HOEK VAN DIE BERG ECO ESTATE: ADDENDUM REPORT FOR ALTERNATIVE 4

Transcription

1 HOEK VAN DIE BERG ECO ESTATE: ADDENDUM REPORT FOR ALTERNATIVE 4 Report Prepared for PHS Consulting Report Number /2- Draft Report Prepared by August 2015

2 SRK Consulting: Project No : Hoek van die Berg GW Specialist Study Page i HOEK VAN DIE BERG ECO ESTATE: ADDENDUM REPORT FOR ALTERNATIVE 4 SRK Consulting (Pty) Ltd Postnet Suite #206, Private Bag X18 Rondebosch 7701 SRK Consulting (South Africa) (Pty) Ltd. The Administrative Building Albion Spring 183 Main Rd Rondebosch 7700 Cape Town South Africa capetown@srk.co.za website: Tel: +27 (0) Fax: +27 (0) SRK Project Number August 2015 Compiled by: Peer Reviewed by: Leon Groenewald Principal Hydrogeologist lgroenewald@srk.co.za GROL Hoek van die Berg Groundwater Specialist Study August 2015 August 2015

3 SRK Consulting: Project No : Hoek van die Berg GW Specialist Study Page ii Table of Contents Glossary... iv List of Abbreviations... v 1 Introduction Changes to Original Development Alternatives Impact Identification and Assessment Proposed Method of Assessing Environmental Issues and Alternatives Impact Assessment Impacts on groundwater arising during the construction phase Impacts on groundwater from the Waste Management Area Impacts on Groundwater from the WWTW Conclusions and Recommendations References GROL Hoek van die Berg Groundwater Specialist Study August 2015 August 2015

4 SRK Consulting: Project No : Hoek van die Berg GW Specialist Study Page iii List of Tables Table 2-1: Changes in Development... 3 Table 3-5: Impact ratings for Impacts during the Construction Phase... 6 Table 3-6: Ratings for Impact of Waste Management Area on Groundwater... 8 Table 3-7: Ratings for Impacts of WWTW on Groundwater List of Figures Figure 2-1: Layout of Alternative GROL Hoek van die Berg Groundwater Specialist Study August 2015 August 2015

5 SRK Consulting: Project No : Hoek van die Berg GW Specialist Study Page iv Glossary Abstraction: The act of removing water from a groundwater resource. Aquifer: A formation, group of formations, or part of a formation that contains sufficient saturated permeable material to store and transmit water; and to yield economical quantities of water to boreholes or springs. An aquifer is the storage medium from which groundwater is abstracted. Electrical conductivity (EC): Electrical conductivity is a measure of how well a material accommodates the transport of electric charge. The more salts dissolved in the water, the higher the EC value. It is used to estimate the amount of total dissolved salts, or the total amount of dissolved ions in the water. Fault: A zone of displacement in rock formations resulting from forces of tension or compression in the earth s crust. Faults can form conduits for groundwater movement and groundwater contamination; as well as impermeable zones where metamorphism of the rocks has taken place. Fracture: Any break in a rock including cracks, joints and faults. Fractures can form the main conduits for groundwater flow. They can also form pathways for the movement of contamination. Groundwater: Water found in the subsurface in the saturated zone below the water table. Groundwater is a source of water and is an integral part of the hydrological system. Hydrogeology: In South Africa the term geohydrology and hydrogeology are used interchangeably. In theory hydrogeology is the study of geology from the perspective of its role and influence in hydrology, while geohydrology is the study of hydrology from the perspective of the influence on geology. Paleochannel: A paleochannel is an old or ancient channel. ph: ph is the negative logarithm of the hydrogen ion concentration in solution. ph is the measure of the acidity or alkalinity of a solution. Recharge area: An area over which recharge occurs. Recharge is crucial for the ongoing replenishment of aquifers and their sustainable use, and recharge areas thus require protection. Recharge: The addition of water to the saturated zone, either by the downward percolation of precipitation or surface water and/or the lateral migration of groundwater from adjacent aquifers. Recharge is crucial for the ongoing replenishment of aquifers. Secondary aquifer: An aquifer in which groundwater moves through secondary openings and interstices, which developed after the rocks were formed. Sustainable yield / safe yield: Safe yield is defined as the maximum rate of withdrawal that can be sustained by an aquifer without causing an unacceptable decline in the hydraulic head or deterioration in water quality in the aquifer. Water table: The upper surface of the saturated zone of an unconfined aquifer at which pore pressure is equal to that of the atmosphere. It marks the top of the groundwater body. GROL Hoek van die Berg Groundwater Specialist Study August 2015 August 2015

