individually in some detail. I then provide two comments on the Settlement Capability Study (dated February 25, 2009) that pertain to the conclusions of the karst and hydrogeology reports. The review then concludes with a summary and recommendations for additional baseline studies and steps required to ensure that the proposed development is sustainable.
Updated Karst Evaluation Report for Beaver Valley Village Proposed Plan of Subdivision,
Municipality of Grey Highlands, Prepared by Daryl W. Cowell & Associates, October 16, 2009.
A draft version of the updated karst report was reviewed a week in advance of the final submission and many of the minor issues were discussed at that time with Daryl Cowell by telephone and resolved. The original report dated September 19, 2007 was updated to include field observations and hydrologic measurement at the Wodehouse Creek ponor and at a spring located in Bowles Gully, which is located along the Niagara Escarpment to the east of the proposed development site. The documentation of the spring and its relationship to the ponor adds important information to the characterization of the aquifer. The following are specific comments related to the updated report:
1) Section 3 (final sentence):
The final sentence of Section 3 is presumably intended to be a general statement on the hydrogeology of the Amabel Formation close to the Niagara Escarpment. Hydrogeological studies often treat the Amabel Formation as a porous medium and do not consider the influence of karst nor utilize field methods and borehole tests to determine the influence of solutionally widened channel networks that result from karst processes. Therefore, the generalization that karst is “highly localized and ‘normal’ fractured aquifer flow tends to occur within very short distances of the karst” is largely unsupported and remains to be determined. For the property in question, there has been little attempt to test for solutionally widened fracture networks and their influence on groundwater flow. The transmissivities measured in the three wells on site exhibit variations of more than two orders of magnitude (78, 7.1, 0.3 m2/day) that may reflect the influence of karstic channeling. Also, cavernous rock was observed in well TW-1 over a 3 m interval during drilling indicating the likely occurrence of karst features in the bedrock well removed from the documented surface karst features. These are both hints that channeling may occur beneath the proposed development site.
2) Section 4.4 Ponor–Spring Connection:
The conclusions made in this section are not entirely convincing given the low accuracy of flow measurements and the limited search for additional springs. First of all, if the spring located in Bowles Gully is the only resurgence for lower Wodehouse Creek, then the spring discharge should not normally be less than the sinking stream recharge at the ponor unless there are other resurgences or unless the flow at the ponor was rising in response to rainfall. Measurements were made on September 1st and again on September 16th. For September 1st, the flow at the ponor and spring was measured to be 12.3 and 8.3 L/sec, respectively. Flow should have been in recession from rainfall three days earlier so the lesser flow measured at the spring suggests the possibility that there may be another resurgence that was not found. On the 16th, two measurements of flow at the ponor suggest a significant decrease in flow from 11.3 to 7.5 L/s over an eleven hour period. No explanation is provided for this apparent decrease in flow. The flow measured downstream from the spring was reported to be 9.4 L/sec, a value that is intermediate between the two flow measurements at the ponor. The water level data from the gauging site downstream from the spring indicate little change in flow over the course of the day. Given the nature of the creek at the ponor and the methodology utilized, it seems likely that the measurements were not sufficiently accurate, especially at the ponor, to reliably determine the difference in flow between the ponor and the spring. This makes it difficult to accurately assess the contribution of regional groundwater discharging at the spring and whether or not there may be additional resurgences.
There are several well documented examples along the Niagara Escarpment where a stream sinks into karst and flows in the subsurface to several resurgences that are widely spaced along the Escarpment slope. Daryl Cowell was questioned in an email regarding this and he indicated that he investigated along the Escarpment slope 1000 m to the north and 500 m to the south of the Bowles Gully spring without finding additional discharge areas. He also indicated that there may be an intermittent spring located roughly 800 m to the south of the Bowles Gully spring but the channel leading from there was dry when inspected. This channel was inspected at the confluence with the channel coming from the Bowles Gully spring. It seems unlikely that there would be resurgences for Wodehouse Creek located farther north or south than this, although this cannot be ruled out entirely. Topographic mapping for the area shows another possible spring located 1000 m south of the Bowles Gully spring, just north of County Road 30. While the Bowles Gully spring is likely the only resurgence for lower Wodehouse Creek, there is insufficient data to be certain. The possibility of divergent flow to other springs creates some doubt regarding the overall quantity of “regional groundwater” from the development site that discharges from the aquifer along the Escarpment.
3) Section 4.5 Pumping Test:
Without continuous monitoring over a period of several days to establish trends in flow at the ponor and spring, there was insufficient data to determine whether or not the pumping test on September 16 had any influence on the discharge at the Bowles Gully spring. The slight drop in water level reported at the stream gauge could be from a decrease in the sinking stream recharge at the ponor or from the pumping test.