6 SRK Consulting: Project No : Hoek van die Berg GW Specialist Study Page v List of Abbreviations EC: GIS: hr: ISO: l/s: m 3 /a: mamsl: MAP: mbc: mbgl: mm: Mm 3 /a ms/m: electrical conductivity Geographic Information System hour International Organization for Standardization ( litres per second cubic metres per annum metres above mean sea level mean annual precipitation metres below collar metres below ground level millimetres million cubic metres per annum milli-siemens per metre GROL Hoek van die Berg Groundwater Specialist Study August 2015 August 2015

7 SRK Consulting: Project No : Hoek van die Berg GW Specialist Study Page 1 1 Introduction SRK Consulting South Africa (SRK) (Pty) Ltd has been appointed, by Saddle Path Properties, as part of an Environmental Impact Assessment to conduct a specialist groundwater impact assessment of a proposed eco-estate development near Vermont, Hermanus. SRK submitted a Specialist Report in September 2012 detailing the impact assessment of two proposed Alternatives. Subsequently a new Alternative has been proposed and is labelled as Alternative 4. This addendum report details the impact assessment of this new Alternative on the groundwater and should be read in conjunction with the September 2012 report.. 2 Changes to Original Development Alternatives The layout of the new Alternative is presented in Figure 2-1 and briefly described below. The changes made to the development options are presented in Table 2-1. Portion A Combination of single dwelling (184 units) and group housing (60 units) with a central mixed use area which would include a community centre. This area falls in the following sub-catchments C1, C2, C3 and C5. Portion B The original hotel site with a limited number (11 units) surrounded by an area of Private Open Space. This area falls in the following sub-catchments C5 and C9 Portion C Area of approximately 12 Ha which will be retained as either agriculturally zoned land or Private Open Space. This area falls in sub-catchment C10. Portion D This portion of land is to be subdivided off the main property and will be retained as either agriculturally zoned land or Private Open Space. This area falls in sub-catchment C5 and C10 Portion E Nature reserve. This portion of land will be declared a Private Nature Reserve and will be rezoned to accommodate this status.

8 SRK Consulting: Project No : Hoek van die Berg GW Specialist Study Page 2 Figure 2-1: Layout of Alternative 4

9 SRK Consulting: Project No : Hoek van die Berg GW Specialist Study Page 3 Table 2-1: Changes in Development Catchment Size (m 2 ) Sand Thickness (m) Planned Development OLD Planned Development NEW Restrictions C m Limited to the southern edge of the catchment. Limited to the southern edge of the catchment. No development on the northern side of the wetland. C m Most of catchment. Most of catchment. None. C m Limited to back dune area. Limited to back dune area. No development on coastal zone due to seep zones. C m Northern section of catchment. None No development on coastal zone due to seep zones. C m Most of development planned for this catchment. C m No development planned, only existing houses. Limited to South Eastern section and small section in North Western corner. No development planned, only existing houses. No restriction due to thick sand cover. N\A. C m No development planned. No development planned. No restrictions. C m Small development planned across watershed into C9. C m Small development planned across watershed into C8. No Development Small development planned across watershed into C8. No restrictions. No restrictions. C m A development to cover most of the southern part of the catchment. No Development planned for. Development allowed, but no sewage treatment works or any other possible pollution sources.

10 SRK Consulting: Project No : Hoek van die Berg GW Specialist Study Page 4 The locations of the new waste treatment facility are located in the north western corner and in the southern section of the C1 catchment. The treatment facilities will consist of Biogas digesters.

11 SRK Consulting: Project No : Hoek van die Berg GW Specialist Study Page 5 3 Impact Identification and Assessment The impacts an activity could have on groundwater can broadly be grouped into the following: Impact on groundwater quality; Impact on yields of existing boreholes; and Impact on groundwater levels (could affect wetlands). The following possible impacts during construction and operations have been identified: Contamination of groundwater during the construction phase as a result of hydrocarbon spills from vehicles and refuelling areas; Lowering of the water table due to abstraction from production borehole; Pollution of groundwater from the planned waste management area; Pollution of groundwater from the planned WWTW; Impact of WWTW on the wetland and seeps 3.1 Proposed Method of Assessing Environmental Issues and Alternatives For each impact, the EXTENT (spatial scale), INTENSITY and DURATION (time scale) are described. These factors are then used to ascertain the SIGNIFICANCE of the impact, both with and without the proposed/recommended mitigation measures in place. The proposed criteria used to evaluate these variables were discussed in the 2012 report. 3.2 Impact Assessment Impacts on groundwater arising during the construction phase. Impacts expected during construction relate to potential hydrocarbon (oil, diesel, grease, petrol) spills from machinery and storage areas and potential releases (e.g. nitrates, bacteria) from on-site sanitation for the construction workers. The impacts of any such contamination will be low and site specific given the likely small quantities involved. The significance of the potential construction related contamination of groundwater for Alternative 4 is Low and Very Low with mitigation. The following mitigation measures are proposed: Maintain good housekeeping measures for on-site storage of hydrocarbon-based products and clean up any spillages and waste on a daily basis. This material should be stored in appropriate containers, in a bunded area, for removal and disposal; Supply appropriate on-site sanitation during construction; and Locate storage areas away from the production borehole and wetland.