4) Conclusion (7):
There is insufficient characterization of groundwater flow to conclude that the conduit between the ponor and the spring is “distinct” with little or no connection to regional groundwater systems. No attempt was made to measure spring discharge during high flow periods when there may be a substantial component of “regional groundwater” discharging from the aquifer. There is also the possibility that “regional groundwater” is directed along fractures parallel to the Niagara Escarpment for some distance north or south before discharging along the Escarpment slope. Furthermore, there is also a complete lack of seasonal data from the wells to assess seasonal variations in head and potential fluctuations in groundwater flow.
Supplementary Hydrogeologic Evaluation, Proposed Residential Development, Part Lots 1 & 2, Concession 6, Township of Grey Highlands (Euphrasia), Prepared by Ian D. Wilson Associates Limited on October 19, 2009.
Additional investigations were conducted to complete the supplementary hydrogeology report, including 1) pumping tests for two additional wells drilled on the development site, 2) interference analysis to determine the cumulative effect of the addition and use of 45 wells at the development site on the existing residential wells in the surrounding area, 3) water quality analysis for samples collected from the new wells at the completion of the pumping test, as well as from the Wodehouse Creek ponor and Bowles Gully spring, and 4) analysis of MOE water well records for existing wells located nearby. The additional investigation improves the quality of hydrogeological reporting substantially and resolves some of the concerns expressed during the conference call held by stakeholders on August 6, 2009. The following are specific comments related to the updated report:
5) Figures 3 and 4 (Generalized cross-sections from west to east and from south to north):
There are some inconsistencies in the geologic cross-sections shown on Figures 3 and 4 that may lead to inaccurate interpretation of the data. The data were reviewed briefly for accuracy. The static water levels in the three wells located on the site were estimated by plotting their locations on the Draft Plan of Subdivision (DWG575-06-CP14) and using the contours illustrated on that plan to estimate ground surface elevations. The results are presented in Table 1 below where they are compared to the static water levels reported in the text of the report (p. 11-12) and as plotted on Figures 3 and 4 of the report. The water levels reported in the text are consistent but well TW-1 appears to be plotted too high on Figure 3 and 4. The other two wells are fine.
Table 1. Comparison of static water levels for the three wells located on site (in metres asl).
In contrast, a review of the static water levels for the various wells plotted on Figure 5 (fromMOE water well records) indicates substantial variations in water levels parallel to the Niagara Escarpment for those wells located about 75 to 150 m from the brow of the escarpment (i.e., in an approximate line from well 25-3559 in the south to well 25-15964 in the north). This is in sharp contrast to farther to the west along Section B – B’. This is an important observation that has been overlooked. It appears that fracturing and/or karst development within 150 m of the escarpment has led to wider variations in static water levels. This appears to support the conclusion that major fractures or large karst conduits do not extend west from the Wodehouse Creek ponor to beneath the development site. However, there are too few wells on site for this to be conclusive. Generally, seasonal variations in water levels have not been measured nor discussed during data interpretation. Static water levels were measured for well TW-1 on both January 10, 2007 and again on September 16, 2009. However, only the earlier measurement is listed in Section 4.4 and there was no discussion of the change in water elevation.For Figure 4, data for MOE 25-0068 or 25-4333 could have been plotted instead of extrapolating to the south of TW1 without any data. If data for either of these two additional wells are plotted and a corrected water level plotted for TW-1, then it appears that there is only about 3 m of variation in water levels in the north-south direction along Section B – B’.
The method for selecting wells plotted on Figure 3 is unclear. MOE Well 25-9308 is plotted, however, the water well record for this well is not included in the print-out in the appendices. It is not clear why well MOE 25-3354 was selected rather than any of the other wells located in its close proximity. Also, wells TW-4 and TW-1 are located a substantial distance from the east- west profile. As such, the profile does not truly reflect groundwater variations perpendicular to the Niagara Escarpment.
The Wodehouse Creek downstream ponor and the Bowles Gully spring are key hydrogeologic features, yet these are not plotted on Figure 3. It would be useful to plot an east-west section that illustrates these features in relation to data from wells.