12 SRK Consulting: Project No : Hoek van die Berg GW Specialist Study Page 6 PHASE & ALTERNATIVE MITIGATION EXTENT INTENSITY DURATION PROBABILITY SIGNIFICANCE STATUS CONFIDENCE Hydrogeology Impact on Groundwater Quality during Construction Phase Clearance of land for construction and construction of Waste Management Area site: Contamination of groundwater due to spillage of fuel used in heavy machinery ALTERNATIVE 4 Without With SS Very Low Construction Possible Low Very Low -ve High Clearance of land for construction and construction of Waste Management Area site: Contamination of groundwater due to spillage of fuel used in heavy machinery ALTERNATIVE 4 Without With SS Very Low Construction Possible Low Very Low -ve High Portable toilets Contamination of groundwater due to leachate from toilets ALTERNATIVE 4 Without With SS Very Low Construction Possible Low Very Low -ve Sure Table 3-1: Impact ratings for Impacts during the Construction Phase

13 SRK Consulting: Project No : Hoek van die Berg GW Specialist Study Page Impacts on groundwater from the Waste Management Area. The main potential impact of the proposed waste management area would be possible seepage of polluted stormwater into the subsurface environment from the Waste Management site. The main contaminants that could be introduced would be nitrate, chloride, potassium, ammonia, phosphate and heavy metals. An increase in Total Dissolved Solids, alkalinity and Chemical Oxygen Demand could also be expected. The proposed waste management site is underlain by sediments that are approximately 18 m thick. However, the water table is expected to be about 13 mbgl and the unsaturated sands would provide adequate conditions for leachate attenuation. It is expected that groundwater flow at the C10 catchment is in a north westerly direction and away from the wetland but towards the Paddavlei system. The spatial extent is rated as Local (Table 3-2) due to low volumes also that the Waste Management Area is situated close to the site boundary and contaminated groundwater would flow off-site in a north western direction towards Hawston. The magnitude of the impact is rated as Low also due to the low volume of stormwater generated. The duration is set as Long Term. The Probability rating is assessed as Possible for both sites. Due to the low magnitude and probability the significance of the impact is Low. Mitigation measurements would include the following: Conduct a geotechnical investigation to obtain soil parameters i.e. infiltration rates, grain size and thickness; Placement of waste management area site in areas with thicker sands; Installation of a downstream monitoring borehole of 18 m depth; and Installation of proper storm water management system. Implementation of the mitigation measures will result in a significance rating of Very Low.

14 SRK Consulting: Project No : Hoek van die Berg GW Specialist Study Page 8 PHASE & ALTERNATIVE MITIGATION EXTENT INTENSITY DURATION PROBABILITY SIGNIFICANCE STATUS CONFIDENCE Hydrogeology Impact of Waste Management Area on Groundwater Polluted storm water entering groundwater Impact on groundwater quality Without Local Low Low ALTERNATIVE 4 Long Term Possible -ve Sure With Site Specific Very Low Very Low Table 3-2: Ratings for Impact of Waste Management Area on Groundwater