6) Section 6.0, page 12 (final two paragraphs of Section 6.0):
Several important points are made here: 1) the groundwater elevation in the vicinity of the
Wodehouse Creek ponor may be 10 to 20 m below the ponor, 2) the karst conduits extending from the ponor to the spring probably draw in local groundwater, 3) the proportion of groundwater in the spring discharge is very low, and 4) the karst conduits extending between the ponor and the spring do not appear to influence the closest well, TW-4. The following comments are provided. Well 25-3535 is quite close to the ponor and the static water level is about 390 m asl, or perhaps 11 m below the elevation of the ponor. No other wells are sufficiently close to give an indication of the water level beneath the ponor. However, during high flow periods, the water level in the conduit system beneath the ponor may rise substantially and possibly all the way up to the elevation of the ponor. The proportion of groundwater versus sinking stream recharge contributing to the spring is inferred to be very low. However, there is insufficient data to reliably calculate the component of groundwater in the discharge. Furthermore, the quantity of groundwater contributing to the spring discharge could be substantially higher during high flow periods, such as during spring melt or after storm events. There are no seasonal measurements of flow at the spring or water elevations at the wells to make any inference in this regard. Therefore, it is premature to conclude that the springshed does not extend beneath the development site and that the karst has little influence on the groundwater beneath the development site. Additional measurements at the wells and spring would be required to adequately characterize the hydrogeology of the site and the influence of karst on the hydrogeology of the aquifer beneath the development site.
Settlement Capability Study, Beaver Valley Village Settlement Area, Township of Grey
Highlands, County of Grey, prepared by Ian D. Wilson Associates Limited on February 25, 2009
The Settlement Capability Study was reviewed for any inconsistencies pertaining to the
development of 45 homes at the Beaver Valley Village. Two comments are provided:
7) Calculations of groundwater infiltration and flux on page 7 and 9:
On page 7, the annual infiltration rate for the BBVSA is calculated to be 185 mm/year. Based on this, the mean annual groundwater infiltration for the BVVSA is equivalent to 13.6 L/s.
On page 9, the mean flow of groundwater into the BVVSA within the Amabel aquifer from the west is calculated to be 8.0 L/s, based on transmissivities measured in wells, hydraulic gradient and aquifer width. The specific data utilized to calculate hydraulic gradient are not provided or discussed in detail and this is perhaps the least reliable variable in the calculation.
The combined groundwater flow from the above two calculations is 21.1 L/s. This groundwater flow will be important for providing adequate water supplies for the proposed development and for diluting any nitrate that infiltrates into the aquifer from septic systems. However, the estimated discharge of this groundwater (excluding sinking stream recharge from lower Wodehouse Creek) from the aquifer at the Bowles Gully spring on September 16, 2009 was in the order of 1 L/s or less (see Updated Karst Report, p. 9). This is an apparent inconsistency that needs to be adequately explained.
Measurements of aquifer discharge from the Amabel aquifer at exsurgences elsewhere along the Niagara Escarpment vary seasonally by as much as two orders of magnitude or more. However, there is insufficient data to suggest typical ranges for karst exsurgences. In the case of the BVVSA, most of the groundwater discharging from the Amabel aquifer at the Niagara Escarpment should discharge to the various surface watercourses that descent the Escarpment slope because the underlying rocks have very low permeability. In all probability, there should be considerable range in the “regional groundwater” discharging at the Bowles Gully spring. However, seasonal measurements at this spring or at other springs to the north or south have not been documented. This casts some doubt as to the reliability of these calculations of groundwater infiltration and flow in the Amabel aquifer.
8) Section 6.0 Groundwater Supply
As indicated previously, the hydraulic gradient used to estimate groundwater flow is not well constrained and could be inaccurate. Therefore, the groundwater flow could be substantially less and the number of homes that could be supported within the BVVSA may also be substantially less.
Summary
The updated karst and hydrogeology reports have done much to respond to previous issues and to alleviate concerns over the proposed development. There is also far better integration of theresults of the two reports. At this point, only a few concerns remain that can be readily rectified. From a hydrogeology and karst perspective, there are three areas of concern regarding the development of 45 new homes at Beaver Valley Village: 1) adequate water supply, 2) potential contamination from septic systems and 3) adequate aquifer characterization to support conclusions.
Of the three wells drilled on site, well TW-5 has the least capacity and may require the use of increased water storage. This suggests that not all wells drilled on site will necessarily have sufficient capacity. There is also potential for the new wells to reduce water levels at existing wells and some of these already have low capacity. In addition, during the pumping test at well TW-5, the water level dropped to an elevation of approximately 373 m asl. The static water elevation in the closest well to the Wodehouse Creek ponor (MOE well 3535) is approximately 390 m asl. This suggests the possibility that prolonged pumping from some wells on site could draw in water from the karst system beneath the ponor, water which is vulnerable to surface contaminants from the sinking stream, especially bacteria.
The modeling performed for the Settlement Capability Study to calculate the effect of increased nitrate loading on the Amabel aquifer from septic systems utilizes estimates of groundwater flow and infiltration rates. The groundwater flow is based on approximate measurement of hydraulic gradients. The calculation of infiltration rates is based on observations from shallow test pits. No deeper geotechnical work has been completed and monitoring wells were not installed within the overburden to measure downward hydraulic gradients. While such additional work is probably not warranted, the single estimate of “regional groundwater” discharging from the Bowles Gully spring (Updated Karst Report, p. 9) is significantly lower than predicted by the modeling and this casts some doubts in the results. Additional seasonal measurements would likely resolve this apparent discrepancy and permit greater confidence in the modeling. Water quality monitoring of groundwater in wells and at the Bowles Gully spring post-construction would quantify any increase in nitrate loading. Thus, construction phasing could be considered, and water quality monitoring of ground and surface water after each phase of development would ensure a sustainable level of development.
There are some deficiencies in the characterization of the Amabel aquifer that should be
addressed. The existing documentation lacks seasonal measurements of water levels and spring discharge and this casts some doubt regarding the modeling of groundwater flow and infiltration. There are also no measurements to determine seasonal variations in water quality. In karst terrain, there can be substantial short-term and seasonal variations in water quality, especially as a result of variations in sinking stream recharge. Finally, the geological sections should be revised to reflect the additional measurements of seasonal fluctuations in water levels. The east- west profile could be improved by including the Wodehouse Creek ponor to better reflect its importance to the local hydrogeology.
Recommendations:
The following recommendations are provided to address the outstanding issues described above. These are considered to be the minimum and a concurrent review by R. J. Burnside & Associates Limited should be consulted for any further or more stringent requirements from a hydrogeological perspective.
1) Completion of a pre-construction water well survey by mail or telephone. This would
document existing problems with downgradient wells and provide baseline data for any claims that may arise as construction proceeds. A water well contingency plan would be useful to identify the steps to follow in the event that a claim is made and the responsibilities of the proponent.
2) Burnside staff have already recommended the satisfactory construction of wells on individual lots prior to the issuance of building permits and I concur.
3) Obtain additional measurements when surface flow is high during the spring to complete the collection of baseline data. The required measurements include:
• Water quality at the monitoring wells, the Wodehouse Creek downstream ponor, and at the Bowles Gully spring. The same parameters should be analyzed at all locations to facilitate data comparison. Parameters should include on site measurements of pH, temperature and specific conductance, and water sampling for major ions, hardness, total dissolved solids, total suspended solids or turbidity, metals, nutrients and bacteria.
• Concurrent (same day) measurements of flow, temperature, specific conductance and a visual estimate of turbidity at the Wodehouse Creek downstream ponor and the Bowles Gully spring. Particular attention should be made to obtaining sufficiently accurate measurements of flow to enable an estimation of the proportion of spring discharge that is from widespread diffuse recharge (i.e., “regional groundwater”) versus sinking stream recharge. This can be calculated by comparing flow and specific conductance data. In addition, the Niagara Escarpment slope should be investigated again and as far south as County Road 30 to document any additional springs. Documentation should include: location, elevation, photographic record, flow, temperature and specific conductance and a visual estimate of turbidity. It is recognized that it may be more effective to measure flow downstream from the actual springs.
• Water levels in the monitoring wells. When added to existing data, this will provide
documentation of the approximate range in water levels at the site.
4) Review the additional baseline data and incorporate into the modeling and aquifer
characterization, if necessary. Update and improve the geologic sections.
5) Phasing of the development. This will provide an opportunity for the review of monitoring
data (water quality and well data, see next bullet) to ensure that additional phases are expected to be environmentally sustainable.
6) A monitoring program to be completed during and after each phase of development. This
monitoring should include the following components:
• Water quality at selected water wells located either at the downgradient edge of the site or
downgradient from site, at the Wodehouse Creek downstream ponor and at the Bowles Gully spring. Parameters should be the same as for baseline data (as described above) and at a minimum should be completed twice annually during high flow in spring and after an
extended dry period in late summer or fall.
• The Wodehouse Creek downstream ponor should be inspected for any accumulation of
sediment or debris that may result from construction. Direct observation and a photographic
record should be sufficient, although an elevation survey of the base of the ponor relative to a local control point would provide quantitative data. This should be completed after any
major grading and after each phase is complete. The sinkholes at Karst Area B should also
be visually inspected to ensure no accumulation of construction debris.
I trust this meets your current requirements. Should you have any questions regarding this review, please do not hesitate to contact me.
Sincerely,
Marcus J. Buck, B.Sc., P.Geo. (Membership No. 1373)
11 San Marino Crescent
Hamilton, Ontario L9C 2B6
905-575-4759
mbuck@karstsolutions.com
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