15 SRK Consulting: Project No : Hoek van die Berg GW Specialist Study Page Impacts on Groundwater from the WWTW. The two proposed WWTW sites are in the C5 catchment and between the C5 and C10 catchment. The main concerns about the WWTWs are: Groundwater contamination from untreated sewage spills; Seepage from pond; and Groundwater contamination due to irrigation with poorly treated effluent. The Alternative 1 site is situated some 30 mamsl and approximately 10 m of sand would be present at the site of which 6 m would be unsaturated. Alternative 2 is at approximately 38 mamsl and it is expected that 18 m of sand would be present of which 13 m is unsaturated. It is assumed that the treated effluent will be stored in lined effluent ponds before being used for irrigation. It is also assumed that the end quality of the effluent will adhere to the DWA standards for treated effluent. The ratings below are for each WWTW alternative and not for the two layout alternatives as the position of the WWTWs are the same. The leaching (due to liner integrity failure) of sewage from the plant or accidental spill would involve low volumes and would not move far off-site. The distance the pollution plume would move off-site would depend on the volume and duration of the leak. An extent rating of Local and a Low magnitude are assigned for leaching of sewage into groundwater. The local extent is mainly due to the shallower water table and close proximity of the property boundary. Due to the small volume of accidental spills an extent rating of Site Specific and Very Low magnitude is assigned.. The duration of leaching of sewage is Long Term if gone unnoticed and the duration of accidental spills is Short Term and probability is Possible. The significance of leaching of sewage is Low and, for accidental spills, Very Low. The planned irrigation areas are mainly situated on areas with a thick zone of unsaturated sand which will provide some measure of attenuation. The irrigation of treated effluent should also conform to DWA standards regarding the quality of the effluent. Due to the thickness of the unsaturated zone and expected quality the extent is Site Specific and magnitude Very Low. The duration is Long Term. The significance of groundwater being polluted by irrigation with treated effluent is Very Low.

16 SRK Consulting: Project No : Hoek van die Berg GW Specialist Study Page 10 PHASE & ALTERNATIVE MITIGATION EXTENT INTENSITY DURATION PROBABILITY SIGNIFICANCE STATUS CONFIDENCE Hydrogeology Impact of WWTW on Groundwater quality Leaching of sewage into groundwater ALTERNATIVE 4 Without With Local Low Long Term Possible Low Very Low -ve Sure Accidental Spills ALTERNATIVE 4 Without With SS Very Low Short Term Possible Low Very Low -ve Sure Irrigation with treated effluent ALTERNATIVE 4 Without With SS Very Low Short Term Possible Low Very Low -ve Sure Table 3-3: Ratings for Impacts of WWTW on Groundwater

17 SRK Consulting: Project No : Hoek van die Berg GW Specialist Study Page 11 The following mitigation measures are proposed to change the significance ratings to Very Low: Use appropriate liners for ponds; Conform with treated effluent quality standards; Install a downstream monitoring borehole to a depth of 20 m; Sample groundwater from this borehole once a year and analyse for EC, NH 4, NOx-N. The ratings for Alternative site 1 and 2 are very similar. However, it is proposed that Alternative site 2 be developed due to its proximity to the waste management area. This would make the management of possible pollution sources easier. 4 Conclusions and Recommendations From a groundwater perspective, there is no reason not to proceed with the development if the following mitigation measures are implemented: Conduct a geotechnical investigation to obtain soil parameters i.e. infiltration rates, grain size and thickness; Placement of waste management area in areas with thicker sands; Installation of a downstream monitoring borehole of 18 m depth; Installation of proper storm water management system. Use appropriate liners for ponds; Conform with treated effluent quality standards; Install a downstream monitoring borehole to a depth of 20 m; Sample groundwater from this borehole once a year and analyse for EC, NH 4, NOx-N Based on the above the following recommendations are made: The Alternative 4 site option for the WWTW is preferred due its close proximity to the waste management area; and Install a downstream monitoring borehole and monitor groundwater quality (sample, analyse, assess) once a year for pollution detection purposes. Prepared by L Groenewald Pr Sci Nat Principal Hydrogeologist

18 SRK Consulting: Project No : Hoek van die Berg GW Specialist Study Page 12 5 References Ractliffe S.G May 2009, Hoek van de Berg, Farm 572, Hermanus: Wetland Scan, The Freshwater Consulting Group Murray R, March 2009, Hoek van die Berg: BH3 Yield recommendations, Groundwater Africa 2009 Whittingham J.K. December 1970, Geological and Geohydrological investigation for groundwater supplies, Department of Mines 1970 Rosewarne P.N. June Groundwater investigation at Hoek van de Berg, Hermanus, Report number , 1997

19 SRK Consulting: Project No : Hoek van die Berg GW Specialist Study Page 13 SRK Report Distribution Record Report No Draft Copy No. 1 Name/Title Company Copy Date Authorised by PHS Consulting 1 August 2015 L Groenewald Project File SRK Consulting 2 August 2015 Library SRK Consulting 3 August 2015 L Groenewald L Groenewald Approval Signature: This report is protected by copyright vested in SRK (SA) (Pty) Ltd. It may not be reproduced or transmitted in any form or by any means whatsoever to any person without the written permission of the copyright holder, SRK.